We report the growth of silicon nanowires (SiNWs) by chemical vapor deposition (CVD) with several catalysts. We performed low temperature photoluminescence (PL) experiments on as-grown SiNWs for the following catalysts: Au, Cu, TiSi, PdSi and PtSi. Nanowires are chemically treated with an aqua regia solution to remove the catalyst droplets, this step is followed by a thermal oxidation process. We compared the PL of as-grown and processed SiNWs for each catalyst.

TbMnO3 is a multiferroic magnetoelectric material known to simultaneously exhibit antiferromagnetism below 40K and ferroelectricity below 28K in the same crystalline phase [1]. Following interesting results of Cu substitution in LaMn1-yCuyO3 [2, 3], we report a study of TbMn1-x CuxO3 (0 < x < 0.15). We describe here our results of crystal structure refinement, together with measurements of magnetic and dielectric properties in the temperature range 2 - 320 K, and magnetic field 0 - 9 T. We find no major changes in structure or symmetry upon substitution of Cu up to x = 0.15 in TbMn1-x CuxO3. Unlike LaMn1-yCuyO3, which exhibits ferromagnetism with very low values of y, we observe antiferromagnetism at x = 0.15. Our study of dielectric properties as a function of temperature suggests increased lossy behavior upon substitution of Cu at the Mn site. In our temperature dependent studies of tan δ at 1 kHz, we observe a well-defined step-like feature near 120K in both pure and substituted samples, possibly ascribable to a change in carrier mobility, or a dielectric-relaxation process mediated by ordered oxygen vacancies [4, 5], which we will continue to study.

Ion beam synthesis of nanoclusters is studied via both kinetic Monte Carlo simulations and the self-consistent mean-field solution to a set of coupled rate equations. Both approaches predict a steady-state shape for the cluster size distribution that depends only on a characteristic length determined by the ratio of the effective diffusion coefficient times the effective solubility to the ion flux. The average cluster size in the steady state regime is determined by the implanted species/matrix interface energy.

We analyzed the effect of electromechanical stressing on the electrical characteristics of hydrogenated amorphous silicon thin-film transistors. It had been shown that the TFTs, fabricated at 150 °C, respond to tension/compression by a rise/fall in electron mobility. In TFTs fabricated using the same process, a slight shift of threshold voltage was observed under prolonged high compressive strain and the gate leakage current slightly increases after ˜2% compressive strain. In general, the change of TFT performance due to pure mechanical straining is small in comparison to electrical gate-bias stressing. From the comparison among Maxwell stress (induced by electrical gate-bias stressing), mechanical stress (applied by bending), and drifting electrical force for passivated hydrogen atom, the most significant cause for the change of electrical characterization of a-Si:H TFTs should be the trapping charges inside the dielectric, under combined electrical and mechanical stressing. The mechanical stress does not act on Si-H bonds to drift hydrogen atoms, while it is mainly balanced by the rigid Si-Si networks in a-Si:H or a-SiNx. Therefore, mechanical stress has very little effect on the instability of low temperature processed a-Si:H TFTs.

Mechatronic systems designed to comply to new EU directives are studied through interconnections by electronic or photonic probes, SEM, TEM, SE or 3D Tomography. Leaded and lead free modules assembled by standard interconnection technologies are studied for robustness relative to thermal accelerated life tests. Results obtained from JEOL 6060LV SEM and Optical Microscopy show that although slow growth rate of inter-metallics (IMC) is consistent with expected reliability, they are responsible for propagation of cracks especially in the presence of gold on PCB side. Innovative Low Temperature Joining (LTJ) technology applied to nano or micro silver pastes which should reduce IMC effects are tested on mechatronic systems. Results obtained from SEM, TEM and 3D Tomography will be shown as well as non destructive Spectroscopic Ellipsometry studies of samples. Pressureless LTJ technology is unsuitable for robust interconnection.

Selective biomolecular functionalization of our all-(111) surface silicon nanowire (SiNW) biosensors using covalently linked alkyl- monolayers is demonstrated. Monolayers were made using a commercially available six member carbon precursor N-(5-Hexynyl) phthalimide and UV based hydrosylilation reaction. Contact angle and x-ray photoelectron spectroscopy (XPS) measurements were used to characterize the monolayer at different stages on planar Si (111) samples. Terminal amine groups on the monolayer surface were used for further conjugation with (+)-Biotin N-hydroxysuccinimide ester after deprotection of the phthalimide group with a methylamine solution. Selective biofunctionalization was demonstrated by reacting the SiNW-monolayer-biotin surface with 5 nm gold nanoparticles conjugated with streptavidin and subsequent high resolution scanning electron microscopy imaging.

This work reports a low-cost method for large scale production of high quality graphene via radio-frequency chemical vapor deposition. High quantities of graphene were successfully synthesized on the Fe-Co/MgO (2.5:2.5:95 wt.%) catalytic system utilizing acetylene as a hydrocarbon source at 1000 °C. The as-produced graphene sheets were purified in a single step by washing with a diluted hydrochloric acid solution under sonication. Next, they were thoroughly characterized by microscopy, spectroscopy, and X-Ray diffraction. Advanced transmission electron microscopy and atomic force microscopy analyses have indicated the formation of 3-5 layered graphene nanosheets. Thorough analyses by Raman spectroscopy were also performed demonstrating the presence of high quality and few-layer graphene samples. This low cost and highly reproducible method may be applied in a straightforward way to produce large quantities of graphene for various advanced applications.

Spent nuclear fuel is in Sweden planned to be disposed of by encapsulating in waste packages consisting of a cast iron insert surrounded by a copper canister. The waste package is heavy. Throughout the manufacturing process from the extrusion/pierce-and-draw manufacturing to the final placement in the repository, the copper is subjected to handling which could introduce cold work in the material. It is well known that the creep properties of engineering materials at higher temperatures are affected by cold working.

The study includes creep testing of four series of cold worked, oxygen-free, phosphorus doped copper (Cu-OFP) at 75 °C. The results are compared to reference series for as-received material carried out in a recent study. Two series of copper cold worked in tension (12 and 24 %) and two series cold worked in compression (12 % parallel to creep load axis and 15 % perpendicular to creep load axis) were tested.

The results show that pre-straining in tension of copper leads to prolonged creep life at 75 °C. The creep rate and ductility are reduced. The influence on the creep properties increases with the amount of cold work. Cold work in compression applied along the creep load axis has no effect on the creep life or the creep rate. Nonetheless the ductility is still impaired. However, cold work in compression applied perpendicular to the creep load direction has a positive effect on the creep life. Cold work in both tension and compression results in a pronounced reduction of the initial strain on loading. Yet the high value of the area reduction, 90 %, is unaffected by the degree of cold work.

Sodium cholesteryl carbonate ester (SCC) was synthesized, and its phase behavior was studied. The chemical structure was assessed by solid-state infrared spectroscopy based on vibration analysis. The wave number at 1705 and 1276 cm−1 corresponds to a carbonyl carbonate and O–C–O stretching of SCC, respectively. Molecular structure of SCC was further investigated with 1H and 13C NMR spectroscopy. The chemical shift, for the carbonyl carbonate resonance appeared at 155.5 ppm. A molecular mass of SCC was at m/z of 452. Differential scanning calorimetry (DSC), video-enhanced microscopy (VEM) together with polarized light microscopy, and small-angle x-ray scattering (SAXS) were used to characterize the phase behavior as a function of temperature of SCC. Liquid crystalline phase was formed with SCC. Based on the thermal properties and x-ray diffraction, it appears that SCC forms a structure analogous to the type II monolayer structure observed with cholesterol esters.

500 nm-thick aluminum-doped zinc oxide (ZnO:Al) thin film is usually used as a front transparent conductive oxide (TCO) contact on photovoltaic devices, and for this application is often deposited by a reactive radio-frequency (r.f.) magnetron sputtering system from a ceramic target. This work reports on the preparation and characterization of AZO thin films on Corning 1737 glass substrates grown by reactive r.f.-magnetron sputtering from a ZnO ceramic target with 2 wt% Al content. It was found that the growth parameters, such as chamber pressure, working power, and deposition temperature, have significant influences on the properties of AZO films. According to the experimental results: (1) Films were polycrystalline showing a strong preferred c-axis orientation. (2) With increasing working power, the resistivity decreased, and mobility and the carrier concentration increased. (3) Lower deposition temperature leads to a decrease in resistivity, with 2.5×10-4 Ω-cm representing the lowest resistivity reached.

This work reports the use of strategies based on Raman scattering for process monitoring of electrodeposited based S rich CuIn(S,Se)2 solar cells. Main vibrational modes in the Raman spectra are sensitive to features related to the crystalline quality, chemical composition and presence of secondary phases in the chalcopyrite layers, being all these features relevant for the optoelectronic properties of the final devices. Ex-situ and in-situ measurements during the electrochemical step allow the direct assessment on the formation of Se rich secondary phases which are related to the stoichiometry of the grown precursors. The analysis of the relative intensity of the spectral contribution from these phases allows early detection of deviations of precursor stoichiometry in relation to the optimum composition range in terms of solar cell efficiency. The applicability of the technique for the in-situ monitoring of the electrodeposition process is also discussed

We have studied the effect of thin metal coatings on the electron emission characteristics of self-assembled silicon microstructures with nearly identical sharp features. We have employed a common template of spikes produced by fs-laser self-driven structuring of Si on which several different metals have been deposited. We find that, in the pristine state and in vacuum conditions achievable in device applications, all metal coatings do not result in marked change of either the minimum electric field necessary for emission or the maximum obtainable current density. In contrast, the durability of the emitters depends strongly on the metal used and is always enhanced with respect to bare Si. Furthermore, no signs of degradation were found within the 3-day time scale of our experiments with gold and chromium. On the contrary, these two metal coatings resulted in emission characteristics improving with time in typical operation conditions.

Temperature-dependent Hall-effect measurements have been performed on three Ga-doped ZnO thin films of various thicknesses (65, 177, and 283 nm), grown by pulsed laser deposition at 400 °C and annealed at 400 °C for 10 min in Ar, N2, or forming-gas (5% H2 in Ar). The donor ND and acceptor NAconcentrations as a function of sample thickness and annealing conditions are determined by a new formalism that involves only ionized-impurity and boundary scattering. Before annealing, the samples are highly compensated, with ND = (2.8 ± 0.3) × 1020 cm-3 and NA = (2.6 ± 0.2) × 1020 cm-3. After annealing in Ar the samples are less compensated, with ND = (3.7 ± 0.1) × 1020 cm-3 and NA = (2.0 ± 0.1) × 1020 cm-3; furthermore, these quantities are nearly independent of thickness. However, after annealing in N2 and forming-gas, ND and NA are thickness dependent, partly due to depth-dependent diffusion of N2 and H, respectively.

Boron carbide (B4C) is currently used in lightweight armors and high temperature materials, because it has high meting point, good hardness, low specific gravity and good mechanical properties. The sintering of boron carbide, however, is restricted by its high covalent bonding and B2O3 coatings on B4C particles surface which can cause a microstructural coarsening during sintering. Therefore, it is necessary to remove B2O3 film of By4C particles surface to restrict microstructural coarsening and densification of B4C. B4C ceramics were fabricated by a hot-press sintering and its sintering behavior, microstructure and mechanical properties were evaluated. The relative density of B4C ceramics were obtained by a hot-press sintering reached as high as 99% without any sintering additives. The mechanical properties of B4C ceramics was improved by a methanol washing which can remove B2O3 phase from a B4C powder surface. This improvement is resulted from the formation of homogeneous microstructure because the grain coarsening was suppressed by the elimination of B2O3 phase. Particularly, the mechanical properties of the sintered samples using a methanol washed powder improved compared with the samples using an as-received commercial powder.

A bioglass of composition SiO2 (67.12 mol%), CaO (28.5 mol%), and P2O5 (4.38%) was synthesized and stabilized by a novel technique using ethanol. Bioactive glasses have a wide range of application in the field of biomaterials promoting bone bonding as well as bonding to soft tissue. Earlier our lab developed a novel PVA-PCL semi IPN porous and 3D scaffold that was found to favor chondrogenesis. In the present study, a composite of this polymer and bioglass is prepared by an emulsion freeze-drying process, as a porous 3 dimensional scaffold. The scaffolds were characterized for their physiochemical properties and ability to support cartilage tissue regeneration. The composite scaffolds were observed to be non-cytotoxic. The chondrocytes cells cultured in vitro for a month on the composite scaffolds regenerate cartilaginous tissue, secreting GAGs and collagen in amounts nearly comparable to the amounts on the control PVA-PCL scaffold. The composite scaffold is also biomimetic and bioactive and favors mineralization by forming a hydroxycarbonate apatite layer, when immersed in simulated body fluid for a 14 day period. The PVA-PCL-bioglass composite is hence expected to have potential implications as a scaffold for osteochondral tissue engineering.

Simulations of metal nanoimprinting by a rigid template are performed with the aim of finding the optimal conditions to retain imprints in a thin film on a substrate. Specifically, attention is focussed on the interface conditions between film and substrate and on the template shape. Deeper imprints are obtained when the interface between film and substrate is penetrable to dislocation motion. When the protruding contacts of the rigid template are closely spaced the interaction between neighboring contacts gives rise to material piles up between imprints.

We investigated 0 to 300 Å thick stepped molybdenum trioxide (MoO3) inter-layer between in-situ oxygen plasma treated conducting indium tin oxide (ITO) and chloro-aluminum pthalocyanine (AlPc-Cl) layer-by-layer evaporated up to 228 Å, with ultra-violet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES). The MoO3 inter-layers were observed to increase the surface workfunction. The workfunction increase was observed to saturate at 20 Å of MoO3 coverage. The increased surface workfunction causes hole accumulation and band bending in the subsequently deposited AlPc-Cl. A possible explanation of reduction in series resistance by the insertion of the MoO3 insulating layer is discussed based on these observations and energy level alignment.

As part of the NSF supported SUMMIT (San Jose State University/IBM Almaden Research Center collaboration) REU and CPIMA (Stanford University/Almaden) SURE undergraduate internship programs we have developed a workshop that emphasizes the scientific community's dependence on ethical behavior for its success and advancement at this nascent stage of a scientific career. We have successfully introduced open-ended role playing based on recent real life ethics cases as reported in the scientific news to a foundation presentation based on the APS Ethics and Professional Conduct Guidelines for Physicists. The goal is to foster discussion of complex cases and their effects not only on the protagonists but on the scientific community.

The wettability of electrochemically deposited conducting polymer films is highly dependent on several parameters including the deposition conditions, the dopant, and the roughness of the working electrode. To produce superhydrophobic surfaces, one must be able to control the micro and nanostructure of the film. In this study, a template-free method of producing superhydrophobic (water contact angle of 154°) polypyrrole films was demonstrated. The polypyrrole was doped with the low surface-energy heptadecafluorooctanesulfonic acid and had microstructures with nanometer-scale roughness. The microstructures served to increase the roughness of the film and amplify the hydrophobicity of the surface. It is also of interest to be able to dynamically adjust the wettability of a polypyrrole surface after deposition. Applications of this functionality include microfluidics, self-cleaning surfaces, liquid lenses, and smart textiles. By oxidizing or reducing a polypyrrole film, one can change the surface morphology as well as the chemical composition, and control the wettability of the surface. This study characterizes the electrochemically-induced changes in surface energy of polypyrrole. The relationship between applied voltage, charge transferred, surface roughness, and water contact angle was investigated. Upon reduction, the polypyrrole film was switched to a superhydrophilic state and the maximum change in contact angle was observed to be 154°. Surface wettability was found to be not fully reversible, with some hysteresis occurring after the first electrochemical cycle.