Adsorbate structure determination on surfaces using photoelectron diffraction

Abstract

Photoelectron diffraction is the name given to the phenomenon resulting from the coherent interference of the directly emitted component of an electron wavefield, emerging from an atom as a result of core level photoemission, with other components elastically scattered by surrounding atoms. Experimental characterization of this effect provides information which can be used to provide quantitative determinations of the structure of surfaces, and particularly of adsorbed species on surfaces, in an elementspecific fashion. Since the initial demonstration of the phenomenon in the late 1970s, an extensive methodology for surface structure determination has been developed. In this review the background physics of the process, and the development of the technique is described. A brief discussion of the high energy forward scattering version of the technique (x-ray Photoelectron Diffraction-XPD), which utilizes zero-order diffraction effects, is included, but the most of the review is concerned with the lower energy backscattering method more relevant to the determination of detailed adsorption sites on surfaces. In addition to the general theoretical, experimental and methodology background, a number of the more recent developments are described including use of 'direct inversion' methods for (approximate) structure determination, including a survey of photoelectron holography, and the realization of chemical shift photoelectron diffrao tion to allow structure determinations of surfaces including atoms of one element in more than one inequivalent site. All of the developments are illustrated with specific examples, mainly of molecular and atomic adsorbates on metal surfaces.

Structure of a Model Dye/Titania Interface: Geometry of Benzoate on Rutile-TiO2 (110)(1 × 1)

“…attachment to the surface is through both of the carboxylate oxygen atoms to two adjacent five-fold surface titanium atoms; scanned-energy mode PhD data are normally most sensitive to nearest neighbor atoms below the emitting atom 23,24 . Such a conclusion is in agreement with previous proposals/predictions of the local adsorption geometry of benzoate on TiO 2 (110)(1×1) 2,4,[25][26][27][28][29][30] .…”

“…This effort involved the usual trial-and-error methodology of generating simulated modulation functions for a systematic series of adsorption geometries, searching for the best fit between experiment and theory as measured using a reliability factor (R-factor) 23,24 ; this Rfactor is defined such that a value of 0 corresponds to perfect agreement between theory and experiment, a value of 1 corresponds to no correlation and a value of 2 to anti-correlation.…”

“…All of the PhD data presented in this paper were acquired from TiO 2 (110)(1×1) surfaces PhD data to a form suitable for structure determination a standard methodology was applied 23,24 . Briefly, the intensity of each of the peaks present in an EDC is extracted by fitting with appropriate functions i.e.…”

The structure of the V2O3(0001) surface: A scanned-energy mode photoelectron diffraction study

“…Each of these data sets was processed following our general PhD methodology (e.g. [25]) in which the individual EDCs are fitted by the sum of Gaussian peaks, associated steps and a template background extracted from the high kinetic energy tails of the individual EDCs.…”

“…The quality of agreement between the theoretical and experimental modulation amplitudes is quantified by the use of an objective reliability factor (R-factor) defined [25,26] such that a value of 0 corresponds to perfect agreement and a value of 1 to uncorrelated data. Note that our general methodology is to calculate the R-factor from the complete set of experimental PhD spectra used in the theory/experiment comparison.…”