γ-B28 is a recently discovered high-pressure phase of boron, with the structure consisting f icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement: (B2)δ+(B12)δ-, and displaying a significant charge transfer δ~0.48. Boron is the only light element, for which the phase diagram has become clear only a few years ago, with the discovery of γ-B28, and this phase diagram is discussed here among other recent findings. γ-B28 was first experimentally obtained as a pure boron allotrope in early 2004 by J.H. Chen and V.L. Solozhenko (although a similar diffraction pattern was published in a 1965 by R.H. Wentorf, in a paper that until recently was believed to be wrong) and its unique structure was discovered by A.R. Oganov in 2006 with the use of the ab initio evolutionary algorithm USPEX (Oganov & Glass, 2006) and later confirmed by other studies. This allotrope, thermodynamically stable at high pressures, is shown to be also quenchable and dynamically stable upon decompression to 1 atm, and we show its phonon dispersion curves. Present discussion includes also the relative stability of other boron allotropes as a function of pressure. We also discuss more recent publications on the putative isosymmetric phase transition in γ-B28 and the nature of chemical bonding in it. We demonstrate that a qualitative difference in the evolution of the band gap of γ-B28 and the related α-B12 structure, which is due to the partial ionicity of γ-B28.

We report on the optical and charge transport properties of novel alkali metal chalcogenides, Cs2Hg6S7 and Cs2Cd3Te4, pertaining to their use in radiation detection. Optical absorption, photoconductivity, and gamma ray response measurements for undoped crystals were measured. The band gap energies of the Cs2Hg6S7 and Cs2Cd3Te4 compounds are 1.63 eV and 2.45 eV, respectively. The mobility-lifetime products for charge carriers are of the order of ~10-3 cm2/V for electrons and ~10-4 cm2/V for holes. Detectors fabricated from the ternary compound Cs2Hg6S7 shows well-resolved spectroscopic features at room temperature in response to ϒ -rays at 122 keV from a 57 Co source, indicating its potential as a radiation detector.

Design of one-dimensional periodic gratings is investigated for enhancing the light absorption in thin-film silicon solar cells due to scattering at rough interfaces that are introduced into solar cells by the gratings. A rigorous full-wave analysis is carried out in order to determine the optical properties of amorphous and microcrystalline silicon solar cells in PIN and NIP configurations, respectively. Optimal geometrical parameters of 1-D gratings for maximizing photocurrent density in thin-film silicon solar cells are determined.

We report plasmon lasers with strong cavity feedback and optical confinement to 1/20th wavelength. Strong feedback arises from total internal reflection of plasmons, while confinement enhances the spontaneous emission rate by up to 18 times.

Two separate pottery types, Kura-Araxes and Velikent Fine Wares can be found together at a number of Early Bronze Age sites in the Northeastern Caucasus. These ceramics are strikingly different in their appearance. Velikent Fine Ware bears indications that it may have been fired at a much higher temperature than Kura-Araxes wares. The obvious contrasts in their production raised suspicions that Velikent Fine Wares represented either an import or an intrusive production regime perhaps linked to the advent of Bronze metallurgy in this region or at least relying on a shared pyrotechnology. Prior results of Xeroradiographic analysis and INAA are merged with recent re-firing analysis to examine these hypotheses. The findings suggest that while a specific link between metal and pottery production cannot be confirmed, the emergence of divergent firing practices within an otherwise unified production tradition speaks to complex relationships between craftspeople within Early Bronze Age communities in the Caucasus.

The irradiation behaviour in two different precipitation hardening types of Ni-base alloys with the ultra high purity grade (EHP), namely, the γ’ type and G phase type was investigated by multi-ion beam techniques simulated to the irradiation conditions in fuel cladding tubes used in sodium cooled FBRs. Single ion-beam irradiation tests were conducted up to 90 dpa (by Fe3+ or Ni3+) at 673 K. Triple ion-beam irradiation tests were conducted up to 90 dpa (by Ni3+, 90 appmHe and 1350 appmH) at 823K. The irradiation behaviour was examined by and the microscopic observation by TEM to the distribution of dislocations, cavities and voids. The behaviour was compared with those of PNC316. The dominating irradiation defects in EHP(γ’) alloy at 673 K by single ion-beam are Frank loops, perfect unfaulted loops and line dislocations. Whereas, those of EHP(WSi) alloy are the irradiation-induced γ’ (Ni3Si) precipitates along {111} planes. Those dominating defect structures at 823 K by triple ion-beam are classified as followings, bimodal distributions in EHP(γ’), bubbles in EHP(WSi) and voids in PNC316. From those results, the excellent irradiation properties of EHP(WSi) alloy is clarified as the inhibition effects of secondary irradiation defects.

We present an investigation of the band offsets in amorphous/crystalline silicon heterojunctions (a-Si:H/c-Si) using low energy photoelectron spectroscopy, ellipsometry and surface photovoltage data. For a variation of deposition conditions that lead to changes in hydrogen content and the thereby the a-Si:H band gap by ∼180 meV, we find that mainly the conduction band offset ΔE V varies, while ΔE C stays constant within experimental error. This result can be understood in the framework of charge neutrality (CNL) band lineup theory.

Accurate Debye-Waller (DW) factors of chemically ordered β-NiAl (B2, cP2, ) have been measured at different temperatures using an off-zone axis multi-beam convergent beam electron diffraction (CBED) method. We determined a cross over temperature below which the DW factor of Ni becomes smaller than that of Al of ~90K. Additionally, we measured for the first time DW factors and structure factors of chemically ordered γ1-FePd (L10, tP2, P4/mmm) at 120K. We were able to simultaneously determine all four anisotropic DW factors and several low order structure factors using different special off-zone axis multi-beam convergent beam electron diffraction patterns with high precision and accuracy. An electron charge density deformation map was constructed from measured X-ray diffraction structure factors for γ1-FePd.

What follows is a commencement speech given to the graduating class of the School of Engineering at San Jose State University in December of 2005. Eminent materials researcher and educator, William D. Nix, offered his insights on finding one’s own passion and internal compass.

Barium strontium titanate solidly mounted resonators were fabricated with patterned and unpatterned acoustic Bragg reflectors on a sapphire substrate. The patterned and unpatterned solidly mounted resonator devices had acoustic Bragg reflectors consisting of Pt/SiO2/Pt/SiO2. The s-parameters of both devices were measured. The results showed that the quality factor increased for the device with the patterned acoustic Bragg reflector structure. The quality factors for the devices with patterned and unpatterned acoustic Bragg reflector structures were 54 and 115 and 28 and 86, respectively at the resonant and antiresonant frequencies. This investigation shows how an unpatterened acoustic Bragg reflector can contribute to the degradation of the overall quality factor of the device.

Photoelectrochemical behavior and Photocatalytic decomposition of Methylene Blue were studied on (Nb,Ti)O2 nanosheets electrode and (Nb,Ti)O2 particles produced from nanosheets, respectively. A detailed characterization of the materials show that Nb-substitution suppresses the transition from anatase to rutile. Depending on the oxygen partial pressure during the transformation, the Nb-substitution into TiO2 provokes different defect situations and also electronic properties. 1% Nb-substitution can drasticly increase the photocurrent and photocatalytic activity of Ti0.9O2 due to the formation of new defects and electron traps that can promote the separation of photoinduced holes and electrons. However, high concentration of electron traps produced by heavy Nb-doping can serve as efficient recombination centers that caused loss of photocatalytic activity of the samples.

Direct energy conversion between thermal and electrical energy, based on thermoelectric (TE) effect, has the potential to recover waste heat and convert it to provide clean electric power. The energy conversion efficiency is related to the thermoelectric figure of merit ZT expressed as ZT=S2σT/κ, T is temperature, S is the Seebeck coefficient, σ is conductance and κ is thermal conductivity. For a lower thermal conductivity κ and high power factor (S2σ), our current strategy is the development of rhombohedrally strained single crystalline SiGe materials that are highly [111]-oriented twinned. The development of a SiGe “twin lattice structure (TLS)” plays a key role in phonon scattering. The TLS increases the electrical conductivity and decreases thermal conductivity due to phonon scattering at stacking faults generated from the 60° rotated primary twin structure. To develop high performance materials, the substrate temperature, chamber working pressure, and DC sputtering power are controlled for the aligned growth production of SiGe layer and TLS on a c-plane sapphire. Additionally, a new elevated temperature thermoelectric characterization system, that measures the thermal diffusivity and Seebeck effect nondestructively, was developed. The material properties were characterized at various temperatures and optimized process conditions were experimentally determined. The present paper encompasses the technical discussions toward the development of thermoelectric materials and the measurement techniques.

This paper presents density functional theory results for the Li-adsorbed C(100)-(1x1):O system. Previously it has been shown that at a single monolayer coverage, the binding energy for Li on oxygenated C(100) diamond is substantially higher than that of heavier alkali metals, while at the same time, the presence of the lithium generates a large shift in the diamond workfunction. The system is therefore promising for electronics applications involving diamond. Here, further calculations are presented showing that additional Li atoms above 1ML coverage are far less strongly bound, suggesting the 1ML surface is the most useful for vacuum microelectronic applications.

In order to reduce the power-generating cost of silicon solar cells, it is necessary to achieve a high conversion efficiency using a thinner crystalline silicon (c-Si) substrate. The HIT solar cell is an amorphous silicon (a-Si) /crystalline silicon (c-Si) heterojunction solar cell that makes it possible to realize excellent surface passivation and hence high open circuit voltage (Voc). In addition, its symmetrical structure and a low-temperature fabrication process that is under 200°C provide advantages in reducing thermal and mechanical stresses within the device so that it can easily be applied to thinner solar cells. We fabricated HIT solar cells using thin wafers from 58-98 μm, and achieved a 22.8% conversion efficiency with a HIT solar cell using a 98-μm-thick wafer, and an excellent Voc value of 0.747 V with a HIT solar cell using a 58-μm-thick wafer.

During summers 2009 and 2010, the Renewable Energy Materials Research Science and Engineering Center (REMRSEC) at the Colorado School of Mines (CSM) successfully piloted a 10-week Research Experiences for Undergraduates (REU) program that addressed fundamental materials issues related to the science and technology of renewable energy. In January 2011, the National Science Foundation (NSF) awarded CSM a three-year grant to establish an REU Site that will strengthen our recruiting of women, underrepresented minorities, and persons with disabilities in research. This paper describes the features of these pilot programs and outlines the nature of our 2011 REU.

Aerogels are regarded as ideal candidates for the design of functional nanocomposites containing supported metal or metal oxide nanoparticles. The large specific surface area together with the open pore structure enables aerogels to effectively host finely dispersed nanoparticles up to the desired loading, to provide nanoparticle accessibility and/or to prevent nanoparticle agglomeration, as required to supply their specific functionalities.

The preparation of highly porous nanocomposite aerogels containing magnetic metal, alloy or metal oxide nanoparticles dispersed into amorphous silica, with high purity and homogeneity, was successfully achieved by a novel sol-gel procedure involving urea-assisted co-gelation of the precursor phases. This method allows fast gelation, giving rise to aerogels with 97% porosity, and it is very versatile allowing to vary composition, loading and average size of the nanoparticles.

The characterization of the morphological and structural features of the nanocomposite aerogels is carried out using different techniques, such as X-ray diffraction, Transmission Electron Microscopy and X-ray Absorption Spectroscopy. The characterization of the magnetic properties is carried out by SQUID magnetometry.

We have developed optical models for the characterization of grain size in nanocrystal thin films embedded in SiO2 and fabricated using low pressure chemical vapor deposition of Si from silane on a quartz substrate, followed by thermal oxidation. The as-grown nanocrystals thin film on quartz was composed of a two-dimensional array of Si nanocrystals (Si-NC) showing columnar structure in the z-direction and touching each other in the x-y plane. The nanocrystal size in the z-direction was equal to the Si nanocrystal film thickness, changing by the deposition time, while their x-y size was almost equal in all the samples, with small size dispersion. After high temperature thermal oxidation, a thin silicon oxide film was formed on top of the nanocrystals layer. The aim of this work was to measure the grain size and the nanocrystallinity of the Si nanocrystal thin films, a quantity related to the change of the dielectric function. We used a definition for the nanorcystallinity that is related to the effective medium analysis (EMA) of the material. The optical technique used for the investigations was spectroscopic ellipsometry. To measure the above sample properties the thickness and composition of several layers on a quartz substrate had to be determined by proper modeling of this complex system. We found that the nanocrystallinity (defined as the ratio of nc-Si/(c-Si+nc-Si) decreases systematically with increasing the Si-NC layer thickness. Using this approach we are sensitive to the lifetime broadening of electrons caused by the scattering on the grain boundaries, and not to the shift of the direct interband transition energies due to quantum confinement.

We report a novel concept for the direct integration of capacitors in printed circuit boards using ultra-small BaTiO3 and ZrO2 nanoparticles prepared by a chemical method. Electrical properties comparable to surface mount ceramic capacitors were achieved by proper processing of the nanoparticles, achieving a device-yield of >90% under research environment. The loss factor of the presented integrated capacitors does not exceed 0.05 independent of frequency, capacitor’s electrode area or applied bias voltage.