We use molecular dynamics simulations to analyze dynamic aspects of the assembly process and identify ingredients that are key to a successful assembly of nanoparticle superlattices through DNA hybridization. The scale-accurate coarse-grained model faithfully captures the relevant contributions to the kinetics of the DNA hybridization process and is able to recover the in situ formation of all to date experimentally reported binary superlattices. We investigated the optimal strength of DNA linker interaction, and we propose suitable linker sequences for future nanomaterial design. We also investigate the growth dynamics of these mesoscopic architectures with a colloidal model based on electrostatic core repulsion and localized DNA hybridization. We find a slow-growth coalescence dependent upon orientation. Surprisingly, due to the grain boundary interactions, we report that aggregates of larger nanoparticles have faster growth dynamics compared to smaller nanoparticles provided the DNA surface coverage is constant. This finding provides a new design rule relating nanoparticle size and crystal growth dynamics. We conclude with a prediction of the bcc superlattice growth dynamics and compare to experimentally measured growth rates.

Wrinkling is a self-organization phenomenon that is commonly observed in natural systems over a wide length scale. Wrinkling patterns are formed on a thin film as a result of buckling-based instabilities and the mechanism is similar to Euler buckling of beams under compressive loads. Beyond a critical compressive stress, pure compression becomes unstable and wrinkles are formed via periodic bending of the substrate. As such, wrinkling is an inexpensive technique for fabricating periodic micro and nano scale structures over large areas. Although periodic micro and nano scale patterns have been fabricated via wrinkling in the past, wrinkling has not yet developed into a robust manufacturing process. This is primarily because predictive design and fabrication is limited to a small set of elementary periodic geometries. Herein, we (i) demonstrate the fabrication process for generating complex non-uniform patterns by directed wrinkling and (ii) provide a methodology to perform predictive design of such non-uniform patterns. These complex patterns find applications in areas such as fluidics-based biomedical diagnostics and photonics based sensing.
We have fabricated non-uniform patterns by generating a thin glass film on a uniaxially stretched elastomeric foundation. In the absence of any “directedness”, one-dimensional sinusoidal post-buckling patterns (wrinkles) were formed on releasing the pre-stretch. The wrinkling process was “directed” by locally modifying the stiffness and the geometry of the surface of the elastomeric foundation. This modification locally alters the stress state and leads to the formation of non-uniform wrinkles. Local modification was achieved by performing the thin film generation process through a micro-patterned physical/contact mask. To predict these patterns, we have developed a numerical model that links the patterns on the physical mask to the wrinkle patterns that are formed. A simplified analytical model has also been developed by approximating the wrinkles to be aligned along the principal stress directions. This is based on the experimental observation that the non-uniform wrinkles are composed of bent arrays of 1-D wrinkles. Based on this model, a library of several different types of elementary wrinkle patterns was generated by tuning the shape of the patterns on the mask. Then, design rules were identified for combining different shapes to fabricate complex wrinkle patterns. These design rules and the wrinkle pattern library forms the basis for developing the methodology for predictive design of non-uniform patterns.

De novo design and shaping inorganic nanostructures is a key foundation in nanotechnology and promises diverse applications in photovoltaics, plasmonics, and electronics. From bottom-up approaches, tuning the energy difference of selected crystallographic facets and hence the particle growth dynamics has proven to be an effective strategy, which have produced gold and silver particles with diverse shapes ranging from 40 to 500 nm. However, it remains challenging to rationally predict and de novo design particles with diverse desired shapes with sub-25 nm size. From top-down approaches, e-beam lithography has enabled the production of arbitrary complex shaped two-dimensional shaped materials. But wafer-scale fabrication of pre-programmed graphene structures with sub-10 nm resolution is yet to be achieved. In particular, finding a general approach for constructing inorganic nanostructures with arbitrarily prescribed, asymmetric shapes remains an open challenge.
Meanwhile, DNA self-assembly has emerged as a powerful method to generate nanostructures with arbitrary defined shapes. Two particularly effective strategies for constructing complex discrete shapes are scaffolded DNA origami and modular assembly of single-stranded DNA tiles and bricks. Both strategies have produced 100-nm scale shape-controlled structures with sim;3 nm addressability. In particular, with the help of computer-aided design software, more than 100 three-dimensional structures with intricate cavities and tunnels have been built, which demonstrates the design and synthesis simplicity of DNA nano structures.
Successful transfer of spatial information encoded within the DNA nanostructures to other 2D/3D materials will enable simple and versatile way to produce complex prescribed shaped inorganic nanomaterials. Here we report two different ways, “nanocasting” that uses a three-dimensional DNA origami structure with a sub-25 nm programmable cavity as a “nanomold”, and “etching” that uses a metalized DNA origami structure as a “nanomask”, to produce shape-specific noble metals particle and graphene nanostructures. With “nanocasting” approach, we demonstrate the construction of 3D cuboid silver particles with tunable dimensions; silver particles with equilateral triangle, right triangle, and circle cross-sections; a gold particle with a rectangle cross-section; a Y-shaped silver particle composite; and a hybrid quantum-dot and silver particle sandwiched structure. With “etching” approach, we demonstrate the production of graphene nanorings, three- and four-membered nanojunctions, and extended nanoribbons.

Directional entropic forces that cause particle alignment have recently been proposed in systems of hard polyhedra that order into crystals. Here we provide a means of quantifying these forces and find them to be of the order of a few kT in monodisperse systems of hard particles. Based on the similarity of the anisotropy of these directional entropic forces to the directional enthalpic forces present in systems of enthalpically patchy particles, we propose and show that these forces originate from "entropic patches," which are features of particle shape that promote local dense packing. Using the notion of entropic patches, we engineer particle shape to target the assembly of specific crystal structures. We show that this procedure can be generalized as anisotropy dimensions, similar to those exploited for enthalpically patchy particles, thereby mapping out a large design space for colloidal self assembly with entropy as the sole mechanism underlying ordering. We show how the addition of small depletants to solutions of hard shapes further enhances directional entropic forces, increasing already appreciable bond strengths. Our techniques also allow the quantification of the role of shape in systems where both enthalpic and directional entropic forces are at play.

DNA-driven nanoparticle (NP) assembly has emerged as a powerful strategy for the fabrication of three-dimensional (3D) superlattices, which allows for the exploration of synergetic properties of nano-components and incorporation of multiple functionalities. We have developed a general strategy for the design and creation of heterogeneous materials using DNA-based assembly. We demonstrate, using representative types of nanoparticles, that major classes of material functionalities, such as plasmonic (Au), magnetic (Fe2O3,), catalytic (Pd,) and luminescent (CdSe/Te@ZnS and CdS@ZnS), can be incorporated into heterogeneous systems in a rational manner. We investigated the effect of NP and DNA shell characteristics, including shape heterogeneity, interplay between non-specific and DNA-programmable interactions, and DNA number and flexibility, on the phase behavior of formed hetero-systems. Examples of novel properties of assembled materials are also shown. Our studies demonstrate a pathway for creation of multifunctional materials from multiple and arbitrary nano-components.

Colloidal particles are often directed to assemble by use of applied external fields-e.g. by exploiting particle charge or ferromagnetism, and by applying electro-magnetic fields to induce interactions and to steer the particles into well-defined structures at given locations. Here, we exploit fields that arise spontaneously when microparticles are placed in contact with deformable matter. In particular, we have been exploring energy stored in deformation fields around microparticles as a means of directing colloidal assembly. In one context, we use capillary interactions that occur between anisotropic microparticles at fluid interfaces. The microparticles have undulated contact owing to wetting boundary conditions; the fluid interface deforms, creating an area field around the particle that bears the signature of its shape and wetting. The product of this excess area and surface tension is an energy field, which we exploit to direct particles to migrate, orient and assemble. In another context, we exploit elastic energies that arise in confined liquid crystals. For example, when a nematic liquid crystal is confined using surfaces with well-defined anchoring energies, the director field and associated defect fields can be molded to store elastic energy. This energy can be used to steer particles within the bulk or particles that are trapped at the nematic-air interface. We explore this theme (i) using topographically patterned solid surfaces to define defect fields that steer particles trapped at fluid interfaces into assemblies mimicking the defect texture and (ii) using anisotropic microparticles with well-defined anchoring conditions which assemble in preferred orientations.

Emulsions are generally stabilized by the use of surfactants, but solid particles dissolved in one phase can also stabilize emulsions. This is known as Pickering emulsion. Colloidal particles adsorb strongly at liquid interfaces, and this has been exploited to stabilize emulsions and to produce colloidosomes [1]. Clay minerals and other nanoparticles are known to produce very stable Pickering emulsions [2]. We present a simple and robust method to assemble colloidal shells of controlled heterogeneity. Shells composed of two hemispheres of different colloidal particles, Janus shells, are made by electrocoalescence of two oil-in-oil emulsion droplets covered by different colloidal particles.
The method of Janus shell fabrication presented here is entirely dependent on drop electrocoalscence dynamics and the Taylor circulation flow, resulting in a ribbon formation prior to the coalescence [3]. Therefore the liquids should be chosen such that that Maxwell time in the droplet is longer than that of the surrounding liquid. In principle, any non-polar liquid emulsion system could be used; provided that the droplet and surrounding liquid has the right Maxwell times for producing electrohydrodynamic flow. We also demonstrate that other types of Patchy colloidal shells can be produced by coalescence of several droplets.
The Janus shell creation consists of two steps: Firstly the colloidal shells are made on each droplet, as described in [3]; and then the droplets are brought to a close proximity for coalescence.
References:
[1] Dinsmore, A. D. et al. Colloidosomes: Selectively Permeable Capsules Composed of Colloidal Particles. (2002) Science 298, 1006.
[2] Ashby, N. P. and Binks, B. P. Pickering emulsions stabilised by Laponite clay particles. (2000) Phys. Chem. Chem. Phys., 2, 5640.
[3] Dommersnes, P., Rozynek, Z., Mikkelsen, A., Castberg, R., Kjerstad, K.,A., Hersvik, K. and Fossum J.O. Active structuring of colloidal armour on liquid drops. Nat. Commun. (Accepted May 2013)

Take polymer colloids—simple to make and ubiquitously available—let them self-assemble into a monolayer and you have, readily engineered, a sophisticated mask to create highly symmetric surface patterns with nanometer precision that find increasing applications in a multitude of research fields such as the fabrication of metal nanoparticles with tailored plasmonic properties, the creation of structural colors, the patterning of biologically relevant molecules or the tailoring the wetting properties of macroscopic surfaces.[1] As intriguing this technique is, the devil is in the details and it is far from trivial to pattern large areas of substrates with colloidal monolayers.
Here, we present an experimentally simple method to create highly crystalline monolayers of wafer-scale dimensions on a wide variety of substrates.[2] The air/water interface is used to pre-assemble colloids that are subsequently transferred to solid substrates. The liquid nature of the interface provides sufficient mobility to allow the colloids to find their minimum free energy position in a hexagonally closed packed lattice and provides a mean to tune the degree of crystallinity by modification of the subphase. Addition of mixtures of colloids to the interface also allows for the crystallization of binary monolayers featuring a closed-packed monolayer of large spheres with a highly ordered superlattice of small particles.[3] The preformed monolayer can subsequently be transferred to arbitrary substrates, including topographically structured or curved surfaces.
We show how this simple process can be used to generate sophisticated surface structures for a wide range of applications, including the creation of highly repellent, omniphobic surface coatings[4], the preparation of complex plasmonic structures [5] and the generation of metal nanodot arrays with dimensions below 10 nanometers.[6]
[1] N. Vogel, C.K. Weiss, and K. Landfester, Soft Matter 2012, 8, 4044
[2] N. Vogel, S. Goerres, K. Landfester, and C. K. Weiss, Macromol. Chem. Phys. 2011, 212, 1719
[3] N. Vogel, L. de Viguerie, U. Jonas, C. K. Weiss, and K. Landfester, Adv. Funct. Mater. 2011, 21, 3064
[4] N. Vogel, R. Belisle, B. Hatton, T.S. Wong and J. Aizenberg, Nature Comm., accepted for publication
[5] N. Vogel, J. Fischer, R. Mohammadi, M. Retsch, H.J. Butt, K. Landfester, C.K. Weiss, and M. Kreiter, Nano Lett. 2011, 11, 446
[6] N. Vogel, A. Manzke, C.K. Weiss, U. Ziener, A. Plettl, K. Landfester, and P. Ziemann, Nanoscale 2011, 3, 2523

The demand for lithographic methods that provide rapid, high resolution patterning with a maximum degree of control continues apace. Laser direct write (DW) is an attractive alternative to the slower vacuum chamber particle beam techniques, as it can achieve up to cm/s patterning rates. Laser techniques come at the cost of reduced resolution and require high numerical aperture (NA) immersion objectives, and even the overlapping of multiple beams, to achieve their most impressive subwavelength results. In addition, the materials employed for both laser and charged particle DW are often themselves expensive, designer materials. While nanomachining by femtosecond ablation can also achieve submicron features in a general set of materials, it often results in rough features due to the high energy nature of the ablation process. By taking advantage of the interaction between optical and thermal effects, we have developed a positive-tone DW technique that can achieve sub-wavelength pattering robust enough for transfer by non-linear overlap effects in a conventional polymer systems (polyvinylacetate, polystyrene, polyvinylpyrrilidone, etc.) with relatively inexpensive free-space optics. Via this combination of antireflection, dewetting, and thermal absorption, features <100 nm can be achieved, but with a much greater degree of deliberate control than is usually achieved by bottom-up dewetting. Further, when viewed as a lithographic technique, this method skips the usual development step and promises the possibility of a solvent-free process. Using experiments and simulations, we demonstrate the mechanism and efficacy of this technique and investigate the effects of material parameters such as molecular weight and glass transition temperature.

Dense packings of hard polyhedra have been studied for centuries due to their mathematical aesthetic and more recently for their applications in fields such as granular matter, amorphous matter, and biology. The spontaneous organization of hard polyhedra in solution has only recently been addressed, demonstrating a plethora of assembled complex structures. For any given shape, the densest packings and the structures assembled spontaneously from the fluid are often different. In this talk we investigate connections between packings and assemblies for three families of convex polyhedra. We discuss the possibility of predicting one knowledge of the other, discuss trends, and link with previous works.

Self-organization of precipitate structures during severe plastic deformation (SPD) was investigated in Cu-rich CuAgNb ternary alloys. Cu, Ag and Nb powders were co-milled at room temperature with average Nb atomic concentrations of either 5 or 10 at.% and Ag atomic concentration of 10% at. The ball-milled powders were then compacted, annealed and subjected to SPD by high pressure torsion (HPT). X-ray diffraction indicated the alloy reaches a steady state microstructure, with Ag atoms tending to homogeneously redistribute in the Cu matrix after HPT and Nb atoms increasing its solublilty to approximately 1 at.%. High Resolution Scanning Electron Microscopy reveals that Nb particles reduce their sizes during HPT, with the size distribution changing from bi-modal for as-annealed sample to log-normal after HPT. The precipitate size increases somewhat with increasing Nb concentrations. Atom probe tomography results confirm SEM and XRD results. How the system selects the average precipitate size and density, without any thermal diffusion, is explained using a novel kinetic Monte Carlo simulation model

Relatively noble nanoporous metals (Au, Pt, Cu, etc.) can be formed via electrochemical dealloying - dissolving away one or more component out of an alloy under an applied potential in a dilute acid, which results in a porous structure with pores and ligaments on the order of 1-10 nm. Important limitations to this technique are that the dissolving component(s) must have significantly lower reversible potentials than the remaining component(s) and not oxidize under dealloying conditions. Here we report dealloying using a liquid metal instead of an electrolyte to create novel porous metals comprised of refractory elements. We start with a binary parent alloy and immerse it into a liquid metal that has a lower melting point than either components of the parent alloy. The liquid metal is chosen to be miscible with one of the components and immiscible with the other. The formation mechanism is identical to electrochemical dealloying except the resulting structure is a composite of two interpenetrating porous networks, and we can tune pore size by control of the dealloying temperature. Structure/Processing/Property relationships for porous refractory metals made using this technique will be discussed.

Close-packed arrays of ZrO2 nanocrystals (NCs) have been self-assembled from colloidal solution in a withdraw dip coating process. The benzyl alcohol route was used to obtain narrowly controlled size NCs, and then the capping layer was replaced by oleate using solvothermal treatment. The oleate solubility was explored in chloroform, hexane and toluene to prepare thin films of NCs using a dip coating process. From TEM images, the final structures show that increasing the solvent polarity improved self-assembly to prepare mono- and multi-layer superlattices, during solvent evaporation in a short time. The entangled organic chain in the NCs surface offset the limitations of the faceted NCs, improving the assembly quality, allowing the NCs assembly to approach formation of a hard sphere model, resulting in a FCC closed packed structure. Molecular dynamics simulations with soft potentials supported the conclusion that hexane interacts with the organic capping ligand, increasing the apparent radius of each NC and stabilizing the colloidal suspension, whereas chloroform is partially removed from the capping during the aggregation process, forming an array of nanoparticles.

We have developed an island dynamics model that uses the level-set approach to model epitaxial growth. In recent work we have implemented a numerical scheme to solve the diffusion equation for the adatom concentration with a (mixed) Robin boundary condition. Such a boundary condition properly describes multilayer growth when there is an additional step-edge barrier for atoms to diffuse over a step edge. We will discuss how variations of the boundary condition that correspond to variations of the step edge barrier affect the formation of mounds. We will furthermore discuss how the effect of downward funneling can be implemented within our approach and how it affects the slop of the mounds.

Developing generic platforms to direct the assembly of inorganic nanomaterials into deterministic structures with specific functions remains one of the central challenges in nanoscience. To address this challenge, we are developing a unique bio-inspired approach to tip-based nanopatterning to grow functional nanomaterials. This approach relies on tip-based patterning of peptides selected for their ability to induce material-specific formation of inorganic crystals under mild reaction conditions.
Based on our knowledge of phage display and peptide sequencing, we focused on the study of the physical and chemical mechanisms behind peptide-driven nucleation of of ZnS and Au nanocrystals. We applied our understanding of biotemplating to control the areal density, film thickness, and crystallinity of these materials, all of which strongly depend on the conditions of the precursor solution as well as the peptide sequences. We developed a protocol for growth of continuous nanocrystal films on surface-templated peptides as well as on whole phage.
We related the physical structures and chemical compositions of the resulting nanocrystals to their mechanical, electrical, and optical properties. For the case of ZnS, we observed good electrical conductivity and photo-sensitivity. We also found we can improve the electrical conductivity by up to two orders of magnitude upon thermal annealing due to a drastic improvement of in the crystallinity. Prospects for tip-based fabrication of device architectures using this approach will be disussed.

The self assembly of organic molecules, such as pentacenes, have technological potential for organic photovoltaic (OPV) applications. Pentacene derivatives have been developed that overcome some of the shortcomings of pure pentacene, many of which inhibit the efficiency of its use in electronic devices. Increased solubility, high photo-oxidative resistance, thermal stability, and tailor-able HOMO-LUMO gaps make pentacene derivatives enticing for further study. Scanning tunneling microscopy and density functional theory was used to examine the atomic interface between gold and the pentacene derivatives: 6,13-dichloropentacene (DCP) and 5,6,7-trithiapentacene-13-one (TTPO), electron donors exhibiting self assembled monolayer (SAM) structures on gold surfaces. This is exemplified by DCP&’s observed long-range, highly-ordered SAM of a brick-wall pattern along the length of the stepped Au (788) surface [1]. TTPO was observed to form chain-like structures anchored to the surface at low coverage, as well as a more ordered SAM at close to monolayer coverage. By studying the self assembly of organic molecules on metallic surfaces, we are developing novel pathways toward molecular control of the organic-metal interface as a means of addressing efficiency problems at the nanoscale for OPV devices. It is the understanding of the structure of photovoltaic heterojunctions that can allow for tailoring of interfaces with improved electrical transport and energy-conversion efficiency.
[1] Wang, J., et al., Highly Ordered Assembly of Single-Domain Dichloropentacene over Large Areas on Vicinal Gold Surfaces. ACS Nano, 2011. 5(3): p. 1792-1797.

This work presents a self-assembly process to synthesize nanowires that are aligned to the crystal directions of 2D graphene membranes. Graphene has high anisotropy in its electrical and physical properties, thus aligning nanostructures to its crystal directions is important to realize graphene-based nanodevices. Previously, various nanostructures were synthesized on graphene derivatives (graphene, graphene oxide, and/or reduced graphene oxide) using liquid-phase and vapor-phase techniques. However, it has been challenging to fabricate nanostructures aligned to the graphene lattice directions. With the liquid-phase synthesis techniques, all of inorganic materials formed only randomly-distributed nanostructures on graphene and a few organic materials generated epitaxially-aligned nanopatterns only on thick graphite. The vapor-phase synthesis techniques could align edges of deposited nanostructures to the graphene lattice directions, but it&’s still far from the realization of nanodevice fabrications. This work presents a liquid-based synthesis method that can align inorganic nanowires to the crystal directions of graphene. In our knowledge, this work is the first presentation of the epitaxial alignment of inorganic nanostructures on single-layered graphene.
The key part of the nanowire synthesis process is to incubate graphene and gold together in an aqueous reaction solution. First, single-layered graphene synthesized by CVD is transferred to commercial TEM grids. Then, gold nanoparticles (source material for nanowires) are deposited on top of graphene by drop-casting. Finally, the graphene sample is incubated in the 250 mM aqueous solution of ammonium persulfate ((NH4)2SO4) for 10~17 h.
We experimentally verify the epitaxial alignment using TEM images of the nanowires and SAED (selected area electron diffraction) patterns of the bottom graphene. The synthesized nanowires form equilateral triangular patterns and longitudinal directions of the nanowires are aligned to (1-210) directions of graphene. In addition to the outer nanowire directions, inner molecular structures of the nanowires are also aligned: lattice lines in every nanowire have the same directions (perpendicular to nanowire lengths) and the equal lattice spacing (~5 Å). The AFM image also clearly shows the nanowires and their geometries that are the length of ~100 nm, the width of ~10 nm, and the thickness of ~3 nm. Since the EDX analysis indicates that the nanowires contain Au and O, we expect that the synthesized nanowire is a hydrated form of gold(III) oxide, and further analysis will be performed. One of important characteristics of the nanowires is that we can generate epitaxially aligned arrays of gold nanoparticles on graphene from the nanowires. E-beam or heat can induce a reduction of nanowires to form gold nanoparticle chains. We envision that this method can be useful for bottom-up fabrication of graphene-based nanodevices.

Thanks to their high surface area, nanoporous materials are ideal candidates for a wide range of important applications such as sensor. The challenge is to be able to control the size and distribution of the pores.
On a Si substrate we e-beam evaporated a thin layer of Al2O3 and coated it with an inorganic complex containing Fe and counter-ion inside a solution. With the inclusion of the Fe complex, we synthesized a nanoporous material using chemical vapor deposition (CVD). We controlled the size and distribution of the pores by varying the gas flow. We used this structure to synthesize entangled carbon nanofibers on top of the complex. The effectiveness of the Fe complex was observed for wide variations of process parameters such as growth duration, gas flows, and temperature. High-resolution microscopy confirmed the presence of pores and the additional EDAX confirmed that the Fe complex was the porous material. In order to prove that indeed the counter-ion is responsible for the formation of the pores, we preformed another experiment where we changed the counter-ion to chloride instead of perchlorate, and observed that no pores were formed. We checked the distribution of the porous using a special program. BET measurement showed that Ferroin crystals have high surface area of 407m2/gr. This result is significant as it shows a simple and effective method to synthesize porous materials with good control over pore size and distribution.

Scattering of light by metal nanoparticles can be used to improve the efficiency of solar cells by reducing reflectance and increasing absorption within the semiconductor. However the nanoparticles must be carefully designed to minimize losses, such as parasitic absorption and back-scattering.
A dense array of metal nanoparticles can be fabricated by annealing a thin metal film at relatively modest temperatures of around 100-400C, which causes the film to self-organise into discrete 'islands' due to recrystalization. The film can be deposited using simple PVD approaches such as evaporation or sputtering. The process is well suited for solar cells because it is low-cost, large-area, high-throughput and only requires equipment that is already part of a standard production line. However it is challenging to optimize the optical properties of the metal nanoparticles because their size, shape and arrangement are dependent on many parameters, including the metal type, deposition rate, substrate material, anneal time and anneal temperature. Therefore there is still a need to optimize and improve the metal island film technique for photovoltaic applications.
We demonstrate a combinatorial optimization process for silver and gold island films, in which we vary two deposition parameters orthogonally across a substrate, and hence explore a wide parameter space in a single deposition. Using this approach we explore the relationship between the deposition parameters and the size and shape distribution of the self-organised nanoparticle film, and demonstrate tuning of the mean particle size from 5nm to over 300nm. However the resulting arrays still feature a wide range of size and shape, and are densely packed.
Further improvement can be made by utilising ion bombardment. We show that Ar ion bombardment gradually and controllably removes material from the nanoparticles and can be used to remove small particles, to reduce the overall surface coverage, and to change the particle shape from hemispherical to disc-like. We also show that over-etching of the substrate can be minimized by optimizing the ion-beam angle of incidence. Overall ion-beam milling results in smoother films with reduced parasitic absorption, and offers additional control of the optical properties of metal island films.

Polymer nanocomposites are integral components of coatings and are used in a variety of areas including industrial, medical and opto-electronic applications. We have recently shown that silver nanoparticles can be formed by reduction of their salts by free radicals while the monomeric matrix is polymerized by either free radicals or cations derived from the radicals. We are currently investigating new methods to prepare these nanocomposites. Real time synchrotron SAXS studies have allowed us to monitor the rate of nanoparticle growth and confirmed the cessation of nanoparticle growth upon network gelation. These results have provided further insight into the mechanism of formation of these nanocomposites. We will present our findings including kinetics of nanoparticle/polymer network formation, influence of stoichiometry on nanostructural development and the resulting mechanical, physical, optical and electrical properties of the prepared nanocomposites.
References:
M Sakamoto, M Fujistuka, T Majima: Light as a construction tool of metal nanoparticles: Synthesis and mechanism, J Photochem Photobiol C: Photochem Rev, 10, 33-56 (2009)
M Uygun, MU Kahveci, D Odaci, S Timur, Y Yagci Antibacterial acrylamide hydrogels containing silver nanoparticles by simultaneous photoinduced free radical polymerization and electron transfer processes, Macro Chem Phys, 210, 1867-1875 (2009)
W D. Cook, Q D Nghiem, Q Chen, F Chen, M Sangermano, Simultaneous photoinduced silver nanoparticles formation and cationic polymerization of divinyl ethers, Macromolecules, 44, 4065-4071, (2011)

We report on a new class of materials for laser printer toner applications. These materials were prepared from methacrysilane-in-water emulsions stabilized with colloidal silica particles. In this elegant system the colloidal silica particles reside at the water/oil interface helping to emulsify the oil droplet, self-organizing into raspberry-like morphology. The emulsion formation is followed by the free-radical polymerization, hydrophobic treatment, and drying steps. This one pot synthesis in water affords a hydrophobic material with a particle size in the range of 80 to 300 nm. The particle size could be fine-tuned by changing the oil-to-silica mass ratio or by using colloidal silica particles of different sizes. Results of material characterization by solid-state NMR, electron microscopy, and particle size measurements methods will be presented. Examples of possible extensions of the synthesis towards materials with methacrylsilane partially substituted with other methacrylates will be provided. Application of the new material in toners will be described as will the comparison of its performance with the incumbent material - hydrophobic colloidal silica.

In this work we show that the different reactivities of SiH and SiCl surface groups in partially chlorinated silicon surfaces open pathways for the selective functionalization of flat Si(111) surfaces, therefore allowing the formation of nanopatterns on such surfaces. We also show that the high reactivity of the step edges of fully chlorinated surfaces could also be used for the selective functionalization of vicinal surfaces.
Using density functional theory and a slab model of the surface (1), we investigated the reactivity of the partially chlorinated Si(111) surface towards reactants with N, O and S head groups (NH3, H2O, H2S, CH3NH2, CH3OH, and CH3SH) in relation to the development of selectively functionalized surfaces. The reactivities of the fully hydrogenated and halogenated Si(111) surfaces are also considered as a reference. The results show that the perfect Hminus;Si(111) and Clminus;Si(111) surfaces are unreactive at room temperature. However, the decrease of steric factors on partially chlorinated surfaces, increase the reactivity of the SiCl group towards NH3, CH3NH2 and H2O to such extent that they could react at room temperature.
As the reactivity of SiH and SiCl groups is very different (2), surfaces with a partial coverage of chlorine atoms may allow a selective functionalization of the surface by a chemistry route. Therefore, by controlling the initial chlorine surface coverage during the chlorination procedure, the surface density of molecules grafted to the silicon surface could be controlled as well. The concept of selective functionalization thus relies upon the presence of reactive SiCl groups embedded in a matrix of unreactive SiH groups. Once steric factors around a SiCl group are liberated by the appearance of adjacent SiH groups, the reactivity of SiCl greatly increases, whereas the reactivity of SiH remains unaltered.
Unlike the fully chlorinated Si(111) surface, the SiCl groups on the reconstructed step edges are very reactive showing the lowest activation energy barriers. Fully chlorinated vicinal silicon surfaces seem to offer an opportunity to build molecular lines along the highly reactive step edges. We envisage a two step procedure in which the step edges are first functionalized via the formation of Siminus;N or Siminus;O bonds and then the Clminus;Si(111) terraces are passivated via the formation of Siminus;C bonds by reaction with alkyl Grignards.
(1) F. A. Soria, E. M. Patrito, P. Paredes-Olivera. On the Mechanism of Silicon Activation by Halogen Atoms. Langmuir 2011, 27, 2613-2624.
(2) F. A. Soria, E. M. Patrito, P. Paredes-Olivera. Tailoring the Surface Reactivity of Silicon Surfaces by Partial Halogenation. J. Phys. Chem. C. Submitted.

We have demonstrated the synthesis of Au-Pd core-shell heterostructures with systematic shape evolution from octahedra, truncated-octahedra, cuboctahedra, truncated cubes, cubes to concave cubes having finely- and well-controlled sizes of 40-140 nm using octahedral cores. The localized surface plasmon resonance(LSPR) properties of such Au-Pd core-shell nanocrystals (NCs) are investigated and further compared with theoretical results. The availability of uniform Au-Pd core-shell nanocrystals with finely controllable shell thicknesses and shapes allowed us to investigate the dependence of shell thicknesses and shapes on the optical properties of bi-metallic core-shell nanocrystals. The plasmonic band of gold red-shifts from Au-Pd nanocubes to octahedra, and differs by as much as 8 nm between the nanocubes and the octahedra. Further, we demonstrated that Au-Pd core-shell nanocrystals are excellent and highly responsive materials for hydrogen gas sensing based on localized surface plasmon resonances in real time. Both particle shapes displayed very large spectral red shifts upon exposing to hydrogen gas, but the Octahedral particles showed an even more pronounced red shift because antenna induced electromagnetic fields are more confined in metallic nanostructures with sharper corners or edges, giving rise to a higher sensitivity. When smaller Au-Pd particles are used, direct visual changes can be observed upon exposure to hydrogen gas. This is the first report regarding gas sensing using bi-metallic core-shell nanocrystals in liquid phase. In a wider perspective, the results suggest that the plasmonic nanocrystals from bimetallic antennas may offer many new routes toward novel nanophotonic sensing schemes.

The spinel structure has anisotropic surface energies along the (111) and (001) crystal planes. This strongly affects the crystal growth of spinel nano-structures and thin films. By selecting suitable substrates and growth conditions, it is possible to grow spontaneously-forming nano-pyramid struc-tures along the (001) crystal direction, as has been observed for the CoCr₂O₄ spinel [1]. However, some spinel materials, like a magnetite (Fe₃O₄), show a preferential (111)-oriented crystal growth di-rection at higher temperature, resulting in random intermixing of grains with (001) and (111) plane directions. It is therefore difficult to grow nanoscale pyramids by self-assembly as the film does not have a table (001)-oriented surface. A possible solution is to use a thin self-template layer for film ori-entation control [2]. We investigate the self-template method for nanoscale Fe₃O₄ pyramid growth at temperatures above 1000°C.
Fe₃O₄ films were grown on BHF-etched SrTiO₃(001) substrates by pulsed laser deposition. First, an 8-nm-thick nucleation layer was deposited on a SrTiO₃(001) surface at 400°C, followed by main film growth at 1100°C. The thin self-template layer stabilized the (001)-oriented growth. High-temperature growth resulted in greatly improved crystallinity of the Fe₃O₄ films with films grown at 1100°C having a rocking curve width of 0.28°, much smaller than the 1.41° width of conventionally-deposited Fe₃O₄ films on SrTiO₃(001). Surface analysis by atomic force microscopy (AFM) and scan-ning electron microscopy (SEM) revealed that growth at 1100°C on a SrTiO₃(001) substrate promoted the formation of self-assembled nano-pyramid structures of (001)-oriented Fe₃O₄ crystals. This growth mode is due to the strong anisotropy of the Fe₃O₄ crystal surface energy. The pyramid size was tun-able by varying the deposition time and plays an important role in determining the magnetic character-istics, gradually shifting from a bulk-like ferrimagnetic to a super-paramagnetic phase as the pyramid size is reduced.
[1] U. Lüders et al, Phys. Rev. B 70, 045403 (2004)
[2] R. Takahashi et al. Crystal Growth & Design 12, 2679 (2012)

As a consequence of technological miniaturization trends, surface patterning on substrates at nanoscale [1,2] has become an intensive research topic in Materials Science and Engineering with a wide range of applications varying from sensor design to micro- and nano-electronics. Furthermore, surface patterning is also of interest to Health Sciences since many carcinogens polycyclic aromatic hydrocarbons (PAHs) produced from combustion can be absorbed on the surface of airborne, water or soil particles and can be easily inhalated [3]. In this contribution, the formation and thermal stability of two-dimensional (2D) non-covalent crystalline structures of some organic molecules (coronene, pyrene and pentacene) are investigated by means of classical molecular dynamics simulations, using the AIREBO potential. With unique constraints of being on top of a graphitic layer and subjected to van der Waals forces, it is shown that equilibrium 2D structures of organic molecules resemble the well known Abrikosov hexagonal lattices observed in superconductors as a consequence of energy minimization [4], regardless the type and shape of the molecules. Thermal stability of the obtained 2D structures is also investigated and the interplay between the disorder caused by thermal fluctuations and van der Waals interactions is also discussed. Experiments on confinement and geometric minimization for superconductors [5] and recent data for 2D structures of organic molecules are analyzed in terms of our results [6].
References
[1] Y. Lei, S. Yang, M. Wub and G. Wilde, Chem. Soc. Rev. 40, 1247 (2011).
[2] D. F. Perepichka and F. Rosei, Science 323, 216 (2009).
[3] T. Tran-Duc, N. Thamwattana, B. J. Cox and J. M. Hill, Computational Mater. Sci. 49, S307 (2010).
[4] W. H. Kleiner, L. M. Roth and S. H. Autler, Physical Review 133, A1226 (1964).
[5] V. V. Moshchalkov, L. Gielen, M. Baert, V. Metlushko, G. Neuttiens, C. Strunk, V. Bruyndoncx, X. Qiu, M. Dhallé, K. Temst, C. Potter, R. Jonckheere, L. Stockman, M. Van Bael, C. Van Haesendonck and Y. Bruynseraede, Physica Scripta T55, 168 (1994).
[6] L. D. Sun, J. Gall, G. Weidlinger, C.Y. Liu, M. Denk and P. Zeppenfeld, Phys. Rev. Lett. 110, 106101 (2013).
[7] Authors are research fellows of CNPq and acknowledge grants from CNPq, FAPESP and UNESP.

Metallic nanoparticle deposition plays an important role in advanced materials and devices today, due to their utilization in next generation electronics and optoelectronics [1-2]. Current approaches for metallic nanoparticle deposition prove to be either complex in nature with high production costs or insufficient for high quality dispersion and homogeneity.
Other deposition methods include dip coating and electrophoretic deposition. Dip coating approach uses extremely low speeds of withdrawal to achieve high quality dispersion of particles over the substrate surface [3]. However, Electrophoretic deposition drives the particles with an external field to the substrate. The main advantage of the electrophoretic deposition is that it can be merely controlled by the applied field [4].
We propose a method that combines dip-coating and electrodeposition techniques. The method uses an electric field during the dip coating process. The sample is submerged into the nanoparticle solution while the electric field is applied for a period of time and the sample is withdrawn from the solution with defined speeds.
The process can be separated into the following stages: immersion (10 sec up to 10 min at constant speeds ranging from 1 to 20 mm/min), electric field application (different fields for different periods), withdrawal (speeds from 1 to 20 mm/min), drainage and evaporation of excess liquid). The particle density and distribution was investigated as a function of different deposition parameters including: electric field, submerging time, and withdrawal speed.
Particle distribution and density were found to be associated with the combination of the electrical and kinetic processes during the experiment. Optimizing both withdrawal speed and the time the substrate is exposed to the electric filed allows precise control of the deposition homogeneity and dispersion.
The results show inter-linkage between the kinetic and the electrochemical processes acting upon the particle deposition, resulting in high densities and good dispersions. The method proposed shows to be a promising technique for metallic nanoparticles deposition, having the advantages of both original techniques of electrodeposition and dip-coating separately.
[1] McFarland AD, Young MA, Dieringer JA, and Duyne RPV, “Wavelength scanned surface enhanced raman excitation spectroscopy,” J. Phys. Chem. B., Vol. 109, pp. 11279-11285, 2005.
[2] Elghanian R, Storhoff JJ, Mucic RC, Letsinger RL, and Mirkin CA, “Selective colorimetric detection of polynucleotides based on the distance dependent optical properties of gold nanoparticles,” Science Vol. 277, pp. 1078-1081, 1997.
[3] Sakthivel, S., S. Rajivgandhi, and D. Mangalaraj, "Stannum-Cadmium Composite Nano Rods Nano Wires and Particles by Simple Technique," Nano Vision, vol. 2, pp. 25-47, 2012.
[4] Kooij ES, Brouwer EAM, and Poelsema B, “Electric field assisted nanocolloidal gold deposition,” J. Electroanal Chem., vol. 611, pp. 208-216, 2007.

Photoremovable protecting groups (PPG) like 4,5-dimethoxy-2-nitrobenzylbenzoylchloride (NVOC) are widespread and of increasing interest by now, since they allow the development of unique patterns on inorganic surfaces and give the opportunity to change its chemical and electronic properties.
We report the synthesis of molecules equipped with silane anchor groups, which are bound via a branching unit to the PPG. Silicon surfaces - silica wafers or quartz slides - were functionalized with these molecules. After removing the PPG by irradiation and regaining the reactive functional groups (amines, carboxylic acids or alcohols) the surface is ready for further chemical reactions, whereby alteration of the material properties can be achieved.
We have functionalized silica surfaces with 4,5-dimethoxy-2-nitrobenzyl-
3-(triethoxysilyl)propylcarbamate (NVOC-Silane), irradiated the composites with UV-light (365 nm) and accomplished further modification with Phenylazobenzoylchloride. Characterization was implemented by Contact Angle Measurements (CA), Sum-Frequency-Generation (SFG), Ellipsometry and UV/vis Measurements. Of special importance is the optimization of the monolayer ordering, the anchoring mechanism and the conditions of the chemical reaction on the surface. For this purpose we examined different etching conditions, concentration of NVOC-Silane, adsorption kinetics, solvent influence, temperature and stirring speed, whereby we achieve different ordered NVOC-Silane surfaces, which are characterized by the methods described above.
By irradiation of the NVOC-Silane monolayer, we are able to accomplish further chemical modification on the surface with functional organic molecules like fullerenes, porphyrins or nanotubes. Thereby we have the opportunity to obtain smart electronic materials, create new optical properties on the surface and make advances in the field of “lab in the fiber”.

Under appropriate conditions, gold or silver nanoparticles can self-assemble from colloidal suspension into a wide variety of highly symmetric nanostructures. Examples include chains of spheres or rods, ordered supracrystals, dimers, trimers, and core-satellite constructs. Control of the resulting geometry can be achieved by manipulation of the chemical environment. Here we describe core-satellite nanostructures that can be integrated with functional molecules to provide a hybrid optical functionality. The gold particles are plasmonic and excitation of a plasmon resonance in two closely-spaced (sim;1 - 5 nm) particles is of particular importance because it can provide “hot spots”, i.e. regions of considerably enhanced electric field strength. Inclusion within the “hot spot” of a dye that absorbs strongly in a similar region of the spectrum and that also possesses high intrinsic third-order optical nonlinearities should provide a hybrid system with significantly amplified optical and nonlinear optical properties.
The “hot spots” have been previously studied [1, 2], and the intensity of the dipolar EM field in the region between plasmonic particles is well-known to be sensitive to the distance between the particles. However, the effect of multipolar hot spots that could potentially excite quadrupole or other “forbidden” resonances [3] in a suitably placed molecule is not as well studied or understood.
Here we present an examination into how self-assembled core-satellite nanostructures can be integrated with functional molecules to provide hybrid optical functionalities. Our basic building block is a gold nanosphere that is functionalized with metallophthalocyanine molecules. We will present details on the synthesis and characterisation of particles that form the building blocks of higher-order self-assembled core-satellite nanostructures and show how these can be modified to accommodate a range of satellite nanoparticles.
References
1. Gandra, N.; Abbas, A.; Tian, L.; Singamaneni, S., Plasmonic planet-satellite analogues: hierarchical self-assembly of gold nanostructures. Nano Letters 2012, 12 (5), 2645-51.
2. Kneipp, K.; Kneipp, H.; Kneipp, J., Surface-Enhanced Raman Scattering in Local Optical Fields of Silver and Gold Nanoaggregates. Accounts of Chemical Research 2006, 39 (7), 443-450.
3. Curto, A. G.; Taminiau, T. H.; Volpe, G.; Kreuzer, M. P.; Quidant, R.; Hulst, N. F. V., Multipolar radiation of quantum emitters with nanowire optical antennas. Nature Communications 2013, 4, 1750.

The integration of metallic and dielectric nanoparticles into metallo-dielectric hybrid materials with defined morphologies provides new opportunities for the manipulation of light-matter interactions within subwavelength scales. One major roadblock towards the realization of such material is the requirement for a reliable organization of different components with high spatial resolution. We demonstrate in this contribution a template-guided self assembly approach, which facilitates the positioning of TiO2 nanoparticles (NPs) and Au NP clusters at pre-defined lattice sites. Two different types of hybrid structures were analyzed. In one geometry individual TiO2 NPs were supported by an Au NP cluster of defined diameter; in the second geometry TiO2 NP and Au NP cluster were localized on separate pre-defined lattice sites. The characterization of these materials through elastic and inelastic scattering spectroscopy revealed a cascaded near field enhancement in the gaps of the plasmonic clusters in extended optoplasmonic arrays. Furthermore, both optoplasmonic and extended structures achieve an efficient energy redistribution that leads to an enhancement of electric and magnetic field components in the clusters as well as in the ambient medium.

With increasing demand for complex three-dimensional (3D) nanostructures, nanoimprint lithography (NIL) has received vigorous attention, due to its low cost, high throughput and high print resolution. However, fabrication of NIL molds having nanoscale features has become a bottleneck for NIL development. In our attempt to overcome this problem, SU-8, a widely used photoresist and permanent structural material for MEMS, biochemical sensors, and microfluidics applications, was employed for the first time as a NIL mold. Nanoscale features were patterned on SU-8 using a focused ion beam (FIB) milling technique. The lack of backscattered electrons in FIB processing, which limits the minimum feature size attainable by e-beam lithography (E-Beam), makes this technique a potential tool for producing nanoscale features in NIL mold materials, such as SU-8.
We found that nanofeatures patterned on SU-8 showed both the ‘V-shape&’ side wall and opposing dose deficiency effect. The effects of ion beam current, milling time and SU-8 crosslink density on feature quality were also studied. Finally, the FIB-generated SU-8 mold was utilized in both thermal-NIL and UV-NIL experiments. The FIB imprint results revealed that pattern profile and filling ratio depend highly on NIL processing pressure and physical property of imprinting resists, such as viscoelasticity.

Graphene has recently stimulated enormous research efforts owing to its unique properties including electron and photon transparency, high electrical and thermal conductivity, and high breaking strength and stiffness. However, assembly of monolayer graphene onto substrates of interest remains extremely challenging. Due to the convenience of processing graphene-related materials in solution, an advantageous strategy for preparing graphene involves chemical oxidation and exfoliation of graphite to graphene oxide (GO) followed by subsequent chemical or thermal reduction. Cote et al.1 recently demonstrated that amphiphilic GO can assemble on a water surface in a Langmuir trough, and that the monolayer can be transferred to substrates by Langmuir-Blodgett (LB) deposition. The success of this transfer depends not only on the nature of the substrate surface, but also on the mechanical properties of the GO monolayer on water. GO assembly is particularly complicated due to sheet size and shape variations after oxidation, so understanding the mechanical properties of the highly non-uniform monolayer as it assembles can guide transfer to substrates. Towards this end, we measure the complex shear and elastic moduli of the GO monolayer on water in a Langmuir trough with various subphase pH values, GO sheet sizes, and surface pressures. Oscillatory barrier measurements2 show that the monolayer is primarily elastic and allow us to determine the shear and compressive moduli. Shear modulus development indicates that the GO monolayer assembles as a two-dimensional solid with long-range order rather than behaving as individual sheets. Because the GO monolayer resembles a solid, we hypothesize that it should be critical to minimally disturb the monolayer during transfer in order for it to remain assembled. Based on this reasoning, we dip substrates at a shallow angle relative to the water surface rather than at 90 degrees as is typical for LB dips. Previously LB transfers of GO have been shown to be limited to highly hydrophilic surfaces. We find that dipping at a shallow angle allows transfer to hydrophobic surfaces as well, greatly expanding the versatility of the LB technique. This work characterizes for the first time the mechanical properties of GO monolayers assembled on water and capitalizes on understanding these properties to demonstrate transfer of GO monolayers to hydrophobic and hydrophilic surfaces. We believe the discoveries presented here will be applicable to other two-dimensional, amphiphilic materials.
1. L.J. Cote et al., Soft Matter, 2010, 6, 6096.
2. P. Cicuta et al., Eur. Phys. J. E, 2005, 16, 147.
Supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE&’s NNSA under contract DE-AC04-94AL85000.

Multiferroic composites could provide more than one spontaneous electric, magnetic, and elastic order simultaneously. Recently, the research interest in multiferroics has focused more and more in thin films area with the development of thin film growth techniques, which enable deposition under epitaxial engineering and non-equilibrium conditions. Among the most widely studied two-phase multiferroic composite thin films, self-assembled epitaxial BiFeO3-CoFe2O4 (BFO-CFO) nanocomposite thin films have attracted tremendous research interest. This kind of thin films are known to self-assembly grow and form (1-3) nanostructure with rectangular-shaped CFO nanopillars embedded in BFO matrix by deposited on (001) SrTiO3 (STO) substrates.
Here, by utilizing such specific nanostructure, we pre-deposited one BFO layer on the bottom, and post-deposited another BFO layer on the top of that above mentioned BFO-CFO (1-3) thin film on (001) STO substrate. Hence, we successfully obtain a new quasi (0-3) heterostructures, which have second phase CFO nanoparticles (nanopillars) embedded in a primary BFO matrix phase. This new heterostructures could significantly reduce possible leakage current paths through the ferromagnetic phase substantially. And the good connectivity among the constituents might result in better coupling between the piezoelectric and magnetostrictive phases to enhance the potential magnetoelectric effects, which would provide much wider application for this new heterostructures.

Resistive switching random access memory (RRAM) is known as one of the most promising candidates for next-generation memory device due to its fast speed, low power consumption, good endurance /data retention properties, and scalability. Recently, it is reported that the nanoscale RRAM could be fabricated using self-assembled nano-templates as the mask layer. Among them anodic aluminum oxide (AAO) is a representative self-assembled nano-porous template having uniform hexagonal pore structure. In this study, we fabricated nanodot RRAM devices having Ni/NiO/Ni structure using AAO nano-templates as the patterning mask. Nano-porous AAO template was made by using two-step anodizing method. In order to easily form Ni nanostructures, we used the electrochemical deposition method instead of vacuum deposition process. And NiO layer was formed by using oxygen plasma at low temperature. The structure of nanoscale RRAM devices was confirmed with field-emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM). The electrical properties of the nano-structured RRAM devices were measured with conductive atomic force microscope (CAFM). Device fabrication procedures and nanoscale device characterization will be presented in detail.

In this work we report that the above described cation exchange reactions can be masked by previously exposing the nanocrystal film to an electron beam. With this technique regions of nanocrystals with chemically different composition can be obtained with the precision and resolution of electron-beam lithography. Starting from CdSe, CdS or core-shell CdS/CdS nanocrystal films we demonstrate optically emitting patterns and conductive circuits in a nanocrystal film with homogeneous topography. We use CdS and CdSe/CdS NC. We fabricated thin films by spin-coating, and exposed designed patterns by electron-beam lithography (EBL). The EBL process does not significantly modify the physical properties of the nanocrytals, but is has a strong impact on the morphology of the surface ligands and other possible residual organics in the film. After EBL the film is subjected to the cation exchange reaction (Cd to Cu) that is performed in liquid solvents, for example methanol, and only in the regions that were not exposed to the beam the CdSe (CdS) is transformed to CuSe (CuS).
The successful reaction can by readily imaged by spatially resolved photoluminescence spectroscopy, since CdSe and CdS manifest bright emission while the Cu counterparts remain dark due to their indirect band gap;Spatial chemical analysis confirms the protection by electron-beam exposure from the cation exchange reaction by manifesting Cu solely in the unprotected regions, and Cd in the exposed ones. We demonstrate the utility of this novel lithography approach by designing luminescent patterns and electrical circuit geometries like point contacts, tunnel junctions and conductive channels. One particularly interesting feature of the electrical circuits is that they consist of a semimetallic metallic material (CuSe, CuS) surrounded by a semiconductor nanocrystal film, which allows to exploit the optoelectronic properties of these materials.The electrical characteristics of the above mentioned circuits will be discussed.

The synthesis and patterning of nanostructured materials in a controlled fashion is of great interest for applications in electronic devices, photonics, energy storage, and biological/chemical analysis. Recently, porous, nanostructured materials, such as pure-silica zeolite films, have been used to form 2D and 3D structures for building nano-containers and other intricate assemblies for harvesting light, for sensing applications or for creating microreactors. Traditionally, these films have been synthesized as multilayers of randomly-oriented crystals; however, these types of new applications require precise control of the crystal orientation, surface coverage, film thickness and, most importantly, post-synthetic patterning. The standard methods used to pattern such nanostructured materials are based on either typical microfabrication techniques, which involve several complex steps of long duration, or organization of pre-formed seeds/crystals arranged uniformly by chemical linkages, which requires precise control and positioning and could result in pore clogging. To avoid these challenges, we evaluate the use of femtosecond laser ablation, which has recently shown good potential for patterning of porous film materials. The ablation was done using a CLARK-MXR laser system, generating 150-fs laser pulses at a central wavelength of 775 nm. Trains of laser pulses generated at a repetition rate of 1 kHz were applied to micro-pattern the films. Laser fluence was kept below the ablation threshold of the films&’ underlying silicon substrate. Here, we demonstrate the effects of this technique on the patterning of a model zeolite thin film system, pure-silica MFI, to evaluate its potential for patterning complex, multicrystalline, nanostructured materials. We use SEM, XRD, ellipsometry and FTIR-ATR to determine the crystallinity, film thickness, surface coverage, crystal size, crystal habit, and chemical composition of the films pre- and post- patterning. Using this technique, we demonstrate that it is possible to make 3D structures, such as channels, in these films. This work introduces a one-step, non-destructive and rapid technique to pattern materials with specific framework structures and subnanometer pore sizes.

Alloys of immiscible elements can be prepared using non-equilibrium techniques such as physical vapour deposition. Such alloys have potential applications for the production of nanoporous metals, surfaces of defined or graded roughness and self-aligned nanowires by thermally driven phase separation. In this work, X-ray amorphous Cu-Ta alloys were prepared by co-sputtering and were annealed to induce phase separation. The evolution of phase separation was studied by Local Electrode Atom Probe Tomography, Transmission Electron Microscopy and X-ray Diffraction. Results show that in the metastable copper-tantalum alloys, phase separation is accompanied by crystallization of the individual phases. Depending on the initial Cu content of the alloy, Cu-rich clusters form in the still amorphous matrix at temperatures lower than 400°C. The clusters are fcc structured with (111) out-of-plane texture. At 600°C the amorphous matrix crystallizes into a β-Ta phase. The amount of Ta dissolved in the Cu-rich phase decreases upon annealing.

Metal-oxide-based resistive switching random access memories (RRAM) have recently gained significant attention as a potential candidate for future non-volatile memory technology due to their simple structure, fast switching speed, and CMOS compatibility. Several issues, however, have to be solved for practical application, such as instability of operation, endurance, data retention, and integration. Among the various metal oxides, copper oxide is very attractive as a switching material in RRAM because it is relatively inexpensive and nontoxic. In addition, copper oxide is reported to be compatible with standard semiconductor processes. In this study, we fabricated copper oxide-based RRAM with anodized aluminum oxide (AAO) nanotemplates. Self-organized nanoporous AAO is widely used as the mask for the fabrication of uniform nanoscale patterns. The copper oxide nanodots have been grown on Cu-coated Si substrates with electro-deposition and the nanoscale dots were synthesized with an accurate diameter according to the pore size of the masks. Electro-deposited Ni has been used as the top electrode. The AAO templates and the nanoscale resistive switching memory devices were observed using field-emission scanning electron microscopy. The microstructure and crystal structure of the devices were analyzed using high-resolution transmission electron microscopy and x-ray diffraction, respectively. The resistive switching behavior of the copper oxide-based memory devices was directly examined using the conductive atomic force microscopy (AFM). The topography and the electrical properties of the copper oxide nanodot memory devices were investigated using AFM and semiconductor parameter analyzer. In this presentation detailed device fabrication and characterization of nanoscale resistive memory devices will be discussed.

Anodic oxidation of aluminium is a well-established method for depositing alumina films with hexagonally ordered honeycomb structure.[1] Equal-sized nanopores are formed in water solutions of some acids at certain concentrations and temperatures, and comparatively high electrode potentials. Since porous alumina has numerous applications (filtration, adsorption, coloration, templates for nanotechnology, environmental decontamination),[2] the importance of understanding of its growth mechanism is beyond dispute. Previously, pore formation was reached only with empirically found conditions, and there was no effective theory able to predict new experiments. This lack of a reliable method for theoretical prediction of pore formation in non-familiar electrolytes prompted the search of a viable solution of this problem. Here, we present a novel synergetic model[3] for explanation and prediction of the hexagonal alumina cell formation.
Our proposed model is of simplified and semi-empirical character but nonetheless led to successful prediction of five novel electrolyte compositions (all confirmed with experiments). Thus, we provide a powerful tool for the prediction of pores appearance in unexplored electrolytes, and formulate the principles of rational electrolyte selection for future successful experiments.
[1] a) H. Masuda, K. Fukuda, Science 1995, 268, 1466-1468; b) H. Masuda, M. Satoh, Japanese Journal of Applied Physics Part 2-Letters 1996, 35, L126-L129; c) H. Masuda, H. Yamada, M. Satoh, H. Asoh, M. Nakao, T. Tamamura, Applied Physics Letters 1997, 71, 2770-2772; d) O. Jessensky, F. Muller, U. Gosele, Applied Physics Letters 1998, 72, 1173-1175.
[2] a) E. Moyen, L. Santinacci, L. Masson, W. Wulfhekel, M. Hanbücken, Adv Mater 2012, 24, 5094-5098; b) S. Zhang, F. Y. Cheng, Z. L. Tao, F. Gao, J. Chen, Journal of Alloys and Compounds 2006, 426, 281-285.
[3] a) M. Pashchanka, J. J. Schneider, J Mater Chem 2011, 21, 18761-18767; b) M. Pashchanka, J. J. Schneider, Physical Chemistry Chemical Physics 2013, 15, 7070-7074

Porous anodic aluminium oxide (PAOX) is a versatile material with a growing number of technological and laboratory applications, one of them being the template-based synthesis of quasi-one-dimensional (Q1D) nanostructures by replication of cylindrical nanochannels. The allure of this method is the precise control of functional nanostructures dimensions and uniformity, as well as their organisation into well-ordered aligned arrays. Since particular attention in nanotechnology is paid to size effects (i.e. the qualitative changes in physicochemical properties at unit dimensions less than 100 atomic or molecular diameters[1]), researchers aim at a flexible straightforward method for manufacturing PAOX templates with uniformly decreased pore size and preservation of hexagonal ordering. The direct relation of pore diameter to the anodizing potential difference is well studied,[2] however, the spontaneous self-ordering is a complex process, which requires optimized experimental conditions, and low-voltage anodization inevitably leads to the distortion of hexagonal structure. For example, hexagonal arrangement in 0.3 M oxalic acid is observed at 40 V, but not at 25 V. That is why some sophisticated multi-step methods have been developed to manufacture extra-small hexagonally arranged PAOX nanochannels. [3]
Here, we report a simple and straightforward method for substantial uniform reduction of pore size without pore aspect ratio limitations by pulsed anodization, as well as maintenance of the hexagonal pore arrangement via optimisation of pulsed voltage frequencies. To the best of our knowledge, there are currently several publications on PAOX channels with sequential diameter alternation by pulsed voltage anodization, but none of these papers reports uniform contraction of pore interiors.
In our experiments, nanopore diameters in anodic alumina films were uniformly reduced by half. Spontaneous self-ordering into hexagonal pattern maintained at pulse frequencies 0.5-1 Hz. The results were reproducible in both 0.3 oxalic (long-range ordered domains) and 10 wt.-% sulphuric (incipient short range ordering) acids, and yielded smooth uniform nanochannels of 20 nm and 10 nm diameters correspondingly.
[1] G. B. Sergeev, Nanochemistry, Elsevier B. V., Amsterdam, 2006.
[2] K. Nielsch, J. Choi, K. Schwirn, R. B. Wehrspohn, U. Gosele, Nano Lett 2002, 2, 677-680.
[3] aY. Matsui, K. Nishio, H. Masuda, Small 2006, 2, 522-525; bJ. Martin, C. V. Manzano, O. Caballero-Calero, M. Martin-Gonzalez, Acs Appl Mater Inter 2013, 5, 72-79; cE. Moyen, L. Santinacci, L. Masson, W. Wulfhekel, M. Hanbücken, Adv Mater 2012, 24, 5094-5098.

Almost perfect self-ordering hexagonal nanostructures (PA) can be obtained by aluminum (Al) anodization using anodization technique. The advantage of these low dimension systems is the possibility to decrease the limit detection range for sensors purposes and to build up new lab-on-a-chip devices. We recently reported a different setup consisting of extracting the UV photoluminescence (PL) signal from a limit grazing angle parallel to the porous alumina surface and orthogonal to the porous direction. The high sensitivity of this system is related to the Fabry-Péröt fringes that appear using this optical setup. In this essay, we describe the use of this optical setup on porous alumina/aluminum substrate to detect small quantities of pure ethanol in the gas phase.
Different film morphologies were obtained using galvanostatic techniques. The photoluminescence spectrum was collected using a fluorimeter. The emission was collected in a grazing angle were the polarized emission signal were the most intense. To study the gaseous ethanol detection a sealed glass cell with two quartz windows was constructed. This cell allows the injection of ethanol aliquots in liquid phase that volatilizes due to the vapour pressure and a line for N2 flux for washing after each essay. The PA film was positioned at the centre of this glass cell and the angle was adjusted to the highest PL intensity in the grazing PL setup. A polarizer was positioned in front of the emission window to separate the polarized signal.
The PL spectra showed that the surface morphology and the porous layer affected the interferometric behaviour of the PA/Al system. We tested the system with three different temperatures and different ethanol volume injection. Vertical and horizontal PL fringes spectrum was detected and are function of concentration of ethanol gas phase in the vessel. The samples with opened pores have the highest sensitivity for gaseous ethanol detection due to the large exposed surface area allowing a better interacting between the ethanol molecules and the luminescent centres at the oxide surface. The results pointed out to the fact that the important key to build this sensor is the amount of equilibrium gas phase in contact with the oxide surface, which is dependent of the surface pore morphology and the thickness of the porous layer. Hence, the system allowed direct detection of ethanol gas using the luminescent setup proposed.

Epitaxial germanene on a semiconducting GaAs(0001) substrate is studied by ab-initio calculations. The germanene-substrate interaction is found to be strong for direct contact but can be substantially reduced by H intercalation at the interface. Our results indicate that it is energetically possible to take the germanene off the GaAs(0001) substrate. While mounted on the substrate, the electronic structure shows a distinct Dirac cone shift above the Fermi energy with a splitting of 175 meV. On the other hand, we find for a free standing sheet a band gap of 24 meV, which is due to the intrinsic spin-orbit coupling.

Using self-assembly of block copolymer micelle loaded metal precursors, combined with a seeding-growth route, a newly developed approach was demonstrated to create ordered gold nanoparticle (AuNP) arrays with a series of controllable sizes on solid substrates. As an example, the optical response of the AuNP arrays to local refractive indices has been characterized by UV-Vis spectro-photometry, and atomic force microscopy (AFM), scanning electron microscopy (SEM), as well as theoretical modelling were carried out to characterize the arrays based on the AuNPs size, inter-particle spacing, and embedding ratios. The typical red-shifted of surface plasmon peak (lambda;) agreed with the computations in consideration of AuNP size, spacing, embedding ratio, bulk refractive indices. AuNP arrays functionalized with lipid bilayers (cell membrane analog) and lipid binding proteins (cell surface marker analog) was used to test our hypothesis that surface plasmon enhanced sub-wavelength imaging may be obtained by p-polarization total internal reflection fluorescence (TIRF) microscopy. By fixing fluorophores on conjugated proteins in the proximity of 7 nm and 9 nm, the quenching and enhancement of surface plasmon coupled fluorescence have been detected, respectively. The surface plasmon coupled fluorescence was found to be proportional to the AuNP sizes. Quantitative evaluation and optimization are carried out to further explore the detection sensitivity of e.g., cancer cell surface markers.

Metal nanostructures and nanocarbons are two important classes of nanomaterials that offer unprecedented opportunities in confining and manipulating photons and electrons at the nanoscale. In particular, synergistic ensemble of plasmonic nanostructures with graphene could open a path forward to devices exhibiting unconventional optical, optoelectronic and mechanical characteristics enabled by directed self-assembly. Herein, we demonstrate in-situ reduction of gold nanostars on the graphene oxide sheets that is followed by the large morphological transformation into 1-dimensional high aspect ratio nanorolls enabled by centrifugal force-driven self-assembly. Atomic force microscopy, transmission electron microscopy, dynamic light scattering, uv-vis spectroscopy, and surface enhanced Raman spectroscopy were employed to understand the mechanism for the self-assembly of the 1-dimensional hybrid nanorolls. It appears that differential surface charge density of the hybrid ensemble acting as hydrophilic macroion promotes counter-ion driven anisotropic assemblies by overcoming isotropic solvation forces under centrifugal force. The large morphological transformation of gold interfaced graphene oxide sheets into high aspect ratio nanorolls enabled by centrifugal force-driven self-assembly provides a new tool to control light-matter interactions at the nanoscale and step towards their integration into miniaturized device platforms.

3-Dimensional printing using granular materials is one of the upcoming rapid prototyping processes in the manufacturing industry. With 3-Dimensional printing, it is possible to manufacture objects of varied shapes and sizes, with high accuracy in a short span of time. To determine the material properties of a 3-Dimensionally printed object, it is very important to know the volume filling factor or the packing factor of the particles. There has been insufficient focus on the 3-Dimensional imaging of granular particles. It is difficult to perform a quantitative analysis of the structure without 3-Dimensional imaging.
In this article, we successfully built a new framework to obtain the co-ordinates and sizes of highly cohesive toner particles in a sample prepared by drop deposition. Using Confocal Laser Scanning Microscopy (CLSM), we obtained 3D scans of micro-particle assemblies. The model particles used for this study were micron-sized poly-dispersed electro-photographic printing toners. Toners are known to be highly cohesive and with low volume packing fractions. CLSM images of these structures show the individual particles because the particles can show luminescence. We also obtained the packing fraction of the sample using an automation program written in Matlab. By identifying the boundaries of each particle and knowledge of its depth in the CLSM image, we were able to infer the three dimensional location of each particle in the structure and thus an accurate measurement of the packing fraction. The measured packing fractions were compared with theoretically predicted values for cohesive particles. Extension of these techniques to other materials allows us to relate the physical properties of these materials to the structures that they form.
Acknowledgement:
Our research results are based upon work supported by the National Science Foundation Partnerships for Innovation Building Innovation Capacity (PFI: BIC) subprogram under Grant No. 1237761. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. The RIT confocal microscopy lab is supported through the National Science Foundation Major Research Instrumentation Program (#1126629), the RIT Office of the Vice President for Research, Kate Gleason College of Engineering, and the RIT College of Science. Our research is also supported by the Melbert B. Cary Jr. endowment by the College of Imaging Arts and Science. The authors wish to thank Dr. Cheryl Hanzlik of the RIT Confocal Microscopy Lab.

The ability to control the shape of self-assembly of nanoparticles such as asymmetrical assembly of nanoparticles, is important for the development of nanoparticles as new building blocks to functional architecture. The asymmetry of the nanoparticle assembly is dominated by the surface ligands. The rational design of mixed-ligands allows the control of their distribution on the surface of gold nanoparticles. By systematic variation of the polarity of the ligands around gold nanoparticles, the phase-separation of mixed-ligands and self-assembly of nanoparticles could be manipulated in controllable way. This report describes the results of an investigation of the various control parameters in these processes, which is aimed at understanding the structural characteristic of ligands surrounding the nanoparticles and how the nanoparticles can be assembled into various nanostructures, such as dimers, wires, lamella, and spheres.

The assembly of metal nanoparticles via thin film dewetting at elevated temperatures has received attention due to its potential uses for patterned magnetic recording media, plasmon resonance wave guides, photovoltaic devices and as catalysts for nanowire growth. Dewetting of thin solid films commonly occurs through the formation of voids at grain boundary triple junctions, void growth and coalescence. Some mechanistic studies of dewetting have focused on morphological evolution during film agglomeration, but the evolution in structure crystallography has rarely been reported. In the present study, we dewetted thin Au films on silicon nitride substrates and investigated the crystallographic evolution that was concurrent with film rupture during dewetting. A 12-nm-thick Au film was deposited onto a silicon nitride layer on a silicon wafer or a silicon nitride film on a TEM Cu support grid. The films were then annealed at 400°C in a TEM chamber in situ or in a furnace ex situ for 1-120 minutes to induce solid-state dewetting. The film morphology and microstructure were observed using SEM and in situ TEM, and crystal orientation mapping was performed using an automatic crystal orientation and phase mapping system (ASTAR) for TEM.
In situ observation of the Au films showed rapid growth of fine grains from the very early stage of annealing, followed by three typical stages of film rupture with further annealing: void formation at grain boundary triple junctions, void growth with faceted edges, and particle formation by breakage of void ligaments. Crystal orientation mapping at each stage revealed a strong (111) texture that increased with longer annealing times. The void edges did not show any favorable planes during the early stages when the void was small (<100 nm); however, with further annealing, they were mostly faceted and the exposed planes at the edges oriented to specific planes for surface energy minimization: (111), (443), (211), (221), etc., in order of prevalence. At this stage, the void shapes appeared to be stable until the breakage of void ligaments, and void growth was primarily governed by surface diffusion away from the low energy planes at the edges toward the top surface of the film. Once the ligaments between the voids ruptured, they rapidly retracted and formed isolated particles. Detailed crystallographic analysis at each stage of dewetting is presented, and the evolution of void shapes is discussed in terms of surface energy minimization. A crystallographic understanding of the dewetting mechanism in this study will provide clues to help achieve the desired crystallographic orientation of metal particles and to aid in the fabrication of devices that utilize variations in physical properties that are dependent on the crystallographic orientation of nanoparticles, such as magnetic or plasmonic devices.

Inorganic porous materials have been used for applications including adsorption, catalysis, catalyst supports, and cell culturing substrates, owing their large surface areas, surface activities, and three-dimensional unique structures. Hierarchic porous structures have been used to improve properties of inorganic porous materials further. There are several methods for preparing hierarchic porous inorganic materials, such as the sol-gel process using various sacrificial templates, including polymer particles and surfactant agents. However the method can select a few kind of precursor, and need sacrificial templates. Honeycomb patterned porous films (honeycomb films) are prepared by casting solutions containing hydrophobic polymer and an amphiphilic copolymer dissolved in water-immiscible organic solvents under highly humid condition, called as the breath figure technique. Microporous films with regular arrangements of uniformly sized pores are prepared by the simple casting method. When the honeycomb films are prepared from nanoparticles (NPs), resulting films would have nano-pores among NPs. However inorganic NPs cannot be stably dispersed in organic solvents. In this report, we show a simple surface-coating method of inorganic NPs with amphiphilic copolymers containing catechol groups, which are included in adhesive proteins of mussels and adhere to many kinds of material surfaces. We also show a preparation method of porous films with nano- to micron- sized hierarchic pores by the breath figure technique.
An amphiphilic copolymer (polymer 1) containing catechol groups were polymerized from N-(3,4-Dihydroxyphenthyl)methacrylamide (DMA) and N-dodecylacrylamide (DAA) in mixed solutions of benzene and DMSO. Zinc oxide (ZnO) NPs, which is a model of inorganic NPs, were added to chloroform and ultrasonicated, and then a chloroform solution of polymer 1 was added into the ZnO nanoparticle dispersion. The surface coated NPs were collected by centrifugation and dried in vacuo. The dried powder was re-dispersed in chloroform. Honeycomb films composed of NPs were prepared from surface coated NPs and polymer 1 by applying humid air. To remove polymers, the film was sintered at 600 degrees C for 5 min.
Surface coated ZnO NPs were well dispersed in chloroform. The average size of dispersed NPs was ~200 nm, which was identical to that of uncoated NPs dispersed in water. This indicates that coating NPs with the polymer 1 provides a simple method for dispersing NPs in organic solvents. The structure of as-prepared and sintered films was observed by using SEM. From SEM observation, as-prepared films have hexagonally arranged micron-sized pores, and three-dimensional structures. Sintered films also have their unique structures. Cross-sectional TEM images of the sintered films show that the film has nano- sized pores among NPs. These results suggested that hierarchic porous inorganic films were successfully prepared by the breath figure techinique.

Nanowires have unique electronic and chemical properties and can make sensors more sensitive due to increased surface area. Template synthesis is an attractive method for the formation of nanowires because it involves a simple procedure, which can control the array of the nanowires by manipulating experimental conditions. The goal is to display control over the pore distribution by adjusting the anodization voltage and to control the pore diameter using the pore widening treatment. Temperature and type of electrolyte also affect the order of the pores on the templates but those will remain constant throughout the experiment.
A bench top method was designed for the anodization of 2 cm x 2 cm 99.999% aluminum sheets in a simple two-electrode electrochemical cell with 0.3 M oxalic acid as the electrolyte and Reynolds wrap as the cathode. The 99.999% aluminum sheets were used to make the porous templates via a two-step anodization process. The first anodization parameters were set at 40V for the anodization voltage, temperature was 0°C, the electrolyte used was 0.3M oxalic acid. The first anodization time was 40 hours and the second anodization time was 1 hour. The temperature was controlled by first cooling the electrolyte solution in a freezer to 0°C. The cooled solution was then transfer to a fume hood into an insulated ice bath. All solutions used for this experiment were cooled this way. All other conditions were constant among the first and second anodizations. Prior to the two anodizations the aluminum was strengthened by annealing it at 500°C and then electropolished at 1 °C using a 400 mA current source in order to create a smoother and more uniform surface.
Between anodization steps the oxidation layer that developed on the pure aluminum sheet which served as the anode was removed by dipping the sheet into a solution of phosphoric acid (6wt%) and chromium trioxide (1.8%). The second anodization step was then performed after which pore widening treatments were applied to adjust the pore diameters. The porous aluminum sheet was then put into a 5%wt phosphoric acid solution at 19°C. The pore diameter varied with the amount of time the porous aluminum sheets were placed in the phosphoric acid solution.
Nanowires were then grown through the porous aluminum plates by using electrodeposition. Porous templates with wide distribution of pore diameters (10-50nm) and spacing (90-110nm) were achieved. Copper and nickel nanowires were then grown through these templates showcasing diversity of diameter dimensions on the same chip for the first time.

We explore designs of amphiphilic functionalized icosahedral nanoparticles for developing materials for applications in targeted drug delivery and sensing. We study the effect of anisotropy induced via functionalization and aspect ratio of the particles, and generate a library of self-assembled structures via coarse-grained Molecular Dynamics simulations. We characterize the aggregate morphologies through measurements of the coordination number and radial distribution function. We will present our results for two solvent conditions: one promoting aggregation of the nanoparticle and the other promoting aggregation via the functional groups. Our observations suggest that (a) the excluded volume of the icosahedra plays a key role in controlling aggregation under both these conditions and (b) it also provides us useful clues towards the choice of properties of functional groups that could help in controlling aggregate morphology.

Using a hybrid Brownian Dynamics-Cahn Hilliard (BD-CH) mesoscale computational approach, the coupled morphology of an immiscible binary polymer blend with dispersed colloidal particles is investigated in a confined thin-film geometry under the influence of an applied electric field. When the blend ratio is asymmetric (e.g. 30-70), the resulting microstructure consists of columnar channels of the B-phase perpendicular to the major plane of the film (aligned with the electric field), with the particles segregated along the channel interfaces. Upon selective dissolution of the minority phase, the channels will become pores with partially exposed colloidal particles that can react with an external fluid. This talk will focus on the computational results that illustrate the relationships between the average channel diameter, the channel areal density, and the interfacial particle packing fraction with varying particle number density and polymer blend ratio. Also of interest, the particles assume a hexagonal close-packed arrangement on the channel interfaces, although with a tilted helical angle that increases with decreasing channel diameter.

Core-shell microspheres with a silica nanoparticles shell layer were facilely prepared by the modified one-step suspension polymerization of a polymerizable monomer mixture (styrene as a monomer and ethyleneglycol dimethacrylate as a crosslinker) containing surface modified-silica nanoparticles. The surface hydrophilicity/hydrophobicity balance of silica nanoparticles, which are modified with (3-methacryloylpropyl)trimethoxysilane as a polymerizable silane coupling reagent, is effective to adjust the depth position of silica nanoparticles at the polymer core surface. The obtained core-shell microspheres showed unique morphological features with regularly-ordered silica nanoparticle arrays. By changing the loading amount of nanoparticles toward polymerizable monomers, the packing density of the silica nanoparticle arrays was readily controlled. According to the zeta-potential measurements, the surface-modified silica charged negatively in monomer suspension indicating the silanol groups would be remained on the silica surface after grafting of silane coupling reagent. It is considered that the silica nanoparticles at the interface can keep their distances because of electrostatic repulsions among them. The compression strength measurements indicated that the silica nanoparticles shell layer improved distinctly the mechanical properties. In this paper we will also show the characteristic properties such as diffuse reflectance and surface tension properties.

The self-assembly of block copolymers offers an attractive approach for the nanostructuring and nanoscale patterning of conjugated polymers. Here, we present the solution-phase self-assembly of a polyalkyloxythiophene diblock copolymer, poly[3-(2,5,8,11-tetraoxatridecanyl)thiophene]-block-poly(ethylene glycol) (PTOTT-b-PEG), into a wide array of structures including nanoribbons, sheets, and vesicles depending on the solvent composition and block copolymer concentration. The hydrogen bonding character of the initial solvent used for the self-assembly was important for the formation of the unique nanoribbon structure, indicating that the nanoribbon is formed due to a delicate interplay between hydrogen bonding and π-π interactions. Self-assembly of a polyalkoxythiophene block copolymer analog, poly(3-{2-[2-(2-ethoxyethoxy)ethoxy]ethoxythiophene)-block-polyethylene glycol (PEEEET-b-PEG), led to similar nanoscale morphologies. However, the extended polythiophene conformation of PEEEET resulted in a different molecular packing structure as evidenced in the absorption spectra. Furthermore, PEEEET-b-PEG formed unique large domain crystalline nanosheets and near-infrared absorbing vesicles that are potentially useful for electronic and biological applications. This work demonstrates that solution-phase self-assembly is a powerful approach to control the nanometer scale morphology and molecular packing of conjugated polymers.

Block copolymers (BCPs) consist of two or more chemically distinct polymer fragments, or blocks, covalently bonded together to form a larger, more complex macromolecule. Due to the unique assembly of BCPs into structures in the range of 10-100 nm, they have attracted much interest from both academia and industry, especially in guiding the formation of BCP-nanoparticles composite materials. In this work, we investigate the assembly of poly(ethylene oxide)-stabilized gold nanorods (PEO-AuNRs) directed by mesostructured thin films of polystyrene-block-poly(methyl methacrylate) (SMMA). PEO-AuNRs are selectively sequestered in PMMA block since the surface chemistry on the gold nanorods is less incompatible with PMMA than PS. The morphological properties of the thin film composite materials are studied by scanning electron microscope (SEM). The effect of loading percentage and aspect ratio of gold nanorods, and the processing conditions such as annealing temperature are discussed. Mechanism on the formation of directed assembly of gold nanorods in SMMA thin film is also proposed.

We have investigated methods for driving the self-assembly of iron oxide nanoparticles using a combination of electrophoresis and patterned substrates. 12 nm iron oxide nanoparticles were synthesized using the method of Yu et al. and dispersed in toluene (1). Though these surfactant-coated particles are dispersed in a nonpolar solvent, electrophoretic mobility measurements indicate that most nanoparticles have a charge of either +e or +2e. An electric potential ranging from 20-100 V is applied between two electrodes spaced 2 mm apart and submersed in the nanoparticle solution. The resulting applied electric field drives motion of the charged nanoparticles. Self-assembly takes place on the cathode, which is either bare Si or Si nano-patterned with hydrogen silsesquioxane (HSQ) electron beam resist. A bare piece of Si serves as the anode. As the electrodes are removed from solution, the combination of capillary immersion forces and electrostatic forces drives preferential arrangement and orientation of nanoparticle arrays. A comparison of nanoparticle arrays formed with and without the presence of an electric field suggests that electrostatic and capillary forces are dominant in driving nanoparticle assembly. These experiments also suggest that the HSQ features are significantly polarized in the presence of an applied electric field. This polarization directs electric field lines towards the patterns, driving nucleation of nanoparticle arrays at the edges of templates. Interaction energies for other nano-scale forces such as van der Waals and magnetic dipolar forces are calculated. These forces are found to be small in comparison to the interaction energies associated with capillary and electrostatic interactions, confirming that capillary and electrostatic forces are the prevailing forces driving nanoparticle pattern formation. We take advantage of the selective nucleation at the edge of the patterns and show that it can be used to create novel nanoparticle arrays. By changing the shape of the HSQ templates, it is possible to tailor the geometry of strings of nanoparticles and also packing arrangements within nanoparticle arrays. Finally, we show that the arrays generated via this technique can be used to transfer the patterns of nanoparticles into the underlying substrate.
(1) Yu, W.W.; Chang, E.; Sayes, C.M.; Drezek, R.; Colvin, V.L. Synthesis of monodisperse iron oxide nanocrystals by thermal decomposition of iron carboxylate salts. Nanotechnology 2006, 17, 4483-4487.

Metallic iron nanoparticles (NP) show improved magnetic properties when compared to similar iron oxide ones that are currently more widely used in several applications. However, despite reports on several synthesis methods, their controlled growth remains a challenge, especially when specific anisotropic objects are desired. Forcing the growth of such bcc single crystals in one particular direction is indeed quite subtle and necessarily requires understanding of how the different crystal surfaces are forming and stabilized during the growth medium.
In this work iron NP were grown under soft conditions, using a {Fe(N[Si(CH3)3]2)2}2 precursor. In order to understand the experimentally observed shapes we have performed series of density functional theory calculations to investigate ligand effects of the morphology. These slab-model based calculations involved different Fe surfaces - (100), (110), (111), (211), and (310) - and different ligands (H, Cl, HCl, NH3, NH4+, NH4Cl) presumably present in the growth environment. A wide variety of possible symmetry sites as well as the effect of coverage values were considered for adsorption to yield a deep understanding of the thermodynamical properties of the system. Helped by Wulff constructions, this allowed us to provide ideal shapes of the NP through surface energies calculations.
We find that the experimentally found morphology of the Fe NP can not be solely governed by thermodynamics. In particular, on time scales of up to few hours and at low H and Cl concentrations, the growth is rather governed by kinetics. Contrary, the experimental shape under rising H concentration is well explained by thermodynamics.

Large-area-patterned monolayers have received much attention in recent years due to their wide applications in sensors, catalysis, optical devices, superhydrophobic surfaces, surface-enhanced Raman scattering and so on. In this paper, a facile and novel method of fabricating large-area-patterned monolayer of polytetrafluoroethylene (PTFE) nanoparticles was achieved using surface charge induced colloidal deposition. Chemical process of amination and hydroxylation were used to make the silicon substrates positively and negatively charged, respectively. The PTFE colloidal nanoparticles were anisotropic with an average size of 180nm and a zeta potential of -31.4mv. After colloidal deposition, an ordered monolayer with holes was formed on the amination surface, while an island-like monolayer was achieved on the hydroxylation surface. Both of the two kinds of monolayers were as large as 1.5 square centimeters and with good regularity. It was worth pointing out that these large-area-patterned monolayers were fabricated without any templates and the whole process only took several hours. Because of the electrical double layer force, the total number of nanoparticles deposited on the negatively charged surface was much less than that of the positively charged surface. The formation mechanism of the different nanostructures was not much clear but could be generally attributed to the effect of charge induction and system energy minimization, which needed intensive study. It is believed that the interesting nanostructure formation mechanism, high production efficiency, good adaptability and quality will make this novel method attract widespread attention.

An experimental study of the assembly of novel multicompartment and multigeometry nanoparticles will be discussed. By simply binary blending of different block copolymers, complex nanoconstructs including vesicle-cylinder, hybrid vesicles, and cylinder-disk nanostructures were assembled due to the nanophase separation of immiscible hydrophobic domains. The unlike hydrophobic blocks are kinetically trapped into one particle with a specific assembly pathway. The pathway first includes complexation of unlike block copolymers through a common polyacrylic acid hydrophilic block in each polymer with added organic diamines in THF. Subsequent addition of water, a nonsolvent for the unlike hydrophobic blocks, eventually forms nanoparticles with the two unlike block copolymers kinetically trapped in the same particle. Detailed control of the solvent mixing rates leads to the production of mixed, multicompartment/multigeometry nanoparticles or separate populations of nanoparticles of each block copolymer, thus highlighting the importance of kinetic control of the assembly process. TEM, cryo-TEM with selective staining were carried out to characterize the novel geometrical nanoparticles. Macrophase and nanophase separation processes were tracked during solvent mixing by small angle X-ray scattering (SAXS).

Nanoimprint driven molecular orientation has been investigated in thin films of block copolymer polystyrene-b-polyethylene oxide (PS-b-PEO) by means of solvent vapor assisted nanoimprint lithography (SAIL).The PS-b-PEO microphase separation in the residual layer showed vertically aligned 20 nm diameter PEO nanodots in a PS matrix. In the mesas, PEO cylinders were disorderly aligned parallel to the surface, pointed out an anisotropic chains diffusion process due to the shear forces occurring during the NIL imprint. Grazing-incidence small-angle X-ray scattering (GISAXS) diffraction pattern showed the excellent fidelity of the stamp replication in the film and confirmed the periodicity of PEO cylinders in the mesas. The order of the hexagonally arranged nanodot lattice was quantified from SEM images using the opposite partner method and compared to conventionally solvent annealed BCP films. The imprint based methodology demonstrated an improvement in ordering of up to 50%. The SAIL technique allowed a one-step process to obtain a complex pattern by bottom-up BCP directed self-assembly assisted by top-down NIL, with low defectivity in a large area nanodot array in the trenches. Using the image analysis, it is possible to extract structural information and analysis of corrugated surfaces with alleviated dimensions, which is otherwise not possible solely based on GISAXS experiment. Overall, we demonstrated a facile fabrication technique based on SAIL to produce large-area ordered nanostructure arrays useful for BCP lithography application and others.

Artificially directed hierarchical micro/nano-system is the one of the few feasible strategies for complex nanostructures and ensures molecular-level pattern precision as well as parallel processing. Despite numerous investigations regarding such systems, most research have focused on homogeneous hierarchical micro/nano-systems. Herein, we introduce heterogeneous hierarchical micro/nano-systems that consist of self-organized micropatterns and self-assembled nanopatterns. Especially, we present the interaction of wrinkle structures and block copolymer(BCP). Plasma induced equi-biaxial compressive strain generates micro scale isotropic wrinkle structures that guide BCP alignment.

Ordered mesoporous materials are promising candidates for a wide range of applications. An essential prerequisite for many applications is their mechanical stability under different external and internal stresses caused by, e.g., the adsorption and condensation of fluids or the freezing of liquids within the pores. Adsorption induced deformation of mesoporous powders[1,2] and thin films[3] showed that valuable information about their mechanical properties can be derived from in-situ X-ray techniques using synchrotron radiation. Here, two types of mesoporous silica samples were prepared either by dip-coating or by spin-coating on silicon substrates and were examined by Grazing Incidence Small-Angle X-ray Scattering (GISAXS). GISAXS revealed ordered mesoporous films with 2D hexagonal structure, with the pore axis of the cylindrical pores oriented preferentially within the plane of the substrate. In-situ GISAXS was applied to determine the pore-lattice strain as a function of relative humidity change in the range of RH=5% to RH=95% by using a custom-built in-situ humidity device. The films showed reversible out-of-plane contraction due to the condensation of water in the pores. The nano-deformation of porous network as a function of RH - the so called strain isotherm - showed marked differences between the two types of samples. The structural origin of these differences and their influence on the overall mechanical performance of the films will be discussed.
1. Guenther, G.; Prass, J.; Paris, O.; Schoen, M., Novel insights into nanopore deformation caused by capillary condensation. Phys Rev Lett 2008, 101, (8), 086104.
2. Prass, J.; Mueter, D.; Fratzl, P.; Paris, O., Capillarity-driven deformation of ordered mesoporous silica. Applied Physics Letters 2009, 95, (8), 083121.
3. Dourdain, S; Britton, D. T; Reichert, H; Gibaud, A, Determination of the elastic modulus of mesoporous silica thin films by x-ray reflectivity via the capillary condensation of water. Applied Pysics Letters 2008, 93, 183108

Interface-driven assembly of particles has been demonstrated and the corresponding physics is fairly well established [1,2]. Compared to micron-size particles, the physics of nanoparticles at an interface, however, remains largely unexplored. In the case of nanoparticles, the complexity lies in the delicate balance between the size-dependent thermal fluctuations and interfacial energy. In this presentation, we will present our research in exploiting the asymmetry at an air-liquid interface to assemble carbon nanotubes (CNTs) into ordered structures. CNTs are rolled cylinders of graphene sheets with an aspect ratio (length-to-diameter ratio) on the order of 1000, which is much higher than other rod-like particles reported in the literature (< 10). CNTs represent an extreme case of high-aspect-ratio nanorods, for which the interfacial behavior is not known. Our findings indicate that CNTs adsorb strongly at the air-water interface, leading to a significant increase in surface pressure. The highly compressible nature of an interface also enables the creation of two-dimensional CNT “liquid crystals” by compressing an air-water interface decorated with CNTs. The findings may lead to the development of more stable emulsions by tailoring the particle shape and the production of CNT thin films with controllable packing density and orientational ordering. This work was supported by a National Science Foundation Career Award (NSF CAREER Award #1253613). References [1] Madivala, B., Fransaer, J., and Vermant, J., Langmuir, 25(5), 2718-2728 (2009). [2] Lewandowski, E.P., Cavallaro, M., Botto, L., Bernate, J.C., Garbin, V., and Stebe, K.J., Langmuir, 26(19), 15142-15154 (2010).

Collagen is the major structural protein of bone, dentine and the extracellular matrix and can template the nucleation and growth of numerous mineral phases. Both its molecular-scale conformation and meso-scale architecture are critical for its function. Both of these two structural levels are influenced by interactions with substrates and collagen itself. Thus, understanding the nature of these interactions and the mechanisms of assembly on surfaces may enable us to manufacture complex 2D protein structures and hence engineer surface properties.
At acidic conditions, K+ ions critically affected the collagen-mica interaction leading to assembled structures that evolved from 2D films of randomly oriented fibers to co-aligned fibers and finally to ordered 3D bundles as the K+ concentration increased from 100 to 200 and finally to 300mM. These three types of architecture are partially reversible with potassium concentrations. High-resolution AFM showed the random fibers and co-aligned fibers comprised monolayers while bundles consisted of intertwined single collagen triple-helices.
The magnitude of collagen-mica and collagen-collagen interactions at 200 and 300 mM K+ were measured by dynamic force spectroscopy (DFS). The binding free energy Gb for collagen-mica and collagen-collagen at 200 mM K+ were 13.7kT and 1.4kT respectively, while Gb at 300 mM K+ were 5.7kT and 12.3kT, respectively. The observed reversal in the relative magnitudes of collagen-collagen and collagen-mica binding energies explains why the architecture switches from a 2D film to 3D bundles. The magnitude of these interactions is consistent in with hydrogen bond and dipole-dipole interactions.
Collagen triple-helices were still partially mobile with a diffusion coefficient D1~4×10-17cm2s-1 at 300 mM K+. The stronger collagen-collagen interaction (12.3kT) drove collagen fibers into collagen bundles, which occurred through lateral movement and twisting of individual fibers. This result confirmed that while the film-substrate interactions are not strong enough to enforce a direct registry between a molecule and the substrate lattice, the collagen-collagen interactions are able to drive reorganization, as is characteristic of surface-templated quasiepitaxial growth.
In-situ FTIR and Raman indicated that the vibration band of amide I (~1650cm-1) group in collagen was not influenced by potassium ions, while the intensity of water absorption at 3200 and 3400 cm-1 decreased with increased potassium concentration. X-ray absorption spectroscopy also showed that both the potassium and oxygen absorption edges were not shifted in the different collagen architectures. These observations suggest that the collagen architecture and aggregation state are controlled by potassium ion-induced collagen dehydration instead of by formation of chemical bonds with neighboring collagen molecules.

Meso-scale is the border range obtained by the bottom-up and top-down methods. The micro-phase separation of block copolymers form body centered cubic sphere, hexagonally packed cylinder, lamellar and bi-continuous gyroid in nm scale. In this study, the two-dimensional hexagonal packed alignment of spheres in the meso-scale range obtained by solvent casting from amorphous polymer blend solutions was investigate. The size of sphere was from 0.5 to 3 um, the distance between spheres was from 3 to 7 um.
The meso-scale order structure of spheres was prepared by casting from the toluene solution of acrylonitrile-butadiene rubber (NBR)/styrene-butadiene rubber (SBR) blend. NBR/SBR blend is the immiscible blend, and these toluene solutions indicate the liquid-liquid phase separation in the wide range of blend fraction and the polymer concentration. The upper phase separated layer is SBR rich phase (NBR/SBR = 5/95, the dry state). 3 wt% toluene solution of NBR/SBR blend was kept for 3 days at room temperature until the equilibrium phase separation was obtained. The upper layer of NBR/SBR toluene solution was casted of silicon wafer, and the obtained film was dried under vacuum.
The radial gyration of NBR, SBR and those blends in toluene solution was evaluated by the dynamic light scattering. The structure formation process was observed by the in-situ grazing incidence small angle X-ray scattering (GISAXS) at BL-03XU, SPring-8, Hyogo, Japan. The moso-scale alignment of NBR/SBR blend film was observed by Atomic Force Microscopy (AFM, E-sweep, Hitachi High-Technologies Corp.).
The hexagonally packed sphere structure was observed by AFM and SEM for the solvent casting film from the upper layer of NBR/SBR toluene solution with NBR fraction (Phi;NBR) from 0.3 to 0.6. The diameter of sphere was 1.7 and 3.5 um for NBR/SBR toluene solution with Phi;NBR, 0.3 and 0.5, respectively. Two-dimensional Fourier Transformation pattern of AFM phase image indicated the highly ordered hexagonal alignment. The order aligned spheres existed on the thin film surface (film/air interface). There dimensional AFM images suggested the flatness sphere, The relationship between height and diameter of sphere obtained for various Phi;NBR showed a good linear relationship, the ratio of height/diameter of sphere was about 0.02.
From the phase images of order structure, spheres were mainly consisted of NBR rich phase. The histogram analysis of AFM phase images suggested that the order alignment of sphere composed of soft core and hard shell.

Colloidal dispersions of anisometric particles can display dynamical arrest and ordering involving both translational and rotational degrees of freedom. We show that orientational order can develop in glassy colloidal dispersions of charged platelets when a concentration gradient is imposed through solvent evaporation. Our model system of Laponite (LRD) platelets in deionized water has been extensively studied for its ergodic to non-ergodic transitions, and the existence of an underlying isotropic-nematic phase transition has been a subject of debate. We use small-angle x-ray scattering, dynamical light scattering and birefringence to show that the orientational order we observe does not result from an underlying, uniquely determined equilibrium state with orientational order, but from plastic deformation of the colloidal glass.

Single molecular magnets (SMMs) have great potential for use as nano-scale memory devices or quantum computers. During the last decade, phthalocyanine (Pc)-TbIII double-decker SMMs have attracted much attention because of their considerably higher blocking temperature than other reported SMMs. More recently, it was reported that a Pc double-decker SMM implanted on a carbon material could function as a memory device, a result that can greatly impact the field of nano materials.
This study focuses on the porphyrin-TbIII double-decker complexes and their magnetic properties. Porphyrin has an advantage in that its chemical modification is easier than that of Pc, though its coordination mode with TbIII is same as that for Pc.
First, we synthesized both the protonated and deprotonated forms of tetraphenylporphyrin (TPP)-based TbIII double-decker complexes. We observed that the anionic double-decker complex showed higher molecular symmetry than the protonated double-decker one. Furthermore, based on the ac magnetic susceptibility measurement, we found that only the anionic double-decker complex exhibited the SMM property because of high symmetric coordination. To the best of our knowledge, this is the first report on double-decker complexes whose magnetic relaxation behavior is drastically changed by a single proton.
Though the memory function of the double-decker SMMs implanted on carbon substrates has been reported (already mentioned before), it is still difficult to control their molecular alignment on the carbon material. Because of this problem, we could not observe memory function with high reproducibility. To overcome this problem, we tried to control molecular alignment of the porphyrin double-decker complex on a carbon material. We used scanning tunneling microscopy (STM) and observed the molecular alignment of an octaethylporphyrin (OEP)-based TbIII double-decker complex. The protonated, anionic, and cationic forms of the OEP double-decker complexes were observed and it was found that the different electronic structures of these forms affect the packing structure of each molecule.

Polymeric nanoporous membranes play an important role in mass separation processes in the production of safe drinking water, the biopharmaceutical industry and in the chemical industry[1]. The membrane market is worth billions of dollars per year[2]. Unfortunately, the high cost of these membranes hampers their application in the production of safe drinking water for third world countries [3]. Commercial ultrafiltration membranes are nowadays produced by a technique called phase inversion. However, this process is limited by the number of parameters that have to be controlled simultaneously during production and by the broad pore size distribution that decreases the selectivity of the resulting membranes. [4]. In the last decade new methods created on the use of highly structured nanopatterns (self-assembly of block copolymers[5] or microfabrication[6]) have been suggested but so far could not have been up-scaled to a relevant scale[7]. Such nanopatterns are prone to cracking and their ultrathin morphology makes them mechanically unstable. Therefore, we came up with a completely unconventional approach towards nanoscale patterning that enabled us to overcome these issues. This process is based on the nanoparticle template removal method (nano PTR) and has to be understood as a random nanoscale pattern formation. A polymer solution containing dispersed nanoparticles is used as starting material. At first, this solution is roll-coated on a substrate and after evaporation of the solvent a solid polymer / nanoparticle composite is obtained. During evaporation of the solvent the particles in the polymer film will agglomerate to form a completely interconnected pattern. Thus, in a second step the polymer film can be turned porous by simple dissolution of the soluble nanoparticle template in a mild acid replicating the nanopattern in the polymer[8].
By applying the nanoPTR method we produced 17 m2 of a nanoporous polymer membrane. The membrane was able to remove more than 99.99 % of bacteria from heavily contaminated pond water and showed superior dialysis performance compared to commercial biotechnological membranes.
[1] A. L. Zydney, A. Xenopoulos, Journal of Membrane Science 2007, 291, 180.
[2] H. Strathmann, AIChE Journal 2001, 47, 1077.
[3] G. Hutton, J. Bartram, Bulletin of the World Health Organization 2008, 86, 13.
[4] L. Broens, F. W. Altena, C. A. Smolders, D. M. Koenhen, Desalination 1980, 32, 33.
[5] T. Hashimoto, K. Tsutsumi, Y. Funaki, Langmuir 1997, 13, 6869.
[6] C. C. Striemer, T. R. Gaborski, J. L. McGrath, P. M. Fauchet, Nature 2007, 445, 749.
[7] S. Ludwigs, A. Boker, A. Voronov, N. Rehse, R. Magerle, G. Krausch, Nat Mater 2003, 2, 744.
[8] C. R. Kellenberger, N. A. Luechinger, A. Lamprou, M. Rossier, R. N. Grass, W. J. Stark, Journal of Membrane Science 2012, 387-388, 76.

Recently, π-conjugated low molecular weight organogelators have attracted substantial interest from the perspective of acting as building blocks for supramolecular self-assembly because of their distinctive optoelectronic properties including multicolor emission, improved fluorescence, and sensing ability. The design, synthesis, and photophysical properties of a low molecular weight organogel fabricated from hydrazone-type DCDHF chromophores bearing alkyl chains were evaluated. A straightforward synthesis of the chromophores was achieved via simple azo-coupling starting from 2-(dicyanomethylene)-2,5-dihydro-4,5,5-trimethylfuran-3-carbonitrile and alkoxy bearing aryl diazonium chloride derivatives. The sensing prospective of the DCDHF chromophores to undergo molecular switching imparted by pH stimulus was established by the addition of base and acid to a 2-3×10-5 M solution of the DCDHF-based sensor in acetone or dimethylsulfoxide. Molecular nanowires have been fabricated from the DCDHF-hydrazone chromophores upon gelation. The produced organogel possess responsiveness (as low as 0.1 equivalent gel concentration) to both pH and temperature stimuli with gel-sol reversibility, which is associated with a color change from yellow to purple. SEM and TEM were used to study the novel properties of the obtained nano-scale structures that could be fabricated by self-assembly as a result of the π-π stacking interactions. We anticipate potential applications for these DCDHF-hydrazone gels in diverse areas of chemical and biological selective sensing, and work toward these applications have been already initiated in our laboratory.

Nanomaterials hold exceptional promise to promote the development of future technologies in fields of electronics, opto-electronics, photonics, energy storage, and medicine. One of the great challenges in creating advanced materials lies in the defined ordering of nanoscale materials into higher meso- and macroscale structures. Supramolecular chemistry provides excellent tools for the generation of macroscopic materials based on controlled assembly of molecular modules interconnected mainly by noncovalent bondings. This offers significant advantages over any other methodology for the controlled construction of large assemblies, due to the possibility of determined designing at the molecular level. A well-established building block for supramolecular recognition is the Hamilton receptor, which can strongly bind cyanuric acid derivatives due to six hydrogen bonding interactions. By using the key-lock principle on the surface of nanomaterials a large variety of nano hybrid materials becomes accessible reaching from inorganic hybrids of different composites, sizes, and shapes to mixed hybrid structures by the possibility of linking organic chromophores, semiconductors, or dendrimers as well as organic nanomaterials.
We report on both, the synthesis of Hamilton receptor building blocks equipped with suitable anchor groups for the attachment onto the surface of nanomaterials, and the functionalization of especially zero- and one-dimensional organic and metal oxide semiconductors, namely fullerenes, carbon nanotubes, ZnO quantum dots and nanorods. We synthesized Hamilton receptor building blocks and complementary cyanuric acid derivatives covalently attached to carboxylic acid, catechol and phosphonic acid anchor groups, which are able to bind onto the surface of metal oxides. A successful chemical functionalization of zinc oxide nanoparticles, as an attractive material for a broad range of electronic, optical and piezoelectric applications, could be observed using UV vis and IR spectroscopy, SEM besides TGA-MS, DLS and zeta-potential measurements. The corresponding 0D and 1D organic nanomaterials, the C60 and SWCNTs were functionalized using well-known chemical reactions for covalent functionalization. Here an effective coupling with the supramolecular motif was observed using NMR, UV vis, IR and Raman-spectroscopy. In the second step, supramolecular coupling was successfully performed leading to stable nanomaterial dispersions, nano hybrid structures showing charge transfer events and defined ordered 3D-materials like e.g. layer-by-layer assemblies. Thus, this approach provides a tool box system for a defined surface modification for the generation of new hybrid materials and macroscopic devices.

Self-assembly of small building blocks such as atoms, molecules and nanoparticles into mesoscopic and macroscopic structures, that is, ‘‘bottom-up&’&’ assembly, is an interesting theme that runs through chemistry, biology and material science. Compared to the extensive study of self-assembly of spherical nanoparticles, there are much fewer investigations about how these non-spherical nanoparticles are assembled together.1 Recent theoretical work has predicted the final stacking pattern of non-spherical polyhedral particles,2 which further inspires us to perform research in this field.
Here, I will present our recent progress on the self-assembly of non-spherical colloidal nanoparticles, starting with simple systems such as nanocubes and nanoctahedra.3,4 The use of advanced synchrotron-based small angel and wide angel X-ray scattering (SAXS and WAXS) techniques provides us a powerful tool to perform this study. They display distinct superstructures from naked polyhedral and obvious dependences on some reaction parameters (e.g., solvent type, preparation conditions, temprature), which reveal the unique importance of ligands on the final superlattice symmetry. This feature will enable us to obtain more complex and abundant superlattice type for future device applications.
References:
(1) Quan, Z.; Fang, J. Nano Today 2010, 5, 390.
(2) Damasceno, P. F.; Engel, M.; Glotzer, S. C. Science 2012, 337, 453.
(3) Quan, Z.; Siu Loc, W.; Lin, C.; Luo, Z.; Yang, K.; Wang, Y.; Wang, H.; Wang, Z.; Fang, J. Nano Lett. 2012, 12, 4409.
(4) Zhang, J.; Luo, Z.; Quan, Z.; Wang, Y.; Kumbhar, A.; Smilgies, D. M.; Fang, J. Nano Lett. 2011, 11, 2912.

Self-assembly of molecular building blocks provides an interesting route to produce well-defined chemical structures. However, self-assembly of biomolecules in an ordered pattern has not been widely explored. Self-assembled patterns with tailored physical and chemical properties can have many practical applications. Tailoring the functionalities on the building blocks and controlling the time of self-assembly could control the properties as well as the structure of the resultant patterns. Bio-conjugation on the surfaces having self-assembled ligand is important for covalently attaching biomolecules for sensing. Here, we demonstrate a strategy to design human serum albumin (HSA) self-assembled patterns which are dependent on controlling the conjugation chemistry and protein-protein interactions. In the present work we systematically investigated the conditions favoring the pattern formation by HSA molecules on self-assembled monolayer (SAM) of polyethylene glycol (PEG) functionalized surface. The HSA molecules were found to form three-dimensional structures at the defect locations on PEG monolayer. This approach of forming self- assembled structures without the use of photochemistry offer a simple and efficient approach towards patterns generation. These structured protein micro-patterns, which can be generated by simple self-assembly, could be used for various promising applications in the field of biosensors, biomaterials, bio-MEMS, cell adhesion, and bacteria detection.

Silica nanorods are of interest for their potential applications in dielectric films, sensors, and solar cells. Utilizing them in these applications requires establishing scalable processing routes for producing coatings with controlled morphology. Processing of liquid dispersions is promising, but this requires developing a fundamental understanding of the self-assembly and rheology of silica nanorod dispersions. We report smectic liquid crystal formation for silica nanorods dispersed in mixtures of dimethyl sulfoxide (DMSO) and water. The nanorods were ~ 1.3 mu;m in length and ~ 260 nm in diameter; the average length to diameter ratio of 5 is near the lower theoretical limit for liquid crystalline phase formation. The dispersion stability and phase transitions were both a function of water concentration. Stability was measured using UV-vis spectroscopy; phase transitions were evaluated using both microscopy and rheology. With increasing water concentration, the biphasic region broadened indicating poorer solvent quality. Above a critical water concentration it was not possible to form a single liquid crystal phase from any silica concentration. Biphasic dispersions could be separated into isotropic and liquid crystalline fractions by either sedimentation or centrifugation. Different separation methods resulted in different liquid crystalline domain morphologies. Sedimentation of silica nanorods dispersed in 80% DMSO and 20% H2O resulted in the dispersion separating into three layers. “Oily streak” structures characteristic structures were observed in both the middle layer and bottom layer; the bottom layer resulted in well organized smectic phases. The rheology of the dispersions was consistent with expectations for macromolecular lyotropic liquid crystals. The addition of ~ 14 vol. % silica to 90/10 DMSO/H2O resulted in a biphasic system with a low shear viscosity over four orders of magnitude greater than that of the solvent. The system exhibited classical rheological signatures for lyotropic liquid crystal phase formation including a maximum in the viscosity versus concentration curve. Several methods for assembling the dispersions into solid films were explored. The microstructures of coatings assembled by drying biphasic dispersions in the absence of shear showed the characteristic “coffee ring” structure due to contact line pinning; the rods exhibited circumferential alignment along the outer edge of the drop and radial alignment closer to the center. Applying shear force to the dispersion before drying increased alignment along the shear direction. These studies further extend understanding of the liquid crystalline phase formation of nanocylinder dispersions. They are useful helpful for establishing processing conditions for large-area assembly of silica nanorods highly aligned films/coatings.

We use step growth on predefined patterns of keratin scale step edges of hair strands to demonstrate self-assembly from solution of pre-assembled semiconductor silicon nanoparticles. We demonstrate the reduction of radiation charging and damage as well as improvement of resolution in electron-based imaging. Ultrasmall silicon nanoparticles are insulators, but are conductors for near close packing formations due to electron hopping, resonant quantum mechanical tunneling, or induced electron-hole pairs, creating a nanowire network. Spontaneous assembly of semiconductor nanoparticles to pre-patterned non-conductive surfaces provides radiation hardening, lighting effects, static charge neutralization, as well as effective bacteria and UV protection.

We report an aqueous self-assembly route for creating ordered nanowire based composites with high strength and electronic multi-functionality.
We do this by using cellulose nano fibers as a novel dispersion agent for carbon nanotubes and other conducting/semi-conducting nanowires.
The multi-component nanowire colloidal dispersions are then aligned in the solvent phase by shear flow alignment in microfluidic channels. Subsequently the fluidic aligned nanowires are locked in the ordered state by transitioning the cellulose nanofibers in the colloidal system from solution to a gel phase, using charge screening. The gel is finally extruded out of the microfluic channels and dried, to achieve functional nanowire composite micro-fibers. This aligment procedure creates ordered nanowires in the composites resulting in high Hermans orientation factors, and high electronic conductivities.
We further demonstrate the use of the functional microfibers in application such as electronic textiles, and cables.
This demonstration opens many possibilities for aqueous self-assembly of a range of functional nanowires from water.

A silica-gold core-shell structure is developed as an ex-situ nanothermometer based on the temperature-dependent optical properties tuned by the irreversible thermal dewetting-induced morphological changes. Specifically, gold nanoshells experience morphological instability and self-organization upon thermal-induced dewetting, leading to the variation of optical resonance frequency which can be fast characterized by simply measuring the surface plasmon (SP) band shift in the UV-vis-NIR spectra. The characteristic optical properties of the SP band shift provide as the “finger print” for temperature recording. Of particular importance, this nanoshell structure is extremely sensitive to the morphological changes upon thermal treatments due to its nano-scale shell structure and extensive tunability of its characteristic optical property. The gold-based core shell displays a rapid response time in the sub-second scale (0.1-1.0 s) for temperature recording within an uncertainty of 3% from 300 to 800 °C. Therefore, this ex-situ nanothermometer based on the silica-gold core-shell structure design offers a great potential as an effective and ultra-sensitive sensing tool enabling fast readout and accurate determination of temperatures.

Yolk/shell particles, which are hollow particles containing a movable core, were prepared by removing a middle polystyrene layer from multilayered particles of core/polystyrene/silica shell with heat treatment followed by a slight etching with a basic solution. In the preparation, monodisperse silica particles containing magnetic nanoparticles (MS cores) were used as the cores. An ac electric field was applied to the suspension of the yolk/shell particles to form pearl chains (1D structure) of yolk/shell particles. Observation with an optical microscope showed that the MS cores in silica compartment of the pearl chains took zigzag structure under the electric field. An external magnetic field applied to the suspension could form a novel structure of doublet MS cores in the shell compartment of quasi pearl chain structure. Application of magnetic field was also performed for 2D hexagonally close-packed assemblies of the yolk/shell particles, which could two-dimensionally form doublet structure of MS cores as if they were polarized in the compartment. Switching on/off the magnetic field successfully controlled the positional ordering of cores in the consolidated silica shell.

Nanoparticle self-assembly can generate large area nanopatterns with smaller feature sizes than now available through lithographic techniques.¹ Nanomasking pattern transfer is a solution to this problem whereby the nanoparticle arrays is used as an etch mask. Here we transfer these nanopatterns to underlying thin films.² Monolayers of nanoparticles fabricated by self-assembly at air/liquid or air/solid interface usually result in small interparticle separations (~ 2 nm), making it difficult to fabricate pillar arrays by etching through the gaps by reactive ion etching (RIE). We show that a method can fabricate monolayer of nanoparticles with larger interparticle separations (~8 nm). Hole arrays were first fabricated by irradiating self-assembled nanoparticle monolayers with an electron beam, stripping the particles, and etching to create holes at the original particle positions.³ After that, the hole array is used as a template for self-assembly of slightly smaller nanoparticles, increasing the particle separation and greatly improving the quality of RIE. The non-close-packed nanoparticles in the hole arrays were sequentially irradiated by electron beam, treated by oxygen plasma, etched by CF₄ RIE, and treated by hydrochloric acid to strip mask nanoparticles, which resulted in dense hole arrays of ~ 10 nm silica or silicon nitride nanopillar arrays.
Reference:
[1] T. Wen, and S. A. Majetich, ACS Nano 5, 8868-8876 (2011)
[2] S. A Majetich, T. Wen, and R. A. Booth, ACS Nano 5, 6081-6084 (2011)
[3] T. Wen, R. A. Booth, and S. A. Majetich, Nano Letters 12, 5873-5878 (2012).

Hexagonally close packed sub-microsphere mono- and doublelayers on substrate surfaces can be used as lithography masks for periodic nanoscale patterning of surfaces, e.g. by material deposition, material removal or chemical reactions. Thus, semiconductor quantum dots, metal nanoparticles for plasmonic devices or catalytic nanowire growth, and split-ring resonators can be realized [1-3]. Moreover, nanosphere lithography provides an inexpensive and simple method suitable for treatment of larger areas. Partial sintering of polystyrene (PS) sphere monolayers offers a pathway towards smaller and more round-shaped mask openings than in as-deposited sphere layers [4].
In the present work we analyze the evolution of size and shape of intersphere openings as a function of temperature and time. PS sub-microsphere (diameter 0.6µm) monolayers have been deposited on Si(001) wafer substrates by using a doctor blade technique, in which a wiper moves a drop of the aqueous PS sphere suspension across the substrate. In order to achieve controlled close-packed sphere arrangements, the substrate has been hydrophilized by the RCA method prior to sphere deposition. The heat treatment was done in ambient air at temperatures slightly above the glass transition (110 120°C) for durations up to 27.5 minutes. For monitoring the morphologic changes of the sphere masks top view scanning electron microscopy (SEM) images were taken and quantitatively evaluated with respect to area, circumference and diameter of the mask openings as well as width of the sintering necks. Furthermore, the sphere shape change is also analyzed by means of cross-section SEM. We find that the rate of intersphere space closure is not constant, but shows a characteristic dependence on sintering time. More precisely, the closure rate exhibits two maxima: a first maximum at intermediate time, which can be attributed to the filling of corner spaces, and a second one during final closure related to substantial shape change of the spheres. By applying appropriate sintering temperature and time the mask openings could be reproducibly reduced by ~70% in area and ~55% in diameter. The opening shape varied from equilateral to rounded triangles.
References
[1] C.L. Haynes, R.P. Van Duyne: J. Phys. Chem. B 105 (2001) 5599
[2] M.C. Gwinner et al.: Small 5 (2009) 400
[3] M. Madel et al.: Phys. Stat. Sol. B 248 (2011) 1915
[4] A. Kosiorek et al.: Small 1 (2005) 439

In this contribution we demonstrate 99% porosity aerogels that retain their shape in wet conditions, after repeated compression cycles as well as after repeated drying and rewetting of the aerogels. The aerogels are formed from Nano Fibrillated Cellulose (NFC) - a class of renewable, high aspect ratio, nanomaterials that can be prepared in bulk quantities and at low costs - which have been covalently crosslinked to produce the first examples of a wet stable NFC based aerogel. During the crosslinking of the aerogel the charges on its interior surface is also increased which facilitates functionalization.
We show, using a rapid Layer-by-Layer (LbL) self-assembly protocol, that these aerogels can be used as 3D scaffolds for assembly of conducting polymers, biopolymers and carbon nanotubes (CNT). As a proof of concept of the functionality of the ultrathin LbL coating, the CNT coated aerogel was used in a supercapacitor device. The results show very high gravimetric capacitance (400 F/g) indicating the achievement of a fully interconnected CNT network throughout the aerogel and a very efficient utilization of the CNT coating. Other application areas where the reported concept for assembling nanomaterials could be applied include drug delivery, biosensors, and purification membranes.

We report the formation of novel conformations in finite-length supercoiled nanoribbons. All-atom computations of nanoribbons in an elemental model system, graphene, show that decreasing the end-to-end extension of the torsionally constrained ribbon below its contour length leads to nucleation of these writhed (bent) conformations. The weak long-range interactions in these system modify the energy partitioning between twist and writhe and lead to these novel shapes; in the absence of these interactions we recover classical plectonemes. We present a simple energetic analysis for the conformational phase diagram, and validate our results via macroscale experiments.

Bulk heterojunction (BHJ) solar cells based on polymer donors and PCBM acceptors can achieve power conversion efficiencies (PCEs) >7%.[1] Relying on donor-acceptor principles, polymer donors based on N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) and benzo[1,2-b:4,5-bprime;]dithiophene (BDT) motifs are some of the best-performing systems, yielding PCEs >8% in standard BHJ devices (single cell).[2,3] With their high open-circuit voltages (VOC) >0.9V and fill-factors (FF) ~70% in BHJs with PC71BM, PBDTTPD and analogs are also outstanding candidates for use in the high-band-gap cell of tandem solar cells. In these systems, the size and branching of the solubilizing side-chains on both the donor and the acceptor motifs along the polymer chains have a direct impact on i) the self-assembling properties of the backbones and ii) the relative orientations of the polymer pi-aggregates in thin-films.[2,3] Important correlations between molecular structure, chain packing and nanostructural order can be established via grazing incidence X-ray scattering (GIXS) experiments. These variations of structural organization in the thin-films are also found to correlate with BHJ solar cell device performance.[2,3] In parallel, our recent developments show that replacing benzo[1,2-b:4,5-bprime;]dithiophene (BDT) by other analogous donor motifs, such as benzo[1,2-b:4,5-bprime;]difuran (BDF), further affect polymer backbone self-assembly and nanoscale morphology.[4] These studies provide additional insight into the critical role that molecular structure plays on material self-organization and BHJ solar cell performance.
[1] P. M. Beaujuge, and J. M. J. Fréchet, JACS 2011, 133, 20009.
[2] C. Piliego, T. W. Holcombe, J. D. Douglas, C. H. Woo, P. M. Beaujuge, and J. M. J. Fréchet JACS 2010, 132, 7595.
[3] C. Cabanetos, A. El Labban, J. A. Bartelt, J. D. Douglas, W. R. Mateker, J. M. J. Fréchet, M. D. McGehee, and P. M. Beaujuge, JACS 2013, 135, 4656.
[4] J. Warnan, C. Cabanetos, A. El Labban, M. R. Hansen, C. Tassone, M. F. Toney, and P. M. Beaujuge, Manuscript Submitted

Complex functional structures in nature are made by directed self-assembly. The “direction” is induced by the anisotropic structure of the colloid, either by shape or charge distribution. Here we will describe a method to induce “direction” due to transient state in an otherwise isotropic system. Spontaneous formation of microns long one dimensional (1D) necklace of 10 nm Au particle is mediated by ion bridges in solution. The suspension is patterned on a surface to form a 2D network array of 1D necklaces. The array size ranging from micron to nanometer scale exhibits robust single electron behavior at room temperature. The ions bridges connecting the necklace are subsequently reacted to nano-cement the particles with CdS. On bias, discreet electroluminescence (EL) spots above a certain threshold are observed. The location of the EL spots are independent of bias magnitude and polarity. The electroluminescence and photoluminescence spectra are consistent indicating the discreet emission is from the individual CdS nano-cement. The EL and stationary nature of the spots are explained by local charging that is the cause of the single electron effect.

Crystalline 2D materials such as grapheme, boron nitride, transition metal dichalcogenides and composites of these materials have received attention for their potential applications in logic, energy storage and optoelectronics. In this talk, we introduce a phase-eld for the CVD growth of 2D crystals on metal substrates. Our simulations account for anisotropic edge energies, attachment kinetics and difusion, with second order (thin-interface) corrections. We are mainly interested in the limit in which kinetic anisotropy dominates, and hence we study how the expected shape, which in the long-time limit is the kinetic Wulff shape, is modified by anisotropic diffusion. We present results that prove that anisotropic diffusion has a very important, counter-intuitive role in the definition of the shape of the island, and we add second order corrections to the model that provide a great increase of accuracy for small supersaturations. We also study the interaction of diffusion anisotropy with the deposition rate and present results for different crystal symmetries. This is joint work with Estaben Meca and John Lowngrub (UCI).

Many modern material systems consist of alloys of two or more species. These systems often have strain due to a lattice mismatch of the different materials. It is established by an exact solution of a ball and spring model of a binary alloy that continuum theory fails to predict its elastic energy. This result also shows that finely mixed alloys tend to have more elastic energy than segregated systems, which is the opposite of predictions made by continuum theories. Results using density-functional theory are in qualitative agreement. This work demonstrates that it is critical to include the microscopic arrangements in any elastic model to achieve even qualitatively correct behavior.

A quantum dot mesocrystal (QDMC) is a three dimensional, ordered array of quantum dots in a confining matrix material. By manipulating the characteristics of the array; including size, periodicity, symmetry and chemical composition of the dots, we can potentially tailor the relevant electrical, thermal, optical and magnetic properties of the crystal. While the dots themselves can possess size-dependent properties due to electronic confinement and discrete energy states, bringing the quantum dots close enough together on the nanometer scale can result in electron wavefunction overlap and extended state or even miniband formation. Control of these properties can lead to potential applications in optoelectronics, nanoelectronics and thermoelectrics.

We have synthesized rudimentary crystals of Ge quantum dots (QDs) embedded in Si by first patterning Si (001) to induce self-assembly of laterally ordered arrays of Ge quantum dots on the Si surface that will act as a seed layer for 3D mesocrystal formation. We reproducibly achieved highly-ordered, monodisperse 2D arrays with Ge interdot spacing as small as 50 nm, and with evidence that 35 nm is achievable with further optimization. These small QD interdot spacings are highly non-trivial, given the intrinsic islanding length scales and the strong tendency for Ostwald ripening. 3D mesocrystals are subsequently formed by alternating Si and Ge layer growth: when the Si interlayer is thin enough, Ge QDs will form on the Si interlayers and preferentially align to the seed layer due to the residual strain field. Pre-patterning of the Si surface was performed using a focused ion beam (FIB) to create nanoscale templates on the Si (001) surface. Multi-parameter arrays are generated by varying ion dose and pattern spacing, allowing for combinatorial investigation of the various experimental parameters. We find that optimal patterning occurs at relatively small ion doses (10² - 10³ Ga+ per site), which actually forms raised surface features, followed by defect-selective chemical etching that occurs during wafer cleaning. The latter creates nanoscale pits whose size and shape can be controlled. Subsequent Si and Ge deposition is by ultra-high vacuum magnetron sputtering. Extensive literature reports show that surface pits on Si (001) can localize Ge QDs, at least for pattern spacings greater than 90 nm. However, for the small spacings, small pit sizes, and relatively gentle surface topography produced here, we have found that the Ge accumulates interstitially between the pits in a highly reproducible fashion. Ostwald ripening is suppressed in these QD arrays to a surprising degree, suggesting that topographic effects on diffusion are at play.
This work is generously supported by the II-VI Foundation. Research performed in part at the NIST Center for Nanoscale Technology.

We report the experimental and theoretical study of the self-assembly of planar organic molecules of the type tris-X-biphenyl-benzene (with X=N, I, Br, CH) on a passivated, boron-doped Si(111)-radic;3xradic;3 (R=30°) surface. Ordered molecular structures are observed by high-resolution STM. We perform multi-scale atomistic simulations, by DFT structure relaxation (Gaussian), metadynamics, molecular dynamics (MD) with empirical forces, and kinetic Monte Carlo with condensed degrees of freedom. Al low coverage, we identify by metadynamics the lowest-energy adsorption sites consistently with the STM images. Upon increasing molecular coverage, structural phase transitions of the molecular network are observed, in excellent agreement with experimental STM data. Our theoretical models allow to elucidate the subtle interplay between dispersion forces and hydrogen bonding, leading to some unexpected phenomena. Biasing the MD by a simple elastic-band constraint method, we identify the kinetic path leading from a low-density to a high-density ordered phase. Next, kinetic Monte Carlo simulations over a frozen Si:B surface, with energy parameters derived from the MD, help explaining the apparently striking experimental observations, according to which lower-density phases are favoured over higher-density phases.

Studying and understanding the conditions under which organic semiconductors can be engineered to form aligned single crystals in thin films is of primary importance owing to their unique orientation-dependent optoelectronic properties [1]. Efforts to reach this goal by self-assembly from solution processed films have been rewarded only with limited success [2]. In this work we present a new method to grow organic single crystalline thin films via solvent annealing of a dewetted cyanine droplet morphology [3]. The obtained single crystals are 100-1000 nm thick and cover up to 1000 µm². We identify solvate crystal growth in combination with a specific film dewetting morphology as key to successful fabrication of single crystals. Furthermore, these crystals self-align on chemically patterned substrates thus minimizing their interfacial energy. The statistical distribution of the single crystals&’ orientation on micro-contact printed substrates [4] can indeed be explained by a simple interfacial energy minimization model. We explore in situ the conditions for crystal formation and alignment under solvent annealing. We show that the crystals are wet by a solvent film which allows low-friction displacement of the crystal as a whole as it grows over the chemically patterned substrate. Such a control on the crystal formation an orientation may prove useful for the fabrication of organic electro-optical devices.
References:
[1] Briseno, A. L. et al., Nature, 2006, 444, 913
[2] Goto, O., et al., Adv. Mater., 2012, 24, 1117
[3] Tisserant, J.-N. et al., ACS Nano, 2013, DOI: 10.1021/nn401679s
[4] Kumar, A. & Whitesides, G. M.,Appl. Phys. Let., 1993, 63, 2002

In many first order phase transitions pattern formation is observed and the velocity of the transformation can be related to some feature of the evolving microstructure, for example the spacing-velocity relation in eutectic growth. However, the unique velocity chosen by the transforming system is, in general, an unsolved problem. In this work velocity selection is investigated for the case of plate-like precipitates in alloys growing by the ledge mechanism. As a first step, the concentration field in the matrix phase during growth is formulated by a boundary integral technique, which correctly accounts for the step-terrace structure of the advancing precipitate. By examining the conditions at the plate tip and by invoking a stability argument for the plate thickness, a modified Ivantsov relationship is established between the growth velocity, the radius of curvature of the plate tip and the supersaturation. When compared with previous theoretical treatments that have assumed a smooth parabolic precipitate interface, the boundary integral result is able to describe more accurately the velocities obtained in experiments on the Al-Ag system.

Numerical simulations of production and aggregation of BaTiO3 nanocrystals synthesized in aqueous solution without surfactants under ultrasound have been performed under the experimental condition reported in [Dang, Kato et al., Jpn.J.Appl.Phys. 48, 09KC02 (2009)]. In the experiment, the crystal axes of BaTiO3 nanocrystals of 5-10 nm in diameter were surprisingly aligned in an aggregate of 100-400 nm in diameter, which is called a mesocrystal. As a first step to study the mechanism of mesocrystal formation, the particle (aggregate) size distribution was numerically simulated taking into account the following three processes; chemical reaction in the solution, nucleation, and aggregation. The result has indicated that large aggregates do never aggregate each other in order to reproduce the experimentally observed particle size distribution [Yasui et al., Ultrason.Sonochem. 18, 1211 (2011)]. Next, numerical simulations of collisions of two particles (aggregates) were performed based on the dipole-dipole interaction model in order to study the mechanism of oriented attachment. Due to the repulsive double-layer interaction, large aggregates do never aggregate each other. Furthermore, crystal axes are aligned by the dipole-dipole interaction [Yasui and Kato, J.Phys.Chem.C 116, 319 (2012)]. These results are consistent with the experimental results as well as the numerical ones on the particle size distribution. It suggests that a 5-10 nm BaTiO3 nanocrystal has spontaneous polarization. On the other hand, there are numerous reports on the size effect of BaTiO3 nanocrystal that below a critical size of around 20-30 nm the crystal structure is cubic and that it does not spontaneous polarization. Thus, numerical calculations of free energy of a BaTiO3 nanocrystal have been performed taking into account the depolarization energy. It is suggested that adsorbate-induced charge screening as well as defect-induced micro-strain is the reason for the diversity in the critical size [Yasui and Kato, J.Phys.Chem. C (submitted)]. A BaTiO3 nanocrystal synthesized in aqueous solution under ultrasound is suggested to have spontaneous polarization because the surface is completely covered with adsorbate (-OH) and there is strong charge screening due to the adsorbate which stabilizes the tetragonal crystal structure by decreasing the depolarization energy.

Far-from-equilibrium shape and composition profiles for bimetallic nanoclusters can be exquisitely sensitive to the thermally-activated attachment-detachment and diffusive relaxation kinetics for the aggregating species. However, the relevant rates and activation barriers are impacted by the local environment in which these processes occur, and of which there are hundreds of distinct possibilities. For low-strain epitaxial nanoclusters formed by deposition onto crystalline surfaces, we have developed a multi-site lattice-gas (msLG) formalism which allows precise determination of all these barriers from high-level DFT analysis and incorporation into KMC simulations for self-assembly on the appropriate time and length scales [Han et al., PRL 108 (2012) 216102; PNAS 108 (2011) 989]. Results are presented for mixed and core-ring nanoclusters including (Au+Ag)/Ag(100) and (Ni+Al)/NiAl(110) (and, for the latter, compared with images from STM experiments).

Fabricating substrate-supported arrays of metal nanoparticles is widely important for applications including catalysis, nanomaterial synthesis, and photonic devices. Researchers have shown myriad techniques for producing such arrays, yet there still is not a scalable bottom-up approach for making monodisperse, small-diameter (< 20 nm) particles with high spatial order (for non-close-packed systems). Previous work has shown that the topography of the substrate (e.g., pits) or pre-patterning of a film can control film dewetting into particle arrays, but the studies have been limited to larger particles.
We show that self-ordered metal nanoparticle arrays can be formed by dewetting of thin films on hexagonal mesh substrates made of anodic aluminum oxide (AAO). We sputtered metal films (i.e., Fe, Au, Pt) onto the top surface of commercially obtained AAO (18-nm pore size), and we performed dewetting in a tube furnace under atmospheric pressure. We studied the morphology and dynamics of dewetting using a combination of atomic force microscopy (AFM), grazing-incidence small-angle X-ray scattering (GISAXS), and numerical simulations.
We found that the metal film dewets onto the interstitial sites (i.e., the node points) between the pores on the top surface of the AAO; this is driven by surface tension about the edges of the holes in the film, which are self-patterned by the geometry of the template. Metal particles formed on AAO were more monodisperse (from modeling σ = 0.05 versus 0.35 nm) and had higher local ordering than those formed by the same process on flat, nonporous alumina on a Si wafer. The degree of order depends on the initial film thickness, and for the optimal thickness tested (2 nm), we achieved uniform coverage and high order (comparable to that of the AAO template itself). Computational modeling of dewetting on mesh templates of various pore order and size showed that the order of AAO pores is primarily influential in determining particle position and spacing, while the variance in pore size is less impactful. Importantly, our study suggests that while high local hexagonal order is achievable, long-range order in these particle arrays is ultimately limited by the ability to synthesize highly ordered AAO.
Our ongoing work includes further computational studies of dewetting kinetics on mesh templates as well as engineering the plasmon resonance spectra based on the diameter and spacing of particles established by AAO-templated dewetting.

Anodic Aluminum Oxide (AAO) is a promising and versatile template or mask material for the fabrication of surface nanostructures from metal or semiconducting nanoparticles to organic fibers or tubes by various deposition techniques. Its hexagonal porous structure can be easily adjusted in terms of size and spacing from some 10 nm to several 100 nm. But even after decades of investigations there are still gaps in the range of regular pore growth and neither can the anodization parameters leading to a highly regular pore arrangement be predicted for many feature sizes. In general the nature of the pore self-arranging process is still not understood while on the other hand structural uniformity / regularity of functional nanostructures is essential for many possible applications in electronics and optics.
Our investigations focused on several aspects ranging from macroscopic AAO growth via nanoscale pore regularity to the atomic structure of AAO formed under different anodization conditions. Our goal was to extend the range of regular pore formation as well as to gain a deeper understanding of the AAO growth mechanism itself.
Starting with a novel cooling concept we were able to conduct anodizations even at elevated voltages with a significantly increased process control. These stability-improved anodization conditions allow detailed investigations of AAO formed under anodization voltages and electrolyte combinations never reported before. In combination with a quantitative regularity analysis based on a graphical / computational analysis of high resolution SEM micrographs we were able to tune anodization conditions such as temperature and elelctrolyte concentration to obtain highly regular AAO structures over extended intervals of processing conditions. Furthermore, novel fabrication routes have been established, extending the range of accessible AAO structures. In order to reveal and understand the general composite structure of AAO, TEM analyses of its crystalline structure have been made. These results have been combined with calorimetric investigations, mass spectroscopy, X-ray analysis and scanning probe imaging to determine the effect of specific heat treatments to the AAO and the herein contained structural transformation processes. These results are discussed with respect of increasing the understanding of the growth process of AAO.

Our group previously solved a key challenge for nanotechnology: programmable self-assembly of complex, three-dimensional nanostructures. Our solution was to build custom three-dimensional structures that can be conceived as stacks of nearly flat layers of DNA. I will discuss applications of this technology for molecular biophysics and therapeutics: (1) weak-alignment media for NMR structure determination of membrane proteins such as UCP2, a 30 kDa six-transmembrane helix mitochondrial proton transporter; (2) scaffolds for determining the number of SNARE complexes required for lipid-bilayer fusion; (3) how shape and size of DNA nanoparticles affects the rate of cellular internalization.

The use of DNA as a ligand for directing nanoparticle assembly offers the ability to independently tune parameters such as the interparticle spacing, lattice symmetry, and nanoparticle composition to produce materials with tailored physical and chemical properties. Despite the advantages of using DNA during assembly, one of the post-synthetic limitations inherent in this system is that the superlattices exist only in solution and collapse/dissociate under conditions in which DNA duplexes dehybridize (e.g. high temperatures, in air, in common organic solvents). Structural characterization for solution-phase superlattices is limited to in situ small angle X-ray scattering (SAXS) because these porous lattices collapse under the vacuum environment of an electron microscope. In this work, a method is presented for transferring DNA-interconnected nanoparticle superlattices from solution to the solid state via silica encapsulation. This method preserves the lattice symmetry and lattice parameter of the solution-phase lattice, thereby maintaining the structural diversity of superlattices achievable by solution-based DNA-programmable assembly. Once transferred to the solid state, the superlattices are stable in air and in common organic solvents, which greatly enhances their materials processability. One direct application of this technique is the use of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to directly visualize the nanoparticle crystals to corroborate the structural information obtained by X-ray scattering. Additionally, this technique allows for analysis of nanoparticle superlattices by electron tomography, which can be used to reconstruct a three-dimensional lattice. Importantly, because this silica embedding technique “locks” the solution phase into the solid state, it can also be used to track crystal growth and study crystallization processes on the nanoscale for comparison against traditional crystallization of atomic solids.

In nature, helical macromolecules such as collagen, chitin and cellulose are critical to the morphogenesis and functionality of various hierarchically structured materials. During morphogenesis, these chiral macromolecules are secreted and undergo self-templating assembly, a process whereby multiple kinetic factors influence the assembly of the incoming building blocks to produce non-equilibrium structures. A single macromolecule can form diverse functional structures when self-templated under different conditions. Collagen type I, for instance, forms transparent corneal tissues from orthogonally aligned nematic fibres, distinctively coloured skin tissues from cholesteric phase fibre bundles, and mineralized tissues from hierarchically organized fibres. Nature&’s self-templated materials surpass the functional and structural complexity achievable by current top-down and bottom-up fabrication methods. However, self-templating has not been thoroughly explored for engineering synthetic materials.
In my presentation, I will demonstrate a facile biomimetic process to create functional nanomaterials utilizing chiral colloidal particles (M13 phage). A single-step process produces long-range-ordered, supramolecular films showing multiple levels of hierarchical organization and helical twist. Using the self-templating materials assembly processes, we have created various biomimetic supramolecular structures. The resulting materials show distinctive optical and photonic properties, functioning as chiral reflector/filters and structural colour matrices. Through the genetic engineering of the M13 phages, I will also show how resulting materials can be utilized as functional nanomaterials for biomedical bone or soft tissue engineering materials, biosensor and bioenergy applications.

Plasmonic nanoparticles can be assembled into a wide variety of crystalline arrays using DNA functionalization and hybridization. Here we demonstrate that such DNA-NP superlattices can be grown epitaxially, eliminating grain boundaries and enabling fine control over orientation and size of the assemblies up to hundreds of square microns.
We use for our experiments a DNA-NP superlattice with a BCC crystal structure, consisting of a 30 nm diameter Au nanoparticle and a 62 nm lattice parameter. This superlattice is composed of interpenetrating lattices of nanoparticles with complementary DNA functionalization (A and A&’), enabling it to be grown from a surface layer-by-layer, by exposing the surface alternately to nanoparticles with A and then A&’ type DNA. We use electron-beam lithography followed by Cr/Au deposition and liftoff to engineer a silicon surface to resemble lattice-matched and strained BCC (100), BCC (110), and BCC (111) faces of this superlattice. We then functionalize this surface with DNA and expose it overnight to particles of complementary type. By continuing in this manner, multilayer epitaxial DNA-NP superlattice thin films may be built up. We characterize the resulting crystal growth by embedding the grown crystal in a silica sol-gel, drying and imaging via scanning electron microscopy.
With crystallization at 23 degrees C and for monolayer growth, we observe defect densities as low as 2% on a 10x10 micron lattice-matched BCC (100) template, clearly demonstrating the viability of large-scale crystal growth using this technique. We also achieve excellent results for BCC (110) and (111) orientations. However, after counting over 5000 attached particles across different substrates, we find that on average 14% of the particles attached to a lattice-matched BCC (100) surface are incorrectly attached. We are able to understand this defect density thermodynamically on the basis of our template geometry and crystal growth parameters.
For lattice mismatch up to +/- 10%, we observe pseudomorphic growth on BCC (100) templates, albeit with slightly higher defect densities than on lattice-matched substrates. At high (20%) strain, defect binding sites become thermodynamically favorable, and we observe growth of novel crystal structures. Finally, we demonstrate that epitaxial growth allows for systematic introduction of designed defects, which extends the range of structures that can be made using superlattice assembly. Ultimately this leads to the possibility of integrating self-assembled plasmonic materials into on-chip optical or optoelectronic platforms.

Specific, reversible interactions between colloidal particles can be engineered by functionalizing the particles with DNA oligonucleotides. Because of the wide separation in lengthscales between the oligonucleotides and the particles, the interparticle interactions can be viewed as a mean field resulting from local chemical equilibrium at the molecular scale. In principle these effective interactions can be used to direct the assembly of novel bulk phases or even prescribed, non-periodic microstructures. But in practice, the self-assembly is difficult to control due to the steep temperature dependence of the interaction strength. I will present experimental results showing that the temperature dependence of the DNA-mediated interactions can be softened, eliminated, or even inverted by introducing dissolved DNA strands that compete to bind with the grafted strands, an idea that originated in the DNA nanotechnology field. Strand competition enables the local equilibrium of the system to be programmed and reprogrammed in unusual ways -- for example, to create suspensions of colloidal particles that can freeze on heating, or display transitions between a fluid phase and two different colloidal superlattices. This scheme may prove useful for the design of synthetic self-assembling systems that approach the robustness and complexity of biological systems.

Active matter is an emerging branch of non-equilibrium soft matter encompassing novel, dissipative structures formed from collections of particles driven via externally applied local forces. Examples include self-propelled particles and switchable colloids. Such systems can exhibit nontrivial, emergent behavior fundamentally different from behavior seen in traditional thermodynamic equilibrium, and for which there is no established theoretical framework and no general predictive capability. As such, active matter lies at the forefront of materials research, with unique opportunities afforded by working at the nanoscale. In this talk we describe simulation studies of active colloidal matter in which externally applied forces drive the self-organization of unexpected structures, producing emergent, effective, interparticle interactions arising solely from the driven, active aspects of the system. We investigate the role of shape in systems of active colloids, and show that in some cases these emergent forces can be harnessed to perform meaningful work.

Plasmon rulers consisting of optically coupled metal nanoparticles linked by biological macromolecules have provided a tool for bio-imaging and enzymology that is non-bleaching, non-blinking, and biocompatible. A pair of plasmonic nanoparticles couple when they are in spatial proximity, resulting in spectral shifts and increased scattering intensity. Two self-assembled plasmonic nanoparticles exemplify an enzyme-responsive material in one-dimension. In order to visualize the subtle conformational changes ubiquitous in biological systems, three-dimensional multicomponent nanoparticle assemblies are required.
We report a stimuli-responsive chiral DNA-mediated nanoparticle assembly based on circular dichroism (CD) detection. This structure exhibits a sensitive optical response and provides a unique substrate for detecting handedness in biological events. Using a coupled dipole model to calculate the optical response of metal nanoparticle assemblies which takes into account parameters such as the polydispersity of colloidally synthesized nanoparticles and the flexibility of DNA, we designed a four nanoparticle structure. Four DNA strands, each attached to a gold nanoparticle, hybridize such that each strand folds into one face of the pyramid. The sequence of the four strands was designed to maximize the yield of one enantiomer based on tertiary structure of the double helices and to minimize thermodynamically favorable alternate structures. Taking into account design rules from the model and the constraints of our DNA template, we synthesized a distorted DNA tetrahedron of side length 26 base pairs (~9nm), save one side, of 16 base pairs (~5.5nm), decorated with two 10 nm and two 20 nm diameter gold nanoparticles. The shorter side breaks the mirror plane between the two sizes of nanoparticles, forming a chiral assembly.
This structure can be synthesized in high yield in aqueous solution. Colloidal nanoparticles of 10 and 20 nm are reacted with 5' thiol modified oligonucleotides in a buffered solution of moderate ionic strength. Anion-exchange high-performance liquid chromatography separates the mixture of products to produce mono-conjugated nanoparticles for assembly. Ensemble circular dichroism measurements show a bisignate feature near 520 nm, the absorbance maximum of gold nanoparticles.
Calculations show that small changes in the length of the shorter, symmetry breaking arm of the DNA tetrahedron will change the intensity and spectral position of the CD. Our structure will find application as a nanoparticle ruler for subtle biological events, such as the extension of DNA by a DNA-binding protein. Large changes in length of this arm can invert the handedness of the chiral structure completely, and therefore the sign of the bisignate curve. Thus, in addition to biomolecular recognition, this chiral nanoassembly represents the first of a category of switchable metamaterials which can change handedness as a response to external stimuli.

We report the synthesis and assembly of anisotropic patchy spheroids that combine both shape and interaction anisotropy. These particles are synthesized by combining evaporative deposition of chrome and gold with the uniaxial deformation of polymeric colloidal particles. We assemble these patchy particles at various salt concentrations and demonstrate the functionality of the patches of our particles using newly developed two-channel confocal imaging and image processing techniques. We subsequently use AC electric fields to direct the assembly of the spheroidal patchy particles. The metallic patches on these colloidal particles have a significantly higher polarity in AC fields as compared to the polymer component of the particle and this leads to formation of colloidal chain assemblies. We explore the scope for rapid reconfiguration between assembled structures by manipulating the applied AC electric field.

Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base of particle-stabilized emulsions [1] and templating [2]. Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control (micro and sub-micro sized) colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal “ribbons”, electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface. In addition, we demonstrate the size control of “pupil” like openings in colloidal shells. We anticipate that electric field manipulation of colloids in leaky-dielectrics can lead to new routes of colloidosome assembly and design for “smart armoured” droplets [3].
Colloidal particles can bind strongly to fluid interfaces and assemble into thin layers. Monodisperse colloidal beads can form 2D ordered colloidal crystal monolayers [4], and poly-disperse and anisotropic particles form amorphous shells [5]. This effect is currently much studied in relation to particle-stabilized “Pickering” emulsions [1] where particle coatings on droplets effectively prevent droplet coalescence and produce very stable surfactant-free emulsions. Solid colloidal capsules; colloidosomes, can be produced by fusing or linking the colloidal particles at the surface of Pickering emulsions droplets [6].
References:
[1] Aveyard, R., Binks, B. P. and Clint, J. H. (2003) Emulsions stabilised solely by colloidal particles. Adv. Coll. Int. Sci. 100, 503-546.
[2] Shah, R. K. et al. Designer emulsions using microfluidics. (2008) Mater. Today 11, 18-27.
[3] Dommersnes, P., Rozynek, Z., Mikkelsen, A., Castberg, R., Kjerstad, K., Hersvik, K. and Fossum, J.O. Active structuring of colloidal armour on liquid drops. Nat. Commun (Accepted May 2013)
[4] Pieranski, P. Two-dimensional Interfacial colloidal crystals. (1980) Phys. Rev.Lett. 45, 569-572.
[5] Yan, N. X. and Masliyah, J. H. Adsorption and Desorption of Clay Particles at the Oil-Water Interface. (1994) J. Colloid Interface Sci. 168, 386-392.
[6] Pickering, S. U. Emulsions. (1907) J. Chem. Soc., Trans. 91, 2001-2021.

Under low energy noble gas ion exposure in the keV-range the clean Si(001) surface remains flat for a large range of incidence angles, temperatures and beam parameters. Despite this resistance to morphological destabilization, here we identify three specific regimes of pattern formation on Si(001).
First, using simultaneous supply of metal impurities by sputter deposition or evaporation, ripple and dot pattern formation is observed for a variety of supplied species. By comparing the effect of neighbor metals in the periodic table, like Ag (no silicide formation) and Pd (silicide formation), the ability to form a silicide turns out to be a necessary, but not a sufficient condition for pattern formation. Whether or not a pattern forms depends sensitively on deposition geometry and the history of the sample. The steady state concentration of the supplied impurity does not define the morphological state of the sample. Moreover our investigations point to the importance of in situ pattern analysis to properly interpret the resulting morphology.
Second, under grazing angles > 60° with respect to the surface normal, ripple patterns evolve for pure Si. We follow the evolution of such patterns for two distinct angles, 63° and 75°, and distinguish different stages in pattern formation accompanied by exponential growth of the pattern amplitude, initially, and a subsequent power law growth of roughness. In the late stages, also a rapid coarsening of the pattern is observed for 75°, which is linked to ion reflection and facet formation.
Lastly, upon increasing the temperature, somewhere between 650 K and 700 K, Si changes from the ion beam amorphized state to a situation, where it remains crystalline during the ion exposure. As soon as with increasing temperature the crystalline state is maintained, pattern formation sets in abruptly for conditions, where otherwise no pattern would be present. This sharp transition is associated with the onset of anisotropic diffusion and the formation of a terrace-step structure.
The contributions to this work by M. Engler, S. Macko, S. Mueller, D. Foerster, F. Frost, B. Ziberi, R. Feder, D. Spemann, S. Facsko, J. Grenzer, D. Hirsch, R. Huebner, M. Fritzsche, T. Hoeche and A. Muecklich are gratefully acknowledged.

Crater function theory predicts surface stability or instability under ion bombardment from the crater function, which is the average response of a flat surface to a single ion impact. A recent simplification of the theory assumes that surface evolution can be predicted based upon the crater function for a flat surface, a quantity which can be readily predicted by molecular dynamics simulations. Here it is pointed out that the structure of thise formalism allows sensitive experimental tests of its accuracy that are independent of any a-priori knowledge of the crater function itself. The theory&’s linear stability analysis predicts that, in the projected direction of the ion beam, the integral over off-normal bombardment angle of the coefficient governing the surface&’s stability/instability is zero. Moreover, in this formalism the surface response in the directions parallel to and perpendicular to the projected ion beam are closely related to each other. Existing in-situ grazing-incidence small-angle x-ray scattering (GISAXS) measurements for 1 keV Ar+ bombardment of Si and Kr+ bombardment of Ge are compared to these predictions and shown to disagree with them at high bombardment angles.

Since the first observation in 1999 of highly-ordered, hexagonal arrays of nanoscale dots on the surface of an ion-irradiated semiconductors, consensus has emerged that these structures require the presence of two atomic species in the irradiated target. A variety of models have emerged to describe such systems, including the regimes of eroded binary materials, eroded pure materials with impurity co-deposition, and the ion-assisted growth of a multi-component film. These models show great promise, but a large number of unknown parameter values limits direct comparison with experiment.
Here we consider the use of atomistic simulation to estimate several important parameters within models of irradiated two-component systems. By extending the "crater function" formalism to the case of multiple species, and comparing the result to underlying physics within a given model, we are able to estimate a number of the final parameters determining morphology evolution; in particular, the parameters governing the behavior of the long waves, which in turn determine the nature of any instability, and the qualitative behavior of the system at late times.
Finally, because parameters for at least one of the existing models do not seem to meet the model's own pattern-formation requirements, we present a generalization of previous models to include a treatment of ion-assisted phase separation. Depending on material parameters for a given pair of target atoms, this effect can admit a chemically-driven instability in the concentration field even when the effects of the kinetically-dominated collision cascade are stabilizing.

Energetic ion irradiation of surfaces can cause nanopatterning, ultra-smoothening, or degradation (e.g. fission and fusion reactor components). We have previously studied Si and Ge roughening under Ar⁺ and Kr⁺ irradiation, respectively, showing that impact-induced mass redistribution dominates the nanopatterning or ultra-smoothening process [1,2]. These studies had been confined to the linear regime of exponential amplification or decay at early time and low fluence. Here we present the results of our recent investigation into self-organized pattern formation by Ar⁺ on Si in the nonlinear, high-fluence regime. We use a high-flux ion source, atomic force microscopy (AFM), and real-time, in situ grazing incidence small angle x-ray scatterning (GISAXS) to investigate nonlinear roughening of an ion/substrate system that has been thoroughly investigated in the linear regime. We discuss the implications of these results for theory and application.
1 C.S. Madi, E. Anzenberg, K.F. Ludwig, Jr., and M.J. Aziz, Phys. Rev. Lett.106, 066101 (2011).
2 E. Anzenberg, J.C. Perkinson, C.S. Madi, M.J. Aziz, and K.F. Ludwig, Jr., Phys. Rev. B86, 245412 (2012).

Irradiating a surface with keV ions often leads to the formation of nanosized periodic undulations. This phenomenon has been attracting a lot of interest, both from fundamental point of view and as a potential nanofabrication tool due to its relative simplicity and high throughput. Despite substantial effort towards a complete theoretical description of this phenomenon, various aspects of the ion-induced pattern formation are still not satisfactorily understood.
We will focus on the patterning of a specific group of materials, i.e. metals. In contrast to other surfaces typically studied in this context (e.g. Si, SiO2), metals do not amorphize during the ion irradiation process and their persistent crystalline nature may significantly influence the patterning behavior. The existing theory for the pattern formation, however, usually does not explicitly account for the crystalline structure of the surface and it is inconsistent with many experimental observations for metallic surfaces.
A characteristic observation for a majority of metallic surfaces is that grazing incidence ion irradiation leads to the formation of ripples parallel to the ion beam direction. In the context of the conventional theory, these ripples are seen as waves with a specific periodicity and wavelength which are formed and amplified due to the presence of an anisotropic linear instability resulting from the erosion process. In contrast to this paradigm, we propose a different mechanism which can explain the formation of these ripples. Its action can be described as follows: if a localized protrusion or depression appears on the surface, the oblique irradiation leads to the elongation of this feature in the direction of the ion beam leaving behind a structure which can be more accurately described as a 'scratch' on the surface. In contrast to the linear instability mechanism, the ion scratching is a purely non-linear phenomenon, stemming from the variation of the local irradiation conditions between up-stream and down-stream slopes of the existing surface protrusion/depression. We show that the initial formation of roughness on metals is related to their specific crystalline structure. This scratching tendency is a very general consequence of the oblique irradiation process and is present on any surface exposed to grazing angle irradiation.
We will apply this mechanism to single-crystalline and polycrystalline metallic surfaces and will show that the predictions of the numerical simulations are in an excellent agreement with the experiments. An important conclusion follows from our study: the ripples which are parallel to the ion beam (characteristic for metallic surfaces) result from a significantly different mechanism than the ripples perpendicular to the ion beam (typically observed on amorphous surfaces). In order to distinguish the origin of the surface waves, we can refer to the former as scratches rather than ripples.

In contrast to their bulk form, nanosized metals surrounded by a dielectric medium exhibit a remarkable optical phenomenon known as localized surface plasmon resonance (LSPR) when they interact with light. Excitation of surface plasmons in metal nanoparticles at the resonance wavelength gives rise to specific effects (i.e., an intense optical absorption and a strong enhancement of the local field around the nanoparticles), which are the bases of recent developments, with various applications ranging from photonic and photovoltaic devices to biochemical sensors and markers. Despite the progress in nanofabrication techniques, the realization of nanostructured materials with optimized plasmonic properties remains a significant challenge, which demands a full control of the size, shape, organization, and environment of the nanoparticles. In this context, it has recently been shown that periodic nanoripple patterns produced by ion-beam sputtering of insulating surfaces can be used as templates to fabricate self-aligned noble metal nanoparticles and nanowires by glancing-angle deposition (GLAD) [1-3]. It has been proved that these systems possess original dichroic properties, reflected in a polarization-dependent excitation of their LSPR and strong coupling between particles for a longitudinal polarization, which might be exploited, e.g., for surface enhanced Raman scattering applications [4].
In this presentation, we will focus on the formation of self-organized arrays of Au and Ag nanoparticles prepared by GLAD on periodic nanoripples produced by Xe+ sputtering of alumina thin films. We will show that reciprocal space mapping by grazing incidence small-angle X-ray scattering (GISAXS) associated with quantitative analysis in the distorted wave-Born approximation provide accurate information, averaged over macroscopic dimensions, on the morphology and organization of both the nanorippled alumina surfaces and the nanoparticle arrays deposited thereon. Moreover, we will show that the combined use of real-time and in situ GISAXS and surface differential reflectance spectroscopy (SDRS) [5] experiments can deliver unique insights into the growth mechanisms and LSPR characteristics of anisotropic plasmonic nanostructures produced by GLAD, from the early stages of nucleation to the formation of continuous films [6].
References
[1] S. Camelio, D. Babonneau, D. Lantiat, L. Simonot, and F. Pailloux, Phys. Rev. B 80, 155434 (2009).
[2] D. Babonneau, S. Camelio, L. Simonot, F. Pailloux, P. Guérin, B. Lamongie, and O. Lyon, Europhys. Lett. 93, 26005 (2011).
[3] D. Babonneau, S. Camelio, E. Vandenhecke, S. Rousselet, M. Garel, F. Pailloux, and P. Boesecke, Phys. Rev. B 85, 235415 (2012).
[4] M. Ranjan and S. Facsko, Nanotechnology 23, 485307 (2012).
[5] L. Simonot, L. Simonot, D. Babonneau, S. Camelio, D. Lantiat, P. Guérin, B. Lamongie, and V. Antad, Thin Solid Films 518, 2637 (2010).
[6] R. Dohrmann et al., Rev. Sci. Instrum. 84, 043901 (2013).

Many times surfaces driven out of equilibrium by growth or erosion processes, as in thin-film production, solid fracture, etc. self-organize in such a way as to display scale-invariant behavior without the need to fine-tune control parameters (kinetic roughening). For observables in real or in Fourier space, power-law behavior ensues whose exponents characterize the large scale properties of such systems.
We are interested in the competition between surface kinetic roughening and two different types of properties that in principle break simple scaling behavior, while also being pervasive in surface nanostructuring [1]: (i) Morphological instabilities by which typical scales are selected leading to pattern formation and (ii) space anisotropies inducing different scaling behaviors along different substrate directions (strong anisotropy, SA).
As a paradigm for (i), we study the noisy Kuramoto-Sivashinsky equation for two-dimensional substrates, which arises in a wide variety of contexts, such as erosion by ion bombardment, dynamics of steps on vicinal surfaces, solidification of binary alloys, or growth by CVD or ECD [1,2]. In [2] we show, by means of numerical simulations, that the large scale behavior of such equation is actually dominated by noise, and belongs to the well known Kardar-Parisi-Zhang universality class.
In order to study (ii), we formulate a SA Ansatz that, being equivalent to other proposals that can be found in the literature, is more naturally adapted to the type of observables that are frequently measured in experiments on the dynamics of thin films, such as one and two-dimensional height structure factors [3]. We test our Ansatz on paradigmatic linear and nonlinear stochastic equations displaying SA that are relevant to surface nanostructuring. Our hypothesis is further validated against experimental data from Si targets eroded by ion-beam sputtering at low energies, with and without concurrent impurity deposition [4]. Our analysis reveals that certain observables are more prone to finite-size effects which can hinder a clear-cut assessment of SA, and provides a self-consistent methodology for avoiding such complications when studying experimental strongly anisotropic systems.
Additionally, we study from a theoretical point of view the appearance of strong anisotropy in nonlinear stochastic equations, both with conserved and non-conserved dynamics [5]. Our preliminary results suggest that, in order to take place, asymptotic SA requires special (non-generic) conditions from the shape of the terms appearing in the dynamical equation.
[1] R.Cuerno, M. Castro, J. Muñoz-García, R. Gago, and L. Vázquez, EPJ Special Topics 146, 427 (2007).
[2] M. Nicoli, E. Vivo, and R. Cuerno, PRE 82, 045202(R) (2010).
[3] E. Vivo, M. Nicoli, and R. Cuerno, PRE 86, 051611 (2012).
[4] E. Vivo, M. Nicoli, M. Engler, T. Michely, L. Vázquez, and R. Cuerno, PRB 86, 245427 (2012).
[5] E. Vivo, M. Nicoli, and R. Cuerno, in preparation.

We have made comprehensive studies on the temporal evolution of initially rippled Au(001) under ion beam sputtering (IBS) normal to the surface, employing both the experimental investigation and model development. The initial ripple pattern guided the growth of nano dots along the ripple that we call nabobeads. The sophisticated pattern of nanobeads served nicely as a test bed for the examination of previously proposed models for the pattern formation induced by IBS. We find that the local redeposition represented by conserved KPZ term in the extended Kuramoto-Sivasinski (eKS) equation plays an essential role for the development of the bead pattern and its conservation.[1] Furthermore, temporal evolution of the nanobead patterns with varying ripple wavelengths and amplitudes is consistently reprodued by the eKS model,
reinforcing our observation of the critical role of nonlinear effects for the evolution of the
nanobead pattern.[2]
[1 ] J.-H. Kim, N.-B. Ha, J.-S. Kim, M. Joe, K.-R. Lee, and R. Cuerno,
Nanotechnology 22, 285301 (2011).
[2] J.-H. Kim, J.-S. Kim, J. Munoz-Garcia and R. Cuerno,
Phys. Rev. B 87, 085438 (2013).

The strong field enhancement between two narrow, sharply pointed metallic tips subjected to a DC or AC electromagnetic field gives a unique possibility to either position, modify or analyse nanoobjects between the tips. The aim of this study is therefore to explore a new route to achieve a long chain of pairs of metallic tips, which point to each other and which are separated by a narrow gap. To this end the self-organisation of nanospheres in trenches on the surface of silicon wafers is studied, since such an arrangement of spheres could serve as a nanoscale shadow mask to form such pairs of metallic nanotips by physical vapour deposition (PVD) techniques.
Optical lithography combined with reactive ion etching was used to define linear trench geometries at the surface of silicon wafers. Using confocal light microscopy, the exact shape, depth and width of the trenches was measured. Both, the width and depth of trenches were varied, as was the areal density of trenches at the wafer surface. A spreading knife technique was used to move a droplet of a colloidal suspension of polystyrene (PS) nanospheres (diameter up to 2.1 µm) in water across the lithographically pre-patterned silicon surface, enabling template-assisted self-organized arrangement of PS spheres in the trenches and on the Si top surface in between. It is shown that by functionalizing the pre-patterned Si surface with a self-assembled molecular monolayer (SAM) of octadecyltrichlorsilane OTS and by optimizing the sphere self-arrangement conditions, the deposition of spheres on the silicon top surface can be largely suppressed while the thin trenches (width commensurate with the diameter of PS spheres) get filled with a linear chain of contacting PS beads. Chain lengths of up to 0.5 mm were obtained. These chains of beads were used as a shadow mask during the PVD of thin metallic layers. By this, linear chains of metallic nanotips pointing pairwise to each other are obtained after mask removal. The tips are formed at the opposite side walls of a trench while the Si top surfaces next to the trench form the two macroscopic contact pads to the nanotips. The tip geometries are characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. First experiments with such chains of tip pairs are presented.

Semiconductor crystalline nanomaterials are highly desirable, e.g. for their unique electrical and optical properties, and have been adapted for novel applications such as optoelectronics, sensors, and energy conversion and storage. Recently, bottom-up self-assembly structure formation coupled with pulsed excimer laser irradiation has been demonstrated as a viable route to fabricate high quality porous single-crystal nanostructures. Here, we report the generation of complex crystalline silicon nanostructures from bimodal self-assembly-directed nanostructure templating. We will show that self-assembly driven bottom-up is highly compatible with top-down lithographic patterning to achieve hierarchically structured semiconductor nanostructures. Our results suggest a general strategy coupling soft-matter self-assembly with laser thermal processing to direct and design intricate nanopatterned crystalline inorganic materials.

Although there has been considerable research into the self-assembly of thin films of block copolymers, little attention has been paid to morphological changes in bulk-gyroid block copolymers as the film thickness approaches the microdomain period. Here, the self-assembly of thin films of a block copolymer with a bulk gyroid structure was examined for a range of thicknesses and annealing conditions using both theoretical and experimental approaches. Self-consistent field theory simulations for effective chi.N = 14 and volume fraction f = 40% predict a transition from wetting layer - perforated lamella - cylinder - lamella - gyroid transitions with increasing thickness, and the energy of each structure as a function of thickness was calculated to determine the stability of each structure. The predictions were tested using films of polystyrene-b-polydimethylsiloxane (SD75, 75.5Kg/mol, fPDMS =41.5%, PDI =1.07) which formed a gyroid structure in bulk with a microdomain period, Lo~46 nm. Thin films were spin-cast from 1% solution of SD75 in cyclohexane and annealed in cosolvent vapors consisting of mixed toluene and heptane vapors. The morphology of the microdomains was revealed by removing the PS with oxygen plasma. Thick films (>2Lo) showed gyroid-like morphologies, but thinner films (Lo) exhibited perforated lamellar structures in agreement with modeling. By tuning the solvent vapor annealing conditions, cylinders (period~60 nm) or perforated lamellae (period~ 90 nm) with excellent long range order, as well as coexisting morphologies such as lamellae plus cylinders, were produced. These self-assembled nanostructures can be potentially useful for nanolithography templates, nanoparticle synthesis, patterned information storage media, solar cell heterojunction, fuel cell templates, or membranes for water desalination or heat transfer.

Block copolymer (BCP) self-assembly provides access to well-ordered nanostructures with tunable morphology on a typical length scale of 5-50 nm. Furthermore, BCPs can be employed to structure direct the assembly of various inorganic materials from oxides to semiconductors to metals, thereby combining the advantages of polymer processing and self-assembly with the properties of typical inorganic solid-state materials including high conductivity and etch resistivity.(1) Recently it has been demonstrated for AB diblock copolymers and ABC triblock terpolymers that the combination of BCP self-assembly and non-solvent induced phase separation (SNIPS) conveniently produces graded porous superstructures that can be used as ultrafiltration membranes.(2-4) The asymmetric superstructure is composed of a uniform mesoporous dense surface layer of 50-100 nm thickness on top of a sponge-like macroporous support layer of tens of micrometers thick. Here we extend this method from polymeric systems into producing asymmetric porous hybrid materials.
1. S. C. Warren et al., Science 320, 1748 (2008).
2. K. V. Peineman et al., Nat. Mater. 6, 992 (2007).
3. R. M. Dorin et al., ACS Macro Lett. 1, 614 (2012).
4. W. A. Phillip et al., Nano Lett. 11, 2892 (2011).

Block copolymers, comprised of two dissimilar polymers covalently coupled at one end, can self-assemble into arrays of nanoscopic morphologies, including lamellar, cylindrical, and spherical microdomains, that serve as ideal templates for the fabrication of nanostructured materials. The size of the microdomains is a function of the polymer size so tuning the copolymer's molecular weight allows for a precise control over the dimension of the block copolymer morphologies. Moreover, the heterogeneous chemical nature of block copolymers allows them to be used as templates for well-defined protein adsorption.
Here, we used nanoscopic block copolymer patterns as templates to study the assembly of S-layer proteins SbpA from Lysinibacillus sphaericus (ATCC 4525) by in-situ Atomic Force Microscopy (AFM). Studies were performed on substrates comprised of block copolymers where the microdomains are oriented parallel to and normal to the surface of the film, essentially line and dot patterning, to determine the influence of the type of patterning on the assembly and crystallization of S-layer proteins. To clearly define the crystal orientation on the surface, block copolymer films with well-defined patterns were used. The templates were formed by polystyrene-b-poly(ethylene oxide) block copolymers of various molecular weights after spin coating on faceted sapphire surfaces and subsequent controlled solvent-vapor annealing. Our results show that by controlling the chemical contrast in templates of different geometry and periodicity, protein assemblies could be directed exclusively to the hydrophobic domains of the template. More importantly, our high-resolution AFM measurements indicate that the proteins crystallized in their native lattice while following the structure of the underlying template by preferential adsorption.
Block copolymers provide a powerful tool for immobilizing S-layers on substrates in a highly periodic manner with high areal density while the proteins retain their native structure and function. This provides a unique platform that enables both basic investigations and control of the protein function.

In order to fabricate nanofibers of an elastomeric styrene-isoprene-styrene block copolymer (SIS), we controlled the sol-gel characteristics of SIS solution with different viscoelastic features during electrospinning. In fact, by equally mixing toluene with N, N-dimethylformamide (DMF) (50:50) to control the viscoelasticity of the SIS solution, we successfully fabricated elastomeric SIS fibers with 350 nm in diameter. The average diameter of the fibers fabricated by SIS in pure toluene was above 5 mu;m. Only a few researches have previously linked the synthesis of block-copolymer nanofibers by electrospinning with the sol-gel behavior of the block-copolymer solution, which should eventually be strongly related to the self-organization and the viscoelasticity behaviors of the block-copolymer solution. Toluene is a good solvent for both styrene and isoprene molecular blocks in SIS. DMF is a relatively poor solvent for the isoprene block as compared with the styrene block. To evaluate the self-organization behavior of SIS in mixed solution, the viscoelastic properties of the SIS solution were examined by the dynamical mechanical analysis (DMA) with the strain-controlled rheometer. The solution prepared with pure toluene presented almost complete liquid sol characteristics. As the ratio of DMF in toluene increased, the dynamic modulus of the solution gradually increased. When DMF and toluene were mixed at 40:60 and 50:50, the resulting solution became turbid to be in a more solid gel state around the concentration of 15wt%. The structural analyses of the SIS solution were conducted by a dynamic light scattering method (DLS). It was found that, just when DMF and toluene were mixed at 40:60, the radius of the self-organized structures in SIS solution began to increase. In more detail, the radius of the self-organized structures was approximately 50 nm at 40:60, and 100 nm at 50:50 measured by DLS, while below the DMF ratio of 40:60, the radii were almost unchanged at 20 nm in average measured at the compositions of 30:70, 20:80, and 10:90. The resulting thinnest elastomeric SIS nanofibers could be used as a prospective candidate for dispersed materials in composites with e.g. high impact resistance.

Nanoparticle assemblies in block copolymer (BCP) thin film have been widely studied experimentally and theoretically. The phase behavior of BCP-based nanocomposites is determined by the combination of enthalpic interactions between the nanoparticle ligands and the polymer matrix and the entropic contribution of the polymer chain conformations. Recently, it has been shown that this exquisite balance can be used to position nanoparticles of certain sizes at precise locations in block copolymer matrices. Given the long-range order that can be achieved with current directed-self assembly techniques, it is possible to envision that one could one day precisely position nanoparticles within these templates. In addition, recent research has also shown that defects, such as dislocations, can play a significant role in determining the position of nanoparticles within the block copolymer matrix. By exploiting the patterning capabilities of directed self-assembly and exploiting defects it is then foreseeable that one could position nanoparticles in arbitrary patterns, or separate them according to size in block copolymer inhomogeneous structures with many applications in the realm of photonics, plasmonics, and nanoelectronics.
Here we present our work on the distribution of nanoparticles having various shapes (sphere, rod or disk) in different types of directed-self-assembled BCP morphologies using hybrid particle-field simulations. The BCP patterns are first obtained by modeling a nanoscale template consisting of ordered posts that are attracted to one of the blocks of BCPs. Once a desired pattern is obtained, we run simulations using the pattern as the initial condition while also including nanoparticles with different shapes, sizes and positions. By calculating the mean-field free energy of the entire system, we study the role that chain stretching and nanoparticle shape and size play in the equilibrium location of the NPs in the BCP matrix. Our results can have important implications in directing the self-assembly of multi-component hierarchical materials.

The directed self-assembly (DSA) of block copolymers (BCP) is a new lithographic approach which offers the potential of a cost effective supplement to traditional optical lithography. The BCP is aligned over a chemical template, resulting in a complex distribution of stresses which guide the development of the internal morphology. Simulations are used to predict the impact of key parameters on the self-assembly process, but these require experimental validation in order to connect the results to real world process parameters. Utilizing soft x-rays near an absorption edges can provide enhanced contrast between organic components. This enables the use of resonant critical dimension small angle x-ray scattering (res-CDSAXS) for the characterization of the internal morphology of DSA BCPs. This technique has the ability to differentiate between the lamellar profiles which reside on the neutral brush and those which are anchored to the underlying substrate. In addition to the shape information res-CDSAXS can reveal the presence of periodic pitch offsets within the lamella and provide information on the interfacial roughness between BCP components. This technique has the potential to provide critical information during the process development stage along with much needed model validation.

In order to create the next generation of biobased nanomaterials it is of paramount importance to develop techniques to have an improved control over the individual material constituents.1 Colloidal rodlike cellulose particles with lengths of 200 nm and diameters of 5 nm, commonly referred to as cellulose nanocrystals (CNC), are known to partially organize into ordered domains as the particle concentration exceeds a threshold value.2 Long range order or larger ordered domains are however difficult to achieve with these materials.
One approach for controlled assembly of colloidal particles that has recently been introduced is the deposition onto wrinkled PDMS substrates,3 where a periodic pattern is used to geometrically confine the particles. In this contribution we show that cellulose nanocrystals can be assembled in wrinkled PDMS and subsequently printed in ordered linear patterns on different substrates. To prove the versatility of this assembly technique we also demonstrate that the transfer of particles can be repeated cross wise on the same surface. This we believe is of general interest and may open up possibilities for creating 3-dimensional layered particles assemblies with different functionality in each layer. In a second step, as a proof of concept for further functionalization, cationic latex nanoparticles are deposited on the cellulose nanorods by electrostatically driven self-assembly with excellent site specificity.
References
1. Balazs, A.C., T. Emrick, and T.P. Russell, Nanoparticle polymer composites: Where two small worlds meet. Science, 2006. 314(5802): p. 1107-1110.
2. Habibi, Y., L.A. Lucia, and O.J. Rojas, Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications. Chemical Reviews, 2010. 110(6): p. 3479-3500.
3. Schweikart, A. and A. Fery, Controlled wrinkling as a novel method for the fabrication of patterned surfaces. Microchimica Acta, 2009. 165(3-4): p. 249-263.

A common challenge in nanotechnology is the fabrication of materials with well-defined nanoscale structure and properties. One of the most exciting developments in addressing this issue is the use of biological components as scaffolds for programmed self-assembly. Here we report on assembly processes observed in genetically engineered and/or chemically modified Tobacco Mosaic Virus (TMV) coat protein. As a detailed example, we show that the addition of azide functionality onto the N-terminus of the TMV coat protein allows for facile addition of nanoscale components containing alkyne moieties to the TMV template, including polymers such as polyethylene glycol and polyarginine. The introduction of new functionality into TMV coat proteins allows for control of the self-assembly by chemical modification of the coat protein, or by solution additives. In contrast, assemblies in wildtype TMV are controlled by solution pH and ionic strength, making some structures incompatible with desired nanocomponents. Thus, our modified TMV is a more versatile scaffold for the programmed self-assembly of nanostructured materials.

Nanoparticles can be combined with nucleic acids to program the formation of three-dimensional colloidal crystals where the particles&’ size, shape, composition and position can be independently controlled. This enables us to define DNA densely functionalized nanoparticles as programmable atom equivalents, or PAEs. However, the diversity of the types of material that can be used is limited by the lack of a general method for preparing the basic DNA-functionalized building blocks needed to bond nanoparticles of different chemical compositions into lattices in a controllable manner. Thus far, most superlattices assembled from DNA-directed assembly methods are based on gold nanoparticles densely functionalized with alkylthiol-modified DNA strands. Unfortunately, the vast majority of nanoparticles synthesized in organic media have strongly bound ligand shells, and simple ligand exchange chemistry does not allow one to create the corresponding PAEs with the density of DNA required for programmable assembly. Here we show that by coating nanoparticles protected with aliphatic ligands with an azide-bearing amphiphilic polymer, followed by the coupling of DNA to the polymer using copper-free azide-alkyne click chemistry, nanoparticles bearing a high-density shell of nucleic acids can be created regardless of nanoparticle composition. This method provides a route to a virtually endless class of programmable atom equivalents for DNA-based colloidal crystallization.

Tobacco Mosaic Virus (TMV) is a RNA virus which in its native form is made up of a protein capsid that self-assembles around a single stranded RNA (ssRNA) genome.TMV coat protein (TMV-CP) can self-assemble into multiple forms including TMV rods without the aid of the genome. The type of structure formed is dependent on pH and ionic strength. However, at neutral pH where the TMV normally self-assembles into disks, only the native genome, containing the “origin of assembly” RNA sequence can nucleate TMV rod formation. Since RNA nucleated TMV assembly is highly stable and is formed from a single coat protein, it provides the opportunity for periodic, accurate and tuneable binding sites in three dimensions on the nanometer (nm) scale, which is very helpful for the construction of materials with novel optical and electronic properties.
Prior work suggests that Poly A RNA is able to nucleate TMV-like rods in a similar fashion to the native RNA genome. While the mechanism of nucleation is different, the rods have the same characteristics as those formed from native TMV genome. Poly A has several advantages over the native genome including that it can be produced for a fraction of the cost and the resulting rods are free of any potentially infectious material which is an important consideration in the development of TMV based bionanotechnology. Here, we demonstrate under which conditions TMV rods will form at neutral pH in the presence of Poly A, using not only UV difference spectroscopy and Circular Dichroism to detect changes in TMV and poly A helicity, but also Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) to visualize the TMV rods.

Nanotexturing polymeric surfaces changes their surface properties while their bulk properties remain unchanged. Recent work has shown that wrinkles and folds can increase the efficiency and mechanical stability of optical and electrical devices. This presentation shows a parallel method to create nanometer-scale textures over large areas with unprecedented control over wrinkle wavelength. We found that through reactive ion etching (RIE) we can create polymeric nanowrinkles on the surface of thermoplastic polystyrene (PS) substrates. This RIE treatment of PS is a new material system (skin and substrate) that can be used to vary the wrinkle wavelength in the nanometer regime. This wavelength could be continuously tuned from several microns down to as small as 30 nm simply by decreasing the exposure time in the RIE. We found that ellipsometry can measure the thickness of the modified layer. The thickness of the skin layer was used to (i) determine the Young&’s moduli of the skin and substrate and (ii) to control wrinkle wavelength. Using RIE and ellipsometry, we were able to control the average wrinkle wavelength within ± 5 nm. We anticipate that our work will facilitate understanding of the mechanism underlying optical and electrical device enhancement and improve their performance.

Programmed self-assembly using nucleic acids is a powerful method for producing nanostructures with precisely defined shapes and sizes. Recently, a new strategy has emerged for constructing such structures using short DNA oligonucleotides or tiles. This single-stranded tile (SST) approach utilizes multiple nucleic acid strands each containing four binding sites that are complementary to the four nearest neighbors of the tile in the specified structure. This simple yet versatile construction motif has been successfully applied to fabricating complex one-, two-, and three-dimensional DNA architectures. SST nanostructures however have so far been limited to DNA, leaving RNA with its distinct structural, chemical, and biological properties completely unexplored as an SST building material. Here, we describe how the SST paradigm can be successfully applied to the assembly of complex RNA-based molecular architectures. These RNA SST structures are constructed from enzymatically synthesized RNA tiles that are subsequently pooled and assembled through thermal annealing in a one-pot process. We have used this approach to construct one-dimensional RNA nanoribbons and nanotubes with prescribed widths and diameters, respectively. Furthermore, we have assembled complex two-dimensional lattices with well-defined dimensions and shapes composed of up to 95 unique RNA tiles. These RNA nanostructures offer distinct biochemical properties compared to their DNA counterparts. Notably, we have found that RNA SST assemblies can be successfully processed by recombinant human dicer enzyme into siRNAs and offer the potential to encode dozens of siRNAs within a single nanostructured delivery vehicle.

Photonic crystals, which have a periodic spatial modulation of refractive indices, exhibit photonic bandgap. The photons in the energy gap are forbidden in the crystals due to low photon density of states. Using this exceptional property of photonic bandgap, a variety of novel photonic applications including waveguides, lasers, displays, microsensors, and encoders have been demonstrated. Colloidal self-assembly has emerged as one of the most facile approaches to prepare 3D periodic nanostructures. Through convective assembly of colloids, colloidal crystals with face-centered cubic (fcc) lattice, or opal structures, are produced in a controlled manner. Furthermore, inverse opals which are composed of air cavities in fcc lattice can be prepared, which provide higher contrast of refractive index and enhanced mechanical stability. More importantly, inverse opals can possess full bandgap for high enough contrast of refractive index, which is otherwise impossible to achieve with opal structure. However, conventional methods for preparation of inverse opals require multiple steps of material deposition and removal: materials which form frame of inverse opal should be deposited in the interstices between particles in preformed opal film and then the particles need to be selectively removed by etching process. In each step, delicate chemical and physical processes are required, thereby severely limiting practical use of inverse opals. Therefore, facile fabrication scheme for inverse opal structures still remains an important challenge.
In this study, we report a simple route for fabrication of polymeric photonic crystals which have high structural similarity with inverse opals. Through convective assembly of silica@poly(methyl methacrylate) (PMMA) core-shell particles, colloidal crystals with fcc lattice are prepared, which are then thermally annealed to partially fuse PMMA shells. The continuous colloidal films made by the fusion are subjected to selective wet etching of silica core, thereby resulting in porous photonic films composed of arrays of air cavities. To accomplish this, highly monodisperse silica@PMMA core-shell particles are synthesized by two steps: monodisperse silica cores are obtained by sol-gel reaction (Stöber method) and the cores are used as seeds for growth of PMMA shell by emulsion polymerization. To promote the formation of covalent bond between silica and PMMA, silica particles are treated with 3-(Trimethoxysilyl) propyl methacrylate prior to polymerization step. The core-shell particles are convectively assembled on the surface of a silicon wafer, which form a film of colloidal crystals with a controlled thickness. The film is thermally treated slightly above glass transition temperature of PMMA, thereby resulting in partial coalescence between the PMMA shells and decrease of inter-core distance as the molten PMMA fills the interstices between the particles. The resultant silica-PMMA composite films are further subjected to treatment with hydrogen fluoride solution, which selectively etch out the silica cores from PMMA matrix, thereby making inverse opal-like porous photonic crystals. During thermal annealing step, the thickness of PMMA shell and annealing time determines the filling fraction of the interstices; this enables the control of optical properties in the porous photonic crystals. We could fabricate not only the silica-PMMA photonic composite but also polymeric inverse opal with using just only silica@PMMA core-shell particles without infiltration process. Our approach does not involve any complicate material deposition process and provides simple and facile means to create photonic crystals with high index contrast and mechanical stability. Therefore, this approach can be useful for a wide range of photonic applications.

Isotopic, hydrogen-to-deuterium substitution has been an invaluable tool for the characterization of small molecules and biological nanostructures. The natural variability in size and surface chemistry in inorganic nanostructures (i.e. nanocrystals and nanotubes) currently limit us from gaining meaningful differences using isotopic substitution. In this contribution we show for the first time that the helical wrapping of flavin mononucleotide (FMN) around single-walled carbon nanotubes (SWNTs) provides an ideal system to study surfactant-surfactant and surfactant-nanotube interactions using isotopic substitution. For this we employed the ideal helical wrapping of FMN around (8,6)-SWNTs, whose lateral stability is intimately coupled to the quadruple H-bonds responsible for forming the isoalloxazine ribbon. Depending on the surrounding solvent (i.e. H2O vs. D2O), the facile proton-to-deuterium exchange of the imide group enabled us to alter the intermolecular surfactant-surfactant interactions, while keeping the overall 8/1 FMN-dimer helix intact. The higher FMN helix stability in D2O against H2O was verified in terms of: (a) replacement with SDBS (sodium dodecylbenzenesulfate) surfactant; (b) thermal dissociation; and (c) pH-induced helix dissociation. This study demonstrates the architectural fidelity of FMN-wrapped SWNTs, which is expected to further enhance the assembly repertoire of carbon nanotubes since it bares strong resemblance to that of DNA and protein organizations.

During the past decade there has been a significant progress in the synthesis and characterization of nanocomposites, which can have unique properties due to the effect of the size of nanoparticles dispersed in a polymeric matrix. Within this context, conducting polymers (CP) are quite interesting materials in obtaining synergistic effects between a polymer matrix and nanoparticles in a myriad of applications due to their relatively high electrical conductivity, chemical stability and low cost. For example, CP have been extensively employed to improve selectivity of modified electrodes in electrochemical sensor technology and also act as an immobilizing matrix reducing interfering molecules. On the other hand, the use of gold nanoparticles (AuNPs) can increase the catalytic activity of sensors having modified electrodes, due to greater diffusion of electrons in the process. Here, nanocomposites formed from polyaniline (PAni) and gold nanoparticles (AuNPs) were obtained by the layer-by-layer (LbL) technique, being characterized by UV-vis spectroscopy at each adsorbed bilayer. Results showed a good adsorption in the multilayer nanostructure formed, enabling the identification of PAni characteristic bands at ~ 300 nm (π - π* transitions) and at approximately 800 nm, attributed to the formation of a polaronic band corresponding to the doped state of PAni (electron delocalization due to the conjugation formed in the polymeric backbone). It was possible to verify that the conductivity of polyaniline was not affected by the presence of AuNPs. It was possible to identify the oxidation peaks of PAni at 0.2 to 0.5 V from electrochemical measurements acquired for the PAni/AuNPs LbL films soaked in an HCl 0.1 mol.L-1 electrolyte solution, assigned respectively to the doped and undoped states of PAni by chloride ion. The sensor activity was evaluated by electrochemical measurements, being promising for application in environmental control for the detection of heavy metals, such as copper, lead and cadmium. These metals could be identified by standard potentials in approximately -0.04V for copper, -0.4V for lead and -0.7V for cadmium vs saturated calomel reference electrode (SCE).

The ability to form ordered nanostructures at the wafer level with low cost methodologies has represented a challenge in the last decade in many research fields spanning from nanoelectronics to photovoltaics. To fabricate ordered nanostructures many solutions have been proposed but they provide feature densities lower than 10⁹ cm^-2 or present high fabrication costs. Lithography based on block CoPolymers self-assembling (LCP) allows the formation of nanofeatures controlled down to 10 nm and density higher than 5×10¹⁰ cm^-2. We use this technique to form a thin porous layer of polystyrene with nm-sized pores ordered in hexagonal configuration. Post-lithography dry etch processes based on a modification of the Bosch process and optimised, also with the aid of specific simulations, for such extremely critical sizes and density of the pores allow for the formation of scalloped ordered nanoholes on the Si surface [Garozzo et al. ECS J. Solid State Sci. Technol. 1(3) Q52 (2012), Garozzo et al. Physica Status Solidi A 1-7 (2013) DOI 10.1002/pssa.201200949]. Optical characterization demonstrates that the scalloped nanopores present a reflectivity 30% less than flat Si. The nanoporous material is here proposed as photo-active material on the surface of Si solar cells prototypes. While in a conventional planar solar cell under direct sunlight, light is received from the solar disk, but is re-emitted isotropically, in the inverted nanocones the restricted emission angle allows for much thinner and efficient cells [Kosten et al., Light: Science & Applications (2013) 2, e45]. This paper intends to exploit this approach to investigate the efficacy of these ideas also for nanometer-sized structures.

In this work microfluidic devices were used to self-assembly phthalocyanine derivatives, poly(allylamine hydrochloride) (PAH), polypyrrole (PPy) and also poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) in different molecular architectures. The layer-by-layer (LbL) technique was employed as it is a simple, facile and efficient strategy to allow multilayers with distinct molecular structure and composition with meticulous control of thickness. Microfluidics was used due to the advantages offered in the integration of multiple functionalities in devices, despite the use of only microliters for sampling and discharge. Different LbL nanostructures were self-assembled inside polydimethylsiloxane (PDMS) microchannels mounted onto gold micro interdigitated electrodes (IDEs). The fabrication of the microchannels and IDEs used was made in collaboration with the Microfabrication Laboratory at the Centro Nacional de Pesquisa em Energia e Materiais (CNPEM). The film growth was in-situ monitored using impedance spectroscopy measurements, which was also evaluated by an equivalent electric circuit that indicated a distinct pattern and rougher interface formed for the phthalocyanines. The presence of the LbL films inside the microchannels was confirmed by Raman mapping analysis at distinct regions, which also indicated good uniformity of the nanostructures formed. The LbL films were also applied as sensing units in a microfluidic e-tongue system, comparing static and flow measurements of standard patterns of taste. Principal Component Analysis pointed out no loss of sensitivity of the sensor when compared with a traditional system.

We present a detailed study aimed at understanding the mechanism and dynamics of self-assembly of gold nanoparticles (AuNPs) using molecular linkers such as aminothiols. An experimental model is established that enables a fine control and prediction of both assembly rate and degree. Furthermore, we have found that under certain conditions, the increase in the molar ratio of linker/AuNPs beyond a certain threshold unexpectedly and dramatically slows down the assembly rate by charge reversal of the zeta potential. As a result, the assembly rate can be easily tuned to reach a maximum growth within seconds to several days. The decrease of the same ratio below a certain value leads to self-termination of the reaction at different phases of the assembly process, thus providing nanoparticles chains of different length. The results reported here pave a way towards deterministic self-assembly of inorganic nanostructures and offer a powerful tool to gain new mechanistic insights into the self-assembly and its intermediate stages. This work also introduces new handles that provide a remarkable control for the design of novel self-assembled architectures in a very cost- and time-effective manner.

The perfect control on the morphology and orientation of block copolymer (BCP) thin films deposited on pre-patterned surfaces is a mandatory step in view of their application in nanoelectronics[1]. In this work, we analyze the morphological/orientational evolution as a function of the annealing time of cylinder forming BCP thin films when confined inside periodic topographical structures with dimension ranging from 90 to 240 nm. High temperature thermal treatment in Rapid Thermal Processing (RTP) system allows systematic investigation of early stages of the self-assembly process. We unveiled the flipping of the cylinder orientation with respect to the substrate from parallel to perpendicular or viceversa depending on the surface treatment prior to block copolymer deposition. These order-to-order transitions point out the influence of the boundary conditions, including the lateral confinement and the matching of the trench size with the BCP periodicity, on the kinetic of the self- assembly process.
This research activity was partially funded by the ERANET PLUS “NanoSci-E+” consortium through the NANO-BLOCK project. Nanofacility is a Laboratory supported by “Compagnia di San Paolo” Foundation.
[1] K. Galatsis et al., “Patterning and Templating for Nanoelectronics”, Adv. Mat., Vol. 22, pp. 769-778, 2010.

The oxidation of the perfect Hminus;Si(111) surface and surfaces containing silicon dangling bonds surrounded by SiH groups were investigated for H2O and O2 oxidizing agents to identify elementary reaction steps and their corresponding energy barriers, in an effort to unveil the mechanism of oxidation of the first silicon bilayer of Hminus;Si(111) in air. Density functional theory was employed to calculate the energy profiles along the reaction coordinate (1).
The oxidation of the perfect Hminus;Si(111) towards H2O and O2 has high energy barriers which prevent the room temperature oxidation. However, the presence of silicon dangling bonds (surrounded by SiH groups) readily catalyzes the reaction with O2 yielding a silanone intermediate of the form (Si2O)SiO where one of the silicon back bonds is oxidized. In the next step, the oxygen atom of the silanone inserts into a Siminus;Si backbond. The surface silyl radical (SiO2)Si is thus regenerated and this moiety initiates a chain reaction by hydrogen atom abstraction from a neighboring SiH group yielding a new silyl group ready to be oxidized by O2.
This oxidation mechanism, which propagates by the hydrogen transfer from SiH towards oxidized silyl groups, explains two main experimental observations concerning the oxidation of Hminus;Si(111) in air at room temperature. First, the oxidation proceeds by the growth of two-dimensional oxide patches which only involves the outer silicon bilayer. Second, the absence of SiOH groups and the presence of (O3)Siminus;H groups.
Based on the details of the oxidation mechanism, a procedure may be devised for the controlled formation of 2D oxide patterns on Hminus;Si(111) in order to perform further functionalizations on selective regions of the surface. Both the surface density and the size of oxide patches can in principle be controlled. First, by exposing the Hminus;Si(111) surface to gas phase regenerated OH radicals, silyl radicals may be randomly produced with a surface density which is expected to depend on the exposure time and the concentration of OH radicals in the gas phase. Second, the growth of oxide patches can be initiated by subsequent exposure to O2. The patch size could also be controlled by the exposure time to O2.
In conclusion, we propose that the controlled oxidation of the Hminus;Si(111) surface may allow the development of surfaces suitable for selective functionalization in the most reactive oxide patches.
(1) Federico A. Soria, Eduardo M. Patrito, Patricia Paredes-Olivera. Oxidation of Hydrogenated Si(111) by a Radical Propagation Mechanism. J. Phys. Chem. C 2012, 116, 24607-24615

The use of ferroelectric templates, i.e., lithium niobate (LN) for the photoreduction of metallic nanostructures has received attention for potential applications in nanoelectronics through conducting nanowires, biosensing via the adsorption of molecules, and cell sensing. These nanostructures can also be harvested via sonication as nanoparticles, which can be used for other applications, i.e., antibacterial coatings. By patterning the ferroelectric template via electric field poling, one can control the location of photoreduced nanoparticle nucleation. We have shown that compared to conventional electric field poling, i.e., periodically poled LN (PPLN), a chemical patterning technique, i.e., a proton exchange process, enables more control over these photoreduced nanostructures. Here, we investigate the effect of AgNO3 concentration and illumination time on the nanostructures that form on chemically patterned ferroelectric templates. In addition, the effect of the depth of the proton exchange process, which is controlled by the exposure time to the proton source, benzoic acid, is determined. We find that the height of the nanostructures can be controlled by concentration (4.3 to 9.4 nm for a given duty cycle) and that the width can be controlled by the proton exchange depth (widths of 0.5 to 4.6 µm for a range of proton exchange depths of 0.6 to 3.1 µm). We can also control the location of deposition on PPLN surfaces whereby we can either create regions of deposition on +z domains for unannealed surface compared to nanowire deposition on the domain wall for annealed surfaces. We demonstrate that the resulting nanostructures can be functionalized with Raman and fluorescent probe molecules. We also discuss the potential application of such substrates for combined nanoelectronics and cell sensing.

We present self-assembled, tunable structures made from gold/nickel segmented nanorods. The nanorods were synthesized through electrodeposition into a porous alumina template, and were assembled under a strong magnetic field. Due to the scale of the nanorod dimensions and the coupling of nickel and gold segments, the nanorods exhibit a unique spectral response which is not seen in nickel only or gold only nanorods. Further, the nickel segments allowed for a large degree of control of the tilt angle on the nanorods via an external magnetic field. By controlling the tilt angle of the nanorods, it was found that the spectral response of the assembly could be drastically altered and tuned to a desired spectral signature.

A simple and widely applicable approach to assemble long-range two dimensional mobile arrays of functionalized nickel nanorods with tunable, highly open, and mobile lattice structures is presented. Under the influence of an external magnetic field, nickel nanorods were found to fall out of suspension and assemble into open lattice structures. The nanorod assemblies retained a high degree of mobility on the surface, allowing for the positioning of rods using magnetic field gradients. We were able to control the lattice structure by varying the nanorod length and the angle of the external magnetic field relative to the sample. Finally, a layer-by-layer approach was implemented to tether the nanorods to a substrate in a way that maintained the ordering of the assemblies, whilst still allowing for their rotational reorientation. The tethered rods can then be manipulated via a magnetic field in order to actuate the rods in the structure. These strategies allow for the tunable alteration of the optical/plasmonic properties of the nanorods.

Inverse opal,which works as a photonic crystal,shows various optical properties including wavelength-selective light transmission,control of refractive indices and so on. Binary colloidal particle assembly is one of the ways to create inverse opals. In the binary colloidal systems,larger colloidal particles are usually surrounded by smaller colloidal particles. If the particles composed of polymers and Tg of smaller particles is lower than that of larger particles,smaller particles spontaneously melt and fill the gaps among larger particles by heating over Tg. Subsequently inverse opal structure is prepared by removal of larger particles.
1,2-poly(butadiene) (PB) is one of the synthetic rubbers,and has some unique properties; low Tg than room temperature and containing cross-linkable double bonds in their side chains.
We have reported that a simple preparation method of polymer particles by evaporating a good solvent from a polymer solution containing a poor solvent (SORP method).
In this research,PB particles were prepared by using the SORP method. We found that SiO2 particles and PB composites were spontaneously formed by casting the mixture of PB particles and SiO2 particles onto solid substrates. PB inverse opals were also obtained by removal of SiO2 particles by treating with HF.
PB was dissolved in THF,and water was added to the solution with stirring. THF was evaporated,and PB particles were prepared. The average diameter of PB particles was determined as 667nm by DLS. To prepare composite films,the mixture of PB particles and SiO2 particles was cast onto a PET substrate and dried. The SEM images of the composite films showed that SiO2 colloidal particles were arranged hexagonally and the gaps among the SiO2 particles were filled with fused PB. After cross-linking of PB moieties with OsO4,the samples were treated HF. The SEM images of the films after HF treatment showed hexagonally-arranged porous structures. These results indicate that the PB particles are confined among the SiO2 particles during binary colloidal self-assembly. Since the Tg of PB is lower than room temperature,PB particles melt and fill the gaps of SiO2 particles during water drying up,and SiO2 particles and PB composites were formed spontaneously at room temperature. The composite films were also cross-linked by irradiation of UV through a photomask. After immersion of the cross-linked films in chloroform,the patterned PB porous films were also obtained with HF treatment. The SEM images of the patterned PB porous films showed that the mask pattern was successfully transferred to PB porous films. At the cross-linked area,the porous structure was observed.
We showed the simple preparation method of PB inverse opals from spontaneously formed SiO2 and PB composites. This method can be used for preparation of photonic crystals,wave guides and so on.

The concept of using single molecules as key building blocks for logic gates, diodes, transistors and switches to perform the basis function of digital electronic devices was well established over the past decades.To achieve this, it is crucial to control the electronic, magnetic or optical properties of individual functional molecules on surfaces. Molecular switches, which can be interconverted between bistable or even multiple states by external stimuli like electric field, light , electrons and temperature,have attracted much attention. Single molecular switches can be operated by a variety of ways, for instance, conformational changes, examples are cis-trans isomerization of the azobenzene molecules, mechanically interlocked switches formed by catenanes and rotaxanes, flip flop of dipole molecules, atom tunneling through molecule plane and hydrogen tautomerization reaction in naphthalocyanine; other ways like controlling the charge states of single atoms or molecules, switching the chirality of the adsorbate on surfaces, manipulating the spin state of spin crossover (SCO) complexes, modifying the bond formation, controlling the orbital sequence of a negatively charged copper(II)phthalocyanine molecule have also been realized.
However, most of the studies of these molecular switches were performed either individually or in self-assembled single-component monolayer. The incorporation of these molecular switches into more complex and rationally designed nanoarchitectures are needed for practical applications. To achieve this, single molecular switches should be interconnected with other molecules via intermolecular interactions to form desired long-range ordered nanostructures over macroscopic area; at the same time, the molecular functionality responsible for molecular switching must remain intact during the self-assembly process. Self-assembly of binary molecular systems on inert graphite surface via the formation of multiple intermolecular hydrogen bonding represents a versatile approach to fabricating ordered and robust molecular nanostructure arrays.By varying the binary molecular ratio, the inter-dipole distance of the molecular dipole dot arrays and hence the dipole densities can be easily tuned with atomic precision. Moreover, the formation of the multiple intermolecular hydrogen bonding can further enhance the structure stability of these molecular nanostructure arrays during the device operation.

Bulk heterojunction (BHJ) polymer solar cells are an area of intense interest due to their flexibility, and relatively low cost. The mixture of polythiophene derivatives (donor) and fullerenes (acceptor) is spin coated on substrate as the active layer, and are phase-separated into interconnected domains. However, due to the disordered inner structures in the active layer, donor or acceptor domains isolated from electrodes and long path conduction, the power conversion efficiency (PCE) of BHJ solar cell is low. Therefore, morphology optimization is among the most important techniques to improve the efficiency of BHJ solar cell. Here we report a self-assembled columnar structure formed by phase separation between poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and poly(3-hexylthiophene) (P3HT). The BHJ solar cell device based on this structure is promising for exhibiting higher PCE due to the shorter carrier transportation pathway and larger interfacial area between donor and acceptor. The surface morphology is observed under atomic force microscopy (AFM) and the columnar structure is confirmed by investigation of cross-section of the blend thin film of MEH-PPV and P3HT under the transmission electron microscopy (TEM). The effects of different parameters, including solvents and annealing time, on morphology are discussed. The different morphological structures formed via phase segregation are correlated with the performance of the BHJ solar cells fabricated at the Brookhaven National Laboratory.

Block copolymer assembly in solutions provides a large variety of structures which partially exhibit a complex hierarchical organization. Next to the commonly known nanostructures, i.e., spherical and rod-like micelles and vesicles more complex structures can be obtained when changing from diblock to triblock copolymer systems. Here the degree of organization can be increased by the utilization of compatibility and immiscibility properties of the individual blocks. Therefore, one convenient tool for the manipulation of the obtained nanostructures is the design of tailor-made well-defined block copolymer assemblies via controlled living polymerization reactions.[1-3]
We will provide a detailed morphological and systematical study of different block copolymer systems to elucidate generic guidelines for the self-assembly of organized structures in solution. In particular block copolymers containing a fluorine containing block are in focus of our studies as here a large diversity of highly organized and well-defined structures can be obtained by these systems, ranging from 2-dimensionally rolled-up cylindrical structures resembling the form of a spiral up to the formation of bicontinous structures[4] with a different degree of organization in their interior.
The shape control of the molecular building blocks and an understanding of the influence of the individual blocks is essential to tune the morphological features of self-organized nanoparticle systems to optimize their structure for a large variety of applications, i.e. in catalysis, drug delivery, etc..
[1] C. Pietsch, et al., Macromolecules 2012, 45, 9292-9302.
[2] C. Weber et al., J. Polym. Sci. Part A: Polymer Chemistry 2013, 51, 139-148.
[3] K. Kempe et al., Chem. Commun. 2010, 46, 6455-6457.
[4] U. Mansfeld, et al. Soft Matter 2013, 9, 3509-3520.

Recently developed synthetic strategy of organic semiconductors, frequently termed as "building blocks approach", facilitates the preparation of molecules with optoelectronic properties precisely tuned to a given application. This can be done by combining appropriately designed electron accepting and electron donating segments in one molecule (macromolecule). However, the usefulness of such compounds in real applications is a complex issue, governed not only by the properties of an individual molecule but also by supramolecular interactions between the molecules, resulting in their self-assembly in 2D or 3D. The knowledge concerning these interactions and resulting molecular self-organization is therefore essential for the determination of the optimal electrical transport conditions inside active layers in organic electronic or optoelectronic devices.
In our presentation we will discuss the effect of the electron-accepting unit and the alkyl substituents position on the type and extent of supramolecular organization in monolayers and thin layers of new penta-ring donor-acceptor-donor (DAD) semiconductors. The studied adsorbates are alkyl derivatives of 2,5-bis(2,2&’- bithiophene-5-yl)-1,3,4-thiadiazole - promising compounds for the fabrication of light emitting diodes and photodiodes. They consist of an electron withdrawing thiadiazole central ring to which two bithiophene groups are symmetrically attached. Monomolecular layers of these derivatives deposited on HOPG were imaged by scanning tunnelling microscopy. The observations performed at molecular resolution indicate a strong effect of the thiadiazol groups on 2D supramolecular organization of studied adsorbates. The dominant interactions between the central electron withdrawing groups of neighbouring molecules lead to an unexpectedly large intermolecular separation for all investigated alkyl derivatives. The measured separation is larger than that deduced from the geometrical size of the adsorbate. As a consequence, ordered monomolecular layers are characterized by stacking of low density with nano-cavities formed between the conjugated backbones of every second neighbouring molecules. Moreover, the observed effect of the alkyl substituent position on the monolayer organization (changing from rectangular to hexagonal pattern) is analysed in the light of different alkyl chains interdigitation patterns.
In the second part, a comparative study of 3D supramolecular organization in thin layers, deduced from the X-ray diffraction patterns, will also be presented. This comparison clearly confirms the polymorphism of the studied adsorbates, yielding different and much denser stacking in the 3D crystals as compared to the monomolecular layers.

One-dimensional assembly of nanoparticle has been made by various approaches, where one should go through relatively complicated processes, at the same time carefully excluding unavoidable impurity. Here, we report the formation of one-dimensional assembly of silica nanoparticles by simply changing the solvent concentration and temperature.
Silica nanoparticles of 20 nm in size were synthesized by hydrolysis and by condensation of tetraethoxysilane with L-lysine. Ethanol was added to the 0.4 wt% mono-dispersed silica-nanoparticle suspension at different temperatures of 2°C, 25°C, and 60°C. The microstructures of the silica suspensions were observed by transmission electron microscopy (TEM). It was found that the synthesized silica nanoparticles were one-dimensionally arranged after 7 days, presenting chain-like entangled structures when the ethanol concentration became over 70 wt% at lower temperatures of 2°C and 25°C. In contrast, no chain-like structures but dispersed silica nanoparticles were observed at 60°C. In more detail, at 2°C, 2-10 silica nanoparticles were linearly connected each other to construct chain-like structures in 7 days, which became even longer chains in 28 days consisting of 20-40 nanoparticles. As for the 25°C specimen, 2-10 silica nanoparticles were connected as was observed in the 2°C specimen, but the length of the chains would not grow by time. The one-dimensional structure of 2-10 silica nanoparticles at 25°C retained its structure for more than 3 months. Intriguingly, the length of the one-dimensional silica-nanoparticle chains observed at 2°C and 25°C became even longer by adding more alcohol, eventually constructing 3D nanoparticle-chain networks at the ethanol concentration of 75 wt%. Such 3D-nanoparticle networks could be established within a day, which would not be decomposed into the original one-dimensional chains once the 3D networks were formed. Zeta potential was measured and it was found that the Zeta potential was about -60 mV for pure silica nanoparticle suspension, which became nearly -40 mV by adding ethanol up to 70 wt. The addition of the alcohol led to the compression of the electrical double layer around each nanoparticle, causing decrease in the repulsive force between the nanoparticles, eventually leading to the nanoparticle self-organization.

We present a model for the effect of stress on thin amorphous films that develop atop ion-irradiated silicon,
based on the mechanism of ion-induced anisotropic plastic flow. Using only parameters directly measured or
known to high accuracy, the model exhibits remarkably good agreement with the wavelengths of experimentally
observed patterns and agrees qualitatively with limited data on ripple propagation speed. The predictions of the
model are discussed in the context of other mechanisms recently theorized to explain the wavelengths, including
extensive comparison with two other mechanisms based on effective forces.

Nanoclusters of inorganic particles are expected to exhibit various optical, magnetic, and electrical properties that emerge from the periodicity and interaction of nanoparticles. We have synthesized cubic CeO₂ nanoassemblies comprising octahedral primary nanocrystals that shared the same crystallographic orientation [1,2]. In this presentation, we report the structural evolution of CeO₂ nanoassemblies during their hydrothermal synthesis.
Cerium oxide nanoassemblies were synthesized using a lab-scale plug-flow reactor. An aqueous solution of Ce(NO₃)₃ and glutamic acid was used as a reactant. The stream of the reactant was mixed with a pre-heated stream of water and instantaneously heated to 250~300 °C. After passing an isothermal zone, the mixed stream was cooled by a jacket cooler. The residential time, that is, the reaction time, was varied in the range of 0.7 ~ 8.0 s. The reaction pressure was 25 MPa. Secondary electron microscopy images of the products indicated that the products were spherical assemblies at the reaction time of 0.7 s. On the other hand, longer reaction time led to the formation of cubic products with ordered primary nanocrystals. These results suggested the two-step formation mechanism of ordered nanoassemblies. Firstly, the synthesized primary nanocrystals loosely agglomerate to form spherical products. Then, the nanocrystals ordered in the agglomerate and formed the ordered nanoassembly.
[1] S. Takami, et al., Dalton Trans., 5442 (2008).
[2] S. Asahina, et al., ChemCatChem, 3, 1038 (2011).

The hierarchical assembly of inorganic nanoparticles in microphase-separated block copolymer (BCP) matrices has been intensively studied to create novel functional hybrid materials, such as high-performance catalysts, photonic crystals, chemical sensors, and electronic devices. However, the precise control over the arrangement of particles in polymer matrices is still challenging but critical to the properties of the resulting hybrid materials. Chemical modification of nanoparticle surface properties has proven to be an effective approach to sequestering nanoparticles in certain domains of block copolymer templates by introducing favorable interactions between the surface ligands and specific blocks. In this work, we demonstrate the in-situ synthesis of micelle-like gold nanoparticles capped with UV-sensitive block copolymers poly(styrene)-b-poly(o-nitrobenzene acrylate) (PS-b-PNBA), which were synthesized by using RAFT method. The core size of the obtained nanoparticles can be well controlled around 2.5 nm with a narrow distribution during nanoparticle sysnthesis. The assembly of these gold nanoparticles has been achieved by using a lamellae-forming poly(styrene)-b-poly(2-vinyl pyridine) (PS-b-P2VP) block copolymer as the template. Although these nanoparticles present PS as the outer layer of the corona, they partition along the interface of PS and P2VP domains, probably due to a high affinity between PNBA and P2VP blocks. Moreover, PNBA blocks in PS-b-PNBA ligands can be deprotected into a highly hydrophilic block containing poly(acrylate acid) (PAA) by simple exposure to a UV-light of 365 nm. After UV exposure, most of the gold nanoparticles are released from the interface of PS/P2VP into the P2VP domain due to a strong hydrogen-bonding between PAA and P2VP.

It was reported previously that biocompatible peptide amphiphile (PA) solution could construct 3D-networks to present gelation at relatively low PA concentrations. The salt concentration around PA should be one of the key parameters dominating the gelation behavior of the PA solution, but there have been few researches that directly analyzed the effects of salt concentrations on the gelation behavior of PA solution. In this work, the gelation behavior, especially the gelation speeds for our designed peptide amphiphile C16-W3K (80 mu;M) in aqueous solutions were analyzed by changing NaCl concentrations from 0 mM to 5 mM. C16-W3K consisted of 17 amino-acid chains that were composed of thirteen alanines (A), one tryptophan (W) (for the fluorescence measurements to detect PA concentration), and three spatially separated lysines (K) (to increase solubility in water), which was then attached to a 16-carbon alkyl tail. The C16-W3K solution was known to present hierarchical structural transitions from spherical micelles with α-helix molecular conformations in the sol state to worm-like micelle with β-sheet conformations in the gel state. The structural transitions could be induced by external stimuli such as heat, shear, and processing time. The viscosity and the dynamical mechanical analysis (DMA) measurements were performed to investigate the gelation speed of C16-W3K solutions. The cyclic viscosity testing was repeated using the same PA solution until the viscosity reached at its stable solid-like state. It was found that the number of the testing cycles required to reach the equilibrium state decreased by increasing the NaCl concentrations. For example, the number of the required testing cycles for the PA solution without NaCl (0 mM) was twenty six, whereas that of the PA solution with 5 mM of NaCl was only seven. In addition, it was confirmed by the DMA measurements that, before the mechanical testing, all specimens were in the sol state, whereas the specimens experienced gelation after the testing. It was also found that the gelation speed became higher as the NaCl concentration became higher. The self-assembly structures of PA, which caused the gelation, were observed by transmission electron microscopy (TEM). C16-W3K formed spherical micelles with ~10 nm in diameter before the viscosity testing, which transformed into worm-like micelles after the mechanical testing.

The ability of the usage of the ideas of the complex system (self-organization) theory concerning the processes of growth of different micro - and nanoscale materials was shown earlier. The basis for this is the characteristic features of the growth dynamics: bifurcation character of the changes, the break symmetry, non-equilibrium, the existence of the dissipation processes. All these are essential ingredients of the self-organization. It exists in all spatial scales: from macro to nano levels. Taking all these into account we have solved some important problems of the micro- and nanoscale formation research.
1. We have developed the direct means of the analysis of the growth process based on non-linear dynamics:
- by any characteristics of the substance in situ, according to the ideology of embedding method. For this purpose we can use the methods of scattering of the light, ellipsomethry and some others
- by the structure of the material, which stores the information about its previous time evolution. We have adopted well-known means of the processing of the time sequences for the analysis of the two-dimensional surfaces. Besides, we were able to find the connection between the structure and the parameters of the dynamics of its formation.
2. We have given the explanation of the phenomena of non-reproductivity of the growing structure. It has a very important meaning for the most technologies of the materials on all levels of the structure and first of all on the nano-level. We have shown why the reasons of non-reproductivity are connected with the peculiarities of the dynamics of growth.
Thus we have come to the conclusion that instability of the growth process which is characteristic to chaotic dynamics with aggregation with inaccuracy of the maintenance of the parameters of the technology and unavoidable fluctuations is the cause non-reproductivite of the structure.
We have developed the criteria of non-reproductivity. They are invariant for different technologies. We have shown that there is the limit of reproductivity. Beyond this limit the growth of the accuracy of the technological parameters becomes senseless.
We have developed the analytical connection between the sizes of the system (the number of atoms which make the independent micro- or nanostructure) and the degree of reproductivity.
3. We have suggested the effective methods of the growth control which are based on the correspondence of the technological parameters in the inner dynamic process. Methods for the resonance of inner frequencies of substances with the external influences are developed.
It is justified that the irreproducibility problem can be treated by techniques developed for controlling chaos.

While the plasmonic properties of single, isolated nanoparticles have been extensively studied, the fabrication and understanding of hierarchical mesoscale structures with unique plasmonic properties is still in early development. We are specifically interested in mesoscale structures consisting of mask-aligned nanoparticle formations. The structures are specifically tailored to form a plasmonic enhancement which is caused by the plasmonic resonance overlapping of the metastructure and the particle aggregation. To adjust the plasmonic enhancement, the gold gratings were systematically modified by varying the block length and periodicity. Further tuning and enhancement of the plasmonic resonance were done by including a metallic and dielectric sandwich layer. Experimental Rayleigh scattering spectra were obtained using hyperspectral imaging, and the spectra were validated by numerical simulations based on the finite-difference time-domain method.

The mechanism by which small molecules assemble into microscale tubular structures in aqueous solution remains poorly understood, particularly when the initial building blocks are non-amphiphilic molecules and no surfactant is used. It is here shown how a subnanometric molecule, namely p- aminothiophenol (p-ATP), prepared in normal water with a small amount of ethanol, spontaneously assembles into a new class of nanovesicle. Due to Brownian motion, these nanostructures rapidly grow into micrometric vesicles and start budding to yield macroscale tubular branches with a remarkable growth rate of sim; 20 mu;m s-1. A real-time visualization by optical microscopy reveals that tubular growth proceeds by vesicle walk and fusion on the apex (growth cone) and sides of the branches and ultimately leads to the generation of centimeter-long microtubes. This unprecedented growth mechanism is triggered by a pH-activated proton switch and maintained by hydrogen bonding. The vesicle fusion-mediated synthesis suggests that functional microtubes with biological properties can be effi ciently prepared with a mixture of appropriate diaminophenyl blocks and the desired macromolecule. The reversibility, timescale, and very high yield (90%) of this synthetic approach make it a valuable model for the investigation of hierarchical and structural transition between organized assemblies with different size scales and morphologies.

Colloids and polymers are often used in industrial applications to obtain desired properties in formulations such as paints and cosmetics. Clay-polymer interactions have significant effects on both the structure and changes in material properties. We focus on a model colloidal dispersion of Laponite, a synthetic clay mineral and probe the effects of adding a thermoresponsive triblock copolymer, Pluronic F127, on the dispersion properties. Our results using variable temperature rheology demonstrates a temperature induced increase in the storage modulus, G&’, resulting in a bulk liquid to gel transition. Synchrotron SAXS measurements exhibit a change in the peak position of the structure factor (S(q)) and corresponding particle assembly resulting in a decrease in characteristic spacing of particles at high temperature. The results show that the presence of the surfactant leads to on-demand temperature responsive gelation in these triblock copolymer /Laponite dispersions and demonstrates a direct link between nanoscale reorganization and bulk gel formation.

Automated Electron Diffraction Tomography (EDT) is a fast and efficient technique, recently developed in our group, which can perform fast three-dimensional (3D) reciprocal space fine scanning. Although the method has been used to determine crystal structures at the atomic scale, in this work we utilize it to study nanoparticle packing arrangements at the mesoscale providing an alternative to X-ray based methods or real space imaging.
The mesoscale structure of self-assembled spherical palladium nanoparticles arrays was evaluated from the 3D EDT data collected in the small angle selected area electron diffraction mode. The maximum angular coverage defined by the single tilt goniometer was ±70°. The structure of the investigated arrays was found to be an fcc-like structure with a= 15 nm lattice parameter. Reconstructed reciprocal 3D space of the arrays exhibited intricate diffuse scattering which revealed stacking faults and even a superstructure. Stacking faults oriented along [111]-zone axis reflected random stacking faults of fcc and hcp packing. Satellite spots found around (-hk0) reflection series indicated a superstructure. A 3D model of the arrays, including its defects, was built combining the 3D EDT data set and real space images of the most representative projections of the arrays.
EDT is a powerful technique that offers a facile and systematic way to investigate the packing arrangement and quantify defects within a nanoparticle array. Moreover, EDT is carried out with a low electron dose (approx. 1000 electrons/square Å or less) which is essential to minimize the electron-induced structural changes within a material especially for beam sensitive materials.

The Au induced reconstruction of Ge(001) is studied by STM/STS and LEEM. The obtained STM iamges depend extremely strongly on the sharpness of the STM tip. The surface corrugation amounts up to 0.6 nm. A structural model explaining this observation will be presented. The gold induces nanofaceting of the surface, resulting in gold-covered (111)-facets, forming 6 layers deep grooves. High resolution STM images reveal clear similarities with gold induced (radic;3 x radic;3)R30 reconstucted Ge(111). A low surface free energy of the gold covered (111)-nanofacets is believed to provide the driving force for the gold induced nanofaceting of Ge(001). STM/STS measurements demonstrate that the top ridges terminating the (111)-facets consist of buckled Ge dimer rows.

1D, 2D, and 3D superstructures were selectively produced on a substrate through self-assembly of tetragonal Mn₃O₄ cuboids with sizes of tens of nanometers by evaporation of a medium from the dispersion. Rectangular nanoblocks of Mn₃O₄ which were slightly elongated in the c direction and covered with four {100} and two (001) faces were synthesized by a two-phase solvothermal method containing oleic acid and tert-butylamine. The formation of micrometer-sized superstructures from the nanocuboids surrounded with oleic acid was tuned by changing the particle concentration and the medium of the dispersion.
1D chains of the nanocuboids aligned in the a direction were formed on a silicon substrate from a mixture of hexane and toluene at a low particle concentration through rapid evaporation at 250°C. 2D arrays exposing the a face were obtained through parallel arrangement of the chains with increasing the particle concentration and lowering the evaporation rate. Another type of 2D arrays exposing the c face and 3D superlattices of the nanocuboids were produced on the substrate through rapid evaporation by using pure toluene and ethanol as a dispersion medium, respectively.
The anisotropic nanocuboids covered with oleic acid are basically aligned in the a direction and form the 1D chains on the substrate through advection with evaporation of the dispersion medium. The 2D arrays exposing the a face are produced by parallel assembly of the 1D chains with increasing the particle concentration. The nanocuboids would form small 2D clusters in the dispersion with an increase in the polar character of the medium. In consequence, the 2D arrays exposing the c face are obtained on the substrate through assembly of the clusters with evaporation of the medium. The 3D superlattices are prepared through accumulation of the 2D arrays in the polar medium. The dimension- and orientation-controlled self-assembly of the nanoscale units is regarded as a novel fabrication technique of a wide variety of functional nanomaterials.

We report growth of various self-assembled thin film structures, e.g. BaTiO3-NiCo2O4 (BTO-NCO) and NaNbO3-Nb2O5 (NNO-NO) self-assembled thin films by pulsed laser deposition. BTO-NCO can form ultra-small feature size down to 3 nm whereas the nanostructures in NNO-NO are in the scale of 100 nm. Crystal structure was analyzed by both X-ray diffraction and transmission electron microscopy, where well-crystallized and separated phases were well recognized. Dielectric, piezoelectric properties and magnetic properties corresponding to the functional phases were studied by piezoelectric force microscopy and vibrating sample magnetometer and the coupling effects were discussed.

Synthesis of nanopatterned magnetic materials offers advanced capabilities in tailoring material structures and opens up new opportunities for engineering innovative devices (i.e. electronic and biomedical). In the frame of magnetic materials, the most demanding application consists in fabricating high-density arrays for use in data storage and magnetic sensors for spintronics [1]. In the last decade, many routes for the reliable fabrication of magnetic nanostructures have been extensively investigated, including top-down lithography and bottom-up self-assembly processes. Conventional electron beam lithography (EBL) soon turned out to be limited by low-speed and high costs while self-assembling emerged as a viable and handy alternative technique for designing nanostructures over a wide area on magnetic thin films. The capability of soft materials such as block copolymers (BC) to form a rich variety of low-dimensional, uniform periodic patterns offers unique opportunities to develop large area nanometer scale features. The domain spacing typically depends on molecular weight, segment size, and the strength of interaction between the blocks. In this work, the application of BC to sputtered Ni₈₀Fe₂₀ thin films (having thickness ranging in the interval 10 - 40 nm) for large area nanopattering is reported. A Random Copolymer (RCP) brush layer was deposited on the magnetic film in order to obtain the surface neutralization. A PS-b-PMMA Block Copolymer (BCP) film was subsequently deposited on the RCP, obtaining lamellar or cylindrical features perpendicularly oriented with respect to the substrate. The self-organization is promoted by means of a thermal annealing higher than the glass transition temperature of the BCP [2]. An accurate study of the grafting conditions of the RCP and of the annealing conditions of these BCP nanostructures has been carried out. A careful evaluation of the effect of propagation of the nanometric pattern to the magnetic thin film has been performed with the aim to optimise nanostructures and preserve the magnetic properties of the continuous film. Sputter-etching and FeCl3 chemical solution have been employed. A systematic morphological study has been performed by Atomic Force (AFM) and Scanning Electron (SEM) microscopy. Room-temperature magnetic behavior has been studied by magnetisation measurements by ultra-sensitive magnetometry. Chemical etching resulted to be effective in propagating a fine antidot pattern on Ni₈₀Fe₂₀ thin films, while sputter etching totally remove all the polymer without any transferring of the nanoscale as indicated either by magnetic hysteresis loops and SEM investigation.
[1] C. A. Ross, Annu. Rev. Mater. Res. 31, 203 (2001).
[2]A Andreozzi et al.; Nanotechnology 22 (2011) 335303

While anodizing the Si in HF acid under specific conditions the porous silicon (PS) is formed. This material represents the self-organized network of pores which penetrate from the surface of Si into its volume. The length and diameter of the pores are controlled by the anodizing regimes and may be varied in the range from several nanometers to microns. The open porous structure of PS has motivated scientists to introduce different materials, especially metals, into the pores to fabricate ordered metallic nanostructures. The aims of nanostructuring are different, but the major idea is using PS as the template which defines sizes and shape of the depositing metals.
The present work observes our research which was devoted to the fabrication, properties and application of nanostructures formed by the deposition of different metals on/in PS.
Electroless deposition
Metals with positive redox potential (Cu, Ag, Au, Pt, Pd) may be deposited as nanoparticles (NPs) on/in PS by electroless technique from water solution of metal salt. Managing dimensions of metallic NPs is provided by the variation of immersion time and porosity of PS [1]. Final nanostructures are prospective for a number of applications. For instance, depending on the initial PS porosity, Cu NPs/PS materials demonstrate various adhesions to the Si substrate. This effect was used to develop the Layer Transfer technology approved for MEMS [2]. Moreover, it was revealed that Cu electroless deposition from HF-based solutions allowed conversion of PS into porous copper membrane as a result of complete PS dissolution [1]. The porous Cu membranes are actively studied to be exploited as flexible electrodes for biomedical electroporation [3].
Electrodeposition
Recently [4] Ni nanowires (NWs) were formed by electrochemical deposition of Ni into PS. The synthesized Ni NWs demonstrated ferromagnetic properties [5]. The anisotropy of the magnetic properties of Ni NWs in the matrix of PS was observed. This nanostructured array of magnetic NWs could be used in perpendicular magnetic recording with high packing density. Similar Co and Fe structures were grown in this way.
Sputtering
PS may be applied as a template to fabricate interconnected networks of ultra thin Nb nanoislands [6]. The formed Nb islands had extremely small dimensions, which were comparable to the superconducting coherence length. The samples exhibit nonzero resistance over a broad temperature range below the critical temperature, fingerprint of phase slippage processes.
References
1. H. Bandarenka et al. J. Nanoscience and Nanotechnology 12, 1 (2012).
2. M. Balucani et al. Proc. ESTC: September 13-16, 2010; Berlin. New York: IEEE 186 (2010).
3. M. Balucani et al. Proc. IEEE 61st ECTC: May 31-June 3, 2011; Lake Buena Vista. New York: IEEE 1319 (2011).
4. Dolgyi et al. J. Electrochem. Soc.159, D623 (2012).
5. Dolgyi et al. Thin Solid Films, available online 1.02.2013.
6. Cirillo et al. Appl. Phys. Lett. 101, 172601 (2012).

We present results for 2 - 10 nm metal clusters formed by an inert-gas condensation and deposited onto various substrates. The nanoclusters were filtered using a quadrupole mass spectrometer attached to the output of the nanoparticle source. X-ray Scattering measurements were performed during the deposition of the cluster to the substrates to study the correlations of the particles on the surface, and its evolution in real time. Results will be reported for nanoclusters deposited on flat surfaces as well as surfaces patterned by ion bombardment.

Nanoscale patterning of noble metal thin films, and in particular Ag and Au, has attracted considerable attention due to the exploitation of Localized Surface Plasmon Resonance (LSPR), an enabling optical phenomenon for a number of exciting applications including chemical and biomedical sensing, information and communication technologies, solar cells and lighting, cancer treatment, environmental remediation, optical encoding and many others. Amongst the methodologies followed for nanostructuring thin films, Laser Annealing (LA) has been proven to be a promising innovation in the field of plasmonics [1].
In this work Ag and Au thin films (5-10 nm in thickness), grown by RF Magnetron Sputtering were subjected to LA, using pulsed UV laser sources; thus causing the as grown layers to be transformed into clusters, forming NP&’s of various shapes and size distributions. These laser processed nanoparticle arrays can serve as a platform that will stimulate further progress towards the engineering of plasmonic devices. A systematic study over the applied laser wavelength, fluence and sample environment pressure is presented for a single pulse process. A key feature for a potential future large scale processing is simplicity and speed for high capacity and low fabrication costs; thus our motivation to study LA effects with only one single pulse.
We used two laser sources, ArF (193 nm) and KrF (248 nm), and varying fluences (up to 1 J/cm2). A pressure cell was used to study the effect of LA whilst the sample is pressurized with an inert gas (up to 10 bar) and comparisons with experiments conducted under ambient atmosphere were made. The derived nanostructures were evaluated in terms of their topography employing Atomic Force Microscopy and their plasmonic behavior employing Optical Reflectance Spectroscopy (ORS). In summary we report the influence of the laser annealing parameters on tailoring the structural and optical properties of the NPs that are derived by nanostructuring thin metal films of Ag and Au.
[1] A. Siozios, D.C. Koutsogeorgis, E. Lidorikis, G.P. Dimitrakopoulos, Th. Kehagias, H. Zoubos, Ph. Komninou, W.M. Cranton, C. Kosmidis, P. Patsalas, Optical encoding by plasmon-based patterning: hard and inorganic materials become photosensitive, Nano Letters 12 (2012) 259-263.
Acknowledgements: The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n° PIEF-GA-2012-330444.

Upon annealing below their melting point, thin metal films can degrade into particles in a process known as solid-state dewetting. This process has several stages, including void initiation, void growth and void coalescence. In this work a comprehensive study on dewetting of gold films on SiN_x substrates is reported and a dewetting zone model is proposed. The morphology as a function of annealing conditions can be divided into three zones. In zone A the film remains continuous, in zone B dewetting takes place, and in zone C dewetting is complete.
Zone A (void initiation): Pores are formed at the film-substrate interface by heterogeneous nucleation of vacancies. Once formed, the pores grow preferably along grainboundaries until they penetrate the film surface. The number of pores that have no access to grain boundaries (i.e., that have to grow by volume diffusion) increases with increasing film thickness. The activation energy of void initiation E_ai thus depends on film thickness.
Zone B (void growth): The voids (pores that penetrated the film surface) are growing in a branched manner. This can be explained by surface energy minimization of the grains at the void boundaries. Coverage measurements were used to determine the activation energy for void growth E_ag, which was 1.05 +/- 0.1 eV.
Zone C (particle formation): Upon long annealing, the particles formed by dewetting will attain an equilibrium shape. Using AFM and FIB tomography, the Au/SiN_x interfacial energy γ_fs was determined from the particle shape: 0.93 +/ 0.05 J/m².

We report on the synthesis of silver nanoparticles by reduction with glucose, and stabilization in water using poly(N-vinyl pyrrolidone) (PVP) as a capping agent. The reaction time was extended up to 120 hours under different light and air exposure conditions. Aliquots of the reaction mixture were taken at interval stages, and isolated by ultracentrifugation to remove by-products from the synthesis, i.e. nitrate, excess polymer, excess glucose and glucose oxidation products. The particles were subsequently analyzed by dynamic light scattering, SEM, TEM, UV-Vis Spectroscopy, and X-ray powder diffraction with Rietveld refinement (Le Bail method). We describe the relationship between the ultrastructural properties of the prepared quasi-spherical silver nanoparticles and their average particle size. The crystallite size as determined by Rietveld refinement, and the domain size distinguishable by TEM displayed a linear increase as a function of particle diameter. Additionally, there was evidence of a multisystem with the evolution of secondary morphologies, predominantly triangular nanoprisms, as the synthesis progressed. At early reaction stages, there was a rapid increase in particle size for both dominant morphologies, followed by a plateauing effect at reaction times greater than ~500 minutes. Rigorous particle counting, by percent morphology and morphology by average size were provided for three different reaction conditions: In air, refluxed in ambient light, and refluxed in dark. With these three experimental variables altered, no significant differences in average particle size, or percent morphology were seen.

Mesoporous Fe₃O₄ nanoparticles coated with ZnO nanocrystals were successfully synthesized by a simple solution method at low temperature. The transmission electron microscopy analysis indicates that the mesoporous Fe₃O₄ nanoparticles are monodispersed with a mean diameter of 160 nm and the thickness of ZnO layer is 15 nm approximately. The porosity of the products was further substantiated by the nitrogen (N₂) sorption measurement. The N₂ adsorption-desorption isotherm curve can be identified as type IV, which is a characteristic of mesopores. Electromagnetic (EM) wave absorption properties of the as-prepared Fe₃O₄@ZnO mesoporous spheres-wax composites were investigated at a room temperature in the frequency range of 0.5~18 GHz. Interestingly, the Fe₃O₄@ZnO mesoporous spheres exhibit an enhanced EM wave absorption due to the mesoporous structure. The multiple absorbing mechanisms result from the interface polarization induced by the special core/shell and mesoporous structures as well as dipole polarization of both Fe₃O₄ and ZnO. The results demonstrate that the Fe₃O₄@ZnO mesoporous spheres are attractive candidates for a new kind of EM wave absorption materials with wide absorption frequency band.

Colloidal silica particles are being intensively studied due to their potential applications in catalysis, intelligent materials, optoelectronic devices, photonic bandgap crystals, masks for lithographic nanopatterning, etc. On the other hand, in nanoscale electronic, photonic and plasmonic devices, feature dimensions shrink towards a critical limit, and new experimental approaches have to be explored in lithographic patterning in order to create ordered arrays of metallic nanostructures with useful optical properties. For this work, spherical submicrometer-sized silica particles were prepared by the sol-gel technique and deposited as a self-assembled monolayer onto silica glass plates using a spin coater system. This silica monolayer is then used as a mask to create regular arrays of nanoscale features in the sample by 1 MeV Ag ion implantation. By this way, after removal of the silica particles and an adequate thermal annealing of the as implanted samples, the formation of Ag nano-objects was confirmed by the presence of the surface plasmon resonance in the optical absorption spectra. The size and shape of the array of metallic deposits were studied by scanning and transmission electron microscopy, respectively. The total amount of implanted Ag was measured by Rutherford Backscattering Spectrometry (RBS). Finally, the long range order of the Ag nanoparticle assembly and its plasmonics properties were characterized by means of a Fast Fourier Transform study and optical absorption measurements, respectively.

Biological scaffolds are a powerful tool in controlling self-assembly due to their ability to work under mild, aqueous conditions. Peptides are one such example and have been shown to participate in the synthesis, binding and self-assembly of inorganic materials. It is further possible to make them multifunctional by fusing two different peptide domains enabling the design of hybrid nanomaterials. Furthermore, viruses such as the tobacco mosaic virus have also been shown to serve as excellent scaffolds and offer the advantage of monodispersity.
This work takes advantage of fusion peptides and viruses to form large scale gold nanoparticle assemblies. Gold nanoparticles are first synthesized using the Flg-A3 peptide. The A3 stabilizes the gold nanoparticles while the Flg domain then controls their assembly via interactions with divalent metal ions. These nanoparticles are covalently bound to tobacco mosaic virus coat protein disks and the self-assembly of the rings is controlled via interactions of the Flg domain with divalent metal ions.

In this work, we will report a strategy to produce Ag@Au nanostructures by combining galvanic replacement reaction (GRR) with co-reduction of gold and silver ions by ascorbic acid (AA). This novel approach embraces a number of unique characteristics. Firstly, at early stage of reaction, gold ions were reduced by AA to generate gold atoms with a selective deposition at the corners and edges of Ag nanocubes. Secondly, GRR occurred as the reaction progressed, leading to the formation of Ag@Au cubes with hollow interiors. However, with the presence of AA, these newly formed silver ions by GRR were further reduced and deposited on the cubes, leading to a no loss of Ag in the reaction process. In fact, these Ag enriched Au-Ag alloy hollow structures are promising candidates for SERS applications. At the end, unlike GRR, dealloying process was totally avoided at late stage of reaction in which AA continuously reduced gold ions for an epitaxial growth, leading to the formation of AuAg@Au hollow cuboctahedron. We evaluated the SERS properties of Ag@Au with a conclusion that we could optimize their SERS intensity to reach a value that is 15 times higher than Ag nanocubes by tuning the composition of Au for Ag@Au nanostructures at excitation wavelength of 785 nm. These Ag@Au nanostructures will find potential applications in biomedical applications.

Plasmonics is the manipulation of light using sub-wavelength metallic structures. The most common methods to realize such nanostructures are top-down approaches, such as e-beam lithography or focused ion beam milling. These techniques present a lot of advantages like high repeatability and dimensional control, but are often limited at one thousand micron square area. This makes difficult their utilization as metamaterials. From this perspective an issue for the plasmonic community is to achieve metal nanostructures on large areas.
In this communication, we demonstrate the assembly of ring-shaped metallic nanostructures in a controlled way. Our method is based on self-assembly of metal colloidal nanoparticles (NPs) during an evaporation step. The solution is composed by metallic NPs and polystyrene microspheres. Microspheres self-assemble in a hexagonal packed array and the metal NPs become confined at the meniscus of the spheres during evaporation, which drives ring assembly via capillary forces at the polystyrene sphere/glass substrate interface. After removing the polymer spheres, a hexagonal network of metallic nanorings is created on square millimeter area. The ring size can be adjusted by different parameters like microsphere diameter or NPs concentration. Control of the geometry enables to tune under control the optical response of nanorings.
We will present such nanostructures realized on large areas (mm2) and correlate their final shapes with their optical response in single nanoring spectroscopy. The measured optical properties are consistent with the ones obtained on continuous rings, indicating that self-assembled nanorings are a viable substitute to lithographied rings for various plasmonic applications [1].
REFERENCES
1. T. Lerond et al. Appl. Phys. Lett. 99, 123110 (2011)

Attempts to develop new radiation resistant alloys presently focus on creating high densities of unbiased sinks for point defects. These sinks, moreover, must be stable under extreme conditions, high temperatures and high irradiation fluxes. We have explored the possibility of creating such nano-composite materials using self organization reactions during severe plastic deformation, e.g., accumulative roll bonding, ball milling, etc. These materials, in principle, should be stable under irradiation. For example, exposure of immiscible alloys to such driving forces as severe plastic deformation (SPD) or intense particle irradiation (IPR) at elevated temperatures creates a dynamic competition in their response: the driving forces tend to homogenize the alloy, while thermally activated diffusion leads to phase separation. While many attempts have been made to determine which of these dynamics prevails in order to predict microstructural evolutions, we have found that for understanding compositional patterning in these systems, the relevant question is which dynamics prevails over what length scales. We will show that while compositional patterning during SPD and IPR derive from this concept and materials responses are often very similar for SPD and IPR, the mechanisms and length scales of mixing by these two mechanisms are quite different. We will further show using a series of Cu alloys that there are two distinct mechanisms of patterning for both SPD and IPR, which depend on the degree of immiscibility of the alloy. Finally, we will report on unique self-organized core-shell precipitate structures in the immiscible Cu alloys produced both by SPD and IPR.
This work was supported by the U.S. DOE Office of Basic Energy Sciences under grant DEFG02-05ER46217 and the NSF under grants DMR 10-05813 and DMR 08-04615.

Ordered arrays of Cu-Ni nanopillars (with diameters ranging from 100 to 200 nm and constant height of 450 nm) have been obtained by template-assisted electrodeposition on e-beam patterned Si(111)/Au(400 nm)/Ti(15 nm) substrates. Potentials between -0.8 and -1.2 V (vs Ag/AgCl) have been applied to precisely tune the average composition of the nanopillars (from 34 at% to 70 at% Ni). The nanopillars are Ni-rich at the bottom with a composition gradient expanding about ±20-25% of the average composition, as evidenced by energy-dispersive X-ray mappings. Magneto-optic Kerr effect (MOKE) measurements reveal that the Cu-Ni nanopillars are ferromagnetic, with coercivity values around 100-150 Oe (in-plane) and 200-500 Oe (out-of-plane), which are larger than for continuous films of similar average composition [1,2]. Such enhancement of coercivity is attributed to the small size of the pillars, i.e., either the formation of single domain states or the hindrances imposed by the limited lateral size of the pillars on the propagation of domain walls. 3D atom probe tomography has been used to reconstruct the top part of the nanopillars, which have indicated the segregation of Ni-rich clusters for compositions that are below the onset for ferromagnetism. It is envisaged that the fabricated magnetic Cu-Ni nanostructures will have widespread applications ranging from patterned recording media to remotely actuated MEMS/NEMS devices.
[1] E. Pellicer, A. Varea, S. Pané, B.J. Nelson, E. Menéndez, M. Estrader, S. Suriñach, M.D. Baroacute;, J. Nogués, J. Sort, Adv. Funct. Mater. 20 (2010) 983.
[2] E. Pellicer, A. Varea, K.M. Sivaraman, S. Pané, S. Suriñach, M.D. Baroacute;, J. Nogués, B.J. Nelson, J. Sort, ACS Appl. Mater. Interf. 3 (2011) 2265.

Nanocarbon has been successfully incorporated in molten metals and metal alloys using a new method of manufacturing in which the molten metal (or metal alloy) acts as ionizing medium causing nanocarbon structures to self-assemble in-situ within the metal lattice. C in concentrations up to~10% weight was incorporated in Ag, Al and Cu and other metals. The bonding between the carbon and the metal is very strong and persists after re-melting and resolidification. These materials, called “covetics,” show improved properties over those of the host metal. For example, the thermal conductivity of Cu covetic is higher than pure Cu. The electrical conductivity of Al covetic is higher than for pure Al. The yield strength of Al and Cu covetics is higher than the pure metals. We have used X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy to investigate the incorporation of C in the metal. Scanning and transmission electron microscopy (TEM) were also employed along with energy dispersive X-ray spectroscopy and electron energy loss spectroscopy (EELS). The nanocarbons in the covetics are in the form of graphene nanoribbons, and amorphous nanocarbon, and all are bonded to the metal. The C-K edge in the EELS, and the Raman spectra from these samples show signals characteristic of graphitic sp2 bonding. We have also performed density functional theory calculations to complement the measurements of the structure of Ag covetic and found that Ag can form bonds with C at the edges of graphene-like ribbons and at C vacancies. The bonds are covalent with energy of 1.2-2.2 eV/bond. We have deposited Cu covetic films that show high optical transmittance in the visible range and high resistance to oxidation compared to Cu metal films. The films are highly crystalline and have slightly lower C content than the covetic target used for deposition.

Galvanic replacement reactions have been widely used to transform sacrificial solution dispersed silver template structures into intricate nanoshell geometries. Few studies, however, have been dedicated to the synthesis of substrate-supported nanoshells. This is despite the fact that substrate-based sacrificial templates have the opportunity to provide unique capabilities in terms of shape-engineering the properties of the template through the adjustment of the heteroepitaxial relationship between the template material and the underlying substrate. Substrate-based galvanic replacement reactions also provide the opportunity to place the structures at site-specific locations on the surface of the substrate, a capability which would enable the fabrication of pixilated sensing devices with plasmonic nanoshells as the active component. Here, we report the first synthetic strategy yielding periodic arrays of Au-Ag hollow metal nanoshells derived from sacrificial Ag templates exhibiting a heteroepitaxial relationship with the underlying substrate. The periodic arrays originate from silver templates formed using a lithography-free route referred to as dynamic templating. The resulting hollow metal nanoshells are exceedingly smooth, show a high degree of crystallinity, are quite robust and exhibit a well-defined pattern of geometric openings in the <111>-directions. The work also provides insights into the mechanisms guiding galvanic replacement reactions. Specifically, it demonstrates that the hollowing out of the interior of the template proceeds through the formation of a hollow channel which first extends from one side of the structure to the other and then widens until the hollowing process is complete. The mechanistic requirements needed to obtain a smooth shell which preserves the overall shape of the original template will also be elucidated.

The dynamical competition between the chemical mixing forced by energetic particle irradiation and thermally activated decomposition can lead to the stabilization of self-organized steady states in alloy systems comprised of immiscible elements. Continuum modeling and atomistic simulations predicted the stabilization of steady-state nanoscale compositional patterns for a well-defined range of ballistic mixing frequency normalized by the irradiation-enhanced thermal atomic jump frequency. While irradiation-induced compositional patterning has been observed experimentally, a quantitative comparison has been lacking because models and simulations had relied on a simplified treatment with a fixed point defect concentration. We have developed a novel kinetic Monte Carlo code that treats vacancies and interstitials as non-conserved species, including their production, recombination, and elimination on sinks. By controlling the sink density for the point defects to be in the sink dominated elimination regime, steady-state compositional patterns can be stabilized over a much larger temperature range than predicted before. We use the KMC simulations to show that for alloys like Cu-Ag, Cu-Fe or Cu-Co, these conditions can be met using multilayered structures, or by introducing a high density of nanoprecipitates playing the role of sink, as in the case of nano-oxide dispersion strengthened materials. Lastly, the KMC simulations also reveal that irradiation-induced non-equilibrium segregation on sinks can locally or globally prevent the stabilization of compositional patterns.

Nanostructured thin films carry an immense potential in diverse fields of applications such as photovoltaics, energy storage, drug delivery, gaseous and liquid material sensing or communication, for example. The unique character of the materials is defined by a large surface area and a high void fraction which makes nanostructured thin films ideal for constituents in hybrid material fabrication. We employ oblique angle of incidence deposition for thin film fabrication. The films posses a variety of nanostructure geometries ranging from slanted columns, zig-zags, posts to spirals. We will demonstrate the performance of highly spatial coherent nanostructured thin films upon Li intercalation, for chromatography applications and during organic material attachment. Thereby, the response of the films to immediate changes in their surroundings is obtained using an optical fingerprint method by means of generalized ellipsometry.

Construction of structurally-defined, patterned metal films is a fundamental objective in the emerging and active field of “bottom-up” nanotechnology. We present a new strategy for constructing macroscopically-organized Au nano-structured films. The approach is based upon a novel phenomenon in which incubation of water-soluble gold thiocyanate with amine-displaying surfaces gives rise to spontaneous crystallization and concurrent reduction, resulting in formation of patterned metallic gold films. The Au films exhibit unique “nano-ribbon” morphology, likely corresponding to aurophilic interactions between the complex moieties anchored to the amine groups through electrostatic attraction. Critically, no external reducing agents were needed to initiate or promote formation of the metallic Au films; in essence, the thiocyanate ligands provide the means for surface targeting of the complex, guide the Au crystallization process, and, importantly, donate the reducing electrons. We show that the Au films exhibit electrical conductivity and high transparency in a wide spectral range lending the new approach to possible applications in optoelectronics, catalysis, and sensing.
- Reference: Morag et al, Advanced Functional Materials, 2013, DOI: 10.1002/adfm.201300881

3D ordered macroporous (3DOM) ceramic coatings with morphology of an inverse opal are attractive for various applications, such as next-generation thermal barrier coatings (TBC), due to their low thermal conductivity and unique optical properties facilitating strong reflection of thermal radiation. One of the main obstacles precluding their practical utilization is in tedious manufacturing.
Inverse opals are obtained by replication of colloidal crystals. Usually, a polymeric artificial opal template produced by self-assembly of monodisperse particles is infiltrated with a ceramic phase and inverted by calcination of the polymer in separate processing steps. Established infiltration techniques, along with involved and time-consuming processing, have severe limitations for deposition of ternary compounds, such as yttrium-stabilized zirconia (YSZ) - a key material for TBCs.
We report an alternative all-colloidal fabrication method of YSZ-infiltrated polymeric opals. Crystalline nanoparticles of YSZ with primary size below 10 nm were produced by a mild hydrothermal synthesis route from corresponding nitrates and then co-assembled with sacrificial microspheres in a facile single-step deposition process. The inverted YSZ 3DOM coatings demonstrated a pronounced photonic response and retained their periodical structure after annealing at 1000 °C for several hours. Although certain co-assembly methods are known for reduced density of defects in inverse opals, 3D photonic crystal films produced by co-assembly of YSZ nanoparticles were prone to drying-induced cracks.
We suggest ways for further improvement and also present a modified co-assembly method for deposition of macroporous YSZ coatings with deliberately introduced disorder, which usually deteriorates the performance of photonic crystals but could be advantageous for TBCs because it can increase the total reflectance of the thermal radiation.

Micro-electromechanical systems (MEMS) are electrically controlled micro-machines. Here we present a MEMS based device for precisely controlled atom deposition, which enables us to directly fabricate nanoscale circuits and structures, leading to a regime of experiments on a small amount of atoms.
The core component of this device is a thin silicon plate with apertures smaller than 50 nm. The plate can be displaced in three dimensions under the precise control of four linear MEMS motors. A flux of metal atoms generated by thermal evaporation passes through the aperture and condenses on a substrate as the motors are actuated, following a pre-designed pattern. A MEMS shutter is also integrated to provide more flexibility and real-time control.
Complex nanoscale structures with multi-layers made from different materials can be manufactured by repeated passes and using multiple sources and apertures. The nano-structures can be further studied and accessed, via fabricated contact leads running to pre-deposited electrodes.
Here we present some nanoscale structures fabricated using this technology, including nano-electromechanical systems (NEMS) bridges, nano Mobius loops and quench condensed metallic nano-rings. The average line width can be as low as 50nm, while the thickness can be dynamically controlled from 0 up to 500nm. We also present results showing the dynamic mechanical properties this MEMS device, including the aperture filling and resonance ring-down. These structures form the basis of new mesoscopic experiments.

This contribution presents a detailed study of a procedure that allows to produce periodic nanocolumn arrays on GaAs wafer surfaces in a self-organized manner. Nanostructured III-V semiconductors are of key interest for realizing state-of-the-art optoelectronic and photonic devices, e.g. solar cells [1,2], LEDs [3] and photonic crystal nanocavities [4]. Moreover, nanopatterned semiconductors can serve as templates for the growth of nanoscale low-defect heteroepitaxial structures including quantum dots and wires, which then offer the possibility of examining physical size effects [5]. In the past, GaAs sub-microscale and nanoscale GaAs patterning was achieved by reactive ion etching (RIE) through Si oxide, Si nitride or metallic masks. For the definition of the masks electron beam [6], laser interference [5], and nanosphere lithography [2] was used.
In the present work, we combine nanosphere lithography with RIE to obtain periodically arranged GaAs nanocolumn arrays. For the deposition of close packed polystyrene nanosphere layers different suspension drying techniques are employed. In order to obtain larger areas (~1 cm2) of nanosphere mono- and doublelayers appropriate parameters such as sphere content of the suspension are determined. Two different substrate cleaning and hydrophilization methods, oxygen plasma and H2O2-H2O solution treatment are compared. It is found that a short exposure to oxygen plasma decreases the H2O contact angle below 5°, whereas the increase in surface oxide thickness, determined by ellipsometry, does not exceed few nanometers. Subsequently, a ~20 nm thin Ni metal film is thermally evaporated onto the substrate covered with spheres. After nanosphere removal the remaining metal islands act as an etch mask in the course of the following RIE step using SiCl4 with or without Ar addition. Finally, the Ni mask is lifted off by means of wet chemistry. We analyze in detail the conditions of the individual steps that are favourable for obtaining regularly arranged, anisotropic columnar structures characterized by low surface roughness and damage. It is shown that in this way periodic arrays of GaAs columns with nearly vertical sidewalls and diameters down to ~25 nm can be generated. The etch patterns are evaluated on the basis of oblique view scanning electron microscopy and cross-section transmission electron microscopy. For roughness determination atomic force microscopy is employed.
References
[1] J.A. Czaban, D.A. Thompson, and R.R. LaPierre: Nanoletters 9 (2009) 148
[2] B.-J. Kim, J. Kim: Optics Express 19 (2011) A326
[3] E.D. Minot et al.: Nanoletters 7 (2007) 367
[4] D. Englund et al.: Phys. Rev. Lett. 95 (2005) 013904
[5] D. Zubia et al.: J. Vac. Sci. Technol. B 18 (2000) 3514
[6] M.B. Stern et al.: Appl. Phys. Lett. 45 (1984) 410

Ferromagnetic shape memory alloys (FSM), including the Ni-Mn-Ga and Fe-Pd systems,
constitute a new upcoming class of functional materials, that can yield magnetically
switchable strains of several percent at constant temperature. Operating within the martensite phase, strains are mediated by magnetically assisted reorientation of twin variants in presence of a large magneto-crystalline anisotropy. For miniaturized FSM films and foils, twin variants and magnetic domains allign as regular nanoscale patterns, that form self-organized for temperatures lower than the martensite and Curie temperatures, respectively. While generally reduction of elastic and magnetic energies is the basic principles behind structural and magnetic pattern formation, they are severly coupled magneto-structurally within the martensite phase. Decoupling can, at least partially, be reached upon traversing the austenite and/or Curie temperatures. In fact, this prospect of an adjustable coupling parameter makes structure formation in FSM alloys a physically highly interesting scenario.
From a more technical point of view, performance in terms of macroscopic magnetically induced strain originates from changes within structural and magnetic domain patterns at the nanoscale. This makes a detailled understanding highly relevant also from an application point of view.
After reviewing these fundamentals, we report about synthesis of freestanding and substrate-attached Fe-Pd and Ni-Mn-Ga thin films, that were grown by molecular beam epitaxy (MBE) under highly optimized deposition and annealing conditions. Temperature dependent atomic- and magnetic force microscopy (AFM/MFM) studies were subsequently employed to systematically explore the relation between magnetic domain pattern and underlying structure across the thermally induced phase transitions. We find experimental evidence, that pattern formation is severely affected by applied constraints; freestanding
films reveal a hierarchical structure of micro- and nanotwinning. For quantitative interpretation of MFM measurements and magneto-structural coupling, three-dimensional micromagnetic simulations were conducted, based on which MFM micrographs are calculated, that perfectly reproduce the experimental data and open the venue for a detailled physical understanding. The influence of twin variant dimension and orientation on micromagnetic domain formation and wall structure are addiationally derived from a theoretical point of view.
[1] A. M. Jakob, M. Hennes, M. Müller, D. Spemann and S. G. Mayr, Adv. Funct. Mat.
early view (DOI: 10.1002/adfm.201300165)

The phenomenon of time-averaged structuring of diffusing adatoms on a solid substrate under the action of standing surface acoustic waves is investigated theoretically and computationally. A new mechanism of diffusional structuring which involves interplay between acoustically-induced variation in the diffusion energy barriers, local barrier asymmetry and adiabatic temperature variations is revealed in a theoretical analysis and confirmed by the results of kinetic Monte Carlo simulations. We demonstrate that relatively weak variations in the diffusional barriers due to the acoustically-induced surface strains can result in substantial variation in the concentration of surface adatoms that can lead to controlled surface patterning. The analysis of the acoustically-induced surface structuring reveals several distinct patterning regimes (gathering of adatoms either in nodes or antinodes of standing surface waves) and establishes direct connections between the characteristics of the acoustically-induced surface patterns and the parameters of the acoustic wave.

Understanding the mechanism and the factors governing the self-organization of nano-scale filaments such as carbon nanotubes (CNTs) is crucial for manufacturing of engineered CNT ensembles that are promising for many applications such as electrical interconnects, thermal interfaces, filtration membranes and chemical sensors. In this study, we focus on the mechanochemical effects in coupled growth of self-organized "forests" of vertically aligned CNTs, whereby the forest structure grow as a collective despite the intrinsic heterogeneity in sizes/geometries of individual CNTs. Although mathematical models have been developed to describe the growth of a single CNT from a single catalyst nanoparticle, none currently takes into consideration the population growth behavior of mechanically-coupled CNTs growing and self-organizing simultaneously. Combining these developed models for individual CNT growth with experimentally collected information about the nanoscale morphology of CNT forests, we model the effects of mechanical coupling forces during the successive stages of growth (crowding, lift-off, density-decay, and self-termination). We use high-resolution X-ray scattering and absorption measurements, in combination with models of diameter-dependent growth kinetics, to determine the time-dependent and diameter-dependent forces exerted on catalyst particles during CNT forest growth. These forces arise from growth rate mismatch between neighboring CNTs having different diameters (hence different growth rates). The resultant axial load on the catalyst is calculated based on the stiffness of curved beams under axial deflection that arises from the difference between the apparent CNT forest lengthening rate and the diameter-dependent rates predicted by a mathematical growth model. We find that these forces are sufficiently high to perturb the activation energy for CNT growth, and could be a major cause of structural defects and the intrinsic tortuosity that limits the properties of CNT forests. Motivated by these insights, we built a custom instrument to apply measurable axial loads in situ during forest growth, and derive the exact influence of mechanical forces on chemical growth kinetics. This mechanochemical feedback between CNTs during growth arises intrinsically due to the polydispersity of CNT diameters within the growing population, so fabrication of highly monodisperse catalyst arrays is a promising route for directing the self-organization of CNTs to produce more aligned, straighter and more dense CNT forests that have improved collective electrical, thermal, and mass transport properties.

The helical assembly of self-organized flavin mononucleotide (FMN) around single-walled carbon nanotubes (SWNTs) presents among the highest organization order in nanotube surfactants. In this contribution, we quantitatively analyze and model for the first time the cooperative hydrogen bonding of adjacent flavin moieties as well as the concentric π-π interactions between the isoalloxazine moieties and the underlying graphene lattice as a function of (n,m)-SWNT chirality. For this we use dissociation thermodynamics of FMN-wrapped (n,m)-SWNTs dispersed in both H2O and D2O as a function of FMN concentration. The binding strength of these FMN assemblies has been assessed in terms of ΔH, ΔS and ΔG. Atomistic molecular simulations were used to modeled these data and link their dependence in terms of nanotube diameter (dt) the chiral angle (phi;). The findings of this study provide quantitative understanding of SWNTs enrichment in terms of (n,m)-chirality and FMN helical repeat (i.e. 8/1 vs. 7/1 type of helix). This study demonstrates the architectural fidelity of FMN-wrapped SWNTs that closely emulates the dissociation mechanics of double-stranded DNA in its aqueous solutions.

Porosity evolution during dealloying is a dynamic pattern forming instability seen in solid solution binary alloys (A/B) that results from the competition between dissolution of majority component A, and interface diffusion that reorganizes component B into a three-dimensional porous network. In this work, we present recent work in which we have controlled the dealloying process by modifying the interface mobility of component B. Specific methods we have employed include (i) addition of a ternary component to the parent alloy, both to reduce the surface mobility but also to control stress evolution during dissolution, and (ii) employing high temperature dealloying. These techniques add to the flexibility of dealloying to form extended nanostructures in three dimensions, and have resulted in new materials including nanoporous refractories.

Severe Plastic Deformation (SPD) techniques have been used for decades in single-phase materials to refine grain sizes in a top-down fashion. These techniques typically provide large densities of high-angle grain boundaries that range widely in their degree of order and relative misorientation. However, we have found that at diminished length scales in two-phase metallic composites, stable preferred interfaces evolve as a function of increasing strain. In this presentation, we report on the microstructural evolution in Cu-Nb lamellar nanocomposites processed via Severe Plastic Deformation as a function of decreasing layer thickness. We utilize Accumulative Roll-Bonding (ARB) to process bulk Cu-Nb nanolamellar composites from 1 mm thick high-purity polycrystalline sheet down to layer thicknesses of 10 nm. This processing technique has the advantage of producing bulk quantities of nanocomposite material, and also exposes the interface and bulk constituents to large strains (1000&’s of percent). It is found that at submicron layer thicknesses where only one or two Cu or Nb grains span a given layer, a dominant interface type forms. This interface is a chemically sharp, ordered, faceted {112}<111>Cu//{112}<110>Nb interface, and its prevalence is strongly dependent upon processing conditions. This interface is found to promote deformation twinning in the Cu phase at sub-100 nm layer thicknesses, which results in self-organization to the {551}<1 1 10>Cu//{112}<110>Nb at nano-layer thicknesses. The evolution of preferred interfacial structures during processing will be linked to the structure and energetics of a given interface type, as well as the kinetics of slip in the constituents and across interphase boundaries. Mechanical properties and behavior will be discussed in terms of the effects of interfacial content on deformation processes at diminishing length scales, and defect/interface interactions at the atomic scale.

We present a simple and scalable method for the patterning of complex nanostructures over nanometer to micrometer length scales. We employ a variety of electrochemical techniques, including cyclic voltammetry and chronoamperometry, to directly pattern electrochemically and catalytically active interfaces. The nanoscale dimensions of the patterned structures can be finely controlled and exhibit < 2% dispersion over arrays extending to the millimeter scale. We discuss the mechanism underlying such pattern formation and will consider its generality to other material systems. We will conclude by demonstrating how our strategy can enable synthesis of new active surfaces for biological detection and catalysis, and direct nanopatterning of electronic and optical elements.