In the nip or substrate configuration thin film silicon solar cells, the choice of front TCO contact is critical because there is a trade off between its transparency which influences the current in the solar cell and its conductivity which influences the series resistance. Here, we investigate the optical behavior of two different TCO front contacts, either a 70 nm thick, nominally flat ITO or a 2 μm thick rough LPCVD ZnO. The back contact consists of LP-CVD ZnO with random texture. First we investigate the influence of the rough and flat front TCOs in μc-Si:H and a-Si:H solar cells. With the back contact geometries used in this work, the antireflection properties of ITO are effective at providing as much light trapping as the rough LP-CVD ZnO. In the second part, we demonstrate that total of 25 to 26 mA/cm2is achievable in nip micromorph tandem cells and show short circuit current up to 11.7 mA/cm2 using an SIO based intermediate reflector.

Silicon-germanium (Si1−x Gex :H) thin films have been prepared by plasma enhanced chemical vapor deposition of SiH4 and GeH4 and measured during growth using real time spectroscopic ellipsometry. A two-layer virtual interface analysis has been applied to study the structural evolution of Si:H films prepared in multistep processes utilizing alternating intermediate and low H2-dilution material layers, which have been designed to produce predominately amorphous films with a controlled distribution of microcrystalline particles. The compositional evolution of alloy-graded a-Si1−x Gex :H has been studied as well using similar methods. In each case, depth profiles of microcrystalline content, f μc , or Ge content, x, have been extracted. Additionally, real time spectroscopic ellipsometry has been used to monitor post-deposition exposure of a-Si:H, a-Si1−xGex:H, and a-Ge:H films to a hydrogen plasma in situ in order to determine sub-surface amorphous film modification similar to that which would occur when a highly H2-diluted layer is deposited on a layer prepared with lower dilution. These analyses provide guidance for enhanced performance of Si:H based solar cells, through controlled bandgap grading using compositionally graded amorphous binary alloys (a-Si1−xGex :H) or the incorporation of controlled fractions of microcrystallites into bulk amorphous i-layer materials, and by providing a fundamental understanding of the modification of component layers during the deposition of subsequent layers in multilayer stacks.

This is the first submission

Performances of AlGaN/GaN HFETs have much improved recently and very high potential of this hetero- structure for high power and high frequency electronic devices has been verified. Application of new device technologies such as field plate, recessed gate, digital pre-distortion circuit and dual field plate was essential to realize such high device performances both at 2 GHz, 5GHz and 26 GHz. However, practical requirements on the quality and structure of these material systems for production of these devices are still not clear. Extensive studies on correlation among material quality, device performance and reliability were investigated under Japanese NEDO project. Firstly, this paper reviews recent progress of the performances of high power and high frequency AlGaN/GaN HFETs. Then, several interesting results which suggest practical requirements on material quality and structure will be discussed based on our extensive characterization studies in terms of device performances and reliabilities.

The interaction between dislocation sliding and damage structure in ion-irradiated austenitic stainless steels was investigated. Solution annealed type 316 and 304 stainless steels (316SS and 304SS) were irradiated with 2.8 MeV Fe2+ ions at 300 °C up to 10 dpa and tensiled to 2% plastic strain at 300 °C. Dislocations moving from unirradiated matrix were prevented due to the interactions with the damage structures consisted of dislocation loops and voids in the damage region. The prevention of dislocation movements by the damage structures became strong in 304SS compared in 316SS; probably due to lower stacking fault energy in 304SS. The prevention of dislocation movements was weak for Fe ion-irradiated specimens in which the increase in shear strength calculated from the size and number density of the defects was small compared to He ion-irradiated specimens.

We have measured the 121Sb NMR spectra, which are highly sensitive to the electric field gradients at the nuclear site, for crystalline Sb2Te3, Ge1Sb2Te4, Ge2Sb2Te4, and Ge2Sb2Te5. Estimates of the coupling constants, which are a measure of the field gradient, based on these spectra compare well with compounds containing Sb sites that are approximately 6-fold coordinated. The coupling constants of amorphous phase counterparts are roughly an order of magnitude larger and compare favorably with compounds where the Sb sites are 3-fold coordinated. We argue that the difference in the coupling constants arises primarily from a change in the local coordination, as opposed to the slight differences in the Sb-Te bond lengths and bond angles. The NMR data agree best with a structural model of amorphous phase based upon the “8-N” rule.

Silicon nanocrystals with diameters up to 30 nm are used as nucleation seeds for fast solid phase crystallization of amorphous silicon films. Purely amorphous films required an incubation time of up to 12 hours at 600°C prior to the onset of nucleation, while films with nanocrystals embedded between layers of amorphous silicon grew immediately upon annealing in a quartz tube furnace. Structural characterization was performed by heated-stage transmission electron microscopy and Raman spectroscopy.

The influence of boron on the kinetics of oxidation of iron in silicate melts relevant to nuclear waste storage has been investigated by XANES experiments. The measurements have been performed isothermally as a function of time at the iron K-edge. The redox kinetics become slower with increasing B2O3 content either close to the glass transition range, where the redox kinetics are controlled by diffusion of network-modifying cations, or at superliquidus temperatures where oxygen diffusion is the rate-limiting factor. In both ranges the kinetics can be interpreted in terms of boron speciation and interaction with alkali cations. Below the liquidus, however, the long times needed to reach redox equilibrium allow sintering of the powders investigated to take place so that the resulting changes in sample geometry prevent determinations of oxidation kinetic parameters from being made.

Junction capacitance measurements were used to characterize the properties of nanocrystalline silicon (nc-Si:H) solar cells. These methods included drive-level capacitance profiling (DLCP) to obtain spatially-resolved defect densities, as well as transient photocapacitance (TPC) and transient photocurrent (TPI) spectra to reveal optically responsive states in the band-gap, and to estimate minority carrier behavior before and after lightsoaking. Crystalline volume fractions were estimated using Raman spectroscopy. Previously we had identified at least two types of distinct behaviors in such nc-Si:H materials that depended on the crystalline volume fraction. Here, in one case, we report results indicating that both types of behavior can occur in a single sample, possibly indicating that the structural properties of that sample have evolved during growth.

This paper focuses on how to extrapolate current knowledge of spent fuel matrix alteration processes from laboratory to repository conditions, i.e., the influence of changes in both the initial surface oxidation level and the evolution of the specific surface area during the alteration process. Therefore, a spent fuel matrix alteration model allowing the alteration rate evolution to be predicted as a function of both the host rock considered and evaluation time scale of interest is described. At present, the model assumes that alteration of the spent fuel will start when the groundwater reaches the solid surface and that only the radiolytic species of the groundwater (oxidants generated by a-radiation of spent fuel) will produce the surface oxidation process and subsequent matrix dissolution; O2, H2O2 and OH are the species that react with UO2(s) for oxidation of the pellet surface. The dissolution process of the surface sites that are oxidized is modelled in two steps: first, a surface co-ordination of the oxidized layer with aqueous ligands and, second, detachment (dissolution) of the product species. Taking this mechanism into account, the model gives the evolution of the spent fuel matrix alteration rate over periods as long as 1,000,000 years. In this work is focussed on input the experimental results obtained of UO2 surface area behaviour (presented in previous MRS conference), on the MAM model. The matrix alteration rate results obtained, with MAM model, for repository granitic environment will be presented and compared to those performed for SFS project. Furthermore, a sensitivity analysis study has been performed on the influence of the following variables: Influence of the initial power size distribution and the initial oxidation state

The electrochemical cycling performance of high purity single wall carbon nanotube (SWCNT) paper electrodes has been measured for a series of electrolyte solvent compositions. The effects of varying the galvanostatic charge rate and cycling temperature on lithium ion capacity have been evaluated between 25-100 °C. The measured reversible lithium ion capacities for SWCNT anodes range from 600-1000 mAh/g for a 1M LiPF6 electrolyte, depending on solvent composition and cycling temperature. The solid-electrolyte-interface (SEI) formation and first cycle charge loss are also shown to vary dramatically with carbonate solvent selection and illustrate the importance of solvent alkyl chain length and polarity on SWCNT capacity. SWCNT anodes have also been incorporated into full battery designs using LiCoO2 cathode composites. An electrochemical pre-lithiation sequence, prior to battery assembly, has been developed to mitigate the first cycle charge loss of SWCNT anodes. The pre-lithiated SWCNT anodes show reversible cycling at varying charge rates and depths of discharge with the cathode system. The summary of data shows that the structural integrity of individual SWCNTs is preserved after cycling, and that free-standing SWCNT paper electrodes represent an attractive material for lithium ion batteries.

Scandia-doped zirconia is a very promising material for solid oxide fuel cells due to its high oxygen conductivity in the 700-850°C temperature range. 10 mol% Sc2O3 - 1 mol% CeO2 - ZrO2 ceramics were sintered at temperatures 1100-1600°C using different heating rates and dwell times. Ceramics sintered at temperatures higher 1300°C were found to exist in cubic phase at room temperature and exhibit slow phase transformation from cubic (c) to rhombohedral (beta) phase between 330 and 400°C. Analysis of c-β phase transition efficiency in the ceramics shows a strong correlation between the transition rate and sintering temperature. Kinetics of phase transitions were studied by high temperature X-ray diffractometry (HTXRD) and differential scanning calorimetry methods. The reversible c-β phase transition was found to have very wide hysteresis (45-70°C), which depends on sintering temperature and density. Coefficients of thermal expansion of c- and β-phases were calculated from temperature dependence of lattice parameters obtained by HTXRD in the temperature range of 25-800°C. Microstructural changes on the surface of the cubic phase due to c-β phase transition studied by SEM and AFM.

The kinetics of formation of palladium nanoparticles with well-defined morphologies (rods, cubes, MTP icosahedra, bipyramids) was studied using a combination of TEM and dynamic light scattering (DLS). The present study was focused on the role of the concentration and the size of seeds on both the kinetics of growth and the morphology distribution. Results clearly emphasize the role of the seed concentration (and not the size) on the growth kinetics in agreement with a collision theory model.

The physical properties of the layered iron superconductors and related phases are discussed starting from first principles calculations. The electronic structure is described as that of metallic Fe2+ square lattice sheets with substantial direct Fe-Fe hopping and interactions with the neighboring anionic pnictogens or chalcogens. The materials have a semi-metallic band structure, and in particular the Fermi surface consists of small cylindrical electron sections centered at the zone corner, and compensating hole sections at the zone boundary. The density of states N(EF ) is high placing the materials near itinerant magnetism in general, and furthermore the small Fermi surface sections are well nested leading to a tendency towards a spin density wave. Comparison of experimental and density functional results imply the presence of exceptionally strong spin fluctuations in these materials. Superconductivity is discussed within this context.

Near-infrared (NIR)-absorbing nanoparticles synthesized by the reduction of tetrachloroauric acid (HAuCl4) using sodium sulfide (Na2S) exhibited absorption bands at ∼530 nm and at the NIR region of 650−1100 nm. A detailed study on the structure and microstructure of as-synthesized nanoparticles was reported previously. The as-synthesized nanoparticles were found to consist of amorphous AuxS (x = ∼2), mostly well mixed within crystalline Au. In this work, the optical properties were tailored by varying the precursor molar ratios of HAuCl4 and Na2S. In addition, a detailed study of composition and particle-size effects on the optical properties was discussed. The change of polarizability by the introduction of S in the form of AuxS (x = ∼2) had a significant effect on NIR absorption. Also, it was found in this work that exposure of these particles to NIR irradiation using a Nd:YAG laser resulted in loss of the NIR absorption band. Thermal effects generated during NIR irradiation had led to microstructural changes that modified the optical properties of particles.

To improve the IPD reliability of NAND flash memory, plasma oxidation was introduced as the post-treatment process of ONO (Oxide/Nitride/Oxide) IPD. The LP-CVD SiO2 modified by plasma oxidation showed the excellent electrical properties. e.g., low leakage current, high breakdown voltage etc. By the analysis of Tof-SIMS and XRR, we could observe the several changes of physical characteristics such as the reduction of impurities (H, N etc.), the increase of oxide density, and the improvement of oxide surface roughness. We found out the appropriate treatment condition to be able to densify oxide layer without the addition of ONO Equivalent Oxide Thickness (EOT). The LP-CVD SiO2 prepared by plasma oxidation was used for the ONO IPD of 50nm NAND flash device and also compared with the conventional LP-CVD SiO2 in the aspect of the IPD reliability.

We report recent progress in 2G-HTS wire technology at Superpower Inc. The throughputs of 4mm-wide tape have reached 750m/h for sputtering AlO3+Y2O3 base layer, 360m/h for IBAD MgO template, 345m/h for sputtering Homo-epi MgO+LMO buffer, 180m/h for MOCVD REBCO. Critical current (Ic) of 813A/cm-width at 77K and self-field has been achieved on 1 meter length of 12mm-wide tape in which the thickness of GdYBCO film is 3.3 microns. Ic in a magnetic field has been significantly improved through composition modification, doping and MOCVD condition optimization. Ic of 185.6A/cm-width at 77K and 1Tesla has been obtained. For Ic on long lengths, 314A/cm-width on 202m, 221A/cm-width on 610m and 170A/cm-width on 935m have been achieved. A coil of 19.1mm diameter we made with our 2G wires generated 26.8T magnetic field in the magnet. A 30m-long cable made with nearly 10,000 meters of Superpower 2G wires showed excellent overall performance and has been installed and energized in the power grid.

The novel low-dimensional nanostructural self-alignment of molecular nanowire composed of a C60 anion radical moiety (fulleride) formed by electrocrystallization was revealed by single crystal structure analysis of C60 fulleride salts stabilized by triphenylmethane dye cations. The structure should be noted as molecular nanowire and anticipated to be an organic novel semiconductor from the preliminary four-probe conductance measurement. C60 fulleride has drawn much attention because of its interesting physical properties, such as superconducting of alkali-metal doped C60(A3C60) and unique ferromagnetic behavior of tetrakis(dimethylamino)ethane salts of C60 fulleride, (TDAE)C60.[20]. These intriguing solid-state properties of C60 fulleride should arise from electronic cooperative interactions, mainly due to electron-accepting ability of C60 and the ball-to-ball van der Waals interaction. However, there have been rather a limited number of well-characterized C60 anion radical salts, in particular, molecular discrete fulleride, predominantly because of their sensitivity to air.

We have succeeded in obtaining highly ordered single crystals of C60 anion radical salts stabilized by cationic triphenylmethane dyes, some of which were found to give rise to an intriguing nanostructural columnar alignment like molecular nanowire of C60 fullerides. The single-crystal structure of [Crystal Violet]+C60 −. C6H5Cl, reveals that the C60 fulleride aligns like molecular nanowire with the columnar structure along the a axis (crystal growth direction), as well as a zigzag structure along the b axis, with contacts of almost van der Waals magnitude (ca. 10 Å, distance of the C60–C60 center of mass), stabilized by mutual interactions of C60 −. and dye, due to such as CH-π, π-π, and face-to-face mutual interactions.

Magnetic susceptibility measurements for crystal violet salts demonstrate antiferromagnetic behavior, which can be fitted fairly by one-dimensional Heisenberg model (uniform chain), associated with the one-dimensional columnar crystal structure of the C60 fulleride molecular nanowire. These results also account for the semiconducting properties of the corresponding salts.

Nanoscratch test used for small area measurements and four-point bending test applied for quantitative measurements were coupled to evaluate the adhesive strengths of SiCN/Cu/Ta,/TaN/SiO2/Si stacked layers. The similarities and differences of the two methods concerning adhesion, position of the delamination interface, and plastic deformation of the delaminated film were estimated. It was found that the nanoscratch test gave similar adhesion properties when the delamination interface was the same as that formed by the four-point bending test. The four-point bending test displayed clearer results compared to the nanoscratch test because energy for delamination was not used in plastic deformation and the crack could propagate further. These results suggest that coupling the nanoscratch and four-point bending tests is powerful way to estimate and understand adhesion of thin film materials.

The segregated vacancies in the A site-ordered oxygen-deficient double perovskites REBaCo2O5+x (RE = La, Pr, Nd, Sm, Eu) (RBCO) are thought to greatly enhance the diffusivity of oxide ions in the bulk of these materials and possibly supply surface defect sites with enhanced reactivity towards molecular oxygen. Some materials in this family of REBaCo2O5+x compounds, such as PrBaCo2O5+x, (PBCO), have already demonstrated high electronic conductivity, rapid oxygen ion diffusion and surface exchange kinetics. Therefore, the family of REBaCo2O5+x compounds were synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (SOFCs) based on gadolinium doped ceria (CGO) electrolytes. The electrochemical performance of symmetrical cells (REBaCo2O5+x + CGO composite cathodes on the CGO electrolytes) was evaluated by using AC impedance spectroscopy. The area specific resistance (ASR) performance was measured as a function of temperature as well as oxygen partial pressure.