X-ray photoelectron diffraction for pure and Nb-doped : site determination for the Nb atoms

Abstract
We present a set of polar-angle-dependent x-ray photoelectron spectra (XPS) obtained from in situ cleaved single-crystalline pure . The variation of the intensity for different angles can be explained by the diffraction of the emitted electrons by the surrounding atoms of the emitter and thus may be used as a `fingerprint' for the location of emitting impurity atoms. Measurements were carried out on niobium-doped . The atomic position of the niobium atoms was deduced from the comparison of the angle-dependent spectra, giving a clear hint that tantalum is replaced by niobium.