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Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid-phase catalytic reactions (e.g., hydrogenation of biomass-derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid-phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X-ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ-Al2 O3 . Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under-coordinated copper atoms on the nanoparticle surface.

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The chemical bonding and electronic properties of wet, chemically treated p-GaN surfaces were studied using synchrotron radiation photoemission spectroscopy. Chlorine-based chemical bonding was identified on the conventional HCl-treated p-GaN surface, which is associated with a shift of the surface Fermi level toward the conduction band edge by ∼0.9 eV with respect to the thermally cleaned surface. Compared to the HCl-treated surface, the surface Fermi level on the KOH-treated surface lies about ∼1.0 eV closer to the valence band edge, resulting in a much smaller surface barrier height to p-type materials than the HCl-treated surface. The smaller surface barrier height to p-GaN after KOH treatment can lead to a lower contact resistivity and can play an important role in lowering the metal contact resistivity to p-GaN.

Well-defined Cu catalysts containing different amounts of zirconia were synthesized by controlled surface reactions (CSRs) and atomic layer deposition methods and studied for the selective conversion of ethanol to ethyl acetate and for methanol synthesis. Selective deposition of ZrO2 on undercoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced by UV–vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The concentrations of Cu and Cu-ZrO2 interfacial sites were quantified using a combination of subambient CO Fourier transform infrared spectroscopy and reactive N2O chemisorption measurements. The oxidation states of the Cu and ZrO2 species for these catalysts were determined using X-ray absorption near edge structure measurements, showing that these species were present primarily as Cu0 and Zr4+, respectively. It was found that the formation of Cu-ZrO2 interfacial sites increased the turnover frequency by an order of magnitude in both the conversion of ethanol to ethyl acetate and the synthesis of methanol from CO2 and H2.

High temperature gas phase reactions between trimethylgallium ͑TMG͒ and ammonia were studied by means of in situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure, and reaction time were chosen to emulate the gas phase environment typical of the metal-organic vapor phase epitaxy ͑MOVPE͒ of GaN. The main gas phase species is ͓(CH 3 ͒ 2 Ga:NH 2 ͔ x , where most probably xϭ3, resulting from the very fast adduct formation followed by elimination of methane. The further gas phase decomposition of this species proceeds through the stepwise elimination of methane. These studies indicate that little TMG exists within the growth ambient under most MOVPE growth conditions. The further gas phase reaction of ͓(CH 3 ͒ 2 Ga:NH 2 ͔ x may be responsible for the strong dependence of the MOVPE GaN growth rate and uniformity commonly observed. © 1996 American Institute of Physics. ͓S0003-6951͑96͒00527-X͔The metal-organic vapor phase epitaxy ͑MOVPE͒ has emerged as the current growth technique of choice for the growth of GaN for device structures.1 Recent successes in the MOVPE formation of commercially viable blue and green light emitters have resulted in an increased activity in understanding the growth process and its relationship to the physical properties of these materials. While MOVPE can produce these materials, the growth of device-quality GaN is complicated by the severe and complicated gas phase interactions, that occur between trimethylgallium ͓͑TMG or (CH 3 ͒ 3 Ga͔ and ammonia, NH 3 which are the commonly used growth precursors.2 These gas phase interactions have been suggested to lead to gas phase depletion of the growth nutrients leading to a degradation in the growth uniformity and efficiency.3 A primary gas phase reaction is the strong adduct forming reaction between NH 3 and TMG. [4][5][6][7] In this present study, we have directly monitored this gas phase reaction in order to better understand its impact on the growth process and system design under those conditions particularly important for MOVPE growth. The species responsible for growth are the direct result of these gas phase reactions.The gas phase reactions of both TMG and NH 3 , individually, are relatively understood at this point. The pyrolysis of TMG has been widely studied. [8][9][10][11][12] The initial step in the TMG decomposition is generally agreed to be the removal of the first methyl radical, resulting in methane as the main product released in the decomposition. In the stepwise first order decomposition of TMG, an apparent activation energy has been measured for the first and second methyl groups, of 58-60 kcal/mol ͑Refs. 8 and 10͒ and 35.4 kcal/ mol, respectively.8 Under similar thermal conditions ammonia is quite stable. The gas phase decomposition of NH 3 occurs only at very high temperatures. 13 The heterogeneous decomposition of NH 3 may, therefore, be essential to GaN growth.The gas phase reaction between (CH 3 ) 3 Ga and NH 3 is less understood, particularly at elevated temperatures characteristic of MOVPE ...

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