Work-function changes accompanying changes in composition of (100) surfaces of HfCx and TaCx

Using angle-resolved ultraviolet photoemission spectroscopy with synchrotron radiation, the absolute work functions of four (100) surfaces having estimated compositions TaC1.0, TaC0.5, HfC1.0, and HfC0.6 were determined to be 4.38, 4.73, 4.63, and 3.87 eV, respectively. The results are interpreted qualitatively by considering the work function as a sum of two terms, one which arises from the presence of a surface dipole layer and another which is associated with the Fermi level. The difference in work-function behavior (its increasing with carbon content x for HfCx but decreasing with x for TaCx) is shown to be associated with a difference in Fermi-level behavior