Adsorbate structures from photoelectron diffraction: Holographic reconstruction or real-space triangulation?

By preselecting the appropriate photoelectron energies with the aid of simple model calculations, we show that the main peaks in angular distributions of core-level photoemission from adsorbed species on surfaces, caused by elastic backscattering, can be directly related to adsorbate-substrate interatomic directions, thus permitting direct real-space triangulation of adsorption sites on surfaces. The method is demonstrated with the aid of experimental data from oxygen and CO on Cu(110), and offers comparable spatial resolution to holographic inversion, but requires a much smaller data set.