Light trapping in microcrystalline silicon thin-film solar cells with integrated lamellar gratings was investigated. The influence of the grating dimensions on the short circuit current and quantum efficiency was investigated by numerical simulation of Maxwell’s equations by a Finite Difference Time Domain approach. For the red and infrared part of the optical spectrum, the grating structure leads to scattering and higher order diffraction resulting in an increased absorption of the incident light in the silicon thin-film solar cell. By studying the diffracted waves arising from lamellar gratings, simple design rules for optimal grating dimensions were derived.

As in our previous work [1] nanoporous silicon periodic supercells with 1000 atoms but now with 80 % porosity were constructed using the Tersoff potential and our novel approach [2]. The approach consists first in constructing a crystalline diamond-like supercell with a density (volume) close to the real value, and then lowering the density by increasing the volume, subjecting the resulting periodic supercell to Tersoff-based molecular dynamics processes at a temperature of 300 K, followed by geometry relaxation [1]. As in the ab initio approach [2] the resulting samples are also essentially amorphous and display pores along some of the crystallographic directions. We report the radial (pair) distribution function (RDF), g(r), the bond angle distribution, the pore structure where prominent and a computational prediction for the vibrational density of states for this structure. We then compare it to the 50 % porous sample presented in Ref [1]. The soft acoustic phonons are displaced towards lower energy in the 80 % porosity sample whereas the optical modes are displaced towards higher energies. The pseudo gap, existing in the 50 % porous sample, is depleted even more in the 80 % sample indicating a tendency towards the creation of a phonon gap for higher porosity materials. Some conjectures that point to the possible engineering of porous materials to produce predetermined phonon properties are discussed.

Experiments on determination of operational effectiveness of track membranes with different diameter of pores (0.2 – 0.05 microns) for additional purification of water of the first contour of the reactor before ion-exchange resins were carried out. The track membranes detain products of corrosion, and also products of wearing of moving parts of the equipment by the size of > 0.05 microns. Filtration experiments on of water of the first contour of the exploratory reactor of VVR-SM have shown high performance of track membranes.

Several wet-processing steps are used in fabricating high-efficiency CdTe/CdS solar cells. These steps can hinder in-line processing; thus, developing an all-dry processing option is attractive for a manufacturing-friendly process. In this study, we systematically modified the baseline process used in our laboratory to replace CdS deposited by chemical-bath deposition (CBD) with sputter-deposited CdS and Cu-doped graphite paste back-contact with Cu-doped ZnTe deposited by radio-frequency sputtering. In addition to CdTe deposited by close-spaced sublimation, we also used conventionally evaporated CdTe. The results show that replacing only CBD CdS with oxygenated CdS deposited by sputtering produces devices with performance comparable to baseline devices if the front bilayer SnO2 is replaced by a Cd2SnO4/ZnSnO alloy. Replacing the graphite paste back-contact with sputter-deposited Cu-doped ZnTe resulted in device performance comparable to baseline devices. Incorporating both dry processing steps gave performance comparable to the devices with sputtered CdS with a SnO2 front contact. We used capacitance-voltage and minority-carrier lifetime measurements to analyze the factors affecting device performance and we present the results here.

Electric-induced resistance switching (EIRS) effect based on transition metal (TM) oxides, such as perovskite manganites (Pr1-xCaxMnO3, La1-xCaxMnO3) and binary oxides (NiO, TiO2 and CoO) etc, has attracted great interest for potential applications in next generation nonvolatile memory known as resistance random access memory (RRAM). Compared with other nonvolatile memories, RRAM has several advantages, such as fast erasing times, high storage densities, and low operating consumption. Up to date, the switching mechanism, property improvement and new materials exploitation are still the hotspots in RRAM research.

In this report, the main results of resistance switching of two kinds of TM oxides including La0.7Ca0.3MnO3 and TiO2 were presented. Based on the I-V characteristics, the field-direction dependence of resistance switching (RS) behavior, and the conduction process analysis, the EIRS mechanisms were studied in detail. For the La0.7Ca0.3MnO3 film, the EIRS mechanism was related to the carrier injected space charge limited current (SCLC) conduction controlled by the traps existing at the interface between top electrode and La0.7Ca0.3MnO3 film. The RS behavior is produced by the trapping/detrapping process of carriers under different voltages. For the TiO2 film, both unipolar and bipolar RS behavior can be obtained in our experiments. The interface controlled filamentary mechanism was proposed to explain the unipolar EIRS in nanocrystalline TiO2 thin films, while the bipolar RS behavior may be related to the charge trapping or detrapping effect. In addition, it was confirmed that the I-V sweeps in vacuum environment, the applying of asymmetry pulse pairs and the oxygen annealing of films can improve the endurance of the EIRS devices. Our researches will provide some meaningful clues to understanding the EIRS mechanism and some useful pathways for the development of RRAM devices.

In 2008, AREVA NC Industrial Vitrification of High-Level Liquid Waste blows out its 30th candle, with always two main objectives during all the time: containment of the long lived fission products and reduction of the final volume of waste. During all this time AREVA with the French Atomic Energy Commission (CEA) developed and use in their industrial installations a selection of borosilicate glass that have been demonstrated as the most suitable containment matrix for waste from spent nuclear fuel. Consistent and long-term R&D programs associated to industrial feed back from operation have enabled continuous improvement of the process: throughput and waste loading factor enhancement. The Vitrification Process used and currently implemented in the AREVA facilities will be described.

The α-, β-, and δ-MnO2 with various morphologies have been synthesized by a novel redox system of KMnO4 and CuCl with HCl added under a hydrothermal condition. The resultant MnO2 products have been characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Upon control of reaction temperature and duration, it was observed that MnO2 polymorphs of different morphology (e.g., flowery δ-MnO2, β-MnO2 nanowires and octahedrons, α-MnO2 nanowires) can be prepared in an adjustable manner. The phenomenon is mainly attributed to the effect of cuprous ions controllably released from CuCl by the action of HCl at different experimental conditions. The corresponding formation mechanism for the MnO2 crystals will also be proposed and discussed.

We report on the heteroepitaxial growth of high-quality single crystal cubic ZnxMg1-xO and NiyMg1-yO thin films by radio frequency oxygen plasma-assisted molecular beam epitaxy (RF-MBE). Film compositions over the ranges x = 0 to x = 0.65 and y = 0 to y = 1 have been grown on lattice-matched MgO (100) and characterized optically, morphologically, compositionally, and electrically. Both of these ternary materials are shown to have bandgaps which vary directly as a function of transition metal (Ni or Zn) concentration. Optical transmission measurements of NiyMg1-yO show the bandgap to shift continuously over the approximate range 3.5 eV (for NiO) to 4.81 eV (for y=0.075). Similarly, the bandgap of cubic ZnxMg1-xO is shifted from about 4.9 eV (for x = 0.65) to 6.25 eV (for x=0.12). Films exhibit good morphological quality and typical roughness of NiyMg1-yO films is 5 Å while that of ZnxMg1-xO is less than 15 Å, as measured by atomic force microscopy (AFM). X-ray diffraction (XRD) is employed to confirm crystal orientation and to determine the films' lattice constants. Film compositions are interrogated by Rutherford Backscattering (RBS) and electrical characterization is made by room-temperature Hall measurements.

A theory of non-crystalline recombination junctions is developed and compared to the experimental data. Junction transport is represented as hopping in both real and energy spaces, dominated by rare yet exponentially effective optimum channels having favorable configurations of localized states. Our work correlates the current-voltage characteristics of non-crystalline devices with material parameters and predicts large non-ideality factors increasing under light, and possible variations between nominally identical devices.

Exploring the cell-material interface is an emerging area of great interest in biomaterial science. Specifically, creating nanostructured surface interfaces to improve biomaterial efficacy is one of these key focus topics. As an example, an increasing number of studies have demonstrated the positive role nanostructured surfaces can have towards promoting various cell functions. However, the relevant mechanism behind this improvement in biological interactions at the cell-implant interface is not well understood. For this reason, here, osteoblast (bone forming cells) and fibroblast (fibrous, soft tissue forming cells) functions (including adhesion and proliferation) on two carefully fabricated diamond films with dramatically different topographies were tested. The results revealed greater cell responses on nanocrystalline diamond (grain sizes <100nm) compared to submicron crystalline diamond (grain sizes 200˜1000nm). In order to understand this positive impact of diamond nanotopography on cell responses, fibronectin absorption and subsequent cell spreading were studied. More importantly, cell filopodia extensions were also studied through computational mechanical modeling. A deflection-diffusion model of cell filopodia extension was established and clearly suggested that increasing the lateral dimension or height of nanometer surface features could inhibit cell filopodia extension and decrease cell spreading. Both the experiments and modeling from this study indicated that a nanometer surface topography can enhance cell responses to promote implant efficacy.

Manufacturers of modern high performance military and commercial electronics are steadily increasing the power density of the components of their devices. The increase of small component size and/or higher power densities results in large component heat flux levels. In applications from laser diodes, radar transmit/receive (T/R) modules and LED lighting, solutions to thermal issues through advancements in heat spreaders and heat sink design are needed to continue the performance improvement of these devices and structures.

Advanced materials for heat spreaders should have high thermal conductivity, a coefficient of thermal expansion (CTE) that matches the electronics die, and a reasonable cost. Diamond, for example, has the highest thermal conductivity of any known solid material at room temperature, combined with a high modulus of elasticity, but has a CTE mismatch with silicon (die material) and a high relative cost.

As an alternative material, PYROID® HT pyrolytic graphite has a thermal conductivity of 1700 W/m °K in the x-y plane of the material (7 W/m °K in the z plane), costs more than 250 times less than diamond produced by chemical vapor deposition (CVD), and has a modulus of elasticity much lower than diamond. The lower modulus of elasticity of this material results in an order of magnitude lower thermal stress level between the spreader and the die than diamond.

In one case study involving a laser diode cooling application, the spreader/die is nearly two-dimensional. Thus, pyrolytic graphite can be oriented with high conductivity in the direction into the spreader and away from the die (x-y plane), and the low conductivity direction (z direction) along the die where minimal conduction is needed. For the cases where a three-dimensional spreader is required, laminated composite structures of pyrolytic graphite have been developed where the equivalent isotropic conductivity is over two times greater than the conductivity of copper. The graphite layers are metallized so that they can be bonded together by soldering and/or dies can also be attached by soldering. The adhesion of the metal layers to the graphite has been tested with several standard techniques. Graphite metallization techniques, thermal performance modeling and analysis of stress levels due to CTE mismatching will be discussed in this paper.

The CdTe thin film module technology can be considered mature for large scale application.

First Solar is now capable of producing more than 400MW/year of CdTe modules and it is still increasing its production. First Solar also announced that they can get a production cost close to 1$/W. A further cost reduction will render this kind of energy production competitive with the energy obtained from fossil fuels.

In our laboratory we developed a novel dry process that could further reduce the production cost.

This process is now being used by a new company (Arendi Spa) in a line that will produce ∼15-18MW/year. Half of the line has been already built and the complete line should be ready in July 2009. The module production will start at the end of 2009.

Several hydrides of Nd2Ni2In with various H concentrations up to 6 H atoms/f.u. have been synthesized. Nd2Ni2In crystallizes in the tetragonal Mo2FeB2 structure type which can be changed upon hydrogenation to an orthorhombic structure, space group Pbma. The unit-cell volume increases by 15.5 % for Nd2Ni2InH4.5 and by 21.6 % for Nd2Ni2InH6. The triangular rare-earth lattice can give rise to magnetic frustration in case of antiferromagnetic interactions in Nd2Ni2In. The frustration is removed upon hydrogenation due to the orthorhombic distortion. The magnetic ordering temperature decreases with H concentration from 8 K in Nd2Ni2In down to 3.5 K in Nd2Ni2InH6.

We have developed an experimental set-up based on time-resolved Magneto-Optical Kerr Effect (MOKE) that allows to retrieve the vectorial magnetization dynamics in thin films with sub-picosecond resolution. This method has been exploited to measure the variations of the magnetization (modulus and orientation) induced by an ultrashort laser pulse. The initial demagnetization is established at the electronic level within a few hundreds of femtoseconds through electron-magnon excitations. The subsequent dynamics is characterized by a precessional motion on the 100 picosecond time-scale, around an effective, time-dependent field. Following the full dynamics of the magnetization, we have unambiguously determined the temporal evolution of the magneto-crystalline anisotropy, providing the clear experimental evidence that the precession is triggered by the rapid, optically-induced misalignment between the magnetization vector and the effective field. This method provides a simple and widely applicable way to study both magnetization and anisotropy in the sub-picosecond regime and therefore to unravel the mechanisms underlying the ultrafast evolution of the spin order in magnetic media.

Changes in protein glycosylation have great potential as markers for the early diagnosis of cancer and other diseases. The current analytical tools for the analysis of glycan structures need expensive instrumentation, advanced expertise, is time consuming and therefore not practical for routine screening of glycan biomarkers from human samples in a clinical setting.

We are developing a novel ultrasensitive diagnostic platform called ‘NanoMonitor’ to enable rapid label-free glycosylation analysis. The technology is based on electrochemical impedance spectroscopy where capacitance changes are measured at the electrical double layer interface as a result of interaction of two molecules.

The NanoMonitor platform consists of a printed circuit board with array of electrodes forming multiple sensor spots. Each sensor spot is overlaid with a nanoporous alumina membrane that forms a high density of nanowells. Lectins, proteins that bind to and recognize specific glycan structures, are conjugated to the surface of nanowells. When specific glycoproteins from a test sample bind to lectins in the nanowells, it produces a perturbation to the electrical double layer at the solid/liquid interface at the base of each nanowell. This perturbation results in a change in the impedance of the double layer which is dominated by the capacitance changes within the electrical double layer.

The nanoscale confinement or crowding of biological macromolecules within the nanowells is likely to enhance signals from the interaction of glycoproteins with the lectins leading to a high sensitivity of detection with the NanoMonitor as compared to other electrochemical techniques.

Using a panel of lectins, we were able to detect subtle changes in the glycosylation of fetuin protein as well as differentiate glycoproteins from normal versus cancerous cells. Our results indicate that NanoMonitor can be used as a cost-effective miniature electronic biosensor for the detection of glycan biomarkers.

Organic materials are attractive for photovoltaics primarily because of the prospect of high throughput solution-processible manufacturing using roll-to-roll or spray deposition. In the formation of polymer based photovoltaic devices, the aspect that limits the power conversion efficiency is the bottleneck between short diffusion lengths of the excited states (excitons) in polymers, in the range of 10-20 nm. Optical absorption length, which is in the range of 50-200 nm and much larger than the exciton diffusion length, poses the limit on charge generation and collection. It is important to achieve complete optical absorption in active layers much thinner than optical absorption length to minimize losses due to recombination of charge carriers. Previously, light trapping techniques have been coupled with organic solar cell but without significant success. In this paper, three-dimensional sub micron grating structure is analyzed using finite element method (FEM) simulations for finding the optical absorption in different layers of solar cell to optimize the photonic concentrator effect of the grating structure. The energy dissipation of electromagnetic field in the active layer is studied as a function of active layer thickness, grating pitch and height. The superiority of grating structure in terms of light trapping feature as compared to planar geometry is clearly demonstrated by simulation results.

Distributed Bragg Reflectors (DBRs) remain critical to the fabrication of various nitride based optoelectronic devices. In particular, DBRs are often employed for cavity formation in Resonant Cavity Light Emitting Diodes (RCLEDs) to enhance and obtain a more directional emission and also in Vertical Cavity Surface Emitting Lasers (VCSELs). As a result, epitaxially grown reflectors are attractive for direct integration in the device, reduced processing requirements, and the formation of narrow cavities. In the III-Nitride material system, Aluminum Nitride (AlN) and Gallium Nitride (GaN) offer a large contrast in refractive index and are therefore well suited for fabricating DBRs with high reflectivity and wide bandwidths using relatively few periods. However, material cracking arising from to the 2.4% lattice mismatch and difference in thermal expansion coefficient decreases reflectivity and is detrimental to the efficiency of subsequent device fabrication. Several techniques, such as superlattice insertion layers or the growth of AlxIn1-xN layers, have been employed to reduce strain and cracking in such structures. In this work, results of the use of indium as a surfactant in the Metal Organic Vapor Phase Epitaxy (MOVPE) of AlN/GaN DBRs will be discussed. Specifically, this study targets AlN/GaN DBRs with peak reflectivity at ranging from 465 nm to 540 nm. Indium has been used as a surfactant during growth by introducing trimethylindium into the system. It has been shown that crack formation is dependent on the flow of the indium precursor despite minimal indium incorporation into the lattice. Image processing techniques were used to quantify the crack length per square millimeter and it was observed that indium has a significant effect on the crack formation and can be used to reduce the total crack length in these structures by a factor of two.

Ion-beam induced etching and deposition rates are proportional to the flux of recoils reaching the surface. Based on this finding we propose an improved algorithm for etching and deposition simulations. In this algorithm the recoil flux at each point on the surface is calculated by summing up the recoil fluxes originating from ions impinging on any other surface point. The latter are determined by interpolation in tables calculated by binary collision simulations. For concave surfaces a correction to this algorithm is proposed. Fluxes calculated by this model are in good agreement with binary collision simulations of collision cascades in the same 2-d structure. Consistent with experimental findings, the model predicts that deposited pillars are broader than the ion beam, while etched trenches do not show such broadening. The pillar broadening is related to the lateral straggling of the recoils.

Carbon nanocones are the fifth allotropic form of carbon, first synthesized in 1997. They have been selected for investigating hydrogen storage capacity, because initial temperature programmed desorption experiments found a significant amount of hydrogen was evolved at ambient temperatures. The aim of this work was to study the effect of impregnation conditions on metal catalyst dispersion and to investigate whether the metal loaded cones had improved hydrogen storage characteristics. Pre-treatment of carbon nanocones with hydrogen peroxide was carried out, followed by metal decoration in aqueous solution by an incipient wetness technique. Two methods of reducing the metal catalyst have been applied: in hydrogen at room temperature (RT) and in an aqueous solution of NaBH4. XRD confirmed the complete metal reduction and TEM showed that the reduction technique affected the catalyst dispersion. Very fine dispersions of ca. 1 nm diameter metal clusters at catalyst loadings of 5 wt.% were achieved and high dispersions were retained for loadings as high as 15 wt.%. Hydrogen uptakes at RT were measured and an increase with metal loading was observed.

We present analysis of thermal stability of thin GdScO3 films grown on silicon and InAlN/GaN substrates. The GdScO3 films were prepared by liquid injection metal organic chemical vapor deposition at 600 °C. The films were processed after deposition by rapid thermal annealing in nitrogen ambient at 900, 1000 and 1100 °C during 10 s. In addition, annealing of the GdScO3 films on InAlN/GaN substrate at 700 °C during 3 hours was performed. The samples were analyzed by grazing incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectroscopy (ToF SIMS). GIXRD confirmed that the as-deposited GdScO3 films were amorphous. Recrystallization of the films on both substrates occurred at 1100 °C. ToF SIMS depth profile of the films annealed at 1000 °C indicated strong reaction of the GdScO3 film with the Si substrate. For the InAlN/GaN substrate rapid thermal annealing at 900 °C induced diffusion of the In and Al atoms into the top GdScO3 layer. Thermal treatment at 700 °C for 3 hours presents upper limit of the acceptable thermal budget for the GdScO3/InAlN interface.