Electronic and structural properties of transition-metal carbide and nitride surfaces

Findings concerning the electronic and structural properties of clean surfaces of transition-metal carbides and nitrides are reviewed. Topics treated are: investigations of the occupied and unoccupied bulk band structure and of occurrence of surface and vacancy-induced states, occurrence of chemical shifts and surface shifts in core electron level binding energies, occurrence of surface relaxations/reconstructions on the low-index surfaces and of vacancy concentration gradients in the surface region. A considerable amount of information concerning these topics has been collected to date in both experimental and theoretical investigations. These results are summarized and discussed. The results also show, however, that much remains to be done before a detailed systematic knowledge about the structural and electronic properties and their interrelation has been achieved for this class of compounds.