To update the status of knowledge on the recombination-enhanced dislocation glides (REDG) in semiconductors, which is one of the causes of serious degradation in bipolar devices, research progress achieved for the last decade has been surveyed. Rather than presenting a complete review over a wide range of material systems, a particular attention has been paid to the REDG effect in 4H-SiC for which a lot of information has been accumulated owing to extensive studies. Although the REDG effect exhibits features that could be interpreted in terms of the phonon-kick mechanism, conclusive proof is still lacking.

The coefficient of merit, ZT of nanostructured thermoelectric materials increases with reduction in thermal conductivity through phonon scattering. The ideal thermoelectric is considered to be an electron crystal and a phonon glass. This paper explores such a material concept by developing a theory for phonon localization in rough nanowires with crystalline cores. Results based on this theory suggest that the reported hundredfold decrease in thermal conductivity of rough silicon nanowires arises due to multiply scattered and localized phonons. Phonon localization presents a new direction to further enhance ZT through nanostructuring.

Low dislocation density epitaxial layers of AlxGa1-xN can be grown pseudomorphically on c-face AlN substrates prepared from high quality, bulk crystals. Here, we will report on initial characterization results from deep ultraviolet (UV) light emitting diodes (LEDs) which have been fabricated and packaged from these structures. As reported previously, pseudomorphic growth and atomically smooth surfaces can be achieved for a full LED device structure with an emission wavelength between 250 nm and 280 nm.

A benefit of pseudomorphic growth is the ability to run the devices at high input powers and current densities. The high aluminum content AlxGa1-xN (x∼70%) epitaxial layer can be doped n-type to obtain sheet resistances < 200 Ohms/sq/μm due to the low dislocation density. Bulk crystal growth allows for the ability to fabricate substrates of both polar and non-polar orientations. Non-polar substrates are of particular interest for nitride growth because they eliminate electric field due to spontaneous polarization and piezoelectric effects which limit device performance. Initial studies of epitaxial growth on non-polar substrates will also be presented.

We show that the fluorescence of peridinin-chlorophyll a-protein complexes can be strongly enhanced via coupling with plasmon excitations localized in metal nanostructures. The results of ensemble and single-molecule spectroscopy experiments at room temperature demonstrate six-fold increase of the emission intensity of the light-harvesting complex when it is placed in the vicinity of chemically prepared silver islands. Irrespective of the enhancement, we observe no effect of the metal nanoparticle on the fluorescence emission energy of the complex. This observation implies that plasmon excitations may be applied for controlling the optical properties of complex biomolecules.

Alport Syndrome is a genetic disease characterized by the breakdown of the glomerular basement membrane (GBM) around blood vessels in the kidney, leading to kidney failure in most patients. It is the second most inherited kidney disease in the US, and many other symptoms are associated with the disease, including hearing loss and ocular lesions. Here we probe the molecular level mechanisms of this disease utilizing a bottom-up computational materiomics approach focused on the mutation associated with the most severe form of Alport Syndrome. Since the GBM is under constant mechanical loading due to blood flow, changes in mechanical properties due to amino acid mutations may be critical in the symptomatic GBM breakdown seen in Alport Syndrome patients. Through full-atomistic simulations in explicit solvent, the effects of a single-residue glycine substitution mutation are studied in a short segment of a collagen type IV tropocollagen molecule. Major changes are observed at the single molecule level of the mutated sequence, including a bent shape of the structures after equilibration with the kink located at the mutation site and a significant alteration of the molecule’s stress-strain response and stiffness.

The efficiencies of hydrogenated polymorphous silicon (pm-Si:H) solar cells have been previously demonstrated to show superior stability under light-soaking. This stability arises due to the fact that the decrease they show in fill factor (FF) is partially offset by an accompanying increase in open circuit voltage (VOC ). Recently, high-deposition rate (9Å/s) pm-Si:H material deposited by standard RF-PECVD at 13.56MHz has been investigated as the intrinsic layer in photovoltaic modules as it has shown excellent electronic properties. The degradation behaviour of these high-deposition rate cells, however, differs significantly from that of lower deposition rate material. In particular, no beneficial increase in Voc is observed during light soaking. We investigate the degradation dynamics of solar cells made from this high growth rate material using a Variable Illumination Method (VIM) during light soaking to quantify the changes to these high-rate cells during light-soaking and directly contrast them with those of low-rate (1.5Å/s) cells. In particular, we discuss the importance of bulk recombination effects vs interface quality changes, as well as the dynamics of changes in VOC .

Spectroelectrochemistry was used to study the electron trapping and rectifying behavior in several diphenylamine endgroup polymeric bilayers. Various combinations of the following monomers were pairwise sequentially electropolymerized onto ITO transparent electrodes: FD, DNTD, DPTD and Cl4DPTD. Poly(FD) is a p-type material while poly(DNTD), poly(DPTD) and poly(Cl4DPTD) are bipolar materials being both n-type and p-type. Bilayers of ITO|poly(FD)|poly (DNTD) or ITO|poly (FD)|poly (DPTD), block electrons from reducing the outer layer even at -1.0 V vs Ag/AgCl, yet holes effectively oxidize both layers. The LUMO differences between poly(DNTD) and poly(Cl4DPTD) or poly(DPTD) and poly(Cl4DPTD) provide a large enough electronic barrier that electron trapping can occur between these n-type materials. The visible spectra results imply that these polymers, poly(DPTD) or poly(Cl4DPTD) can be used as photovoltaic materials.

Silicon nanowire arrays grown by chemical vapour deposition were successfully integrated into functional photovoltaic devices. A crucial planarization step, achieved by embedding the nanowires in a spin-on glass matrix and subsequent polishing of the front surface, allowed to deposit a continuous and uniform conductive film on top of the nanowire array, and thus to form a high-quality front electrical contact. The silicon nanowire array solar cells fabricated using this process exhibited a parasitic series resistance as low as 5 Ω.cm2, which is a clear improvement compared to the recent literature.

Light trapping effect in hydrogenated amorphous silicon-germanium alloy (a-SiGe:H) and nano-crystalline silicon (nc-Si:H) thin film solar cells deposited on stainless steel substrates with various back reflectors is reviewed. Structural and optical properties of the Ag/ZnO back reflectors are systematically characterized and correlated to solar cell performance, especially the enhancement in photocurrent. The light trapping method used in our current production lines employing an a-Si:H/a-SiGe:H/a-SiGe:H triple-junction structure consists of a bi-layer of Al/ZnO back reflector with relatively thin Al and ZnO layers. Such Al/ZnO back reflectors enhance the short-circuit current density, Jsc, by ˜20% compared to bare stainless steel. In the laboratory, we use Ag/ZnO back reflector for higher Jsc and efficiency. The gain in Jsc is about ˜30% for an a-SiGe:H single-junction cell used in the bottom cell of a multi-junction structure. In recent years, we have also worked on the optimization of Ag/ZnO back reflectors for nano-crystalline silicon (nc-Si:H) solar cells. We have carried out a systematic study on the effect of texture for Ag and ZnO. We found that for a thin ZnO layer, a textured Ag layer is necessary to increase Jsc, even though the parasitic loss is higher at the Ag and ZnO interface due to the textured Ag. However, a flat Ag can be used for a thick ZnO to reduce the parasitic loss, while the light scattering is provided by the textured ZnO. The gain in Jsc for nc-Si:H solar cells on Ag/ZnO back reflectors is in the range of ˜60-75% compared to cells deposited on bare stainless steel, which is much larger than the enhancement observed for a-SiGe:H cells. The highest total current density achieved in an a-Si:H/a-SiGe:H/nc-Si:H triple-junction structure on Ag/ZnO back reflector is 28.6 mA/cm2, while it is 26.9 mA/cm2 for a high efficiency a-Si:H/a-SiGe:H/a-SiGe:H triple-junction cell.

We perform ab-initio computations to investigate the family of CoSb3 skutterudites in an attempt to develop deeper understanding of the effect of fillers. Primary focus is on Ba-filled CoSb3 systems, while Ca and Sr-filled systems are also compared for checking consistency. We analyze both global and local structural effects of filling. We show the specific deformation of Sb network introduced by the filler. Such a deformation is localized around the filler site since soft Sb rings accommodate the distortion. Rearrangement of Sb atoms affects the band structures, and we perform additional analysis to clarify the effect of volume on the band gap. Phonon dispersions are briefly discussed, and filler-dominated vibrations are identified. These modes form the first optical modes at Γ. They manifest themselves in phonon dispersion curves as flat lines, showing that they are localized, while filler vibration is strongly coupled with nearby Sb atoms.

Optical and schottky diode characteristics of unintentionally doped GaN films grown by MOCVD were reported. GaN epilayers were grown with different V/III ratio by varying the source ammonia (NH3) flowrate. It exhibit changes in the density of threading dislocations (TDs) and reduced carbon and oxygen impurity incorporation. The density of dislocations determined from hot-wet chemical etching and atomic force microscopy show that on decreasing the ammonia flowrate, threading dislocations decreases. Low energy positron beam was employed to study the Ga vacancies in the epilayers. S-parameter vs. positron beam energy curves clearly shows increase in SL on increasing the V/III ratio indicating that the point defects trapping positron increases. Corroborative HRXRD, Photoluminescence and Hall measurements confirm the reduction in trapping defects and threading edge dislocations with reducing V/III molar ratio. The effects of such variation of compensating centres and radiative centres as a function of MOCVD growth conditions on optical properties and schottky device characteristics like radiative decay lifetime, barrier height and reverse leakage current respectively were discussed.

Semiconductors or metal nanoparticles (NPs) using their monolayer bindings with self-assembly chemicals are an attractive topic for device researchers. Electrical performance of such structures can be investigated for a particular application, such as memory device. Currently, Au NPs has been reported to show a substantial potential in the memory applications. In this study, Au NP and gluing layer were fabricated through a new method of monolayer formation of a chemical bonding or gluing.In this study, a new NPs memory system was fabricated by using organic semiconductor, i.e., pentacene as the active layer, evaporated Au as electrode, SiO2 as the gate insulator layer on silicon wafer. In addition, Au NPs coated with binding chemicals were used as charge storage elements on an APTES (3-amino-propyltriethoxysilane) as a gluing layer. In order to investigate chemical binding of Au NP to the gate insulator layer, GPTMS (3-glycidoxy-propyltrimethoxysilane) were coated on the Au NPs. As a result of that, a layer of gold nanoparticles has been incorporated into a metal-pentacene-insulator-semiconductor (MPIS) structure. The MPIS device with the Au NP exhibited a hysteresis in its capacitance versus voltage analysis. Charge storage in the layer of nanoparticles is thought to be responsible for this effect.

Nanoparticles were incorporated into poly(methyl methacrylate) matrix by the mean of in situ bulk polymerization. Particle chemistry, size, shape, and percent loading were experimental variables in the synthesis and mechanical properties were assessed, particularly impact resistance, which showed improvement at the optimal particle loading. In assessing the mechanisms of this improvement, the elongated shape of zinc oxide particles appears to promote crack deflection processes to introduce a pull-out mechanism similar to that observed in fiber composite systems. Raman spectroscopy was performed to examine the effect of polymer chain conformation and configuration with the addition of nanoparticles.

Radiation damage and the effect on physical and chemical properties is an important component in the prediction of the long-term stability of waste form materials. As part of the ongoing goal of increasing the accuracy of long-term predictions of radiation damage, two types of material, based on proposed materials with a waste form application have been irradiated. Results have shown that Y2TiO5 (Y2.67Ti1.33O6.67), and Yb2TiO5 (Yb2.67Ti1.33O6.67), both of which are non-stoichiometric, disordered pyrochlore-based compounds, behave significantly different to the stoichiometric, ordered pyrochlore equivalent. For example the critical temperature, the temperature above which materials remain crystalline during irradiation, is found to decrease from the ordered equivalents, e.g. Y2Ti2O7. A second material based on La2TiO5 has been found to behave differently to both La2/3TiO3 and La2Ti2O7, with a change in Tc of ∼ 200 K.

An Al58Cu25Fe17 alloy composition was produced by conventional casting technique. In order to take advantage from the hydrogen-environmental embrittlement reaction, which affects these alloys, this research was carried out subjecting prealloyed powders to wet-ball milling. Through these experiments it has been possible to evaluate the particle size reduction as consequence of hydrogen fracture and milling energy. The morphological and structural characteristics of the samples were performed using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The experimental results indicate that the samples with higher contents of humidity have a good particle size reduction. With the increment of milling time, the particle size was diminished even more reaching nanometer size scale.

This work focuses on the development of a new bio-inorganic nanocomposite glucose-responsive membrane to be applied as a single self-regulated platform for insulin delivery. Crosslinked bovine serum albumin (BSA)-based membranes were prepared containing impregnated pH-responsive poly(N-isopropyl acrylamide-co-methacrylic acid) nanoparticles (hydrogel NPs), glucose oxidase (GOx), catalase (CAT), with or without MnO2 NPs. The membrane acts as a glucose sensor and insulin release attenuator. In this system glucose is oxidized by GOx to produce gluconic acid, which regulates the permeability of the membrane to insulin. CAT and/or MnO2 NPs are introduced into the membrane in order to quench unwanted H2O2 produced by GOx turnover cycles, which can cause inactivation of GOx and toxicity. The glucose-modulated insulin release through the membrane is determined by alternating glucose concentration between 100 – 400 mg/dL (normal and hyperglycemic levels, respectively). The results show that the combination of CAT and MnO2 NPs in the membrane formulation leads to better efficiency in quenching the H2O2 and better long-term stability of GOx than using either alone. Very small amounts of insulin permeate though the membrane at the normal blood glucose level while a four-fold increase in the release rate is observed when glucose concentration is raised to a hyperglycemic level. The release rate of insulin drops when the glucose level is reduced to a normal value. These results demonstrate the self-regulated capability of the system.

We have recently developed a self consistent light-emitting diode (LED) model that accounts for the current transport and internal heating in AlGaAs-GaAs LEDs. In this paper we extend the model to describe multi-quantum well (MQW) active regions and III-N materials, within the limits of the currently known values and temperature dependencies of the recombination parameters in these materials. The MQW description accounts for the effect of the reduced wave function overlap to the recombination. We present simulation results obtained for an InGaN MQW LED with 4 wells at selected temperatures and discuss the factors limiting the efficiency and luminescent output of LEDs.

Discrete current switching is induced in carbon nanotubes by electron beam irradiation. Switching amplitudes of 3% to 6% are observed at room temperature. Switching is created by electron beam exposure with dosage as low as 1000 pC/cm. Relative switching amplitude remains constant as the bias voltage varies, suggesting that current fluctuation is dominated by mobility fluctuation. Changes in the noise power spectral density following electron beam exposure will be discussed.

This study investigates bactericidal activities of dental porcelain contained silver/cerium/titania against streptococcus mutans in different irradiations, then the effect of modified titanium dioxide on rheological behavior of dental porcelain slurries is studied for rapid prototyping applications. The results show that the silver/cerium/titania has much higher antibacterial efficiency than that of pure TiO2 either in the room light or under the dark. It is potential to apply this photocatalyst in the dental materials for preventing human teeth from caries because the oral cavity is mostly under dark, partly in the visible light. The modified titanium dioxide not only has a antibacterial effect, but also can improve the rheological behavior of dental porcelain slurries for rapid prototyping applications.

Transmission electron microscopy (TEM) and specialized dislocation-density based crystal-plasticity formulations and finite-element schemes were used to investigate the effects of nano-sized precipitates and micro-sized Mn-bearing particles on the behavior of Al-Cu-Mg-Ag alloys. By accurately representing crystallography and the morphology of the different precipitates, accurate predictions can be obtained that indicate that the nano-sized Ω and θ’ precipitates promote ductility and toughness by inhibiting shear-strain localization; whereas the micro-sized dispersed particles intensify localization. Collectively, the precipitates and dispersed particles, however, promote the strengthening of the alloy.