Assembly of molecular clusters and nanoparticles in solution is now recognized as an important mechanism of crystal growth in many materials, yet the assembly process and attachment mechanisms are poorly understood. To achieve this understanding we are investigating nucleation and assembly of iron oxide and calcium carbonate nanoparticles. In-situ TEM using a custom-designed holder and fluid cell to obtain sub-nanometer resolution shows that, in the iron oxide system, primary particles of ferrihydrite can interact with one another through translational and rotational diffusion until a near-perfect lattice match is obtained either with true crystallographic alignment or across a twin plane. Oriented attachment (OA) then occurs through a sudden jump-to-contact, which demonstrates the existence of an attractive potential that drives the OA process. Following OA, the resulting interface expands through ion-by-ion attachment at a curvature-dependent rate. When there is a significant mismatch between the particle sizes and an attachment event does not occur during extended periods of particle interaction, the larger crystal can still grow in size due through Ostwald ripening, resulting in the disappearance of the smaller particle. In contrast to the clear role played by OA in the case of ferrihydrite, analysis of the assembly of akaganeite nanorods to form single crystal hematite spindles shows that attachment does not result in co-alignment, rather the initial mesocrystal is disordered and recrystallizes to a single crystal over time. Finally, in the calcium carbonate system, nanoparticles do interact and undergo aggregation events, however, the smallest particles often appear to be amorphous, with crystallinity presumably arising as a result of attachment. These results highlight the wide range of styles possible in mesocrystal formation, as well as the importance of in situ or temporally resolved studies when attempting to decipher the underlying pathways and mechanisms.

In-depth understandings of crystal growth mechanisms and kinetics provide guidance for particle size control during nanomaterial synthesis. Principally, the descriptions of crystal growths are based on the classical Ostwald Ripening (OR) mechanism and the newly discovered Oriented Attachment (OA) mechanism. However, it is widely held that the OR or OA mechanism cannot explain all the growth behaviors well, e.g. a fast crystal growth directly from nano- to microcrystals. 1
Tailoring the size of tin oxide (SnO2) crystal is also of great interest for its wide applications in nanotechnology. Typically, SnO2 particles grow very slowly, limiting the crystal size to only a few nanometers.2-4 We demonstrated that nano-SnO2 treated hydrothermally could stabilize at a small particle size for a long time (4.2 nm, 250 oC, 180 hr).4 The slow growth of SnO2 was attributed to 1+1 OA growth kinetics of the primary small particles.4 Following the OA growth, we report an ultrafast growth of SnO2 nanocrystals directly from ~4 to ~350 nm (250 oC, time > 180 hr).1 The crystal growth system is characterized by “either small or large” in particle size, that is, only two differently sized SnO2 particles, either several nm or ~350 nm, coexist. During the fast growth process, SnO2 nanoparticles assembled to form densely aggregated aggregates that can quickly transform to big (bulk-like) crystals, which was further described by an aggregation-induced fast crystal growth mechanism. Small angle X-ray scattering (SAXS) study of the aggregates supports that the onset of the fast growth is closely related to an increase in the aggregation degree of the aggregates. Moreover, disintegrating the aggregation state via introduction of other particles (Al2O3) into the system prohibited the fast growth. The finding provides new threads for syntheses of novel nanomaterials that may possess properties not readily obtained via conventional crystal growth routes. In addition, the treatment of industrial sludge containing amorphous/nanophase metal oxides or hydroxides is one of the vital issues in hazardous waste disposal. On the basis of above studies, we developed a strategy involving of tailoring crystal growth of SnO2 to achieve selective recycling of nano-SnO2 from tinplate electroplating sludge. We hope a strategy developed in this way could have a potential ability to the recycling of valuable metals from industrial nanowastes.5
(1) Zhuang, Z. Y.; Huang, F.; Lin, Z.; Zhang, H. Z. J Am Chem Soc 2012, 134, 16228.
(2) Lee, E. J. H.; Ribeiro, C.; Longo, E.; Leite, E. R. Chem. Phys. 2006, 328, 229.
(3) Ribeiro, C.; Lee, E. J. H.; Longo, E.; Leite, E. R. Chemphyschem 2005, 6, 690.
(4) Zhuang, Z. Y.; Zhang, J.; Huang, F.; Wang, Y. H.; Lin, Z. Phys. Chem. Chem. Phys. 2009, 11, 8516.
(5) Zhuang, Z. Y.; Xu, X. J.; Wang, Y. J.; Wang, Y. D.; Huang, F.; Lin, Z. J Hazard Mater 2012, 211, 414.

Oriented attachment is a non-classical crystal growth mechanism that can be exploited to produce nanocrystals with unique and symmetry-defying shapes. In addition, this mechanism can result in twinning as well as the incorporation of defects like dislocations and stacking faults. Primary crystallites attach to one another and reorient with respect to one another. Secondary particles that can have high degrees of crystallographic order result. Comprehensive characterization is critical for elucidating the fundamental processes governing crystal growth by oriented aggregation and how it can influence microstructure and subsequent phase transformations. Transmission electron microscopy (TEM), cryogenic TEM, and in situ fluid cell TEM enable direct imaging of materials throughout the growth process. Correlative techniques, such as X-ray diffraction (XRD), small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), dynamic light scattering (DLS), and UV-visible spectroscopy, as well as kinetic modeling, also lead to important insights. Each of these techniques has advantages and limitations, and a combination of methods is crucial to push our understanding of oriented attachment forward.

The assembly and oriented attachment of semiconductor nanocrystals enables one to prepare two-dimensional supercrystals of these materials. The supercrystals are atomically coherent and have a superimposed nanoscale periodicity[1]. The electronic properties of these materials are remarkable and, in the case of the honeycomb geometry, may have an unconventional (Dirac-type) band structure[2,3].
Here, we study the geometric structure of 2D PbSe systems obtained by NC self-assembly at the liquid-air interface. From transmission electron microscopy (TEM) it is found that several different atomically coherent nanocrystal superlattices can be formed with linear, cubic and honeycomb symmetry depending on the synthesis conditions. We show that, with a combination of scanning tunneling microscopy (STM), TEM and electron-tomography[4,5], the honeycomb supercrystal is actually buckled into a silicene-like supercrystal and not a graphene type.
Atomistic tight-binding theory predicts a very rich band structure for these systems, with two Dirac-type conduction minibands. The experimental characterization of the electronic structure is my personal challenge for the coming years.
References
[1] W. H. Evers et. al, Low-Dimensional Semiconductor Superlattices Formed by Geometric Control over Nanocrystal Attachment, Nano Lett. (2012)
[2] E. Kalesaki et. al., Electronic Structure of Atomically Coherent Square Semiconductor Superlattices with Dimensionality Below Two, PRB (2013)
[3] E. Kalesaki et. al., Dirac Cones, Topological Edge States and Non-Trivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nano-Geometry, under review
[4] K. Overgaag et. al, Scanning tunneling spectroscopy of individual PbSe quantum dots and molecular aggregates stabilized in an inert nanocrystal matrix, ACS Nano (2008)
[5] H. Friedrich et. al, Quantitative Structural Analysis of Binary Nanocrystal Superlattices by Electron Tomography, Nano Lett. (2009)

Oriented attachment represents an important growth mechanism for nanoparticles. In addition, oriented attachment can be used to assemble nanoparticles into 1-, 2- and 3-dimensional structures. However, the size of these assemblies is typically restricted to the sub-micron range.
In this talk we will present an elegant way to assemble surface-functionalized anatase nanoparticles into three-dimensional, highly porous and nanocrystalline aerogel monoliths by oriented attachment [1]. The macroscopic size of the final material is the result of a self-assembly process from the nm to the cm range. The modularity of the approach makes it possible to prepare multicomponent aerogels by co-gelling different types of nanoparticles including gold and iron oxide nanocrystals as well as tungsten oxide nanowires. In addition, the local composition can be tuned on a macroscopic level, giving access to aerogels with nanoparticle distributions in a layered or in a gradient configuration. These aerogels represent illustrative examples, how the controlled assembly of preformed inorganic building blocks results in unique and complex materials with a broad variety of chemical and physical properties.
[1] F. J. Heiligtag, M. D. Rossell, M. J. Süess, M. Niederberger, Template-Free Co-Assembly of Preformed Au and TiO2 Nanoparticles into Multicomponent 3D Aerogels, J. Mater. Chem., 2011, 21, 16893

Numerical simulations of collisions of BaTiO3 nanoparticles have been performed under the experimental condition of mesocrystal formation in an aqueous solution without organic materials such as surfactants under ultrasound [F.Dang, K.Kato, et al., Jpn.J.Appl.Phys. 48 (2009) 09KC02]. The dipole-dipole interaction model has reproduced the experimental results of mesocrystal formation [K.Yasui, T.Tuziuti, and K.Kato, Ultrason.Sonochem. 18 (2011) 1211, K.Yasui and K.Kato, J.Phys.Chem.C 116 (2012) 319]. It suggests that a 5 nm BaTiO3 naocrystal has spontaneous polarization. Indeed, Polking et al. [Nature Mater. 11 (2012) 700] have experimentally confirmed the spontaneous polarization of 8-10 nm BaTiO3 nanocrystal. On the other hand, there are numerous reports on the size effect that spontaneous polarization disappears below a critical size of a BaTiO3 nanocrystal. The critical size ranges from 5 to 200 nm. Numerical calculations of the free energy have indicated that with adsorbate-induced charge screening the size effect is weakened and that 5 nm BaTiO3 nanocrystal may have spontaneous polarization [K.Yasui and K.Kato, J.Phys.Chem.C 117 (2013) 19632]. The influence of mobile carrier concentration inside a nanocrystal as well as defect-induced microstrain is also discussed on the size effect. The stability of domain structures of a BaTiO3 nanoparticle is also discussed.

Nanocrystalline magnesium aluminate was synthesized with coprecipitation method. Its growing behaviors as a function of temperature were studied with synchrotron x-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy. It is found that the particle growth was greatly inhibited at temperature below 1000 oC due to the amorphous reactants. Above 1000 oC, magnesium aluminate nanoparticles start to grow fast. After two hour annealing at 1200 oC, the grain size changes in multiplefolds, suggesting that oriented attachment may occur. Above 1200 oC, in each temperature step the relative grain growth in different direction is less than the particle size, indicating oriented attachment mechanisms become inactive in the growth of MgAl2O4 nanoparticles with size larger than 32 nm.

The kinetics of the anatase to rutile phase transformation have been quantified for hydrothermally treated nanocrystalline anatase (TiO₂). Kinetic models based on interface-nucleation or dissolution-precipitation were used to fit the experimental data. Results show that at highly acidic conditions, anatase phase transforms to rutile predominantly by a dissolution-precipitation mechanism, presumably due to the comparatively high solubility of TiO₂ at 250 °C and pH 1.0. In contrast, the data were fit well to the interface-nucleation model for experiments performed at pH 3.0. However, the kinetic data for the phase transformation at pH 2.2 were not fit well using either model. A new kinetic model was derived, which combines the interface-nucleation and dissolution-precipitation models into a two-step transformation mechanism: interface-nucleation followed by dissolution precipitation. The experimental data, which include both particle size and phase composition versus time, are fit well by this new model. Thus, new insight into the mechanism of the anatase to rutile phase transformation under hydrothermal conditions are gained, demonstrating the importance of oriented aggregation induced interface-nucleation mechanism even under conditions of high titania solubility.

In the early to mid-1990&’s, Ph.D. student R. Lee Penn conducted crystal growth experiments under hydrothermal conditions using nanocrystalline TiO2 (anatase phase). In one experiment, high-resolution transmission electron microscope (TEM) imaging revealed elongate crystals with an extraordinary morphology that were clearly built from individual, crystallographically oriented euhedral anatase crystals. Later, we realized that this phenomenon, referred to as oriented attachment (OA), was widespread in many coarsened anatase samples, although typically far less obvious. The implication of growth via an OA pathway that was of most immediate interest to us was that it represented a source of defects in materials - dislocations, stacking faults, twins, and that these could play key roles in further reactivity (e.g., phase transformations). However, these consequences appear to have attracted less interest than the basic growth phenomenon, its relevance across material types, occurrence in natural systems, and dependence on solution chemistry. Despite the accumulation of a large body of materials research on the topic, some remained skeptical that oriented, particle-by-particle growth was possible. Recent, remarkable fluid cell TEM work by Dongsheng Li in the DeYoreo lab that directly visualized the process put this argument to rest. Recent work in our group using molecular energetic calculations showed the importance of interatomic Coulombic interactions as the driving force for OA. Ongoing work is exploring, in more detail, the inter-particle forces that control particle orientation prior to attachment and the explanation of symmetry-breaking phenomena during OA-based growth. New understanding of these topics may provide routes for improved materials engineering, including tailoring of properties by leveraging the microstructural features that arise via OA-based growth.

Self-assembly of nanometric building blocks is a fascinating phenomenon to provide a wide range of novel functional materials having ordered architectures. The crystallographic direction of the building units is regulated with oriented attachment of specific crystal lattices in the ordered arrays. However, the regulation of the direction and dimension of the oriented attachment is fundamentally difficult by using a uniform building unit without any external fields. In the present work, direction control of oriented assembly for 1D, 2D, and 3D mesocrystals is achieved using anisotropic nanocuboids of tetragonal manganese(II, III) oxide as a building block. We demonstrated the ordered assembly of the nanocuboids covered with oleic acid by a convective self-assembly method. Micrometric liner chains (1D arrays), monolayers (2D arrays), and superstructures (3D arrays) of the anisotropic nanocuboids were produced through direction control of oriented assembly by using evaporation of a dispersion. The liner chains elongated in the <100> direction of the tetragonal crystal were produced on a substrate from highly dispersed nanocuboids through evaporation of a hydrophobic medium. The monolayers and superlattices consisting of the nanocuboids in which their (100) face was parallel to the substrate were produced though stacking the linear chains by increasing the particle concentration. Another type of 2D and 3D arrays having the (001) face parallel to the substrate was obtained through assembly of 2D clusters of the nanocuboids with increasing the polarity of the medium. The affinity of the anisotropic building blocks with the dispersion media and the surface of a substrate is essential to control the crystallographic orientation of the various dimensional assemblies. This direction- and dimension-controlled self-assembly process is regarded as a novel fabrication technique of a wide variety of functional nanomaterials.

Iron Oxide exists under different polymorphs such as maghemite and magnetite, goethite and hematite, the latter being the most stable phase of iron oxide. Iron oxide in hematite phase is an abundant, non-toxic and low cost n-type semiconductor.[1]
The synthesis of hematite mesocrystals offers a valuable tool for exploring new properties arising from the assembling of highly ordered primary building units.[2] Accordingly, the combination of chemical stability of hematite iron oxide together with the mesocrystalline habit makes this material suitable for a number of applications ranging from lithium ion batteries [3] to water splitting [4] and waste water treatment [5]. Mesocrystalline particles can serve also as starting materials for the construction of more complex systems by top-down approaches.[6]
In order to explore the potential of oriented attachment in the production of materials that possess superior functions the fundamental aspects related with the reaction mechanism have to be investigated. A possible strategy is the implementation of in-situ spectroscopies that are able to follow the formation of primary particles as well as their assembly into superstructures in real time.
In the present contribution the synthesis of hematite nanorods with a characteristic narrow neck in the centre of the elongation axis is described. An ex-situ time resolved study by different techniques (UV-Vis, HRTEM, SEM, XRD) allows identifying during the early stages of the reaction the formation of primary building blocks together with larger elongated structures. These structures appear to be amorphous and serve as templating matrix for the growth of the nanorods.
An in-situ study has been carried out by Raman, ATR and UV-Vis spectroscopies that sheds light on the molecular interaction, crystallinity of materials and evolution of the optical properties over time.
The combination of in-situ and ex-situ techniques allows a detailed reconstruction of the reaction mechanism and provides a general strategy for investigating the oriented attachment mechanism in a systematic way.
[1] Libor Machala, Jirí Tucek, Radek Zboril Chem. Mater. 2011, 23, 3255.
[2] R. Yao, C. Cao RSC Advances, 2012, 2, 1979.
[3] X. Duan, L. Mei, J. Ma, Q. Li, T. Wang, W. Zheng Chem. Comm. 2012, 48, 12204.
[4] K. Sivula, F. L. Formal, M. Graetzel, ChemSusChem, 2011, 4, 432.
[5] X.-L. Cheng, J.-S. Jiang, M.Hu, G.-Y.Mao, F.-X. Bu, C.-C. Lin, Y. Zeng, Q.-H. Zhang, CrystEngComm, 2012, 14, 7701.
[6] J. Cai, S. Chen, J. Hu, Z. Wang, Y. Ma L. Qi CrystEngComm, 2013, 15, 6284.

In the last years, several excellent reviews about oriented attachment (OA) have evidenced the advances achieved in this research area, detailing the growth mechanism and the kinetic models. The main focus of this presentation is to examine the dependence of the OA mechanism on the colloidal state and to demonstrate how the colloidal state modifies the OA mechanism. Basically, we can define two main possible approaches to achieve self-organization or mutual orientation of adjacent nanocrystals. One is the effective collision of particles with mutual orientation controlled by the number of collisions. This type of growth occurs in a well dispersed colloidal suspension and results in a statistical growth process. The second way is through coalescence induced by particle interaction and rotation. This mechanism must be dominant in a weakly flocculated colloidal state in which there is significant interaction among particles. This type of process leads to the formation of complex structures. We intend to discuss also a special case of TiO2 nanocrystal synthesis by a colloidal process where the final shape and size of the nanocrystal is influenced by a phenomenon similar to the Rayleigh-instability of freestanding TiO2 nanorods in solution. In this process, a larger structure (the nanorod) is divided into smaller units (nanocrystals), by a kind of detachment process.

We report the synthesis and characterization of Pb-chalcogenide fused QD-QD dimer structures. The resulting QD-dimers range in length from 6-16 nm and are produced by oriented attachment of single QD-monomers with diameters of 3.1-7.8 nm. While smaller QDs contain a larger fraction of high-energy surfaces, QD-monomers with diameters exceeding about 5 nm appear to have the greatest affinity for QD-dimer formation, and therefore, gave the greatest yields of fused structures. We compare the spectroscopy of PbSe QDs, QRods and QD-dimers. We find a new absorption feature in the 1st exciton QD-dimer spectra and assign this to a splitting of the 8-fold degenerate 1S-level. We show calculations of coupled QD-dimers that account for this splitting and discuss the polarization anisotropy of QDs, dimers and rods. We also demonstrate that QD-QD heterostructured dimers structures produced by fusing two PbSe QDs of different size are possible

Magnetite (Fe3O4) is an important magnetic iron oxide of which the magnetic properties depend on the size and morphology of its crystals. Inspired by nature, this work explores the use of randomly sequenced poly(aminoacid)s and commercial poly(aspartic acid) to control the formation of magnetite particles as in the case of magnetotactic bacteria via synthetic methods.
Aqueous partial oxidation, chemical co-precipitation and ammonia diffusion methods are employed for the synthesis of superparamagnetic and ferrimagnetic magnetite nanoparticles at room temperature. Phase identification of crystals formed in the presence and absence of polymeric additives is obtained by X-ray diffraction (XRD) and Low-dose electron diffraction (LDED) methods. Changes in morphology, size and organization of magnetite crystals are analyzed by Cryo-TEM and Cryo-Electron Tomography (Cryo-ET) while corresponding magnetic properties were obtained by vibrating sample magnetometer (VSM).
Fascinating control over the size and shape of magnetite particles are shown to ve achieved mainly by changing the supersaturation level and reaction kinetics. Our present data show that biomimetic formation of magnetite via precursor phase (ferrous hydroxide) is important for manipulating nucleation and growth with polymeric additives which provides effective control over size, shape, organization therewith magnetic properties of magnetite crystals.

Crystal growth, oriented aggregation and phase transformation may be intimately interconnected in the formation of nano- and microcrystalline materials [1-3]. Yet the mechanistic linkages between the different processes are not fully understood. Recently, we studied hydrothermal growth of akaganeite (β-FeOOH) nanorods and their transformation to micron-sized hematite (α-Fe2O3) spindles using high-resolution cryogenic transmission electron microscopy (cryo-TEM) [4]. Only akaganeite particles and hematite spindles were detected in the samples. Futher, cryo-electron 3D tomograms showed that akaganeite nanorods were aggregated into loose three-dimensional networks with some embedded hematite spindles. Based on our cryo-TEM data and additional X-ray diffraction, electron microscopy, and chemical data, we propose the following growth model for the system [4]: First, formation of the early-stage hematite spindles is driven by phase stability change due to increase in size caused by oriented aggregation of akaganeite. Then, akaganeite particles continue to transform to hematite upon contact with and recrystallization onto hematite surfaces, making hematite grow with a constant aspect ratio and forming micron-sized nano-porous single-crystal spindles. This growth model interprets experimental observations well, and it provides a possible solution to a previous long-time debate of whether the hematite spindles are formed via classical Ostwald ripening or by oriented aggregation of hematite nanoparticles. Possibly, this aggregation-based concurrent growth and transformation model [4] may also be applicable to crystal growth and phase transformation in other systems.
1. S. Kumar, Z. Wang, R. L. Penn, and M. Tsapatsis, A Structural Resolution Cryo-TEM Study of the Early Stages of MFI Growth. J. Am. Chem. Soc. 2008, 130, 17284.
2. V.M. Yuwono, N.D. Burrows, J.A. Soltis, and R.L. Penn, Oriented Aggregation: Formation and transformation of mesocrystal intermediates revealed. J. Am. Chem. Soc. 2010, 132, 2163.
3. J. Baumgartner. A. Dey, P.H.H. Bomans, C.L. Coadou, P. Fratzl, N.A.J.M. Sommerdijk, and D. Faivre, Nucleation and growth of magnetite from solution. Nature Mater. 2013, 12, 310.
4. C. Frandsen, B.A. Legg, L. R. Comolli, H.Z. Zhang, B. Gilbert, E. Johnson, and J.F. Banfield, Aggregation-induced growth and transformation of β-FeOOH nanorods to micron-sized α-Fe2O3 spindles, CrystEngComm, DOI:10.1039/C3CE40983J.

The evidence of the intrinsic ability of nanoparticles (NPs) and other nanoscale species to self-organize can be traced in many processes. Some of them are obvious, such as spontaneous formation of stacks of graphene or clay sheets. The others are less obvious, such as formation of the growth of larger crystals by assembly of NP building blocks. While the general propensity of NP to self-assemble is recognized, the mechanisms of these processes are not well understood. From the fundamental perspective better understanding of self-organization phenomena at nanoscale is important because such effort can lead to resolution of central problem of solution-processed electronics that can be described as charge transport dilemma. On one hand the NPs has to form stable dispersion and therefore be coated with a layer of organic shell (stabilizers). On the other hand, after deposition on the substrate this shell needs to disappear to avoid high energy threshold for charge transport. In this talk will address both fundamentals and practical aspects of nanoparticle self-organization phenomena that lead to spontaneous lattice-to-lattice connectivity of NPs involving oriented attachment and other processes. Besides solution processing of electronics the ability of NPs to produce continuous conductive pathways can also be utilized for modulating mechanical properties of materials, such as damping, by applied electrical field.

Low dimensional semiconductors have been extensively investigated during the past few decades due to the abundance of their applications, such as transistors, solar cells, photo-detectors, light emitting diodes and lasers. An alternative perspective to this field, which is traditionally dominated by III-V and II-VI materials grown by gas phase methods in high vacuum, could stem from the oriented attachment of colloidal nanocrystals (NCs). The recently reported formation of chalcogenide-based, square or honeycomb superlattices through NCs oriented attachment [1] could open new pathways to the exploitation of low dimensional systems and hence necessitates determination of their electronic properties.
In the current contribution, we present results of tight binding calculations on the electronic structure of single-crystalline sheets, with an effective dimensionality below two, and graphene- / silicene- like superlattices of PbSe or CdSe NCs [2, 3]. The primary role of both the atomic lattice and the overall geometry on the band structure is evident in all cases. The strong coupling between the wave functions of nearest-neighbor NCs, mainly determined by the number of atoms at the NCs bonding plane, results in electronic structures composed of successive bands. For single-crystalline sheets, band structures markedly differentiate from that of corresponding two-dimensional quantum wells, but the latter can be recovered if nanogeometry effects are gradually reduced. The enhanced width of the bands ascribes highly promising transport properties to square superlattices [2]. In the case of honeycomb lattices, which could combine the usual semiconductor properties with Dirac bands, unusual electronic properties are revealed. In rock-salt PbSe, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende CdSe, the honeycomb nanogeometry leads to band structures which comprise Dirac cones at two distinct energies and non-trivial flat bands in the conduction band whereas in the valence band several bands with topological edge states are present. These systems could serve as platforms for studying complex electronic phases starting from conventional semiconductors [3].
Acknowledgment: This work has been supported by funding of the French National Research Agency (ANR-09-BLAN-0421-01)
References
[1] W. H. Evers et al., Nano Lett. 13, 2317 (2013)
[2] E. Kalesaki et al., Phys. Rev. B 88, 115431 (2013)
[3] E. Kalesaki et al., submitted

Growth of nanocrystals (NCs) via the oriented attachment (OA) mechanism is based on the spontaneous self-organization of adjacent nanocrystals into a single solid particle that share a common crystallographic orientation and often with abrupt edges. Pyrite iron disulfide (FeS₂) has been intensively explored for applications in photovoltaic devices, photoeletrochemical solar cells, cathode material for lithium batteries, and a depolarizer anode for hydrogen production. Here, we report the growth of anisotropic iron pyrite NCs following the OA mechanism at the early growth stage of the hot injection synthesis. The time-dependent X-ray diffraction (XRD) patterns show the pyrite phase NCs are formed even within a very short time after the reaction taking place. The time-dependent transmission electron microscope (TEM) images indicate that the formation of anisotropic iron pyrite NCs involves a nucleation burst and an attachment process at the early growth stage. High-resolution TME (HRTEM) images reveal the OA attachments including two primary NCs, one primary NC with a dimer or a trimer, or multiple primary NCs. By analyzing the HRTEM images, it was found that the attachments tend to occur at the {100} and {210} facets under the sulfur-rich condition. After considering the atomic structures as well as the surface energies of different termination of {100} and {210} surfaces, we propose that the attachments could occur through a primary NC with the {210}-Fe or {001)-Fe facet to another proximately located primary NC with the {210)-S or {001}-2S, respectively. Faceted anisotropic iron pyrite NCs with {100}, {210} and {111} facets and better crystallinity are obtained with longer reaction time. This study opens a way to better understand the growth mechanism of anisotropic iron pyrite NCs and to rationally manipulate the morphology of iron pyrite NCs in order to achieve desired physical properties of iron pyrite NCs for efficient photovoltaic conversions.

Growth of nano- and mesocrystals can proceed via the oriented attachment (OA) pathway. However, the driving force for OA is controversial; surface energy reduction, van der Waals interaction, and/or dipole-dipole interactions have been proposed. Based on molecular energetic calculations and analyses of van der Waals interactions using the Hamaker formulation and surface charge repulsion using the DLVO theory, we conclude that in vacuum, or when two nanoparticles are in close proximity in an electrolyte solution, the strong intrinsic interatomic Coulombic interactions between two nanoparticles provide the primary physical driving force for OA. However, when two particles are far apart in a solution, the interatomic Coulombic interactions are screened and van der Waals interactions become the physical driving force. In both vacuum and a solution, the energy change that occurs following an OA event (i.e., the thermodynamic driving force) comes largely from the interatomic Coulombic interactions arising from both the surface atoms (accounting for the surface energy reduction) and the atoms in interior of the nanoparticles. This energy change is crystallographic orientation-dependent and OA occurs more probably in a direction with larger system energy drop. The findings of this study indicate the range of conditions under which interatomic Coulombic interactions provide the primary driving force for crystal growth by OA and highlight the effects of aqueous solution and ionic strength on the energetics of the process.

Compared to the extensive experimental findings and breakthroughs, fundamental theoretical research on the growth kinetics and thermodynamics in the oriented attachment (OA) field is still at an early stage. The authors believe that developing lacking theory and building connection between theory and experiment in the OA filed are of paramount importance for the OA field to advance to an ever higher level. An important aspect of such investigation is to quantize the interparticle interactions between attaching objects. Such interactions mainly include Coulombic interaction, van der Waals interaction and dipolar interaction. In this presentation, mathematical derivation and quantitative evaluation of interparticle interactions in the OA growth of ultra-thin nanorods are introduced. In particular, the effects of the size and aspect ratio of growing nanorods, the concentration of attaching nanoparticles, surfactants and solvents are analyzed in detail. Following the theoretical input, the experimental synthesis and characterization of several ultra-thin nanorods including metallic Ag, semiconducting EuS and insulating MgO nanorods are presented. We find that the aforementioned theoretical analysis can be successfully employed to quantitatively evaluate a specific oriented-attachment growth system of ultra-thin nanorods before the actual experimental synthesis. In addition, our characterizations confirm that desirable physical properties of the ultra-thin nanorods can be designed and achieved via efficient quantitative control over the interparticle interactions in the OA growth of the nanorods. Our theoretical and experimental investigation is expected to improve the fundamental understanding on the OA growth and facilitate the large scale application of 1D OA nanocrystals.

Biominerals are organic/inorganic hybrids exhibiting versatile functions and morphologies.[1] The hierarchical structures and formation processes in mild conditions have inspired materials scientists to develop functional hybrid materials. Here we report on our recent approaches to the development of new inorganic/organic hybrid materials based on macromolecular templates.[2] The hybrids of CaCO3 and organic polymers have been obtained as thin-film forms. They form a wide variety of morphologies. Oriented[3] and patterned[4,5] complex structures as well as flat surface structures[2] have been achieved for thin films. Moreover, a variety of molecules such as peptides[6] have been used as template for CaCO3 crystallization. For example, photoimaged patterns on CaCO3 thin-films have been prepared using photocrosslinkable polymer gel matrices.[7] Amorphous transparent hybrid thin films consisting of CaCO3 and an acidic macromolecule are also obtained by simple mild process.[8] These self-organized hybrid materials have great potentials in a wide variety of fields for advanced technologies.
1. a) Handbook of Biomineralization (Eds. E. Bäuerlein, P. Behrens, M. Epple, Wiley-VCH, Weinheim, 2007); b) T. Kato, A. Sugawara, N. Hosoda, Adv. Mater. 14, 869 (2002).
2. T. Kato, T. Sakamoto, T. Nishimura, MRS Bull. 35,127 (2010).
3. T. Nishimura, T. Ito, Y. Yamamoto, M. Yoshio, T. Kato, Angew. Chem. Int. Ed. 47, 2800 (2008).
4. A. Sugawara, T. Ishii, T. Kato, Angew. Chem. Int. Ed. 42, 5299 (2003).
5. T. Sakamoto, A. Oichi, Y. Oaki, T. Nishimura, A. Sugawara, T. Kato, Cryst. Growth Des. 9, 622 (2009).
6. a) A. Sugawara, T. Nishimura, Y. Yamamoto, H. Inoue, H. Nagasawa, T. Kato, Angew. Chem. Int. Ed. 45, 2876 (2006); b) H. Kumagai, R. Matsunaga, T. Nishimura, H. Nagasawa, K. Tsumoto, and T. Kato et al., Faraday Discuss., 159, 483 (2012).
7. T. Sakamoto, Y. Nishimura, T. Nishimura, T. Kato, Angew. Chem. Int. Ed. 50, 5856 (2011).
8 . Y. Oaki, S. Kajiyama, T. Nishimura, H. Imai, T. Kato, Adv. Mater. 20, 3633 (2008).

Understanding the nucleation and growth of nanoparticles in solution plays the key role to control the shape and morphology of the products. The growth mechanism of nanocrystals can be revealed from their microstructural details, such as the presence of pores, twins, and dislocations etc. However, conventional TEM images only show two-dimensional projections of three-dimensional (3D) particles, in which much information is lost in such 2D images. Electron tomography is the only technique which can provide a detailed analysis of the 3D shape and morphology at nanoscale. Here, we have firstly conducted a detailed analysis on CeO2 single crystals using electron tomography to demonstrate the shape and internal structures, thus revealing the growth mechanism of the CeO2 in solution. The CeO2 nanocrystals were synthesized by the hydrothermal method. With the assistance of electron tomography, it is found that the porous CeO2 nanocrystals have an irregular truncated octahedral shape with internal pores elongated along the <110> directions. Thus, it is concluded that in the hydrothermal process, the oriented attachment of nuclei through a lattice matched surface and subsequent Ostwald ripening results in the growth of CeO2 nanocrystals with the pores inside. The dominant mechanism for the ripening of nuclei in hydrothermal reactions is the oriented attachment. It is believed that the crystallographic orientation of the pores and corresponding aggregation mechanism for the single crystalline and porous CeO2 discussed here can also be applied to other porous materials synthesized by self-assembly in solution.

Among metal oxides, ZnO is certainly one of the most investigated semiconductor material. The reasons for such an interest can be ascribed to its unique properties: a wide band gap (3.37 eV at 300 K) and a large exciton binding energy of 30-70 meV making it suitable for opto-electronic, catalytic and biological applications. Due to its non-centrosymmetric elemental cell, ZnO grows along [0001] direction leading to anisotropic materials. Additionally, ZnO forms twin structures, i.e. crystals in which facets with the same polarity are coupled to form a single crystal. The twinning process in ZnO can be promoted by inorganic or polymeric species adsorbed onto the coupling interfaces, however, the mechanism that leads to their formation is very little understood.
In the present contribution, the formation of ZnO twin nanostructures under different experimental conditions is reported. It will be shown that the formation of a characteristic seam cut on the surface of the particles is the result of an oriented attachment. The detailed mechanistic path depends on the experimental conditions used. Under ultrasonication and in the presence of the block-co-polymer JeffamineR the formation of multiple cone structures proceeds through a consecutive and oriented aggregation from quantum dots to complex multiple cone symmetries. The polymer provides the matrix in which the building blocks aggregate as a consequence of spatial constraints. Ultrasonication accelerates the rate of the process, whereas the mixing of the polymer and the starting salt precursor plays a fundamental role in ensuring a high control on the structure of the final particles. It will be shown that the as-formed interphases are highly reactive. Consequently, when the oriented attachment is driven by space constrains the interphases have the tendency to be covered by the successive growth of smaller cones around the grain boundary. Additionally, the seam cut undergoes dissolution processes that preferentially start at the interphase in the presence of water. Under microwave irradiation and in the presence of water, the dielectric constant of the solvent used during the synthesis plays a more important role than the presence of polymer.[1],[2] Careful experiments allow excluding any role of the polymer in the formation of the coupling interphases. The presence of polymers allows a unique tuning of the optical properties of the final material, i.e. particles of 200 nm were produced showing high UV-absorption with simultaneously strongly reduced scattering in the visible regime.[3]
[1] Klaumünzer, M.; Distaso, M.; Hübner, J.; Ma#269;kovicacute;, M.; Spiecker, E.; Kryschi, C.; Peukert, W. CrystEngComm 2013, DOI: 10.1039/C3CE41868E.
[2] Distaso, M.; Ma#269;kovicacute;, M.; Spiecker, E.; Peukert, W. Chem. Eur. J. 2012, 18, 13265.
[3] Distaso, M.; Segets, D.; Wernet, R.; Klupp Taylor, R.; Peukert W. Nanoscale, 2012, 4, 864.

Oriented attachment can generate wide range of nanomaterials with unusual morphologies, and is typically driven by reducing their surface energy during crystal growth (1). However, it is not completely understood why anisotropic nanostructures can be formed via oriented attachment when they lacks anisotropic crystal symmetry, as shown in examples of nanowires, nanorods, and nanosheets of lead (Pb) chalcogenide (2-4). So far, inhomogeneous surface dipole or soft template formation of surfactant molecules has been discusses as a key role in oriented attachment of those examples; but it is yet still challenging to achieve precise control over size and shape of Pb chalcogenide nanostructures, which is important to control their carrier dynamics and charge transport (5).
Here we will discuss our recent development on 1D and 2D nanostructures of Pb chalcogenides. Chemical engineering of crystal growth in Pb chalcogenide allows rational control of their morphology and composition, which also tailors their optical and electrical properties. Especially due to the large Bohr radius (PbS 18 nm, PbSe 46 nm) and narrow band gap (PbS 0.41 eV, PbSe 0.28 eV) of Pb chalcogenides (6), the above mentioned Pb chalcogenide nanostructures exhibit the effect of quantum confinement of carriers. We will explore how asymmetric confinement of carrier is manifested in the characteristics of charge carriers, exciton dynamics, and other optoelectric properties for these Pb chalcogenide nanostructures based on theoretical and spectroscopy studies. Furthermore, there are huge opportunities of Pb chalcogenide nanostructures in photovoltaics, sensors, transistors and other optoelectronic devices. We will discuss how the unique properties of anisotropic nanostructures can be utilized for those applications.
References
1. H. Zhang, J. F. Banfield, Energy Calculations Predict Nanoparticle Attachment Orientations and Asymmetric Crystal Formation. The Journal of Physical Chemistry Letters 3, 2882 (2012).
2. K.-S. Cho, D. V. Talapin, W. Gaschler, C. B. Murray, Designing PbSe Nanowires and Nanorings through Oriented Attachment of Nanoparticles. J. Am. Chem. Soc. 127, 7140 (2005).
3. W.-k. Koh, A. C. Bartnik, F. W. Wise, C. B. Murray, Synthesis of Monodisperse PbSe Nanorods: A Case for Oriented Attachment. J. Am. Chem. Soc. 132, 3909 (2010).
4. C. Schliehe et al., Ultrathin PbS Sheets by Two-Dimensional Oriented Attachment. Science 329, 550 (2010).
5. L. A. Padilha et al., Carrier Multiplication in Semiconductor Nanocrystals: Influence of Size, Shape, and Composition. Accounts of Chemical Research 46, 1261 (2013).
6. I. Kang, F. W. Wise, Electronic structure and optical properties of PbS and PbSe quantum dots. J. Opt. Soc. Am. B 14, 1632 (1997).

Incorporation of nanoparticles (NPs) with nanorods (NRs) to fabricate nanocomposites has been intensively studied because the nanostructure containing NPs/NRs nanocomposites can peform unique electrical or optical or biomedical characteristics. Recently, the nanocomposites which combine various NPs and NRs have been widely applied in LEDs, solar cells, and sensors. Among various mixture of NPs and NRs, ZnO with addition of Au NPs have been intensively reported and widely used in semiconductors. In this study, we juxtapose the behaviors of Au NPs on the electrochemical-hydrothermal grown ZnO NRs on the polished Ti substrates and on the sol-gel-hydrothermal grown ZnO NRs on the glass substrate. For electrochemical-hydrothermal grown ZnO NRs, we deposit the seed layer of ZnO nanorods on the substrate but for the sol-gel-hydrothermal grown ZnO NRs, we use Owing to different preparation methods, the material properties of the two types of ZnO NRs are unalike. In addition, we drip the same amount of Au NPs on the two types of NRs. To characterize the NPs on the two types of ZnO NRs, multiple material analysis techniques including field-emission scanning electron microscope (FESEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS), and contact angle analysis are used to study the interaction between the NPs and NRs. The results indicate that Au NPs are more easily to agglomerate on electrochemical-hydrothermal grown ZnO NRs than on the sol-gel-hydrothermal grown ZnO NRs. The ZnO NRs grown by sol-gel hydrothermal method are much more compact and the ZnO NRs grown by electrochemical hydrothermal method are growing to all the directions. Therefore, as shown in the FESEM images, the Au NPs are harder to attach on the top surface of the hexagonal NRs but easier to attach on the side surface of the hexagonal NRs. The XRD and XPS results also show the peaks of Au NPs and ZnO NRs in the spectra. Moreover, the SIMS results present that Au NPs are on the top of the ZnO NRs for the solgel-hydrothermal ZnO NRs but Au NPs can spread deeper between the ZnO NRs. Furthermore, contact angle analysis indicates that the surface tension of the top surface of the ZnO NRs is higher than the side surface of the ZnO NRs. Therefore, fewer Au NPs can be observed from the solgel hydrothermal ZnO NRs than from the electrochemical hydrothermal method.

GaN was grown on Si substrate with the buffer layer of ZnO nanorods arrays (NRA) by metalorganic chemical vapor deposition. The limited lattice mismatch (1.85%) between GaN and ZnO and the ultrasmall diameter of the NRA make ZnO NRA a promising buffer for the epitaxial growth of GaN-on-Si. We aim to achieve the next-generation GaN crystal with advantages of low cost, large scale, and high qualities. Nevertheless, many challenges remain to be overcome, such as H2 back-etching of ZnO NRA, thermal decomposition of ZnO, and the difficult coalescence of GaN. These issues are addressed using low-temperature growth, N2 carrier gas and Al-free buffer layer. The fabrication of ZnO NRA consists of two steps: (1) ZnO seed layer deposition (2) hydrothermal process. The textured ZnO film was deposited on Si substrates by radio-frequency sputtering. In the growth of GaN, low-temperature GaN in N2 ambiance is adopted to form the ZnO-GaN core-shell structure in order to prevent the back etching of NRA at high temperatures. The growth temperature of GaN is then raised to 980 °C to laterally connect every nanorod and to provide further protection of ZnO. Finally, high-quality GaN is grown at 1120 °C in H2. The grown crystal is partially coalesced. Growth optimization includes the duration of low-temperature GaN and the V/III ratios for each layer. Improved surface morphology (i.e. reduced surface roughness) is attained with prolonged growth at the substrate temperature of 980 °C.

KxWO3 nanosheets which possess high surface-to-volume ratios are known as multifunctional materials which can be potentially applied in electronic devices, optical devices, and rechargeable lithium batteries. However, few studies on the tungsten bronze nanosheets have been reported because of the difficulty in synthesizing the nanosheets. This work first provides a general route for the facile synthesis of single-crystalline hexagonal-based KxWO3 nanosheets based on oriented attachment of preformed pseudo-hexagonal KxWO3 nanowires.
The detailed electron microscopy and X-ray diffraction investigations imply that the nanosheets were obtained by self-assembly of individual nanowires with monoclinic superstructures. Assisted by the group theory analysis, the parallel-aligned nanowires can be referred to as the 120o rotation twinning variants in the superstructure phase, which may result from the rotation symmetry reduction induced by the ordered arrangements of K vacancies during crystal growth. Meanwhile, the SAED patterns can be well interpreted by a structural model based on the coexistence of three monoclinic twinning variants. Our results shed light on the interfacial characteristics of self-assembled KxWO3 nanowires and can serve as guidance to the future design of relevant two-dimensional structures for various electrical and optical applications.
This work was supported by the 973 Program (2011CB933300), the National Natural Science Foundation of China (51071110, 51271134, 40972044, J1210061), the China MOE NCET Program (NCET-07-0640), MOE Doctoral Fund (20090141110059), the Fundamental Research Funds for the Central Universities, and the China Postdoctoral Science Foundation (2013M540602).

The formation of biominerals in living organisms highlights an exquisite process which leads to materials with tailor made structures and properties. Calcium carbonate has been extensively studied and analysed, and its ability to form different polymorphs, including aragonite, vaterite and calcite is well-known. However, the method by which living organisms control both the structure and properties is still unclear. An amorphous phase (or phases) is often implicated in the process. For example, in the spines of sea-urchin, the initial phase to precipitate is a hydrous amorphous structure. This subsequently, through a series of steps, transforms into the final polymorph [1]. The role of amorphous calcium carbonate nanocrystals in mesocrystal formation has also been discussed in detail by Ihli et al. [2].
A detailed model of the amorphous phase is therefore needed. We have used molecular dynamics simulations to create models of hydrous amorphous calcium carbonate from different configurational starting points and water content. The models obtained have pair distribution functions and structure factors in good agreement with those observed experimentally [3]. Despite these similarities, analysis of the local environment of the ions and density fluctuations shows clear differences, further highlighting the extent of possible structures for this amorphous material. We also present an analysis of the micro- and mesoporous structures of amorphous calcium carbonate at different water content and discuss a process of amorphous calcium carbonate dehydration and implications for the formation of the final crystalline polymorph.
References
[1] J. Seto, Y. Ma, S.A. Davis, F. Meldrum, A. Gourrier, Y.-Y. Kim, U. Schilde, M. Sztuck, M. Burghammer, S. Maltsev, C. Jäger and H. Cölfen, (2012) Structure-property relationships of a biological mesocrystal in the adult sea urchin spine. Proc. Nat. Acad. Sci. 109 pp 3699-3704.
[2] J. Ihli, P. Bots, A. Kulak, L. G. Benning, and F. C. Meldrum; Elucidating Mechanisms of Diffusion-Based Calcium Carbonate Synthesis Leads to Controlled Mesocrystal Formation (2013) Adv. Funct. Mater. 23, pp 1965-1973
[3] F. M. Michel, J. MacDonald, J. Feng, B. L. Phillips, L. Ehm, C. Tarabrella, and J. B. Parise; (2008), Structural Characteristics of Synthetic Amorphous Calcium Carbonate. Chemistry of Materials. 20, pp 4720-4728;

The oxidant peroxo method (OPM) exhibits several advantages and unique characteristics not found in the traditional methods for the synthesis of lead and bismuth based oxides. First of all, it is a clean method based in hydrogen peroxide that matches perfectly with the green chemistry approach. Secondly, the oxidizing local atmosphere provided by the precursor during its crystallization is unique among all the wet-chemical techniques of synthesis, which usually result in reducing environment. Although these advantages, only a few studies have focused on the use of the OPM to obtain better materials, which makes this field of study an excellent opportunity for the development of materials with higher purity and controlled morphologies. Recently, we could synthesize a series of superior compounds (for instance pure and doped PZT, bismuth titanates with different compositions and structures used for photocatalytic decomposing of dyes) that exhibited functional properties with better performance than those synthesized by conventional routes. The critical step is the transition from the amorphous state to crystalline particles through an oxyreduction reaction that usually releases a huge amount of oxygen gas when done under traditional heat-treatment, resulting in typically spherical nanoparticles that can be partially sintered due the high surface energy of each nanocrystal. However, when performed under hydrothermal conditions, this transition results in large clusters of regular shapes, such as regular and elongated cubes with well-defined surfaces, even in absence of any surfactant compound. Moreover, controlling the experimental conditions, such as temperature, processing time, ionic strength, etc., the crystalline phase of the materials could be modified from the expected thermodynamic to some metastable phase. These unexpected differences resulted from the different crystallization mechanisms of present in solid state and in aqueous media, where the particles are freely move and rotate, finding the better orientation direction to self organize in regular clusters.

This study describes the evaluation of growth parameters in hydrothermal synthesis on the structural characteristics and photoactivity of the materials synthesized from a peroxytitanium complex (PTC) precursor. For the hydrothermal synthesis of Ti oxide nanostructures, the PTC was dispersed in aqueous KOH solution, in Teflon recipients, and these were heated in a stainless steel autoclave at various temperatures (125, 150, 175, 200, 225 and 250 °C for 2 hours) and times (1, 2, 4, 8 and 16 hours at 200 °C) of hydrothermal treatment. After the hydrothermal treatment, the materials were washed by dialysis and then frozen and lyophilized to produce the nanometric powder. After that, the materials were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM). Also, the active oxidative species produced on the photocatalyst surface were investigated by measuring the fluorescence derived from their reaction with terephthalic acid (TPA).The photocatalytic efficiency of the synthesized materials was assessed by monitoring the degradation of the dye methylene blue (MB). Nanoparticles with different shapes and sizes were obtained in this work. The synthesis temperature showed higher influence on morphological characteristics and photocatalytic efficiency than the synthesis time. Two 'groups' of nanostructures with distinct morphological characteristics were observed, one resulting from the rolling-up of the precursor structure, and the other due to dissolution and re-precipitation of the precursor material. The rolling-up process resulted in the formation of larger particles and the nucleation process in the smaller ones. The HRTEM images show the coalescence via oriented attachment of the smaller nuclei on the surface of the larger particles, decreasing their surface imperfections. The photocatalytic results showed that the main factor for improving photoactivity was the crystallinity, which was close connected to the growth mechanisms observed. The presence of defects, associated to the oriented attachment mechanism, were shown as deleterious to this property, in accordance to previous research works. Furthermore, it was observed that the photodegradation process occurred by the attack of active radicals on the MB molecules and not by the direct oxidation of adsorbed MB molecules on the photocatalyst surface.

The comprehension of the physical-chemistry processes related to the nanocrystals growth mechanism is fundamental in controlling the shape and assembly of inorganic nanoparticles. In contrast to aqueous media, the oriented attachment mechanism using organic solvents only very few were reported. In this work, it was studied TiO2 nanocrystal synthesis and growth by a colloidal process using oleic acid as solvent and capping agent. The synthesis using titanium isopropoxide in oleic acid lead to anatase nanorods structures. Analyse by high resolution transmission electron microscope (HRTEM) indicate the nanorods are composed by truncated bipyramidal units. In fact, the small bipyramidal had a high mobility in solution that makes possible their rotation to couple in nanorods, by oriented attachment mechanism. This process reduced the energy by elimination exposed (001) planes in TiO2 anatase. The nanorods growth can be controlled using additional synthesis step, where additional precursor was used to provide the small bipyramidal nanostructures. The provide bipyrimidal structures attached on the nanorods extreme leading to their length growth. Additionally, using prolonged thermal treatment at 250°C, without added precursor, it was observed a fragmentation of nanorods in thermodynamic stable structure for TiO2. In fact, the final shape and size of the nanocrystal was influenced by a phenomenon similar to the Rayleigh-instability of freestanding TiO2 nanorods in solution. In this process, a larger structure (the nanorod) is divided into smaller units (nanocrystals), by a kind of detachment process. The reaction yield and amount of non-volatile organic attached in the nanocrystal surface was evaluated indicating a thermodynamic recrystallization process based on the surface area reduction. A description of nanoparticle evolution was obtained by a statistical analysis of the particle size by TEM characterization. A clear reduction in the mean particle size is observed in the particle population formed by the largest particles. A detailed HRTEM characterization facilitates the identification of a morphological feature, which characterizes a surface diffusion process.The HRTEM/TEM study confirms that nanorod fragmentation occurs from the faceted nanorods. This fragmentation must be promoted by a combination of thermodynamics and kinetics arguments. Through a classical thermodynamic analysis, energetic and geometrics parameters, which lead to fragmentations of TiO2 nanorods, can be established being the process characterized as a kind of detachment mechanism controlled by surface energy minimization. In conclusion, the identification of such phenomena can promote the synthesis of controlled nanorods and nanoparticles as well as a better understanding of the growth processes.

Computer simulations are a useful method to investigate possible mechanisms for control of the oriented attachment of crystals to each other or to substrates. We shall first consider the interactions of crystalline structures with substrates before turning to the simulation of nanoparticle-nanoparticle interactions. Finally we shall consider a general colloidal system and how monodisperse ordered clustered systems can be produced from isotropically interacting monomers which may in turn lead to mesocrystalline behaviour
Ordered organic substrates such as self-assembled monolayers influence the crystallisation of minerals. Different crystal morphologies and polymorphs can be stabilised by varying the substrate properties. We use metadynamics to investigate how crystallisation mechanisms are affected by such factors as alkyl chain length in the monolayer, monolayer flexibility and competition between epitaxial matching and more general electrostatics considerations (see also [1]). We find that the common (012) orientation observed in calcite on such monolayers is probably to be explained by kinetic factors.
Understanding the interactions of nanoparticles in solution is essential for any mechanism of oriented crystal growth. We show how particle shape can produce a complex behaviour as the particles approach each other. We have used atomistic molecular dynamics, coupled with umbrella sampling, to investigate the dimerization of two 36 formula unit calcite nanocrystals in aqueous solution. The calculated potentials-of-mean-force (PMFs) reveal three regions in the self-assembly process: 1) a long-range, weakly attractive region 2) a steep funnel leading to an energy minimum and 3) a short-range repulsive region. The inter-particle angular dependence of these PMFs shows that particle re-orientation plays a role in self-assembly.
Systems with competing short-ranged attractions and long range repulsion [2] have a rich kinetic phase diagram including spherical or elongated clusters, cluster crystals, columnar phases, Wigner glasses, gels or regular Bernal spirals. Recent work [3] gave evidence that renormalizing the repulsive amplitude of large clusters by a volume dependent term produces monodisperse clusters even if the building blocks are polydisperse. The resulting low density regular structure is stabilised by long-range repulsion, which on further compression, leads to high density ordered arrested clusters. We model these systems using an advanced Monte-Carlo simulation algorithm, and discuss a possible crystallization route leading to crystal alignment between individual subunits akin to the mesocrystallization route [4].
References
1. M. Fricke and D. Volmer, Top. Curr. Chem. 2007, 270, 1.
2. J. Toledano, F. Sciortino, and E. Zaccarelli, Soft Matter 5, 2390 (2009).
3. Y. Xia, T. Nguyen, M. Yang, et al Nat. Nanotechnol. 6, 580 (2011).
4. H. Cölfen and M. Antonietti, Mesocrystals and Nonclassical Crystallization (Wiley, 2008).

Oriented attachment (OA) is now widely recognized as an important mechanism for growing complex nanostructures in solution-phase syntheses. However, the microscopic origins of OA are still unclear. To resolve the mechanisms of experimentally observed OA for colloidal TiO2, we performed molecular dynamics simulations to study the aggregation of various titanium dioxide (anatase) nanocrystals in vacuum and humid environments. We use a recently developed ReaxFF reactive force field to describe TiO2/water interactions .
In vacuum, the nanocrystals tend to merge along their direction of approach, resulting in a polycrystalline material. By contrast, in the presence of water vapor, we observed many instances of OA, which is facilitated by adsorbed water and surface OH in several ways. First, adsorbed water and OH protect the nanoparticles and prevent the immediate (and relatively misaligned) aggregation that occurs in vacuum. Thus, when two nanoparticles come within Å distances, they are able to adjust their relative orientation and achieve a configuration with aligned facets. In this configuration, they are loosely associated via a network of hydrogen bonds between the surface hydroxyls on one nanocrystal and the surface oxygens on the other. The particles shift relative to one another, constantly reconfiguring their hydrogen-bonding network, to achieve facet registry. Subsequently, surface hydroxyls combine with protons to form water, which vacates the inter-particle gap and allows the nanocrystals to aggregate. The result is a single or twinned crystal. We find that OA is dominant on surfaces with the greatest propensity to dissociate water. Our results are likely general for aqueous oxide materials and demonstrate the critical role of solvent in OA of these materials.

Ordered organic substrates, such as substrates functionalized with self-assembled monolayers (SAMs), are often used as model systems to study oriented crystal growth and attachment and to gain an understanding of biomineralization processes. Experimental [1] and modelling [2,3] results indicate that the substrate properties influence the crystal orientation but the detailed mechanisms involved in orientation control remain a topic of some debate.
We have employed atomistic simulation methods to investigate calcium carbonate crystallization on SAMs, as such methods provide length and time scale resolution beyond the experimentally accessible regimes. Here we present results from a comprehensive study of the crystallization of calcium carbonate (CaCO3) on a range of carboxylate terminated alkyl thiols. The calculations use potential-based metadynamics with a simple Gaussian addition scheme to overcome the large energy barriers associated with crystal nucleation and growth. We investigate the effect of the alkyl chain length on the structure and energy of the resulting interfaces and find that the magnitude of the interfacial binding energy increases with the length of the alkyl chain. We also investigate the effect of substrate flexibility on orientation selection and find that rigid substrates induce crystallization of surfaces with a close epitaxial match (i.e the (001) orientation) whereas flexible substrates induce (012) oriented crystallization, which has a poorer match to the substrate. Calculations identified the (001) interface as the lower energy interface therefore we conclude that kinetic factors dominate calcite orientation selection on carboxylate SAMs and we propose a mechanism for the enhanced growth in the (012) orientation [4].
[1] J. Aizenberg, A. J. Black, G. M. Whitesides, J. Am. Chem. Soc. (1999), 121, 4500-4509.
[2] D. M. Duffy and J. H. Harding, Langmuir (2004), 20, 7630-7636.
[3] D. Quigley, P. M. Rodger, C. L. Freeman et al J. Chem. Phys. (2009), 131, 094703.
[4] R.D. Darkins, A.S. Cocirc;té, C. L. Freeman and D. M. Duffy J. Cryst. Growth , 367 (2013) 110-114

Although the molecular modeling of self-assembling processes stands as a challenging research issue, there have been a number of breakthroughs in recent years. This report describes the use of large-scale molecular dynamics simulations with coarse grained models to study the spontaneous self-assembling of capped nanoparticles in chloroform suspension.
A model system comprising 125 nanoparticles in chloroform evolved spontaneously from a regular array of independent nanoparticles to a single thread-like, ramified superstructure spanning the whole simulation box. The aggregation process proceeded by means of two complementary mechanisms, the first characterized by reactive collisions between monomers and oligomers, which were permanently trapped into the growing superstructure, and the second a slow structural reorganization of the nanoparticles packing. Altogether, these aggregation processes were over after ca. 0.6 mu;s and the system remained structurally and energetically stable until 1 mu;s.
The thread-like structure closely resembles the TEM images for capped ZrO2, but a better comparison with experimental results was obtained using a model system without solvent molecules, placing the nanoparticles over a graphene sheet as the solid substrate. The agreement between the main structural features from this simulation and those from the TEM experiment was excellent and validated the model system.
In order to shed further light on the origins of the stable aggregation of the nanoparticles, the Gibbs energy of aggregation was computed, along with its enthalpy and entropy contributions, both in chloroform and in vacuum. The thermodynamic parameters arising from the modeling are consistent with larger nanoparticles in chloroform due to the solvent swelled organic layer and the overall effect of the solvent was the partial destabilization of the aggregated state in chloroform as compared to the vacuum system. The Gibbs energy of aggregation is much larger than the average thermal energy at ambient conditions, but there is an unfavorable entropy of aggregation both in chloroform and in vacuum, making the temperature an important factor affecting the thermodynamic stability of the aggregates.
The modeling strategy has been proved effective and reliable to describe the self-assembling of capped nanoparticles, but we must acknowledge the fact that larger model systems and longer timescales will be necessary in future investigations in order to assess structural and dynamical information approaching the behavior of macroscopic systems. Another general and important conclusion regarding the reliability of the modeling strategy is that the model system size matters when it comes to the proper description of the aggregate morphology.

Due to the size- and shape-dependent properties, nanoparticles have been successfully used as functional building blocks to fabricate multi-dimensional (D) ordered assemblies for the development of ‘artificial solids&’ (e.g., metamaterials) with potential applications in nanoelectronic and optical devices. At ambient pressure, entropy driven self-assembly of monosized or binary nanoparticles generally results in polycrystalline 2- or 3D close-packed arrangements, and extensive efforts have been made to develop structural perfection of nanoparticle arrays or ‘single crystal-like&’ domain structures with precise long range order for their definite advantages for electron or energy transfer. To date, fabrications of ordered nanoparticle assemblies have been relied on specific interparticle chemical or physical interactions such as van der Waals interactions, dipole-dipole interaction, chemical reactions, and DNA-templating, etc. The consequent self-assembly scenario is the formation of higher dimensional nanoparticle architectures from single nanoparticles. Recently we have discovered a pressure-directed assembly (PDA) in which an external pressure has been utilized to engineer nanoparticle assembly and to fabricate new nanoparticle architectures without relying on specific nanoparticle interactions. The PDA process essentially allows precise and systematic tuning of interparticle separation distance, which with control of applied pressure can be manipulated reversibly at the angstrom level until the particles make contact and sintering occurs. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle arrays can be manipulated to reversibly shrink, allowing fine-tuning of interparticle separation distance. Under a uniaxial pressure field, nanoparticles are forced to contact and coalesce, forming hierarchical nanostructures. Depending on the orientation of the initial nanoparticle arrays, 1-3D ordered nanostructures including nanorod, nanowire, and cubic network can be fabricated through this pressure induced assembly method. Moreover, we discovered for the first time a transition from an ordered polycrystalline nanoparticle mesophase to quasi-single crystalline nanoparticle lattices induced by PDA process. Exerting pressure-dependent control over the structure of nanoparticle arrays provides a unique and robust system to understand collective chemical and physical characteristics and to develop novel electronic and photonic behavior for energy transduction related applications.
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 term mesocrystal has been used to describe large, 3D particles which diffract as single crystals and yet exhibit internal structures comprising oriented nanoparticles. Evidence for mesocrystal structures is therefore based on structural analysis of crystalline particles by techniques including scanning electron microscopy (SEM), surface area analysis (BET), and transmission electron microscopy (TEM) of thin sections. Here, we use calcium carbonate as a model system to evaluate the effectiveness of these techniques for identifying a nanoparticulate sub-structure. Indeed, although it is now common-place to assign mesocrystal structures based on broadening of XRD peaks and apparent nanoparticulate surface structures, we demonstrate that both of these approaches have to be treated with care. Therefore, high resolution synchrotron XRD analysis demonstrates that line broadening often arises from lattice strain rather than a subunit structure. Finally, electron backscattered X-ray diffraction (EBSD) is used to provide a direct structural comparison of biogenic calcite mesocrystals with their synthetic counterparts.

Self-assembly of nanoparticles into ordered structures is a promising strategy for production and design of nanostructured materials with novel properties. While the assembly of spheres into dense-packed structures is well-established, the assembly of non-spherical, polyhedral nanoparticles is now attracting an increased interest due to the possibility to tune the electronic, optical and magnetic properties by controlling not only the size and shape of the nanosized building blocks, but also utilize the rich structural diversity of the self-assembled arrays that are formed.
We have previously demonstrated how it is possible to assemble iron oxide nanocrystals into ordered arrays or superlattices with both translational and orientational order (mesocrystals) through evaporation-induced self-assembly [1-3]. Here, we will present recent work on the structural diversity and the formation kinetics of highly ordered mesocrystals of superparamagnetic, monodisperse iron oxide nanocubes of different sizes using a combination of time-resolved grazing incidence small angle X-ray scattering (GISAXS), Quartz crystal microbalance with dissipation (QCM-D), video microscopy together with scanning and transmission electron microscopy. The influence of the evaporation rate and the application of external magnetic fields on the crystallographic texture will be discussed and related to recent modeling studies which showed that the degree of truncation and the particle interactions have a pivotal influence on the structures of the self-assembled arrays [4]. The time-resolved investigation show that ordered arrays can form both under convection-controlled and diffusion-controlled conditions and will discuss how growth rates can be extracted from the time-resolved data.
References:
[1] S. Disch, E. Wetterskog, R. P. Hermann, G. Salazar-Alvarez, P. Busch, T. Brückel, L. Bergström, S. Kamali, Nano Letters, (2011), 11, 1651
[2] A. Ahniyaz, Y. Sakamoto, Y. L. Bergström, L. Proc. Natl. Acad. Sci., (2007) 104, 17570
[3] S. Disch et al, Nanoscale, (2013), 5, 3969
[4] N. Volkov, A. Lyubartsev, L. Bergström, Nanoscale, (2012), 4, 4765

A mussel-inspired synthesis method for making iron(III) oxide nanoparticles was developed and the kinetics of nanocrystal formation was studied using in situ X-ray diffraction (XRD).
The magnetic properties of nanoparticles, such as magnetite or maghemite, depend strongly on their size, a feature used in the design of superparamagnetic nanoparticles for magnetic resonance imaging contrast agents. In order to gain control of the nanoparticle size it is important to understand how the particles nucleate and grow, in other words to understand the crystallization kinetics. This can be achieved using e.g. in situ XRD. Magnetite was recently found to form via particle aggregation in solution without the initial formation of an intermediate amorphous phase (1).
Nanoparticle growth can be controlled by additives (2,3). The blue mussel utilizes the catechol containing amino acid DOPA to adhere to inorganic surfaces. The adhesion is facilitated by coordination bonds between metal ions and the catechol. The very strong Fe(III) catechol bond makes the catechol a good candidate for controlling the formation of iron oxide nanoparticles. In this study dopamine and hydrocaffeic acid were used as additives. Thereby nanoparticles decorated with dopamine or hydrocaffeic acid should result.
An Fe(II)/Fe(III) solution containing the organic additive was added dropwise to a warm basic solution, inspired by Larsen et al. (4). In situ XRD studies were performed at MAXLAB using a CCD detector and a custom flow cell with very high temperature stability (3). The flow prevents sedimentation during the reaction.
Rietveld refinement of ex situ XRD data showed that the syntheses result in a sub-stoichiometric maghemite phase, Fe_2-xO_3-1.5x indicating that the added Fe(II) is oxidized during the reaction. The lack of Fe(II) was confirmed by Mössbauer spectroscopy. In situ XRD showed that nucleation happens almost instantaneously upon addition of the iron-containing solution. The crystalline phase co-exists with an amorphous phase that most likely is a highly disordered ferrihydrite. The ratio between the amorphous and crystalline phase is dependent on the additive. For hydrocaffeic acid, the amorphous phase transforms into the crystalline phase, but for dopamine there is a rearrangement of the ferrihydrite phase seen as changes in d-spacing of the broad amorphous peak.
The in situ results shed light on the mechanism of particle formation which is useful for the future development of improved synthesis procedures.
References:
1 J. Baumgartner et al; Nature Materials, 12, 2013, 310-314
2 C. J. S. Ibsen and H. Birkedal; Nanoscale, 2, 2010, 2478-2486
3 C. J. S. Ibsen and H. Birkedal; J. Appl. Cryst, 45, 2012, 976-981
4 E. K. U. Larsen et al; ACS Nano, 3, 2009, 1947-1951

Reactivities and stabilities are two opposite parameters while we are processing nanoparticles. Many kinds of freshly synthesized nanoparticles will be not stable after storage, for example, the oxidation, and erosion or transformation events occur while they are stored in different environment. Herein, we will discuss the stability of freshly prepared ultrathin tellurium (Te) nanowires and their enhanced reactivities towards to other functional one-dimensional (1D) nanomaterials based on chemical transformation. A so-called multiplex templating process has been proposed for controlled synthesis of a huge family of functional ultrathin nanowires using Te nanowires as template. In addition, a series of macroscopic assemblies of ultrathin nanowires, including free-standing membranes, films, hydrogels, and aerogels can be fabricated, which exhibit enormous potentials for attractive applications, such as liquid filtration and separation, continuous-flow catalysis, electrocatalysis, electronic devices, super adsorbent, elastomeric conductors, and polymer-based nanocomposites. The versatility of this templating process, scalable assembling process as well as the large-scale synthesis can together enhance the application reliability of these functional 1D nanostructures.

Cadmium and lead based chalcogenide nanoparticles have been at the forefront of nanomaterials synthesis and applications during the past decade. CdSe, CdTe, PbSe and PbTe nanoparticles have been synthesized using a simple, non-organometallic hybrid solution based, high temperature route. The route involves reacting selenium or tellurium powder with sodium borohydride (NaBH4) to produce selenide or telluride ions; followed by the reaction with a metal salt in a coordinating solvent. By varying the reaction parameters such as temperature, capping group and metal source, cadmium and lead chalcogenide nanoparticles with different shapes and sizes have been obtained. We have found that the metal source plays an important role in the growth mechanism and final morphology of the particles. Nanorods of PbTe and CdTe are grown by the oriented attachment mechanism. We discuss this mechanism of growth in great detail using CdTe and PbTe as examples.
References
1. S.O Oluwafemi and N. Revaprasadu, A new synthetic route to organically capped cadium selenide nanoparticles, New J. Chem. 10, 1432-37, (2008).
2. N.N Maseko, N. Revaprasadu, V.S.R. Rajasekhar Pullabhotla, K. Ramasamy and P.O&’ Brien, The Influence of the Cadmium Source on the Shape of CdSe Nanoparticles, Materials letters, 64, 1037-9, (2010).
3. N. Ziqubu, K. Ramasamy, N. Revaprasadu, V.S.R. Rajasekhar Pullabhotla and P. O&’Brien A Simple to Route to Dots and Rods of PbTe Nanoparticles, Chemistry of Materials, 22, 3817-19,(2010).
4. N.M Mntungwa, V.S.R Rajasekhar Pullabhotla and N. Revaprasadu, A Facile Route to Shape Controlled CdTe nanoparticles, J. Mater. Chem and Phys, 126, 500-6, (2011).
5. K. Ramasamy, N. Ziqubu, V. S. R. Rajasekhar Pullabhotla. O.A. Nejo, A A. Nejo, N. Revaprasadu, and P. O&’Brien, A New Route to Lead Chalcogenide Nanocrystals Eur. J. Inorg. Chem., 5196-5201, (2011).

Self-assembly of nanoparticles into ordered structures is a promising strategy for production and design of nanostructured materials with novel properties. While the assembly of spheres into dense-packed structures is well-established, the assembly of non-spherical, polyhedral nanoparticles is now attracting an increased interest. By choosing anisotropic nanoparticles as building blocks we generate the possibility to tune the electronic, optical and magnetic properties by controlling not only the size and shape of the particles, but also utilize the rich structural diversity of the created self-assembled arrays.
In this work, we present in-situ studies of the formation of large, crystallographically oriented, ordered arrays consisting of self-assembled iron oxide nanocubes with a narrow size distribution. We combined video microscopy (VM) and quartz crystal microbalance (QCM-D) measurements to investigate the temporal evolution of mesocrystal growth during controlled solvent removal. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used for structural characterization of the dried assemblies. A custom-made experimental chamber was employed to manipulate the temperature and the pressure of the droplet environment to direct the three different growth modes occurring during droplet drying. Mesocrystals with translational and orientational order of sizes up to 10 mu;m are formed spontaneously during the final, diffusion-controlled, drop-casting stage when the liquid film is very thin and the particle concentration is high. Convection-driven deposition of ordered nanocube arrays at the edge of the drying droplet is a manifestation of the so called coffee-ring effect. Dendritic growth or fingering of rapidly growing arrays of ordered nanocubes could also be observed in a transition regime as the growth front moves from the initial three-phase contact line towards the center of the original droplet.

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 various binary (i.e. based on rare earth and group IV metals) and doped metal oxide nanoparticles presenting high crystallinity and uniform particle size (ranging from sub-nm to 5 nm). The main weakness of the surfactant-free non-aqueous route can be overcome, by the in situ formation of organic species, which 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]
In this presentation we will discuss novel structural studies and the 3D assembly mechanism of benzoate capped nanocrystals. Moreover, some peaks in low-frequency Raman spectra can be attribute to THz acoustic vibrations of individual nanocrystals which are only weakly coupled due to the strong acoustic mismatch between the capping ligands and the nanocrystals. By progressively removing the ligands, the acoustic vibrations of the nanocrystals couple resulting in an increase of their frequency, suggesting that these 3D supercrystals can be used for manipulating THz phonons.[4]
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] L. Saviot, D. B. Murray, G. Caputo, M. C. Marco De Lucas, N. Pinna, “THz nanocrystal acoustic vibrations from ZrO2 3D supercrystals”, J. Mater. Chem. C, 2014, DOI: 10.1039/C3TC31833H

In this report, we demonstrate that same complex cone-shaped microstructures with hierarchical patterns could be created from various minerals, including BaCO3, CaCO3, SrCO3 and BaSO4, using one simple polyelectrolyte. All these minerals were precipitated in aqueous solution in the presence of poly acrylic acid (but not limited) under similarly formulated solution condition. The formation of the complex cone microstructures in all the cases strongly depended on solution conditions, such as the supersaturation level, ratios of polymer to ions of the solution, but was not limited by precipitation methods. Interestingly, even though all the final products shared the common microstructures, the sub-building units of the complex form from each mineral were varied. For example, while CaCO3 system showed the cone with 30 - 50 um in length, consisting of 20-30 nm in diameter of spherical particles, BaCO3 system resulted in often forming mixture of cone structures of 20-30 um in length and twisted long wires, consisting of co-aligned bundle of nano-rod building-units. SrCO3 system presented the highest yield and reproducibility in wider window of solution conditions out of tested mineral systems, showing the cone structure of upto 100 um in length with rather smooth surface without obvious nano-buidling units. These products were characterized using a range of techniques including SEM, TEM, FT-IR, raman microscopy, and TGA thermal analysis to identify the phases and investigate further their microstructures and formation mechanisms of the products.
Numerous complex crystal forms have been produced particularly using various soluble additives. But those were almost always unpredictive and very component-specific, and often formed within very narrow window of solution conditions. But, the results here demonstrated that an identical non-equilibrium structure from multiple inorganic minerals could be obtained using one simple organic additive only by manipulating solution environment.

Five hundred million years of natural selection provided organisms from different phyla with completely different mechanisms to grow their mineralized endo- or exo-skeletons. Sea urchin spicules (1), spines (2), and teeth (3) use amorphous precursor phases (4) to form micron-to-millimeter size co-oriented single crystals of calcite, in mollusk shell nacre a pre-formed lamellar organic scaffold is filled with aragonite micro-crystals, which are only coarsely co-oriented (5-8). Tunicate spicules exhibit micro-scale non-crystallographic branching of vaterite crystals (9). These biominerals form by different crystal growth mechanisms, but they all result in hard, fracture-resistant, space-filling biominerals, that are fully crystalline, and highly adapted to their biological functions. In contrast with biominerals precipitated by bacteria (10), no eukaryotic biomineral appears to form by oriented attachment (11). We speculate that if they formed by oriented attachment they could not reliably fill space (12), nor be predictably hard or tough (13), which is a clear evolutionary advantage.
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2. Y Politi et al., Science 306, 2004.
3. CE Killian et al., J Am Chem Soc 131, 2009.
4. E Beniash et al., Procs R Soc B-Biol Sci 264, 1997.
5. RA Metzler et al., Phys. Rev. Lett. 98, 2007.
6. PUPA Gilbert et al., J Am Chem Soc 130, 17519, 2008.
7. IC Olson et al., J Am Chem Soc 134, 2012.
8. IC Olson et al., J Struct Biol in press, 2013.
9. L Kabalah-Amitai et al., Science 340, 2013.
10. JF Banfield et al., Science 289, 2000.
11. RL Penn et al., Geochim Cosmochim Acta 63, 1999.
12. L Yang et al., RSC-Nanoscale 3, 2011.
13. RO Ritchie, Nat. Mater. 10, 2011.

Unique mesocrystal Hausmannite Mn3O4 with a single-crystal-like structure was successfully fabricated on to graphene nanosheets via a facile room-temperature synthesis strategy. The formation process of mesocrystal can be ascribed to the transformation from Mn(OH)2 to Mn3O4 during the reaction. Nanopores in the Mn3O4 mesocrystal were favorable for Li ion taransport and would accommodate the volume change during the Li insertion and extraction. Moreover, graphene enhanced the conductivity. Such Mn3O4 Mesocrystal @ graphene nanocomposite exhibited excellent performance in Li-ion batteries, which is superior to the previous reported Mn3O4-based anodes.

Crystalline bacterial cell surface layer (S-layer) proteins are one of the most abundant biopolymers on earth, and form the outermost cell envelope component in a broad range of bacteria and archaea. These S-layer protein lattices represent the simplest biological membranes developed during evolution. S-layer lattices are highly porous protein mesh works with unit cell sizes in the range of 3 to 30 nm, and thicknesses of sim;10 nm. But, one of the key features of S-layer proteins is their intrinsic capability to form self-assembled mono- or double layers in suspension, at solid supports, the air-water interface, planar lipid films, liposomes, nanocapsules, and nano particles.
S-layer proteins have attracted much attention in the literature recently since the reassembly process is entropy-driven and a fascinating example of matrix assembly following a multistage, non-classical pathway. While the formation of extended S-layer protein monolayers is usually in the focus of current research and developments in the life and non-life sciences, S-layer proteins are also able to form more uncommon morphologies (with respect to other biological model systems) such as tubes, ribbons, or extended sheets with a central screw dislocation. In addition, the formation of hollow S-layer protein cages allows to extend the morphogenetic potential of S-layer protein self-assembly into the third dimension.
This contribution summarizes the state-of-the art in the reassembly of S-layer proteins, with a special focus on the uncommon morphologies and the formation of closed three-dimensional S-layer architectures.
Acknowledgements:
The Air Force Office of Scientific Research (AFOSR) (Agreement Awards FA9550-12-1-0274 and FA9550-10-1-0223), and the Erwin Schrödinger Society for Nanobiosciences, Vienna, Austria, funded part of this work.

Atomic Layer Deposition (ALD) is a unique thin film growth technique based on sequential self-limiting surface reactions, which offers high quality, pinhole-free, and conformal thin films with precise thickness control down to sub-nanometers. Thus, obtaining atomic-level understanding of the phase evolution in ALD is critical for achieving morphology, crystal structure, and property control, as well as deposition manipulation and scaling. Through comprehensive atomistic electron microscopy study of ALD TiO2 nanostructures at designed growth cycles, we revealed the transformation process and sequence of atom arrangement during TiO2 ALD growth. Evolution of TiO2 nanostructures in ALD was found following a path from amorphous layers to amorphous particles to metastable crystallites and ultimately to stable crystalline forms. Such a phase evolution is a manifestation of the Ostwaldminus;Lussac Law, which governs the advent sequence and amount ratio of different phases in high-temperature TiO2 ALD nanostructures. The amorphousminus;crystalline mixture also enables a unique anisotropic crystal growth behavior at high temperature forming TiO2 nanorods via the principle of vapor-phase oriented attachment.