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A primary mode of failure of thin-film coatings is the mismatch in thermal expansion coefficients of the substrate and the coating, which results in accumulation of interfacial stresses and ultimately in film delamination. While much attention has been devoted to modulation of interfacial bonding to mitigate delamination, current strategies are constrained in their generalizability and have had limited success in imbuing resistance to prolonged thermal cycling. We demonstrate here the incorporation of rigid thermal expansion compensators within polymeric films as a generalizable strategy for minimizing thermal mismatch with the substrate. Nanostructures of the isotropic negative thermal expansion (NTE) material HfV2O7 have been prepared based on the reaction of nanoparticulate precursors. The NTE behavior, derived from transverse oxygen displacement within the cubic structure, has been examined using temperature-variant powder X-ray diffraction, Raman spectroscopy, electron microscopy, and selected-area electron diffraction measurements. HfV2O7 initially crystallizes in a 3 × 3 × 3 superlattice but undergoes phase transformations to stabilize a cubic structure that exhibits strong and isotropic NTE with a coefficient of thermal expansion (CTE) = -6.7 × 10-6 °C-1 across an extended temperature range of 130-700 °C. Incorporation of HfV2O7 in a high-temperature thermoset polybenzimidazole enables the reduction of compressive stress by 67.3% for a relatively small loading of 26.6 vol % HfV2O7. Based on a composite model, we demonstrate that HfV2O7 can reduce the thermal expansion coefficient of polymer nanocomposite films, even at low volume fractions, as a result of its substantially higher elastic modulus compared to the continuous polymer matrix. By changing the volume fraction of HfV2O7, the overall coefficients of thermal expansion of the film can be tuned to match a range of substrates, thereby mitigating thermal stresses and resolving a fundamental challenge for high-temperature composites and nanocomposite coatings.

FeS nanoplatelets were synthesized using a surfactant-assisted hydrothermal synthesis. The product is highly crystalline and has a preferred growth direction with a [001] plate normal. The platelet...

The search for new functional materials that combine high stability and efficiency with reasonable cost and ease of synthesis is critical for their use in renewable energy applications. Specifically in catalysis, nanoparticles, with their high surface-to-volume ratio, can overcome the cost implications associated with otherwise having to use large amounts of noble metals. However, commercialized materials, that is, catalytic nanoparticles deposited on oxide supports, often suffer from loss of activity because of coarsening and carbon deposition during operation. Exsolution has proven to be an interesting strategy to overcome such issues. Here, the controlled emergence, or exsolution, of faceted iridium nanoparticles from a doped SrTiO3 perovskite is reported and their growth preliminary probed by in situ electron microscopy. Upon reduction of SrIr0.005Ti0.995O3, the generated nanoparticles show embedding into the oxide support, therefore preventing agglomeration and subsequent catalyst degradation. The advantages of this approach are the extremely low noble metal amount employed (∼0.5% weight) and the catalytic activity reported during CO oxidation tests, where the performance of the exsolved SrIr0.005Ti0.995O3 is compared to the activity of a commercial catalyst with 1% loading (1% Ir/Al2O3). The high activity obtained with such low doping shows the possibility of scaling up this new catalyst, reducing the high cost associated with iridium-based materials. Postprint Postprint

Herein we report an ultrasonic- and photobased synthetic approach for the production of size-selective SrTiO3 nanomaterials that are surface-decorated with Pd nanoparticle cocatalysts for applicati...

Nanostructuring inorganic solids has been effective as a tool to control the identity of the thermodynamically stable phase under ambient conditions for many systems. In addition, size effects can ...

The hollow core, concentric graphitic shells, and large surface area of the carbon nano-onion (CNO) make these carbon nanostructures promising materials for highly efficient catalytic reactions. Doping CNOs with heteroatoms is an effective method of changing their physical and chemical properties. In these cases, the configurations and locations of the incorporated dopant atoms must be a key factor dictating catalytic activity, yet determining a structural arrangement on the single-atom length scale is challenging. Here we present direct imaging of individual nitrogen and sulfur dopant atoms in CNOs, using an aberration-corrected scanning transmission electron microscopy (STEM) approach, combined with electron energy loss spectroscopy (EELS). Inspection of the statistics of dopant configuration and location in sulfur-, nitrogen-, and co-doped samples reveals dopant atoms to be more closely situated to defects in the graphitic shells for co-doped samples, than in their singly doped counterparts. Correlated with an increased activity for the oxygen reduction reaction in the co-doped samples, this suggests a concerted mechanism involving both the dopant and defect.

Pyrochlore materials with novel properties are in demand with multifunctional applications such as optoelectronics, scintillator materials, and theranostics. Many reports have already indicated the importance of the synthesis technique for Nd2Zr2O7 (NZO) nanoparticles (NPs); however, no explanation has been provided for the reason behind the nature of its phase selectivity. Here, we have explored the structural and optical properties of the NZO NPs synthesized by a molten salt synthesis method. We have synthesized size-tunable NZO NPs and correlated the particle size with their structural behavior and optical performance. All NZO NPs are stabilized in defect fluorite phase. Neutron diffraction provided insight on the behavior of oxygen in the presence of heavy atoms. We have collected bright amalgam of blue and green emission on UV irradiation due to the presence of oxygen vacancies from these NPs. We have carried out in situ XRD and Raman investigations to observe the temperature-induced phase transformation in a controlled argon environment. Interestingly, we have not observed phase change for the molten salt synthesized fluorite NZO NPs; however, we observed phase transformation from a precursor stage to pyrochlore phase by in situ XRD directly. These observations provide a new strategy to synthesize nanomaterials phase-selectively for a variety of applications in materials science.

Skutterudite crystals are of interest for their thermoelectric properties and in particular for the flexibility the structure offers for tuning such properties. One strategy to enhance the thermoel...

The intention of this chapter is to review and summarize the many approaches to fabricate aligned arrays of metal oxide nanowires (NWs), broadly separated into three classes (i) the growth of catalyst particles, seed particles, or NWs directly, utilizing a template (which is removed after filling); (ii) lithographic methods to fabricate arrays of either catalyst/seed particles or the NWs themselves directly; and (iii) post-synthetic methods of aligning freestanding NWs from powder or solution. Some examples of creative ways in which multiple approaches have been used in combination as well as future avenues for research will be discussed. Our focus in this review is primarily on the alignment of NWs, and for that reason, our descriptions of synthetic methods, properties, and applications of the resulting arrays will be limited.

Metastable materials that represent excursions from thermodynamic minima are characterized by distinctive structural motifs and electronic structure, which frequently underpins new function. The binary oxides of hafnium present a rich diversity of crystal structures and are of considerable technological importance given their high dielectric constants, refractory characteristics, radiation hardness, and anion conductivity; however, high-symmetry tetragonal and cubic polymorphs of HfO2 are accessible only at substantially elevated temperatures (1720 and 2600 °C, respectively). Here, we demonstrate that the core–shell arrangement of VO2 and amorphous HfO2 promotes outwards oxygen diffusion along an electropositivity gradient and yields an epitaxially matched V2O3/HfO2 interface that allows for the unprecedented stabilization of the metastable cubic polymorph of HfO2 under ambient conditions. Free-standing cubic HfO2, otherwise accessible only above 2600 °C, is stabilized by acid etching of the vanadium oxide core. In contrast, interdiffusion under oxidative conditions yields the negative thermal expansion material HfV2O7. Variable temperature powder X-ray diffraction demonstrate that the prepared HfV2O7 exhibits pronounced negative thermal expansion in the temperature range between 150 and 700 °C. The results demonstrate the potential of using epitaxial crystallographic relationships to facilitate preferential nucleation of otherwise inaccessible metastable compounds.

Carbon nanotubes (CNTs) offer unique properties that have the potential to address multiple issues in industry and material sciences. Although many synthesis methods have been developed, it remains difficult to control CNT characteristics. Here, with the goal of achieving such control, we report a bottom-up process for CNT synthesis in which monolayers of premade aluminum oxide (Al2O3) and iron oxide (Fe3O4) nanoparticles were anchored on a flat silicon oxide (SiO2) substrate. The nanoparticle dispersion and monolayer assembly of the oleic-acid-stabilized Al2O3 nanoparticles were achieved using 11-phosphonoundecanoic acid as a bifunctional linker, with the phosphonate group binding to the SiO2 substrate and the terminal carboxylate group binding to the nanoparticles. Subsequently, an Fe3O4 monolayer was formed over the Al2O3 layer using the same approach. The assembled Al2O3 and Fe3O4 nanoparticle monolayers acted as a catalyst support and catalyst, respectively, for the growth of vertically aligned CNTs. The CNTs were successfully synthesized using a conventional atmospheric pressure-chemical vapor deposition method with acetylene as the carbon precursor. Thus, these nanoparticle films provide a facile and inexpensive approach for producing homogenous CNTs.

Nanowires grown using the vapor–liquid–solid (VLS) mechanism are highly attractive components for functional nanomaterials since they grow along unique crystallographic axes to form defect-free single crystals with well-controlled dimensions. To date, however, these free-standing wires have been put to little use, since their ordered arrangement or placement is highly challenging. Here, we report an approach to create ordered arrays of nanoscale interfaces, in which we utilize the reverse of the VLS mechanism (the solid–liquid–vapor (SLV) mechanism) to etch the inverse of a nanowire, a “negative nanowire”, into a single crystal. In this way, we achieve essentially the same array of crystallographic surfaces as would be achieved by growing a large array of nanowires but in a way that creates a single object which is easy to handle. The SLV mechanism is a unique approach in that it is governed by the same crystallography which makes the VLS mechanism attractive but, additionally, poses several key advantage...

This report describes a new route to synthesize single-crystalline manganese-containing spinel nanowires (NWs) by a two-step hydrothermal and solid-state synthesis. Interestingly, a nanowire or nanorod morphology is maintained during conversion from MnO2/MnOOH to CuMn2O4/Mg2MnO4, despite the massive structural rearrangement this must involve. Linear sweep voltammetry (LSV) curves of the products give preliminary demonstration that CuMn2O4 NWs are catalytically active towards the oxygen evolution reaction (OER) in alkaline solution, exhibiting five times the magnitude of current density found with pure carbon black.

N-type and p-type skutterudite samples with the composition Co x Ni4−x Sb12−y Sn y were synthesized with composition range 0 0.8 and negative otherwise. Seebeck coefficients were low, ranging from −40 to 58 µV K−1. The combination of transmission electron microscopy with electron energy loss spectroscopy and powder X-ray diffraction established that Sn can substitute on 2a and 24g sites in the skutterudite structure. Due to the low Seebeck coefficients, the alloys exhibited low figure of merits (ZT)

High-temperature phases of hafnium dioxide have exceptionally high dielectric constants and large bandgaps, but quenching them to room temperature remains a challenge. Scaling the bulk form to nanocrystals, while successful in stabilizing the tetragonal phase of isomorphous ZrO2, has produced nanorods with a twinned version of the room temperature monoclinic phase in HfO2. Here we use in situ heating in a scanning transmission electron microscope to observe the transformation of an HfO2 nanorod from monoclinic to tetragonal, with a transformation temperature suppressed by over 1000°C from bulk. When the nanorod is annealed, we observe with atomic-scale resolution the transformation from twinned-monoclinic to tetragonal, starting at a twin boundary and propagating via coherent transformation dislocation; the nanorod is reduced to hafnium on cooling. Unlike the bulk displacive transition, nanoscale size-confinement enables us to manipulate the transformation mechanism, and we observe discrete nucleation events and sigmoidal nucleation and growth kinetics., The high-temperature tetragonal phase of HfO2 is technologically useful but difficult to stabilize at room temperature. Here, the authors observe in real-time the transformation of a HfO2 nanorod from its room temperature to tetragonal phase, at 1000° less than its bulk temperature, suggesting that size confinement may kinetically trap this phase.

Designing luminescent materials especially nanomaterials with multifunctional applications is highly challenging and demanding. In this work, we explored pyrochlore La2Hf2O7 nanoparticles (NPs) singly and triply codoped with Eu3+, Tb3+ and Dy3+. Under both ultraviolet and X-ray irradiations, the La2Hf2O7 NPs singly doped with Eu3+, Tb3+ and Dy3+ displayed red, green and yellowish-blue emission, respectively. The concentration quenching study revealed a non-radiative energy transfer in Eu3+ doped La2Hf2O7 NPs, which takes place via dipole-quadrupole mechanism. On the other hand, a dipole-dipole interaction prevails in Tb3+ and Dy3+ doped La2Hf2O7 NPs. Lifetime spectroscopy reveals the stabilization of Eu3+ and Dy3+ ions at La3+ site at low doping concentration whereas a fraction of them migrates to Hf4+ site at high doping concentration. For the La2Hf2O7:Tb3+ NPs, Tb3+ ions are localized at Hf4+ site at all doping concentrations. Furthermore, when triply codoped with Eu3+, Tb3+ and Dy3+ ions, the La2Hf2O7 NPs display beautiful warm white light as a new strategy for color tunability through doping percentage. To sum, our complete spectrum of studies on the structure, UV excited photoluminescence, concentration quenching, and local site spectroscopy of the La2Hf2O7:Ln3+ NPs suggests that they are potential candidates as single-component multicolor-emitting phosphors for lighting and scintillating applications.

The Fano interference phenomenon between localized surface plasmon resonances (LSPRs) of individual silver nanocubes is investigated using dark-field optical microscopy and electron-energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). By computing the polarization induced by the electron beam, we show that the hybridized modes responsible for this Fano interference are the same as those present in the resonance-Rayleigh scattering spectrum of an individual nanocube on a substrate.

Plasmonics is a rapidly growing field, yet imaging of the plasmonic modes in complex nanoscale architectures is extremely challenging. Here we obtain spatial maps of the localized surface plasmon modes of high-aspect-ratio silver nanorods using electron energy loss spectroscopy (EELS) and correlate to optical data and classical electrodynamics calculations from the exact same particles. EELS mapping is thus demonstrated to be an invaluable technique for elucidating complex and overlapping plasmon modes.

The use of bottom-up fabrication of nanostructures for nanotechnology inherently requires two-dimensional control of the nanostructures at a particular surface. This could in theory be achieved crystallographically with a structure whose three-dimensional unit cell has two or more—tuneable—dimensions on the nanometre scale. Here, we present what is to our knowledge the first example of a truly periodic two-dimensional nanometre-scale phase separation in any inorganic material, and demonstrate our ability to tune the unit-cell dimensions. As such, it represents great potential for the use of standard ceramic processing methods for nanotechnology. The phase separation occurs spontaneously in the homologous series of the perovskite-based Li-ion conductor, (Nd2/3−xLi3x)TiO3, to give two phases whose dimensions both extend into the nanometre scale. This unique feature could lead to its application as a template for the assembly of nanostructures or molecular monolayers.

We investigated the effect of substrate-induced strain on the metal-insulator transition (MIT) in single-crystalline VO(2) nanobeams. A simple nanobeam-substrate adhesion leads to uniaxial strain along the nanobeam length because of the nanobeam's unique morphology. The strain changes the relative stability of the metal (M) and insulator (I) phases and leads to spontaneous formation of periodic, alternating M-I domain patterns during the MIT. The spatial periodicity of the M-I domains can be modified by changing the nanobeam thickness and the Young's modulus of the substrate.

The well-known vapor-liquid-solid (VLS) mechanism results in high-purity, single-crystalline wires with few defects and controllable diameters, and is the method of choice for the growth of nanowires for a vast array of nanoelectronic devices. It is of utmost importance, therefore, to understand how such wires interact with metallic interconnects-an understanding which relies on comprehensive knowledge of the initial growth process, in which a crystalline wire is ejected from a metallic particle. Though ubiquitous, even in the case of single elemental nanowires the VLS mechanism is complicated by competing processes at multiple heterogeneous interfaces, and despite decades of study, there are still aspects of the mechanism which are not well understood. Recent breakthroughs in studying the mechanism and kinetics of VLS growth have been strongly aided by the use of in situ techniques, and would have been impossible through other means. As well as several systematic studies of nanowire growth, reports which focus on the role and the nature of the catalyst tip reveal that the stability of the droplet is a crucial factor in determining nanowire morphology and crystallinity. Additionally, a reverse of the VLS process dubbed solid-liquid-vapor (SLV) has been found to result in the formation of cavities, or "negative nanowires". Here, we present a series of heating studies conducted in situ in the transmission electron microscope (TEM), in which we observe the complete dissolution of metal oxide nanowires into the metal catalyst particles at their tips. We are able to consistently explain our observations using a solid-liquid-vapor (SLV) type mechanism in which both evaporation at the liquid-vapor interface and adhesion of the catalyst droplet to the substrate surface contribute to the overall rate.

Neutron powder diffraction data for the Li-containing perovskite (Nd7/12Li1/4)TiO3 is compared to simulated patterns, showing that structural refinement should use a ∼4000 atom, 14ap × 28ap × 2ap supercell. To form the nano-checkerboard, periodic phase separation must therefore be occurring throughout the bulk powder sample.

The direct observation of Li diffusion in Li-doped zinc oxide nanowires (NWs) was realized by using in situ heating in the scanning transmission electron microscope (STEM). A continuous increase of low atomic mass regions within a single NW was observed between 200 °C and 600 °C when heated in vacuum, which was explained by the conversion of interstitial to substitutional Li in the ZnO NW host lattice. A kick-out mechanism is introduced to explain the migration and conversion of the interstitial Li (Lii) to Zn-site substitutional Li (LiZn), and this mechanism is verified with low-temperature (11 K) photoluminescence measurements on as-grown and annealed Li-doped zinc oxide NWs, as well as the observation of an increase of NW surface roughing with applied bias.

The study of plasmons is at the core of Surface‐Enhanced Raman Spectroscopy (SERS). Surface plasmons are generated from the interaction of light with the electrons on the surface of a metal and are responsible for the electromagnetic enhancement mechanism in SERS. It is believed that the different modes that are observed in plasmon resonances depend on the shape of the nanoparticles [1].The goal of this project is to correlate the optical measurements of nanostructures generated by the surface plasmons using Resonant Rayleigh Scattering, with high resolution structural information obtained by using Scanning Transmission Electron Microscopy (STEM). This technique will also reveal the different localized surface plasmon modes in the nanostructure as well as the relationship between the optical surface plasmons and the plasmons generated from the inelastic scattering of the electron beam. The measurement of the surface plasmon excitations in a STEM is called Electron Energy Loss Spectroscopy (EELS).The succe...

We present real-time transmission electron microscopy of nanogap formation by feedback controlled electromigration that reveals a remarkable degree of crystalline order. Crystal facets appear during feedback controlled electromigration indicating a layer-by-layer, highly reproducible electromigration process avoiding thermal runaway and melting. These measurements provide insight into the electromigration induced failure mechanism in sub-20 nm size interconnects, indicating that the current density at failure increases as the width decreases to approximately 1 nm.

Electromigrated nanogaps have shown great promise for use in molecular scale electronics. We have fabricated nanogaps on free-standing transparent SiN(x) membranes which permit the use of transmission electron microscopy (TEM) to image the gaps. The electrodes are formed by extending a recently developed controlled electromigration procedure and yield a nanogap with approximately 5 nm separation clear of any apparent debris. The gaps are stable, on the order of hours as measured by TEM, but over time (months) relax to about 20 nm separation determined by the surface energy of the Au electrodes. A major benefit of electromigrated nanogaps on SiN(x) membranes is that the junction pinches in away from residual metal left from the Au deposition which could act as a parasitic conductance path. This work has implications to the design of clean metallic electrodes for use in nanoscale devices where the precise geometry of the electrode is important.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

This paper reviews recent applications of Monte Carlo methods for the study of cation ordering in minerals. We describe the program Ossia99, designed for the simulation of complex ordering processes and for use on parallel computers. A number of applications for the study of long-range and short-range order are described, including the use of the Monte Carlo methods to compute quantities measured in an NMR experiment. The method of thermodynamic integration for the determination of the free energy is described in some detail, and several applications of the method to determine the thermodynamics of disordered systems are outlined.

We illustrate a simple method to synthesize highly ordered ZnO axial p-n homojunction-containing nanowires using a low temperature method, and on a variety of substrates. X-ray diffraction, scanning transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy are used to reveal high quality single-crystalline wires with a [001] growth direction. The study of electrical transport through a single nanowire based device and cathodoluminescence via scanning transmission electron microscopy demonstrates that an axial p-n junction exists within each ZnO nanowire. This represents the first low temperature synthesis of axial p-n homojunction-containing ZnO nanowires with uniform and controllable diameters.