A New Approach to Auger and Quasi-Resonant Processes in Ion-Surface Collisions
Solid State Commun.(to appear 2003). Proofs in pdf format

We present a theoretical model of charge exchange between an ion and a solid surface which includes resonant transfer and Auger coupling processes. The Auger processes are treated through an equation of motion approach which results in an Auger self-energy identical to that obtained through the second order Keldysh-Green functions formalism. The model which we report involves a Lorentzian shaped level width for the resonant processes and a wide band form for the Auger processes. It permits an exact solution of the problem in terms of well known functions. The roles played by the characteristic parameters of the problem, which are related to the atom velocity, energy level positions, interaction potential and band structure are illustrated in some simple cases.

Complete Screening and Quasi-Atomic MVV Double Auger Lineshapes
Physical Review Letter, 86 (2001) 1362-1365.

MVV spectra of ph, Pd, and Ag were measured with and without ionization of their L-3 levels. Extra (MMMVV) structure corresponds to the M45M45 --> M45VV transition following the L3M45M45 transition. We interpret the MMMVV structure for Pd as quasiatomic in nature from its similarity to the corresponding Ag spectral shape and from its agreement with atomic calculations. The Pd quasiatomic MMMVV spectrum arises from a two final-state hole bound state in the Pd d band filled by screening of the core holes. These findings represent the first unambiguous observation of the influence of complete screening on spectral features.

Photoelectron Diffraction from Random Surface Alloys
Theory: Surface Science, 497 (2002) 205-213. - slide presentation
Pd on Cu(111): Surface Science, submitted (2001) - slide presentation

Photoelectron Diffraction (PD) is based on electron scattering from an ordered cluster of atoms, as in applications to single crystal ordered alloys. On the other hand, for random single crystal alloys, the lack of periodicity parallel to the surface, which is consequence of the substitutional disorder, complicates the calculation of PD patterns. One way to calculate the PD spectra from random surface alloys is to evaluate the spectra for each member of the complete ensemble of configurations and to then sum to generate the PD spectra from the alloy. The number of different configurations is very large, which makes this approach very time consuming computationally. A computationally efficient approximation, which has had success in applications to LEED from random alloys, is the average t-matrix approximation, where the scattering properties are described by an effective t-matrix. In this work we implemented both methods described above in the cluster-based photoelectron diffraction theory. The theoretical results are compared with experimental data from a random surface alloy, namely Pd on Cu(111) and Cu on Pd(111).