Interaction of hydrogen with TaC(111) and NbC(111) surfaces: Angle-resolved photoemission study

Abstract

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the interaction of hydrogen with TaC(111) and NbC(111) surfaces. The electronic structures of the TaC(111) and NbC(111) clean surfaces are characterized by the surface-induced state at just below the Fermi level. Hydrogen adsorption induces the shift of the state to the higher-binding-energy side by \ensuremath{\sim}0.5 eV at the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} point for both surfaces. However, no H 1s--induced split-off state is found in the photoemission spectra for both surfaces. This invisible state is proposed to be an adsorption in a subsurface site. The electronic structures of the H-adsorbed TaC(111) and NbC(111) surfaces are investigated by off-normal-emission measurements, and it is found that the surface electronic structures are similar to those of the original clean surfaces; the two-dimensional band structures of the H-modified surface states are similar to those for the intrinsic surface states on both surfaces. A possible hydrogen adsorption site in the subsurface region is also proposed.