Surface reactivity of the alkali-metal-induced Ge(111)-3 x 1 surface under ultrahigh vacuum

We have investigated the surface reactivity of the Li- and Na-induced Ge(1 1 1)-3 x 1 surfaces in ultrahigh vacuum (mid-10(-10) Torr range) using core-level photoemission. The core-level peaks from the Li/Ge(1 1 1)-3 x 1 surface showed significant changes over about 15 min, while those from the Na/Ge(1 1 1)-3 x 1 surface remained unchanged. We identified that the changes in the Li/Ge(l 1 l)-3 x I surface were due to the contamination by residual oxygen-containing gases in the chamber, The contamination rate of the Li/Ge(l 1 l)-3 x 1 surface was higher than that of the Ge(1 1 1)-c(2 x 8) surface, indicating that its surface reactivity is enhanced (in contrast to the passivation of the Na/ Ge(1 1 1)-3 x 1 surface). The Li/Ge(1 1 1)-3 x 1 case is against the notion that the common 3 x 1 reconstruction induced by alkali-metal adsorbates passivates the surface as shown for the Na-induced Si(1 1 1)-3 x 1 and Ge(1 1 1)-3 x 1 surfaces. (C) 2002 Elsevier Science B.V. All rights reserved.