AN UNOCCUPIED SHOCKLEY SURFACE-STATE ON A CARBON DEFICIENT TIC (110) SURFACE

Pendry's one-step model is used to calculate angle-resolved normal inc idence inverse photoemission spectra for a carbon deficient unrelaxed TiC(100) p(1 x 1) surface, as found experimentally. Both a bulk and a surface related peak with GAMMA5BAR(DELTA5) symmetry are present. The latter is identified as a Shockley surface state which is strongly att enuated by carbon vacancies, and exists only for vacancy concentration s well below 20%. Vacancies destroy the hybridization gap between the almost completely occupied lower and unoccupied upper DELTA5 bulk band , necessary for the existence of a surface state of Shockley type. Exp erimental evidence for this particular behaviour is discussed.