Surface electronic structure and off-site Auger transitions on TaC(111) observed with Auger-photoelectron coincidence spectroscopy

The Ta N7-VV Auger spectrum of TaC(111) has been measured in coincidence with photoemission from the bulk and surface shifted Ta 4f7/2 core levels. Good agreement is found between the surface Auger spectrum and a self-convolution of the density of states (SCDOS) at surface Ta sites determined by a first-principles calculation. The bulk spectrum disagrees with the bulk SCDOS but is well described by an incoherent sum of the bulk SCDOS and the surface spectrum. A novel off-site Auger decay mechanism, first observed on Ta(100), accounts for these observations.