Angle-resolved Auger-photoelectron coincidence spectroscopy (AR-APECS) of the Ge(100) surface

We have measured the angular distribution of Ge $L_3{M}_{45}{M}_{45}$ Auger electrons in coincidence with Ge ${2p}_{3/2}$ core photoelectrons along the (001) azimuth of the Ge(100) surface. Intensity modulations arising from diffraction effects are suppressed in the coincidence Auger angular distribution and, when specific emission angles of the photoelectrons are considered, new features appear. We attribute the former effect to enhanced surface specificity of the coincidence technique and the latter to sensitivity of the coincidence measurement to alignment of the core hole state.