Possibility of adsorbate position determination using final-state interference effects

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Abstract
Novel methods for the determination of adsorbate position on surfaces based on final-state interference effects are discussed. The first is the measurement of extended x-ray absorption fine structure (EXAFS) from excitation of the adsorbed atom by monitoring the intensity of the Auger emission line as a function of photon energy. Such an experiment should be feasible with synchrotron radiation. The sensitivity of surface EXAFS to adatom position is demonstrated by calculations appropriate for adsorption of Se on several crystal faces of Ni. We also examine the possibility of measuring EXAFS by monitoring the photoelectron intensity and conclude that an average over a hemisphere outside the crystal is not sufficient to reduce the photoemission data to EXAFS. Relations between EXAFS and angular-resolved photoemission are elucidated and it is shown that the single scattering EXAFS theory includes second-order scattering from the excited atom in photoemission theory.