THEORY OF STM AND STS ON P(2X2)NA AL(111)

Scattering theory and Green function theory is used to study scanning tunneling microscopy (STM) and spectroscopy (STS) on p(2 x 2)Na/Al(111 ). The surface unit cell has two different Na and four Al atoms, howev er, in STM experiments in the constant current mode a single protrusio n is observed per surface unit cell. The theory demonstrates that at r elevant rip-sample separations it is due to me Na atoms in the fee pos ition of the topmost intermixed Na-Al layer. The density of states ind uced by the sodium atoms near the Fermi level is the reason for the en hanced tunneling current in the vicinity of Na-fcc. At smaller tunneli ng distances image inversion is observed due to the tip-sample interac tion. STS has been studied in the voltage range from -5 V to +1 V. Fea tures on the clean Al(111) surface are observed at similar bias voltag es as in the STS experiments, however, they are attributed to bulk ban d structure features and not to surface states. Within the voltage ran ge studied STS on p(2 x 2)Na/Al(111) yields a sodium induced peak at t he Fermi edge.