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Gallium oxide (Ga2O3) and its most stable modification, monoclinic β-Ga2O3, is emerging as a primary material for power electronic devices, gas sensors and optical devices due to a high breakdown voltage, large bandgap, and optical transparency combined with electrical conductivity. Growth of β-Ga2O3 is challenging and most methods require very high temperatures. Nanowires of β-Ga2O3 have been investigated extensively as they might be advantageous for devices such as nanowire field effect transistors, and gas sensors benefiting from a large surface to volume ratio, among others. Here, we report a synthesis approach using a sulfide precursor (Ga2S3), which requires relatively low substrate temperatures and short growth times to produce high-quality single crystalline β-Ga2O3 nanowires in high yields. Even though Au- or Ag-rich nanoparticles are invariably observed at the nanowire tips, they merely serve as nucleation seeds while the nanowire growth proceeds via supply and local oxidation of gallium at the substrate interface. Absorption and cathodoluminescence spectroscopy on individual nanowires confirms a wide bandgap of 4.63 eV and strong luminescence with a maximum ∼2.7 eV. Determining the growth process, morphology, composition and optoelectronic properties on the single nanowire level is key to further application of the β-Ga2O3 nanowires in electronic devices. [ABSTRACT FROM AUTHOR]

Germanium nanowires (NWs) have attractive properties for a variety of applications, including micro- and optoelectronics, memory devices, solar energy conversion, and energy storage, among others. For applications that involve exposure to air, the poor chemical stability and electronic surface passivation of native oxides have remained a long-standing concern. Termination by sulfur-rich surface layers has emerged as a promising strategy for passivation of planar Ge surfaces. Here we discuss experiments on solid-state sulfurization of Ge nanowires in sulfur vapor at near-ambient pressures and at different temperatures. Combined transmission electron microscopy imaging and chemical mapping establishes that Ge NWs remain intact during vapor-phase reaction with S at elevated temperatures, and show the formation of sulfur-rich shells with T-dependent morphology and thickness on the Ge NW surface. Photoluminescence of ensembles of such core–shell nanowires is dominated by strong emission at ∼1.85 eV, consistent with luminescence of GeS. Cathodoluminescence spectroscopy on individual NWs establishes that this luminescence originates in thin GeS shells formed by sulfurization of the NWs. Our work establishes direct sulfurization as a viable approach for forming stable, wide-bandgap surface terminations on Ge NWs. [ABSTRACT FROM AUTHOR]

Reactions of Ge with S vapor, of interest as a potential approach for forming thin passivation layers on Ge surfaces, have been studied by photoelectron spectroscopy and Raman spectroscopy. Exposure of Ge(100) and Ge(111) to S drives the formation of Ge sulfide near-surface layers. At low temperatures, the reaction products comprise a thin GeS interlayer terminated by near-surface GeS2. Above 400 °C, exposure to sulfur gives rise to single-phase GeS2 layers whose thickness increases with temperature. Arrhenius analysis of the GeS2 thickness yields an activation energy (0.63 ± 0.08) eV, close to the barrier that controls Ge oxidation by O radicals. XPS measurements after extended ambient exposure show a stable, ultrathin near-surface GeS2 without significant oxidation, indicating that Ge–sulfides may provide an effective surface passivation for Ge surfaces. [ABSTRACT FROM AUTHOR]

CoxPt100−x nanoalloys have been synthesized by two different chemical processes either at high or at low temperature. Their physical properties and the order/disorder phase transition induced by annealing have been investigated depending on the route of synthesis. It is demonstrated that the chemical synthesis at high temperature allows stabilization of the fcc structure of the native nanoalloys while the soft chemical approach yields mainly poly or non crystalline structure. As a result the approach of the order/disorder phase transition is strongly modified as observed by high-resolution transmission electron microscopy (HR-TEM) studies performed during in situ annealing of the different nanoalloys. The control of the nanocrystallinity leads to significant decrease in the chemical ordering temperature as the ordered structure is observed at temperatures as low as 420 °C. This in turn preserves the individual nanocrystals and prevents their coalescence usually observed during the annealing necessary for the transition to an ordered phase. [ABSTRACT FROM AUTHOR]

Reactions of Ge with S vapor, of interest as a potential approach for forming thin passivation layers on Ge surfaces, have been studied by photoelectron spectroscopy and Raman spectroscopy. Exposure of Ge(100) and Ge(111) to S drives the formation of Ge sulfide near-surface layers. At low temperatures, the reaction products comprise a thin GeS interlayer terminated by near-surface GeS 2 . Above 400 °C, exposure to sulfur gives rise to single-phase GeS 2 layers whose thickness increases with temperature. Arrhenius analysis of the GeS 2 thickness yields an activation energy (0.63 ± 0.08) eV, close to the barrier that controls Ge oxidation by O radicals. XPS measurements after extended ambient exposure show a stable, ultrathin near-surface GeS 2 without significant oxidation, indicating that Ge-sulfides may provide an effective surface passivation for Ge surfaces.

Co(x)Pt(100-x) nanoalloys have been synthesized by two different chemical processes either at high or at low temperature. Their physical properties and the order/disorder phase transition induced by annealing have been investigated depending on the route of synthesis. It is demonstrated that the chemical synthesis at high temperature allows stabilization of the fcc structure of the native nanoalloys while the soft chemical approach yields mainly poly or non crystalline structure. As a result the approach of the order/disorder phase transition is strongly modified as observed by high-resolution transmission electron microscopy (HR-TEM) studies performed during in situ annealing of the different nanoalloys. The control of the nanocrystallinity leads to significant decrease in the chemical ordering temperature as the ordered structure is observed at temperatures as low as 420 °C. This in turn preserves the individual nanocrystals and prevents their coalescence usually observed during the annealing necessary for the transition to an ordered phase.