High Binding Energy Component Research Articles

Core level photoemission and theoretical studies of cyano organic compounds

The X-ray photoemission spectroscopy (XPS) study of the C1 s core level of polyacrylonitrile (PAN), (CH 2CHCN) x , reveals two components separated by 1.0 eV with the following intensity: 2 for the high binding energy (BE) component and 1 for the low one. To interpret the spectrum, the polymer is modelled by molecules where the nearest-neighbour's environment is respected and an ab initio calculation of the C1 s vertical ionization energies (IE) in the series CH 3CN, CH 2CHCN, CH 3CH 2CN, CH 2CNCH 2CH 2CN, CH 3CHCNCH 3, CH 4 and CH 3CH 2CH 3 is performed. A ΔSCF level of approximation is chosen after a detailed study of the smallest CH 3CN molecule. In all the compounds studied the binding energy of the 1 s level of a carbon atom increases as its distance from the nitrogen atom decreases. The use of this rule enables us to interpret the C1 s XPS spectrum of polyacrylonitrile and CH 3CH 2CN together with those of two other cyano molecules: CNC 6H 4CN and CH 2CNCHCHCH 2CN.

X-ray photoelectron spectroscopy study of fluorine-treated YBa2Cu3O7−δ crystals

An x-ray photoelectron-spectroscopy study of flux-grown YBa2Cu3O7−δ crystals left in moist atmospheric conditions has shown some aspects of the degradation process. Besides peaks which correspond to YO and BaO bonding in the superconducting phase, higher binding-energy components can be attributed to BaCO3, YOH, and/or YCO3 bonding. An x-ray photoreduction of the copper species is observed in the ultrahigh vacuum. Fluorine-gas treatments carried out at low temperature drastically modify the surface properties of the crystals. The peaks attributed to MO bonding (M=Y, Ba, or Cu) disappear and are substituted by MF bonding with a subsequent increase in Eb. In the F 1s region, the peak corresponding to those bondings is observed around Eb ≂684.5 eV, a value which is in agreement with those claimed for the corresponding inorganic fluorides. The signature of those surface fluorides remains, even when the samples are left for long periods in moist air. Within the F 1s envelope, chemisorbed fluoro species with Eb ≂686.5 eV are observed, especially when the fluorination process is performed at room temperature. These species are eliminated by vacuum annealing at 350 °C. In specific conditions, a high-binding-energy contribution arises (Eb ≂689 eV) which can be ascribed to the formation of surface ‘‘carbon fluoride.’’

XPS study on the early stages of oxidation of Si(100) by atomic oxygen

Abstract Clean Si(100) surfaces were oxidized at room temperature by N 2 O exposure and by the successive exposure of atomic oxygen formed via the photochemical decomposition of N 2 O. X-ray photoelectron spectroscopy (XPS) was employed to study the oxidation step by atomic oxygen. The O(1s) XPS spectra consist of two bands; the higher binding energy component was ascribed to oxygen bonded to the dangling bond of the top-most Si atom and the lower binding energy component to oxygen bridging two Si atoms. The binding energy (BE) of oxygen showed an abrupt shift for very thin oxide films. This abrupt BE shift may be explained in terms of charge transfer from Si to O in the ground state rather than in the final hole state. Some evidence for layer-by-layer oxidation was obtained in the BE shift, oxide thickness, and the evolution of the suboxide species. The oxidation process by atomic oxygen was simulated, based on a random bonding layer-by-layer mechanism for the 2 × 1 reconstructed surface with Si-Si dimer bonds. Among Si(111) and Si(100), there was no essential difference in the oxidation process by atomic oxygen.

XPS study on the early stages of oxidation of Si(100) by atomic oxygen

Clean Si(100) surfaces were oxidized at room temperature by N 2O exposure and by the successive exposure of atomic oxygen formed via the photochemical decomposition of N 2O. X-ray photoelectron spectroscopy (XPS) was employed to study the oxidation step by atomic oxygen. The O(1s) XPS spectra consist of two bands; the higher binding energy component was ascribed to oxygen bonded to the dangling bond of the top-most Si atom and the lower binding energy component to oxygen bridging two Si atoms. The binding energy (BE) of oxygen showed an abrupt shift for very thin oxide films. This abrupt BE shift may be explained in terms of charge transfer from Si to O in the ground state rather than in the final hole state. Some evidence for layer-by-layer oxidation was obtained in the BE shift, oxide thickness, and the evolution of the suboxide species. The oxidation process by atomic oxygen was simulated, based on a random bonding layer-by-layer mechanism for the 2 × 1 reconstructed surface with Si-Si dimer bonds. Among Si(111) and Si(100), there was no essential difference in the oxidation process by atomic oxygen.

XPS study of the oxidation process of Si(111) via photochemical decomposition of N 2O by an UV excimer laser

Early stages of Si(111) oxidation by N 2O via the dissociative adsorption at room temperature as well as via the photochemical decomposition have been investigated with X-ray photoelectron spectroscopy (XPS). Monolayer coverage was accomplished by 10 4 L N 2O exposure, and further oxidation did not take place by N 2O alone. The asymmetric O(1s) spectra were deconvoluted into two bands. The higher binding energy component was ascribed to the oxygen in the on-top sites and the lower binding energy one to the oxygen in the bridge sites in accordance with the assignment by Hollinger et al. [Surface Sci. 168 (1986) 609]. The ratio of the intensity of these two components was almost the same as that observed in the oxide formed by O 2, suggesting that the adsorbed oxygens for N 2O at monolayer coverage are incorporated into the same sites as those for O 2. Radical oxygen produced by an UV laser (193 nm) via photochemical decomposition of N 2O could enhance the further oxidation. In the plots of the nominal thickness ( d OX ) of the oxide layer versus the yield of the oxygens incorporated into the Si surface, there appeared a distinct inflection region around d OX ≈5 A ̊ , where the rate of growth of the oxide layer seems to become slow in spite of the net uptake of oxygen. This suggests that the radical oxygen atoms supplied make bonds preferentially with the topmost silicon atoms till the SiO 4 are completed. The simulation of the oxidation step based on the layer-by-layer random bonding model can explain the evolution of the intermediary suboxide species in the early stages of oxidation and the appearance of such inflection region. It is suggested that the interface structure between c-Si and a-SiO, may be abrupt.

Bonding of a simulated epoxy resin to aluminium surfaces studied by XPS

A simulated epoxy resin has been synthesized, and its adsorption on anodised aluminium and aluminium, cleaned by ion bombardment and then exposed to oxygen, has been studied by X-ray Photoelectron Spectroscopy. Thick adsorbed layers gave a narrow N 1s spectrum similar to that of the bulk material though assignment of binding energies was complicated by differential charging effects. The N 1s spectra of monomolecular overlayers showed two types of nitrogen were present. The high binding energy component was assigned to nitrogen bonded to the surface in a chelate structure in agreement with previous Inelastic Electron Tunneling Spectroscopy studies. Subsequent exposure to water altered the bonding of the nitrogen to the surface.