We have recently developed a liquid cell for the transmission electron microscope in which a thin liquid layer (<100nm) is trapped between two monolayers of graphene. We are investigating the growth and assembly of colloidal nanocrystals in these ultra-thin liquid films using the TEM.

Controlled growth and assembly of nanoparticles into dimers and complex nanoclusters with asymmetric configurations (in terms of geometries and compositions) is of great interest because of their novel properties and possible promising applications (e.g., biosensing, labeling, display, catalysis, etc.). In this presentation, a number of practical strategies will be discussed to demonstrate their capability in synthesizing asymmetric assemblies of nanoparticles. The first method is heteronucleation and growth of nanocrystals on the existing amorphous nanoparticles that are preloaded to the reaction system. For example, magneto-plasmonic bifunctional dumbbells consisting of solid silver nanodomains and hollow iron oxide nanoshells have been synthesized by reducing silver nitrate in solutions including amorphous iron/iron oxide nanoparticles. The second method is epitaxial overgrowth of crystalline nanoparticles whose surfaces are partially passivated. The third method relies on the spontaneous assembly of nanoparticles with partially protected surfaces through formation of chemical bonds between the nanoparticles. For instance, dimers made of gold and silver nanoparticles have been synthesized by choosing appropriate chemical linkers. Optical properties of the synthesized nanoassemblies have been characterized and the preliminary results reveal some interesting phenomena that were not reported before.
This work has been performed at the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract No. DE-AC02-06CH11357.

The catalytic reactivity and selectivity of metallic nanoclusters are directly correlated to the clusters composition, size and capping molecules. In this work, heterogeneous catalysts for asymmetric reactions were prepared by embedding Au nanoclusters in chiral self-assembled monolayer (SAM), which was utilized as a capping agent. By this process, a unique catalytic reactivity and selectivity, which is not accessible with the naked metallic clusters, was gained. The chiral SAM was immobilized on mesoporous SiO2 support and employed for the preparation and encapsulation of metallic nanoclusters. Using cyclopropanation reactions as an example, it was demonstrated that asymmetric reactions can be catalyzed by Au nanoclusters embedded in the chiral SAM. Up to 50% enhanced enantioselectivity and high diastereoselectivity were measured while employing Au nanoclusters coated with SAM peptides as heterogeneous catalyst. In-situ EXAFS measurements demonstrated that the active catalyst are the highly oxidized Au(III) species, formed by oxidation of the Au clusters during the reaction. The products selectivity was improved while increasing the number of amino-acids links in the peptide chain which construct the SAM. Spectroscopic measurements correlated the improved selectivity to the formation of hydrogen-bonding network in the chiral SAM. The results of this study indicate that the catalytic reactivity of metallic nanoclusters can be widely tuned according to the properties of an encapsulating SAM.

PbSe nanocrystals have shown a promise to increase the efficiency of solar cells through multi-exciton generation. While the exact mechanism is still unclear and is under intensive research, the concept of electronic coupling among the nanocrystals could have a role in both the multi-exciton generation and the subsequent charge transports across the nanocrystal films. Typically, strong electronic coupling between PbSe nanocrystals is achieved by replacing the long insulating ligands (oleic acids) with short ligands such as hydrazine or 1,2-ethanedithiol. This coupling results in the formation of conducting channels between nanocrystals that lowers the band gap of the nanocrystal films. In this work, the electronic coupling on the localized surface plasmon resonance (LSPR) of the PbSe nanocrystal films was studied using Electron Energy Loss Spcetroscopy (EELS) measurements conducted in analytical Scanning Transmission Electron Microscope (STEM). A new type of LSPR interaction in the as-synthesized nanocrystal arrays capped with oleic acid ligands, which is different from plasmonic interactions in hydrazine-treated nanocrystals, was discovered. In hydrazine-capped nanocrystals, both LSPR and bulk plasmon interactions are observed since both conduction and valence bands of the nanocrystal assembly are affected by the ligand exchange process. In contrast, only LSPR interaction is detected in oleic acid-capped nanocrystals, which is mediated by oxygen induced dehydrogenation of the oleic acid ligands to support plasmon modes that helps increase the lifetime of the LSPR of the nanocrystals. Our EELS confirms the presence of conjugated π bonds in the oxygen induced dehydrogenated oleic acid ligands, which appears to act as conducting channels to sustain the LSPR lifetime of the PbSe nanocrystals.

Seeded growth is a simple and versatile approach to the synthesis of nanocrystals with controlled sizes, shapes, and morphologies. It can also be used for the production and even nanomanufacturing of nanocrystals with well-defined, exotic structures. For example, we have demonstrated a simple and versatile method based on kinetic control for achieving site-controlled nucleation and growth of one metal on the cubic seeds of another metal enclosed by six {100} faces. By simply using a syringe pump to manipulate the rate at which atoms were generated from a salt precursor, the atoms could be directed to nucleate and epitaxially grow on one, two, three (adjacent), four, five, and six faces of the cubic seeds. This strategy has also been successfully extended to many other systems to generate mono- and bimetallic nanocrystals with well-defined and controllable structures, shapes, and morphologies.

The functionality of nanophotonic systems based on colloidal nanoparticles depends sensitively on their shape and arrangement. Plasmonic nanoparticles possess high resonant scattering and absorption cross sections, are non-blinking, and exhibit strongly distant-dependent optical spectra, making these nanoparticles ideal for integration into metamaterials and biological sensors. Here we present the design and implementation of a three-dimensional chiral assembly of colloidal metal nanoparticles, assembled using DNA. These assemblies exhibit circular dichroism (CD), which arises from the three-dimensional coupling between the dipole moments of the plasmonic nanoparticles. This assembly acts as both a sensitive and specific plasmon ruler for biological monitoring and as an active metamaterial that switches handedness in response to external stimuli. Our assembly is based on a pyramid with spherical gold nanoparticles at each of the corners, where active and tunable chiroptical response is induced via symmetry breaking. Starting with an assembly of two 10 nm Au nanoparticles and two 20 nm Au nanoparticles arranged symmetrically with 10 nm DNA connecting the edges of each particle, we break symmetry by gradually changing the distance of one arm connecting the two particle sizes. Shortening the length of this side produces a structure of one handedness, while extending the length of this side produces the opposite. The color and intensity of the CD spectra depend on the length of the arm, with wavelength shifts as large as 1 nm per angstrom of distance. This assembly represents a reconfigurable metamaterial with optical response in the visible spectrum where the handedness of the structure inverts in response to external stimuli such as DNA-binding events. We then designed four strands of DNA that hybridize to form the pyramid, consisting of five sides of length 26 base pairs (~9 nm) and one side of 16 base pairs (~5.5 nm). The sequences were designed considering the tertiary structure of the double helices and thermodynamically favor one enantiomer. Solutions of 10 nm and 20 nm Au nanoparticles are reacted with 5&’-thiol modified oligonucleotides in a tris-buffered solution of ionic strength greater than 50 mM. The resulting statistical mixture is purified to obtain monoconjugated DNA-Au nanoparticle building blocks, which are then hybridized to form the pyramid. CD measurements show bisignate features near the plasmon resonance of the Au nanoparticles at 520 nm, corresponding to calculations. We have formulated several design rules for achieving strong CD response, accounting for the 10% polydispersity in nanoparticle size and flexibility in both the DNA frame and linker molecules. We find that nanoparticles with higher extinction can improve the CD figure of merit by two orders of magnitude, and show that including nanoparticles with distinct resonant characteristics allows us to design broadband chiral materials with complex spectra.

Self-assembly of small objects such as atoms and nanoparticles (NPs) into mesoscopic structures is a frequently-used building approach in material science and chemistry. The self-assembly of NPs attracts great attention for its potential application in the fabrication of hybrid systems with collective properties from different types of materials. There were great efforts devoted to understanding of the mechanisms that govern the self-assembly both from experimentals and theoretical approaches. It is now understood that different types of interactions can drive self-assembled superstructures with different packing arrangements of individual NPs. Recent developments of transmission electron microscopy (TEM) liquid cell provide a direct imaging platform that enables to watch the nano objects growth and assembly. Here, the in-situ liquid TEM technique was employed to visualize real time self-assembly of Au NPs with positively charged (CTA+) and negatively charged (citric CI) surfactants in solution in order to unravel the mechanism of NP self-assembly. We find that positively charged Au NPs self-assemble when the electron beam intensity exceeds a threshold, while negatively charged particles do not move under the e-beam. We also find that the NPs having a similar size prefer to attach each other to form segregated one dimensional chain. The individual particles show a preference to attach to the ends of existing dimers, trimers to form trimer and tetramer. The attachment between the short self-assembled chains and between individual particles and short chains took place simultaneously and the process proceeds until all individual particles are exhausted to form longer chains. The dipolar interaction is recognized as the dominant control factor in the formation of one dimensional self-assembly because it is anisotropic , has a long range effects and is surprisingly strong. The solvated electrons are reacting with Au NPs diminishing the overall positive charge of CT-Au NPs. So, the repelling forces among the CT-Au NPs decrease as the overall positive charge is reduced. Concomitantly, the dipole moment develops between reduced Au NP and positively charged ligand attached to CT-Au NPs promoting ordering of nanoparticles. When dipole-dipole interaction between reduced NPs overcomes the electrostatic repulsion, the neighboring particles will couple and form dimers. Once the dimers are formed, the stronger dipole will be generated. Consequently, there will be a stronger anisotropic energy drive for an extra particle to attach to the end of a chain. The same experiment was carried out with CTA+ coated Au nanorod. The end-to-end self-assembly was found as well. The dipole interaction may play the same role as the Au NPs self-assembly.

This presentation will center on how to directionally control the evolution from seeds to noble-metal nanocrystals during a seed-mediated synthesis. As a distinctive advantage over the one-pot synthesis that involves homogenous nucleation, seed-mediated growth allows us to disentangle growth from extremely complicated nucleation, making it easier to control the formation of nanocrystals by simply concentrating on the growth step. Using cubic seed enclosed by a mix of low-index {100}, {111}, and {110} facets as a model seed, fundamental concepts and mechanistic understanding in controlling the growth of a seed are detailed. Important examples of recent studies are highlighted, followed by extension of the concept to seeds of different shapes and crystallinities. We believe that our insights in growth of nanocrystal may inspire new ideas/trends in shape-, size-, and structure-controlled synthesis of noble-metal nanocrystals.

Though the chemistry of organic/inorganic interface in colloidal nanocrystals (NC) strongly affects their physical and chemical properties, and in spite of advances in the synthesis of NC [1], experiment and theory have yet to produce a consistent atomistic model of the surface passivation for colloidal NC. The present work proposes an atomistic model of colloidal NC with facets passivated by organic ligands based on periodic DFT calculations.
Two facets most frequently exposed by Pb chalcogenide NC are the {001} and {111} [2]. It should be noted that Pb chalocogenide NC are nonstoichiometric with the excess of the Pb ions and Pb:X (X=S, Se, Te) ratio ranging from 1.2 to 1.6 [3]. Next experimental fact to be taken into account is that the synthesized NC are capped almost exclusively by the oleic acid ligands (OA). Moreover, a number of the OA matches the number of excess Pb ions [3]. Additionally, increasing of the OA concentration increases the growth rate of {001} facets while the decreasing of the ligand concentration increases the growth rate of {111} facets, eo ipso changing the shape of the NC.
In our study, we are focusing on the reactions that take place in solution and on NC surfaces in order to describe organic/inorganic interface of PbS-NC at atomistic level. We predict that the {111} facets are passivated by deprotonated OA- anions and OH- groups, so that all Pb ions on the {111} facets are completely passivated and the number of OA- matches the number of the excess Pb ions. Our model explains the changes of the facet growth rate and shape of NC based on the surface Gibbs energy.
In the thermodynamic equilibrium, the shape of a NC is determined by the minimization of the surface Gibbs energy for a given volume according to the Wulff construction. Taking into account the models of the NC surface-ligand interface and the calculated surface Gibbs energies of the passivated NC facets determined by their equilibrium ligand coverage, we define the theoretical Wulff ratio of 0.816 to be in agreement with the experimental ratio of 0.815 determined from TEM images.
Based on the atomistic models of the facet passivation, we constructed first atomistic model of the colloidal PbS-NC with the surface ligands which satisfies the experimental findings. The constructed model has Pb:S ratio of 1.194 close to the experimentally measured value of 1.211. The model has ratio of excess Pb ions to OA- of 1.178 which is satisfies the experimentally measured ratio of 1.0.
Hence, we developed the successful multi-scale procedure for the investigation of the NCs surface passivation. Using this procedure, the atomistic models of the NC facets passivation are determined and the atomistic model of the colloidal NC is constructed. The model satisfies and explains the key experimental findings.
1. Yin Y., Alivisatos A. P. Nature 437, 664 (2005).
2. Jun Y. et al. J. Phys. Chem. B 109, 14795 (2005).
3. Moreels I. et al J. Am. Chem. Soc. 130, 15081 (2008).

The superhydrophobic silica aerogel was prepared by using less expensive sodium silicate as a main silica source through a cost-effective and simple route via ambient pressure drying. The sodium impurity was first eliminated by mixing sodium silicate with a co-precursor methyltriethoxysilane (MTES) followed by ion exchange process. The hydrogel was formed by gelation and the alcogel was further obtained by alcoholization of the hydrogel. The surface of alcogel was modified by reacting with trimethylchlorosilane (TMCS) diluted in n-hexane. It was suggested that MTES accelerated water expelling from the hydrogel, while TMCS modified the surface of silica network by replacing Si-OH with Si-C. As a result, the obtained silica aerogel exhibited excellent physical properties with less than 10 % volume shrinkage. The density, surface area and cumulative pore volume were 0.12 g/cm3, 684.44 m2/g, and 3.55 cm3/g, respectively. The optical transmission reached 82.8 % with the water contact angle of 146 degree centigrade.

Semiconductor nano crystals or quantum dots are becoming increasingly popular in research fields as wide ranging as cancer therapies, solar energy and disease detection. Colloidal synthesis provides a low-cost method of producing high quality quantum dots with narrow size distributions. The controllable nature of colloidal synthesis allows researchers to design the size, shape and surface functionalization of the resulting particles.
Here we investigate a variety of low temperature routes to produce CdSe, CdTe and PbS quantum dots. In one method the cadmium chalcogenides were grown in solution by dissolving the CdO precursor in a mixture of macadamia oil, olive oil and oleic acid. Elemental Se or Te was heated separately before the two mixtures were combined under an inert atmosphere. The reaction temperature was varied between 200 and 250C and the reaction time between 2 minutes and 6 hours. Variation of the ratio of the reactants and the relative concentrations of the solvents allowed a range of quantum dots to be produced.
Optical absorption and photoluminescence spectroscopies showed the size of the quantum dots increased with time, temperature and oleic acid concentration. Dynamic light scattering and TEM analysis have shown the particle size to range from 2 to 6nm and the samples are stable to rapid oxidation.

Bottom-up self assembly of two-dimensional nanoparticle arrays with various symmetries and compositions promises to revolutionize device fabrication, enabling print-on-demand nano-bio devices on flexible substrates. Presently, a robust quantitative understanding of the relationship between final structure (close packed, aligned, or random) and density of packing defects to particle shape (sphere, rod), particle-particle repulsion, particle-surface attraction, conditions of the medium (temperature, electrolyte concentration) and processing time remains elusive. Although previous simulations have shown that tuning particle and surface potentials, screening lengths, particle concentrations, and patterned surface geometries result in particle ordering, the appropriate experimental conditions and mechanism responsible for particle mobility and the observed in-plane disorder-order and order-order transitions are still unknown. In order to understand the complex interplay of processing variables impacting assembly and in-plane ordering of nanoparticles on a surface, we discuss Brownian dynamics simulations of absorption, ordering and desorption of electrostatically stabilized spheres using LAMMPS&’ colloid package with approximately 4300 colloidal particles. Ordered assemblies are observed at high particle concentration (10%), intermediate temperature (1-10 kT) resulting in surface coverage around 30%. Lower concentration and temperature lead to disordered arrays. In-plane mobility is accompanied by dynamic absorption-desorption at intermediate temperatures. These general characteristics are modified and additional ordered structures such as strings are seen by changing particle-particle repulsion (e.g. electrolyte content). These insights provide guidelines to experimental conditions necessary to create high resolution patterns, and smaller devices via printing of nanoparticle inks.

It is well known that a strong correlation exists between the size, shape and morphology of the material, and its properties, therefore controlling these parameters is essential for potential technological applications of the materials [1]. Tungstate materials, and especially rare earth tungstates, have promising applications as laser hosts [2], scintillators [3], photocatalysts [4], etc. Nanoparticles of yttrium tungstate oxide hydroxide were synthesized under hydrothermal conditions in a ligand-free environment, and in the presence of dioctyl sodium sulfosuccinate (DSS) surfactant. Longer reaction times led to the formation of spherical microstructures build from nano building blocks. The shape and size of the nano building blocks, and therefore the architecture of the microstructures, could be tuned by controlling the reaction conditions, such as the source of rare earth, and amount of surfactant. X-ray powder diffraction (XRD), elemental analysis, electron microscopy (TEM, SEM), and N₂ adsorption were employed to characterize the obtained products. The photoluminescent properties of Ln³⁺ doped tungstate materials were investigated. Luminescence measurements showed an efficient charge - transfer from the WO₄^2- groups to the lanthanide ions, giving rise to a variety of colors. The Dy³⁺ doped material exhibited white light, which gives it potential application in white LEDs.
(1) Colfen, H.; Mann, S. Angew. Chem., Int. Ed. 2003, 42, 2350.
(2) Kaminskii, A.A.; Eichler, H.J.; Ueda, K.; Klassen, N.V.; Redkin, B.S.; Li, L.E.; Findeisen, J.; Jaque, D.; Garcia-Sole, J.; Balda Fernandez, J.R. Appl. Opt. 1999, 38, 4533.
(3) Lei, F.; Yan, B. J. Solid State Chem. 2008, 181, 855.
(4) Lixia, Z.; Qin, Z. Qingcheng, L. J. Rare Earth 2006, 24, 60.

A method for the fabrication of self-assembled 2D structures of nearly touching gold nanoparticles is presented, which relies on the control of self-organization processes by the specific design of the employed particle-polymer composites. Large areas of highly ordered nanoparticle arrays can be prepared using common spin coating procedures for the nanoparticle deposition. Due to the low distances of the particles, plasmon coupling of multiple particles can be observed.
Introduction
Self-organized patterning of surfaces with gold nanoparticles by block copolymer micellar nanolithographie (BCML) is well known and used for the preparation of antireflective surfaces, cell adhesion studies, and sensor fabrication[1]. Spherical gold particles up to 15 nm in diameter can be assembled by BCML in quasi-hexagonal pattern with adjustable interparticle distances. Recently we described a technique for self-organized patterning of large areas with gold nanoparticles of predefined size, shape and distances[2,3]. In this approach gold nanoparticles were wet-chemically synthesized and functionalized with thiol terminated polystyrene by ligand exchange. The particles were spin coated and assembled into well-ordered monolayers, however the interparticle distances were too large to obtain plasmon coupling. Here we present a method, using this technique, to assemble ordered 2D structures of nearly touching gold nanoparticles with broad extinction in the near infrared spectrum.
Results
Spherical gold nanoparticles were wet-chemically synthesized and functionalized with thiol terminated polystyrene by ligand exchange. The particles were spin coated on substrates and self-assembled into ordered monolayers. Sequential plasma treatments and spin coating procedures led to the formation of ordered 2D structures of nearly touching gold nanoparticles. The assembled structures show strong extinction in the visible and the near infrared spectrum, which can be correlated to strong plasmon coupling of multiple particles. The developed method can be applied for the assembly of more complex structures and other metal nanoparticles exploiting the vast variety of wet-chemically prepared nanoparticles.
References
1. Girard, P. P.; Cavalcanti-Adam, E. A.; Kemkemer, R.; Spatz, J. P., Cellular chemomechanics at interfaces: sensing, integration and response. Soft Matter 2007, 3 (3), 307-326.
2. Scheeler, S.; Ullrich, S.; Kudera, S.; Pacholski, C., Fabrication of porous silicon by metal-assisted etching using highly ordered gold nanoparticle arrays. Nanoscale Research Letters 2012, 7 (1), 450.
3. Ullrich, S.; Scheeler, S. P.; Pacholski, C.; Spatz, J. P.; Kudera, S., Formation of Large 2D Arrays of Shape-Controlled Colloidal Nanoparticles at Variable Interparticle Distances. Part. Part. Syst. Charact. 2012, (accepted).

Nanoporous materials, having a large geometrical area, can be employed as templates for metal nanoparticles deposition.
Recently germanium has received attention as electrode material and has been employed in different morphologies and electrode configurations.
Self-ion implantation allows to prepare stable nanostructured surface layer both in bulk Ge and in Ge thin films, allowing an easy control of the pore size and the pore depth. Actually, electrochemical analyses showed that nanoporous Ge has enhanced charge transfer properties mainly in the cathodic potential region, with respect to the unstructured crystalline or amorphous Ge substrates and this makes such a material a suitable candidate to be employed as template for electrodeposition of Au nanoparticles.
Here we report a study aimed to modulate the Au nanoparticles size and loading by changing the electrodeposition conditions, i.e. the deposition time and the concentration of the Au precursor. The goal of this work is to decorate the Ge walls with Au nanoparticles, avoiding particles aggregation.
This study demonstrates that small nanoparticles, with a mean diameter lower than 5 nm, with a narrow size distribution and homogeneously distributed on the pores walls can be easily prepared.
The resulting Ge electrodes coated with the Au nanoparticles can be successfully employed in the electrocatalytic reduction of iodoethane in acetonitrile solution, a reaction often chosen as a model in organic electrocatalysis. The main result is the observation, at a low cathodic potential (Ep2= -0.55 V vs SCE) of a defined reduction peak whose intensity is proportional to the amount of iodoethane in the solution. The reduction potential is very low if compared to other electrode materials recently reported in the literature for similar reactions and this demonstrates the applicability and the potential of this material in the electrochemical field.

Nanoalloy particles have gained much attention due to their enhanced chemical and physical properties compared to monometallic ones. Solid-state dewetting of metallic thin films is one of the simplest methods to create nanoalloy particles. In this work, dewetting of bilayer and multilayer thin films with thicknesses of 25 nm was used to form CoPd alloys. The thin films were annealed in forming gas ambient (10% H2) at temperatures ranging from 600-900°C. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) reveal that some of the CoPd particles have two different grains in one particle with different CoPd compositions, for example, one grain has 55 atomic % Co and the other grain has 59 atomic % Co. EDX also indicates that compositional variation among particles is more pronounced in particles formed by bilayer film compared to particles formed from multilayer films, for example, 58-63 at. % of Co for bilayer film c.f. 59-60 at. % of Co for multilayer film. Effects of the seeding layer, annealing temperatures and annealing times are also studied to understand the dewetting mechanisms for bilayer and multilayer thin films.

Semiconductor nanoparticles (NPs) are the focus of continuous research due to their potential applicability in many areas of technology [1] . One of their major advantages is the ability to fine tune their properties by varying certain parameters in their synthesis protocols. One of these parameters is the capping agent, which is the surrounding ligand that covers the surface of the NPs, commonly a molecular layer. The capping agent influences crucial properties of the NPs such as their size, surface passivation, and shape. In fact, it was recently shown that by replacing organic with atomic ligands it is possible to significantly change surface passivation, to enhance electronic transport and to raise the efficiency of quantum-dot photovoltaic devices [2].
Here we wish to show that in the case of NPs that are characterized by large thermally activated structural fluctuations, the capping ligands can be used to alter this dynamic behavior and, as a consequence, affect the related changes in the electronic structure of the NPs. We demonstrate this approach using highly anisotropic Bismuth (Bi) NPs which were prepared by colloidal synthesis and protected by two essentially different types of capping ligands: 1-dodecanethiol and ethylene di-amine tetra-acetate (EDTA). The NPs were probed by Transmission Electron Microscopy and Scanning Tunneling Spectroscopy in the temperature range between 80K and 300K. Both types of nanoparticles show temperature dependent structural fluctuations leading to pronounced changes in their anisotropic conductance properties as probed at 80K. We show that the different capping ligands dramatically alter the mechanism of structural dynamics in these particles. This finding suggests that molecular control of structural and consequently electronic switching in anisotropic nano-systems is feasible.
[1] A. P. Alivisatos. Semiconductor Clusters, Nanocrystals, and Quantum Dots. Science, Vol. 271 no. 5251 pp. 933-937.
[2] Tang J., et. al. Colloidal-quantum-dot photovoltaics using atomic-ligand passivation. Nature Materials, Vol. 10, 765-771 (2011).

One-dimensional nanotubes (NTs) that consist of multiple metallic components are promising platforms for potential applications, whereas only a few synthetic methods of multi-metallic NTs have been reported to date. In the present work, we developed a general synthesis route for the production of uniform multi-component one-dimensional tubular nanostructures with various combinations of Pt, Pd, and Ag by using ZnO nanowires (NWs) as sacrificial templates. The ZnO NWs serve not only as physical templates but also as nucleation sites for the reduction of metal precursors, and thereby several metal precursors could be reduced simultaneously to produce multi-metallic NTs. By using this approach, Pt-Pd, Pt-Ag, and Pd-Ag binary alloy NTs, and even Pt-Pd-Ag ternary alloy NTs could be successfully prepared. The prepared Pt-Pd binary alloy NTs exhibited improved electrocatalytic activity and stability toward ethanol oxidation due to their characteristic tubular morphology with well-interconnected nanoporous framework and synergism between two constituent metals. Furthermore, our approach can facilitate the fabrication of patterned multi-metallic NT arrays on solid and flexible substrates with strong mechanical robustness. The present templating method does not require any extra steps to remove templates or additional surfactants which are often required to control the shape of nanostructures. This strategy offers a convenient, versatile, low-cost, and highly valuable approach to the fabrication of multi-metallic nanostructures with various components and compositions.

In nanotechnology, scientists have been developed smaller and more compact devices to satisfy our growing demands. There are many challenges in nanotechnology to develop nanomaterials, manufacturing, functionalization, assembly, and integration since nanotechnology is a part of the molecular-domain. We demonstrate a microfluidic synthesis of MIP&’s nanoparticles, which can be produced by molecular imprinting technique for synthesizing receptor sites. The use of microfluidic reactors offers us a number of advantages over existing technology. For example, chemical reactions run in microfluidic reactors have shown high thermal and mass transfer rates with an opportunity to use more aggressive reaction conditions allowing for increasing product yields. Additionally, high chemical homogeneity, especially for nanoparticle synthesis can be also achieved by mixing multiple components at the micro-scale in microfluidic reactors. The microreactors can be coupled to additional manufacturing and functionalizing processes at the nano-scale to develop, for example, uniform assembly and integrations using those nanoparticles obtained from microfluidic reactors. Naoparticles directly produced from microreactors can be used to integrate into active devices or as part of bio-arrays by align nano- or periodicity. The overall object is to carry out the entire process of synthesis, functionalization, assembly, integration, and continuous operations for a scaling up, normally performed in a chemical laboratory efficiently using small amounts of reagents, which makes reactive motion smoothly.

This work presents a facile approach to centimeter-scale colloidal photonic crystals (PCs) with narrow stopband assembled on low-adhesive superhydrophobic substrates. The full-width-at-half-maximums of the stopbands are just 12 nm. The narrow stopbands of colloidal PCs are ascribed to the combined effects of perfectly-ordered assembly structure, large-scale crack elimination, decreased void fraction and sufficient thickness of the colloidal PCs. These properties are profited from self-assembly process on a low-adhesive superhydrophobic substrate. Latex suspension on this substrate displays a receding three-phase contact line during evaporation, which releases tensile stress induced by latex shrinkage and results in complete elimination of cracks in the colloidal PCs. Furthermore, the simultaneous assembly of latex particles on the outermost layer of a spread liquid film contributes to the perfectly ordered assembly structure. This facile fabrication of centimeter-scale colloidal PCs with narrow stopbands will offer significant insights for the design and creation of novel optical devices.
This work has been accepted by J. Am. Chem. Soc. DOI: ja-2012-04751k. In press.

Nanoparticle arrays have been garnering much interest in recent research for their potential applications in sensors, filters, photonic crystals, and electronic materials. Hybrid nanoparticle-molecule arrays are of particular interest as electronic materials because the nanoparticles act as “artificial atoms”, and the molecules that interlink them control the electronic coupling between particles by controlling both the width and height of the energy barrier. In this work we have studied both the self-assembly processes and electronic properties of hybrid 2-dimensional nanoparticle-molecule arrays.
We have formed and characterized nanoparticle arrays of varying dimensions, particle sizes, and ligand lengths via multiple deposition methods. Commercially available nanoparticles in aqueous solution are transferred to organic solution, and their capping layer is replaced with alkanethiols or alkylamines. Liquid-phase assembly and microcontact printing have been investigated to enable controllable multilayer and monolayer formation on substrates. The resulting arrays have been characterized by Scanning Electron Microscopy (SEM) to determine the thickness and orderliness of the arrays and enable extraction of quantitative information about particle monodispersity and interparticle separation.
The molecular linkers have an important effect on the electronic properties of the nanoparticle arrays. Different molecules have varying lengths, bonding mechanisms, and energy gaps. By controlling the nanoparticle capping ligand in solution, or by performing post-deposition molecule exchange, we can investigate the effects of tunneling barrier height and length on electron transport through arrays. Furthermore, controlling the size (diameter) of particles in the arrays and varying the ambient temperature can allow investigation of charging and coulomb-blockade effects on transport. Forming these arrays on top of microfabricated electrode devices has allowed us to study the array&’s effective sheet resistance as a function of array size, nanoparticle size and separation, and energy gap of the molecular interlinker.

We describe a new method referred to as “silica-assisted” for the easy synthesis of discrete and highly dispersible mesoporous carbon nanospheres, hollow mesoporous carbon nanospheres, and yolk-shell mesoporous carbon nanospheres that have both tailorable particle size and cavity structure by using phenolic resols as a polymer precursor, tetraethylorthosilicate as an inorganic precursor, commercial available hexadecyl trimethylammoniumchloride as a template. Carbonization was followed by etching of the silica in the carbon/silica nanocomposite, resulting in the formation of mesoporous carbon nanospheres. The mesostructures were retained while the spherical diameters were tuned from 180 nm to 850 nm by simply varying the ethanol concentration for these three types of mesoporous carbon nanospheres. Through the presence of silica in the walls, additional porosity is produced by its removal and shrinkage is reduced during carbonization; therefore, very high porosity is created. All three types of mesoporous carbon nanospheres exhibit promising properties for supercapacitors with high capacitance and favorable capacitance retention, showing great potential in prospected applications of energy conversion, storage and as adsorbents for drug delivery and water treatment processes.

Deterministic nanoparticle assemblies dispersed in solution have numerous interesting applications, including in vivo sensing or imaging based on Surface Enhanced Raman or Fluorescence Spectroscopy, but fabricating such assemblies with consistent structure remains a challenge. Self-assembly in solution can be used to rapidly generate large numbers of aggregates, but it is difficult to maintain consistent morphology and particle number across all aggregates. Lithographically directed self-assembly has been used to fabricate arrays of nanoparticle assemblies with specific geometry, but these assemblies are typically trapped in wells or otherwise confined on a substrate, limiting transfer into solution. Here we present a technique to address this problem through a combination of lithography and self-assembly. First, we define a large area array of flexible nanopillars by deep UV and nanoimprint lithography. We then deposit a thin metal layer on top of the pillars by e-beam evaporation. When these pillars are exposed to a volatile liquid and allowed to dry, microcapillary forces pull the pillars together, collapsing the metal nanoparticles on top of them into deterministic assemblies. Molecules included in this volatile liquid can be designed to maintain nanometer-scale gaps between the nanoparticles in these assemblies. These spacer molecules can also include Raman or fluorescence tags, which are then simultaneously trapped between nanoparticles in “hot spots” for Surface Enhanced Raman or Fluorescence Spectroscopy based imaging or sensing applications. The nanoparticle assemblies are released into solution by dissolving a sacrificial layer, maintaining their structural integrity due to the binding of spacer molecules with specific terminal groups, or through the use of an oxide coating.
To demonstrate the feasibility of this process, Au nanoparticles with a height of 70 nm and diameter of 120 nm were assembled into uniform pentamers and transferred to solution using two different sacrificial layer schemes. In the first scheme, a 20 nm Al layer is included under the Au particles. The Al is dissolved in a dilute hydrochloric acid solution after assembly. In the second scheme, the gold particle assemblies are transferred off of the nanopillars and into a 200 nm thick PMMA film by thermal imprinting. The PMMA is dissolved in acetone, releasing the particles into solution. SEM images of the residue of dried solutions verify the presence of a relatively high density of gold pentamers in solution that maintain their original structure. Structural integrity was demonstrated using thiol terminated molecules as well as with a 10 nm silicon oxide coating. The oxide coating also serves as a surface for silane-based functionalization schemes. Based on standard nanofabrication processes, this approach provides a flexible technique for fabrication of 2D deterministic nanoparticle assemblies in solution compatible with a wide variety of material systems.

Chiral plasmonic nanoparticles have been predicted to exhibit both strong circular dichroism in the visible spectral range and non-linear optical effects. These properties open up applications for chiral nanoparticles in sensing, enantiomer separations, and non-linear optics. Unfortunately, to date the fabrication of colloidal nanoparticles with chiral shape has posed a significant challenge due to a very limited ability to transfer chirality from chiral template molecules to nanoparticles. Here we report a novel route to enantiopure chiral gold nanoparticles. Importantly, we do not use in principle any chiral molecules or biomolecules and therefore create chiral shapes artificially. Template stripping is applied to achiral silicon wafers to prepare nanoparticles with chiral shape of only one handedness and with sizes between 100 nm and 1 micron. Both experimental and simulated circular dichroism spectra from suspensions of the template-stripped chiral nanoparticles will be discussed.

Lattice mismatch in a bimetallic core-shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. This work reports on the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd interfaces in core-shell nanoparticles. The nanoparticles present a Au octahedral core 11 nm in size, while the Pd shell thickness layer is varied from 3 Pd(111) layers up to 10 nm. Pd starts growing on Au(111) layers form into cubic shapes. This change in geometry is interesting since it will change the size of the Pd (111) surfaces, changing the mechanism to release strain in the nanoparticle. Our results show direct imaging with atomic resolution that Shockley partial dislocations (SPD) combined with stacking faults (SF) at the outer Pd layer is the first mechanism to release interfacial strain. Subsequently, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations for a wide range of Pd thickness. Finally, the diffusion of Au into the Pd layer (as confirmed by energy dispersive x-ray spectroscopy) will move the dislocations to the free surfaces, leaving behind most of the nanoparticle defect-free. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shells growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles.

Over the last 15 years, colloidal semiconductor nanocrystals (NCs) or quantum dots (QDs) have proliferated as an alternate opto-electronic material used in photovoltaics, photodetection, color conversion or fluorescent labeling. This application development requires materials with predefined sizes and low size dispersion in larger quantities. As a result, research on the hot injection synthesis - which is typically used to synthesize these materials - is focusing on optimization and scale-up. This involves the high throughput screening of various synthesis parameters to achieve a desired end result, preferably at close to full chemical yield. Essentially, this involves a search for relations between the reaction conditions and the properties of the synthesized NCs, such as size and size dispersion.
Here, we use a combination of reaction simulations and experimental synthesis screening using an established CdSe NCs synthesis to map different reaction conditions/nanocrystal property relations and link them to specific simulation parameters. We first show that the simulation model, which combines established expressions for the rate of NC nucleation and growth with the finding that a monomer formation reaction precedes the formation of NCs, captures the main features of the time development of the CdSe synthesis used.[1] Based on the simulations, we predict that the size NCs obtain at close to full yield can be tuned either by changing the rate of monomer formation or by changing the time span of nucleation. For both predictions, we find experimental evidence using the synthesis of CdSe NCs. First, we show that increasing the precursor concentrations results in a faster reaction and a decrease of the NC size, in line with the predicted link between monomer formation rate and nanocrystal size. Second, we find that increasing the concentration of free carboxylic acid leaves the reaction rate constant, yet results in larger NCs. In accordance with the simulations, we interpret this in terms of a reduction of the time span of nucleation linked to an enhanced monomer solubility.
We demonstrate that these findings are not limited to the specific CdSe NC synthesis used. We therefore conclude that the enhanced understanding of reaction conditions/nanocrystal property relations following from this work provides a conceptual basis for developing size tuning strategies for the hot injection synthesis.
[1] S. Abe et al., ACS Nano 2012, 6, 42-53

Nanomaterials play an important role in lubrication and energy application or, in general, in surface technology. They can provide special properties to the treated surface. For creating e.g. electrical conductivity on the surface, either ILs or nanomaterials (CNTs, Ag) can be applied, e.g. to a polymer. Over the past years the combination of ionic liquids and nanomaterials was investigated in more detail. Since nanomaterials often have to be dispersed in order to process them and in order to allow a safe handling of these materials, IoLiTec has developed its IL-Dispersion-Technology, allowing to form a broad variety of nanomaterials of stable dispersions in different solvents, if ionic liquids are added as dispersants.
Ionic liquids (ILs) - new materials that consist entirely of ions and are liquid at temperatures below 100°C - show an interesting and often unique set of physical and chemical properties that cannot be found in other materials. These unique properties include e.g. low vapor pressure, non-inflammability, good electrical and thermal conductivity, good heat capacity, tunable viscosities, (electro-)chemical and thermal stability (above 250°C), and tunable miscibility with other solvents. In addition, they dissolve a number of different substances, which are often only partially soluble in other solvents
In our contribution, the use of ILs as green solvents for the synthesis of nanoparticles will be highlighted. Furthermore, the preparation and stability analysis of dispersions of nanomaterials such as CNTs, fullerenes or graphenes using ILs as stabilizing agents will be presented. Results for dispersion stability are obtained by Photon-Cross-Correlation Spectroscopy-technique (PCCS, Nanophox®). We will further report, how inkjet-like printing of conductive nanomaterials dispersions decrease the surface resistance compared to the uncoated surface.

Ordered arrays of colloidal particles are promising building blocks for future optoelectronic devices such as sensors, waveguides or photovoltaic cells. A versatile method for producing such arrays is the convective assembly of particles on topographically structured templates.[1] Recently, surface-wrinkled elastomers have been utilized as templates for the fabrication of highly regular nanoparticle chains with submicron line spacing.[2] While this simple and lithography-free procedure is compatible with a variety of functional particles, potential technological applications require a subsequent transfer of the formed colloidal assemblies onto flat solid substrates. In this contribution we present a novel transfer process in which colloidal assemblies are transferred by capillary forces.[3] In contrast to classical “lift-off and transfer” methods, conformal contact between the particles and the target substrate is not required. Colloids carrying either surface bound charges or polyelectrolyte brushes are employed to study the influence of interfacial properties on the transfer process. It turns out that successful transfer of such particles depends strongly on the wettability of the target substrate and can be completely suppressed by a hydrophobic self-assembled monolayer. We demonstrate that chemically patterned substrates grant access to locally controlled particle transfer with high precision. The resulting hierarchical particle assemblies display features on the micron and submicron scale, while covering macroscopic surface areas. Multiple deposition steps can be conducted subsequently, yielding more complex colloidal assemblies than so far accessible by wrinkle-assisted self-assembly. Further, we show how the optical properties of the coated substrates depend on the arrangement the deposited nanoparticles. The possibility to break the symmetry of colloidal assembly in a controlled fashion opens avenues for the realization of complex structures with potential applications in plasmonic sensing or the construction of metamaterials.
1. Yin, Y.D., et al., Template-assisted self-assembly: A practical route to complex aggregates of monodispersed colloids with well-defined sizes, shapes, and structures. Journal of the American Chemical Society, 2001. 123(36): p. 8718-8729.
2. Lu, C., H. Möhwald, and A. Fery, A lithography-free method for directed colloidal crystal assembly based on wrinkling. Soft Matter, 2007. 3(12): p. 1530-1536.
3. Müller, M., et al., Wrinkle-assisted linear assembly of hard-core/soft-shell particles: impact of the soft shell on the local structure. Nanoscale, 2012. 4(7): p. 2491-2499.

Self-assembly of semiconductor nanorods into close packed superstructures where each nanorod adopts a side by side and uniform axial orientation is an area of intense research interest allowing unique materials to be realized by precisely tuning the placement of each nanorod building block. This geometry would allow the collective properties to be maximized in a densely packed superstructure and have a potential applications ranging from field emission devices to nanorod photovoltaics. To date, significant progress has been seen in the development of procedures and understanding for the formation of superstructure with perfect facets for spherical nanocrystal by slow crystallization but there is no such report for the nanorod crystallization. Here we present the complete colloidal crystallization of nanorod into micron-size hexagonal superstructure with well-defined facets habits. The growth mechanism for nanorod supercrystals is more complicated than that for spherical nanocrystal as it requires that an incoming nanorod should orientate vertically before landing on the most preferred site on the growing supercrystal. This has been achieved when highly monodispersed nanorod solution was allowed to crystallize slowly over time by a traditional destabilization-driven assembly approach. The nanorod superstructure are extensively characterized by HRSEM, DF-STEM, TEM, and XRD.

Forward Osmosis (FO) technology has been intensively studied for its use in desalination, water reuse, as well as protein enrichment processes and power generation. Forward osmosis utilizes the osmotic pressure difference of two solutions separated by a semi-permeable membrane to induce spontaneous movement of water molecules from the less concentrated solution (feed solution) to the other solution (draw solution) while most solutes are rejected by the FO membrane. The selection of a suitable draw solute can greatly influence the efficiency of FO. In general, entitled draw solutes in FO for water production possess the qualities of being able to generate high osmotic pressures and easy recovery of the water obtained. Magnetic nanoparticles with hydrophilic surface functionality and high surface area-to-volume ratio may generate high osmotic pressures for desalination and water reclamation purposes. Although draw solute based on magnetic nanoparticles can be regenerated using magnetic fields, high field strength is generally required. Therefore, we designed a new class of “smart” draw solute -- thermoresponsive polymer-functionalized magnetic nanoparticles. With the assistance of thermal stimuli-induced aggregation, the nanoparticle draw solute can be readily recovered.

Vertically aligned carbon nanofibers (VACNFs) were grown by plasma-enhanced chemical vapor deposition using Ni nanoparticle (NP) catalysts that were deposited by airbrushing onto Si, Al, Cu, and Ti substrates. For VACNF growth on metal foils, Si micropowder was added as a precursor for SiN_x coatings on the VACNFs that impart mechanical rigidity. Growth of carbon nanostructures on Cu is particularly noteworthy because the miscibility of Ni with Cu poses challenges for VACNF growth, and carbon nanostructures anchored to Cu substrates are desired as anode materials for Li-ion batteries. Free-standing VACNF arrays embedded in polydimethylsiloxane (PDMS) were obtained by spin coating PDMS onto VACNF arrays, curing, and then etching away the Al. The VACNF arrays protrude from the PDMS film and can penetrate cell membranes. A free-standing VACNF array in PDMS was functionalized with pVENUS-C1 plasmid and was used for impalefection of human brain microcapillary endothelial cells.

A new structure for nanoshell composition is presented. This structure consists of a spherical barium titanate (BaTiO3) core and a gold shell. The combination of self-assembly method and seed growth technique was used to synthesize the gold nanoshells (S.J.Oldenburg et al., Chem. Phys. Lett., 288:243-247, 1998). As first step to functionalize their surface with amine groups, the core nanoparticles were treated with (3-aminopropyl) triethoxysilane. Barium titanate is not a trivial material to be functionalized, as a consequence, this step is considered a particular important starting point to achieve a proper final product. The amine groups on the surface were then exploited for a proper gold seeding, so that the electrostatic force between these positively charged groups (at the appropriate pH conditions) and the negatively charged gold nanoparticles with which they were in reaction, allowed a very homogenous seeding to be obtained. Gold nanoparticles were synthesized following the method pioneered by Weiser (H.B. Weiser, The colloidal elements, Wiley, 1933). To achieve the gold shell, the gold seeds on the surface were further reduced in reaction with a reducible gold salt. Sodium borohydride was the reducing agent used. The presence of the gold seeds on the surface provided proper conditions for the attachment of reduced gold ions to the gold seeds. This helped the seed particles to start coalescence and eventually to form the shell. FTIR, UV-Vis and Raman spectroscopy, as well as TEM were the characterization methods exploited to monitor the assembly process. The results revealed changes in the optical features of the composite nanoparticles corresponding to the coverage density of the core particles by the gold shell. Results from FTIR spectroscopy confirmed a suitable bonding of the APTES molecules with the surface of the core material and thus the presence of the amine groups. The UV-Vis absorption spectra at different steps were collected. By gradually growing the metal shell, the results from UV-Vis analysis demonstrated a red shift of the Surface Plasmon Resonance (SPR) position, from visible to near infrared region of the electromagnetic spectrum, a region of particular interest for biological applications. Images from synthesized gold nanoshells were recorded by TEM and confirmed the former results, showing a quasi-complete coverage of the core by metal shell. As a supplementary method and to study the different resonance modes of plasmons we performed Raman Spectroscopy (FarrokhTakin E. et al, Collids Surf. A, DOI 10.1016 /j.colsurfa.2012.09.021). The photothermal properties of the nanoshells were verified through a dedicated set up through which we could lively record the temperature increase in the media containing the nanoshells exposed to a laser beam (wavelength 800 nm). Finally, preliminary in vitro evaluations on neuroblastoma cells showed convincing results for promising use of this new structure for hyperthermia therapy.

Nanoscience is driven by the curiosity of the unknown but yet existent vast possibilities to develop new materials with novel properties. The most important factor in the fabrication of functional nanomaterials is concise control over the architecture of such systems, i.e., size, composition, structure and pattern formation. The selected fabrication route of a nanomaterial determines its competence for any designated application.
Pure self-assembly techniques provide some means to control feature size and architecture to orders as low as a few nanometres and are practically applicable since the resulting structures are pre-programmed in the molecular structure or colloidal properties. Structures achieved thereof can later serve as foundation stones for the further development of hierarchal nanostructures. Such configurations provide domains within which the functionality of the resultant system can be exploited in a synergistic manner to enhance or impede physical phenomena, to pitch the performance of future nanomaterial-based devices.
This presentation will elucidate the facile achievement of two-dimensional (2D) arrays of multi-functional nanoparticles arranged in triangular lattice on various substrates via self-assembly route. Emphasis will be laid on the vehement impact of minute alterations in the fabrication process on the optical properties of the nanoparticles. Furthermore, an illustration on how these changes can be exploited to synthesize and tailor the architecture of silicon nanotubes under mild synthesis conditions will be shown.

Surfactants or surface-functionalizing molecules such as PEG (polyethylene glycol) are essential for synthesis and stabilization of inorganic colloidal nanocrystals. However, they often disturb physical and chemical behaviors of the particles thus making it challenging to manufacture well-stabilized surfactant-free colloidal systems. We present a lanthanum phosphate nanorod suspension exhibiting a spontaneous liquid crystalline (LC) organization thanks to the stabilization of the nanorods without using a surfactant.[1] Nanorods were synthesized via hydrothermal route carefully controlling the temperature variation - rapidly heating up the precursor mixture from low to high temperature (0°C→160°C) - that allowed to avoid aggregation. Then the nanorods were transferred and concentrated in ethylene glycol (EG) solvent for the permanent solubilization by complexation of EG molecules on the charged particle surface as the same with PEGs. Due to the exceptional dispersion stability in EG, as-prepared nanorod suspension shows a clear LC behavior following the Onsager&’s lyotropic model, which has been easily interrupted by aggregation or gelation in other systems. The absence of surfactants or surface-functionalizing molecules permitted the observation of the LC phase transitions (isotropicharr;nematicharr;columnar) by polarization optical microscopy and SAXS analysis on the wide range of ionic strength (10^-4~10^-1M) and particle density (up to 30wt%) so that a complete phase diagram was established. A remarkable feature of this inorganic LC system is an efficient electro-optical switching ability, i.e. optical Kerr effect, associated with high optical transparency, which is promising for real applications in devices (e.g., smart windows and active optical retarders).
[1] J. Kim et al., Adv. Funct. Mater. doi: 10.1002/adfm.201200825 (2012)

Nanoscaled poly(styrene-block-acrylic acid)(PS-b-PAA) fibers covered with a silica shell with average diameter ranging from 100 to 500nm were obtained via coaxial electrospinning. The thermal stability of the silica shell enables us to anneal the PS-b-PAA fiber at higher temperature and longer time to get various self-assembly morphology including stacked lamellar disk and alternated concentric cylinders. Multifunctional PS-b-PAA nanofibers with palladium (Pd) nanoparticles selectively depositing on one of the domains were fabricated by electrospinning the THF solution of the diblock copolymer mixed with palladium chloride (PdCl2) after by in-situ reduction of the palladium ions with NaBH4 aqueous solution. To investigate the distribution of the Pd nanoparticles, we observed that these nanoparticles are mostly sequestered into the PAA domains formed in the self-assembly structures and migrate with them during annealing without obvious aggregation. This result meets our expectation since the Pd ions are marginally selective with respect to the electronegative PAA domains through electrostatic attraction. In addition, it is observed that the Pd nanoparticles prefer to stay near the domain boundaries. These multistructured composite nanofibers serve as a template for further investigation on the interactions between the nanoparticles and the domains.

Significant progress has been made during the past decade in preparing nanosheets from a wide range of materials, which are actively pursued for various applications such as energy storage, catalysis, sensing, and membranes. One of the next critical challenges is developing a robust and versatile assembly method which allows construction of the nanosheets into functional structures tailored for each specific purpose. An interesting characteristic of nanosheets is that they often behave as charged macromolecules, and thus can readily interact with an oppositely charged polyelectrolyte to form a stable complex. In this report, we demonstrate how such complexation process could be utilized for directing the self-assembly of nanosheets. By confining the nanosheet-polyelectrolyte complexation at air-liquid or liquid-liquid interfaces, the nanosheets are successfully assembled into various mesoscale architectures including fibers, capsules, and films. Furthermore, incorporation of additional components such as nanoparticles or small molecules can be easily achieved for further tailoring of material properties. This novel assembly method opens pathway to many useful nanosheets superstructures, and may be further extended to other types of nanomaterials in general.

We model stabilization of clusters and lattices of spherical particles with dominant electric and magnetic dipolar coupling, and weak van der Waals coupling. Our analytical results [1] demonstrate that dipolar coupling can stabilize nanoparticle clusters with planar, tubular, Möbius, and other arrangements. We show the effects of interparticle vdW coupling and entropic effects associated with different lattice arrangements at finite temperatures. We also explain for which parameters the nanoparticles can form lattices with fcc, hcp, sh, sc, and other types of packing. Although these results are valid at different scales, we illustrate that realistic magnetic and semiconducting nanoparticles need to have certain minimum sizes to stabilize at room temperature into nanostructures controlled by dipolar coupling. The obtained results can provide guidance for the self-assembly of unique structures at different scales, but their formation might require a careful control of the particle kinetics. The assembled particles can have applications as new materials for electronics, magnetism, and optics.
[1] Baskin A. and Král P. Clusters and Lattices of Particles Stabilized by Dipolar Coupling, ACSNano 2012, 6, 6083-6090.

There have been significant advances recently in the use of magnetic nanoparticles for various biomedical applications, with one potential use as contrast enhancement agents in magnetic resonance imaging (MRI). In order to study the effect chain formation on MRI contrast enhancement and its relationship with the stabilizing brush length, a matrix of 22nm particles with varied ligand lengths was synthesized using iron oxide particles with poly(ethylene glycol) ligands. These systems were characterized with dynamic light scattering, transmission electron microscopy, dark-field scattering, and proton transverse relaxation measurements. The dark field scattering experiments and transverse relaxation measurements were done in a similar magnetic field under the same time scale to correlate the reduction of the transverse relativity with the formation of linear magnetic chains. Our results suggest that varying the ligand length has a direct effect on the transverse relaxation mechanism due to the contribution of ligand length to the colloidal stability of the system, including differences in chain formation rate and size. With increasing ligand length, interparticle interactions are limited, which results in slower chain formation and shorter widespread chains. This data indicates that understanding the colloidal arrangement of these systems is paramount, and that both particle stability and time dependence both play a key role in determining the effect of iron oxide nanoparticles on surrounding water protons.
In this talk we will discuss the synthesis of unique heterobifunctional polymers, magnetite particle synthesis and functionalization, as well as calculations of interparticle interaction based on a modified DLVO theory.

Nowdays, as to prepare the highly desirable controlled drug delivery system that can release the loaded drug in the specific environments by responding to external stimuli, a variety of stimuli-responsive surface-functionalized, end-capped mesoporous silica nanosphere (MSN) have been developed based on various gatekeeper release mechanisms, because of the stable mesoporous structures, large surface areas, the ability to easily functionalize the external (or internal) surface and especially the advantageous “zero premature release” property. However, most of these systems are complicated to synthesize, and the removing of caps might induce toxic reaction or molecules which cannot be produced by cells to human bodies.
Taking into account of the disadvantages of current MSN controlled drug delivery systems, we were particularly interested in developing easily synthesized systems showing delivery functions triggered by inputs existed in bio-system. Based on this, a MSN-based controlled-release delivery system has been synthesized and characterized using L-cysteine derivatized gold nanoparticles (AuNPs) as removable caps to encapsulate drug molecules inside the amino functionalized MSN mesoporous framework. Instead of the complicated and hardly synthesized chemical bond, the encapsulating mechanism involves ion-ligand bond between AuNPs, Cu2+ and MSN, which make our system be prepared efficiently. These tiny amount of Cu2+ existing in the system (3.91 ppm by ICP) is close to the minimum dietary value for healthy growth in mammals, making our system has negligible cytotoxicity to the living cells, which has been revealed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Moreover, the developed platform operates in aqueous solution and can be triggered by two simple external stimuli such as pH changes or adenosine triphosphate (ATP) adding. When the system pH is 4, obvious breaking of the ion-ligand bond of AuNPs, Cu2+ and MSN (AuNPs-Cu2+-MSN) takes place between Cu2+ and MSN, which results in rapid delivery of the captured drugs from the pore voids into the aqueous solution, and no leaking of Cu2+ into the solution. However, at pH 5 the pores are capped with AuNPs and the delivery is strongly inhibited. The kinetics of the delivery was studied at different pH, assuming a simple diffusion process. It is possible to deliver drugs in small portions by carrying out onminus;off aperture cycles via changing the pH from 4 to 5. AuNPs also open the possibility of ATP as a suitable stimulus for release procedures using the stronger ion-ligand bond between Cu2+ and ATP than that between Cu2+ and amino group on MSN. The former ion-ligand bond not only leads the cleavage of the latter one that anchors the AuNPs to the surface of the mesoporous silica-based material, but replaces the latter one forming new ligand complex with AuNPs and Cu2+, allowing the release of the entrapped drugs and no release of Cu2+.

Ensembles of 100 µm long Si microwires with ferromagnetic Ni coatings have been oriented vertically in the presence of magnetic fields. The vertical alignment and lateral spacing of these ensembles have been characterized using X-ray diffraction and image analysis of optical micrographs. The degree of vertical alignment and minimum field strength required both depended on the length of the microwires and the thickness of the Ni coating. Longer microwires experienced more magnetic torque and aligned at lower field strengths than shorter microwires. Thicker Ni coatings on the microwires enabled a higher percentage of vertical alignment at a given magnetic field strength. Additionally, the surface interactions of the substrate and solvent were tuned to produce more facile alignment of the microwires. Microwire ensembles with vertical alignment over 97% within ±5° of normal were achieved over cm2 scale areas, and the oriented microwires were successfully embedded into polymer membranes with lateral and vertical ordering retained. The magnetic alignment of micron scale Si wires was investigated, however this procedure is equally applicable to the assembly of high aspect-ratio nanowires and nanorods. This method is of interest for the clean-room-free fabrication of flexible, array-based solar and electronic devices, in which preferential orientation of microwire-type objects is desired.

Conductive metal line is an essential element in electronics. Conventionally, the metal interconnect is fabricated by photolithography, vacuum deposition or electroplating. However, these processes either require expensive facility or generate large volume of hazardous waste. Inkjet printing of metal nanoparticle is an attractive method for direct patterning of conductive lines owing to low cost, low waste and simple process. In this paper, we synthesized air stable metal nanoparticles (Ag, Cu) with a capping polymer by chemical reduction method, from which a conductive ink applicable to inkjet printing is formulated. XRD, SEM and TEM were used to characterize the morphology of nanoparticles and printed films. Four-point probe was used to monitor the conductivity of the printed films. It was found that the properties of printed metal lines, such as conductivity and printing resolution, depends on the characteristic of the metal nanoparticle used and the formulation of the ink. We also investigated the sintering processes that are compatible with plastic substrate, including low temperature thermal sintering at 100-150 °C and photonic sintering at room temperature.

Magnetic nanoparticle(MNP) suspensions have been studied actively in recent years due to a variety of technological and biological applications like site-specific targeted drug delivery, magnetic hyperthermia, manipulation of cell membranes, and magnetic resonance imaging.

The magnetic nature of the suspension attributes some inherent tendencies such as clustering and chaining of MNPs. The aggregation dynamics of magnetic nanoparticles is governed by a large number of factors including material parameters as well as external parameters. The presence of an external force field enhances the aggregation process in MNP suspensions. This is reported in a large number of research papers. It is important to understand these influences as most biomedical application of MNP suspensions require a smooth flow of these through blood vessels when used in vivo as well as in in vitro assays without aggregating and settling.
In this work, we report on the effects of external magnetic fields along with gravity within these suspensions. The direction of the applied field affects the orientation of chains formed due to the presence of magnetic field. Apart from this, the particle size and material parameters also play a significant role in aggregation dynamics. The properties of the magnetic suspension can actually be tailored by varying the amplitude and direction of the applied field as well as particle size. Light intensity measurements of a colloidal suspension are observed for different particle sizes by varying the direction of the applied field. The aggregation and sedimentation behavior is observed by monitoring light transmission coefficient versus time measurements taken using PMD connected to the system.
The present work aims at estimating the effect of presence of a low field in different directions on the aggregation dynamics of MNP suspensions. The influence of gravity can be minimized by appropriately choosing the magnitude and direction of the applied field. The aggregation rate is altered with the direction of the applied field as seen by light intensity measurements. These real time measurements describe the behavior of the magnetic nanoparticle suspensions as they progress through the body during numerous applications like targeted drug delivery under the influence of an external field. It is also possible to extract information about fundamental processes responsible for aggregation and sedimentation of magnetic nanoparticles, we estimate the aggregation dynamics by growth models that correctly predit both short-term and long-term stability of the MNP suspensions.

Different chain length of poly(vinyl pyrrolidone)-b-poly(ethylene glycol) diblock copolymers were synthesized through the reversible addition-fragmentation transfer-mediated(RAFT) polymerization. Monodisperse silver nanowires with little nanoparticals were synthesized through a simple one-step method by reducing AgNO3 with ethylene glycol in the presence of PVP-b-PEG diblock copolymer without seed forming procedure. The diameter of silver nanowires can be controlled by changing the molar ratio of AgNO3 and PVP-b-PEG diblock copolymers from 100nm to 700nm with the average length of 17mu;m. Importantly, these nanowires can disperse in not only polar solvent such as ethanol but also non-polar solvent like toluene and THF. This may be attributed to the PEG block tails on the surface of silver nanowires.

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. Moreover, 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. For this work, spherical submicrometer-sized silica particles were prepared by the sol-gel technique and deposited as a self-assembled monolayer onto high-purity silica glass plates by means of a spin coater system. This monolayer is then used as a mask to create regular arrays of nanoscale features in the sample, either by MeV Ag ion implantation or by Ag evaporative patterning of metallic deposits. On the other hand, previously to the ion implantation or metal evaporation, the masks can be modified by Si ion irradiation to tailor the size and arrangement of these embedded features or metal deposits as a function of the ion fluence. Indeed, amorphous glassy materials like silicon dioxide can undergo extreme deformations under exposure to high-energy beams, which induce damage and structural changes in solids due to energy losses of MeV heavy ions via ionization events and atomic collisions. Some of the samples were irradiated at room temperature with Si ions at 4 and 6 MeV under an angle of 90° with respect to the sample surface. After the irradiation the silica particles turned into oblate particles, as a result of the increase of the particle dimension perpendicular to the ion beam and the decrease in the parallel direction. By this way, the mask openings of the silica particle monolayer were modified down to the nanoscale and a subsequent Ag ion implantation or Ag thermal evaporation allowed the formation of ordered arrays of Ag nano-objects, after removal of the silica particles. The size, size distribution and shape of both the silica particles and the array of metallic deposits were determined by scanning electron microscopy as a function of the preparation and ion irradiation parameters. Finally, the long range order of the nanoparticle assembly and its plasmonics properties were characterized by means of a Fast Fourier Transform study and optical absorption measurements, respectively.

Mixing in microscale is challenging as the flows are laminar and Reynolds numbers are generally low (Re ~ 0). Therefore, even though diffusion in this length-scale is fast, creating turbulence to increase the contact area where the molecules can diffuse is very difficult. To overcome this problem, various types of active and passive micromixers have been designed to facilitate mixing in microfluidic systems. In this work we show how specially fabricated colloidal microswimmers which have an inherent spin, and which demonstrate spiralling trajectories, can be used as nanoscale and microscale mixing devices. To determine the degree of mixing imparted to the solution surrounding these mixing devices we have determined the diffusion coefficient and the average velocity of colloidal tracer particles adjacent to the micromixers. In the absence of the fuel for the mixing particles, the obtained diffusion coefficient for the neighbouring particles is in accordance to its theoretical value and the average velocity of these particles is virtually zero demonstrating a pure Brownian motion. In the presence of the fuel, the spiralling motion of the micromixers dramatically increases the average velocity and the diffusion coefficient of the neighbouring particles, equivalent to a change in size, an increase in “solution temperature” or a propulsive behaviour. Finally, we show that the rotation speed of the micromixers can be controlled by modifying the fuel concentration of the solution.

Nanocrystals with different morphologies such as nanorods, nanotubes, nanorings, nanowires, and nanoflowers can be synthesized experimentally. However, formations of diverse and highly asymmetric morphologies typically cannot be expected from crystal symmetry. For example, crystal bending and curling are unexpected, given that they generate lattice strains that increase the system energy. Nevertheless, in hydrothermal processing of ~ 4 nm anatase particles, we observed the formation of curved anatase nanorods elongated along one <111>. These nanorods were produced by oriented attachment (OA) of anatase particles on {101} surfaces. To understand why curved nanorods were formed, molecular dynamics simulations were used to study the energetics of both linear and curved anatase nanorods formed by OA. Results show that the energy of the curved anatase nanorods is actually lower than that of the linear ones, in contrast to conventional wisdom. In principle, OA growth tends to progress in energetically favorable orientations. For OA of anatase on {101}, one energetically favorable growth direction is [001]. Thus, in attachment propagating along one <111>, an attaching particle tends to tilt toward [001]. This forms a curved nanorod, despite the creation of strains on attaching boundaries due to imperfect lattice matching. The strain energy is offset by a portion of the long-range electrostatic interaction energy of atoms in the curved nanorod. The latter effect compensates for the increased strain energy thereby lowering the total system energy below that of the linear nanorod. Our results indicate that formation of asymmetric, curved nanocrystal morphologies is actually favored due to minimization of system energy by changing crystal shapes.

Bimetallic nanocubes synthesized by seed-mediated growth have the advantage of coupling the optical or catalytic properties of one metal with those of another metal and form multifunctional nanocrystals. Nanocrystals with concave faces have attracted great interest because of the high-index facets on surfaces. Recently, we have studied two kinds of bimetallic concave nanocubes, Rh on Pd seeds (Pd@Rh) and Au on Pd seeds (Pd@Au). High resolution transmission electron microscopy (HRTEM), aberration (Cs) corrected high angle angular dark field (HAADF) - scanning transmission electron microscopy (STEM) with energy dispersive x-ray spectroscopy (EDS) have been proven to be an unique and effective site-specific analysis tool at atomic and nano scale to study the crystal structure and chemistry of nanocrystals. We report here the structure and chemistry of bimetallic concave nanocubes synthesized by controlled kinetics seeded growth and characterized by HRTEM, HAADF-STEM/EDS techniques.
STEM/EDS mapping and line scans confirm that the out-extending corners and edges were dominated by Rh or Au, while the cubic core was essentially made of pure Pd. HRTEM and HAADF-STEM images reveal the continuous lattice fringes from the Pd core to the Rh or Au shell, which indicates an epitaxial relationship between the core and shell metals. Distinct atomic steps extending from the corner to the edge suggest that the overgrowth of Rh or Au atoms started from the corners of a Pd seed and then extended to the edges. Through TEM characterization, a site-specific growth mechanism of the bimetallic concave nanocubes has been demonstrated. [1-2].
[1] S. Xie et al., Angewandte Chemie - International Edition 51 (2012) 10266.
[2] G. He et al., ChemCatChem 4 (2012) 1668.

Colloidally synthesized semiconductor quantum dots (QDs) receive substantial attention as candidates for next-generation, low-cost light emitting devices (LEDs). The hopes for QD-based lighting and displays stem from the versatility of the colloidal synthesis technique and the excellent optical properties of the QDs, including tunable optical bandgaps and near-unity photoluminescent (PL) quantum yield (QY). While the first demonstration of electroluminescence using QDs dates back to 1994, the best reported external quantum efficiency (EQE) from QD-LEDs is 7.3% [1]. In order to improve the performance of QD-LEDs to the point of commercial relevance, a detailed understanding of the physical origins of these low EQE values is needed.
In this work we investigate the luminescence properties of CdSe/CdS core-shell QDs in dependence of the electric field. Our field-dependent luminescence lifetime measurements show that the QY is quenched by a factor of 50 at high fields, even when no charge is injected to the QDs. At the same time, the PL lifetime is only weakly field-dependent, excluding many non-radiative processes as the source of the field-dependent quenching, most importantly exciton dissociation[2], phonon-coupling [3], and surface state coupling [4].
We combine the experiments with tight-binding simulations to identify that the source of reduced QYs at high fields is the field-dependence of the radiative exciton decay rate. This effect stems from the field-induced spatial separation of electron and hole wavefunctions, which is particularly pronounced in QD band structures with relaxed confinement potentials, such as CdSe/CdS.
Our findings have two key consequences for the design of high performance QD-LEDs. First, QD-LED architectures must feature low operating fields (< 0.5MV/cm) in regions where QDs are located. Second, current trends in the development of QD band structures must be reconsidered. While CdSe/CdS giant shell QDs have largely eliminated quenching due to charging [5], the reduction of the quantum confinement of the electrons introduces strong field-driven quenching. This can explain why recent demonstrations of QD-LEDs based on these materials have not achieved high efficiencies [6].
[1] J. Kwak et al., Nano Letters 12, 2362-6 (2012).
[2] C. Leatherdale et al., Physical Review B 62, 2669-2680 (2000).
[3] S. A. Empedocles and M. G. Bawendi, Science 278, 2114-2117 (1997).
[4] S.-J. Park et al., Chem. Phys. 341, 169-174 (2007).
[5] B. Mahler et al., Nature Materials 7, 659-64 (2008).
[6] B. N. Pal et al., Nano Letters 12, 331-6 (2012).

Nanotechnology holds a great promise for treatment of diseases such as cancer and neurological disorders by providing highly specific and efficient delivery vehicles for therapeutic agents. In this context, polymer- and lipid-based nanoparticles have been widely applied for delivery of a variety of therapeutic and imaging cargos. While each of these systems have their limitations, hybrid nanoparticles that combine advantages of polymeric nanoparticles and nanoliposomes offer new promising delivery platforms with excellent loading capacities, outstanding serum stabilities, and tunable release profiles. Here, we aim to fabricate novel hybrid lipid/polymer nanoparticles for delivery of curcumin potentially for treatment of Alzheimer&’s disease.
Curcumin, a member of the ginger family and a herbaceous tuberous plant, is known to have unique anti-amyloid, anti-oxidant, anti-tau hyperphosphorylation, and anti-inflammatory properties that make this compound an appealing candidate to tackle Alzheimer&’s disease (AD). Application of curcumin for AD treatment has, however, remained limited due to the hydrophobic nature of this compound resulting in its insolubility in water. To overcome this issue, we encapsulate curcumin in poly(lactide-co-glycolide) acid (PLGA) nanoparticles using a simple fluidic-based nanoprecipitation technique. PLGA is a FDA approved polymer that degrades within body and has, therefore, been widely used for drug delivery systems. Here, we combine biodegradable PLGA nanoparticles with nanoliposomes to create a new vehicle for targeted delivery of curcumin potentially to AD affected neurons. We fabricate curcumin-loaded PLGA nanoparticles by a fluidic-based nanoprecipitation technique and coat the resulting particles with lipid bilayers that carry specific targeting ligands. The fluidic-based nanoprecipitation technique used here offers precise control over the mixing and precipitation process, compared to the conventional nanoprecipitation. It, thus, enables controlling the size of nanoparticles through changing the fabrication parameters such as flow rate and polymer concentration. Resultant loaded nanoparticles are characterized by scanning electron microscopy and dynamic light scattering. Release profile is monitored by UV spectroscopy measurements. Long-term goal of this work is to deliver curcumin through these hybrid nanoparticles to neurons affected by Alzheimer&’s disease in vivo.

Self-organization of nanoparticles (NPs) and nanoscale objects represents one of the most dynamic areas of materials science. Better understanding of these phenomena is important from both fundamental and practical perspectives because nanoparticle self-organization processes identify similarities between biological and non-biological nanoscale species, lead to unusual optical properties from different combinations of nano- and microscale features, and can potentially simplify manufacturing of electronic, photonic, and sensing devices.
Intricate 1D, 2D, and 3D systems from CdTe, CdS, Au, ZnO NPs could be formed. These assemblies led to much better understanding, of attractive and repulsive interactions between the NPs. Large expansion of the variety of self-assembled structures can be related to the fine tuning of anisotropy of the force fields around NPs: geometry of the NP facets, crystal lattice, dipole moments, distribution of a stabilizer, and intrinsic chirality of the NP cores. Conceptual relations between the topology of the self-assembled structures and the structure of individual building blocks in the framework of contributions different force will be presented. The analysis of the self-assembly processes for NPs also revealed surprising analogies with self-organization behavior of proteins. The idea of NP-protein analogy can also be extended not only to geometry but to biological functions of proteins. Latest data on the design of inorganic biomimetic inhibitors, enzymes, and cellular signaling agents based on inorganic NPs will be discussed. Advantages and limitations of the “protein analogy” will be discussed. New optical materials utilizing chiral NPs and their superstructures originating from small discrete assemblies of NPs and their anisotropies will also be considered. The latest results will also include the finding of NP assemblies into chiral nanostructures reminiscent of viruses. Such systems open a new pathway to the self-assembled systems with unique optical properties
References.
1. Z. Tang, N. A. Kotov, M. Giersig, Science, 2002, 297, 237-240.
2. Z. Tang,. et al., Science, 2006, 314 (5797) 274-278.
3. J. Lee,et al. Angew. Chem. Intern. Ed. 2005, 44, 7439-7442.
4. J. Lee, et al, Nature Materials. 2007, 6(4), 291-295.
5. S. Srivastava, et al. , Science, 2010, 327, 1355-1359.
6. M. Yang, K. Sun, N. A. Kotov, J. Am. Chem. Soc., 2010, 132 (6), pp 1860-187.
7. Y. Zhou, M. Yang, K. Sun, Z. Tang and N. A. Kotov, J. Am. Chem. Soc., 2010, 132 (17), 6006-6013
8. N. A. Kotov, Inorganic Nanoparticles as Protein Mimics, Science, 2010, 330 (6001), 188-189.
9. S. I.Yoo, N.A. Kotov, Angewandte Chemie, 2011, 50(22), 5110-5115.
10. Y. Xia et al, Nature Nanotechnology, 2011, 6, 580-587.
11. W. Yan, et al, J. Am. Chem. Soc. 2012, J. Am. Chem. Soc. 134 (36), 15114-15121

The ligand shell of nanoparticles is responsible for a good fraction of the particles&’ properties. In the case of gold nanoparticles, it is relatively easy to use mixtures of ligand molecules to form a mixed ligand shell. If these ligand molecules have a negative enthalpy of phase separation, then the resulting ligand shell is patchy at equilibrium. In this talk, the conditions that lead to the formation of stripe-like domains, or to macro-domains (i.e. Janus particles) will be discussed. New characterization techniques to distinguish between these two cases will be presented. Finally, some of the properties that most relate to the patchiness of the particles will be discussed.

The delocalized electronic states present in nanoscale semiconductors should offer distinctive ways to interact with and report on the biological environment. Such applications require good control of the interfacial chemistry of inorganic nanoparticles: in particular, to guide the formation of core/shell heterostructures to optimize brightness, and to introduce a surface coating that can enable the particles to function properly in the biological environment while limiting hydrodynamic size and, in the case of fluorescent quantum dots (QDs), avoiding quenching of the QD excited state. Significant progress has been made in identifying specific examples that comprise these features, especially for the case of metal chalcogenide semiconductors, but there remains only a limited understanding of the reaction mechanisms and thermodynamics associated with the elaboration of the surfaces of such particles with inorganic and organic layers. I will describe recent work at USC in which we have investigated the formation of inorganic shells on CdSe nanocrystals under alternating layer addition conditions to evaluate the proposed selective ionic layer adhesion and reaction (SILAR) mechanism of shell growth, and ongoing work to directly measure the thermodynamics of ligand exchange reactions as part of a long-term effort to negotiate the trade-offs of binding strength against other properties such as fluorescence quenching in the design of molecular monolayer coatings for biological applications of QDs.

When two dislike thiols self-assemble on the gold nanoparticle (NP) surface, they can separate into stripe-like domains. The striped surface provides unique surface properties to the NPs. One example of these properties is divalency. A particle coated with stripe-like domains implies two defect points at the poles of NPs. We have shown that these two polar defects can be selectively functionalized with molecules and make them to act as handles for further assemblies. With this approach, we can make chains of the divalent NPs and create 1-D assembly of NPs. Here, we apply a recently published theory on the gelation of patchy NPs [1], and develop functional 3-D network of NPs. We will show NP gels consist of the water soluble striped NPs. The network structure is formed by self-assembly of divalent and multivalent NPs when they are mixed with divalent metal ions. Gelation occurs only using ionic interaction between NPs, and it is thermally reversible. At different concentrations of NP solutions, gels are investigated to determine the gel transition temperatures and the gel properties. A rheological characterization is also discussed.
[1]E. Bianchi, P. Tartaglia, E.L. Nave, F. Sciortino, J. Phys. Chem. B. 2007, 111, 11765.

Nanoscopic objects stabilized with charged organics exhibit properties fundamentally different from either molecular or macromolecular ions, and can combine ionic-like properties with electronic and ionic conductivity and/or photoexcitability. By careful control of electrostatic interactions, ”nanoions” of various shapes and material compositions can be assembled into functional nanomaterials including 3D supracrystals, ”layered” crystals, or extended films. Depending on the properties of the charged organics, these nanomaterials can act as chemical amplifiers, photoconductors and inverse photoconductors, or batteries. Also, charged metallic nanoparticles can combine electronic and ionic conductance to provide a basis for all-nanoparticle electronics comprising current-steering switches, diodes, transistors and other elements. In the talk, I will illustrate how the integration of these elements yields fully operational nanoionic circuitry.
Key References:
1. A.M. Kalsin, M. Fialkowski, M. Paszewski, S.K. Smoukov, K. J.M. Bishop & B.A. Grzybowski Electrostatic self-assembly of binary nanoparticle crystals with a diamond lattice, Science, 312, 420 (2006).
2. H.Nakanishi, K.J.M. Bishop, B.Kowalczyk, E.A. Weiss, A. Nitzan, K.V. Tretiakov, M.M. Apodaca, R. Klajn, J.F. Stoddart & B.A. Grzybowski* Photoconductance and inverse photoconductance in films of functionalized metal nanoparticles Nature 460, 371-375 (2009).

Colloidal semiconductor nanocrystals (NCs) are a class of materials with unique optical and electronic properties that make them suitable for photovoltaic and optoelectronic applications. NCs have been already demonstrated to be an excellent material system for tailoring the optical properties through the quantum confinement, the band offset, charge separation, and emission polarization. Moreover, they exhibit large molar absorption coefficient, high photo-stability compared to typical organic luminophores and are size-tunable emission wavelengths across the visible to IR spectral range. For light-emitting devices, the crucial parameter related to the efficiency of photoemission is the photolumiscence quantum yield (QY), which can be enhanced (up to 90%) by coating the nanocrystal surface with another semiconductor shell. Using colloidal synthetic route, CdS rods have been epitaxially grown onto a spherical CdSe core. Despite many investigations, the core-size dependence of these CdSe/CdS heterostructures is not very well understood. Indeed, the results by photoemission measurements of absolute QY, PL decay lifetime and transient absorption feature are usually difficult to interpret essentially due to the role of strain and interface states in the emission dynamics. We have used EXAFS (extended x-ray absorption fine structure) spectroscopy, high resolution STEM (GPA analysis) and pair distribution function (PDF) measurements to characterize pure CdSe NCs, CdSe/CdS core/shell NCs with different core size and also CdSe/CdS/ZnS NCs. EXAFS and XANES measurements have done been at Cd K-edge, Se K-edge and Zn K-edge. A decrease in coordination number with decrease in size is observed for both Cd and Se edges for the pure CdSe NPs. After the growth of the CdS shell onto CdSe NCs, the coordination number becomes higher for small core size (2 nm) whereas for big core size (5 nm) the coordination number increases slightly. The 5 nm core CdSe-CdS particles exhibit more disorder and defects sites compared to 2 nm sized particles. This is in accordance with the results obtained from HR-STEM measurements, which show an important presence of stacking-faults in 5 nm core CdSe-CdS nanocrystals. These structural results for these systems will be correlated with photoluminescence properties as a function of the CdSe core size.

Nanocomposite thin films containing hierarchically-ordered nanoparticle (NP) arrays demonstrate unique collective properties that may be useful for electronic, photonic, and plasmonic applications. Understanding the thermodynamics of nanoparticle assembly in thin films paves the way for the “bottom-up” fabrication of next-generation NP-based devices. Here, we use block copolymer-based supramolecules (PS-b-P4VP(PDP)) to achieve not only 1D chains and 2D lattices but also 3D arrays and networks of NPs with precisely controlled inter-particle ordering in the interior of thin films. Layered NP sheets with in-plane 2D hexagonally-packed lattices and 3D ordered arrays of NP chains are obtained upon blending NPs into supramolecules with lamellar and cylindrical morphology in thin films, respectively. Moreover, due to the rigid architecture of the coil-comb supramolecule, the assembly of supramolecular nanocomposite is predominantly entropy-driven and highly dependent on NP size, allowing for precisely tailored 3D spatial organization of NPs in thin films by simply varying the ratio of the NP size to the block copolymer periodicity. This gives us a useful tool to fabricate 3D hybrid arrays of metallic and semiconducting NPs with tunable optical properties. The simple yet versatile supramolecular approach enables us to fabricate a rich library of hierarchically-structured nanocomposite thin films to potentially meet the demands in NP-based device fabrication and understand structure-property correlations in functional nanocomposites.

Mesoscale materials generated from block copolymers and naked nanocrystals will be presented, where compositional heterogeneity manifests within an ordered architecture to produce novel function for energy devices. We will highlight the specific role of block copolymer design in directing the co-assembly of ligand-stripped, or naked, nanocrystals into precise 3-D architectures for a variety of nanocrystal compositions. Insight into co-assembly pathways will be presented through a detailed TEM study of the synchronous assembly of naked nanocrystals and a new class of amphiphilic block copolymer architecture directing agents. These data capture critical aspects of the emergence of suprastructures through their order-to-disorder transition, and through morphological transitions in the architecture directing agent. We will also show how these processes differ as the chemical nature of the nanocrystal tethering domain are modified with various functional groups that modulate the enthalpy of adsorption to the bare nanocrystal surface. Our results will highlight the role of materials chemistry to map the phase space alongside the co-assembly trajectory in order to build robust processing strategies for mesoscale materials to impact next generation energy batteries, electrochromics, and pseudocapacitors.

With the advent of size- and shape-controlled nanocrystals of myriad compositions, the next frontier is to assemble the nanocrystals into functional superstructures. We demonstrate how a careful manipulation of the chemical affinity between the nanocrystal surface and a block copolymer templating agent is the key to obtain long-range ordered hierarchical mesoporous films with control over pore dimensions and wall thickness, independent of the nanocrystal shape, size, and composition. By tuning the interfacial interactions through a combination of nanocrystal surface chemistry and block copolymer design, we are able to extend this method from large families of oxides to chalcogenides.
In-situ GISAXS experiments demonstrate the importance of interfacial attraction in determining assembly conditions for different material combinations. Using a cation exchange technique, we are able to access an even greater range of chalcogenide compositions, some of which cannot be assembled directly into mesoporous films due to incompatibility with processing conditions.

Nanoparticles in solution are often stabilized with functional coatings to prevent aggregation. I&’ll discuss the use of explicit-atom molecular dynamics simulation to determine how these coatings affect the forces between nanoparticles and present recent simulation results showing that small (2-8 nm diameter) spherical nanoparticles spontaneously produce highly asymmetric coating arrangements, when coated with commonly-used simple polymer chains. These asymmetric coatings often fail to encapsulate the particle and strongly affect the shape. At the liquid/vapor interface, these coating asymmetries are amplified and oriented by the surface, and play a significant role in the interactions between aggregating nanoparticles. Using many-nanoparticle simulations we demonstrate that the self-assembly of nanoparticle films and the resulting structure within these many-nanoparticle surface aggregations can be controlled by manipulating these very simple functionalized coatings.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

We have performed experimental and theoretical studies of self-assembled colloidal nanoparticles (NPs). First, we study small gold NPs with positively charged TEG-NMe_3 ligands at the water and 1,2-dichloroethane (DCE) electrified interfaces. X-ray reflectivity and GISAXS measurements demonstrate that the NPs form a hexagonal closed-packed lattice with the lattice constant of ~6.1 nm under small voltage of 0.1 V. Upon increasing the voltage to 0.3 V, the NPs submerge deeper into DCE and the lattice constant increases by almost three times. A similar trend was observed and analyzed in detail in our molecular dynamics simulations [1]. Second, we present our study of a molecular passage across membranes formed by 5 nm diameter Au NPs ligated with dodecanethiol [2]. We show that molecules with cross-sections smaller than 2 nm can pass through the membranes, but their rejection rate depends on the net molecular charge. Using atomistic molecular dynamics simulations, we show that the molecular passage is related to the presence of nm-sized pores formed between the NPs due to fluctuations of their parameters.
[1] Bera, M.; Chan, H.; Tatur, S.; Yu, H.; Bu, W.; Amoanu, D.; Moyano, D.; Rotello, V.; Lin , B.; Meron, M.; Vanysek, P.; Kral, P.; Schlossman, M., in preparation (2012).
[2] He, J.;Lin, X.-M.; Chan, H.; Vukovic, L.; Kral, P.; Jaeger, H., Nano Lett., 11, 2430, (2011).

Organizing nanoparticles into a desired super-structure is crucial for their technological applications. We present molecular dynamics simulations of the assembly of nanoparticles during the evaporation of solvent from 3-component nanoparticle/polymer/solvent mixtures. We consider two systems. In the first, the nanoparticles and polymer chains are dispersed in the solution while in the second, the chains are end-grafted to a substrate to form a brush. In the first, as the solvent evaporates, the polymer chain density is enhanced at the liquid/vapor interface, which slows down the solvent evaporation significantly. The organization of nanoparticles strongly depends on their interaction with polymer chains. For a strong mutual attraction, a layer of nanoparticles is entrapped in the concentrated polymer film at the interface and assembles into a close-packed hexagonal lattice. When the interaction is reduced, nanoparticles are depleted in the enriched polymer film near the interface and are mostly dispersed in the relatively solvent-rich solution below the film. For polymer brushes, the opposite trend is observed. At a relatively weak attraction between the nanoparticles and brush, the nanoparticles straddle the brush surface and form a more ordered lattice. For a strong attraction between the nanoparticles and polymer, the nanoparticles are engulfed inside the brush and the packing quality diminishes, because the lateral diffusion of the nanoparticles is suppressed.

We report a general strategy for crafting a large variety of functional nanocrystals with precisely controlled dimensions (i.e., plain, core/shell, and hollow nanoparticles) by capitalizing on a new class of amphiphilic unimolecular star-like block copolymers as nanoreactors. This strategy is effective and able to produce highly monodisperse nanoparticles, including metallic, ferroelectric, magnetic, luminescent, semiconductor, and their core/shell nanoparticles, which represent a few examples of the kind of nanoparticles that can be produced using this technique. We believe these nanoparticles can be utilized as building blocks or additives for bottom-up nanofabrication to develop low-cost nanoscale materials and devices with integrated functionalities enabled by the properties of individual nanoparticles and their proper spatial arrangement, and can also serve as model systems for fundamental research in self-assembly, phase behavior and crystallization kinetics of nanoparticles.

Nanowires and nanorods synthesized with tailored compositions and properties are essential components for the future nanoscale electronics and optics, as well as biochemical sensors. Current use of nanowires greatly relies on the precision and the efficiency in their solution-based assembly into complex function networks. The Brownian fluctuation of nanowires and their hydrodynamic interactions with interfaces critically affected their accurate positioning and the packing density of devices. However, unlike the well-studied case of spheres, both the experimental and theoretical studies of the near-wall Brownian motion of anisotropic bodies have been elusive due to the lack of ideal imaging techniques and the intrinsically complex system. Here we present the experimental and computational study of the rotational Brownian motion of silicon nanowires tethered on a substrate. A uniquely developed interference method enables the direct visualization of the microscopic rotations of nanowires in three dimensions with high angular (< 0.000005 rad) and temporal resolutions (> 200Hz) with normal CCD camera. The quantitative measurement at short time scales revealed the anisotropic reduction in their rotational diffusivities as a function of the inclined angles, resulting in the decrease more than 40-80 % at long time scales. We then developed an implicit hydrodynamic model from a string-of-beads idealization and the calculation showed excellent agreement with the experimental observations. The demonstrated interferometric method, together with the versatile numerical simulation, provides a systematic approach for studying the interfacial rheology of anisotropic colloids as model biophysical systems. Our observation also provides insights into the fundamental diffusive processes, useful for understanding the anisotropic behavior of anisotropic macromolecules near interfaces. The demonstrated combination of the experimental and numerical methods provides a systematic approach for exploring the optimal self-assembly conditions that contain the positioning inaccuracy as well as for studying rheology of various colloidal and biophysical systems near interfaces.

A computational methodology combining self consistent field theory (SCFT) and Brownian dynamics simulations is employed to study the self assembly of asymmetric block copolymer and the superparamagnetic nanoparticles in the presence of external magnetic fields. Superparamagnetic nanoparticles respond to the external magnetic field, and depending on the orientation of the external field (in-plane or out of plane), assemble into either chain like aggregates or hexagonal array type nanostructures. These nanostructures significantly influence the morphology of the block copolymer contingent upon the critical selectivity of the nanoparticles to one of the block copolymer domains. Chain-like nanoparticle aggregates cause either a phase transition from hexagonal phase to lamellar phase or a change in the orientation of the cylinders depending on the nanoparticle loading, while hexagonal array of nanoparticles lead to lowering of defect densities in the hexagonal phase of the block copolymer. The 2D simulations reveal an interesting interplay of nanoparticle size and nanoparticle volume fraction on the morphology of the asymmetric block copolymer. For a given nanoparticle loading, nanoparticle sizes commensurate with the domain sizes yield a good alignment of the nanodomains while larger particles lead to higher defect densities, or disordered morphologies. Defect free morphologies of the hexagonal phase are obtained using out-of-plane magnetic fields for those nanoparticle loadings wherein the inter-lattice spacing of the nanostructures matches that of the hexagonal phase of the block copolymer. Higher volume fractions lead to either change in orientation of cylinders or an order-to-order phase transition, while lower volume fractions lead to higher defect densities. Similarly, an optimal window of nanoparticle volume fraction exists for domain alignment using in-plane magnetic fields.

Electrophoretic deposition (EPD) is an industrially relevant process in which colloidal particles suspended in a liquid are deposited on a electrode under an applied electric field. In this paper, we present techniques for assembling nanoparticles with controlled crystallinity over large areas as well discuss the effects of electric field gradients on overall deposit morphology. Furthermore, our efforts to develop a numerical model describing the deposition process that predicts resultant microstructure and morphology will be detailed.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-597552

The synthesis and organization of functional nanomaterials via bottom-up self- and directed assembly represents a critical challenge for the future of nanoscience. Generating arrays of nanoparticles with controlled size and spatial distributions is key to this challenge, and processes that exploit morphological instabilities, such as liquid-phase dewetting, offer the potential to attain these fine-scale spatially correlated structures. Consequently, there have been numerous studies [1,2] on pulsed-laser-induced dewetting of thin metallic films with the goal of improved synthesis and controlled assembly routes.
Previously, the nanosecond liquid-phase dewetting dynamics of metallic thin films have been inferred largely by ex-situ observations of the re-solidified metal quenched after different liquid lifetimes [3], as unlike polymeric systems where the dynamics based on viscosity and surface energy are accessible in the second, minute, or even hour timescales, thin-film metal dewetting uniquely has nanoscale time- and length scales. Here, we present results from in-situ observations revealing the assembly dynamics in metallic thin films using the nanoscale spatio-temporal resolution of the dynamic transmission electron microscope [4]. Correlated time and length scales suggest that the assembly of thin nickel films into nanoparticle arrays is induced by a spinodal instability. Complementary simulations agree well with the time-resolved observations. Initial results on the assembly dynamics in alloy thin films that form core-shell nanostructures will also be shown [5].
References
[1] Rack, P.D. et al., Appl. Phys. Lett.92 (2008) 223108.
[2] Fowlkes, J.D. et al., Nano Lett.11 (2011) 2478.
[3] Favazza, C. et al., J. Appl. Phys.102 (2007) 104308.
[4] LaGrange, T.B. et al., Ultramicroscopy108 (2008) 1441.
[5] Work at Lawrence Livermore National Laboratory was performed under the auspices of the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Contract DE-AC52-07NA27344. Work at the University of Tennessee and Oak Ridge National Laboratory was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering. N.A.R was supported by an ASEE/NSF fellowship. J.D.F., P.D.R., and N.A.R. also acknowledge that film deposition was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.

The photoreduction of metallic nanostructures onto patterned ferroelectric templates (i.e., illumination with super bandgap light of a sample immersed in aqueous AgNO3 leading to the reduction of silver nanoparticles on the surface) has received attention for potential applications in biosensing. The process can be used to place spatially defined arrays of nanostructures onto surfaces. These nanostructures can be harvested via sonication as nanoparticles, which can be used for other applications. The location of the nanostructure arrays can be controlled by patterning the ferroelectric template via electric field poling or a proton exchange process, which reverse or modulate the ferroelectric polarization, respectively. 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 and that the width can be controlled by the proton exchange depth. We demonstrate that the resulting nanostructures can be functionalized with Raman and fluorescent probe molecules.

Anisotropic particles display many unique electrical, mechanical, and optical properties. Developing strategies to generate nanocomposites with control over the spatial distribution and macroscopic alignment of nanorods will build a material foundation for a variety of applications ranging from photovoltaic devices, plasmonic devices, and sensors to mechanically strengthened composites. Ligand passivation of nanorods is critical for many applications and it is desirable to decouple the ligand surface chemistry from the nanocomposite formation. We have recently demonstrated a supramolecular approach where hierarchical assemblies of nanorods with control over the spatial distribution and, in some cases, the local orientation of nanoparticles can be obtained by combining the self-assembly properties of block copolymers (BCPs) and small molecules [1]. Alkyl-passivated nanoparticles can be readily arranged into aligned arrays, sheets, continuous networks, and clusters. Here, we will present a systematic study of supramolecular nanocomposites as a function of nanorod aspect ratio. Nanorods with lengths greater than the BCP periodicity are found to assemble parallel to the microdomain interfaces, potentially enabling fine control of nanorod orientation through alignment of the BCP microdomain. In contrast, short nanorods do not demonstrate similarly strong alignment and instead deviate from parallel to the microdomain interfaces by a small angle. These findings can be accounted for by considering the interparticle interactions, the particle-supramolecule interactions and the phase behavior of supramolecules.
1. Thorkelsson, K.; Mastroianni, A. J.; Ercius, P.; Xu, T. Direct Nanorod Assembly Using Block Copolymer-based Supramolecules. Nano letters 2012, 12, 498-504.

Block copolymer (BCP)-based supramolecules which combine the nanoscopic assembly of BCPs and molecular ordering can generate hierarchical structures with built-in functionality. Here, we investigated the phase behavior of BCP-based supramolecules containing cholesteric liquid crystal (LC) moieties and achieved directed assembly of nanoparticles. Specifically, a BCP-based supramolecule was constructed by attaching a cholesteric small molecule, 3-hydroxylphenyl cholesteryl succinate (ChHP) to a diblock copolymer, polystyrene-block-poly-4-vinylpyridine (PS-b-P4VP) via hydrogen bonding. The supramolecule, PS-b-P4VP(ChHP), retained both block copolymer and liquid crystalline phase behavior in the form of hierarchical assembly on multiple length scales to form lamellar-within-lamellar and lamellar-within-cylinder morphologies. Upon thermal annealing, the supramolecule demonstrated thermoresponsive behavior in the form of a series of morphological transitions from a P4VP(ChHP) majority morphology to a P4VP(ChHP) minority morphology. This supramolecule was used to direct the assembly of Au nanoparticles, which also demonstrated thermally driven morphological transitions similar to supramolecule host. A model, based on the thermal phase transitions of ChHP and the non-covalent interaction between ChHP and PS-b-P4VP, is proposed to explain the observed thermally driven morphological transitions. The present studies demonstrate the viability of constructing liquid crystalline BCPs via a supramolecular approach and application of these supramolecules towards directed nanoparticle assembly. The observed hierarchical assembly and thermoresponsiveness of the nanocomposites could potentially be applied optical and photonic applications.

The results from our study of the fabrication, character and properties of nano crystals arrayed on model substrates are presented. The samples were prepared using self-assembled, mono dispersed polystyrene spheres acting as a deposition mask. Different metals were then evaporated, filling the regular array of gaps made by the spheres to form a nano particle array on the substrate. Samples of Au and Ag particles have each been prepared using this method on Ti and TiO2 substrates. The resulting particles have then been characterized using a combination of microscopy, diffraction, and spectroscopy techniques. Such micro and nano particle arrays on substrates such as TiO2 find application in catalysis, deposition and corrosion studies, and in the fabrication of high precision sensors.

There is growing interest in nanoscale forms of complex (multivalent/mixed valent) oxides which emanates from the novel changes in their properties with size. The crystalline quality of low temperature synthesized oxide nanomaterials is generally not very good. Hence, it is desirable to first make crystalline oxide powders by high temperature processing and then mill them down to nano-meter size. We show here that simple citric acid treatment of BiFeO₃ and Bi₂O₃ powders leads to the desired micron-scale to nanoscale transformation, yielding nearly monodispersed nanoparticles. Importantly, these are highly dispersible and stable in water. TEM images clearly show nearly mono-dispersed ultrafine nanoparticles with average size of about 5 nm after citric acid treatment on bulk-sintered large particles. The band gap energies for citric acid treated samples are found to increase with respect to the untreated samples, as expected, due to dramatic size reduction. For BFO the band gap is seen to increase from 2.0 eV to 2.7 eV and for Bi₂O₃ from 2.75 eV to 3.8 eV as a result of quantum size effect. Photoluminescence (PL) spectra reveal that the emission peak (observed at 520 nm) for Bi₂O₃ is significantly blue shifted to lower wavelength around 360 nm after citric acid treatment. Significant reduction in maximum magnetization of citric acid treated BFO was also observed due to drastic size reduction and surface layer effects. The bifurcation of FC and ZFC curves for BFO and citric acid treated BFO at low temperatures indicates spin glass behavior. By performing similar experiments on Fe₃O₄ and Fe₂O₃ we have elucidated the possible mechanism, which hinges on valence-controlled dissolution and ripening phenomenon.

ZnO nanoparticle is one of the most promising materials to realize the useful nano scale devices because of their unique properties such as a 3.37 eV of direct wide band gap and high sensitivity for chemical and optical species. The synthesis of ZnO nanoparticles has been developed in various methods, such as sol-gel, plasma, and solution based reactions. Among them, the solution based reaction is one of the most attractive synthetic methods due to its low temperature, rapid and environment benign characteristics. However, in order to obtain more cost effective production of ZnO nanoparticles, the synthetic process has to be simplified with continuous manufacturing system such as microfluidic reaction system. In this study, the continuous ZnO nanoparticles synthetic process by using microfluidic reaction system with time pulse mixing enhancement for rapid manufacturing was investigated by numerical and experimental methods. The microfluidic reaction system for ZnO nanoparticles synthesis was designed as three parts; preheating, mixing, and synthesis regions with channel dimension of 200 µm width and 200 µm depth respectively. As the synthetic reagents, 0.03 mM NaOH and 0.01 mM Zn(OAc)₂ in ethanol solutions were used. For the numerical simulation, T-shaped microchannel at the confluence of mixing region was adopted as computational domain. The flow rate of NaOH and Zn(OAc)₂ solutions were 0.855 µL/min and 1.645 µL/min respectively. This flow rate was determined by maximum flow rate that expected total pressure drop was under 20 kPa for stable process. The flow rate at each inlet was expressed as 0.855(1+sin(f×2pi×t+pi)) and 1.645(1+sin(f×2pi×t)) µL/min for NaOH and Zn(OAc)₂ solutions respectively (f: frequency, t: time). The phase difference of pulse injection between two inlets was designed to results the same flow rate at the outlet and to compare the effect of frequency difference. To find the effective mixing condition in numerical simulation, the degree of mixing was measured based on the mass fraction data of synthetic solutions. From the numerical simulation, the efficient mixing was obtained via the frequency range of 4~15 Hz. Especially, the 5 Hz mixing frequency showed the best performance of mixing enhancement. Based on the numerical simulation, the ZnO nanoparticles were synthesized by using microfluidic reactor with 5 Hz pulse. To analyze the synthetic result, the transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), and x-ray diffraction (XRD) techniques were conducted and compared with batch processed ZnO nanoparticles. As a result, the ZnO nanoparticles synthesized by microfluidic system showed 3-5 nm in diameter with its own crystalline structure and well matched with batch synthesized ZnO nanoparticles. This microfluidic reaction system based ZnO nanoparticles synthetic process is expected to provide a powerful mean of efficient mass production system with integrating to large plant system.

Controlling the shape and size of metal nanocrystals is of great importance in maneuvering their fascinating properties for a variety of applications. Here we repot the synthesis of silver octahedrons with controlled edge lengths by using seed-mediated growth. The key to the success of this synthesis is the use of single-crystal Ag seeds with uniform, precisely controlled sizes to direct the growth and the use of citrate as an effective capping agent for the {111} facets of Ag. Both cubic and spherical Ag seeds could be employed for the growth of octahedrons. For the first time, we could precisely control the edge lengths of Ag octahedrons in the range of 20-100 nm with high purity. Moreover, by employing the as-prepared Ag octahedrons as templates, octahedral Au nanoboxes/nanocages with tunable optical properties were synthesized via galvanic replacement reaction. Such hollow nanostructure could be promising candidate for various applications in optical, catalytic, and biomedical areas.

This paper reports a synthesis of Pd-Rh nanocubes with a core-frame structure and concave side faces through site-specific overgrowth of Rh on Pd cubic seeds, and their subsequent conversion to Rh cubic nanoframes via selective etching of the Pd cores. The overgrowth of Rh was confined to the corners and edges of Pd cubic seeds using a combination of kinetic control (enabled by the use of a syringe pump) and selective capping of Pd {100} facets by Br- ions. Our structural and compositional analyses indicated that the surfaces of these core-frame nanocubes were simultaneously presented with Pd {100} and Rh {110} facets, suggesting great potential for catalytic applications. By taking advantage of the difference in resistance to corrosion between Pd and Rh, the core-frame nanocubes were converted into Rh cubic nanoframes with a highly open structure via selective removal of the Pd cores by oxidative etching.

Superparamagnetic iron oxide (SPIO) particles offer an excellent opportunity for development of therapeutic and diagnosis devices such as drug delivery systems, magnetohyperthermia and contrast agents for magnetic resonance imaging. Tailoring of the nanoparticles surface chemistry is the key for successful achievement of these potential biomedical applications. In particular, surface chemistry must provide sufficient stability in the physiological environment (pH and ionic strength) and also suppress the uptake by the reticuloendothelial system. SPIO particles coated with biocompatible polymers are suitable platforms for in vivo biomedical applications. Herein, we present a one-pot synthesis procedure for obtaining SPIO particles coated with chondroitin-4-sulfate (C4S) and structural characterization. Chondroitin sulfate (CS) is a natural anionic polyelectrolyte consisting of repetitive disaccharide units of D-glucoronic acid and N-acetylgalactosamine, sulfated at either 4- or 6- positions. CS is an important cartilage matrix component known for its anti-inflammatory effect and also believed to induce the production of syndecan, a cell receptor that can interact with adhesion proteins, cells and the extracellular matrix. The SPIO-C4S bioconjugate was synthesized coprecipitating, with sodium hydroxide, a mixed aqueous solution of Fe(II), Fe(III) and C4S. The black precipitate of SPIO-C4S, after proper washing, was suspended in ultra-pure water and dialyzed against water for two days. The pH of the resulting suspension was set to 7.2 after which underwent structural and morphological characterizations. The suspension displayed a negative zeta potential (-33.5 mV) that confirms the attachment of C4S to the nanoparticles surface. ATR FT-IR spectrum revealed the presence of sulfate groups (850 cm^-1 and a wide peak centered at 1242 cm^-1) from C4S, while micro Raman spectroscopy confirmed the presence of magnetite phase with the characteristic vibrational modes at 307 cm^-1, 345 cm^-1, 510 cm^-1 and 676 cm^-1. A small amount of maghemite phase was also detected. The SPIO-C4S bioconjugate presented high purity composed exclusively of Fe, O and C, as confirmed by EDS analysis. Transmission electron microscopy (TEM) images showed spherical nanoparticles with an average diameter of 20 nm while dynamic light scattering measurements indicated a hydrodynamic diameter of 149 nm. The results of this study demonstrate that this synthesis procedure can be successfully performed to produce SPIO-C4S bioconjugates with high control over material's chemical structure and morphology. These findings represent initial requirements for explore the use of these magnetite nanoparticles in tissue and cartilage regeneration as well as in other therapeutic needs.

A systematic study of nanoparticles formation by post-implantation thermal annealing is expected to provide a useful database for the parameters of manufacturing. In this study, a combination of Cahn-Hilliard equation and Monte-Carlo calculation was used to develop a theoretical model of nanoparticles formation by thermal annealing after ion implantation. While the distribution profile of implanted ion was dealt with Monte-Carlo TRIM code calculations, the kinetic mechanism of the nucleation and growth of nanoparticles during thermal annealing was fully illustrated with the phase field model. To investigate the evolution of nanoparticle formation along the depth direction after ion implantation, the initial conditions of implanted ions were performed in various Gaussian distributions for different ion energies and doses. Under an appropriate ion energy, the nanoparticles started to precipitate while the ion dose is large enough. The morphologies of nanoparticles changed with the time, and the coalescence or connection with others was revealed to form oval-shaped nanoparticles.

ZnO films have been widely used in electronic applications because of their well-known semiconducting and piezoelectric properties. ZnO also has attractive optical characteristics including a wide bandgap of 3.4 eV and a large exciton binding energy of 60 meV at room temperature [1]. In recent years, a number of studies focusing on the synthesis and investigation of ZnO nanostructures such as nanowires, nanorods and nanobelts have been reported. A ZnO nanostructure has been shown as a candidate material for broad applications including UV lasers, field emitters and solar cells. ZnO nanorods are also widely used as sensing materials in humidity sensors, gas sensors and biosensors because of its properties including high sensitivity, rapid response and fast recovery [2]. In the present work, we report the controllable growth of ZnO nanorod on Si/SiO2 substrates. The deposition process of ZnO nanorods consist of two steps: (1) deposition of ZnO seeding layer and (2) ZnO nanorod arrays by hydrothermal assisted by microwave method. For the deposition of seeding layer, we used pechini method at 500oC for 2 hours. For growth ZnO nanorod by hydrothermal assisted by microwave we used aqueous solution containing zincacetate-2-hydrate [Zn(CH3COO)2 2H2O] mixed with hexamethylenetetramine(C6H12N4, HMTA) at 110oC for 1 hour. The density of ZnO nanorod arraysis strongly dependent on the initial seed deposition; so the seed layer has an influence in the growth direction. Good quality of ZnO films were deposited on Si/SiO2 substrates by the polymeric precursor method, X-ray diffraction confirmed the crystallinity of the zinc oxide film and SEM study revealed uniform deposition of fine grains.

Atomic layer deposition (ALD) is a rapidly developing thin film deposition technique based on a series of surface saturated chemical reactions. Due to its self-limiting nature, each ALD cycle forms an atomic monolayer on the substrate, enabling sub-nanometer thickness control in the vertical direction. However, ALD does not provide effective control in the lateral direction, which limits its applications in fabricating 3-D nanostructures such as nanoparticles.
Some recent work has shown that noble metal nanoparticles,[1] such as Ru, Pt, and their alloys, have been synthesized via ALD methods. These nanoparticles are well suited for catalysis and other applications. The results reveal that sub-nanometer particles with compositional control and uniform size distribution can be obtained during ALD early nucleation stage, especially on non-flat surfaces. Here we demonstrate the growth of 3D nanostructures with controllable density and size on self-assembled monolayers (SAMs) modified substrates.[2] The SAMs systems include the mixture of molecular with different chain lengths and functional end-groups.[3] We optimize the ALD-SAMs combo systems to obtain nanoparticles with desired properties such as size and distribution, interface and stoichiometry, morphology and stability. Catalytic performance is analyzed and compared to nanoparticle catalysts from conventional synthesis methods.
With precise structural and compositional control of nanoparticle, as well as interface tuning between nanoparticle and supported oxide substrate, we have obtained system with reduced noble metal load and enhanced catalytic performance.
[1] S.T. Christensen, H. Feng, J.L. Libera, N. Guo, J.T. Miller, P.C. Stair, J.W. Elam, Supported Ruminus;Pt Bimetallic Nanoparticle Catalysts Prepared by Atomic Layer Deposition, Nano Lett., 10 (2010) 3047-3051.
[2] R. Chen, S.F. Bent, Chemistry for Positive Pattern Transfer Using Area-Selective Atomic Layer Deposition, Advanced Materials, 18 (2006) 1086-1090.
[3] R. Chen, H. Kim, P.C. McIntyre, S.F. Bent, Investigation of Self-Assembled Monolayer Resists for Hafnium Dioxide Atomic Layer Deposition, Chem. Mat., 17 (2005) 536-544.

The surface plasmon resonance (SPR) effect allows to metal nanoparticles as the gold, absorbs radiation in the visible range with a high intensity and this can be applied in several fields such as surface-enhanced Raman spectroscopy (SERS), gas sensing and other optical devices. There are many advantages to the use of ZnO as an inert matrix. Among others it has the ability to change the dielectric interface, can stabilize the metallic nanoparticles and can handle the SPR wavelength^{1, 2}.
In this work we present Au-ZnO nanocomposites that present the SPR effect. The synthesis of Au-ZnO films was performed by reactive DC-magnetron co-sputtering of Zn and Au targets and we varied experimental conditions as Au composition, oxygen pressure and annealing temperature. By spectrophotometric measurements we observe an absorption at a wavelength of 590 nm (orange region) at high gold compositions and annealing temperatures above 200 °C. Besides, as the size of the gold nanoparticles determines the presence of the SPR, we evaluate the average size of the nanoparticles to 6 nm using X ray diffraction using the diffraction peak of the (111) gold plane located at 38°. TEM micrographs allowed capturing more precisely the microstructure of the nanocomposite films. Electrical measurements by four points probe show a sheet resistance of a magnitude of 10⁶ to 10⁸ ohms/sq that is a function of the Au content and the annealing temperature.
References
1. Y. K. Mishra, S. Mohapatra, R. Singhal, and D. K. Avasthi, Appl. Phys. Lett. 92, 043107 (2008)
2. Y. B. Zheng, T. J. Huang, A. Y. Desai, S. J. Wang, L. K. Tan, H. Gao, and A. C. Hon-Huan, Appl. Phys. Lett. 90, 183117 (2007)

Pt-nanoparticles-laden graphene (GR) crumples was directly synthesized from a colloidal mixture of aqueous chloroplatinic acid (H2PtCl6) and graphene oxide (GO) nanosheets via aerosol spray pyrolysis (ASP). Effects of Pt content in the Pt/GR composite and temperature of heating zone on the particle morphology, diffraction pattern and specific surface area were investigated. The morphology of Pt/GR was the shape of a crumpled sheet of paper and the average size of the composite was around 1.3 µm in diameter. As Pt content increased from 2 to 20 wt %, higher numbers of Pt nanoparticles are observed on the GR at higher Pt content and the specific surface area of the composite also increased from 122 to 146 m2/g. Also, the intensity of the GR peak decreased but that of the Pt peak increased. As temperature increased from 500 to 900 oC, an increase of the particle size of Pt due to sintering was observed. Electrocatalytic application of the Pt/GR composites was examined through methanol oxidation reaction. The 20 wt% Pt/GR synthesized at 900 oC showed higher performance on methanol oxidation than a commercial 20 wt% Pt/carbon black catalyst.

In this presentation we describe our work related to the synthesis and processing of core/alloy nanoparticles. In particular, 15-nm Fe/FeCr nanoparticles with a stainless steel like interface have been prepared. These particles show a unique morphological transformation that is induced by surface oxidation, oxide passivation, and vacancy coalescence. The Kirkendall diffusion that occurs within the particle results in a tailorable oxide layer thickness, Fe-core size, as well as void size and symmetry. Much like a bulk stainless steel interface, the interfacial FeCr oxide passivates oxidation, resulting in self-limited diffusion. Because of this, a highly uniform and stable core-void-shell morphology is observed. The oxidation was observed via XRD and XPS, while the alloying was observed by selective area EDX, and final morphology was characterized by HRTEM. The mechanism for growth, as well as the potential use of these materials in sensing, gas absorption, and drug delivery will be discussed.

Ultrafine sub-2nm Pt nanoparticles with homogeneous size distribution and high number density were prepared using a unique tilted-target sputter deposition system. The Pt nanoparticle size and number density can be precisely controlled by varying select deposition parameters such as - deposition time, target angle, sputtering power etc. Studying the nanoparticle size, distribution and number density statistics based on HRTEM images helps differentiate between three regimes encountered during the nanoparticle growth process. The first is the nucleation regime where particle growth is strictly governed by the interactions at the nucleation sites available on the substrates; second is the coalesce regime where ultrafine nanoparticles diffuse on the substrate to form bigger particles and third is the agglomeration regime where big nanoparticles are static on the substrate surface and further growth results in formation of nano islands and finally thin films. Using this system for nanoparticle growth allows precise control over nanoparticle sizes from 0.5 nm - 2 nm with very small size distribution. This narrow size distribution allows size dependent study of Pt nanoparticle catalytic activity in a multitude of chemical/electrochemical systems. The effect of substrate on nanoparticle size, distribution and stability was also studied. Pt nanoparticles on graphene substrates displayed the highest stability under prolonged electron beam exposure and this enhanced stability was also evident in catalytic activity experiments where Pt nanoparticles on few layer graphene substrates showed higher stability after multiple potential cycling when compared to Pt nanoparticles on other conducting oxide surfaces. Through HRTEM analysis, it was confirmed that Pt nanoparticles in the 0.5 nm - 1 nm regime are non-crystalline clusters which have strong charge retention characteristics due to the Coulomb blockade effect. Meanwhile, Pt nanoparticles in the 1 nm - 2 nm regime are highly crystalline and exhibit fast charge transfer characteristics. These characteristic properties make these nanoparticles viable candidate to increase reaction rates in specific systems. The sub-nm Pt nanoparticles act as excellent charge trap centers and recombination inhibitors and the 1 nm - 2 nm crystalline Pt nanoparticles show excellent charge transfer characteristics, e.g. for triiodide reduction at dye sensitized solar cell counter electrodes. These studies help understand fundamental size dependent catalytic properties of sub - 2 nm Pt nanoparticles and suggest their application in more chemical/electrochemical systems.

In the last two decades, metal-based nanomaterials have attracted significant attention due to their unique physical and chemical properties arising from the quantum confinement effects and the large surface area.[1] These interesting properties opened the gate into a wide range of potential applications including catalysis, sensors, fuel cells, coatings, data storage, magnetic materials, photovoltaics, and electronics.[2, 3] A variety of chemical and physical techniques have been developed to produce metal-based nanoparticles.[4-6] Most of these techniques are not commercially viable to economic, environment, or reproducibility issues. Therefore, a reliable, scalable, economic, and environmentally benign synthesis method is still required. Herein, we report the first synthesis of cobalt carbide nanoparticles in supercritical ethanol without using reducing agents or surfactants at 100 bars and 255 oC. The as-synthesized nanoparticles have a uniform size distribution with average particle size of 10 nm and displayed soft magnetic properties with coercivity and magnetization of 396 Oe and 93.44emu/g, respectively. The phase transformations of the as-synthesized nanoparticles at elevated temperatures have been studied using elevated temperature x-ray diffraction (ETXRD).

Referances
1. W.C.W. Chan, S. Nie: Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection. Science. 281, 2016 (1998).
2. P.K. Jain, X.H. Huang, I.H. El-Sayed, M.A. El-Sayed: Noble Metals on the Nanoscale: Optical and Photothermal Properties and Some Applications in Imaging, Sensing, Biology, and Medicine. Accounts of Chemical Research. 41, 1578 (2008).
3. J.Z. Zhang, C. Noguez: Plasmonic Optical Properties and Applications of Metal Nanostructures. Plasmonics. 3, 127 (2008).
4. H. Bonnemann, R.M. Richards: Nanoscopic metal particles - Synthetic methods and potential applications. European Journal of Inorganic Chemistry. 2455 (2001).
5. C.J. Murphy, T.K. San, A.M. Gole, C.J. Orendorff, J.X. Gao, L. Gou, S.E. Hunyadi, T. Li: Anisotropic metal nanoparticles: Synthesis, assembly, and optical applications. Journal of Physical Chemistry B, 109, 13857 (2005).
6. S.P. Gubin, Y.A. Koksharov, G.B. Khomutov, G.Y. Yurkov: Magnetic nanoparticles: Preparation methods, structure and properties. Uspekhi Khimii, 74, 539 (2005).

Following their increasing use, the supply of larger quantities of monodisperse colloidal nanocrystals(NC) necessitates a scaling up of their production. As a result, synthesis cost, tuneability of the NC size at full yield and synthesis reproducibility have become key issues. Finding an optimal approach in this respect is a matter of methodology, involving the use of larger scale or automated batch reactors or continuous flow-line approaches, yet it also concerns a reassessment of the reagents used and the reaction conditions needed. This is especially true for selenium precursors used to synthesize metal selenide nanocrystals such as CdSe. These involve selenium dissolved in either tri-octylphosphine (TOP) [1]- which is expensive and oxygen sensitive - or 1-octadecene, which leads to a precursor (homogeneous ODE-Se) with a low reactivity and a limited reaction yield [2].
Here, we propose an alternative approach to synthesize metal selenide NC&’s using a Se precursor that adds a high reactivity to the advantages of homogeneous ODE-Se. The method involves the direct injection of a heterogeneous mixture of selenium powder dispersed in a carrier liquid in a hot solvent containing a metal carboxylate as the cation precursor and excess carboxylic acid. Both in the case of cadmium and zinc carboxylates, we find that the injection of this heterogeneous ODE-Se precursor is followed by the formation of monodisperse nanocrystals, reaching chemical yields up to 80-90% within a few minutes. Moreover, the reaction can be run under ambient conditions without compromising the quality of the end product and the NC diameter reached at close to full yield can be tuned by changing the carboxylic acid chain length. In addition, since the amount of selenium injected is not limited by the solubility of selenium, the reaction can be executed with a high solid load, thus minimizing the amount of solvent needed. Finally, we demonstrate that syntheses involving the heterogeneous Se precursor as proposed here can be reproducibly executed on an automated synthesis platform, thus showing the potential of this novel approach for scaling up the production of colloidal metal selenide nanocrystals.
[1] J. Am. Chem. Soc., 2001, 123 (1), pp 183-184
[2] J. Phys. Chem. B, 2005, 109 (44), pp 20665-20668

A series of microspheres with tunable properties have been prepared by design by coating these spheres with functional nanoparticles. A simple solution-based process has been used to make these decorated microspheres. Nanoparticles were first synthesized with a water soluble polymer coating and subsequently attached onto the surfaces of polystyrene microspheres. These colloidal composites were purified by centrifugation and readily dispersed into aqueous and alcohol solutions. The nanoparticle coatings on the surfaces of the microspheres were stable to sonication for several minutes and during storage for prolonged periods of time (e.g., months). Properties of the microspheres can be tuned by varying the composition and density of the nanoparticle coatings with applications in plasmonics, catalysis, and environmental remediation. The coating method has been demonstrated for nanoparticles of different shapes, sizes and compositions including gold nanorods, lanthanide upconverting nanoparticles and FePt alloy nanoparticles. Our method has also been used in combination with physical vapour deposition techniques to make asymmetric (or Janus-type) particles. Close-packed arrays self-assembled from the designer microspheres exhibit tunable photonic properties and a surface enhanced Raman spectroscopic signal strength proportional to the density of the nanoparticle coatings. In addition, the designer microspheres are catalytically active and can be readily isolated from a reaction mixture by filtration or centrifugation; this makes these materials well suited for water based environmental remediation. This talk will discuss how we make these multifunctional materials, the characterization of the colloidal composites and their properties, and will illustrate how these properties can be fine-tuned for a range of applications.

In the present contribution we demonstrate that semiconducting PbSe nanocrystals can be produced via ion beam synthesis in Si (001) substrates following specific solid-state-reaction routes. The NCs were synthesized in 70 nm thick Silicon-On-Insulator (SOI) substrates and investigated by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) techniques, including high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images. The ion implantations were performed at 400 °C using only Pb or Se ions; or sequential implantation with both Pb and Se ions in alternate order. A major issue of the solid-state-reaction process concerns about the losses of Pb and Se atoms. Hence, the retention and redistribution of the implanted ions is investigated before and after high vacuum thermal treatments at 500, 750, 800 and 1000 °C. High resolution TEM micrographs and selected area diffraction patterns reveals three preferential orientations for the PbSe NCs with respect to the silicon matrix: i) co-planar PbSe[200]//Si[200]; ii) high misfit 45° tilted PbSe[220]//Si[200]; and iii) low misfit case PbSe[111]//Si[200]. Energy Dispersive X-Ray (EDS) line profiles and STEM-HAADF observations suggest an excess of Se atoms at the NC interface. In addition, core-shell particles with a PbSe core and a pronounced Se-rich shell are also observed. Based on the experimental data, the results are discussed considering solid state reaction model were Pb particles are initially formed and then start to react with Se atoms in order to form PbSe NCs. As the PbSe NCs grow, their structural misfit with the Si matrix tend to relax forming treading dislocations which seems to provide fast diffusion paths enhancing and allowing Pb and Se losses respectively.

Ferroelectric ceramics are very promising candidates for the fabrication of embedded capacitors with high electrical energy densities for applications in electronics and computing. Such devices have been conventionally based on ceramic-polymer film structures with a high dielectric permittivity and low losses. To prevent undesirable electrical properties associated with the presence of aggregated oxide grains, ceramic-polymer nanocomposites are obtained by mixing perovskite nanoparticles with ferroelectric polymers. Until now, it was difficult to prevent the aggregation of the nanoparticles as high quality ferroelectric nanocrystals are generally hydrophobic and they do not mix uniformly with ferroelectric polymers, which are generally polar in nature.
We developed recently a new approach for the surface modification of aggregate-free, monodisperse hydrophobic BaTiO3 nanocubes which enables their stabilization in polar solutions of ferroelectric polymers such as Polyvinylidene Fluoride (PVDF) and Poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP). To prove the versatility of this method, highly stable colloidal solutions of cube-like BaTiO3 nanocrystals and PVDF-HFP in dimethylformamide (DMF) with various volume fractions were used to obtain uniform nanocomposite films. These structures were interfaced with metal electrodes in capacitor geometry. The electronic characteristics of these nanoparticle-based capacitors, including the dielectric constant, loss tangent and stored energy density were measured at room temperature with a ferroelectric tester. The experimental results were in good agreement with ferroelectric domain studies performed by piezoresponse force microscopy (PFM).

Gold nanorods, and rod assembly structures, show promise as a breakthrough technology in many applications including single-molecule surface enhanced Raman scattering based sensors, biological tags, drug delivery vectors, and as a potential source for enhanced efficiency mechanisms in organic photovoltaics [1, 2, 3]. Gold nanorods have gained the most attention compared to other gold particle morphologies due to their tunable optical response, which is brought about through simply changing the rod&’s aspect ratio. Advances in bottom-up synthetic methods of gold nanorods have greatly improved yields as well as allowing access to a range of aspect ratios [4].
Despite great strides being made in synthetic methods, the growth mechanism of gold nanorods has been debated in recent years. A recent mechanism outlined by Park et al. shows that nanorods undergo 5 distinct stages of growth [5]. Stages II and III of this growth mechanism are dominated by epitaxial surfactant micelle adsorption to the growing crystal, and adatom migration during rod reconstruction, respectively. Both of these processes, occurring early in particle growth, clearly dominate the production of anisotropic species, as well as the resultant morphology. Therefore, our hypothesis is that nanorod growth should be most susceptible to crystal habit modification (CHM) during early growth stages.
In this work, we show that the addition of surfactants, having similar structure to the primary morphology-guiding surfactant cetyltrimethylammonium bromide (CTAB), during stages II and III of nanorod growth drastically influence the final dimensionality and morphology of nanorods. In contrast, addition at longer times has little or no influence on rod structure. Our results bolster the growth mechanism outlined by Park et al. proving nanorod growth is most susceptible to CHM during growth stages which are dominated by epitaxial micellular adsorption, and adatom reorganization. Furthermore, this work emphasizes the sensitivity of nanorod growth to the existing micellular state of the solution.
[1] Kosuda, K.M. et al., Comprehensive Nanoscience and Technology, 2011, 3, 263.
[2] Ferry, V.E. et al., Adv. Mater., 2010, 22, 4794.
[3] S. Rana et al., Adv. Drug Deliv. Rev., 2011, 64, 200.
[4] Vigderman, L. et al., Adv. Mater., 2012, ASAP.
[5] Park, K. et al., Growth Mechanism of Gold Nanorods. In Review.

The generation of polymer latex particles is typically carried out in aqueous emulsion or miniemulsion using commercially available emulsifiers. However, the presence of moisture and oxygen in these systems can cause problems. Polymerizations containing air and/or moisture sensitive compounds are impaired due to the chemical instability. Furthermore, moisture sensitive procedures, such as step-growth polymerization, can suffer from side-reactions and become unfeasible. Thus there is a strong need for a suitable technique, where the absence of water is ensured. The non-aqueous emulsion polymerization has proven its applicability towards these sensitive reactions.
A non-aqueous emulsion consists of an aprotic polar organic solvent, which is dispersed in a nonpolar organic solvent and stabilized by a tailor-made amphiphilic block copolymer. A variety of sensitive monomers like diisocyanates[1], diacid chlorides[2] as well as sensitive carbene-based catalysts[3-4] have been successfully applied in a non-aqueous emulsion polymerization. This technique therefore allows the formation of particles consisting of numerous different classes of polymers, e.g. polyurethanes, polyesters and even allows the formation of more complex morphologies such as core-shell structures.[1-6] The dispersions resulting from these one-pot reactions contain particles with a narrow size distribution.
[1] K. Müller, M. Klapper, K. Müllen, Colloid & Polymer Science, 2007, 285, 1157-1161.
[2] K. Müller, M. Klapper, K. Müllen, Journal of Polymer Science Part A: Polymer Chemistry, 2007, 45, 1101-1108.
[3] R. Haschick, M. Klapper, K. B. Wagener, K. Müllen, Macromolecular Chemistry and Physics, 2010, 211, 2547-2554.
[4] R. Dorresteijn, R. Haschick, M. Klapper, K. Müllen, Macromolecular Chemistry and Physics, 2012, 213, 1996-2002.
[5] M. Klapper, S. Nenov, R. Haschick, K. Müller, K. Müllen, Accounts of chemical research, 2008, 41, 1190-1201.
[6] R. Haschick, K. Müller, M. Klapper, K. Müllen, Macromolecules, 2008, 41, 5077-5081.

Colloidal semiconductor nanocrystals (NCs) have elicited considerable attention for their size-tunable properties as well as the potential for scalable, cost-efficient liquid-phase processing of optoelectronic devices. Heavily-researched Group II-VI and VI-VI (metal chalcogenide) semiconductor NCs rely on surface passivation by long-chain organic ligands for colloidal stability by providing a steric barrier to agglomeration. Since these ligands hinder charge carrier transport when NCs are cast into thin films for optoelectronics, significant efforts have been focused on ligand exchange and removal in solution or during film assembly. This work has recently spawned an alternative mechanism for colloidal stability - Charged inorganic ligands are exchanged at the NC surface to provide electrostatic stability.
In parallel, Group IV NCs are particularly desirable for their non-toxicity and abundance in comparison to their group II-VI and IV-VI counterparts. Similar to metal chalcogenide NCs, group IV NCs stabilize in non-polar solvents after long-chain ligand attachment; however, there is an important distinction. The ionic surface of group II-VI and IV-VI NCs facilitates ligand exchange whereas the surface species of group IV NCs are covalently bound, and chemical exchange methods cannot be applied. Alternative strategies must be applied.
Here we utilize Cl-terminated Si NCs to introduce a third mode of colloidal stability that does not rely on steric repulsion from bulky organic ligands or electrostatic repulsion from inorganic ions. This unique NC solvation mechanism relies on dipole-dipole interactions between Lewis acidic surface Si-Cl groups and solvents with hard, Lewis basic donors. As a result, this strategy may preclude any need for chemical treatments in going from NC synthesis to film fabrication. We discuss in detail the NC surface chemistry as well as solvent characteristics that lead to colloidal stability.
This work was supported by the DOE Energy Frontier Research Center for Advanced Solar Photophysics.

Nano- to microscale Au patterned structures are of great interest for use in a number of fields, such as e.g., electronics/plasmonics, biotechnology/biosensing and life sciences (e.g. for lab-on-chip architectures). A superb way to create such small site-specific three-dimensional Au structures of precise shape and location is to write them directly on a substrate with an electron beam via Electron-Beam-Induced Deposition (EBID). This technique is mask-free and is compatible with a multitude of substrates and patterns. In our case, we worked with one of the most commonly used Au organometallic precursor - the dimethyl gold acetylacetonate [Me₂Au(acac)]. It is known that direct writing of gold structures from this precursor results in a very low concentration of gold, only 8 - 12 at. %, the rest being carbon. In order to purify the deposits and increase the amount of metallic content in the EBID structures, post-deposition annealing at 600°C for 1 h in air was performed. It led to a dramatic purity increase - up to 92 at. % of Au (and above for very small single-grain nanostructures). However, thermal treatment of gold patterns leads to undesirable shape changes. In our work we resolved this problem to a large extent by using two different types of buffer layers: Ta and Cr, which are well-known for their superb adhesion properties. We established that for our purpose Ta serves as a more favorable buffer layer and leads to formation of a fine granular structure in annealed EBIDs that retain their original shape, while Cr itself undergoes a structural transformation, which in turn enhances reconfiguration of the Au deposits.
For device applications it is often undesirable to have a continuous metallic layer on the substrate. We show that wet etching can be used to remove the buffer layer from those areas that have not been patterned, following deposition and annealing. It was observed that the buffer layer could be completely removed from the areas not covered by EBID, without affecting the gold patterns.
References:
[1] A. V. Riazanova, Y. G. M. Rikers, J. J. L. Mulders, L. M. Belova, Pattern Shape Control for Heat Treatment Purification of Electron-Beam-Induced Deposition of Gold from Me₂Au(acac) Precursor. Langmuir 2012, 28, 6185-6191. http://dx.doi.org/10.1021/la203599c

A continuing goal in catalysis research is to engineer the size, shape and composition of noble metal nanomaterials in order to precisely tune their catalytic activity. In this contribution, we present proof-of-concept results on the synthesis of supported bimetallic core/shell nanoparticles (NPs) entirely by atomic layer deposition (ALD). ALD is a novel and scalable method, which can be used to prepare noble-metal catalysts particles directly on substrates with demanding three-dimensional (3D) surface topologies, as well as on materials with high surface-to volume ratios. Moreover, since only volatile byproducts are formed during ALD, the synthesized nanoparticles are contaminant-free (no surfactants etc.) and post-treatment steps (cleaning, reduction, separation and collection) are not necessary.
Two properties of ALD of noble metals, namely the Volmer-Weber island growth on oxides and surface selectivity on catalytic metal surfaces, are exploited to decouple NP core growth from subsequent selective shell growth. This allows for independent tuning of the core and shell diameter by varying the number of ALD cycles applied. We demonstrate the feasibility of this method through the synthesis of Pd/Pt and Pt/Pd core/shell NPs supported on alumina substrates. For ALD of Pd, a plasma-assisted process employing palladium hexafluoroacetylacetonate (Pd(hfac)2) and a hydrogen plasma at 100°C was used. An ALD process using methylcyclopentadienyl(trimethyl)platinum (MeCpPtMe3) and oxygen gas at 300°C was applied to deposit Pt. The tailoring of the properties of core/shell NPs in terms of particle sizes and compositions by changing the ALD process parameters will be addressed.
High angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) studies provide independent proof of the core/shell geometry and narrow size distribution (3-4 nm) of the synthesized core/shell NPs, while X-ray photoelectron spectroscopy (XPS) show that both the core and shell are in the metallic state.
Our results show that the self-limiting nature of the ALD process allows for independent control of the core and shell dimensions. Since selective ALD is not limited to Pt or Pd, our approach enables full control of the dimension and composition of multi-metallic core/shell nanostructures. It is therefore anticipated that many applications, including fuel cells and advanced sensors, can benefit from core/shell nanoparticles prepared by ALD.
[1] M. J. Weber et al., Chem. Mater. 24, 2973-2977 (2012).

While early works on nanoparticles were mainly focused on novelty, in order to develop a large variety of morphologies (nanocubes, nanostars, etc.) and size (from clusters to submicronic particles), today&’s effort also include robustness and reproducibility of the synthesis as well as fine control of structural features, such as core-to-shell ratio or composition control for bimetallic nanoparticles. Moreover, recent studies have pinpointed the role of surfactant partial decomposition for correctly assessing the surface chemistry of the nanoparticles.
Core-shell nanoparticles provide a unique access to bimetallic systems with well-defined interfaces and spatial distribution of elements. This is of major interest for studying structure-property relationships in magnetism and catalysis on a fundamental level, but also to develop more selective catalysts or more robust nanomagnets.
We designed a new solution-route synthesis for Ni-Co core-shell nanoparticles, where the core diameter and the shell thickness and the composition can be independently tuned in a highly reproducible fashion. The reproducibility is due to the use of a straightforward protocol with a minimal number of parameters.
Surface composition and core-shell evolution were studied under reactive gas exposure and heating, typical of those encountered in further integration steps. In situ ambient pressure XPS and ex situ HRTEM and STEM-EDS analyses revealed the change in morphology of the nanoparticles under exposure to H2, O2, CO, CO2 and syngas mixtures. The nanoparticles were found to develop a shell of oxide when exposed to air, but they could be reduced back to a metallic state at 330°C under 1 Torr of H2. Changes in the apparent surface ratio of Co and Ni were also probed by XPS depth profiling by generating photoelectron with a range of kinetic energies. The nanoparticles also showed the non-trivial role of ligand decomposition upon oxidation/reduction cycles, resulting in phosphorus doping of the surface, which affects surface-related properties such as self-assembly and catalysis.

Pulsed laser ablation (PLA) of solid targets immersed in liquids has recently been used to synthesize metal and ceramic nanostructures. The PLA method is highly advantageous compared to other techniques because nanoparticle (NP) synthesis is possible without organics or complex precursors. Here we report on the preparation and magnetic properties of ZnO nanoparticles by PLA of a solid zinc oxide (ZnO) target in water. The existence of ZnO is confirmed by energy-dispersive spectroscopy. The particle size (~ 100 nm) was dependent on the laser parameters like energy and frequency and not number of pulses on the target. The samples were also displayed ferromagnetic characteristics at room temperature. The saturation moment of the ZnO NPs is almost unchanged when comparing hysteresis loops obtained between 5K and 300K. So called d0 magnetism has been invoked to explain the magnetic characteristics which is different from traditional ferromagnetic models.

We report here on the transfer of hierarchical and periodic linear, square, oval, and triangular features unto Si <100> substrates. Laser interference ablation from a 266nm pulsed Nd-YAG laser on a phase separated PS-b-P4VP block copolymer was utilized for the generation of periodic large scale secondary ordering. The secondary ordering is variable with periodicity from 250nm to 2 µm depending on the angle of interference of the light beams. The laser patterned films are loaded with gold by dipping in a gold salt solution followed by an oxygen reactive ion etching resulting in the generation of gold features with primary ordering ~40nm. Feature transfer unto Si<100> was enabled using a plasma reactive ion etching with SF6:O2 reactive ion gases. A new phenomenon, Gold-metal catalyzed etching was effectively utilized on a large scale for feature transfer to Si<100> resulting in the generation of periodic and hierarchical linear, square, and triangular arrays with secondary periodicity from 600-200nm and primary ordering ~30nm. The flow rate of the gases, electrical power, and etch duration in the RIE chamber was optimized for both primary and secondary feature transfer from the patterned block copolymer unto Si (100) substrate. The isotropic etch profile in an SF6:O2 RIE plasma when maintained for about 30 seconds can retain both the primary and secondary orderings.
The feature height at different etch times was investigated using SEM and AFM, and ranges from 20nm to 100nm. Surface analysis with an XPS confirmed the presence of gold, silicon, fluorine and silicon oxide on etched Si (100) substrate. Gold was removed by dipping the etched substrate in an aqua regia solution, and the crystallinity of the etched substrate was confirmed with an XRD.
The technique can be readily integrated into the electronics industry where silicon processing for Very large Scale (VLSI) and Ultra Large Scale Integration (ULSI) integrated circuits is continually geared towards miniaturization and efficiency improvement for logic devices, MOSFETs, transistors etc. Furthermore, because most of the currently available advanced lithographic techniques use photo-resists that require several processing steps including: primer step, pre-bake, post-bake etc; gold catalyzed plasma reactive ion etching eliminates the need for those steps, and when combined with block-copolymer phase separation and laser interference ablation large area hierarchical features can be easily fabricated on Si<100> substrate and other silicon substrates with different orientations.

Size, shape, distribution and volume fraction of second-phase particles in the matrices of engineering materials exert strong influence on the resulting material properties, such as strength, ductility and chemical reactivity. Nitriding is a widely employed thermo-chemical surface treatment to improve the chemical (corrosion) and mechanical (fatigue and wear) properties of engineering components. Upon nitriding of iron or iron-based alloys containing dissolved alloying elements such as Cr, V, Ti, Al and Mo, the inwardly diffusing interstitial nitrogen atoms react with the nitride-forming alloying elements in the matrix frequently leading to the formation of nanosized alloying element nitride particles in the ferrite matrix. Thereby pronounced improvement of properties like fatigue and wear resistance can be achieved.
In a research project devoted to the nitriding of ferritic Fe-4.5at.%Si alloy, development of unusual, octapod-shaped (eight-legged), nanosized amorphous silicon-nitride particles was observed. Additionally, a strong temperature dependence of the shape of the amorphous precipitate particle was found: cuboidal shape at lower temperatures (< 580 °C), cube with concave faces and edges at intermediate temperatures (580 °C - 620 °C), and octapod at higher temperatures (> 650 °C). The faces of the cubical particles are parallel to the {100}-planes of the ferrite matrix and the legs of the octapod-shaped particle are oriented along <111>-directions of the ferrite matrix.
The development of an amorphous silicon-nitride modification instead of the thermodynamically stable crystalline modification can be ascribed to the relatively low interfacial energy of the amorphous/crystalline interface.
The occurrence of the octapod morphology for the amorphous precipitates in the crystalline matrix can be attributed to the strongly anisotropic nature of the kinetics of the diffusional growth process within the stress and concentration fields evolving around the growing precipitates: the initially cubical particle shape (a shape likely governed by favourable interface energy), the very high precipitate/matrix volume misfit (> 100%) and the elastically strongly anisotropic nature of the ferrite matrix cause outgrowth of the amorphous particles especially along <111>-directions of the crystalline ferrite matrix, in particular at higher nitriding temperatures where the elastic anisotropy of the ferrite matrix is higher. Thereby an avenue is opened to control the shape of amorphous nanosized precipitate particles.

Thermal and microwave radiation assistance procedures based on the polyol route have been optimized to obtain high concentrated ferrite magnetic nanoparticles [MFe2O4 (M=Mn, Fe, Co, Ni, Zn)] dispersible in a huge range of polar dispersants. Both methodologies generate similar ferrite nanoparticles (Oslash; 5-10 nm) , being more advantageous in efficiency microwave procedure owing to their lower time (10 min vs 150min) and annealing temperature (220oC vs 280oC). The high concentration of the nanoparticles as synthesized (up to 256 mM of free Fe3O4), the possibility to disperse them into high ionic force solutions, and the scalability of the process, makes the colloidal nanoparticles very useful in a wide range of applications.
Common laboratory techniques have been performed in order to characterize the ferrite nanoparticles (HR-TEM, XRD, IR, SQUID, TGA-DSC, etc.). Results have demonstrated the expected structural and magnetic properties of the ferrite magnetic nanoparticles. Deeper studies trough neutron diffraction and XAS/XMCD analysis with synchrotron radiation have been applied in order to characterize the structure and magnetic behaviour of the synthesized nanoparticles:
Neutron diffraction analyses with Rietveld refinement methodology demonstrate the spinel structure jointly to the cation distribution into the octahedral and tetrahedral sublattices and their magnetic moment. Pure ferrite magnetic nanoparticles are obtained without secondary phases, except for the magnetite, where maghemite structure can be found.
XAS data for some of nanoparticles synthesized shows a first approximation of the chemical composition that agrees with the expected ferrite composition, while XMCD results demonstrate their magnetic properties. Sum rules have been applied to know the orbital and spin moment of the magnetic atoms present in the samples.
All results of the different techniques applied show that thermal route and microwave radiation assisted synthesis generate chemical and structural equal nanoparticles, confirming that microwave route is an eco-friendly more efficient methodology for nanoparticles generation.
Properties of synthesized nanoparticles make them very useful in different application fields. The main objective under study (among others) of the synthesized ferrite nanoparticles is to be applied into YBa2Cu3O7-δ superconducting thin layers to improve their intrinsic behaviour. Nanoparticles embedded inside the superconducting matrix has been also study with XAS/XMCD synchrotron radiation.

Within the III-V semiconductor family, indium antimonide is a material of particular interest. In the bulk, InSb exhibits the largest electron mobility (78 000 cm²/Vs) of any inorganic semiconductor. Compared to the other III-V compounds, InSb shows the narrowest band gap (0.18 eV) along with the largest exciton Bohr radius (65.5 nm) and a high static dielectric constant (17.9). Therefore, in form of nanocrystals, InSb constitutes an ideal candidate for obtaining strong quantum confinement over a large range of sizes. According to theoretical predictions, one can expect to increase the band gap of InSb nanocrystal quantum dots by several electron volts when reducing the diameter from around 20 nm to <6 nm. This could lead to a wide range of applications such as LEDs, photodetectors, and other optoelectronic devices.
The main difficulty in the chemical synthesis of colloidal InSb NCs arises from the lack of appropriate antimony precursors. For InP and InAs NCs, generally tris(trimethylsilyl) derivatives of the corresponding group V elements have been applied. Translating this synthetic scheme to InSb met only limited success due to difficulties in the synthesis and handling of (TMS)₃Sb. We developed a novel method using in situ generated stibine gas as the antimony precursor in the synthesis of InSb NCs. The fine-tuning of the reaction parameters allowed us to produce nanocrystals with a mean size of 7 nm and a size distribution of 13%. Larger particles (~100 nm) can also be obtained by increasing the reaction temperature. X-ray diffraction shows that the nanocrystals exhibit the zinc-blende structure (space group F4-3m) with a lattice parameter of 6.48 Å at 300 K. Elemental analysis using EDX results in In_0.48Sb_0.52, i.e. a close to equiatomic composition. UV-vis spectroscopy indicates that the band gap of the 7 nm nanocrystals is below 1.5 eV. This value is significantly lower as the one calculated with the effective mass approximation (around 2 eV), pointing out the limits of this model for narrow band gap semiconductors with extremely small electron effective masses.
These results are an important step toward the integration of colloidal InSb NCs in a wide range of applications such as for example infrared photodetectors, solar cells, and LEDs. They also pave the way for the synthesis of other antimony-based nanoparticles.

Physical vapor deposition, in combination with gas-aggregation (PVD-GA), is a controllable method for creation of diverse nanoparticle structures. Given the size effects that dominate the physics of nanoparticles, a particular advantage of the PVD-GA technique is the compatibility with in situ mass filtering of the nanocluster beam.
In the current work, PVD-GA has been utilized to deposit Ag and Si nanoparticles. Nanoparticles were analyzed using in situ quadrupole mass spectrometry (charge/mass ratio), atomic force microscopy (nanoparticle height), and transmission electron microscopy (nanocluster diameter & crystallinity). The results for particle size distribution were cross-correlated, with excellent agreement.
Different growth methods & conditions were explored, resulting in controlled differences in the measured particle size distributions and surface coverage. A novel growth configuration utilizing a conventional sputter source in combination with a linear magnetron allowed a significant (fivefold) increase in Ag cluster yield.

Novel permanent magnets comprised of nanostructured ferromagnetic cores with hard magnet shells may provide alternatives to critical rare-earth-based permanent magnets. Applications include energy conversion devices such as electric vehicles and wind turbines. The proposed structure has isolated soft-magnetic domains in magnetically aligned hard-magnetic matrix with critical domain dimensions of 5- to 10-nm. In addition, high aspect-ratio soft-magnetic cores facilitate magnetic alignment and magnetic domain integration. The continuous fabrication of discrete, high aspect ratio FeCo alloy nanofibers by electrospinning and appropriate post-heat-treatments will be discussed. Simulations of the electrospinning process will be presented. Envisioned applications require the nanofiber diameter to be below 10-nm; fabrication methods and achieved magnetic properties will be discussed and compared with bulk material. The application of hard-magnetic shells to the soft-magnetic cores will be discussed and magnetic properties of composite core-shell nanoparticles and ordered assemblies will be presented.

Extensive research has been devoted to the development of metal nanostructures to manipulate the propagation, intensity and polarization of light. Within these materials gold is known to have some unique properties such as surface plasmon resonance (SPR) which arises from the collective oscillation of conduction electrons. Furthermore, the plasmonic nanoparticles with unique, tunable optical properties make them attractive targets of wide range of potential applications including biosensors and solar cells. However, such diverse applications require the ability to tune the plasmonic properties, i.e. to prepare particles with controlled composition, morphology and size.
In this paper, we present a new atmospheric aerosol synthesis method for the preparation of nanocolloidal gold. A novel metal-organic gold complex was synthesized and used as a precursor in the studies. The precursor was dissolved in ethanol and atomized using a constant output atomizer. The aerosol was then carried to the heated zone of the reactor, which temperature was varied between 200 oC and 800 oC. In addition, the effect of the reaction atmosphere, i.e. inert, oxidizing, reducing, on the particle formation was investigated.
The particle formation is based on the reaction of the precursor that leads to formation of gold nanoparticles. The colour of the produced particles collected on the filter varied from bright yellow to deep purple depending on the reaction temperature and atmosphere. The particles formed at temperatures below 400 oC were liquid-like droplets consisting of nanocolloidal gold with a uniform primary size with the crystallite size below 5 nm. The particles formed at 800 oC were solid crystalline particles. The particles had a uniform coating layer around the particles that consisted of amorphous carbon.
This work was supported by the strategic funding of the University of Eastern Finland (NAMBER spearhead project).

Semiconductor nanocrystals (NCs) are attractive materials for light-emitting devices due to their size-tunable band gap, compatibility with solution processing and high photoluminescence (PL) efficiencies. Interest in Group IV NCs has increased in recent years due to the observation of photoluminescence in quantum confined particles, allowing applications ranging from biological imaging to optoelectronic devices. Silicon NCs are also attractive materials due to their low toxicity. The use of reverse micelle templates for nanocrystal synthesis has been well reported for the ability to control the nucleation and growth kinetics of a wide range of metal and semiconductor systems. However, while there have been a number of reports on the effect of surfactant choice on the size and shape of metal nanostructures, there have been fewer reports on their influence on semiconductor NCs.
Here we report the solution-phase synthesis and characterization of size monodisperse Si NCs with well defined core diameters between 2 to 6 nm. Si NCs were synthesized under inert atmospheric conditions via the reduction of Si halide salts (SiX₄) by hydride reducing agents within inverse micelles. Regulation of the Si NCs size was achieved by variation of the cationic quaternary ammonium salts used to form the inverse micelles. Covalent attachment of alkyl- or amine-terminated monolayers to the nanocrystal surface produced NCs that were stable under ambient atmospheric and lighting conditions over a period of months, which were readily dispersed in a variety of solvents. Transmission electron microscopy (TEM) imaging confirmed that the NCs are highly crystalline with a narrow size distribution; the diamond cubic crystal structure of Si was confirmed by selected area electron diffraction (SAED). Energy dispersive X-ray spectroscopy (EDX) indicates the presence of Si and the absence of other contaminants. UV-Visible absorbance (UV-Vis) and photoluminescence spectroscopy (PL) showed strong significant quantum confinement effects, with moderate absorption in the UV spectral range, and a strong blue emission with a marked dependency on excitation wavelength. These findings contrast with the relatively long-wavelength red emission observed for oxide-coated Si NCs, showing the importance of the surface chemistry on their photophysical properties. Determination of the photoluminescence quantum yield (Phi;_f) of the Si NCs showed an inverse relationship with the NC core diameter, with a maximum of 13% measured for 2 nm NCs.
This work was supported by the European Commission under the FP7 Security Projects SNAPSUN (grant agreement number 246310) and CommonSense (grant agreement number 261809) and the Irish Higher Education Authority under the PRTLI program (Cycle 3 “Nanoscience” and Cycle 4 “INSPIRE”).

Transmission X-ray Microscopy (TXM) is a powerful tool to obtain two-dimensional and three-dimensional projected images, as well as composition profiles at nanometer resolution using variation of X-ray transmittance in two-dimensional incident angle (~140°) and mathematic reconstruction of internal microstructure. So far, the TXM has been employed in biology to observe cell structure, in rechargeable batteries to record electrode reaction in-situ, and in semiconductors for defect identifications. In this work, we adopt the TXM to conduct structural characterizations on colloidal crystals and their inverse opals so the crystallinity and defects distribution can be determined in relatively short time. Currently, the observation of colloidal crystals and their inverse opals employs scanning electron microscope (SEM) in a vacuum state, and to obtain cross-sectional view, the sample is deliberately broken to expose edges. As a result, the structural integrity is compromised and the observed packing order might be altered. In addition, the top-view image provides colloidal arrangements at the top-most layer, and microspheres underneath become indiscernible. In contrast, the TXM enables top-down structural projection in a non-damaging mode and three-dimensional tomography so an in-depth profile can be determined exactly. Hence, critical crystallographic parameters such as packing order (ABCABC vs. ABABAB), grain size and shape, as well as grain boundary can be obtained while the sample integrity is nicely maintained.
In our laboratory, we adopt an electrophoresis process to fabricate colloidal crystals (basing on polystyrene microspheres of 300-800 nm) with superb surface uniformity. Subsequently, the colloidal crystals are served as a template to allow electroplating of Ag, Ni, Au, Cu, or ZnO into the interstitial voids, followed by removal of the polystyrene microspheres to acquire an inverse structure with controlled layers/thickness. These structures are of promising potentials in many engineering applications.

We report a transformative, all inorganic-based method for synthesis of supported bimetallic alloy nanoparticles by rupturing corresponding bulk alloys, for example, Pd3Ag alloy into Pd3Ag nanoalloys in liquid lithium. Subsequently, metal Li is converted to LiOH powder, in which the Pd3Ag alloy nanoparticles are embedded. The Pd3Ag nanoparticles are readily transferred onto any non-water soluble support materials by simply mixing the LiOH powder with the support material, followed by leaching off the LiOH with water under ambient conditions. The size of the resulting Pd3Ag nanoparticles is narrowly distributed around 2.3 nm characterized by transmission electron microscope (TEM). In addition, X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy suggest that the resulting Pd3Ag nanoparticles inherit similar atomic ratio and alloy structure as the starting bulk alloy. This top-down method is based on a purely inorganic process with merits envisioned as below. (1) The method is potentially cost competitive and environmentally friendly, as it does not use any expensive and/or toxic organic solvents or ligands. Thus, no hetero atoms that can cause unwanted catalyst poisoning such as chloride, will be present in the final product; (2) This process bypass the reduction of metal ions, thus, the difference in reduction potentials of metal ions is no longer an constrain in the synthesis of precious intermix bimetallic nanoalloys; (3) Since the leaching process is conducted under ambient conditions, the support materials require no pretreatment, provided they are not water-soluble. Thus, a variety of support materials become applicable for this method; (4) Except the precious metals themselves, lithium metal appears to be the only costly agent used in this method, but it can be conveniently recycled in the form of LiOH/Li2O, which are the starting materials in existing industrial production of metal lithium.

Iron carbide nanoparticles have been long considered of great potential in new energy conversion, nanomagnets and nanomedicines. However, the conventional relatively harsh synthetic conditions of iron carbide hindered its wide applications. In this article, we presented a facile wet chemical route for synthesizing Hägg iron carbide (Fe5C2) nanoparticles, in which bromide was found as the key inducing agent for the conversion of Fe to Fe5C2 in the synthetic process. The as-synthesized Fe5C2 nanoparticles were further applied in FTS and exhibited intrinsic catalytic activity in FTS, demonstrating that Fe5C2 is an active phase for FTS. Compared with conventional reduced-hematite catalyst, the Fe5C2 nanoparticles showed an enhanced catalytic performance in terms of CO conversion and product selectivity.

Nanoparticles (NPs) are well known to display properties that differ distinctly from their bulk counterparts. Also, ensembles of NPs are known to exhibit collective properties, which differ from the characteristics of an individual NP. These collective properties have potential in many different applications. This has motivated the broad investigation of self- and directed-assembly techniques for the production of controlled arrays of NPs.
In this presentation, we discuss the development of a new technique for fabricating locally-ordered arrays of NPs, electrophoretic deposition (EPD). EPD is a rapid, safe, and facile method for depositing suspended nanomaterials on a large scale. In one minute of deposition, we can fabricate homogeneous NP monolayers on surfaces 1.0 cm x 4.0 cm or larger. The size of the substrate can easily be scaled with little change in the deposition time or resulting film. Because the collective properties of NP arrays are dependent upon the ordering of the particles, the spacing between particles, and so forth, we developed and demonstrate techniques for quantifying the order and spacing between the NPs. By quantifying the order of the films, not only can we optimize ordering within the system, but we also can determine the mechanisms that create order within the films. Further, quantification of order, applied to monolayers deposited on patterned and unpatterned substrates, confirms that patterning does influence nanoparticle ordering. Also, interparticle spacing measurements along with magnetic measurements are used to calculate the strength of nanoparticle-nanoparticle magnetic dipole and van der Waals interactions, which indicate that two-particle interaction energies are much less than the thermal energy present within the system.

The spontaneous self-assembly of materials into complex architectures leads to the emergence of advanced materials and convenient tools for nano-device fabrications. Colloidal dispersions of interacting particle subjected to an external periodic forcing often develop original self-organization patterns [1] and complex collective behaviors. The last decade, a wide variety of studies has been carried out on the assembly and motion control of particles at micro and nano-scale by using different mechanisms to trigger the motion, such as electric/magnetic guidance [2] and electrochemical reaction. Furthermore, the colloidal order-disorder transitions offer unique opportunities for reversibly assembling and disassembling in liquid media [3]. Electric-field-tunable colloids exhibit a rich diversity of stable equilibrium structures and remarkable novel self-assembled phases such as toroidal vortices and pulsating rings.
The non-equilibrium phase properties of fluorescent PMMA colloidal suspensions under AC electric field were investigated in real-space with experiments in organic solvent. The formation of chain-like organized structures was observed in a long-range order. Thickness and inter-distance of chain structures were demonstrated to be dependent on both the frequency and the intensity of the applied electric field, as showed in the phase diagram. Kinetics of assembly, hydrodynamic aspect and surface state charge were investigated to improve our insight into these non-equilibrium assembly processes.
On the other hand, a study of the self-assembly of active colloids was carried out at nanoscale by using a liquid cell specimen holder TEM/STEM (Poseidon-Protochips). Direct imaging of CdSe/CdS nanorods in liquid (static and flow mode) with electron microscopy provided quantitative information on the self-assembly and collective properties at nanoscale. Furthermore, electrodes within the liquid cell allow us to apply a local electric field in order to modify the motion of nanorods in suspension, by tuning parameters (TEM, solution, field) we were able to control the motion and the self-assembly process and image these processes at nanometer scale.
[1] Henry Chan, Arnaud Demortière, Lela Vukovic, Petr Král, Christophe Petit, ACS-Nano, 2012, 6(5), 4203.
[2] Alexey Snezhko, Igor Aranson and, Wai Kwok, Phys. Rev. Lett., 2005, 94, 108002.
[3] Alexey Snezhko, J. Phys.: Condens. Matter, 2011, 23, 15310.

The development of novel electrically conductive adhesives (ECAs) to provide robust bonding and multifunctional properties is important for electronics manufacturing at ever-smaller scales. In this talk, we will present our recent progress on the synthesis and functionalization of very small silver nanoparticles (less than 5 nm) as conductive fillers in the ECAs. Thiocarboxylic acids with different chain lengths, i.e., mercaptoundecanoic acid (MUA) and mercaptopropionic acid (MPA), were used to synthesize and functionalize the silver nanoparticles (NPs). We found that self-assembly of organic materials with different chain lengths lead to formation of NPs with different sizes. Electrical conductivity measurements of the NPs films showed that NPs functionalized with short-chain acids were electrically conductive while the long-chain functionalized ones were nonconductive. According to the information extracted from thermal gravimetric analysis results, the number density of the organic chains covering the surface of Ag-MUA is almost 3 times larger than that of Ag-MPA NPs. We found that the denser and longer chains on Ag-MUA effectively insulated the silver particles. By controlling the rate of nucleation formation and the self-assembly mechanism of thiocarboxylic acid we are able to synthesise high aspect ratio nano-structure, which can cause a significant influence on electrical performance of ECAs. Thermal, morphological, and electrical properties of this nano-structure with respect to its application as conductive filler are investigated.
It is well known in the literature that incorporation of silver NPs before percolation value improves the electrical conductivity of ECAs while beyond that addition of NPs has a negative effect on electrical conductivity. We found that silver NPs can have a positive effect in the all range of filler contents (either before or after percolation value) if the size of NPs were small enough. The short-chain functionalized NPs were incorporated into a system consisting of micron-sized silver particles and an epoxy matrix to form a hybrid-designed electrical conductive adhesive. The electrical conductivity measurements combined with SEM images of the cross-section of the cured hybrid composite showed that a lower content of the NPs (< 20 wt %) increased the electrical conductivity. We attributed the positive effect of synthesized NPs on the electrical conductivity of the nanocomposite to their very small size and specific design of covering layer over the surface of NPs. These research findings provide insights into the relationship between the overall properties of the nanocomposites and the nanoparticles&’ surface chemistry, size and weight fractions.

Surfactant-free non-aqueous (and/or non-hydrolytic) sol-gel routes constitute one of the most versatile and powerful methodologies for the synthesis of nanocrystalline metal oxides with high compositional homogeneity and purity.[1] A representative example is the solvothermal reaction of zirconium isopropoxide in benzyl alcohol leading to the formation of uniform zirconia nanocrystals, which can also be doped by the addition of various metal complexes to the reaction mixture.[2]
In the present work the “benzyl alcohol route” was exploited to synthesize pure and rare-earth (Tb3+, Y3+, and Eu3+) doped zirconia nanoparticles presenting high crystallinity and uniform particle size (ranging from 3 to 4 nm). The main weakness of the surfactant-free non-aqueous route can be overcome, here, by the in situ formation of benzoate species, which are believed to act as stabilizing and structure-directing agents leading to the self-assembly, in the reaction medium, of the as-synthesized nanoparticles into highly ordered supercrystals with well defined morphology.[3] Furthermore, the as-synthesized nanoparticles present excellent luminescent properties in the UV to blue spectral region, with quantum yield values one order of magnitude higher than that reported in the literature for similar size zirconium nanoparticlesascribed to the cooperative effect between the capping benzoate species and defects associated to the zirconia nanoparticles such as oxygen vacancies.[4] Furthermore, as fine and reactive nanopowders can in principle be sintered at lower temperatures than conventional powders, the feasibility of the as-synthesized zirconia nanoparticles to be processed for the production of dense ceramic materials has been investigated.
The supercrystals morphology and structure, the 3D assembly mechanism, the optical and sintering properties are investigated as a function of doping and of the capping benzoate species.
References:
[1] N. Pinna, M. Niederberger, “Surfactant-free non-aqueous synthesis of metal oxide nanostructures”, Angew. Chem. Int. Ed., 2008, 47, 5292
[2] A. Pucci, G. Clavel, M.-G. Willinger, D. Zitoun, N. Pinna, “Transition metal doped ZrO2 and HfO2 nanocrystals”, J. Phys. Chem. C, 2009, 113, 12048
[3] A. Pucci, M.-G. Willinger, F. Liu, X. Zeng, V. Rebuttini, G. Clavel, X. Bai, G. Ungar, N. Pinna, “One-step synthesis and self-assembly of metal oxides nanoparticles intp 3D superlattices”, ACS Nano, 2012, 6, 4382
[4] X. Bai, A. Pucci, V. T. Freitas, R. A. S. Ferreira, N. Pinna, “One-step synthesis and optical properties of benzoate- and biphenolate-capped ZrO2 nanoparticles”, Adv. Funct. Mater., 2012, DOI: 10.1002/adfm.201200759

Nanostructured metal architectures exhibit important capabilities for catalytic, sensor, and fuel cell technologies. The ability to control an interconnected metal framework over the nanometer scale is essential for these applications. “Dealloying” is one of several effective methods to fabricate 3D continuous metal nanostructures. Through chemical reaction or thermal melting processes, the most electrochemically active elements are selectively removed leaving nanostructured metal architectures with disordered porosity. This method generally requires lengthy, aggressive chemical reactions; high temperatures; and toxic, corrosive processing. A mild “etching” process was developed using silver nanocubes as sacrificial templates to synthesize nanostructured hollow gold architectures. Other methods include block copolymer-templated growth and physical deposition on a patterned substrate. Here we show a pressure-directed self-assembly (PDSA) method we have recently developed to fabricate 3D ordered, interconnected, porous metallic nanostructures (Au, Ag, etc) through high pressure-induced sintering of spherical gold nanoparticle arrays at room temperature. The fabrication process is simple and clean without requiring complicated chemical reactions, thermal processing, or purification to remove reaction byproduct. Through in-situ high pressure small angle x-ray scattering and high resolution TEM studies, we show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle array can be reversibly manipulated allowing fine-tuning of the interparticle separation distance. 3D nanostructured metallic architectures can be formed when external pressure is greater than 9 GPa. The resulting architectures have a nanoporous skeleton with a pore size of ~ 5 nm. High resolution TEM imaging shows that twinning faults within an individual branched metallic framework (or skeleton) are formed during sintering of spherical nanoparticles, which confirms that the metallic networks are formed by the multidirectional sintering of spherical gold nanoparticles. This work opens a new pathway for engineering and fabrication of a new class of chemically and mechanically stable metal nanostructured architectures.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

The membrane-based systems with an array of small aperture have proven successful in a wide range of applications such as quantitative control of diffusion or filtration and precise patterning of various nanomaterials. However, the most inorganic-based membrane system is difficult to be integrated with microfluidic applications for synthesis of nanomaterial due to its rigid nature. We report that a monolithically integrated, hierarchical polymeric membrane with various sizes of apertures can be utilized to form highly uniform lipid vesicles under quantitative control of molecular diffusion.
In addition, the possibility to synthesize monodisperse asymmetric lipid vesicles is of significant interest but challengeable for bio-inspired drug delivery system, in terms of efficient encapsulation of drug and precise targeting for drug. We demonstrate that one can take advantage of the above-mentioned polymeric membrane and microfluidic setup to generate highly uniform asymmetric lipid vesicles. Specifically, the sizes of the vesicles are easily controllable from micro- to nanoscale, which can be applied to various drug delivery and biosensor applications.

Multiplex analysis using suspended encoded particles have received much attention in high throughput bio-molecule screening thanks to their outperforming scalability and fast reaction kinetics over conventional 2D biochips. In the first part of this talk, I will present various functional encoded particles with surface bound molecules such as spinning color barcoded microparticles and encoded hydrogel particles with viral vector. We fabricated color barcoded microparticles based on structural colors from magnetically self-assembled nanoparticle composite called ‘M-Ink&’. Our color-barcoded magnetic microparticles offer a coding capacity easily into the billions with distinct magnetic handling capabilities including active stirring for improved reaction kinetics in microscale environments. A DNA hybridization assay is done using the color-barcoded magnetic microparticles to demonstrate multiplexing capabilities and it is proven that the spinning motion of the particle reduces incubation time of the DNA binding assay by an order of magnitude.
The second part of the talk will be focused on how to handle millions of different liquid using encoded particles. Current multiplexed assays based on encoded beads are limited to multiplexing of surface bound probe molecules such as DNA or proteins and are not able to handle chemical compound liquid libraries, which is essential for drug screening. Highly heterogeneous liquid chips for high throughput liquid cell based screening assay has not been developed yet due to challenges mainly in small volume liquid handling. We present an ultraplex compound screening platform based on our new liquid handling method named ‘partipetting&’. Partipetting is defined as a single pipetting operation of simultaneously self-assembling million different liquid drug-laden microparticles into million separate reaction wells in a microfabricated well plate, implying ‘Pipetting encoded Particles&’. By partipetting our ‘liquid capped encoded microshell&’ on to the million reaction well, we have demonstrated an ultraplex liquid chip array can replicate conventional well based screening with much higher throughput. We envision that this technique will enable users simply choose and order a type of chemical compound chips from a catalog instead of repeating million pipetting in-house.

Quantum dots (QDs) have attracted great attention as good candidate for the next generation displays due to their narrow emission, and high luminescence efficiency, and tunable emission covering all visible range. However, QDs easily lost their initial optical properties during the process for a device fabrication and practical operation. We have synthesized novel structure of alloyed core/multishell CdSe//ZnS/CdSZnS structures that have larger size with less surface area compared to the simple core/shell CdSe/ZnS QDs with same energy band gap. The alloyed core/multishell QDs employ blue light emitting CdSe//ZnS alloy core and the emission wavelength can be controlled by additional CdS shell layer thickness, exhibiting almost 100% of QE. We applied the highly luminescent green and red light emitting QDs thus obtained as color converters in InGaN blue LEDs. Resulting cool white QD-LEDs showed 41lm/W and more than 100% of color reproducibility compared to NTSC standard in CIE1931 and maintained their optical properties for a long time operation. We also demonstrated a 46-inch LCD panel using the white QD-LED backlight was successfully demonstrated.

The design of electronic circuits from metal nanoparticles has been a challenge because arrays of metal nanoparticles typically exhibit linear current-voltage characteristics: such characteristics are only useful for the construction of resistors. Here we report a class of ligand-stabilized metal nanoparticles that greatly expands the range of electronic properties that can be accessed. We present six electrical components that are built from metal nanoparticles: transistors, diodes, resistors, thermistors, and two types of sensors. In most cases, the nanoparticles have alkanethiols ligands that are terminated in the omega-position with N,N,N-trimethylammonium chloride. We describe how the coupling of ionic current from the charged ligand with the electronic current via electron tunneling leads to non-linear current-voltage characteristics that enable these new components. We show how these components can be combined to construct complex circuits, including logic gates, a half-adder circuit, and random access memory. At the same time, the individual components—most especially, the thermistors—provide a performance that exceeds that of state-of-the-art semiconductors. In this way, we illustrate how materials assembled from nanoparticles may emerge as an important new platform in new classes of electronic devices.

Shape control is one of the most exciting aspects of the nanoparticle synthesis, which allows for manipulating the chemical and physical properties of nanomaterials. The control of the nanoparticle physical properties also leads to new types of nanoparticle applications. In this talk, the key concepts in the shape control of iron oxide nanoparticles will be discussed using ultrathin nanowires and nanoflowers as examples. Further, the surface functionalization of spherical and cubic iron oxide nanoparticles will be introduced, yielding nanoparticles with different properties. Finally, the developmental effects and innate immune response of nanoparticles on Drosophila flies will be covered.

The high surface area and short path lengths from bulk to surface in nanoporous Pd lead to improved kinetics for hydrogen uptake and release in metal hydride battery electrodes, gas separation membranes, and isotope separation systems. In tritium storage and separation applications, the helium decay product can more easily diffuse out, mitigating damage caused by bubble formation. We prepare batches typically on a 0.1-1 g scale through chemical reduction in a lyotropic liquid crystal template or within dendrimers. In situ transmission electron microscopy reveals that seed nanoparticles form in the reduction step that then fuse around the template. Removal of the template by solvation or degradation yields micrometer-scale particles with nanometer-scale pores, which in the liquid crystal case are highly ordered. Subsequent treatments allow surface functionalization with other metals to enhance reactivity and improve thermal stability. We demonstrate the integration of the material into an isotope separation device for fractionation of a mixture of H2, D2, and HD.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Assembly of anisotropic nanoparticles over a large area is a key issue towards devices performing collective anisotropic physical properties. Although various self-assembly techniques have been developed since decades, extending the organized domain size to the macroscopic scale is not straightforward. We present a simple method for parallel (in-plane) assembly of colloidal nanorods based on a conventional coating process applicable to a large area thin film fabrication. The orientation of nanorods was promoted by their shear-aligning behavior in flowing liquids. And the typical problems of this approach such as orientation relaxation, texturing, and defects were eliminated by tuning the colloidal suspension into a thixotropic gel phase, in which rod orientation can be frozen after a temporary application of shear. As-prepared aligned lanthanum phosphate (LaPO₄) nanorod films show an almost perfect orientation (S>0.99) over the whole film area (demonstrated with a size of 7.5cm x 2.5cm), which was evidenced by polarization optical microscopy, SEM, and XRD analysis. Thanks to the high band gap and the crystalline anisotropy of hydro-thermally synthesized LaPO₄ nanorods^[1], the film exhibits remarkable birefringence (Δn=0.13) associated with high transparency on the entire UV-Vis-IR range^[2]. Such a large birefringence is found to be an optimal combination of form birefringence from the ordered structure and the intrinsic birefringence of the LaPO₄ crystal itself (Δn_LaPO4=0.05). This film can be directly used as a cheap inorganic thin film wave plate for a variety of optical applications (e.g., UV optics, high power laser devices, and telecommunication). Additionally, we also present a sharply polarized fluorescence emission from the same type of film when LaPO₄ nanorods were doped with europium, which are indeed efficient rare-earth phosphors.
[1] J. Kim et al., Adv. Funct. Mater. doi: 10.1002/adfm.201200825 (2012)
[2] J. Kim et al., Submitted to Adv. Mater. (2012)

In recent years, solar cells incorporating colloidal nanocrystal quantum dots (QDs) as the absorbing material have emerged as leading class of third generation photovoltaics. While the highest efficiencies are somewhat low today (~7%), the rate of improvement is faster than any other type of solar cell technology with a slope of ~1.5%/yr. With bulk band gaps of 1.0-1.5eV, one of the largest extinction coefficients among direct gap semiconductors, high carrier mobilities, and lack of toxic components, CuInSexS2-x shows great promise as the absorbing component of solar cells. We have shown that gram scale quantities of CuInS2 quantum dots can be synthesized with a range of sizes (and increased band gaps) with 90%+ chemical yield. More recently, we have modified the synthesis to incorporate controlled amounts of Se to shift the band gap to the near-IR without increasing quantum dot size. By applying mild Cd or Zn treatments to the dots, their photoluminescence (PL) can be enhanced more than 400-fold and the exciton lifetime increases by an order of magnitude without significant changes in absorption. High PL quantum yields imply suppressed non-radiative recombination pathways, crucial for high efficiency photovoltaics. Composition analysis indicates a selective surface-cation exchange gives rise to the enhanced PL. Electron transfer from CuInSexS2-x QDs to meso-porous TiO2 is not significantly hindered by the mild cation-exchange while the increased exciton lifetime results in higher photocurrent. In collaboration with Sharp Corporation, we are sensitizing meso-porous TiO2 with CuInSexS2-x QDs to fabricate high efficiency QD-sensitized solar cells (QDSSCs). On-going device studies are giving new insights into strategies for enhancing the performance and durability of QDSSCs including the importance of reducing recombination pathways such as surface traps without deterring charge transfer.

Here we report flexible and low voltage nanocrystal integrated circuits (NCICs), constructed from high performance nanocrystal (NC) field effect transistors (FETs). Colloidal semiconductor nanocrystals (NCs) can be processed like "inks" by a variety solution-based material deposition techniques to form uniform NC thin films over large areas. Long chain ligands are commonly used in synthesis to control NC size and shape. However, these long ligands provide insulating barriers that limit interparticle coupling and carrier transport. Recent advances in NC surface modification has shown that these long insulating ligands can be replaced with compact ligands to greatly enhance NC coupling and transport. We introduced the thiocyanate ligand, a compact ligand that is environmentally benign and non-corrosive, compatible with flexible, plastic substrates. Here, we fabricate flexible, low voltage, and high performance CdSe NC-FETs with average carrier mobilities of 22 cm^2/V^-1s^-1 and current modulation of 10^6. We developed vertical interconnect access (VIA) holes to connect multiple NC-FETs with uniform device parameters over large-area to form NCICs. We use nanocrystal integrated inverters as building blocks to demonstrate voltage amplifiers, with a bandwidth of 900 Hz, and 5-stage ring oscillators with a 600 µsec delay per stage operating at a supply voltage of 2V, demonstrating that colloidal semiconductor nanocrystals can be employed as technologically viable electronic materials for low-cost, large-area, low-voltage and flexible devices and integrated circuitry.

Current efforts of nanoscale science and technology are related to the fabrication of functional materials and devices in which the individual units and their spatial arrangement are engineered down to the nanometer level. One promising way of achieving this goal is by assembling of colloidal inorganic nanocrystals as the novel building blocks of matter. This trend has been stimulated by significant advancement in the wet-chemical syntheses of robust and easily processable nanocrystals in a wide range of sizes and shapes. The increase in the degree of structural complexity of solution-grown nanostructures appears to be one of the directions towards which nanoscience will increasingly orient. The talk will highlight the recent advances in the synthesis of colloidal nanocrystals, with emphasis on the strategies developed in our group for the fabrication of colloidal nanocrystals, as well as on their properties and their assembly into both ordered and disordered architectures. Particular attention will be devoted to the driving forces involved in nanocrystal assembly. Also, we will describe the peculiar assembly behaviour followed by monodisperse colloidal octapod-shaped nanocrystals, which display a rich variety of assembly patterns, depending on experimental conditions.

In this report, we will show that the crystallinity of nanoparticles can be controlled. It is well known that by submitted nanocrystals to laser beam, quadrupolar and breathing modes are observed. Here it is demonstrated for Au and Ag nanoparticles that the quadrupolar modes are splitted due to elastic anisotropy lifting of degeneracy mode whereas for Co nanoparticles, no changes in the breathing mode are observed.
Variations in the chemical properties of the nanocrystals of different structures, self assembled in compact hexagonal network are also observed.
We propose two mechanisms of fcc Au supracrystal (assembly of Au nanocrystals) growth. The solvent in which the Au nanocrystals are dispersed and their sizes are major parameters that determine the final morphology of nanocrystal assemblies in either films by layer-by-layer growth (heterogeneous growth), characterized by their plastic deformation, or well-defined shapes grown in solution (homogeneous growth). Specific properties related to the nanocrystallinity of supracrystals composed by nanocrystals are presented. Furthermore, low temperature electron transport properties measured by STM will be discussed.

The morphology of metal nanoparticles and their spatial organization explicitly determine their plasmonic, sensing, and catalytic characteristics. Accordingly, several strategies have been developed for preparing metal nanoparticles with well-defined geometries and for constructing two- and three-dimensional assemblies of nanoparticle building blocks with ordered structures. However, the lack of simple and versatile methods for preparing multi-scale structures with designed properties and spatial regularity has slowed the adaption of these unique structures to practical applications. Herein, facile wet-chemical synthetic processes for the fabrication of metal nanoparticle assembly and patterning toward functional materials are reported. Topics include the fabrication of patterned arrays of tubular nanoparticle assemblies, fabricating tunable plasmonic substrates based on the reshaping of metal nanoparticles, and their applications in catalysis, sensors, and plasmonics.

Semiconductor nanocrystals (NCs) can be used as light-harvesting materials in solution processed solar cells, giving the possibility to adjust the absorption spectrum and electronic energy levels with size and composition. Tin sulphide, showing a bulk band gap of 1.3 eV, large earth abundance and environmentally benign character is an appealing alternative to widely studied toxic PbS. However, to date SnS NCs have not been integrated successfully into solar cells. We will present a novel synthesis method for the preparation of 5-20 nm SnS NCs of low size dispersion. It relies on the use of Sn(II) chloride and thioacetamide as the tin and sulphur precursors, respectively. When using Sn(IV) chloride instead, surprisingly the shape of the obtained SnS NCs can be tuned from spherical particles to quadratic nanoplatelets. Electron tomography combined with 3D image reconstruction of the obtained nanotiles reveals their facetted shape. Controlling the precursor concentration, their dimensions can be controlled in a large range, yielding an edge length comprised between 20 and 100 nm and a thickness between 5 and 15 nm. Both the spherical particles and nanotiles exhibit a close to stoichiometric Sn:S composition and crystallize majorly in the orthorhombic herzenberghite structure (space group Pbnm).
We investigated the obtained SnS NCs by means of Sn-Mössbauer spectroscopy, which is a very accurate tool for identifying the oxidation state of tin. Using this technique, we reveal that SnS NCs exhibit a strong tendency for surface oxidation. Already after some minutes exposure to air the NCs surface is oxidized through an amorphization process, yielding a ternary phase composed of Sn, S and O and an overall Sn(IV):Sn(II) ratio on the order of 40:60. Therefore, we processed the SnS NCs without any air contact under inert atmosphere. They were incorporated in a planar heterojunction solar cell using the fullerene derivative PCBM as electron acceptor. In the first step, a 180 nm layer of SnS NCs has been deposited on an ITO-covered glass substrate containing a PEDOT:PSS hole transporting layer and treated with mercaptopropionic acid in order to increase the charge carrier mobility within the film. In the second step, a 60 nm layer of PCBM was evaporated on the SnS layer and finally an Al electrode was evaporated on top. The obtained device (active area of 0.4 cm2) showed a clear photovoltaic response under AM1.5 conditions with a high fill factor of 0.5. The comparably low open-circuit voltage of 0.23 V and current density of 0.34 mA.cm-2 suggest that further improvement could be obtained through adapting the electron accepting material in the p-n junction and by enhancing the interparticle electronic coupling.

Within the past few decades, exciting developments have been made to one-dimensional (1D) semiconductor nanowires, especially ultrathin nanowires, due to their fundamental significance in basic scientific research and novel applications. The extensive research into nanowire films has proven to be a promising building blocks and powerful platform for the exploitation applications. Many of the achievements have been made possible due to successful progress in both the macroscopic scale synthesis and wafer scale assembly of nanowires. Moreover, there has been an increasing trend of the use of well-defined nanowire films or films with nanowires random placement to develop more efficient and green nano-devices. Developing organized and interconnected well-defined arrays and assemblies of functional nanowires is central to the efforts directed toward their ultimate applications. Herein, we report the controlled synthesis of high quality nanowires and their assembly techniques. We take the elemental Te nanowires with a diameter of several nanometers as a model to illustrate how to realize scale-up synthesis and their effective multiplex templating effect for controlled synthesis of other families of nanowires, as well as their assemblies. The potential applications of these macroscopic-scale assemblies will be discussed.

The booming demand for portable electronics, hybrid and full electric vehicles brings tremendous interest in lithium ion batteries (LIBs) with high energy density over the past decades. However, current lithium-ion batteries still cannot meet the high power and lifetime requirement. To address these challenges, great effort has been devoted to develop high-power electrodes based on nanostructured materials whose low dimensions shorten pathways of both ions and electrons transportation. Spinel LiMn2O4 has been intensively studied for LIBs cathode on account of its natural abundance, environmental benignity, as well as its theoretical capacity of 148 mA h g-1. Conventional solid-state reaction often produces highly crystalline LiMn2O4 with large particle size and broad size distribution. On the other hand, a number of soft chemistry techniques have been explored to prepare LiMn2O4, however, the syntheses are generally complex and costly. In this context, synthesis of ultrafine LiMn2O4 nanocrystals (NCs) and engineering the NCs to fabricate electrode with fast kinetics is the key to the application of LiMn2O4 in high power systems. This work presents the synthesis of ultrafine LiMn2O4 NCs through a facile two-phase approach, and the fabrication of high power cathodes based on such NCs. These ultrafine NCs can be well dispersed in organic solvent, so that transparent nanoporous thin film can be made by coating above nano-ink on ITO substrates; flexible thick electrodes can be fabricated by casting a large amount of the same ink into pre-formed 3D CNT paper substrates. Post-sintering treatment in air removes all the organic ligands on the surface of NCs and enables fast ion access to the open channels in NCs onto various substrates. As-resulted electrodes show capacitive-like high rate-capability and long-term cycling stability, offering a material platform for high-rate lithium cathode.

Magnetic field is as an effective stimulus to guide the rapid assembly of colloidal building blocks into one-dimensional (1D), 2D and 3D photonic structures. The optical properties, or the structural color, of the photonic structures can also be dynamically modulated by changing the interparticle separation, the orientation or crystal structures through the manipulation of the external magnetic fields. We also demonstrate the assembly of uniform colloidal particles in a spatially patterned magnetic field to dynamically produce a high contrast in color patterns. The magnetic assembly approach can be extended to rapidly organize nonmagnetic particles into photonic structures through the "magnetic hole" strategy, which greatly broadens the applicability to different materials. Finally, by introducing nonmagnetic templates, we further realized local magnetic assembly of general colloidal superstructures in the feature size of a few micrometers. The magnetically responsive photonic system provides a new platform for chromatic applications, such as color displays, anti-counterfeiting devices, security features, camouflage, and information storage.

The ability to assemble nanoparticles into well-controlled ensembles enables the unique properties of nanoparticles to be exploited for emerging nanotechnological applications. Herein, we present a simple and facile strategy for the directed self-assembly of nanoparticles into complex geometries using a minimal set of guiding features patterned on a substrate. Linear, dense-packed, circular, and star-shaped arrays of nanoparticles were formed upon spin-coating solutions of the nanoparticles onto patterned substrates in just 30 seconds. The nanoparticles were observed to assemble primarily in the regions where the patterned features were present. The type of nanoparticle array that formed depended upon the spacing and arrangement of the predefined post arrays, as well as the concentration of the nanoparticles in solution. As proof of this concept, we demonstrate the successful directed self-assembly of the “IBM” simultaneously in a deterministic manner. This approach combines the advantages of bottom-up solution-processed nanoparticles with top-down lithographic patterning which serves as the foundation for fabricating functional nanodevices.

Self-assembly occurs in many natural systems, from the geologic formation of opals to biological formation of virus crystals, showing an extensive existence of self-organization in nature. Currently, 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. (1) As a direct outcome of size-controlled nanoparticle synthesis, most self-assembly preparations have used spherical nanoparticles as their building blocks. Nevertheless, progress in colloid chemistry has made it feasible to prepare diverse classes of well-defined nonspherical nanocrystals, which allow the possibilities of fabricating nonspherical nanoparticle-based supercrystals. (2, 3)

In this study, we present a new, novel type of superstructures assembled from In2O3 octahedral nanoparticles, which have been confirmed by our analyses using a series of techniques including SAXS, WAXS, SEM, and TEM. In particular, simultaneous high-pressure SAXS and WAXS were conducted to reveal changes in the octahedral nanoparticle superstructures as a function of pressure. The obtained results provide insights into the packing behavior of nonspherical nanoparticles, which is important for exploring their potential technical applications, such as enhanced conductivities, chemical sensors, and transitors.
Reference:
(1) Zewei Quan and Jiye Fang*, Nano Today, 5 (5) 390-411, (2010).
(2) Zewei Quan, Welley Siu Loc, Cuikun Lin, Zhiping Luo, Kaikun Yang, Yuxuan Wang, Howard Wang, Zhongwu Wang* and Jiye Fang*, Nano Lett., 12 (8), 4409-4413, (2012).
(3) Zhongwu Wang*, Ou Chen, Charles Y. Cao, Ken Finkelstein, Detlef-M. Smilgies, Xianmao Lu, and William A. Bassett, Rev. Sci. Instrum. 81, 093902, (2010).

Although multiple methods have been developed to detect metal cations, only a few offer sensitivities below 1 pM, and many require complicated procedures and sophisticated equipment. Here, we describe a class of simple solid-state sensors for the ultrasensitive detection of heavy-metal cations (notably, an unprecedented attomolar limit for the detection of CH3Hg+ in both standardized solutions and environmental samples) through changes in the tunnelling current across films of nanoparticles (NPs) protected with striped monolayers of organic ligands. The sensors are also highly selective because of the ligand-shell organization of the NPs. On binding of metal cations, the electronic structure of the molecular bridges between proximal NPs changes, the tunnelling current increases and highly conductive paths ultimately percolate the entire film. The nanoscale heterogeneity of the structure of the film broadens the range of the cation-binding constants, which leads to wide sensitivity ranges (remarkably, over 18 orders of magnitude in CH3Hg+ concentration). Overall, the high sensitivity of our solid-state sensors derives from a subtle interplay between cation/striped-NP macromolecular recognition, electron transport over the NP/cation/NP bridges, and the formation of conductive paths through heterogeneous NP films. Together, these phenomena provide a new principle for solid-state sensing and enable inexpensive, sensitive and portable environmental sensors. With further tailoring—both in terms of ligand chemistries and stripe dimensions—it should be possible to extend the applicability of our nanostructured materials to other sensing systems whose properties derive from macromolecular recognition on NP surfaces.

The robust and facile fabrication strategies for surface-enhanced Raman scattering (SERS) active substrates are important for developing practical SERS sensors. As comparing to traditional SERS substrates such as roughened metallic surface or randomly distributed metal nanoparticles, the highly ordered SERS substrates with controllable geometries are essential to obtain large and stable Raman enhancement with reproducibility. Several approaches to creating dielectro-metallic nanostructures have been developed for the SERS application, including the fabrication of metal-shell nanoparticles and bimetallic nanowires. For the practical SERS application, the individual plasmonic nanostructures are required to integrate as one- or two dimensional arrays with highly periodicity and uniformity. However, most attempts recently made have focused on fabricating dielectric-core metal-shell particles, which resulted in somewhat irregular structures due to the difficulties in precisely controlling the geometry and in positioning the individual units at a desired location.
Here, we report a novel SERS platform composed of highly periodic Au or Au-Ag /chitosan hybrid nanopatterns. The chitosan can not only play a role as the matrix for Au nanoparticles adsorption but also can be readily manipulated into well-ordered patterns via soft nanolithography. The fabrication strategy employing chitosan nanopatterns will provide reliable reproducibility and good sensitivity for SERS based detection of DNA hybridization.

The morphological aspects of new catalytic materials is presented in here. Catalytic materials where synthesized using hydrothermal methods of synthesis. This ternary phase have been studied using aberration corrected (Cs) high-resolution transmission electron microscopy techniques and scanning electron microscope. Results indicate a porous nano-rod like structures with bending layers of MoS2 laminar structure.

Copper nanoparticles have been studied extensively as the material for conductive inks due to its good thermal and electrical conductivity as well as its low cost. However, copper nanoparticles have weaknesses such as easy oxidation and poor dispersion stability. Therefore, it is important to develop a method to minimize oxidation of copper nanoparticles so that its conductivity can be improved after sintering. In this study, novel method of coating copper nanoparticles using SAM (Self-Assembled Multi-layers) with quantum dot RGO(reduced graphene oxide) particles, was developed to prevent oxidation. Graphene has higher electrical properties than that of copper and has excellent oxidation prevention properties. However, it is not easy to coat graphene on the metal surface because of its inert properties. Therefore, dodecanethiol which can form self-assembled multi layer on freshly exposed copper nanoparticles, was used to coat with quantum dot RGO. Conductive inks were fabricated using this novel method followed by sintering. After sintering process, these patterns were measured for electrical properties. As a result, copper paste using dodecanthiol-quantum dot RGO complex was found to have comparable conductivity as that for the paste that was made with non-oxidized copper nanoparticles. The coating layers were observed using TEM to confirm its nm-sized coating, and were characterized by XPS, FTIR, and Raman spectroscopy measurement. Therefore, quantum dot graphene was successfully adhered to copper nanoparticles through dodecanethiol for oxidation prevention and good conductivity.

Solids constructed with multicomponent nanocrystals represent a new form of condensed matter, as they can potentially capture not only the quantum features of the individual building blocks but also novel collective properties that arise from thermal, electrical, magnetic and optical interactions between nanocrystal components. The ability to choose individual nanocrystals with specific properties and assemble them into a periodic structure serves as an effective bottom-up approach for functional device fabrication and provides us with an excellent materials platform to explore new solid state physics. To date, there have been numerous reports of binary nanocrystal superlattices (BNSLs) formed from various materials, including noble metals, semiconductors, and magnetic quantum dots (QDs). Although these materials have been subject to extensive structural investigations, measurements and interpretations of their physical properties are still very limited.
In this work, we report for the first time BNSLs assembled from highly luminescent 8 nm CdSe/ZnS and 4 nm PbS/CdS core/shell QDs. Single superlattice domains with an average size of 2.5 mu;m show formation of cub-AB13 structures as confirmed by scanning electron microscopy, transmission electron microscopy, selective area electron diffraction, and structural modeling. We characterized these BNSLs optically via micro-photoluminescence spectroscopy of single superlattice domains formed on a Si/SiO2 substrate. We probed resonant energy transfer from CdSe/ZnS to PbS/CdS QDs, enabled by the spectral overlap of their emission and absorption spectra, respectively. A combination of spectral and time-resolved dynamics was used to elucidate differences in energy transfer between amorphous and ordered superlattice arrays. These results will be discussed in the context of applying these BNSLs to QD light-emitting diodes.

Recently, ultra-high density of electronic devices has been progressing rapidly. There are some kinds of needs for technologies those make up the high conductive and high density circuit pattern. In addition, there are needs for some technologies for building a microstructure. Take advantages with effects with structures, construct efficient electron emission devices those I can be. If it is possible to build a very fine three-dimensional structure, it can be utilized for future type device. In addition, if having excellent conductivity, a large field of use is expected.
Silver is a material that has excellent high conductivity. We have developed a process silver mirror is a simple process technology to build a high purity thin layer film, even using silver nanoparticles. MRS in the spring of 2010, we reported on the outcomes of the development of technology to improve the durability of the silver thin film. This improves the durability technology for the silver coating layer, it was possible to obtain a strong adhesion. In addition, in the spring of MRS2011, we proposed a copper plating process utilizing the process silver mirror.
In this paper, we report a technology to optimize the reaction conditions of silver mirror process, make up the single particle layer with nano silver particles. The size of those particles is about 5 nm. I constructed using this technology, one particle layer was coated with the nano silver particles on the surface of the nanostructure, nano-cone structure. For these, we report the results of observation at a high resolution electron microscope or the like, is proposed application to electronic devices.

Due to excellent optical and electrical properties, the quantum dot (QD) is very enticing and extensively known as a potential material in multifarious applications such as transistors, diode laser, solar cells, photo-transformation films, LEDs, and etc. Its commercial applications, however, are still limited because quantum yield of QD continuously drops while it is dispersed in matrix and/or in severe environments such as hot and humid condition. Here we challenged to encapsulate quantum dot with microcapsules which was prepared from temperature-induced self-assembly using high crystalline and hydrophobic polymer with little polar components on the main chain. QDs were massively incorporated and well-dispersed in the microcapsule while the self-assembly, which was checked by SEM and TEM. We found that QD was securely encapsulated in the microcapsule, which is confirmed by measuring quantum yield of the microcapsule dispersed polydimethylsiloxane resin filled and cured in LED chip after few month test in hot and humid condition.

ABSTRACT: The components of supramolecular hydrogels are resulted from the self-assembly of the building blocks via non-covalent interactions upon external perturbations. Compared with physical or chemical perturbations (e.g., pH, temperature, ionic strength, ligand-receptor interactions, et al) for initiating the process of self-assembly, enzymatic regulations (e.g., assembly or disassembly) associating with hydrogelation have drawn increasing attention because they integrate the processes with biological events. Herein, we report the rational design of a hydrogelator Acetyl-Asp-Glu-Val-Asp-Gly-Gly-Gly-EDA-Fmoc (1) which is susceptive to caspase-3 (CP3), and its scrambled control hydrogelator Acetyl-Asp-Glu-Asp-Val-Gly-Gly-Gly-EDA-Fmoc (2). Self-assembly of 1 in water results in flexuous, long nanofibers to form supramolecular hydorgel I which has higher mechanical strength than that of gel II composed of rigid, short nanofibers self-assembled with 2. MTT and western blot analyses indicated that 1 could help HepG2 cells survive due to its inhibition to CP3 activity in the cells while 2 could not. This survivin-like property of 1 suggests gel I as promising biomaterial for three-dimensional (3D) cell culture and tissue engineering in the future.

MPA capped CdTe Quantum dots (QDs) are synthesized by Organometallic route in aqueous solution. The QDs thus obtained are encapsulated with glycolipid by the EDC-NHS (1-Ethyl-3-(3dimethylaminopropyl)carbodiimide hydrochloride-N-hydroxysuccinimide) coupling reaction. We used microbially synthesised lipid (Sophorolipid, SL) for the encapsulation of CdTe in order to make them biocompatible. Various characterization techniques such as UV-visible-NIR, Photoluminescence (PL), X-Ray Diffraction (XRD), Zeta potential, Dynamic light Scattering (DLS), Fourier Transform Infrared Spectrocopy (FTIR), Confocal microscope, High Resolution Transmission electron microscope (HRTEM), Scanning electron Microscope (SEM), Energy dispersive X-Ray spectroscope (EDAX) analysis are employed to validate the various properties of the material. FTIR shows that encapsulation of CdTe by sophorolipid is based on bond formation between carboxylic group of thiol capped QDs with Carboxylic group of sophorolipid via EDA linker. Photoluminescence of CdTe Quantum dots and SL coated QDs are similar but with a small blue shift. Quantum yield was also calculated for the composite. EDAX analysis confirms the presence of lipid on the surface of Quantum dots. Cytotoxicity testing was done by MTT assay to check the biocompatibility of the particles on two different cell lines- NIH3T3 (mouse fibroblast cell line) and MCF7 (Breast cancer cell line). The particles were studied under fluorescence microscope to image Mycobacterium smegmatis cells. Cell imaging is also done to study the fate of the particles inside the cells. Zeta Potential of the SL-coated QDs shows good dispersibility and stability which is required for the biological applications. Confocal microscopy shows the internalization of lipid coated QDs in the cell line suggesting that the particles have good potential in bioimaging and disease diagnosis applications. Cytotoxicity testing of SL coated QD with NIH3T3 and MCF 7 show a far better viability as compared to the cases of a) the QDs and b) a physical mixture of QDs and SL without the EDA linker. These results will be presented and discussed.

The growth of wireless communication has made rejection of spurious carriers a key concern. Filters play critical roles in many microwave/mm-wave applications. Filters, with optimum frequency selectivity, smaller size, and high stop-band attenuation, have been used for mobile and satellite communications systems. Microstrip filter appears to be one of the appropriate choices for integrating all the rf front-end components into one module [1].
In this work, we designed, fabricated, and characterized few novel ultra-small tunable signal processing devices using Co nanowires (in alumina matrix). These devices can be integrated with high-frequency electronics. Co nanowires were electrodeposited in porous alumina template. The quality of the nanowires was tested by SEM which reveals 200nm diameter and length of 10 µm. XRD shows the structural properties to be polycrystalline, oriented in (111) reflection plane.
For band-stop filter and phase shifter a 50 Omega; Al line of width 100 mu;m and length 7 mm was fabricated. For band-pass filter and isolator two 50 #8486; Al transmitting/receiving antennas of length 2.25 mm (one side fed and other side shorted) were fabricated on top of Co-nanowires templates. The microwave characterization was done using a vector network analyzer in the frequency range from 0.1 to 50 GHz. External magnetic field (Hdc) varied along the easy-axis of nanowires to tune the operating frequency at a bias field upto 3.5 kOe.
The transmission response for band-stop and band-pass filters shows a linear increase in resonance frequency. As the bias magnetic field is varied, the center frequency varies from 24 to 29 GHz giving a maximum frequency tunability of 20%. For band-stop filter, insertion loss over most of the region is of the order of 2-3 dB over 50 GHz range, while the power attenuation is close to values of 10 dB/cm. It is also observed that the frequency linewidth initially decreased as the field is increased and then subsequently increased. For coupled line band-pass filter, the external quality factor Qext(=fc/Δf) is found to be independent of the center frequency increases from 24 to 29 GHz. The coupled line structure can also be used as an isolator. The transmission in the forward direction (S21) is reduced at the ferromagnetic resonance of Co, while in the return direction from port 2 to 1 (S12) the attenuation of the signal is small. The difference between these two values represents the degree of isolation [2]. Results on the transmission coefficients show a nonreciprocal effect, which is about 3 dB/cm at 28 GHz. The bandwidth of the device is relatively large in comparison to typical ferrite-based devices. Thus the device can operate over a wide frequency band.
[1] R. E. Camley et al., Journal of Magnetism and Magnetic Materials, Vol. 321, (2009), pp. 2048.
[2] Bijoy K. Kuanr et al., Applied Physics Letters, Vol. 94, (2009), pp. 202505.

We report on a systematic investigation of molecular conjugation of tumor necrosis factor protein-α (TNF) onto gold nanoparticles (AuNPs) and the subsequent binding behavior to its antibody (anti-TNF). We employ a combination of physical and spectroscopic characterization methods, including electrospray-differential mobility analysis, dynamic light scattering, polyacrylamide gel electrophoresis, attenuated total reflectance-Fourier transform infrared spectroscopy, fluorescence assay, and enzyme-linked immunosorbent assay. The native TNF used in this study exists in the active homotrimer configuration prior to conjugation. After binding to AuNPs, the maximum surface density of TNF is (0.09 ± 0.02) nm^-2 with a binding constant of 3×10^6 L/mol. Dodecyl sulfate ions induce desorption of monomeric TNF from the AuNP surface, indicating a relatively weak intermolecular binding within the AuNP-bound TNF trimers. Anti-TNF binds to both TNF-conjugated and citrate-stabilized AuNPs, showing that non-specific binding exists. Based on the number of anti-TNF molecules adsorbed, a substantially higher binding affinity was observed for the TNF-conjugated surface. The presence of thiolated polyethylene glycol (SH-PEG) on the AuNPs inhibits the binding of anti-TNF, and the amount of inhibition is related to the number ratio of surface bound SH-PEG to TNF and the way in which the ligands are introduced.

Upconversion nanoparticles represent a unique class of materials that are capable of emitting visible light upon excitation with a near-infrared light source. This optical property makes them especially useful as biological imaging agents. Owing to their low emission efficiencies, numerous efforts have been introduced to further improve the upconverting capabilities of these nanoparticles. Core/shell NaYF4:Yb,Er/SiO2/Ag nanocomposites with controllable distance between NaYF4:Yb,Er nanoparticles and Ag nanoparticles were prepared in this study to investigate the ability of Ag nanoparticles to enhance the emission of NaYF4:Yb,Er nanoparticles. A 14-fold enhancement of upconversion luminescence was observed at a separation distance of 10 nm. The applicability of these nanocomposites in biological imaging was also demonstrated with B16F0 cancer cells where cell viability remained high after nanoparticle incubation.

Highly monodispersed mPEG coated Fe3O4 nanoparticles are used as a model system to investigate the effects of surface coating on SAR with an AMF system (400 KHz). Investigations of different factors such as particle size, magnetic properties of magnetic core and surface coating have explicitly shown that by fine-tuning the surface coating for an optimal magnetic core size, the SAR could be significantly increased by up to 74% with a very small variation on the saturation magnetization (<5%). By elaborate optimization of both surface coating and particle size, 19nm@2000 exhibited the highest SAR of 930 W/g among these samples. Moreover, this hyperthermia agent with optimized surface coating has shown excellent performance in both water and simulated physiological conditions. Enhanced SAR with decreasing thickness of surface coating was observed that is ascribed to the increased Brownian loss and improved thermal conductivity. In addition, large particle with high Msis favored for high SAR. However, subsequently increased interparticle attraction tends to reduce colloid stability and SAR. Though thickening coating could confer colloidal stability and improve SAR for large particle as demonstrated in the case of 31nm sample, such a thick coating again decrease the Brownian loss and thermal conductivity, leading to a poor SAR. Such an optimization of surface coating of magneticnanoparticles based hyperthermia agent is an indispensable step towards practical biomedical application. The findings obtained from this work provide a general strategy of optimization of biocompatible surface coating for the design and development of novel magnetic nanoparticle based hyperthermia agent for advanced nano-biotechnology applications.

High ordered arrangement of nano-clusters (1-10 nm) can be open new application field on high-sensitive nano-device. Electrical conduction of metal nanoclusters by percolation is a very interesting area in nano-device. For more functional nano-sensors consisting of multiple nanoclusters blending film, various metals, such as Ag, Cu, Ni, and Sn nanocluster films were fabricated using inert-gas condensation method. The percolation threshold of the nano-clusters films was measured. In addition, for the operation of sensors using these nanocluster films in air, aging experiments of the percolated films in air were carried out. While the percolation threshold was in connection not with the material species but with the area coverage of nanocluster films, the conductive characteristics according to the aging temperature depended on the material species. Reversible and irreversible behaviors of conductance of nanocluster films were investigated with nanoscale microstructures with transmission electron microscopes.

Quantum dots (QDs) have been intensively studied as a new probe for bioimaging and biosensor due to their bright fluorescence and excellent photo-stability. There have been many trials to conjugate QDs with other nanoparticles for making a novel multi-modal nanoconjugate. We developed a new binding strategy of linking QDs to magnetic nanoparticles using DNA interaction with metal coordination bonding. Platinum was selected for binding QD to DNA, which was inspired from platinum-based anticancer drug, cisplatin. QD-superparamagenetic nanoparticle conjugate would be a new probe in diagnosing a specific disease more accurately with its double modalities, fluorescence and magnetic property.

Plasmonic nanostructures with tunable optical properties and their designed spatial arrangements can facilitate a variety of application ranging from plasmonics to biosensors with unprecedented sensitivity. Here we describe a facile and versatile method for fabricating tunable plasmonic substrates based on the reshaping of metal nanocrystals. Anisotropic etching and re-deposition of Ag atoms mediated by halide ions transformed Ag nanoprisms deposited on two- or three-dimensional surfaces or in solution into nanostructures with an oblate spheroidal shape, and corresponding localized surface plasmon resonances features could be tuned. The reshaping nanocrystal strategy can even facilitate the preparation of new classes of plasmonic substrates with gradient or patterned plasmonic properties, which cannot be realized easily using existing lithographic techniques. The substrates with gradient plasmonic properties can serve as platforms for tunable surface-enhanced Raman scattering.

A novel one-pot synthetic procedure to obtain magnetic hybrid nanostructured materials (HNM), based on magnetic spinel-metal-oxide (SMO) nanoparticles, such as magnetite and cobalt ferrite, assembled into ovoid-like carboxymethyl-cellulose (CMC)/cetyltrimethylammonium-bromide (CTAB) templates, is reported. The HNM were synthesized from the controlled hydrolysis of inorganic salts of Co(II) or Fe (II) and Fe (III), assisted by the thermal decomposition of urea, into aqueous dissolutions of CMC and CTAB. The synthesis of the HNM was performed at 80 °C, under reflux conditions and nitrogen atmosphere for 24 hours, followed by the HNM purification and dried for its further characterization. Crystalline and morphological characteristics of the HNM were studied by high-resolution transmission electron microscopy (HRTEM) and their related techniques, such as bright field imaging (BF), high angular annular dark field (HAADF), selected area electron diffraction (SAED) and X-ray energy dispersive spectroscopy (XEDS), using a FEI Titan G2 80-300 microscope. The interactions among SMO nanoparticles, CMC and CTAB were investigated by Fourier transform infrared spectroscopy (FTIR) in a Thermo Scientific Nicolet spectrometer. Magnetic response of the synthesized HNM was measured in a Quantum Design PPMS-9. The experimental evidence suggest that, due to the competition between CTAB molecules and SMO nanoparticles to occupy CMC intermolecular sites nearby to its carboxylate functional groups, the size of both, SMO nanoparticles and CMC/CTAB templates, as well as their morphology, can be tuned varying the CTAB:SMO weight ratio. Moreover, it was found that the magnetic response of the HNM depends on the confinement degree of the SMO nanoparticles into the CMC/CTAB template. Hence, its magnetic characteristics can be adjusted controlling the size of the template, the quantity and distribution of the SMO nanoparticles within the template and its sizes. In addition, based on our experimental findings, we propose the synthesis mechanism for the preparation of the reported HNM.

Catechins (CTCs), a group of polyphenolic flavonoids predominantly found in pine bark and green tea, possess antioxidant, antimicrobial, and anti-carcinogenic activities. However, the application of CTCs is still limited because of its high sensitivity to oxygen, light, and pH. To increase the stability of CTCs, several available techniques, such as phase inversion, ionotropic gelation, liposomes, emulsification, spray-drying, and freeze-drying, have been employed to encapsulate CTCs in biopolymers (i.e., chitosan, maltodextrin, and kafirin). However, these conventional techniques still have limitations including generating particles with broad size distributions, requiring large quantities of surfactants, and long processing time. To overcome such limitations, rapid expansion of sub- or supercritical solutions into liquid solvents (RESOLV), in which a homogeneous solution containing a solid solute and a solvent (carbon dioxide (CO2) or a mixture of CO2 and an organic solvent) is rapidly expanded across a micro-orifice into a receiving liquid, could be used to entrap a bioactive compound in polymeric nanoparticles. The objectives of this research were to study the capacity of RESOLV process to produce CTC-loaded poly(L-lactide) (PLLA) nanoparticles and the effects of CTC concentration and processing conditions (i.e., pre-expansion temperature and degree of saturation) on size and morphology of composite particles, loading capacity of CTC, as well as release of CTC from the obtained particles. It was found that RESOLV experiments of 0.1 wt% CTC + 0.2 wt% PLLA and 0.2 wt% CTC + 0.2 wt% PLLA solutions in mixtures of CO2 and ethanol (2:3 wt/wt), with pre-expansion temperature and pressure of 60minus;100°C and 270minus;330 bar, respectively, were able to consistently produce spherical CTC-loaded PLLA nanoparticles with an average size range of ~30minus;40 nm and CTC loading capacity ranging from 2.0 to 7.0%. Pre-expansion temperature, degree of saturation, and CTC concentration had significant effects on the loading capacity of CTC, without affecting the size of composite nanoparticles. Loading capacity of CTC increased with increasing pre-expansion temperature and degree of saturation, while unexpectedly decreased with increasing CTC concentration. The highest loading capacity of CTC in nanoparticles was achieved when supersaturated solution was rapidly expanded at pre-expansion temperature and pressure of 100°C and 270 bar, respectively, with a weight ratio of CTC and PLLA of 1:2. Furthermore, the release profiles of CTC from PLLA particles showed zero-order kinetics of burst release followed by a sustained release of CTC.

Electron tunneling modulation via mechanics of conductive nanoparticle will benefit from low mass mechanical components. Graphene nanostructures with high conductivity and mobility would be ideal for such systems. Graphene quantum dots (GQDs) are atomically thick, conductive nanosheets (< 100 nm) of sp2 hybridized carbons, which exhibit size- and shape- dependent electrical properties. Here, we demonstrate that graphene nanoribbons can be oxidatively cleaved into graphene quantum dots and the electron-tunneling modulation through an array of GQDs selectively deposited on a microfiber produces sensitive change in conductivity changing the interparticle distance between the GQDs attached on a hygroscopic microfiber via change in local humidity

High temperatures and pressures can influence the shape, surface structure and reactivity of solvated nanoparticles through the relative energies of different surfaces, for example bare versus hydroxylated and hydrogenated surfaces in water. In principle these changes can be used to engineer specific nanoparticle arrays by creating reactive surfaces that can chemically bind individual nanoparticles. The key to this capability is to be able to accurately predict relative surface energies and associated properties in fluids as a function of temperature and pressure.
We have been using first principles thermodynamics to characterize surface structures and relative energies of nickel oxide and nickel ferrite with and without surface terminations in water as a function of temperature and pressure. These energies are in turn used to predict cluster shapes and the relative areas of reactive surfaces via Wulff constructions. The surfaces are modeled using semi-infinite metal oxide slabs for a variety of possible surface orientations and terminations, with energies obtained from GGA+U Density Functional Theory calculations. Effective elemental chemical potentials are derived from first principles thermodynamics that are used to calculate surface energies of metal oxides in extreme environments.
For NiO, the calculations predict octahedral clusters with (111) surfaces terminated by H and OH at low temperatures. In high-pressure water above about 475K, or 400K in low-pressure steam, the calculations predict that the termination-free (100) surface energy becomes comparable to that of the (111) surface, which leads to cubo-octahedral shapes. Results for similar calculations on NiFe2O4 will be reported, as well as implications of these results in forming nanostructured materials by cluster condensation.
This work is supported by the Department of Energy through the Consortium for Advanced Simulation of Light Water Reactors.

Gold NPs have attracted broad interest in many scientific and technological fields due to their relative ease of synthesis, diverse surface chemistries, and many practical applications. We describe new experimental schemes in which Au NPs adopted interesting architectures through self-assembly processes, consequently employed as possible platforms for opto-electronic applications. One approach utilized alkylthiol-coated Au NPs as building blocks for organized two-dimensional nanowire patterns assembled in surfactant-templates at the air/water interface. The resultant films exhibit high optical transparency and electrical conductivity, and thus might be considered as substitutes to conventional indium-tin-oxide (ITO) electrodes. In another experiment we demonstrated unique optical-electrical properties of polar Au NPs embedded in a transparent sol-gel matrix. In both examples, the distinctive phenomena observed were directly related to the spatial organization of the Au NPs, rather than the properties of the individual particles.

One of the key advantages of semiconductor nanocrystals is their potential for improving the efficiencies of optoelectronic devices. Spherical nanocrystal heterostructures, sometimes referred to as core-shell quantum dots, have been widely used for quantum dot light emitting diodes (LEDs). In these core-shell heterostructures which mainly consist of type I (straddling) band offset, the heterojunction serves merely as a passivation layer to improve photoluminescence efficiency. However, larger band gap of shell materials may hinder carrier injection processes. On the other hand, double heterostructures, which in the thin film geometry have been widely used as components for LEDs, lasers, photovoltaics and bipolar transistors allow more efficient injection of larger number of charge carriers thereby enhancing device performance. The ability to introduce such heterojunctions in nanocrystals and nanorods which are prepared by solution chemistry allows the benefits of both high performance inorganic semiconductors and the versatile processability of organics. Here, we synthesize anisotropic double heterojunction nanorods (DHNRs) and demonstrate their application in prototype optoelectronic devices. Further, the charge injection and carrier properties of DHNRs are correlated to device performance.

Precise control over interfacial chemistry between nanoparticles and other materials remains a significant synthetic challenge limiting the broad application of nanotechnology in biology. Common strategies for chemically conjugating materials to nanoparticles generate multivalent products that follow a Poisson distribution, causing potential problems of cell function perturbation and artifacts in bioimaging. To resolve this issue, here, we present a “steric exclusion” strategy to achieve exclusive formation of monovalent nanoparticle-oligonucleotide conjugates. The synthesis is scalable, highly modular, and generates a single species of nanoparticles without further purification steps. We use these monovalent quantum dots to image the diffusion dynamics of single Notch receptors on live cells for the first time, demonstrating their utility as modular single-molecule imaging probes in the most demanding of biological applications.

The investigation of metal-ceramic materials has significance both in fundamental science and in many technological applications. Transient and equilibrium shapes of metals in ceramics affect the mechanical, optical, and electronic properties, and the long-time thermal and mechanical stability of the metal-ceramic composites. However, the transient and equilibrium shapes in metal-ceramic composites are not yet fully understood.
In the current work a model system of Pt particles embedded in polycrystalline α-alumina has been investigated. This system is used to study the path and rate of evolution of nanometric metal particles embedded in ceramic material, and specifically the role that the crystallographic orientation relationship (OR) and interfacial structure between the Pt and alumina have on the ultimate equilibrium shape and the kinetics of evolution towards that equilibrium shape.
The experimental system is created by implantation of polycrystalline alumina with Pt ions. The implanted specimens were annealed at 1565°C for 5, 25, and 100 hours in order to reveal various stages of the Pt growth and equilibration. Grain-growth of the polycrystalline alumina occurs in parallel with Pt equilibration, altering the Pt-alumina OR, and thus providing a convenient model system for investigating the kinetics of metal particle shape (re-)equilibration in response to the newly imposed OR.

In this work, we report a semi-automatic process to prepare colloidal crystals and their inverse opals in large quantity and reduced defects. The fabrication scheme for the colloidal crystals involves the synthesis of polystyrene (PS) microspheres (300-800 nm) and electrophoretic deposition of PS colloids in planar or cylindrical arrangement. Since the process parameters are optimized, we are able to obtain colloidal crystals with adjustable layer/thickness and their surface reveals superb uniformity. To render an inverse structure, the colloidal crystals are employed as a template to allow the electroplating of Ag, Ni, Cu, Au, or ZnO into the interstitial voids among the PS microspheres, followed by removal of the PS template to obtain an interconnected porous skeleton. With impressive structural integrity, the inverse opals can be easily removed from the substrate becoming a free-standing opaline film. Materials characterizations including XRD, nano-indentation, porosity measurement, SEM, electrical conductivity, and α-step are carried out. Lastly, we demonstrate several engineering applications (electrocatalysis, light-emitting diode, wetting and electroweting on dielectric) in which the colloidal crystals and inverses opals provide clear advantages in performance improvements.

The shape and size of Cu NPs was controlled by tailoring the surface morphologies of TiN-coated electrodes during the electrochemical synthesis. Employing smooth granular TiN-coated substrates yielded Cu NPs with octahedral shape particle sizes of larger than 10 nm. As for using rough pyramidal TiN-coated substrates the flower-like Cu NPs were produced with particles sizes smaller than 10 nm. From chronocoulometric analyses, the ions accumulated on the pyramidal TiN films were higher than those on the granular TiN films. The flower-like while smaller Cu NPs possess higher electrocatalytic sensitivity and stability than the octahedral Cu NPs during glucose oxidation.

For the first time, a novel Virus-like-particle (VLP) bioreceptor layer has been integrated with an optical disk resonator platform for biosensing applications. This bioreceptor layer is capable of being programmed for selective binding by modifying the exposed coat protein (CP). An optical microdisk resonator has been sensitized for antibody binding with this receptor, demonstrating a resonant frequency shift (Δfo) of 7.00nm, a 300% increase compared to that of the non-specific binding of a control bioreceptor layer. Integrating biologically programmable material into traditional MEMS transducers enhances selectivity, sensitivity, and simplifies fabrication and testing methodologies.
The convergence of biology and micro/nanoscale technologies has enabled the developement of hybrid microscale chem-bio sensors. Through genetical engineering of VLP, we have successfully developed the VLP bioreceptor as selective transduction layers targeting at specific bio/chemical molecules. The VLP has a high aspect ratio nanorod structure formed from CPs. Each CP was genetically mutated to allow for the self-assembly of viruses onto surfaces via a cysteine (nCys) conjugation. An additional VLP construct with a second peptide (cFlag) is expressed for specific binding of analytes to the CP&’s outer surface.
An optical microdisk resonator is functionalized with the VLP layer to conduct Enzyme-linked immunosorbent assay (ELISA) on-a-chip.The silicon nitride disk resonator is 20µm in diameter and 340nm thick. A 0.6µm wide waveguide is coupled to the disk via a 300nm air gap. These types of sensors provide high sensitivity, and real-time measurement without the need for florescent labeling. The microdisk can only working at a specific resonant frequency which is depended on the effective refractive index in the system. The transduction mechanism is based on detection of shifts in resonant frequency caused by the refractive index change due to absorption of analytes on the receptor layer.
The two types of VLPs were assembled on different optical microdisk resonators, in which VLP-nCys-cFlag selectively bound to antibodies while VLP-nCys didn&’t and was used as a negative control. Both chips underwent identical ELISA, allowing for a sequential enzymatic binding of primary antibody, secondary antibody, and indicator assembly. The optical spectrum between pre and post-ELISA of the two transducers was compared. Resonant frequency shifts of 7.00nm and 2.13nm were observed for VLP-nCys-cFlag and VLP-nCys, respectively, indicating the selective bonding of ELISA to the cFlag binding site.
This sensing system has demonstrated the ability to take full advantage of the genetic programmability of VLP nanostructures. It can be integrated with various MEMS sensing platforms, enabling a wide range of applications for these sensors including non-labeling antibody sensing, non-fluorescent tagging biomolecule detection, and even explosive vapor monitoring.

Gadolinium-based contrast agents are used increasingly as tools for noninvasive diagnosis and evaluation of disease by magnetic resonance (MR) imaging. Due to rapid clearance in vivo, Gd frequently takes the form of macromolecular chelation complexes or is immobilized within micro- or nanoparticles, often liposomes, to enhance retention. This is a particularly attractive strategy in the case of theranostics where Gd is co-incorporated with a therapeutic component for simultaneous treatment and diagnosis. However, coencapsulation can reduce loading efficiencies and introduce the potential for undesired interaction between encapsulated functional units. Furthermore, liposomal encapsulation of Gd chelates is known to greatly reduce relaxivity due to decreased interaction with surrounding water, thus requiring higher doses of Gd to provide image contrast. This study therefore presents a strategy to modify pre-formed lipid vesicles through modular surface assembly to mitigate issues of coencapsulation while providing high MR signal enhancement. In this approach, chitosan conjugated with DTPA was used to anchor Gd to the liposome surface post fabrication. Chitosan was then further modified with octadecyl chains to augment the liposome-chitosan association via self-assembly between hydrophobic alkyl chains of lipid and chitosan. Success of this modular assembly approach was confirmed through isothermal titration calorimetry (ITC) and 3 Tesla MR imaging. Overall, this work serves to assemble cutting-edge multi-functional nanocarriers for future diagnostic applications.

Semiconductor quantum dots (QDs) are luminescent nanocrystals offering bright and narrow emissions from UV to near-infrared. As a result, they find numerous applications as light emitters in a wide range of technologies, from photonics to biotechnologies. However, tuning the emission color is usually done by varying the size of the nanocrystals, what can be problematic for their integration in devices. To overcome this limitation, the syntheses of alloyed QDs, such as ternary Cd(Se,Te) or quaternary (Cd,Zn)(Se,S), have been developed in the past years [1,2]. These systems allow a fine tuning of the emission color by varying the composition of the alloy without changing the size of the QDs.
We recently developed a new approach for the synthesis of CdSe and ZnSe QDs based on a heterogeneous Se precursor. This precursor, which consist in a simple dispersion of Se powder in a non-coordinating solvent, shows a high reactivity towards Cd or Zn precursors affording hence very high reaction yields and reaction rates. In addition, the size of the synthesized QDs can still be tuned by the length of the carboxylic acid used as a ligand for the synthesis and colloidal stability of the QDs solution. Thus, this new synthesis method allows the production of high quality CdSe and ZnSe QDs at large scale.
In this contribution, we will show how this new approach can also be used for the synthesis of homogeneously alloyed Cd(Se,S) and Zn(Se,S) QDs thanks to the equivalent reactivity of the Se and S precursors towards the Cd or Zn precursors. In addition, this strategy has also been extended to the synthesis of (Cd,Zn)(Se,S) alloyed QDs across the entire composition range. From point of view of the structural properties, the homogeneous alloying of the synthesized QDs has been verified using Raman spectroscopy. The optical properties will be fully described, with a particular attention to the dependence of the band gap on the composition of the alloy. Finally, the band alignment of the alloyed QDs relatively to CdS will be also demonstrated by means of SILAR grown CdS shells.
References:
[1] R. E. Bailey, S. Nie, J. Am. Chem. Soc. 2003, 125, 7100;
[2] Z. Deng, H. Yan, Y. Liu, J. Am. Chem. Soc. 2009, 131, 17744.

Plasmonic nanoparticles are excellent candidates for their potential use in microelectronic, optical, biomedical applications or to develop new metamaterial properties. Their electromagnetic behaviour is highly dependent on their specific particle size, shape, and surrounding environment. There are different methods which allow us to fine tune the control over the particle shape and size thus, the materials properties. However, the lack of capability to form reproducible organized structures is still a very important challenge to solve in order to use them in new upcoming technologies.
Template assisted self-assembly is a versatile platform to generate particle assemblies in high quality and with high reproducibility. Compared to lithographically prepared templates controlled surface wrinkling on elastomers is a low cost alternative approach to produce structured surfaces with periodicities in the range of nanometres. The use of wrinkled surfaces as templates for nanoparticle alignment via confinement or printing, results in highly ordered nanoparticle arrays. However, with functional particles such as gold particles this is a powerful method to produce SERS sensor probes for quantitative analyses and with high enhancement factors due to hot-spot generation [1, 2]. In this work a new surface enhanced Raman spectroscopy (SERS) platform suitable for gas phase sensing based on the extended organization of poly-N-isopropylacrylamide (pNIPAM)-coated gold nanostars over large areas is presented [3]. This system yields high and homogeneous SERS intensities, and simultaneously traps organic chemical agents as pollutants from the gas phase. pNIPAM-coated gold nanostars were organized into parallel linear arrays. The optical properties of the fabricated substrates are investigated, and applicability for advanced sensing is demonstrated through the detection in the gas phase of pyrene traces, a well-known polyaromatic hydrocarbon.
1. Pazos-Perez, N., et al., Chemical Science, 2010. 1(2): p. 174-178.
2. Schweikart, A., et al., Soft Matter, 2011. 7(9): p. 4093-4100.
3. Mueller, M., et al., Langmuir, 2012. 28(24): p. 9168-9173.

Increased usage of silver nanoparticles (AgNPs) in commercial products underscores the importance of study of AgNps fate in the environment. Here a new model of engineered AgNps stabilized with oleic acid of sizes 2, 5 and 10 nm and then surface modified with mPEG-SH (M.wt 5 KDa) were considered. High temperature organic synthesis facilitated narrow size distributions (< 15 %) and allowed us to understand the size dependent dissolution phenomenon. In this study we found that surface coating dominantly directs the dissolution of silver compared to the core size. Hence, grafting density of the polymer played a crucial role in controlling the leaching of silver, by reducing surface oxidation. Further, dense polymer coverage not only decreased the rate of dissolution of the AgNps in various different environmentally relevant high ionic strength media (such as frac14; th strength hoaglands, EPA hard water, bicarbonate buffer and minimal media) but also prevented aggregation whereas citrate stabilized AgNps crashed within a span of seconds after addition of these media. Moreover, citrate stabilized AgNps when surface modified using mPEG-SH behaved similar to the engineered AgNps. In addition, antimicrobial nature of the engineered AgNps was preserved but 2000 fold less toxic to E.Coli compared to citrate coated AgNPs.Therefore, this study implies that different processes in the environment can increase the stability of the AgNps released from commercial products which increases the life time of the AgNPs that can be a danger to the ecosystem.

Nanoparticle functionalization and assembly is undergoing a period of challenging yet exciting development. Much of this research effort has been focused on the development of new functionalities that might enable strategically-directed assembly of nanoparticles into structures that can be utilized in other important applications.
In order to determine the success of such experiments, researchers often prepare a dried sample and study the assembly patterns with electron microscopy. However, these imaging techniques can be expensive and do not provide a complete illustration of what the three dimensional nanoparticle assemblies truly look like in solution. Moreover, sample preparation presents its own challenges. Most notably, sample preparation may cause alteration to the individual assemblies or unwanted aggregation of the assemblies upon removal of the solution.
To address these concerns, assemblies of anisotropic nanoparticles were tracked free-floating in solution with differential interference contrast (DIC) microscopy. DIC microscopy is an optical technique based on interferometry with high lateral resolution and shallow depth of field. After functionalizing gold and silver nanoparticles for self-assembly, aliquots of the nanoparticle solutions were examined in real-time. Nanoparticle assemblies were observed undergoing rotations, internal vibrations, structural modifications, and interactions with other assemblies. Observations of the dynamic behaviors of nanoparticle assemblies serve as a complement to imaging with electron microscopy and provides new insights into the actual assembly process.

We will present a facile methodology for depositing colloidal semiconductor nanocrystals into all-inorganic solid films with implications both to nanocrystal solar cells and nanocrystal light-emitting devices. The reported strategy utilizes a simple scheme for incorporating PbS or CdSe semiconductor nanocrystals into matrices of a wide-band gap CdS or ZnS semiconductor for stable and efficient operation of solution-processed devices. The two key benefits of this approach include: (i) all-inorganic architecture promoting superior thermal and chemical stability, and - (ii) a unique film morphology, which offers the possibility of tuning the film properties between conducting (for applications in solar cells) and light-emitting (LEDs, lasers) simply by changing the interparticle distance in the matrix. This approach is universal and can be extended to a large number of nanocrystal/matrix combinations.

Beta-irondisilicide (β-FeSi2) is a potent material for a large variety of optical and electronic applications. It is an indirect bandgap semiconductor with Eg= 0.78 eV and an energetically close-lying direct band gap (0.83-0.89 eV). Since β-FeSi2 is nontoxic and composed of ubiquitary elements, it is envisioned for photonic crystals due to its matching emission wavelength with SiO2 fibers. In terms of energy harvesting, β-FeSi2 can be applied in photovoltaic cells to enhance their efficiency due to its high absorption coefficient combined with a favorable band gap characteristic. Moreover, the high Seebeck coefficient and its oxidation resistivity render this material very promising for thermoelectric devices.
β-FeSi2 was synthesized in an easily up-scalable hot wall reactor by thermal decomposition of the precursor materials monosilane and ironpentacarbonyl (IPC). Adjusting the silane to IPC ratio as well as optimization of the synthesis process, with respect to the decomposition kinetics of the precursors, proved to be the key in obtaining pristine and pure phase β-FeSi2 nanoparticles. Phase composition was determined via X-ray and electron beam diffraction revealing no impurity phases. XRD measurements further provided indications for the formation of stacking faults within the particles due to deviations from the bulk diffraction pattern. Transmission electron microscopy investigations demonstrated the formation of agglomerates consisting of single crystalline β-FeSi2 nanoparticles with a typical diameter of about 10-30 nm. The obtained particles are surrounded by an amorphous, oxygen-rich shell [1]. These renders them well dispersible in polar solvents, especially water. To prevent further oxidation and fit those particles for printing processes requiring non-polar solvents, functionalization routes by silanization were applied. Spin-coated layers were coated on interdigital structures to probe the particles electric properties. Hall measurements indicated p-type majority charge carriers in high concentration of 2,9 10^20 per cubic centimeter and relative low mobility of 3,4 10^-2 cm2/Vs, whereas temperature dependent conductivity measurements were applied to investigate the basic properties governing charge transport. The high material purity combined with favorable electric properties and the possibility to manufacture thin films from dispersion is an important step towards utilizing β-FeSi2 for PV applications, especially since our approach enables large product yields.

[1] R. Bywalez, H. Orthner, E. Mehmedovic, R. Imlau, M. Luysberg, H. Wiggers (submitted)

Today there is still an urgent need to develop new types of bioimaging tools. The work presenting here demonstrates how to combine upconverting nanoparticles (UCNPs) and dithienylethenes (DTEs) to assemble a water-soluble hybrid system using an easy ‘mix and stir&’ encapsulation process. Upon 980 nm Near-Infrared (NIR) excitation, the system emits fluorescence with narrow bands centred at 550 nm and 650 nm (‘On&’ state). Upon 365 nm UV irradiation cyclises DTEs encapsulated in the system and the follow-up 980 nm NIR excitation results the quenching of fluorescence due to the energy transfer from the UCNPs to the DTE closed isomers (‘Off&’ state). Upon visible irradiation, the DTE closed isomers are converted back to the open isomers and the system again emits fluorescence by follow-up 980 nm NIR excitation. The ‘On/Off&’ state can be switched back and forth many times without significant degradation. The 550 nm and 650 nm emission can be selectively quenched using different DTEs in the encapsulation process. Our ultimate goal of developing this water-soluble hybrid system is to use it enhancing the resolution of cell or living organism images.

This work reports recent advances on the structural and optical characterization of thiol-capped gold nanoparticles, which were prepared starting from previously synthesized gold nanoparticles via chemical reduction of HAuCl4 by sodium borohydride in aqueous medium. Dodecanethiol-capped gold nanoparticles (DDT-AuNPs) were prepared by using a phase transfer process in which the as-prepared gold colloid was thoroughly mixed in a DDT-hexane mixture. The resultant sol composed of hexane- dispersed DDT-AuNPs was then subjected to a digestive ripening process to modulate the particle size. Thioglycolic acid- capped gold nanoparticles (TGA-AuNPs) were directly prepared from as-prepared gold sol by adding a determined amount of thioglycolic acid. The TGA-AuNPs were used to prepare TGA-Au/PDDA (poly(diallyldimethylammonium chloride)) self-assembled multilayer structures by layer-by-layer deposition.
The optical and structural characteristics of gold nanoparticles were assessed by optical absorbance, TEM, SEM and X-rays diffraction measurements.
According to our observations, the as-prepared gold colloid comprises quasi-spherical particles around 3.6 nm in size with its absorbance spectrum displaying a plasmon peak at 525 nm. After being functionalized, the plasmon peak of DDT-AuNPs and TGA-AuNPs-colloids shifts at 522 and 534 nm, respectively. In addition, the particle size decreased with the digestive ripening for time process shorter than 4 h, as indicated by the plasmon peak shifts (525 - 506 nm). Otherwise, the particle size increases because the plasmon peak shifts to longer wavelengths than 525 nm.
In regard to TGA-Au/PDDA structures, the plasmon peak shows a red-shift respect to the TGA-AuNps sol (567 nm). Additionally, SEM measurements reveal that AuNPs self-assemble giving rise to small and unifom agglomerates, which are responsible for the observed red shift. Additional TEM and X-rays diffraction analyses confirm the size, shape and purify of gold nanoparticles.

Recently, there has been great attention to tunable photonic crystal in an effort to develop photonic devices such as sensors and reflective displays. Bottom-up research using colloidal self-assembly is one of the promising technology to create 3-dimensional photonic crystal in order to endow response of the photonic crystal layer to any kind of external stimuli. Such colloid-based tunable photonic crystal has recently been demonstrated as a new class of display element, which allows the full-color emission from a single pixel under ambient lighting condition [1-3]. In particular, long-range interaction between charged colloids is considered as one important colloidal system to help create enough opportunity to manipulate photonic stop-band. However, this long-range self-assembly known as crystalline colloidal arrays usually exhibit a narrow bandwidth owing to the low refractive index contrast between the particles and the matrix/dispersion medium.
In this talk, we will demonstrate our approaches to endow high refractive index contrast in order to increase bandwidth of the stop-band through creating highly charged core-shell nanoparticles. Through modulation of the refractive index of the particle and the applied electric field, not only the photonic stop-band but also the bandwidth of the photonic stop-band could be systematically manipulated. As a result, full color modulation with high optical quality was recently achieved [4]. Understanding behaviors of the electro-response of crystalline colloidal arrays in dispersion media is crucial in both creating and manipulating photonic properties. Therefore, the colloidal behavior of submicron-sized, negatively charged particles in confined media under electric field have been extensively studied both by experimental and computer-aided numerical analysis/simulation. This new findings of the behavior of colloidal particle under variation of electric field can give us key factors to develop new devices such as novel reflective-type display utilizing tunable structural color from photonic crystal.
Reference
1.A. C. Arsenault, D. P. Puzzo, I. Manners, and G. A. Ozin, Nat. Photon., 2007, 1, 468.
2.J. Ge, Y. Hu, and Y. Yin, Angew. Chem. Int. Ed. 2007, 46, 7428.
3.T. S. Shim, S-H. Kim, J. Y. Sim, J.-M. Lim, and S.-M. Yang, Adv. Mater. 2010, 22, 4494.
4.M. G. Han, C. G. Shin, S.-J. Jeon, H. Shim, C.-J. Heo, H. Jin, J. W. Kim, and S. Lee, Adv. Mater. In press.

At cryogenic temperatures, the current flowing through a two-dimensional (2D) array of nanoparticles does not obey Ohm&’s-law. The non-ohmic behavior is a result of local charging of nanoparticles at a single electron level. The charge centers are fixed that pose a Coulomb blockade to the passage of the current through the array. The single electron behavior is characterized by a threshold bias, V_T below which the current is blocked. Above V_T the current rises nonlinearly with an exponent of ~2. However, the V_T vanishes upon heating to room temperature. We will describe a self-assembled network of 1D necklace of 10 nm Au particles that exhibit robust single electron effect with V_T > 10kT/e, where k is Boltzmann&’s constant, e is charge of electron and T is temperature. The 2D array spans from 10 to 100 microns. The 1D necklace morphology is mediated by cadmium ion (Cd²⁺) or zinc ion (Zn²⁺) which is subsequently cemented by hydrogen sulfide gas to form CdS or ZnS “nano-cement”. The necklace exhibits electroluminescence that also exhibits single-electron-like behavior that is commensurate with the electrical characteristics. The electroluminescent spectrum obtained on a home-built spectrometer is in strong agreement with the photoluminescence spectrum of the cemented necklace network. We will discuss the fabrication process of the necklace network, the cementing process including monitoring of the electrical behavior during the cementing process, and the electrical and optical behavior of the nanoparticle array.

The ability to control the plasmonic properties of supported hollow gold nanocages assembled in 2D arrays by varying environment and nanocages density is reported. The gold nanocages were deposited as monolayers by Langmuir-Blodgett and self-assembly techniques onto thin silicon films and fiber optical sensors. The effect of substrate and surrounding media refractive index was investigated using transmission and reflection UV-vis and NIR spectrophotometry, whereas the monolayer morphology was monitored with AFM and SEM/TEM. The shift of the localized surface plasmon resonance modes with respect to changing environment and nanostructure characteristics determined the tuneability of the plasmonic signatures of the gold nanocage assemblies, as desired for various plasmonic applications. Finally, effect of this plasmonic monolayer on the performance of fiber optical Bragg grating sensor was investigated.

Surface enhance Raman scattering (SERS) spectroscopy is a powerful ultrasensitive technique which allows detection down to single molecule levels. The production of active SERS substrates is based on the generation of hot spots created by plasmonic nanoparticles. However, the controlled formation of these hot spots is still a challenge in order to produce homogeneous and reproducible SERS intensities over large areas.
On the other hand, plasmonic nanoparticles are still in the focus of interest because of their potential use in microelectronics, optical devices, and biomedical applications or to develop new metamaterial properties. Their individual electromagnetic response is highly dependent on the specific size, shape, and surrounding environment of the particles. At the moment, there are different methods which allow us to fine tune the control over these parameters and thus, the materials properties. However, the control over the collective behaviour of these individual particles and their incorporation into new technological devices, relay on the ability to form reproducible organized structures at large scales.
In this work we report novel methods to produce highly organized structures made of plasmonic nanoparticles in a macro-scale range using a completely lithography-free approach. Monolayers, supercrystals, and periodic linear arrays with tuneable width and spacing between lines, were created via spin coating, confinement controlled drying, and their combinations.
Furthermore, these structures, were effectively use for sensing using surface-enhanced Raman scattering (SERS) spectroscopy showing the good reproducibility of these structures among big areas. This fact, make them perfect candidates as quantitative ultrasensitive SERS substrates due to the controlled formation of hot spots. Which provide high and uniform SERS enhancement over extended areas.
References:
Pazos-Perez, N., et al. Soft Matter, 9, 4093, 2011.
Schweikart, A., et al. Chemical Science, 1, 174, 2010.
Mueller, M., et al. Langmuir., 2012, 28, 9168-9173.
Pazos-Perez, N., et al.Langmuir, 28, 8909, 2012.
Pazos-Perez, N., et al., Angew. Chem. Int. Ed., 201, DOI: 10.1002/anie.20120701.

A fast and robust method of producing high-quality cobalt nanocrystals with ~5% size polydispersity is demonstrated by using inexpensive test tubes as single-use reactor vessels. The presented non-injective synthesis method is executed by immersing a test tube filled with cobalt precursor (cobalt carbonyl), surfactants, and organic solvent into a preheated oil bath; this results in an extremely rapid and well-controlled temperature rise to isothermal reaction conditions extremely quickly at a speed on the order of 300 C/min, followed by the nucleation and growth of the nanocrystals from the decomposing precursor within 10 minutes. In the light of its simplicity, the method yields remarkably reproducible narrow particle size distributions and enables rapid and inexpensive screening of reaction conditions (solvents, surfactants, concentrations, temperatures etc.) that would be difficult with regular glassware and injective synthesis methods utilizing the same chemistry.[1] The isothermal test tube method was used to identify the critical reaction conditions in the case of cobalt nanocrystals, which pointed toward the importance of the selection of the solvent and surfactants as opposed to the heating profile that can vary from hot-injection[1] to heating-up[2] or even to isothermal conditions[3] without a marked change in the nanocrystal morphology or size. The results are highly promising for upscaling the production of monodisperse cobalt nanocrystals to technologically relevant levels without need to sacrifice the particle quality.
REFERENCES
[1] Puntes, V. F., Krishnan, K. M. and Alivisatos, A. P., Colloidal Nanocrystal Shape and Size Control: The Case of Cobalt, Science 291, 2115-2117 (2001).
[2] Timonen, J. V., Seppala, E. T., Ikkala, O. and Ras, R. H., From hot-injection synthesis to heating-up synthesis of cobalt nanoparticles: observation of kinetically controllable nucleation, Angew. Chem. Int. Ed. 50, 2080-2084 (2011).
[3] Timonen, J. V., Gombault, T., van Rijssel, J. and Erné, B. H., Remarkably Robust Synthesis of Monodisperse Cobalt Nanocrystals in Single-Use Test Tubes, (submitted).

In this paper, results of the dispersion of phosphotungstate (PTA), cure reaction kinetics, and mechanical properties of PTA loaded epoxy nanocomposites are presented. PTA is a 1 nm size particle composed of a tungsten oxide shell and a phosphate group at the core and is part of a class of metal oxides called polyoxometalates. PTA is dispersed in the epoxy resin up to volume fractions of 0.1. PTA forms a stabile dispersion in the epoxy resin due to the formation of a PTA-epoxy resin molecular complex. Differential scanning calorimetry measurements show the cure of the epoxy resin to be sensitive to the concentration of PTA. A kinetics study of the cure exotherm suggests that PTA acts as a catalyst promoting cationic homopolymerization of the epoxy resin. A cure mechanism based on cationic propagation and termination reactions is proposed. The cure kinetics are discussed in light of the activated chain end (ACE) and activated monomer (AM) reaction pathways. High resolution TEM of the cured epoxy nanocomposite show the PTA to be well dispersed in the epoxy matrix. Thermal mechanical and dynamic mechanical temperature sweep measurements show a reduction in the glass transition temperature and coefficient of thermal expansion and an increase in modulus of the cured nanocomposite as the PTA loading is increased.

The fascinating size- and shape-dependent optical properties of metallic nanoparticles have made them very promising building blocks for nanosensing devices. In this study, gold nanorods (AuNRs) synthesized from the seed-mediated growth protocol were assembled onto the electrospun polycaprolactone (PCL) fibers via polyelectrolyte decoration. Specifically, surface modification with poly(sodium 4-styrenesulfonate) (PSS) endowed the AuNRs with net negative charges. At the same time, positive charges on the electrospun PCL fibers were developed using the polyelectrolyte layer-by-layer (LBL) deposition technique. Under the driving force of electrostatic attraction, AuNR assemblies were produced on the PCL fiber surfaces. Various characterization techniques, including Fourier transform infrared (FTIR) spectroscopy, UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been utilized to study the fabrication process. Using 4-mercaptopyridine (4-MPy) as the probe molecule, the obtained AuNR/PCL nanocomposite fibers exhibited usable Raman signal enhancement in surface enhanced Raman scattering (SERS) measurements. As low as a 10-7M concentration of probe molecule was detected in solution with an excellent reproducibility (intensity variation less than 5%). Further optimization of the SERS performance of the AuNR/PCL nanocomposite fibers was achieved by tuning several parameters in the fabrication process, including the surface plasmon resonance properties of AuNRs, the diameter of PCL fibers and the immobilized AuNR density in the assembly.

Multicomponent, multi-layer nanoparticles have potential applications in cancer theranostics, where the different nanoparticle chemical components and layers enable imaging, heating, drug delivery and targeting. Key challenges for manufacturing such nanoparticles include control of the dimensions, morphology, chemical composition and functional properties of each layer, avoidance of impurity residues, stability in aqueous suspension, and scalability to commercially relevant production rates.
We have developed an approach to producing multilayer magnetic/plasmonic nanoparticles that is based on sequential gas-phase processing. Compared to conventional wet chemistry methods, this approach has several potential advantages. It involves a continuous flow rather than batch processing, with residence times of at most a few seconds rather than several hours or days. Surfactants are not required on each layer as it is produced, and therefore surfactants do not need to be removed before addition of each layer. Gas-phase processes are less prone to contamination than liquid processes, and are scalable to high production rates.
Here we report use of this approach for production of nanoparticles consisting of a superparamagnetic iron oxide core that is encapsulated in successive layers of silica, gold and polyethylene glycol (PEG). The PEGylated nanoparticles are then dispersed into stable aqueous suspension. The iron oxide cores are produced in a plasma, and are then transported in a carrier gas through several chambers that sequentially grow layers of silica, gold and PEG. Processes utilized include UV photoinduced chemical vapor deposition for the silica, hot-wire generation of sub-5-nm gold nanoparticles, particle scavenging for attachment for decoration of the silica surface with the gold particles, and PEGylation by attaching a bifunctional thiol to the gold and then inserting ethylene oxide into the hydroxyl end of the thiol. The resulting particles are readily dispersible in water, and can be further functionalized for active targeting and/or drug delivery. Total diameters of the multicomponent nanoparticles are typically in the range 20-50 nm, which is suitable for transport and deposition in tumors.
Several methods are used for online characterization of nanoparticles and of individual layers as they are produced, including scanning mobility particle sizing, tandem differential mobility analysis and in-situ Fourier transform infrared (FTIR) spectroscopy. Particles are also collected onto transmission electron microscopy (TEM) grids for offline characterization by TEM and related high-resolution chemical characterization. Bulk powder samples are collected on filters for characterization by X-ray diffraction, FTIR, magnetic property measurement instruments, and optical absorption and fluorescence.

A key issue in the use of nanomaterials is controlling how they interact with themselves and with the outer world. Our research program focuses on the tailoring of nanoparticles of surfaces for a variety of applications, coupling the atomic-level control provided by organic synthesis with the fundamental principles of supramolecular chemistry. Using these engineered nanoparticles, we are developing particles for biological applications, in particular delivery and sensing. This talk will focus on the interfacing of nanoparticles with biosystems, and will discuss our use of nanoparticles for delivery applications including our studies of small molecule, nucleic acid, and protein delivery. This presentation will also feature the use of nanoparticles for diagnostic applications, including the use of array-based sensing paradigms for the sensing and identification of proteins, bacteria and cell /tissue type and state.

Solution synthesis of inorganic nanomaterials with precise maneuver over morphology has always been a central goal in many fields of chemistry and physics since the physical and chemical properties of nanomaterials heavily lean on their size and shape. Small molecules and polymers have been extensively explored for this purpose although the organic-inorganic interface interaction in the colloidal system is still far from understood. In this talk I will share our efforts in decoding the origin of selective molecular adsorption to noble metal facets. The selection of facet specific short peptides and their abilities in guiding predictable shape control of Pt nanocrystals will be first demonstrated. Then detailed experimental and theoretical studies on binding mechanism will be discussed. The end of the talk, the discovered molecular signature for facet specific adsorption will be applies to the design of small molecules that deliver the expected colloidal synthesis results. These studies open up opportunities in understanding the molecular details of inorganic-organic interface interaction, which could one day lead to the development of a library of molecular functions for predictable materials engineering.

The intriguing properties of DNA have attracted substantial interest for their use toward engineering solid-state devices from nanomaterials. For example, DNA has been used to mediate nanoparticle assembly and control particle packing in both bulk solids and thin films. In addition, the ability of double stranded DNA to transfer electrons or holes imparts unique opportunities for enhancing carrier mobility in thin film devices. However, the study of charge transport within DNA-nanoparticle hybrid thin films has been challenging due to difficulties in engineering well-ordered DNA-nanoparticle films on surfaces with control over film thickness, film uniformity, and particle packing. We demonstrate in this talk our recent efforts in fabricating DNA-CdSe nanoparticle thin film devices and the role of DNA on nanoparticle ordering, interparticle spacings, and electron transport. Semiconductor quantum dots (QDs) have been widely studied as optoelectronic materials due to their optimal band tuning. In this work, we demonstrate different methods to produce DNA conjugated CdSe QDs that undergo minimal oxidation and are stable in varying pHs and salt conditions. In order to produce the well-ordered DNA-QD films, DNA oligonucleotides that promote interparticle hybridization (“linker DNA”) were first dried on an ITO surface. Next, different sets of DNA-QDs complementary to the linker DNA were adsorbed to the surface at varying concentrations. To promote ordering in the DNA-QD film, the entire sample was thermally annealed above the melting temperature of the DNA strands to form either BCC or FCC active layers, After a back electrode was deposited on the active layers, current-voltage (I-V) measurements were run. The I-V curves showed rectifying behavior with a relevant current density indicating that the DNA strands did not act as an insulator. Furthermore, we observed that the current density increased dramatically as the amount of linker DNA increased. This is believed to be because the linker DNA helps the CdSe QDs become better ordered and because double stranded DNA between all the particles provides an electron transport path which results in more efficient electron transport from one nanoparticle to the next. This work to date thus demonstrates the potential for using DNA as a material for overcoming current limitations of nanoscale thin film devices, including nanoscale manipulation and inefficient charge transport.

Even when treated with aggressive current therapies, most patients with primary or metastatic malignant brain tumors survive less than two years. Although immunotherapy is being studied as a potential treatment, the blood-brain barrier and local tumor immunosuppressive milieu may prevent penetration of cytotoxic antibodies or immune cells into the brain. Local delivery of immunostimulatory molecules such as CpG can overcome this suppressive environment, but at high doses may also cause toxic brain inflammation. Thus, there is a pressing need for a safer, more effective targeted strategy to enhance CNS immune responses to malignant brain tumors. We recently demonstrated that carbon-nanotubes (CNTs) are efficient nontoxic carriers of macromolecules into tumor inflammatory cells, and when conjugated with CpG (CNT-CpG), result in robust activation of inflammatory cells. Remarkably, even a single low-dose injection of CNT-CpG (but not free CpG) eradicated brain tumors in animal models and protected surviving animals from tumor rechallenge. These findings suggest that enhanced delivery of immunostimulatory molecules into the brain can induce a strong local and systemic anti-tumor response. Here we describe optimizing this novel immunotherapy strategy for treatment of human brain tumors. We have evaluated other nanoparticles as carriers for the CpG as well as progressed towards Good Manufacturing Practices preparation of the CNT-CpG in preparation for translation to humans. If successful, the nanoparticle-CpG developed here can be used in human clinical trials for treatment of not only glioma, but also cancers that metastasize to the brain, thereby greatly benefiting patients with these devastating diseases.

III-V semiconductors, such as GaAs, InP, InAs and InSb, are known for their excellent properties that combine direct band gap and very high carrier mobility with reliable n- and p-type doping. These materials are used in laser diodes, the fastest commercial transistors and the most efficient solar cells. However, despite all the benefits of III-V semiconductors, very limited attention has been paid to their applications in large area devices, such as printable electronics and thin-film solar cells. Colloidal III-V nanocrystals (NCs) can provide a convenient route for low-cost manufacturing of a solution-processed form of III-V semiconductors. In this presentation we will discuss new advances in synthetic and surface chemistry for III-V NCs and demonstrate the possibility of building advanced functional materials from these building blocks.
We will report the colloidal synthesis of monodisperse InSb NCs, which is an important member of III-V semiconductor family. InSb NCs showed well-resolved excitonic transitions and band edge photoluminescence in the near-infrared spectral range. We will also discuss new surface chemistries for III-V nanomaterials. We found that molecular metal chalcogenide complexes (MCCs) and chalcogenide ions can quantitatively displace organic ligands from the surface of III-V NCs and serve as the inorganic capping groups for III-V NC surface. These inorganic ligands greatly facilitate charge transport between individual NCs leading to high electron mobility in the films of MCC-capped InP and InAs NCs. For example, we found that the electron mobility in the arrays of InAs NCs bridged with Cu₇S₄^- MCC ligands exceeding 15 cm²/Vs. In addition, we observed ambipolar (positive/negative) photoresponse of MCC-capped InAs NC solids that changed sign depending on the ligands chemistry, illumination wavelength and doping of NC solid. We propose an explanation of this unusually complex photoconductivity of InAs NC solids.

Gold nanorods (NRs) are attractive for externally controlled release of biomolecules, which has been demonstrated by laser irradiation of the NR at the longitudinal surface plasmon resonance peak (SPR). The SPR is tunable by changing the NR aspect ratio; therefore, NRs with different aspect ratios can be independently excited at different irradiation wavelengths, to release different payloads. We are using this approach to create a biological switch for blood clotting by releasing a ssDNA thrombin binding aptamer (TBA) upon laser irradiation. Blood clotting can be controlled by releasing TBA that binds and inhibits thrombin and an antidote that restores its activity. In addition, a DNA strand antidote can be used to reverse the effect of the TBA. The TBA and its antidote are loaded onto NRs with different aspect ratios. This enables us to use laser excitation at one wavelength to deliver the TBA and inhibit thrombin and consequently blood clotting itself. We then use a different wavelength to deliver the antidote and reverse the effect of the TBA. We take advantage of serum protein coronas for loading, which enable enhanced loading capacities on the NRs. This localized, selective and externally controlled release of biomolecules represents an advance in a number of biological applications, where the current practice is systemically administering drugs though the whole bloodstream and relying on physiological clearance to restore the system&’s activity.

Gold nanorods (Au NRs) are of intense technological interest due to their broadly tunable surface plasmon resonances, which provide ways to manipulate electromagnetic fields at the nanoscale. Optimizing the plasmon resonance wavelength and relative contribution of absorption and scattering to total extinction coefficient are critical for sensing, imaging, medical diagnostics, therapeutic, and energy harvesting technologies. Among the many synthetic routes, the seed-mediated procedure is most commonly chosen due to its versatility, robustness and relatively low concentration of nanoparticle impurities. The aspect ratio of these NRs is between 2 and 10, but it is challenging to obtain short nanorods with small diameter (less than 10nm) and long nanorods with large diameter (larger than 20nm). Following our prior work demonstrating that the distribution of seed size determines the final rod morphology and fraction of byproducts, we demonstrate here in that the diameter and length of the AuNR can be independently tuned by tuning the stability of the initial Au seed. A more monodispersed rod with less byproducts can be obtained by optimizing the seed via the concentration of reducing agent, type/concentration of stabilizer and aging time. Furthermore, the molar ratio between seeds and Au precursor in the growth medium enables control of AuNR dimensionality. For example, Au NRs of various aspect ratios (2 to 8) with diameter ranging from 5 to 35nm were fabricated with high mono-dispersity. Using this ability to fabricate AuNRs of the same aspect ratio but various dimensionality, we demonstrate that the extinction cross-section, and the relative contribution of scattering, depend on both aspect ratio and rod dimensionality in contrast to commonly used first order theoretical estimates. This refined, quantitative structure-property correlation will improves selection of AuNRs for emerging applications.

Ferritin is a major iron storage protein found in human and most living organisms. Each ferritin is comprised of 24 subunits, which self-assemble to form a cage-like nanostructure. Apoferritins (FRTs) refer to those that are without iron encapsulated. FRT is an interesting nanoplatform and holds great potential in cancer imaging and drug delivery for several reasons. 1) Biosafety. Compared to many other biomaterials, FRTs have fewer concerns in toxicity and immunogenicity. 2) Unique nanostructure. Despite the stability in a physiological environment and even at high temperature (60°C), the FRT nanoarchitecture can be broken down into FRT subunits in an acidic environment (pH = 2). Interestingly, such a process is reversible. When the pH is tuned back to neutral, the FRT subunits will be reconstituted into a nanocage structure, and almost in an intact fashion. Such a feature can be harnessed to form hybrid nanostructures and to allow for efficient drug loading. 3) Easy surface modification. As a protein, FRT nanocages can be genetically modified to present a recognition peptide sequence on the surface. In addition, FRTs have multiple lysine and cysteine groups on the surface that can be easily linked with functional molecules, such as a fluorescence dye or a targeting peptide. 4) High loading capacity. In addition to iron and other metals, many small molecules are able to be encapsulated into FRT interiors efficiently. Making use of these unique characteristics, we developed several FRT-based probes for tumor imaging. Very recently, we found that doxorubicin (Dox) can be internalized into RGD modified FRTs (RFRTs, up to 70 wt%) and site-specifically delivered to tumor for efficient therapy.

In this study, a hybrid instrument was developed to characterize nanoparticles. Real-time particle size discrimination was achieved using an electrospray coupled to a differential mobility analyzer (ES-DMA). The ES-DMA was coupled to two detectors: a condensation particle counter (CPC) for particle concentration measurements and an inductively coupled plasma mass spectrometer (ICP-MS) for quantitative elemental analysis. A gas-exchange device (GED) was designed to convert the air flow from the electrospray to an argon flow for ICP-MS analysis. The individual components and the hybrid instrument were tested, optimized, and validated for the real-time characterization of gold nanoparticle suspensions. The GED was systematically studied to optimize exchange efficiency and particle transport. A range of gold concentrations was used (5 to 250 mu;g/g) to calibrate detectors. By combining the data obtained from the CPC and the ICP-MS using ES-DMA sample introduction, the hybrid instrument can provide real-time quantitative elemental analysis of size-resolved nanoparticles. This is a powerful measurement technique for the simultaneous characterization of particle size and elemental composition. Moreover, it can be further optimized for analysis of more complex colloidal systems, such as core/shell particles and particle-ligand conjugates. The advantages, challenges, and potential biomedical applications of this measurement technique are discussed.