M.Y. Zhou

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 investigations of the surface structure designated Zr(0 0 0 1)-(2 x 2)-O

Abstract Initial crystallographic investigations have been made with low-energy electron diffraction for the (2 x 2) structure obtained by adsorbing oxygen on the (0 0 0 1) surface of zirconium. Intensity vs energy curves were measured for six diffracted beams at normal incidence, and levels of correspondence with calculated curves for models in which O atoms occupy octahedral holes between close-packed Zr layers were assessed with the reliability index proposed by Pendry. This analysis suggests that O atoms incorporate into the zirconium structure, and that the metal atoms pack as the f.c.c. structure for the region probed by LEED.

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.

XPS investigations of the interactions of hydrogen with thin films of zirconium oxide I. Hydrogen treatments on a 10 Å thick film

Interactions of hydrogen with the interface formed between ZrO2 and zirconium suboxide (ZrOx, x < 2) were studied on a 10 A zirconium oxide film prepared on gold foil for X-ray photoelectron spectroscopy (XPS) analysis. This film was subject to a set of sequential treatments. Reaction with H2 gas at 2 mbar pressure and room temperature indicates that the ZrO2ZrOx interface appeared to undergo a redox-type reaction and convert to a new ZrO2ZrOy (x<y<2) film. Heating this structure at 300°C in a 10−9 mbar vacuum (residual gas dominantly H2O) resulted in more ZrO2 in the outer region and less ZrOy in the subsurface. By contrast, when this film was treated with a hydrogen plasma, XPS showed enhanced formation of OH groups and complete conversion to the ZrO2-like form. On heating to 300°C, this uniform film regenerates the ZrO2ZrOy interface structure, apparently with desorption of H2O.

The passivation of gallium arsenide surfaces with atomic sulfur

A new technique for bonding sulfur atoms to gallium arsenide surfaces is described. In this technique the surface is exposed to gas‐phase atomic sulfur at 60–70 °C. The resulting surfaces were characterized by angle‐dependent x‐ray photoelectron spectroscopy. The data show that, in contrast to passivation of GaAs by H2S at low temperatures, this technique yields a surface on which the sulfur is almost exclusively bonded only to gallium atoms.

LEED investigations of the Rh(111)-(2 × 2)-O surface structure: measurements with a video analyser in the presence of some electron beam disordering of the adsorbed layer

Abstract A multiple-scattering analysis of LEED intensities has been made for the Rh(111)-(2 × 2)-O surface structure. The measurements were made with a video LEED analyser under conditions where the O layer disorders in 2 min in the incident electron beam. The experimental and calculated intensities were compared with Pendrys reliability index, which was minimised with O atoms adsorbed 1.23 A above the “expected” hollow sites of three-fold coordination.

LEED crystallographic studies for the Cu(110)-(2×3)-N surface structure

Abstract An initial multiple-scattering analysis of LEED intensities has been performed for the Cu(100)-type top-layer reconstructions. The best R -factor analysis supports neither simple N overlayer models nor models with Cu(100)-type top-layer reconstructions. The best correspondence between calculated and experimental intensities appears with models where every other 〈001〉 row is missing, similar to that observed for the Cu(110)-(2 × 1)-O surface. The favoured surface structure has N atoms chemisorbed on long-bridge sites such that chains of (Cu a NCu b NCu a ) x create a surface analogous to the ideal Cu 3 N(110) sur face, except that every third N atom is missing from the surface chains. There is evidence that lateral displacement of copper atoms from the ideal positions leads to two different NCu surface bond lengths with values near 1.83 and 1.90 A. Each N atom also bonds to two Cu atoms in the second layer with equal bond lenghts of about 1.88 A.

XPS studies of the nitridation of MoO3 thin films on alumina and silica supports

Abstract X-ray photoelectron spectroscopy has been used to characterize thin films of MoO3 formed on planar oxidized supports, namely AlOx (from aluminum strip) and SiO2 (from silicon wafer). Comparisons are made with behaviour for MoO3 on metallic Mo substrate. It is observed that on calcination at 450°C, the Mo 3d spectral features shift to higher binding energy for MoO3/AlOx and to lower binding energy for MoO3/SiO2. On nitridation by heating in NH3, it is found that the samples on the oxide supports show easier O–N replacement compared with the MoO3/Mo system. In general, the nitridation behaviour for MoO3/AlOx is similar to that of MoO3/Mo, but Mo species in MoO3/SiO2 seem to be more easily reduced (Mo(0) is detected for the SiO2 system but not for AlOx). Comparisons of heating rates for the second nitridation step from 350 to 450°C were made for the MoO3/Mo and MoO3/AlOx samples. Differences between the high heating rate (100 K/h) and the low heating rate (40 K/h) are incremental but definite. The lower heating rate is favourable both for the O–N replacement and for the metal reduction. For example, more Mo(+3) is present after the nitridation to 450°C when the low-heating rate regime is used, compared with that formed when the heating is done at the higher rate.

Optimization of zinc phosphate coating on 7075-T6 aluminum alloy

A zinc phosphate coating process on 7075-T6 aluminum alloy has been significantly improved through a combined approach of titanium colloid pretreatment, pH level adjustment, fluoride additive and ZnO/H 3 PO 4 ratio adjustment. In particular, optimum phosphate coatings were formed in coating baths with a ZnO/H 3 PO 4 ratio of 0.205 and 0.256. Coating morphology studied by SEM reveals that the adjustment in the coating procedure produces an improved crystalline coating layer with high coverage and small grain size. For coatings formed in a bath with a ratio of 0.205, the coverage of the crystalline patches on top of the amorphous coating base is almost complete. The chemical composition of the coating layers has been characterized by XPS and SIMS. The crystalline and amorphous coating phases formed in the bath with a ratio of 0.205 were found to have compositions given schematically as Zn x (PO 4 ) and Zn x Al y (PO 4 ), respectively. In contrast, neither coating phase formed in the bath with a ratio of 0.256 shows the presence of Al.

The effect of Ti-colloid surface conditioning on the phosphating of 7075-T6 aluminium alloy

Abstract7075-T6 aluminium alloys panels were surface conditioned in a titanium colloid suspension, under a variety of different conditions, and subsequently these samples were immersed in a ZnO + H3PO4 coating mixture, and the phosphate coating layers characterized. Morphologies observed by scanning electron microscopy (SEM) reveal that the coating layer consists of two phases, namely an amorphous phase, which is directly bonded to the substrate, and a crystalline phase, in which larger crystal grains grow on top of the amorphous base. Chemical compositions of the coating layers were analysed by X-ray photoelectron spectroscopy (XPS) and by static and imaging secondary ion mass spectroscopy (SIMS). It is found that the details of the surface conditioning affect the final coating, both in terms of morphology and chemical composition. For example, larger amounts of Zn and P are detected in coatings for which the initial conditioning is done at 40°C, compared with room temperature; a similar statement can be made for surfaces which are water rinsed after the Ti pretreatment, compared with those which are not water rinsed prior to the coating treatment.