An integrated approach to adsorbate structure determination using photoelectron diffraction: Direct ''imaging'' and quantitative simulation

Using scanned-energy mode photoelectron diffraction (PhD) we have developed a two-stage methodology for the quantitative determination of the local geometry of molecular adsorbates on surfaces. The first stage involves the inversion of the experimental adsorbate photoelectron diffraction spectra using a direct method to obtain an ''image'' of the nearest neighbour substrate atoms. The underlying physics is essentially the same as that of inversion in photoelectron holography, but our method has been shown to be effective for many cases and does not require the collection of additional data. The second stage is to optimise the detailed structure indicated by this ''image'' using an iterative trial-and-error comparison of the same experimental spectra with the results of simulations based on multiple scattering calculations. Specific examples of this approach which relate to ammonia, CO and hydrocarbon surface chemistry are outlined in this short review; NH3 and NHx (NH or NH2) adsorbed on Cu(110), CH3O- on Ni(111) and C2H2 on Ni(111).