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MnO(001) thin films were grown on commercial MgO(001) substrates at 520 °C by reactive molecular beam epitaxy (MBE) using Mn vapor and O2-seeded supersonic molecular beams (SMBs) both with and without radio frequency (RF) plasma excitation. For comparison, MnO(001) films were grown by reactive MBE using O2 from a leak valve. X-ray photoelectron spectroscopy confirmed the Mn2+ oxidation state and 10%–15% excess oxygen near the growth surface. Reflection high-energy electron diffraction and x-ray diffraction evidenced that the films were rock salt cubic MnO with very strong (001) orientation. High-angle annular dark field scanning transmission electron microscopy with energy-dispersive x-ray spectroscopy demonstrated abrupt MnO/MgO interfaces and indicated [(001)MnO||(001)MgO] epitaxial growth. Ex situ atomic force microscopy of films deposited without RF excitation revealed smooth growth surfaces. An SMB-grown MnO(001) film was converted to Mn3O4 with strong (110) orientation by post-growth exposure to an RF-discharge (RFD) SMB source providing O atoms; the surface of the resultant film contained elongated pits aligned with the MgO 110 directions. In contrast, using the RFD-SMB source for growth resulted in MnO(001) films with elongated growth pits and square pyramidal hillocks aligned along the MgO 110 and 100 directions, respectively. [ABSTRACT FROM AUTHOR]

X-ray absorption fine structure (XAFS) spectroscopy, temperature-programmed reduction (TPR), and temperature-programmed hydride decomposition (TPHD) were employed to elucidate the structures of a series of PdRe/Al2O3 bimetallic catalysts for the selective hydrogenation of furfural. TPR evidenced low-temperature Re reduction in the bimetallic catalysts consistent of the migration of [ReO4]− (perrhenate) species to hydrogen-covered Pd nanoparticles on highly hydroxylated γ-Al2O3. TPHD revealed a strong suppression of β-PdHx formation in the reduced catalysts prepared by (i) co-impregnation and (ii) [HReO4] impregnation of the reduced Pd/Al2O3, indicating the formation of Pd-rich alloy nanoparticles; however, reduced catalysts prepared by (iii) [Pd(NH3)4]2+ impregnation of calcined Re/Al2O3 and subsequent re-calcination did not. Re LIII X-ray absorption edge shifts were used to determine the average Re oxidation states after reduction at 400 °C. XAFS spectroscopy and high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) revealed that a reduced 5 wt.% Re/Al2O3 catalyst contained small Re clusters and nanoparticles comprising Re atoms in low positive oxidation states (~1.5+) and incompletely reduced Re species (primarily Re4+). XAFS spectroscopy of the bimetallic catalysts evidenced Pd-Re bonding consistent with Pd-rich alloy formation. The Pd and Re total first-shell coordination numbers suggest that either Re is segregated to the surface (and Pd to the core) of alloy nanoparticles and/or segregated Pd nanoparticles are larger than Re nanoparticles (or clusters). The Cowley short-range order parameters are strongly positive indicating a high degree of heterogeneity (clustering or segregation of metal atoms) in these bimetallic catalysts. Catalysts prepared using the Pd(NH3)4[ReO4]2 double complex salt (DCS) exhibit greater Pd-Re intermixing but remain heterogeneous on the atomic scale. [ABSTRACT FROM AUTHOR]

MoO3/γ-Al2O3 catalysts containing 0.3–3 monolayer (ML) equivalents of MoO3 were prepared, characterized, and tested for ethane oxidative dehydrogenation (ODH) in cyclic redox and co-feed modes. Submonolayer catalysts contain highly dispersed (2D) polymolybdate structures; a complete monolayer and bulk Al2(MoO4)3 are present at >1ML loadings. High ethylene selectivity (>90%) in chemical looping (CL) ODH correlates with Mo+VI to Mo+V reduction; COx selectivity is <10% under these conditions. Mo+V and Mo+IV species trigger CH4 production resulting in much higher conversion albeit with <20% selectivity. In CL-ODH, submonolayer catalysts exhibit ethylene selectivities that decrease linearly from 96% at near-zero conversion to 70% at 45% conversion. >1ML catalysts provide higher conversions albeit with 10%–18% lower selectivity and greater selectivity loss with increasing conversion. In co-feed mode, ethylene selectivity drops to <50% at 46% conversion for a 0.6ML catalyst, but selectivity is virtually unaltered for a 3ML catalyst. We infer that at <1ML loadings, small domain size and strong Mo—O—Al bonds decrease 2D polymolybdate reducibility and enhance ethylene selectivity in CL-ODH. [ABSTRACT FROM AUTHOR]

Ultrathin Si oxynitride films grown by low-temperature remote plasma processing were examined by on-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy to determine the concentration, spatial distribution, and chemical bonding of nitrogen. Although both processes were found to incorporate nitrogen near the Si-SiO(sub 2) interface in a N-Si(sub 3) bonding configuration, the nitrogen areal densities and spatial distributions differed.

A study relating to research on the applications of bimetallic catalysts especially Pd-Au catalysts was conducted to investigate the structures of silica-supported Pd-Au clusters prepared using variations on a particular method developed by two scientists. The reduced catalysts were characterized by a variety of edge X-ray absorption spectroscopic techniques. Experimental methodology, results and implications are discussed.

Research was conducted to examine the ultrathin silicon oxynitride films grown by Ar/N2O remote plasma processing. The methodologies used included on-line Auger electron spectroscopy, secondary ion mass spectroscopy and angle-resolved x-ray photoelectron spectroscopy. Results indicate that atomic oxygen produced in N2O plasma decomposition scavenges nitrogen from the bulk of the film which confines nitrogen to a very narrow region near the substrate.

The (HCpW(CO)3) deprotonation on MgO, gamma-Al2O3 and K/Al2O3 yields surface-bound (CpW(CO3))- complexes which interact with M(n+) counter cations through sigma-CO-ligands. The anion structure resembles that of cyclopentadimethyltricarbonyltungstate(-1) crystalline compounds. Isocarbonyl adducts are present on each surface. Ion adducts with two sigma-CO-ligands in each complex are formed on MgO and gamma-Al2O3.

Homoepitaxial GaN films were grown on GaN(0001)/6H-SiC substrates by NH3 supersonic jet epitaxy at 750°C using a constant Ga flux of 2.9×1014 cm-2 s-1 and varying the NH3 flux and average kinetic energy. Atomic force microscopy (AFM), scanning electron microscopy, and in situ reflection high-energy electron diffraction evidence an abrupt transition from quasi-two-dimensional basal-plane growth to three-dimensional faceted growth at approximately 1/2 of the maximum Ga-limited growth rate, irrespective of NH3 kinetic energy. Topographical scaling analysis of the AFM images reveals that the smooth and rough GaN(0001) films have static scaling exponents (α) of 0.88±0.05 and 1.10±0.06, respectively. The dynamic scaling exponent (β) for rough films is approximately 0.25. A comparison of these scaling exponents with predictions based on continuum growth models indicates that competition between surface diffusion and stochastic roughening governs the evolution of surface morphology during GaN growth. [ABSTRACT FROM AUTHOR]

Low-temperature nitridation of 3 nm SiO[sub 2] films using He/N[sub 2] and N[sub 2] remote radio frequency (rf) plasmas was investigated. On-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy (ARXPS) were employed to determine the concentration, spatial distribution, and local chemical bonding of nitrogen in the resultant films. Experiments were performed using a substrate temperature of 300 °C and 30 W rf power. Nitridation using an upstream He/N[sub 2] remote plasma at 0.1 Torr incorporates nitrogen at the top surface of the SiO[sub 2] film. In contrast, a lower concentration of nitrogen distributed throughout the film is obtained when the process pressure is increased to 0.3 Torr. ARXPS indicates a N–Si[sub 3] local bonding configuration, irrespective of the spatial distribution of N atoms. Slightly more nitrogen is incorporated using a downstream He/N[sub 2] plasma at each process pressure. By comparison, nitridation of SiO[sub 2] films using a N[sub 2] remote plasma at 0.1 Torr is very slow. Optical emission spectroscopy indicates that He dilution enhances the generation of N[sub 2][sup +](B [sup 2]Σ[sub u][sup +]) species by altering the plasma electron energy distribution and by providing an additional kinetic pathway (Penning ionization). Changing the He/N[sub 2] remote plasma configuration from upstream to downstream (at 0.1 and 0.3 Torr) also enhances N[sub 2][sup +](B [sup 2]Σ[sub u][sup +]) generation. For upstream He/N[sub 2] remote plasmas, the intensity of N[sub 2] first positive emission from N[sub 2](B [sup 3]Π[sub g]) states increases with pressure, whereas the N[sub 2][sup +] first negative emission from N[sub 2][sup +](B [sup 2]Σ[sub u][sup +]) states decreases. We infer from these observations that N[sub 2][sup +] species are primarily responsible for top surface nitridation at 0.1 Torr, and that neutral species [N[sub 2](A [sup 3]Σ[sub u][sup +]) metastables and N ... [ABSTRACT FROM AUTHOR]

Homoepitaxial GaN(0001) films grown on metal-organic chemical-vapor deposition (MOCVD) GaN/6H-SiC substrates by using NH3-seeded supersonic beams and Ga from an effusion cell characterized by atomic force microscopy (AFM) in situ reflection high-energy electron diffraction (RHEED) and scanning electron microscopy (SEM) is discussed. A comparison of scaling exponents with predictions based on continuum growth models suggests that competition between surface diffusion and stochastic roughening controls the evolution of surface morphology during GaN growth.

Molybdenum oxide films were deposited on α-Al2O3 (0001) at 580 °C using MoO3 from a conventional molecular beam epitaxy Knudsen cell. A relatively smooth film (RMS roughness 1.1 nm) was deposited in 1 min at 580 °C using a Knudsen cell temperature of 620 °C; however, after 15 min deposition under these conditions, isolated islands (30–50 nm wide × 10–20 nm tall) develop that are stable to annealing at 600 °C for 60 min. XPS evidenced that the films are oxygen deficient with an average formula of MoO2.7. The authors infer that this oxygen deficiency is responsible for their thermal stability and may have significant effects on their catalytic and electronic properties. In contrast, stoichiometric MoO3 films deposited at 400 °C sublime completely during annealing at 600 °C. [ABSTRACT FROM AUTHOR]

Low-temperature nitridation of 3 nm SiO2 films using He/N2 and N2 remote radio frequency (rf) plasmas was investigated. Nitridation using N2 remote plasmas at 0.1 Torr is very slow. N(sub 2)(super +) species are primarily responsible for top surface nitridation.