G. Loubriel

C(KVV) Auger line shape of chemisorbed CO

Using x‐ray excitation, the C(KVV) Auger spectrum for CO chemisorbed on Ni(100) has been measured and deconvoluted to provide the undistored line shape. This line shape is compared with spectra for gas phase CO and Fe(CO)5(g). The magnitude of Ueff, a final state interaction term, is shown to be near zero for chemisorbed CO, indicating that significantly different relaxation/screening processes occur in this case as compared to gas phase CO and metal carbonyls. Charge–transfer screening of the core hole in the Auger initial state is proposed to account for the small value of Ueff.

Photon-stimulated desorption of H+ and F+ from BeO, Al2O3 and SiO2: Comparison of near edge structure to photoelectron yield

Abstract Photon-stimulated desorption (PSD) spectra of H + and F + from BeO, Al 2 O 3 and SiO 2 are compared to surface and/or bulk photoelectron yield (PEY) spectra at photon energies near the Be(K), Al(L) and Si(L) edges, respectively, as a demonstration of the spectral content of the PSD spectra. The PEY spectra can serve as fingerprints of local geometry and electronic structure from which to deduce the local environment of the desorbed species. This is especially true for these materials in which the near edge structure is determined primarily by the first coordination shell of the excited atom. The main features in the spectra consist of core excitons at threshold followed by a series of “inner-well resonances” whose structure is characteristic of the local environment. Spectral shifts and structural differences are observed between H + and F + spectra and between the PSD spectra and PEY spectra. At the Si(L 23 ) edge in SiO 2 there is ~0.5 eV shift in the excition peak between the H + and F + spectra. The peaks in the spectra closely resemble those for the “first monolayer” of oxide on Si(111) and display significant shifts relative to those of “bulk” SiO 2 . On Al 2 O 3 , H appears to be bonded at a tetrahedrally coordinated Al site as seen in α-Al 2 O 3 while F is bonded at a site with spectral features having both tetrahedral and octahedral characteristics. On BeO both H and F bonded Be sites appear to be essentially identical to bulk sites. A contaminant on the BeO surface in the form of Si fluoride first appears with a Si spectral shape line SiO and then transforms with time to an SiO 2 -like (tetrahedral) spectrum, indicating that the Si has reacted from SiF to SiF 4 . The implications for these kinds of measurements for this class of materials is discussed.

Theoretical calculation of shakeup intensities using Xα–SW wave functions

The ground and 1s core hole state molecular wave functions of CH4, NH3, H2O, and HF obtained from Xα–SW calculations using the touching spheres (TS) and overlapping spheres (OS) approximations are used to calculate the intensity of shakeup satellites observed in their ls core level photoelectron spectra. The sudden approximation was assumed in the calculation. In case of TS Xα–SW wave functions, the one electron overlap integral inside the intersphere was calculated via Green’s theorem. For OS Xα–SW wave functions, the integration over the awkwardly shaped intersphere region was circumvented by distributing the intersphere charge into the atomic spheres according to the charge partition scheme suggested by Case and Karplus. Our results show that there are no significant differences between the shakeup energies calculated from the TS and OS approximations. However, shakeup intensities calculated from TS Xα–SW wave functions are more reliable and in better numerical agreement with experiment.

Photon- and electron-stimulated desorption from rare earth oxides

Resonance in the photon‐stimulated desportion (PSD) spectra of La, Ce, and Er oxides are reported at photon energies near the La(4d), Ce(4d), and Er(3d) edges. These resonances, also seen in soft x‐ray absorption (SXA), arise from excitations of d electrons to the 4f shell. Comparisons of SXA and PSD show how PSD can be used to determine surface valency. ESD data from Ce and Er oxides is used to establish the importance of the 5p level in the electronic pathways which lead to desorption.