ZnO nanorods can be readily produced by hydrothermal methods on glass substrates at low temperature (95°C) in a short period time (4 hours). The initial pH value of the aqueous solution makes a big difference on the morphology of ZnO nanorod arrays. Under acid condition (pH=5), ZnO nanorods are much bigger and sparser than the final products under neutral condition (pH=7). Another significant feature is that the nanorods from pH=5 randomly tilt from the substrate to a certain angle, whereas, the nanorods from pH=7 are standing vertically.
In order to explain how the direction of ZnO crystal growth was influenced under distinct condition, the growing process of the nanorods was monitored by SEM. The initial pH value is believed to have a great effort on the appearance of the ZnO crystal nucleation in the early stage, and continuously affects the nanorod development. The crystalline structure and optical properties of ZnO nanorods were also studied by using XRD, TEM and Photoluminescence techniques.

Designing, fabricating and integrating arrays of nanodevices into a functional system is the key for transferring nano-scale science into applicable nanotechnology. Despite of the numerous efforts devoted to achieve uniformly ordered assembly of various low-dimensional nanomaterials, planar metal-oxide-semiconductor field-effect-transistor (MOSFET) is still the dominant configuration for implementing functional nanodevices. Novel architecture like 3D integrated circuits has also been adopted to facilitate integration of nanostructure-based planar building blocks by sequentially assembling them into vertically stacked layers. Nevertheless, lack of cost-effective technology for aligning and integrating these nanodevices into circuitry with sufficiently high density hinders further practical applications.
For the emerging applications of bio-integrated electronics such as smart skin and human/machine interfacing, schemes for integrating functional nanomaterials with peripheral circuits on deformable/stretchable substrates at low temperature and low cost are highly desirable. To address these application needs, we demonstrate the first and by far the largest 3D array integration of vertical ZnO nanowire (NW) piezotronic transistors circuitry on 4-inch PET flexible substrates, by combining the patterned bottom-up solution synthesis of vertically aligned ZnO NWs at low-temperature (85 oC) with state-of-the-art top-down microfabrication. The as-fabricated array circuit possesses device density of 8464/cm2, which is much larger than the number of mechanoreceptors embedded in the human fingertip skins and enables a 15-to-25-fold increase in number of taxels and 300-to-1000-fold increase in taxel area density compared to recent reports.
The position, dimension, crystal orientation, morphology and material properties of synthesized ZnO NWs can be well controlled by the hydrothermal solution synthesis and optimized via engineering measures. The solution-synthesized ZnO NWs array exhibits good uniformity in electrical characteristics and response to applied pressure among all of the devices. The reliability and stability of device operations have also been probed, which indicates a good stability of the array operation for future applications like in vivo physiological sensing in complex environments. Moreover, the feasibility of the fabricated array for self-powered active and adaptive artificial skin without external bias has been presented as well. The scalability of this demonstrated technology in integrating solution-derived single-crystalline with interfacing circuitry at low temperature and low cost enables future implementation of nanomaterials for bio-integrated applications in human-machine interfacing and biomedical diagnosis/therapy.
Ref: Wu W. Z.*, Wen X. N.*, Wang Z. L. Taxel-addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging. Science 340, 952-957, 2013.
*Authors with equal contributions

ZnO continues to attract considerable attention due to its potential applications in UV detection, LEDs, spintronics, gas sensors, field effect transistors, field emission, photovoltaics and photocatalysis. Many of these applications require epitaxial films or nanostructured morphologies and ZnO is popular for these applications due to the ease of synthesizing a myriad of nano-forms (e.g. rods, rings, particles, belts) by solution methods. Solution methods are of particular interest because of the low temperatures employed (often < 100oC) and the ease of forming single crystal films and nanostructures.
This talk will present our observations concerning the growth of ZnO in water both as nanostructures and in film form. In the film form, epitaxial films have been grown at <100oC and much of the work has looked at reducing the defects in the grown films. Epitaxial films with threading dislocation densities in the low 108 cm-2 values utilizing lateral epitaxial overgrowth with and without photolithographic masking will be discussed. Recent results from initial works on the growth of homoepitaxial ZnO and MgZnO films and also nanostructured polycrystalline films will also be presented. For the latter, functional surface properties such as wetting will also be reported.
In addition, post growth annealing is required to optimize properties of solution grown ZnO and this study shows that such annealing leads to the formation of pores within epitaxial films and also in single crystal rods. It is believed that these pores form upon coalescence of anion and cation vacancies. Pore formation can be detrimental, adversely affecting transparency and mobility and as such, more detailed investigations has been undertaken utilizing a variety of characterization techniques such as scanning transmission electron microscopy (STEM), tomography and absorption spectroscopy.

As the most promising candidates for Diluted magnetic semiconductors (DMSs) with high Curie temperature (Tc), TM-doped ZnO has attracted considerable attention of scientific community due to its attractive advantages such as low cost, abundance, friendly environment and optoelectronic property. Although there are many reports on room-temperature ferromagnetism (RTFM) of ZnO diluted magnetic semiconductors doped with transition-metal (TM), the origin of RTFM is still quite controversial. Recently, some computational results calculated using the first-principles method based on density functional theory (DFT) show that codoping appears to be a potential approach to obtain intrinsic and enhanced ferromagnetism in TM-doped ZnO.[1,2] Stirred from the above mentioned facts, it would be quite interesting to synthesize and investigate the properties of codoping ZnO DMS, such as Cr-Ni codoped ZnO DMS. Meanwhile, magnetic field has been used as an efficient way to modulate the growth, morphology and the properties of the crystalline materials while it is applied in the synthesis process. In this work, Cr-Ni codoped ZnO powders were synthesized by hydrothermal method under the high pulsed magnetic field. The effects of pulsed magnetic field on the morphology, structure and magnetic properties of Cr-Ni codoped ZnO were investigated by X-ray diffraction, scanning electron microscope, high resolution transmission electron microscope, Raman scattering spectra and vibrating sample magnetometer. It was found that high pulsed magnetic field processing not only affects on the morphology of ZnO nanocrystallines, but also improves the Cr-Ni ions doping into the ZnO matrix. The room temperature ferromagnetism observed in the samples demonstrates clearly that codoping is an optional method to fabricate intrinsic ferromagnetism in TM-doped ZnO. According the bound magnetic polaron model (BMPs) proposed by Coey et al,[3] Cr and Ni ions incorporation may prompt the formation of bound polaron (oxygen vacancies, Vo), which may be the reason for the field processing sample with better ferromagnetism.
Acknowledgements
The authors thank the project supported by Shanghai Science and Technology Commission(11nm0501600), and the Analysis and Research Center of Shanghai University for their technical supports.
Reference
[1] B. Lu et al. Appl. Phys. Lett, 101:242401, 2012.
[2] P. Gopal et al. Phys. Rev. B, 74:094418, 2006.
[3] J.M.D. Coey et al. Nat. Mater, 4:173, 2005
*Corresponding author contact: [email protected]

We recently put forward a solution based method of laser induced chemical deposition for nanomaterials. The grow rate of SnO2 nanotube by laser induced chemical deposition can reach a value more than 300 nm/s. The method can be applied to produce various chalcogenide nanomaterials. Nanomaterials synthesized by laser-induced chemical deposition share the characteristic of uniform fine microstructure. In this paper, we demonstrate that this method can be used to coat 3 dimensional porous structure with uniform nanoparticles. Paper fibers coated with iron oxide nanoparticle as an example is studied in this paper. Heavy loading of Iron Oxide nanoparticles can achieved in a short time. The relationship between the laser power and production rate is shown. The size and crystal structure of the coated nanoparticle are investigated by SEM and TEM. The hybrid structure of nanoparticle coated paper fibers is used as an effective sorbent for heavy metal in water treatment.

In this presentation, we discuss our recent results in developing an electrochemical-liquid-liquid-solid (ec-LLS) growth process that relies on an unconventional aqueous electrodeposition strategy to produce crystalline covalent Group IV and III-V semiconductor nanomaterials. This process employs a liquid metal as a traditional cathode substrate and as a recrystallization flux to directly produce crystalline Group IV and III-V semiconductors at or near lab ambient conditions. The first half of the talk will focus on general features of the ec-LLS process used for the direct electrodeposition of crystalline GaAs and InAs thin films from aqueous solutions without any thermal annealing. Here, dissolved As2O3(aq) in water is electrochemically reduced on reactive Ga or In to produce the respective binary crystalline semiconductor. The necessity for clean (i.e. oxide free) group III metal interfaces will be discussed. Spectroelectrochemical data will then be presented that detail the extent of this electrodeposition process at low and elevated temperatures, highlighting a key balance between the rates of several electrochemical, metallurgical, and transport processes.. The second half of the presentation will highlight recent data that extends the ec-LLS strategy to using arrays of liquid gallium (Ga(l)) nanodroplet electrodes supported on Ge or Si wafers for the electrodeposition of epitaxial and single crystal Ge nanowires from dissolved GeO2(aq). High resolution transmission electron microscopy investigations will be presented which verify the epitaxial nature between the nanowire/substrate interface as well confirm the position of the Ga(l) nanodroplet at the tip of the nanowire following growth. The influence of the substrate crystal orientation on the resultant nanowire growth direction will be revealed by scanning electron microscopy. The observed uniformity in as-grown nanowire height will be discussed within the context of the traditional instantaneous electrochemical nucleation model. In the same vein, the propensity for this ec-LLS strategy to be used for wafer-scale preparation of homogenous Ge nanowire arrays will be described.

Titanium dioxide (TiO₂) has found its applications in many important areas including dye-sensitized solar cells, photocatalysis, and lithium-ion batteries (LIBs). It has been demonstrated that some structural features of TiO₂ materials, such as the particle size, geometric shape, and surface property would have tremendous effects on their physicochemical properties, thus influencing their performance. For example, TiO₂ has been studied as a promising anode material for high-performance LIBs. However, the low electrical/ionic conductivity of TiO₂ limits its electrochemical performance. By utilizing nanostructured TiO₂ materials, such as low-dimensional nanowires or nanosheets with reduced Li-ion/electron transport length and increased electrode/electrolyte contact area, lithium storage properties of TiO₂ could be significantly improved.
We have developed several solvothermal systems for the facile preparation of various TiO₂-based nanostructures, namely ultrathin anatase TiO₂ nanowires, asymmetric anatase TiO₂ nanorods with exposed high-index facets, and hierarchical spheres constructed by titanate nanosheets. Mixtures of some common organic solvents were used for these syntheses, including isopropanol, dimethylformamide and acetic acid, without the assistance of other additives (except for the synthesis of nanowires, in which lithium salt was added). It is speculated that the organic solvent molecules not only serve as reaction media, but also play as efficient structure directing agents to facilitate the anisotropic growth of nanocrystals, thus resulting in the various low-dimensional nanostructures. Electrochemical investigation shows that these TiO₂ nanostructures are promising candidates as high rate and long cycle life anode materials for LIBs.
Reference
[1] H. B. Wu, H. H. Hng, X. W. Lou, Direct synthesis of anatase TiO₂ nanowires with enhanced photocatalytic activity, Adv. Mater. 2012, 24, 2567-2571.
[2] H. B. Wu, J. S. Chen, X. W. Lou, H. H. Hng, Asymmetric anatase TiO₂ nanocrystals with exposed high-index facets and their excellent lithium storage properties, Nanoscale 2011, 3, 4082-4084.

Reverse micelle synthesis is a solution-based synthesis technique that takes advantage of confined water nanodomains in a bulk oil phase via self-assembly of surfactant molecules at the water-oil interface. This technique can be used for synthesizing functional nanoparticles for a wide variety of applications. The technique can be used to make unagglomerated nanoparticles with a narrow size distribution or compositionally layered nanoparticles, for example. Although some aspects of this synthesis method are well understood, other aspects are based on trial-and-error modifications. In this study, we describe and analyze the fundamental aspects of electrostatic interactions on reverse micelle synthesis. One of the fundamental aspects to be studied includes how solutes affect the size and stability of reverse micelles that define concentration stability limits. The interaction between a precipitated particle in suspension and the stability of the reverse micelle that contains the precipitate will also be evaluated to define precipitation limits. The effect of surfactant substitution, non-aqueous solvent substitution, and the water to surfactant ratio will also be evaluated for optimizing the combination of solute concentration stability and precipitation limits that can be used for the design of controlled nanoparticle formation.

The advances in synthesis of of high-quality epitaxial thin films and heterostructures of inorganic materials have led to the improved functional and multifunctional behavior. The important role that interfaces play in the behavior of these materials requires a detailed understanding of their structure. Electron microscopy approaches provide powerful information regarding local structure relevant to this challenge. The advent of correctors for spherical and chromatic aberrations (Cs and Cc, respectively) in transmission electron microscopy (TEM) has led to significant improvements in imaging, especially for high-resolution TEM, and some new imaging modes are now possible. One of the primary benefits of chromatic aberration correction is that it significantly reduces the focus blur in images formed from electrons with an energy spread, improving high resolution imaging in energy-filtered TEM (EFTEM) mode. Since EFTEM is formed using inelastically scattered electrons, atomic resolution EFTEM offers another method to determine structural and chemical information at atomic resolution. Although image formation in energy filtered high resolution electron microscopy (EF-HREM) is complex, it provides another approach to obtain “Z”-like contrast in atomic resolution images. Similarly, a new high-resolution TEM imaging technique allows the direct observation of A-site associated oxygen octahedral rotations in perovskite oxide superlattices. In this approach, we exploit the difference in extinction distance for atomic columns that arise due to channeling effects when a high-energy electron beam passes through them. Using this approach, we are able to distinguish between Ba and Ca and resolve oxygen octahedral rotations at the interfaces of a BaTiO3/CaTiO3 superlattice structure, helping to explain the mechanism for enhance ferroelectricity in this tailored structure.
*Research sponsored by the U.S. DOE, Office of Science - Basic Energy Sciences under contract DE-AC02-06CH11357. The Electron Microscopy Center at Argonne is supported by the Office of Science.

Sb2Te3 is a narrow band gap semiconductor with a broad spectrum of applications e.g. in thermoelectric power generation or as a phase change material in nonvolatile data storage. It consists of covalently bonded Te-Sb-Te-Sb-Te layers in ab direction. These quintuple layer stacks are interconnected via v. d. Waals forces resulting in a layered structure in c direction. For enhanced thermoelectric power generation, the thermal and electrical transport properties can be tuned by applying Sb2Te3 in nanosized form. [1] In data storage applications a temperature induced phase change between the amorphous and crystalline state in polycrystalline Sb2Te3 thin films exhibiting low and high electrical conductivity, respectively, is utilized. [2] However, the microstructure of such thin films affects the performance of the devices and the interplay of intrinsic and grain boundary effects is rather unexplored. Therefore it would be highly desirable to study the phase transition in Sb2Te3 on the level of individual micro- or nanocrystals.
In this work we introduce the solution based synthesis of defect free, hexagonally shaped Sb2Te3 single crystals following a modified protocol of Zhang et al. [3]. These hexagonal platelets (HPs) have an average lateral dimension of about 1.5 µm and a few tens to 250 nm in thickness. We will show that the reaction pathway towards this HPs passes via spherical and layered amorphous intermediates, whereas the latter surprisingly already show a hexagonal morphology. The detailed analysis of the reaction pathway is enabled by nanodiffraction analysis of the intermediates in a FEI TITAN 80-300 STEM, which allows to locally probe the crystallinity of a sample with nm resolution.
[1] W. Shi, L. Zhou, S. Song, J. Yang, H. Zhang, Adv. Mater. 2008, 20, 1892
[2] D. Lencer, M. Salinga, B. Grabowski, T. Hickel, J. Neugebauer, M. Wuttig, Nat. Mat., 2007, 7, 972
[3] G. Zhang, W. Wang, X. Lu, X. Li, Cryst. Growth Des. 2009, 9, 145

The multiple properties exhibited by copper and copper oxide nanomaterials, i.e. conduction, plasmonic, surface reactivity, have recently attracted a considerable interest due to their use in many applications (microelectronics, photovoltaics, catalysis or biology). [1, 2, 3, 4, 5] Because the copper oxidation state is a pivotal issue for the targeted applications, the control of the nanomaterial stability against ambient air is of prime importance. For example, attempts were made to block the oxidation process by using alkyl thiol molecules deposited as a monolayer onto a copper film. [6] However, discrepancies still remain concerning the nature of the environment able to efficiently control copper crystals oxidation: long chain carboxylic-acids, -amines, -thiols or pi-donor solvent. [7, 8, 9]. Recently, our group has developed a metallorganic chemical approach which allows to master the surface state of copper nanomaterials. [10] In addition to the usually employed characterization techniques (TEM, IR or UV-Vis spectroscopies) we have tracked the coordination and exchange mechanisms of ligands at/or close to the crystal surface by liquid NMR tools. In the present work, we have studied the role of hexadecylamine (HDA) or tetradecylphosphonic acid (TDPA) on the air stability of ca. 6 nm copper nanoparticles. The tremendous improvement of copper crystals&’ air stability functionalized by HDA compared to TDPA ligands will be presented and detailed. Depending on the choice of the terminal function carried by the ligand, amine or phosphonic acid, the fine tuning between slow oxidation and dissolution of NPs is monitored. This latter effect directly controls the release rate of copper ions potentially useful for bactericide applications. These results have been valuable for the preparation of copper nanoparticles layers stabilized by multivalent ligands (dendrimers bearing phosphonic acid functions) employed in bactericidal/bacteriostatic films.
[1] Hung L.-I., Tsung C.-K., Huang W., Yang, P. Adv. Mater 2010, 22, 1910.
[2]. Wang Z., von dem Bussche A., Kabadi P. K., Kane A. B., Hurt R. H. ACS Nano, 2013, 7, 8715.
[3] Jeong S., Woo K., Kim D., Lim S., Kim J. S., Shin H., Xia Y., Moon J. Adv. Funct. Mater. 2008, 18, 679.
[4] Park J. C., Kim J., Kwon H., Song H. Adv. Mater. 2009, 21, 803.
[5]. Lignier P., Bellabarba R., Tooze R. P. Chem. Soc. Rev. 2012, 41, 1708.
[6] Laibinis P. E., Whiteside G. M. J. Am. Chem. Soc. 1992, 114, 9022.
[7] Kanninen P., Johans C., Merta J., Kontturi K. J. Colloid Interface Sci. 2008, 318 , 88,
[8] Rice K. P., Walker E. J., Stoykovich M. P., Saunders A. E. J. Phys. Chem. C 2011, 115, 1793,
[9] Mott D., Galkowski J., Wang L., Luo J., Zhong C.-J. Langmuir 2007, 23, 5740.
[10] Barriere C., Piettre K., Latour V., Margeat O., Turrin C.-O., Chaudret B., Fau P., J. Mater. Chem. 2012, 22, 2279.

The tunability and performance of magnetic nanoparticles have garnered interest from a diverse set of technologies, ranging from environmental applications, such as groundwater treatment and site remediation, to magnetic resonance imaging (MRI), contrast agents, power electronics, optical isolators, and data storage. In particular, the remarkable properties of metallic iron have sparked significant interest in large-scale synthesis and assembly of zero-valent iron (Fe(0)) nanoparticles. The inherent susceptibility of these materials toward oxidation, however, challenges adoption. Techniques for surface-modification beyond the structure-directing ligands used in the nanoparticle synthesis are key to imparting stability against oxidation, as well as tuning properties and processibility. Here in, we discuss the synthesis, magnetic properties, and stability of Fe(0) nanoparticles with grafted polymer shells. In one approach, iron nanoparticles (e.g. 13 nm) are synthesized in 1-octadencene via microwave irradiation of Fe(CO)₅ in the presence of oleylamine. Thiol-terminated polystyrene is subsequently grafted-to the nanoparticle surface under inert atmosphere via ligand exchange with oleylamine. In a second approach, microwave irradiation of Fe(CO)₅ is conducted directly in a non-oxidizing polymer solution. The synthetic relationship between polymer molecular weight, graft density, and shell size will be discussed. The impact of the structure of the polymer shell on surface oxidation of the nanoparticle, and ultimately, on the magnetic properties of these materials, is also explored. Finally, the optical properties of self-assembled thin films of these hairy magnetic nanoparticles are summarized.

Silica nanoparticles are extensively used in a various areas of science. Their universalism is due to the ease of preparation and possibility of controlling size, a high surface-to-volume ratio, and the biocompatibility of silica.[1] In the last decades different functionalization protocols have been developed depending on the final purpose: sensing,[2] drug delivery [3] or synthesis of smart material [4].
Following this vision we decided to synthetize new silica nanoparticles and to functionalize their surface with bilayers of molecules taking advantage of the principle of Dynamic Combinatorial Chemistry. DCC is defined as combinatorial chemistry under thermodynamic control; that is, in a dynamic combinatorial library (DCL), all constituents are in equilibrium. At equilibrium, the expression of the products in a dynamic combinatorial library (DCL) is governed by thermodynamics and as a consequence, the additional presence of molecular targets can lead to the in situ screening of the ‘best-fitted&’ constituents.
Adapting approaches used in synthetic organic chemistry for applications such as pharmaceutical sciences and chemical discovery, materials scientists have developed a variety of approaches to create libraries in the solid state in order to rapidly examine a broad range of materials characteristics; the ultimate hope is to accelerate the discovery of new materials and/or new materials properties. [5]
Here we present a set of new self-assembled bilayer coated silica nanoparticles synthesized using different dynamic libraries having as common feature the possibility to form a reversible iminic bond. Amino- and Aldehyde-terminated silica nanoparticles were synthesized using a modified Stötber method and the coating analyzed by NMR, IR and TGA. The reaction with different corresponding members (aldehyde or amine respectively) has been tested in order to obtain homo- and mixed-ligand dynamic particles able to assemble/disassemble/exchange depending on the external condition they are exposed to. We investigate the assemble/disassemble of such a bilayer formed on the surface mainly using classical analytical techniques as well as and the arrangement of the molecules on the surface by AFM imaging.
[1] Feifel, S.V.; Lisdat, F. Journal of Nanobiotechnology 2011, 9, 59.
[2]Teolato, P.; Rampazzo, E.; Arduini, M.; Mancin, F.; Tecilla, P.; Tonellato, U. Chem. Eur. J. 2007, 13, 2238.
[3]Mackowiak, S. A.; Schmidt, A.; Weiss, V.; Argyo, C.; von Schirnding, C.; Bein, T.; Braüchle, C. Nano Lett. 2013, 13,
[4]Mori, H.; Müller, A. H. E.; Klee, J. E. JACS 2003, 125, 3712.
[5]Rajan, K. Combinatorial Materials Science and EBSD: A High Throughput Experimentation Tool. Annu. Rev. Mater. Res. 2008, 38, 299.

Metal/intermetallic nanostructures extend the range of bulk metallic properties by virtue of their manifold compositional, structural, phase, and morphological variations. The ability to tune structure-property characteristics of metal/intermetallic nanoparticles (NPs), via controlled synthesis techniques, can enable unique physico-chemical, and optoelectronic properties that find wide-spread scientific applications in new classes of energetic, plasmonic, catalytic and thermoelectric materials. To this end, a novel one-step, one-pot solution-phase experimental route is developed that, for the first time, combines “top-down” laser ablation synthesis in solution (LASIS) with “bottom-up” wet chemical reduction method (CRM). LASIS endows the NPs with metastable crystalline structures and phases due to the extreme liquid-confined plasma conditions, while the simple kinetics of CRM allows for systematic control of their sizes and shapes. We present results from a comprehensive study for the synthesis of Co/Co-oxide and Co/Pt NPs using the tandem LASIS-CRM technique. The effect of laser fluence, ablation time, temperature and solvents condition used were investigated. In most cases of LASIS on pure cobalt, cobalt(II) oxide (CoO) was the main product, except for ablation using a laser fluence of ~20 J/cm2 at high pH conditions (pH = 14), wherein large amount of cobalt(II,III) oxide (Co3O4) nanorods with spinel crystalline structure were formed. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) data revealed the lattice constant and d-spacing of (111) plane for these structures to be 0.808nm and 0.466nm respectively, which are in good agreement with the standard data for Co3O4 (JCPDS-ICDD No. 42-1467). Added to this, CoO@Pt shell-core NPs and intermetallic Pt-CoO NPs were generated by laser ablation in K2PtCl4 solution, which is demonstrated by the elemental mapping fromenergy dispersive X-ray spectroscopy(EDX). The formation of Co3O4 nanotubes with substantially increased size were found during LASIS in K2PtCl4 solutionsat pH = 14, which is due to the galvanic replacement reactions between Co and K2PtCl4. The present results report the first-ever tandem LASIS-CRM synthesis of controlled nanostructures such as Co3O4 nanorods and CoO@Pt shell-core NPs. Currently, systematic characterizations for magnetic properties and water oxidation catalytic activities of the aforementioned Co3O4 nanorods as well as electrocatalytic activities of the CoO@Pt shell-core nanostructures are in progress.

The use of nanosize silver, and its alloys, represents an interesting alternative to common food preservation methods, which are based on radiation, heat treatment and low temperature storage. These metal nanoparticles, embedded within a polymeric matrix for instance, would extend the shelf life of perishable foods while acting as a bactericidal agent to prevent food-borne illnesses. Common methods used in the synthesis of metal nanoparticles require toxic solvents and reagents that could be harmful to health and the food itself. In addition, several steps are required to obtain aqueous stable, i.e. dispersible, silver nanoparticles. In this work we propose the microwave-assisted aqueous synthesis of silver nanoparticles, (AgNPs) functionalized by gluthatione (GSH) in a single-step using sodium sulfite (Na2SO3), as reducing agent. Different molar ratios of Ag/GSH/Na2SO3 were evaluated. Best results were obtained at molar ratios of 1:3:1 and 1:3:3 at pH 6. UV-Vis measurement clearly showed the plasmon peak attributed to silver nanoparticles, which was confirmed by XRD analyses. The hydrodynamic diameter of AgNPs was <10 nm. FT-IR measurements suggested the actual GSH-Ag surface interaction through -SH and -COOH groups; the functionalization by GSH explained the high stability of the nanoparticles in aqueous suspensions. These Ag-GSH nanoparticles exhibited remarkable antimicrobial activity against E. Coli.

Fluorine doped cesium tungsten bronze (Cs0.33WO3Fx) has been successfully synthesized by hydrothermal method using sodium tungstate and cesium carbonate as raw materials, and hydrofluoric acid as fluorine source. The microstructure and morphology of the as-prepared Cs0.33WO3Fx products were characterized by XRD, SEM, TEM and XPS analyses, and the visible light transparency and near-infrared (NIR) shielding ability were evaluated. The results indicate that hydrofluoric acid plays a role in inducing the formation of rod-like Cs0.33WO3Fx particles, and with the increase of hydrofluoric acid addition amount, the nano-rod like morphology becomes more conspicuous. The XPS analysis results indicate that W atom exists in two forms of W5+ and W6+, and the doped fluorine atoms substituted for oxygen atoms in the lattice. The UV-Vis-NIR transmittance spectra indicate that the as-prepared Cs0.33WO3Fx particles exhibit higher visible light transmittance and near-infrared shielding ability than that of the non-doped Cs0.33WO3 particles, which is considered to be related with the increased band gap and free carrier concentration in the Cs0.33WO3Fx products. Particularly, the as-prepared Cs0.33WO3F0.45 sample shows best visible light transmittance with reaching 48% and near-infrared shielding property with reaching 90%. However, a dramatic decrease on NIR shielding ability has occurred in the sample Cs0.33WO3F0.79, which possibly results from the W-defect generated by the excessive etching of hydrofluoric acid. In addition, the effects of N2 annealing on the microstructure and properties of Cs0.33WO3Fx were also investigated. It is suggested that the hydrothermal synthesized Cs0.33WO3Fx particles with appropriate fluorine doping will have greater potential applications in the field of architectural and automotive window glasses for transparent heat shielding purposes than the non-doped Cs0.33WO3 particles.

Branched metal nanoparticles (NPs) are of current interest due to their unique properties, dependent on their size, shape and composition. However, many syntheses to branched NP yield NPs with inhomogeneous branching patterns from one particle to the next. Seed-mediated co-reduction is a method developed in the Skrabalak Laboratory to synthesize architecturally controlled bimetallic nanocrystals. By manipulating the synthetic parameters, a variety of architecturally complex nanostructures were produced through a general co-reduction approach in which Au and Pd precursors are simultaneously reduced to deposit metal on to shape-controlled metal cores. Previously, we have synthesized symmetrically branched core@shell Au@Au/Pd and Pd@Au/Pd nanocrystals. Here, we explore the roles of the seed symmetry and composition during seed-mediated co-reduction, where it was found that the final symmetry of the branched nanostructure depends on core geometry, shape and crystallinity. By decoupling the parameters that govern branched nanocrystal overgrowth, we can move towards rational design of new branched and bimetallic nanocrystals.

The two most important requirements for the use of nanocrystals in various applications like bio-imaging, solar energy conversion and light emitting devices are accurately defined sizes and narrow particle size distributions. Therefore the synthesis of nanoparticles must fulfill these two points. In the case of sparingly soluble materials, Ostwald Ripening is commonly accepted as the main growth mechanism and is the main reason for the broadening of the particle size distribution. Herein, we investigated the Ostwald ripening of colloids containing nanocrystals of two different crystal phases of the same material. For such polymorphic systems, we can show that in this case Ostwald Ripening leads to a narrowing of the particles size distribution of the thermodynamically more stable phase and the particles of the less stable phase just act as a monomer source. To realize such a system we mixed small NaEuF₄ nanocrystals of the cubic α-phase and hexagonal β-phase having the same mean size and size distribution and followed the temporal evolution of the particle sizes of both phases by XRD and TEM. An explanation of the experimentally observed narrowing of the particle size distribution is found by numerical simulations within the LSW framework. Small changes in the material parameters like bulk solubility or surface energy are sufficient to simulate a narrowing of the particle size distribution. Next to the explanation of the narrowing, we found a method for the preparation of nanoparticles with adequate defined sizes and narrow particle size distributions.

Ceria nanoparticles (NPs) are regarded as high potential materials for three-way catalyst and water-gas-shit catalyst and so on.
In our previous studies, ceria nano-cubes having active {100} facets on their surfaces were successfully synthesized by oleate-modified hydrothermal growth method1,2.
Sodium stearate (SS) is also a kind of surfactant which has a chemical structure similar to sodium oleate (SO). In this study, SS was also used as surfactant in the process and the size and shape control of ceria NPs were investigated.
0.5M Cerium nitride solution was added to 0.5M sodium oleate solution or 0.5M sodium stearate solution. The surfactant metal complexes were hydrothermally treated at 200oC for 6 hours, and the products were collected by centrifugation at 3000 rpm for 5 min.
All products were assigned to CeO2 (JCPDS: 34-0394) in XRD patterns. Ceria NPs synthesized using SO was about 12 nm in size and cubic in shape having {100} facets. On the other hand, ceria NPs synthesized using SS was about 6 nm in size and sphere in shape having many kinds of facets. Both NPs exhibited very high dispersibility in non-polar solvent.
(1) Taniguchi, T. et al., Crystal Growth & Design 2008, 8, 3725-3730.
(2) Taniguchi, T. et al., Crystal Growth & Design 2011, 11, 3754-3760.

Nanozirconia powders have been used for making structural ceramics as well as an electrolyte for solid oxide fuel cells. Forming of dense sintered components from nanopowders requires use of deagglomerated powders. In the present study 3YSZ powders were synthesized through coprecipitation and conditioning of the precipitate was carried out by treatment with different amounts of ethanol. Deagglomeration attained in calcined YSZ nanopowders improved with increase in amount of ethanol used for washing of the yttrium-zirconium hydroxide precipitate. Presence of adsorbed ethanol on the yttrium-zirconium hydroxide precipitate was confirmed through TG-DTA. BET specific surface area measurements, CHN analysis, tap density measurements and pressure-displacement curves for powder compaction revealed that a minimum ethanol amount with respect to water present in the precipitate was required to reduce extent of agglomeration considerably in the calcined powders. Green compacts produced from ethanol washed powders when subjected to nanoindentation were found to be “harder” than compacts produced from water washed powders due to superior particle packing. This was also was also evident from the SEM observations of the green compacts. Ionic strength of the suspending medium and zeta potential of the precipitate suspended in the medium showed no correlation to the obtained powder characteristics.

Nano-size Magnesium Aluminum Titanate dielectrics (eleven samples with different amount of TiO2) have been prepared by a modified Pechini-type soft chemistry technique. Also conventional solid state ceramic sample preparation methods were used to have a reference. Obtained powders were isostatically pressed (200-800 MPa) and heat treated at various temperatures (between 1000-1500°C). As the temperature and pressure were increased an increment in relative density was observed resulting higher dielectric quality factor compared to conventional sample preparation techniques. Dielectric constant was affected not only by sample composition but also by grain size, relative density and oxygen stoichiometry. Thermal conductivity at room temperature was measured by laser flash technique. It was also determined that, by using wet chemical methods, spinodal decomposition reaction hindered which improves dielectric properties of the materials.

Alumina-silicone hybrid nanolaminate films were synthesized by plasma enhanced chemical vapor deposition (PECVD) process. PECVD allows digital control over nanolaminate construction, and may be performed at low temperature for compatibility with flexible substrates. These materials are being considered as dielectrics for application such as capacitors in thin film transistors and memory devices. In this work, we present the temperature dependent electrical and dielectric properties of the nanolaminate dielectric films in the range of 200- 340 K to better asses their potential applications for different devices. It is observed that the frequency dependent dielectric constant (εr) and dielectric loss (tanδ) increase with the temperature. Both quadratic (α) and linear (β) voltage coefficient of capacitance (VCC) increases as the temperature increases. The temperature coefficient of capacitance (TCC) decreases whereas α and β increases as the Al2O3 composition increases in the alumina/silicone nanolaminates. The nanolaminate films show low leakage current density (J) and better dielectric loss tangent compared to that of single layered films.

Rare-earth-doped nanocrystals (NCs) have attracted great research interest in the past decades for their wide application in lighting, displays, lasers, including their emerging potential in biological imaging. Much effort has been devoted to the phase-controlled synthesis of these NCs and studies on their structure-dependent luminescence properties. Our work is focused on two types of rare-earth-doped NCs: ultraviolet-excited phosphor LaVO4:Eu, and near-infrared-excited phosphor NaREF4:Yb,Er/Tm. Phase-controlled synthesis was realized in both systems by rational design, and drastic change in luminescent properties was observed.
LaVO4:Eu NCs. While La is an abundant and cheap RE element, La compounds are less employed as phosphor host material, because of the structural difference between La and other RE compounds induced by the larger radius of La3+. For RE orthovanadates, while other REVO4 NCs tends to crystallized to tetragonal (t) phase, LaVO4 NCs usually crystallize to monoclinic (m) phase, which shows poorer luminescence properties. In our work, pure m-LaVO4:Eu and t-LaVO4:Eu NCs were both obtained by a hydrothermal method, with their phase controlled with additives. We found that chelating ligands, such as ethylenediaminetetraacetic acid (EDTA), favour the formation of t-LaVO4:Eu NCs. The phase transformation from m-LaVO4:Eu to the metastable t-LaVO4:Eu NCs resulted in a remarkable improvement of the luminescent properties.
NaREF4:Yb,Er/Tm NCs. Recently, studies on upconversion (UC) phosphors have grown rapidly, owing to their potential applications in near-infrared-excited bioimaging. NaREF4:Yb,Er/Tm NCs are most important type of UC materials, which exhibit large anti-Stokes shifts, high resistance to photobleaching and low biotoxicity. NaREF4 NCs exist in two phases, cubic phase (α) and hexagonal phase (β). As particle size and UC luminescent properties of the NCs are concerned for biological applications, phase-controlled synthesis are desirable. By tuning Na/RE ratio, solvent composition, reaction temperature and time, this is achieved in the thermal co-decomposition method. Further more, in-situ phase transition (from hexagonal to cubic phase ) of NaREF4 NCs were observed with electron beam irradiation. Spectral studies of NCs before/after phase-transition showed a remained branch ratio and a drop in emission intensity.

The pursuit of complex nanoscale architectures resides in our inspiration from nature, i.e. biomineralization processes, where the diversity and complexity of crystals produced is far from being rivaled by synthetic nanomaterials. Understanding the role of organic molecules in the fundamental crystal nucleation and growth processes that yield such biominerals can also enable precise and efficient crystal morphology engineering of functional nanomaterials. We previously reported the screw dislocation-driven growth of one-dimensional (1D) nanomaterials, such as nanowires and nanotubes, and two-dimensional (2D) nanoplates of various compositions in aqueous solutions. We are now assessing the influence of amino acids, as well as other small molecules, such as citric acid, on the screw dislocation-driven growth to achieve different 2D morphologies, such as hexagonal nanoplates vs. triangular ones. Further, we utilize this mechanism as a controllable “dimension-switch” from 2D to 1D morphologies, and vice versa, to construct homo- or heterostructures. To observe these changes, we are using nanoplates of zinc hydroxyl sulfate that can be easily converted to ZnO as convenient platforms for various imaging techniques. We mainly use in situ fluid atomic force microscopy and fluid optical microscopy to visualize growth spiral evolution under the influence of select molecules, and different growth conditions. These screw dislocation-driven building blocks could be useful for many applications, such as solar energy conversion and electronics.

The I-III-VI₂ ternary nanocrystals (NCs), such as copper indium sulfide (Cu_xIn_yS₂, CIS) or silver indium sulfide, are gaining great interest as a new field of strongly light-emitting semiconductor nanocrystals in visible to near-infrared (NIR) region or solar-harvesting applications due to their markedly low toxicity compared to Cd-based NCs. While developing the new synthetic strategies to utilize relatively nontoxic and chemically well-defined precursors, two metal dialkyldithiocarbamate single-molecular sources, we discovered the characteristic phase transformation of Cu₂S@In₂S₃ heterogeneous alloy structure to homogeneous CIS in the sizes of 2 - 8 nm. Even though the phase transformation of CIS was a well-studied phenomenon, we first observed that it could be related to the optical properties of CIS NCs. Due to the different thermal decomposition temperature and kinetics, Cu precursor decompose earlier than In precursor, resulting the heterogeneous alloy showing PL close to 800 nm NIR region, whereas the band-edge emission of bulk CIS is 827 nm in theory. Upon heating the 2 - 4 nm CIS NCs at relatively low temperature, the red emission in the range of 600 - 700 nm evolves upon reaction time while the NIR emission portion becomes lower and quantum yield in overall increases irrespective to the size and composition change, confirmed by ICP-AES, UV-VIS, and PL analysis. Similar phenomenon could also be observed for the CIS NCs with Cu/In ratio varied. We propose the reason behind this occurrence is the little lattice distortion and the chalcocite Cu₂S in superionic conducting state. This study gives insight to the understanding CIS formation mechanism for various syntheses.

Food packaging is indispensable to preserve the quality and safety of the food from the time of manufacturing to the final use by the consumer. It is indispensable to evaluate new or enhanced antimicrobial materials to be dispersed in biodegradable polymers for food packaging applications. The present work focuses on the synthesis and evaluation of the bactericidal capacity of Zn_xMg_1-xO solid solutions. Zn_xMg_1-xO solid solutions were synthesized through the thermal decomposition of ZnMg- precursor synthesized in aqueous and ethanol solutions via a two-steps process. X-Ray diffraction and FT-IR spectroscopy analyses confirmed the formation of two isolated phases at Zn concentrations of 10 at.% and above; below this Zn concentration, only the signal of MgO phase was detected. The antimicrobial activity of Zn_xMg_1-xO solid solution against E. coli was evaluated using the spread plate method in presence of Zn_xMg_1-xO powders (x= 0.00-0.50) of different composition. The powder concentrations were 500, 1000, and 1500 ppm. Zn_0.05Mg_0.95O powders exhibited a bacterial growth inhibition from 26% up to 100% when the particles&’ concentration increased from 500 up to 1500 ppm, respectively. On the contrary, a decreasing trend was observed for powders containing 30% and up of Zn (Zn_0.30Mg_0.70O); the corresponding bacterial growth inhibition was, respectively, 12%, 6%, and 5% when the particles concentration was 500, 1000, and 1500 ppm. The formation of two-isolated oxide phases at higher Zn concentrations could explain the observed inhibition of the corresponding bactericidal capacity.

Size-dependent melting decouples melting temperature from chemical composition and provides a new design variable for phase change applications. To demonstrate this potential, we embedded monodisperse bismuth colloidal nanoparticles into matrix materials. The melting temperature in these composites can be tuned by more than 20 Celsius by only varying the nanoparticle size. Adjusting the nanoparticle volume fraction also allows control over the composite's thermal energy density. Our further studies have generalized this approach to other nanoparticle compositions (e.g. In and Sn), and thereby provide a much broader temperature range for phase change applications. Additionally, we have developed a solution-phase chemistry approach to embed nanoparticles into inorganic matrices. This composite consists of a nanoparticle ensemble dispersed in a metal matrix, hence we anticipate a much higher thermal conductivity relative to polymer matrices and a corresponding improvement in thermal charging and discharging rate.

Fabrication of mesostructured silica materials has attracted a great deal of attention due to the potential applications of these unique materials in variety of fields including catalysis, energy, optical coatings, nano-medicine and sensors. Various methods have been developed to prepare mesostructured silica materials with different morphology (e. g. sphere, rod, plate, foam, and fiber) and well-defined pore structures (e. g. hexagonal, worm like, helical and lamellar) using different surfactants or surfactant mixtures, co-solvents or organosilane co-monomers. However, new methods, with vast control over the structure, are still needed to produce, especially, nanosized mesostructured silica materials.
In this research, we developed a facile one-pot method to synthesize mesoporous silica nanoparticles exhibiting variety of different structures such as helical structured nanorods, core-shell nano- spheres/rods and their hollow counterparts. In the first step, we condensate the tetraethyl orthosilicate (TEOS) monomer in the presence of cetyltriammonium bromide (CTAB) surfactant and rose Bengal (RB) dye to prepare helical mesoporous silica nanorods. Negatively charged RB molecules interact with the positively charged CTAB micelles to change their shape from spheres to helical mesostructured rods. Note that in the absence of RB common MCM-41 type mesoporous silica nanospheres were obtained. In addition, it is possible to tune the aspect ratio of nanorods by simply changing RB amount in the synthesis solution. In the second step, after the formation of initial particles, we added excess TEOS to form a thin silica layer around the particles. Finally, particles were calcinated at 550 °C to remove surfactant and RB molecules from the structure. Hierarchically porous nanorods or nanospheres were produced after the calcination process with microporous thin silica shells and mesoporous cores. Interestingly, mesoporous cores of the particles can be simply etched by stirring the particles in PBS (pH 7.4) solution for one day which results in hollow nanospheres and nanorods.

Membranes for ultrafiltration were prepared from polysulfone (PSf) composites with poly(1-vinylpyrrolidone) grafted silica nanoparticles (PVP-g-silica). For the synthesis of PVP-g-silica, hydroxyl terminated silica nanoparticles were reacted with (3-methacryloxypropyl)trimethoxysilane (γ-MPS) to form γ-MPS terminated silica nanoparticles (silica-MPS), which were further reacted with VP monomer. Formation of PVP-g-silica was confirmed by FT-IR, XPS, TGA, FE-SEM, and HR-TEM. PSf/PVP-g-silica membranes exhibited higher water flux than PSf membranes without any loss in solute rejection for membranes containing less than or equal to 5 wt% of PVP-g-silica. The water flux of a membrane containing 1 wt% PVP-g-silica was 2.3 times higher than that of PSf membrane. The hydrophilicity of the PSf/PVP-g-silica membrane also increased with increasing PVP-g-silica content. The hydrophilicity of the PSf/PVP membrane decreased with increasing retention time in a water bath, while the hydrophilicity of the PSf/PVP-g-silica membrane did not change with retention time. PSf/PVP-g-silica membranes exhibited enhanced fouling resistance in fouling experiments using nonionic surfactants.

We report the synthesis of compositionally asymmetric, core-Janus shell plasmonic nanostructures comprised of Au and Ag. Kinetic control was employed to achieve asymmetric shell growth on Au nanoparticles acting as cores. Subsequent differential surface functionalization of the nanostructures enabled programmed shell growth resulting in core-Janus shell nanostructures. UV/vis extinction spectra reveal that the localized surface plasmon resonance of the nanostructures depends on composition and distribution of the components, providing additional handles for tuning the optical properties of metal nanostructures. The core-Janus shell nanostructures demonstrated here are highly Raman-active making them attractive candidates for Raman-based biosensing and bioimaging applications.

Transparent amorphous oxide semiconductors (AOSs) are of great interest for low-cost smart windows and thin film transistors (TFTs) used in flat-panel displays. Creating AOSs that use inexpensive, low-temperature solution synthesis routes with the capability of large-area deposition are thus important. However, the formation of dense high-performance thin film semiconductors at low temperatures by conventional solution routes is challenging due to its use of organic ligands and large numbers of non-functional counterions. These organics and counterions often create porous films when combusted during the deposition, reducing device performances. New solution chemistry is essential to develop “ink-precursors” for high-performance films.
Here we report the electrochemical synthesis of InGaZn clusters using an aqueous precursor for solution-processed amorphous transparent IGZO thin films. The starting solution was prepared by dissolving In(NO₃)₃, Ga(NO₃)₃, and Zn(NO₃)₂ salts in nanopure water. A three-electrode electrochemical cell was used to synthesize clusters without utilizing additional chemical reagents. The working and counter electrodes were placed in the same beaker with the counter electrode enclosed in a medium fritted tube. A constant voltage was applied with respect to reference electrode to reduce the nitrate counterions as well as precisely control the solution pH during the cluster synthesis. The size and stability of the resulting cluster precursors were investigated using dynamic light scattering (DLS) in comparison to the starting salt solution. The electrolyzed precursors are stable for less than 2 h, displaying cluster radius of 0.8-1.0 nm. The optical, electrical, structural, and morphological properties of films, deposited from both cluster and salt solution precursors, were explored. These films are amorphous when annealed below 550 ^oC. SEM and XRR investigations indicate that the cluster films are uniform and crack-free with minimal thickness shrinkage due to thermal annealing. Electrical characterizations indicate that films made from cluster precursors have significantly larger mobility values than those from salt solutions. The best electrical properties are observed in a cluster film composed of In:Ga:Zn=0.4:0.4:0.2 annealed at 550 ^oC in air, yielding a Hall mobility of ~ 10 cm²/Vs and a carrier concentration of 10¹⁵ cm^-3. The TFT characterization using the IGZO film as an active channel layer will be performed in order to support the Hall effect results. This new method would allow for developing aqueous solution precursors to enable a variety of functional mixed-metal-oxide conducting/semiconducting films.

Optical micro-resonators composed of are designed, and fabricated on rare-earth doped thin films using sol-gel solution process. We evaluate the photoluminescence when the concentrations of Er dopant are modified from 0.1% to 5 %. We use finite difference time domain (FDTD) method to optimize the structures of our light emitting resonator, where a high Q factor of 105 is observed and used to enhance the photoluminescence efficiency due to the existing of a whispering-gallery mode. Optical emission spectrum between lambda; = 1.45 µm -1.65 µm and its enhancement factors are characterized by confocal microscopy. Our sol-gel synthesized micro-resonator can provide a small footprint light source for optical interconnect and integrated photonic circuits.

Here we present a shape recovery phenomenon of Pt-Ni bimetallic nanocrystals, which is unequivocally attributed to the defect effects. Further experiments and theoretical investigations indicate that the intrinsic defect-dominated growth mechanism allows the site-selective nucleation of the third metal M around the defects to achieve sophisticated designing of trimetallic core-shell structures (Pt₃Ni @ M, M=Au, Ag, Cu, and Rh). Trimetallic atomic steps in Pt₃Ni @ M as reactive sites could significantly improve catalytic performance, which are corroborated by several model reactions. The synthesis strategy based on our works paves the way for the atomic level design of trimetallic catalysts.

Here we developed a novel hydrothermal method by using alkali metallic nitride (LiNO3) as surfactant to synthesize tetragonal PbTiO3 octahedral-shaped nanocrystals (PT OCT). Systemically microstructure characterizations reveal that PT OCT nanocrystals with a size of 50~100 nm adopt a fascinating hybrid configuration, where tetragonal perovskite PTO crystalline core was surrounded by a lithium-concentrated amorphous thin layer of several nanometers in thickness. Under the mediation of the surfactant, the PT OCT nanocrystals were probably formed through an oriented attachment of primary particles [1]. In particular, such as-prepared nanocrystals demonstrate an excellent performance in the degradation of MB solution under visible light irradiation than the perovskite oxide systems in the emerged reports [2, 3], and the first-order kinetic constant for the PT OCT nanocrystals has been determined to be 0.042. On the basis of microstructure analysis and detailed catalysis experiments, it is proposed that the amorphous layer should be the position to generate electron-hole pair under visible light irradiation, while the electric polarization of ferroelectric core could significantly accelerate the carrier separation, leading to the unique catalytic property of PT OCT nanocrystals. The findings present here may offers an opportunity to design and explore novel high efficient visible photocatalyst by using ferroelectric nanomaterials.
Reference
[1] Jillian F. Banfield, Susan A. Welch, Hengzhong Zhang, Tamara Thomsen Ebert, R. Lee Penn, Science, 2000, 4, 289
[2] Feng Gao, Xinyi Chen, Kuibo Yin, Shuai Dong, Zhifeng Ren, Fang Yuan, Tao Yu, Zhigang Zou, Jun-Ming Liu, Adv. Mater. 2007, 19, 2889
[3] Xiaobo Chen, Lei Liu, Peter Y. Yu, Samuel S. Mao, Science, 2011, 331, 746

Much of the current research has been oriented towards lead-free piezoelectric materials, both in bulk, and due to requirements for miniaturization of electronic and micro-electro-mechanical devices, also in thin film form. (K0.5Na0.5)NbO3 (KNN) is one of the widely studied lead-free materials compositions which could replace lead-based piezoelectrics.
Due to the presence of two volatile alkali oxides, the KNN coating solutions should include an excess of alkalis to preserve the perovskite phase upon annealing. The thin films were prepared by spin-coating the acetate-alkoxide derived solutions with 0, 5 or 10 mole% sodium or potassium acetate excess, pyrolysis at 300 oC and rapid thermal annealing at 750 oC for 5 min. The amount of alkali excess in the solutions influenced the degree of {100} perovskite orientation, the monoclinic distortion of the unit cell, and the nucleation and growth processes of the films. The microstructure of about 250 nm thick films, prepared from the 5 mole% alkali excess solutions, consisted of fine equiaxed grains of about 50 nm across, whereas the films, prepared from the 10 mole% alkali excess solutions, were about 200 nm thick and consisted