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The successful synthesis of high crystalline quality and high aspect ratio GaAs nanowires (NWs) with a uniform diameter is needed to develop advanced applications beyond the limits established by thin film and bulk material properties. Vertically aligned GaAs NWs have been extensively grown by Ga-assisted vapor-liquid-solid (VLS) mechanism on Si(111) substrates, and they have been used as building blocks in photovoltaics, optoelectronics, electronics, and so forth. However, the nucleation of parasitic species such as traces and nanocrystals on the Si substrate surface during the NW growth could affect significantly the controlled nucleation of those NWs, and therefore the resulting performance of NW-based devices. Preventing the nucleation of parasitic species on the Si substrate is a matter of interest, because they could act as traps for gaseous precursors and/or chemical elements during VLS growth, drastically reducing the maximum length of grown NWs, affecting their morphology and structure, and reducing the NW density along the Si substrate surface. This work presents a novel and easy to develop growth method (i.e., without using advanced nanolithography techniques) to prevent the nucleation of parasitic species, while preserving the quality of GaAs NWs even for long duration growths. GaAs NWs are grown by Ga-assisted chemical beam epitaxy on oxidized Si(111) substrates using triethylgallium and tertiarybutylarsine precursors by a two-step-based growth method presented here; this method includes a growth interruption for an oxidation on air between both steps of growth, reducing the nucleation of parasitic crystals on the thicker SiOx capping layer during the second and longer growth step. VLS conditions are preserved overtime, resulting in a stable NW growth rate of around 6 µm/h for growth times up to 1 h. Resulting GaAs NWs have a high aspect ratio of 85 and average radius of 35 nm. We also report on the existence of characteristic reflection high-energy electron diffraction patterns associated with the epitaxial growth of GaAs NWs on Si(111) substrates, which have been analyzed and compared to the morphological characterization of GaAs NWs grown for different times under different conditions. [ABSTRACT FROM AUTHOR]

ZnO/TiO2 composite ceramics have been prepared by solid-state reaction technique at 900°C. The X-ray diffraction results revealed the formation of secondary phases referred to as spinel Zn2TiO4 and hexagonal ZnTiO3. The structural analysis showed that all the composites that have been prepared have a polycrystalline nature and a hexagonal wurtzite structure. The complex modulus ( M) and electric impedance of the samples have been investigated by broadband dielectric spectroscopy in a wide range of temperature (40°C-110°C) and frequency (0.1 Hz to 10 MHz). The modulus plots (M′′, M′) illustrate the presence of non-Debye type of relaxations attributed to the effects of interfacial and dipolar polarizations. The real and the imaginary parts of the impedance are well fitted to equivalent circuit models. At high temperatures, Z″max varies from 0.03 × 106 to 4.9 × 106 Ω when the TiO2 doping concentration increases from 1 to 7 wt%. From the obtained results, the secondary phase ZnTiO3 plays an important role in the electrical properties. [ABSTRACT FROM AUTHOR]

This paper investigates the electrical behavior of the C-V and G-V characteristics of $$\mathrm{Al}/\mathrm{SiO}_{2}/\mathrm{Si}$$ structure. The modeling of capacitance and conductance has been developed from complex admittance treatment applied to the proposed equivalent circuit. Poisson transport equations have been used to determine the charge density, surface potential, total capacitance, and flatband and threshold voltages as a function of the gate voltage, frequency ( $$\omega )$$ , and series $$({R}_{\mathrm{s}})$$ and parallel $$({R}_{\mathrm{p}})$$ resistances. Results showed a frequency dispersion of C-V and G-V curves in both accumulation and inversion regimes. With increasing frequency, the accumulation capacitance is decreased, whereas the conductance is strongly increased. The shape, dispersion, and degradation of C-V and G-V characteristics are more influenced when parallel and series resistances $$(\mathrm{R}_{\mathrm{s}}$$ , $$\mathrm{R}_{\mathrm{p}})$$ are dependent to substrate doping density. The variation of $$\mathrm{R}_{\mathrm{s}}$$ and $$\mathrm{R}_{\mathrm{p}}$$ values led to a reduction of flatband voltage from −1.40 to −1.26 V and increase of the threshold voltage negatively from −0.28 to −0.74 V. A good agreement has been observed between simulated and measured C-V and G-V curves obtained at high frequency. [ABSTRACT FROM AUTHOR]

We investigate the photovoltaic performance of solar cells based on n-Al x In 1-x N (x = 0-0.56) on p-Si (100) hetero-junctions deposited by radio frequency sputtering. The Al x In 1-x N layers own an optical bandgap absorption edge tuneable from 1.73 eV to 2.56 eV within the Al content range. This increase of Al content results in more resistive layers (≈10 -4 -1 Ω·cm) while the residual carrier concentration drops from ~10 21 to ~10 19 cm -3 . As a result, the top n-contact resistance varies from ≈10 -1 to 1 MΩ for InN to Al 0.56 In 0.44 N-based devices, respectively. Best results are obtained for devices with 28% Al that exhibit a broad external quantum efficiency covering the full solar spectrum with a maximum of 80% at 750 nm, an open-circuit voltage of 0.39 V, a short-circuit current density of 17.1 mA/cm 2 and a conversion efficiency of 2.12% under air mass 1.5 global (AM1.5G) illumination (1 sun), rendering them promising for novel low-cost III-nitride on Si photovoltaic devices. For Al contents above 28%, the electrical performance of the structures lessens due to the high top-contact resistivity.

Purpose: Gastrointestinal stromal tumors (GIST) are a distinctive group of mesenchymal neoplasms of the gastrointestinal tract. The oncogene KIT has a central role in the pathogenesis of GIST, with c-kit receptor tyrosine kinase (KIT) protein expression being the gold standard in its diagnosis. The identification of GIST patients has become crucial, because the tyrosine kinase inhibitor Imatinib is effective in the treatment of this malignancy. However, a small set of GISTs remain unrecognized, because KIT protein expression is not always evident. The aim of this study was the identification of new markers for the differential diagnosis of GIST., Experimental Design: By analyzing publicly available data from transcriptional profiling of sarcomas, we found that protein kinase C theta (PKC-theta), a novel PKC isotype involved in T-cell activation, is highly and specifically expressed in GIST. PKC-theta expression in GIST was confirmed by reverse transcription-PCR and Western blot. PKC-theta was analyzed by immunohistochemistry in a panel of 26 GIST, 12 non-GIST soft-tissue sarcomas, and 35 tumors from other histologies., Results: We found that all of the GISTs expressed PKC-theta, whereas this protein was undetectable in other mesenchymal or epithelial tumors, including non-GIST KIT-positive tumors. PKC-theta immunoreactivity was also observed in interstitial cells of Cajal., Conclusions: Our results show that PKC-theta is easily detected by immunohistochemistry in GIST specimens and that it could be a sensitive and specific marker for the diagnosis of this malignancy.