Thin films of c-axis-oriented LiCoO2 were epitaxially grown by pulsed laser deposition (PLD). The ablation laser conditions greatly affect the crystal quality of the epitaxial LiCoO2 thin films. In addition, high-quality LiCoO2 thin films were found to grow without any impurity phases under relatively low oxygen partial pressure, although high pressure had been often selected to suppress the formation of Co3O4 with a lower valence state as an impurity. This result clearly indicates that the ablation laser conditions are an essential growth parameter, and that composition control is indispensable to grow high-quality complex compound thin films by PLD.

The synthesis of monodisperse magnetite nanoparticles (Fe3O4 NPs) has been widely investigated over the last decade. Among the various synthetic methods, thermal decomposition of iron acetylacetonate, Fe(acac)3, or the premade iron-surfactant complex, was demonstrated to be promising to obtain monodisperse Fe3O4 NPs with controllable size and morphology. However, toxic and expensive precursors or tedious experimental procedures are normally required in these approaches. In this communication, we report a facile chemical top-down method to synthesize monodisperse magnetite NPs by using rust, which is mainly composed of γ-Fe2O3, as the iron source and oleic acid as the capping agent. The particle size, and hence the magnetization, of NPs can be readily controlled by adjusting the rust/oleic acid ratio and reaction temperature. This process is a green chemical approach and is easy to be reproduced and scaled up, which could be developed as an effective way to convert waste materials into high quality nanocrystals.

Photoelectrochemical (PEC) water splitting for hydrogen production is a promising technology that uses sunlight and water to produce renewable hydrogen with oxygen as a by-product. In the expanding field of PEC hydrogen production, the use of standardized screening methods and reporting has emerged as a necessity. This article is intended to provide guidance on key practices in characterization of PEC materials and proper reporting of efficiencies. Presented here are the definitions of various efficiency values that pertain to PEC, with an emphasis on the importance of solar-to-hydrogen efficiency, as well as a flow chart with standard procedures for PEC characterization techniques for planar photoelectrode materials (i.e., not suspensions of particles) with a focus on single band gap absorbers. These guidelines serve as a foundation and prelude to a much more complete and in-depth discussion of PEC techniques and procedures presented elsewhere.

This review represents recent research on using chemical prelithiation to improve cycling performance of nanostructured electrode materials for lithium ion batteries in our group. We focus on two typical cathode materials, MoO3 nanobelts and FeSe2 nanoflowers. Methods of direct or secondary hydrothermal lithiation of MoO3 nanobelts and FeSe2 nanoflowers are described first, followed by electrochemical investigation of the samples before and after lithiation. Compared with pristine materials, lithiated samples exhibit better cycling capability. Prelithiation of other kinds of materials, such as V2O5, MnO2, etc. is also briefly reviewed. This demonstrates that prelithiation can be a powerful general approach for improving cycling performance of Li-ion battery electrode materials.

Using nanoindentation, this study develops the criteria to evaluate the creep performance of the intermetallic compounds (IMCs) formed at the interface of microelectronic solder joints. Regardless of crystal structure and melting point, the creep stress exponent (X), one of the parameters determining creep resistance, is in good agreement with tendencies of the work-hardening exponent (n) and also the ratio of yield stress (Y) to Young's modulus (E), which reveals the ability against plastic deformation.

The increasing worldwide interest in MnO2 for supercapacitor applications is based on anticipation that MnO2-based high-voltage aqueous supercapacitors will ultimately serve as a safe and low-cost alternative to state-of-the-art commercial organic-based electrochemical double-layer capacitors or RuO2-based acid systems. In this paper, the physicochemical features, synthesis methods, and charge storage mechanism of MnO2 as well as the current status of MnO2-based supercapacitors are summarized and discussed in detail. The future opportunities and challenges related to MnO2-based supercapacitors have also been proposed.

We investigated the structural stabilities of the intermetallics and the solid-state phase transformations induced by lattice vibration effects in the Al–Zr system by first-principles calculations. The calculated lattice parameters of all the phases and the phonon dispersion relations for pure Al and Zr are in good agreement with the experimental data. AlZr(oC8), Al4Zr5 (hP18), and Al3Zr5 (tI32) are predicted to be the high-temperature phases. To study the structural stabilities at high temperatures, the thermodynamic properties of the intermetallics are calculated via the linear response approach within the harmonic approximation. Thanks to the calculated enthalpies of formation at high temperatures, Al3Zr5 is predicted to be stabilized above 1163 K with respect to AlZr2 and Al2Zr3, in good agreement with the phase transformation temperature (1273 K) in the experimental phase diagram.

Given the limitations of the materials available for photoelectrochemical water splitting, a multiphoton (tandem) approach is required to convert solar energy into hydrogen efficiently and durably. Here we investigate a promising system consisting of a hematite photoanode in combination with dye-sensitized solar cells with newly developed organic dyes, such as the squaraine dye, which permit new configurations of this tandem system. Three configurations were investigated: two side-by-side dye cells behind a semitransparent hematite photoanode, two semitransparent dye sensitized solar cells (DSCs) in front of the hematite, and a trilevel hematite/DSC/DSC architecture. Based on the current-voltage curves of state-of-the-art devices made in our laboratories, we found the trilevel tandem architecture (hematite/SQ1 dye/N749 dye) produces the highest operating current density and thus the highest expected solar-to-hydrogen efficiency (1.36% compared with 1.16% with the standard back DSC case and 0.76% for the front DSC case). Further investigation into the wavelength-dependent quantum efficiency of each component revealed that in each case photons lost as a result of scattering and reflection reduce the performance from the expected 3.3% based on the nanostructured hematite photoanodes. We further suggest avenues for the improvement of each configuration from both the DSC and the photoanode parts.

The deformation behavior of amorphous selenium near its glass transition temperature (31 °C) has been investigated by uniaxial compression and nanoindentation creep tests. Cylindrical specimens compressed at high temperatures and low strain rates deform stably into barrel-like shapes, while tests at low temperatures and high strain rates lead to fragmentation. These results agree well with stress exponent and kinetic activation parameters extracted from nanoindentation creep tests using a similarity analysis. The dependence of the deformation modes on temperature and strain rate can be understood as a consequence of material instability and strain localization in rate-dependent solids.

The structural evolution of the Ti40Zr10Cu34Pd14Sn2 bulk metallic glass (BMG) upon was investigated by means of in situ high-energy x-ray diffraction. The position, width, and intensity of the first peak in diffraction patterns are fitted through Voigt function below 800 K. All the peak position, width, and intensity values show a nearly linear increase with the increasing temperature to the onset temperature of structural relaxation, Tr = 510 K. However, these values start to deviate from the linear behavior between Tr and Tg (the glass transition temperature). The changes in free volume and the coefficient of volume thermal expansion prove that the aforementioned phenomenon is closely related to the structural relaxation releasing excess free volume arrested during rapid quenching of the BMG. Above 800 K, three crystallization events are detected and the first exothermic event is due to the formation of metastable nanocrystals.

The dynamic uniaxial compressive behavior of Zr-based metallic glasses under a wide high strain rate was studied by a miniaturized split Hopkinson pressure bar, including high strain rate up to 104 s−1. Experimental results indicate that the uniaxial compressive failure stress would decrease suddenly and then tend to hold steady with increasing strain rate. This phenomenon provides a generalized perspective for understanding the effect of local heat generation on the deformation of metallic glasses under dynamic loads.

The present work reports on the conditions of nanoparticle growth and splitting under energetic ion irradiation. Cohesive energy that determines the thermal stability of a given nanoparticle system was calculated by extending surface area difference (SAD) and liquid drop model (LDM). Based on the size-dependent cohesive energy calculations, the interparticle coalescence mechanism is discussed for a ZnS-based nanoparticle system with special reference to a variety of matrices. The interparticle separation is found to play key role in particle–particle coalescence leading to nanoparticle growth or partial evaporation that results in splitting.

Synchrotron x-ray μ-tomography has been used to reconstruct the three-dimensional view of a rough surface extracted from a heterogeneous ceramic coating composed of Pr2NiO4+δ. Radiographs with a resolution of 0.7 μm have been recorded at T = 300, 600, and 900 K. The analysis of surface geometry makes use of the geometrical optic approximation up to T = 900 K possible. Subsequently, a large number of rays (105) are impinged onto the numerical surface, as revealed by x-ray tomography, to reproduce the normal emissivity of the coating. This normal emissivity was obtained beforehand by infrared emittance spectroscopy at T = 1000 K. Comparison of the two approaches suggests that the optical contribution of the coating micropores can be integrated into the ray tracing code. The effective medium approximation is used for this purpose. Finally, the applicability of this hybrid approach is discussed.

In situ residual gas analyzer techniques were used to identify process-property relationships that regulate microstructure evolution in chemical solution-deposited BaTiO3 films. In situ analysis of furnace exhaust gasses enabled quantitative exploration of thermolysis and crystallization reactions and an ability to identify processing parameters that influence the temperature ranges over which they occur. The atmospheric analysis was instrumental in identifying heat treatments that produced optimally consolidated precursor gels that crystallized into BaTiO3 layers with optimized structure and properties. Slow ramp rates resulted in higher porosity, larger grain size, and a dramatic drop in the capacitor yield. Fast ramp rates produced similar trends; however, the mechanisms were distinct. The effects of oxygen partial pressure were also explored. BaTiO3 grain size increased with increasing pO2, whereas there was no appreciable influence on density and capacitor yield. Optimal firing parameters, i.e., 20 °C/min ramp rate at a pO2 of 10−13 atm, were identified as those that produced an overlap in the temperature ranges of thermolysis and crystallization reactions and thus a precursor gel with a density and compliance that supports crystallization and densification while tolerating the associated volume contraction. This in situ approach to analyze downstream furnace gas is shown to be a generically applicable means to understand synthesis methods that are complicated by simultaneous mechanisms of precursor decomposition, extraction of volatile components, and crystallization.

The effect of Pd concentration on the soldering reaction between Ni and Sn–xPd alloys (x = 0–0.5 wt%) was investigated in this study. When the Pd concentration was low (x ≤ 0.05 wt%), the predominant reaction product was a layer of Ni3Sn4. In contrast, an additional (Pd,Ni)Sn4 layer deposited over the Ni3Sn4 in the case of above 0.2 wt%. This microstructure evolution significantly weakened the strength of the interface, deteriorating the reliability of solder joints. A Pd–Ni–Sn isotherm simulated by the CALPHAD method was used to rationalize the above transition in the reaction product(s).

We used conductive-atomic force microscopy (c-AFM) for electrical characterization of self-assembled epitaxial iron silicide nanowires (NWs) on Si (110). The NWs, 6 nm high by 10 nm wide and several micrometers long, were partially covered by a macro-gold-pad as one electrode. Another electrode is the conductive AFM tip. The resistance of a single FeSi2 NW was measured to be 29.7 kΩ, corresponding to a resistivity of 150 ± 30 μΩ·cm. A Schottky barrier formed between NWs and silicon substrate was clearly demonstrated, which offers electrical isolation for NWs. An equivalent circuit model based on the Schottky barrier was proposed and was correlated with measurement results. This simple electrical characterization approach may find wide applications for various one-dimensional nanostructures.

In this paper we focus on indium oxide and indium iron oxide as an alloy to fabricate a protective thin film (transparent, conductive, and corrosion resistant; TCCR) for amorphous silicon-based solar cells, which can be used in immersion-type photoelectrochemical cells for hydrogen production. From the work completed, the results indicate that samples made at 250 °C with indium and indium iron oxide targets powered at 30 and 100 W, respectively, and a sputter deposition time of 90 min produced optimal results when deposited directly on single-junction amorphous silicon solar cells. At 0.65 V (versus SCE), the best sample conditions display a maximum current density of 21.4 μA/cm2.

Technological applications of high temperature superconductors (HTS) require high critical current density, Jc, under operation at high magnetic field strengths. This requires effective flux pinning by introducing artificial defects through creative processing. In this work, we evaluated the feasibility of mixed-phase LaMnO3:MgO (LMO:MgO) films as a potential cap buffer layer for the epitaxial growth and enhanced performance of YBa2Cu3O7-δ (YBCO) films. Such composite films were sputter deposited directly on IBAD-MgO templates (with no additional homo-epitaxial MgO layer) and revealed the formation of two phase-separated, but at the same time vertically aligned, self-assembled composite nanostructures that extend throughout the entire thickness of the film. The YBCO coatings deposited on these nanostructured cap layers showed correlated c-axis pinning and improved in-field Jc performance compared to those of YBCO films fabricated on standard LMO buffers. Microstructural characterization revealed additional extended disorder in the YBCO matrix. The present results demonstrate the feasibility of novel and potentially practical approaches in the pursuit of more efficient, economical, and high performance superconducting devices.

Following earlier work of Huggins and Nix [Ionics6, 57 (2000)], several recent theoretical studies have used the shrinking core model to predict intraparticle Li concentration profiles and associated stress fields. A goal of such efforts is to understand and predict particle fracture, which is sometimes observed in degraded electrodes. In this paper we present experimental data on LiCoO2 and graphite active particles, consistent with previously published data, showing the presence of numerous internal pores or cracks in both positive and negative active electrode particles. New calculations presented here show that the presence of free surfaces, from even small internal cracks or pores, both quantitatively and qualitatively alters the internal stress distributions such that particles are prone to internal cracking rather than to the surface cracking that had been predicted previously. Thus, the fracture strength of particles depends largely on the internal microstructure of particles, about which little is known, rather than on the intrinsic mechanical properties of the particle materials. The validity of the shrinking core model for explaining either stress maps or transport is questioned for particles with internal structure, which includes most, if not all, secondary electrode particles.

Application of high intensity electric pulse (HIEP) to a severely deformed eutectoid microstructure in high carbon steel wire has resulted in spheroidized microstructure. The observed spheroidization on electropulsing is compared with that reported for isothermal/thermo-mechanical annealing of the pearlite structure. The faster kinetics observed in this study has been rationalized in terms of accelerated kinetics induced by HIEP.