The atomic and electronic characteristics of homoepitaxial C(100) thin films and their reactions with very thin erbium deposits have been studied by low-energy electron diffraction (LEED) and photoelectron spectroscopy (X-ray photoelectron spectroscopy [XPS] and ultraviolet photoelectron spectroscopy [UPS]). These films, of 3 mu m thick, are grown by microwave chemical vapor deposition (CVD) and p-doped (10(17) B/cm(3)). Measurements are made on two types of surfaces: plasma-hydrogenated and chemically oxidized. The hydrogenated surfaces exhibit 2(2 x 1) LEED pattern and negative electron affinity (NEA). Under annealing at high temperature (500-650 degrees C) in oxygen (1 to 5 x 10(-5) mbar), the hydrogenated surface is transformed slowly into an oxidized one which has the same atomic and electronic structures as the chemically oxidized surface, namely a (1 x 1) LEED diagram and a positive electron affinity (PEA). Under annealing at high temperature, erbium deposits react with the hydrogenated surface and not with the oxidized one. The reaction is not complete and produces a very thin interface erbium carbide layer. Internal photoemission measurements performed on erbium carbide/diamond contacts, protected against oxidation by a layer of erbium silicide, show potential barrier heights close to 1.9 eV.