Here we study the effect of radiation-induced point defect distributions on the optical reflectivity signal in GaAs using coherent acoustic phonon spectroscopy. We demonstrate that the presence of point defects significantly modifies the optical response, allowing estimation of the depth-dependent defect distribution in a nondestructive and noninvasive manner. We show that the observed changes are dependent on defect-induced changes to the electronic structure, namely defect-induced band tailing of the direct 1.43eV band edge. This provides a method for subsurface investigations on the complex interaction between different defects species and optoelectronic structure.

We report the magnetic field splittings of emission lines assigned to the 5D0–7F2 transitions of Eu3+ centres in GaN. The application of a magnetic field in the c-axis direction (B ‖ c ) leads to a splitting of the major lines at 621 nm, 622 nm and 622.8 nm into two components. The Zeeman splitting is linear with magnetic field up to 5 Tesla for each line. In contrast, a magnetic field applied in the growth plane (B ┴ c ) does not influence the photoluminescence spectra. The estimated g-factors vary slightly from sample to sample with mean values of g‖ ~2.8, ~1.5 and ~2.0 for the emission lines at 621 nm, 622 nm and 622.8 nm respectively.

The effects of silanising using the coupling agent γ-glycidoxpropyltrimethoxysilane on microstructural stability and magnetic properties of Sm-Co powder particles have been investigated. The silanisation provides structural stability by improving the oxidation resistance at 400oC for 10 hours. The untreated particles undergo microchemical changes by redistribution of alloying elements which mainly accumulate in parallel black and grey streaks in the interior of the particles. The silanised particles after heat treatment show coercivity of 836 Oe and the untreated particles show a much lower coercivity of 376 Oe. The difference in magnetic properties of uncoated particles is caused by diffusion of oxygen and microstructural instability.

Cobalt hydroxide thin films with a thickness of 100 nm were deposited onto glass, Si and indium tin oxide (ITO)-coated glass substrates by reactively sputtering a Co target in H2O gas. The substrate temperature was varied from -20 to +200°C. The EC performance of the films was investigated in 0.1 M KOH aqueous solution. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy of the samples indicated that Co3O4 films were formed at substrate temperatures above 100°C, and amorphous CoOOH films were deposited in the range from 10 to -20°C. A large change in transmittance of approximately 26% and high EC coloration efficiency of 47 cm2/C were obtained at a wavelength of 600 nm for the CoOOH thin film deposited at -20°C. The good EC performance of the CoOOH films is attributed to the low film density and amorphous structure.

A new photonic structure was demonstrated to achieve strong optical coupling between nanoparticle and photonic molecule by utilizing a notched micro ring resonators. By creating a notch in the ring resonator and putting a nanoparticle inside the notch, large spectral shifts and splittings at nm scale can be achieved, compared to only pm scale observed by fiber tip evanescently coupled to the surface of microsphere, thereby significantly lowered the quality factor requirement for single nanoparticle detection. The ability for sorting the type of nanoparticles due to very different mode shift and splitting behavior of dielectric and metallic nanoparticles is also emphasized.

Cowpea chlorotic mottle virus (CCMV) has been a model system for virus studies for over40 years and now is considered to be a perfect candidate as nanoplatform for applicationsin materials science and medicine. The ability of CCMV to self assemble invitro into virus-like particles (VLPs) or capsids makes an ideal reactionvessel for nanomaterial synthesis and entrapment. Here we report expression of codonoptimized CCMV coat protein in Pichia pastoris and production of selfassembled CCMV VLPs by large-scale fermentation. CCMV coat protein gene (573 bp) wassynthesized according to codon preference of P. pastoris and cloned intopPICZA vector. The recombinant plasmid pPICZA-CP was transformed into P.pastoris GS115 by electroporation. The resulting yeast colonies were screenedby PCR and analyzed for protein expression by SDS-PAGE. After large-scale fermentationCCMV coat protein yields reached 4.8 g L−1. The CCMV VLPs were purified bymodified PEG precipitation followed by cesium chloride density gradientultracentrifugation, and then analyzed by size exclusion fast performance liquidchromatography (FPLC), UV spectrometry and transmission electron microscopy. Myoglobin wasused as a model protein to be encapsulated in CCMV VLPs. The fluorescence spectroscopyshowed that inclusion of myoglobin had occurred. The results indicated the production ofCCMV capsids by P. pastoris fermentation now available for utilization inpharmacology or nanotechnology fields.

Ion irradiation with 130 keV Ge+ or 120 keV Sb+ has modified, by thermal spike effect, the local atomic arrangement in the structure of as-deposited sputtered amorphous GeTe and Ge2Sb2Te5 thin films. The changes in the local order have been analyzed by Raman and EXAFS spectroscopy. In addition the crystallization kinetic, measured by “in situ” time resolved reflectivity and optical microscope analysis, is found to be faster in the irradiated samples. The nucleation rate and the grain growth velocity are enhanced by a factor of about ten with respect to the unirradiated samples in the investigated temperature range (120°C –170°C).

Nanocrystalline anatase titania thin films were prepared by using two different precursor solutions, a highly acid solution (Sol-1) and a polymer-like solution (Sol-2), via the dip-coating technique on different substrates (<100>-Si wafer, fused silica and soda lime glass). The influence of the two sol-gel titania precursor solutions and of the substrate type on the film morphology, coating porosity, surface roughness, crystalline phases and grain size of the titania films were investigated. Our experimental results clearly indicate that the sol - composition and substrate type remarkably influence the microstructural/morphological properties of the titanium dioxide. They consequently modify the optical response and hydrophilic performances of the samples. The photocatalytic oxidations of the methylene blue in water of the samples grown on the glass substrate were monitored to investigate the influence of the sol-gel precursor solution on the photocatalytic activity of the titania coatings, and the results were put in relation with the hydrophilic and optical properties of the films. The outcome demonstrates that the optical properties and the hydrophilic and photocatalytic performances of nanocrystalline titania can be opportunely tailored tuning the size dimension of the crystalline domain according to the specific coating applications.

Cobalt Ferrite/Barium Titanate nanotube arrays were obtained in anodic aluminum oxide templates (AAO) of 100 nm pore diameter by a two step sol-gel process. Each phase was grown in several wetting – drying cycles starting from the cobalt ferrite layers with the barium titanate on top. As-dried composite structures were sintered at 700 C. The composite nanotubes showed a fine polycrystalline microstructure with an average grain size of 5 nm. The formation of both spinel and perovskite structures was verified by High Resolution Transmission Electron Microscopy (HR-TEM) on isolated nanotubes. The growing rate by layer was found to be lower for the BaTiO3 on top of CoFe2O4 than the later on top of the AAO. Wall sizes were estimated by Z-contrast as 9.8 nm for one layer of CoFe2O4 and 6.6 nm for six layers of BaTiO3. Magnetic properties were studied by VSM. Samples showed ferromagnetic behavior with low coercive values. By means of a finite element model the deformation and stress on the piezoelectric phase was estimated and used to simulate the magnetization reversal under stress in the composite nanotubes, using an updated micromagnetic framework to include the magnetostriction effect. Simulation results showed that a curling mode is expected with opposite vortex states at the end of the nanotubes. The change in the vortex domain structure under voltage driven applied stress is presented and discussed.

Processing of transparent materials by non-linear absorption mechanisms induced by short pulse lasers has been applied in many fields. Silicon (Si) is widely used materials in microelectronics, MEMS and photonics. It is, however, not transparent for commonly used processing lasers in near infrared to ultraviolet spectral range and has not been a subject for the non-linear processing by lasers so far. In this paper, possibilities and capabilities of non-linear processing of Si by 900 fs, 1552nm laser radiation are described with special emphasis on application to frequency adjustment of a crystal oscillator in a package made from Si.

A self resonating bimorph cantilever structure for fast temperature cycling in a pyroelectric energy harvester has been modeled using finite element method. Effect of constituting material properties and system parameters on the frequency and magnitude of temperature cycling and the efficiency of energy recycling using the proposed structure has been investigated. Results show that thermal contact conductance and heat source temperature play a key role in dominating the cycling frequency and efficiency of energy recycling. Studying the performance trend with various parameters such as thermal contact conductance, heat source temperature, device aspect ratio and constituent material of varying thermal conductivity and expansion coefficient, an optimal solution for most efficient energy scavenging process has been sought.

We have recently developed an accurate and easily implemented approach to many-electron calculations, based on a modified Thomas-Fermi approximation. Specifically, we derived an electron density approximation, the first term of which is the Thomas-Fermi result, while the remaining terms substantially corrected the density near the nucleus. In a first application, we used the new density to accurately calculate the details of the self-consistent ion cores, as well as the ionization potentials for the outer s-orbital bound to the closed-shell ion core of the Group III, IV and V elements. Next, we demonstrated that the new density expression allows us to separate closed-shell core electron densities from valence electron densities. When we calculated the valence kinetic energy density, we showed that it separated into two terms: the first exactly cancelled the potential energy due to the ion core in the core region; the second was the residual kinetic energy density resulting from the envelopes of the valence electron orbitals. These features allowed us to write a functional for the total valence energy dependant only on the valence density. This equation provided the starting point for a large number of electronic structure calculations. Here, we used it to calculate the band structures of several Group IV and Group III-V semiconductors. We emphasize that this report only provides a summary; detailed derivations of all results are in Reference 5.

In this work, the deposition of boron using low pressure chemical vapor deposition (LPCVD) has been investigated on planar and deep reactive ion etched (DRIE) Si substrates. Deposition rate and conformal coverage have been studied. Additional studies of “dry” RIE etching and “wet” chemical etching of the deposited boron films are presented. Deposition rates as high as 1 μm/hr and conformal coverage ratios of ~80% have been achieved. Etching rates for various methods studied range widely from 0.35 μm/hr to 1.2 μm/min.

In this study, we use THz spectroscopy in the energy range between 45 GHz to 3000 GHz (1.5 cm-1 and 100 cm-1) as a non-destructive diagnostic tool to characterize the corrosion by-products (rust) on aged steel structural components that are usually embedded in concrete. The THz radiation has been shown to penetrate concrete with extinction coefficients between (1.0 to 2.3) x 10-2 GHz-1 cm-1, depending on the composition and the moisture content of the concrete. The previously reported antiferromagnetic resonance (AFR) near 140 GHz in iron oxide composites was found to be less than our current detection sensitivity (fractional absorbance sensitivity of >10%). However, a strong transition centered near 725 GHz (24 cm-1) has been observed for the first time. This feature has appeared in reflection from several different samples of mildly corroded steel plates and has been tentatively attributed to a broad phonon density of states commonly referred to as the “Boson peak” found in disordered materials. By taking advantage of this strong transition and a powerful excitation sources in the AFR region, we expect THz spectroscopy and imaging to be an effective diagnostic tool with broad applications in corrosion diagnostics and inspection.

A simple theoretical five-state Potts model for the investigation of magnetocaloric effect in systems with competing ferromagnetic and antiferromagnetic interactions has been proposed. It is shown that this simple model can be applied to the description of the origin of the negative and positive magnetocaloric effect in systems with competing interactions, for example, Heusler alloys.

The oxygen reduction reaction (ORR) mechanism of non-Pt catalysts was elucidated by investigating electronic structures of carbon alloy catalysts (CACs) for polymer electrolyte membrane fuel cells (PEMFC). For metal phthalocyanine-based carbon alloy catalysts with 1-2% of nitrogen and less than 0.1% of Co or Fe, photoelectron spectroscopy, X-ray absorption spectroscopy (XAS), and X-ray Absorption Fine Structure (XAFS) have revealed that Co or Fe metal sites are not the ORR active site, whereas the carbon atoms adjacent to graphitic nitrogens at a zigzag edge of graphite may act as the ORR active site, which is in good agreement with first principles calculations. These studies have also revealed that the zigzag edges, detected as a XAS shoulder component, are well evolved for catalysts pyrolyzed at 600°C, which show the maximum ORR activity. Based on these analyses, we have realized significantly improved carbon alloy based ORR performance, up to about 70 % of that with Pt catalysts. Further, to analyze the electronic structure of CACs during operation, we constructed a new in situ soft X-ray emission spectroscopy system with very high energy resolution (ΔE) of 120 meV at 640 eV at the University of Tokyo beamline BL07LSU in SPring-8.

A robust, stable and thin primary amine functionalization is applied to gold and silver nanoparticles from poly(allylamine hydrochloride) (PAH) by converting a fraction of the amine groups in the polymer to dithiocarbamate (DTC) ligands, which absorb strongly onto noble metal surfaces. We observe marked improvements in the properties of gold nanospheres with a DTC-anchored rather than physisorbed PAH cap. The same level of improvement is not seen in silver nanoparticles, although it is clear from a distinct change in the plasmon spectrum in silver nanocubes that the DTC ligand does interact with the silver surface. In spite of their amine functionalization, both silver and gold particles show low cytotoxicity, possibly due to absorption of serum proteins forming a protective coating on the positively charged particle surface.

Hysteresis is unattractive for magnetocaloric applications because it introduces loss in the cooling cycle. It is however usually associated with a first order transition and large entropy change. In this paper we review the sources of hysteresis in magnetocaloric materials and in particular in manganite systems where the nature of the transition in terms of whether it is indeed a first order transition remains elusive.