P.C. Wong

Oxide thickness effect and surface roughening in the desorption of the oxide from GaAs

The temperature for thermal desorption of the gallium oxide from GaAs is shown to increase linearly with oxide thickness. In addition, we show by diffuse light scattering that highly polished GaAs substrates roughen during the oxide desorption. These results are interpreted in terms of a model in which the oxide evaporates inhomogeneously.

A comparison of bulk metal nitride catalysts for pyridine hydrodenitrogenation

A comparison of various group IV–VIII bulk metal nitride catalysts identified Co4N and Fe3N as having higher pyridine hydrodenitrogenation activity per unit area than Mo2N. Formation of the metal nitrides was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy, and all the nitrides were prepared from metal oxide precursors using the same temperature-programmed reaction technique. In general, the specific activity of the metal nitrides decreased with increased heat of formation of the metal nitride.

XPS investigations of the interactions of hydrogen with thin films of zirconium oxide II. Effects of heating a 26 Å thick film after treatment with a hydrogen plasma

Abstract In order to help establish the role hydrogen plays in the oxidation and reduction of zirconium oxide thin films, XPS was used to study the effects of heating a 26 A thick ZrO2 film after a hydrogen-plasma treatment. The latter treatment produced a uniform hydrogen-trapped ZrO2 film. Heating to 425°C yielded a reduced suboxide, ZrOx, particularly in the deeper regions of the film, but near the surface this heating produced a zirconium state with Zr3d 5 2 binding energy at 183.4 eV, which is higher than that of ZrO2 by about 0.5 eV. This new chemical state of zirconium appears especially related to ZrOH bonding. This result, with the observed inhomogeneity of the film, strongly suggests that either H2O or OH− species migrate to the surface region of the hydrogen-trapped ZrO2 film during the heating process.

UV photoemission study of sulfide passivated GaAs surfaces

Abstract The aqueous sodium sulfide surface passivation treatment, recently shown to greatly reduce the surface recombination velocity on GaAs surfaces, has been investigated with high resolution UV photoemission spectroscopy. The treatment is found to produce a mixed oxide-sulfide layer on the GaAs. The sulfur is present as a fraction of a monolayer, bonded to arsenic and gallium with no evidence for sulfur-oxygen bonding.

Characterization of sputter deposited tungsten films for x‐ray multilayers

The microstructural and optical properties of tungsten thin films prepared by dc magnetron sputtering were investigated as a function of the argon pressure. The films were characterized by x‐ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), x‐ray diffraction (XRD), grazing x‐ray reflectometry (GXR), and spectroscopic ellipsometry (SE). From the analysis of the XPS data, the films were found to consist of a base tungsten layer, a graded oxide transition layer, and a surface oxide layer. Also, the thickness of the oxide layers were determined. XRD indicated that the films were either amorphous or composed of crystallites with grain size <100 A. STM and GXR have revealed that the films grown at low pressures were the smoothest. Finally, SE measurements allowed the determination of the dielectric function of a compact tungsten layer. Further SE analysis of the films indicated that with increasing argon pressure, the films developed into a more voided columnar structure.

XPS studies of interfaces between γ-glycidoxypropyltrimethoxysilane and aluminum surfaces

Abstract Angular-dependent X-ray photoelectron spectroscopy (ADXPS) has been used to characterize interfaces formed by γ-glycidoxypropyltrimethoxysilane (γ-GPS) deposited on to aluminum panel surfaces. The application of a negative biasing potential to the sample with a thin γ-GPS layer on chemically etched aluminum reveals an extra peak in the Al2p spectra which is tentatively assigned to the effect of direct SiOAl bonding between silane and aluminum oxide. The dual approach of combining the ADXPS and bias potential techniques should have more general application to the non-destructive study of polymer/metal interfaces.

LEED crystallographic analysis for the Rh(111)-(2×1)-O surface structure

An intensity analysis with low-energy electron diffraction is reported for the c(2×2) surface structure obtained on the (100) surface of copper by the adsorption at room temperature of nitrogen activated by an ion gun. The surface was annealed at around 270°C before sets of intensity-versus-energy curves were measured with a video LEED analyser. The curves measured for ten independent diffracted beams were compared with those calculated by full multiple scattering methods. The structural conclusions differ markedly from those in two earlier reports in the literature. We find this surface structure involves N atoms incorporated deeply into the expected hollow sites to become closely coplanar with the topmost copper later. Each N atom becomes essentially 5-fold coordinated with bonding to the atom directly below in the second copper layer, and the topmost Cu−Cu interlayer spacing is indicated to be expanded by about 8% from the bulk value. Further second-order relaxations are possible, but these basic structural features fit a model for the surface derived from the structure of bulk Cu 3 N.

Investigations of the interface between magnesium and polyethyleneterephthalate by X-ray photoelectron spectroscopy

Abstract The interfacial chemistry between in-situ thermally evaporated magnesium and a polyethyleneterephthalate (PET) film is studied by X-ray photoelectron spectroscopy (XPS). The initially deposited Mg atoms adsorb on the PET surface, via an addition reaction to the CO groups, with the simultaneous formation of MgO and MgC bonds. Further metallization shows condensation in the agglomeration mode, with metallic clusters formed by adsorption on to the initial Mg at the PET interface. With exposure of the Mg/PET film to air, the interface does not change although the outer metallic component oxidizes. Rinsing this air-oxidized Mg/PET film with water removes all the magnesium and leaves a modified PET surface compared with its initial state.

XPS studies of the stability and reactivity of thin films of oxidized zirconium

Abstract X-ray photoelectron spectroscopy (XPS) has been used to characterize thin films formed by the deposition of zirconium on to gold foil. With deposition rates of the order of 1 A min-1, in the presence of an atmosphere of 10-9 mbar H2O, the film has an outer region of ZrO2 and inner regions of a lower oxidation state material, ZrOx, and Zr-Au alloy. Initially both ZrOx and Zr-Au alloy are oxidized by either H2O or O2 at 300°C, although this process is hindered as the ZrO2 layer gets thicker. However, even with the protective oxide layer, heating in 5 x 10-7 mbar D2 (with a partial pressure of 10-9 mbar H2O) can convert ZrOx to ZrO2, a reaction apparently facilitated by migrating D atoms.

Leed crystallographic investigations of the lowest-coverage surface structure designated Zr(0001)−(1 × 1)−O

Abstract An intensity analysis with low-energy electron diffraction is reported for the initial (1 × 1) surface structure formed by the adsorption of oxygen on the (0001) surface of zirconium. Comparisons between the intensity-vs-energy curves from experiment and those from multiple-scattering calculations suggest that the structural arrangement involves O atoms occupying octahedral holes below the metal surface. The LEED-determined Zr-O bond distance is 2.30 A, in very close agreement with the value (2.31 A) in bulk ZrO, however at this stage it is not possible to distinguish convincingly between the model involving a single O underlayer immediately below the zirconium surface and those with O incorporated several layers deep.