Molecular beam epitaxy growth of GaN and InGaN nanowires is accomplished on Si (111) substrates using Ga-droplet nucleation. Typical diameters range from 25-80 nm and lengths can be varied by increasing the growth time; the growth rate is ∼0.25 microns/hour. The nanowires have been characterized structurally and optically. Photoluminescence spectra show band-edge emission of GaN nanowires centered at 362 nm at 290 K. Transmission electron microscopy images unveil that the nanowires are highly crystalline, and grow along the 0001 polar direction. Indium has also been successfully incorporated into GaN nanowires by modifying the growth conditions; the InGaN nanowires emit at ∼520 nm, which provides a possible route to solving strain related problems of high In-composition InGaN based efficient green emitters.

At the moment, over 1100 borate crystal structures are listed in the Inorganic Crystal Structure Database ICSD. High-pressure investigations in this field are rare and were mainly performed from a geological point of view. Starting in 1999, systematic high-pressure / high-temperature experiments up to maximum pressures of 16 GPa have been carried out, using the multianvil technique to explore the synthetic possibilities in the field of borates under extreme conditions. This approach led to a variety of interesting new materials, which are unattainable via conventional solid state syntheses. The communication will give a short survey of the most important results in the last years.

SSZ-based ceramics were obtained by sintering of nanopowders derived at room temperature by mechanochemical synthesis from refined technical grade ZrO2 nano-precursors. RT-treatment by 2.5 MeV electrons up to 1563 K was used for the modification of ceramics. Powders and ceramics were characterized by XRD, Raman, SEM and EDS, TEM, SIMS techniques. The phase composition of Zr0.89Sc0.1Ce0.01O1.95 ceramics was very close to cubic structure but better fitting of XRD patterns was obtained for rhombohedral lattice. Conductivity of solid electrolytes for IT SOFC was studied by complex impedance method. To stabilize cubic structure and increase conductivity at operation temperature of To ∼ 1000 K, the composition of SSZ solid electrolyte was optimized by addition of yttria and sintering aids. The interaction of admixtures with minor dopants leading to intergrain phase was revealed. During fast sintering, ceramics keep a memory about inhomogeneous disordered solid solutions in a form of nanostructuring. Conductivity data indicate nanostructuring of ceramics too: activation energies of bulk and grain boundary conductivities are close (Eb ∼ 0.9 eV, Egb ∼ 1.05 eV). Annealing of ceramics at high temperatures increases conductivity at To and promotes grain growth.

We have fabricated polycrystalline OFETs of two different liquid crystalline materials i.e., ω,ω'-dihexylquaterthipohene (6-QTP-6) and N, N'-ditridecylperylenediimide (13-Per-13) by solution process. Liquid crystalline materials help fabricating uniform thin films on the substrate when spin-coated at their temperature range of liquid crystalline phase. The FETs fabricated with 6-QTP-6 exhibited p-channel performance and its mobility was determined to be 0.04 cm2/Vs, which was comparable to that determined by time-of-flight experiments. The FETs fabricated with 13-Per-13 exhibited n-channel performance and its FET mobility was 0.008 cm2/Vs, while the mobility was increased up to 0.11 cm2/Vs after thermal annealing of the film at a liquid crystalline temperature of 220°C for an hour. Judging from these facts, the grain boundaries are controlled not so as to across the conduction channels formed by self-aligned π-conjugated aromatic cores in liquid crystalline molecules. We conclude that liquid crystalline material is a good candidate for quality polycrystalline thin films for OFETs.

Electrospun composite scaffolds were prepared by mixing gelatin with nanoparticles of hydroxyapatite (nanoHA) in 2,2,2-trifluoroethanol (TFE) solution. The fibrous composite scaffolds with nanoHA content from 0 to 40 wt% were compared in terms of structure and morphology via x-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that dispersion of nanoHA in the scaffolds is uniform for 0%, 10%, 20%, and 30% nanoHA content, but significant nanoHA agglomeration can be observed for scaffolds with 40% nanoHA. In order to study the effect of nanoHA content on mechanical properties at the nanoscale level, the fibrous scaffolds were pressed into dense pellets and tested by nanoindentation to determine Young's modulus. Young's modulus was found to increase linearly with nanoHA content, reaching unexpectedly high values of 10.2 ± 0.8 GPa. Results are compared with other polymer/HA composites including those made with polycaprolactone or collagen.

Performance metrics of every class of semiconductor amplifier or laser system depend critically on semiconductor QW optical properties such as photoluminescence (PL), gain and recombination losses (radiative and nonradiative). Current practice in amplifier or laser design assumes phenomenological parameterized models for these critical optical properties and has to rely on experimental measurement to extract model fit parameters. In this tutorial, I will present an overview of a powerful and sophisticated first-principles quantum design approach that allows one to extract these critical optical properties without relying on prior experimental measurement. It will be shown that an end device L-I characteristic can be predicted with the only input being intrinsic background losses, extracted from cut-back experiments. We will show that textbook and literature models of semiconductor amplifiers and lasers are seriously flawed.

Spent nuclear fuel from the Swedish energy programme will be stored in an underground repository situated in saturated fractured rock at a depth of approximately 500 m. This paper describes numerical simulations of radionuclide migration in the near-field (consisting of a canister filled with spent fuel and an engineered system backfilled with swelling clays) for the recently completed safety assessment SR-Can [1] using a Matlab / Simulink code. Handling of input data for the models from the site descriptive programme from on-going investigations at two candidate sites and the numerical modelling concept are discussed.

The thermal characteristics of the spent fission fuel from a hybrid fusion-fission system (LIFE) capable of extremely high burnups are described. The waste has higher thermal output per unit mass of heavy metal, but lower thermal output per unit energy generated. Plausible designs for interim storage containers and cooling configuration can remove the heat without exceeding fuel temperature limits. Calculations show that a spent LIFE fuel repository would perform within the limits established for the proposed repository at Yucca Mountain.

In order to achieve the widespread use of HIT (Hetero-junction with I etero-Intrinsic T ntrinsic Thin-layer) solar cells, it is important to reduce the power generating cost. There are three main approaches for reducing this cost: raising the conversion efficiency of the HIT cell, using a thinner wafer to reduce the wafer cost, and raising the open circuit voltage to obtain a better temperature coefficient. With the first approach, we have achieved the highest conversion efficiency values of 22.3%, confirmed by AIST, in a HIT solar cell. This cell has an open circuit voltage of 0.725 V, a short circuit current density of 38.9 mA/cm2 and a fill factor of 0.791, with a cell size of 100.5 cm2. The second approach is to use thinner Si wafers. The shortage of Si feedstock and the strong requirement of a lower sales price make it necessary for solar cell manufacturers to reduce their production cost. The wafer cost is an especially dominant factor in the production cost. In order to provide low-priced, high-quality solar cells, we are trying to use thinner wafers. We obtained a conversion efficiency of 21.4% (measured by Sanyo) for a HIT solar cell with a thickness of 85μm. Even better, there was absolutely no sagging in our HIT solar cell because of its symmetrical structure. The third approach is to raise the open circuit voltage. We obtained a remarkably higher Voc of 0.739 V with the thinner cell mentioned above because of its low surface recombination velocity. The high Voc results in good temperature properties, which allow it to generate a large amount of electricity at high temperatures.

This work emphasizes room temperature deposition and fabrication of staggered bottom-gate ZnO and IZO TFTs. We synthesized these oxide thin films by RF sputtering in an Ar/Oxygen ambience with no intentional heating of the substrates. Bottom gate staggered structure ZnO TFTs were fabricated (Ti/Au/Ti gate and Au/Ti source/drain) and characterized. ZnO TFTs retained well-behaved transfer characteristics down to a channel length of 4 μm with field effect mobility of 5 cm2/V.s, on/off current ratio exceeding 106 and threshold voltage around -5V. The IZO TFTs, with ITO as gate metal layer and highly conducting amorphous IZO forming the source/drain material had reasonably high field effect mobility of 20 cm2/V.s and on/off current ratio exceeding 106, which are well suited for active matrix display applications. Finally, to demonstrate the viability of oxide-based device integration, simple circuits such as inverters and pseudo-logic circuits are designed, fabricated and tested.

Having superior mechanical properties, 3C-SiC is one of the target materials for power MEMS applications. Growing 3C-SiC films on Si is challenging, as there is a large mismatch in lattice parameter and thermal expansion between the SiC film and the Si substrate that needs to be accommodated, and results in high residual stress. Residual stress control is critical in MEMS devices as upon feature release it results in substantial deformation.

3C-SiC single crystalline films were deposited on 50 mm (100) and (111) Si substrates in a hot-wall CVD reactor. The film tensile residual stress was so high that it fractured on the (111) Si wafer. The resulting film thickness on the (100) Si wafer was non-uniform, having a linear profile along the growth direction. This presented a challenge of using the substrate curvature method for calculating residual stress. Finite Element Method correction was applied to the Stoney's formula for calculating the residual stress along the wafer radius. Suggestions for reducing the amount of residual stress are made.

The hydrogen absorption properties of the Ti-Al-Nb system intermetallics subjected by ball milling were studied. It was found that the hydrogenation of the titanium aluminides during ball milling in hydrogen atmosphere could occur at room temperature without any special requirements to the quality of hydrogen. The crystal structure of the hydrides and phase transformations were also studied.

ZnO nanowires are directly integrated into a working device by a single-step chemical vapor deposition (CVD) method. Gold catalyst is patterned on a quartz glass substrate using a comb-shaped shadow mask and then ZnO is grown on the patterned substrate by CVD. Thick ZnO layers formed on the gold-patterned areas serve as native electrodes. Ultra-long (˜100 μm) ZnO nanowires grown across the gap between the ZnO electrodes and the nanowires serve as the sensing elements of the device. The device exhibits high sensitivity and fast response to UV illumination in air. Our method can be used to fabricate other metal oxide semiconductor bridging nanowire devices, which have promising applications in photodetection and gas sensing.

New experimental results on pyrochlore and defect fluorite phases in HfO2-La2O3 and HfO2-Gd2O3 systems are summarized. Fluorite Hf0.5Gd0.5O1.75 was formed by containerless melting and quenching. Melts with 25-65 mol% La2O3 did not produce any fluorite-type phases, but pyrochlores with cell parameters 10.74 to 10.86 Å. The fluorite phase of Hf0.5La0.5O1.75 can be formed on crystallization of an amorphous precursor from aqueous precipitation. Both La- and Gd- fluorite phases transform to ordered pyrochlore on annealing at 1450 °C. The enthalpies of formation from oxides are −107 ±5 kJ/mol for Hf2La2O7 and −49 ±5 kJ/mol for Hf2Gd2O7 as measured by high-temperature solution calorimetry. Further experiments are needed to elucidate the nature of stabilization of fluorite phase in thin films and powders. Occurrence of disordered phases in thin films, nanoparticles and radiation damaged materials is discussed.

We report structural and electronic properties of Aligned-Crystalline Si (ACSi) films on glass substrates. These films show enhanced majority carrier mobilities and minority carrier lifetimes with increasing crystallinity, i.e., with improving alignment and connectivity of the grains. A 0.4-μm-thick ACSi film with a total grain mosaic spread of 4.2° showed Hall mobility of 47 cm2/V.s for a p-type doping concentration of 1.9×1018 cm−3. A prototype n+/p/p+–type diode fabricated using a 4.2-μm-thick ACSi film showed minority carrier lifetime of ∼3.5 μs and estimated diffusion length of ∼30 μm in the p layer with a doping concentration of 5×1016 cm−3.

To improve the cell efficiency of thin film solar cells textured back reflectors (BR) are widely used. This is particularly important in a-Si:H based solar cells due to low absorption coefficient at longer wavelengths. In this work we present a cost effective way to fabricate uniformly textured ZnO by using electrochemical methods. Further it was observed that Quantum Efficiency (QE) of shorter wavelengths also improved for highly textured ZnO BR. Together this resulted in more than 2mA increment in short circuit current density (Jsc) and 19% relative improvement in solar cell efficiency over sputter deposited BR. A possible mechanism responsible for the improved blue QE is also discussed.

ZnO grown on α-Al2O3(0001) generally possesses an orientation such that α-Al2O3(0001) is parallel to ZnO(0001) and two in-plane domains nucleate, so that α-Al2O3[11¯20] is parallel to ZnO[11¯20] and/or α-Al2O3[11¯20] is parallel to ZnO[10¯10]. In this paper, we report a new growth mode for ZnO grown on α-Al2O3(0001) using metalorganic chemical vapor deposition (MOCVD). We find that α-Al2O3[11¯20] is parallel to ZnO[10¯10], but the (0001) plane of ZnO is tilted relative to the (0001) plane of α-Al2O3 such that ZnO(0001) is almost parallel to the α-Al2O3(¯1104) plane. This orientation reduces the extent of lattice mismatch. The interface between ZnO and α-Al2O3 is abrupt and possesses periodic dislocations.

Nb-doped anatase TiO2 films were deposited on unheated glass by dc magnetron sputtering using a slightly reduced TiO2-x–Nb2O5-x target with oxygen flow ratios [O2/(Ar+O2)] in the range from 0.00 to 0.20%. After post-annealing in a vacuum (6 × 10−4 Pa) at 500 and 600 °C for 1 h, the films were crystallized into the polycrystalline anatase TiO2 structure. The resistivity of the both films decreased to 6.3-6.8 × 10−4 Ω·cm with increasing [O2/(Ar+O2)] to 0.10%, where the carrier density and Hall mobility were 1.9-2.0 × 1021 cm−3 and 4.9-5.0 cm2·V−1·s−1, respectively. The films exhibited high transparency of over 60-70% in the visible region of light.

Semiconductor nanowires are attractive nano- building blocks for microelectronics. However, the requirements for their manufacturing and application in the microelectronics industry are very demanding. Beyond compatibility with Si technology, full control on the characteristics of the grown wires (diameter, location, crystallinity, etc..), homogeneity on wafer –scale and reproducibility are essential. In this study we review critically important challenges for a controlled process of In –mediated growth of Si nanowires. First, we stress the importance of surface type for both particle catalysts and growth substrates. Both selection and preparation of such surfaces have large impact on growth, as they influence the initiation and the driving forces for the VLS growth mechanism. Moreover, wire characteristics such as morphology, crystalline quality and growth orientation appear more difficult to control when growing from particles with sizes below 40-50nm. This limitation arises as a result of both fundamental mechanisms and more specific constrains linked to the In-Si system.

A few perspectives are given for the achievement of a controlled Si nanowire growth in a Si –technology compatible fashion.

A new thermodynamic assessment of the Co-Nb system is presented. All experimental phase diagram data available from the literature have been critically reviewed and assessed using thermodynamic models for the Gibbs energies of the individual phases (Thermo-Calc). Compared to previous assessments more elaborate models for the description of the C14 and C36 Laves phases and for the μ phase were employed. Thereby a calculated phase diagram is obtained which satisfactorily agrees with the experimental data.