AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP35
STM Barrier-Height Imaging of Alkali Adsorbed Si(111)7x7

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: S. Kurokawa, Kyoto University, Japan
Authors: S. Kurokawa, Kyoto University, Japan
A. Sakai, Kyoto University, Japan
Correspondent: Click to Email
The chemisorption of alkali metals on silicon is one of the most studied adsorption systems, and a large number of theoretical and experimental investigations have been carried out to understand its atomic and electronic structures. However, little has been known on atomic-scale properties of the K adsorption on Si(111)7x7. Hashizume and his coworkers have investigated the initial stage of K adsorption on Si(111)7x7 by STM, and identified some adsorption geometries of K. They also concluded that the bonding between K atoms and Si(111)7x7 surface atoms changes from ionic when K atoms adsorb individually to weakly covalent when they form clusters. We have performed STM imaging and local barrier-height (BH) measurements upon adsorbed K atoms and clusters. The K coverage is about 0.01ML, which corresponds to a very initial stage of adsorption. We found that the local BH decreases at K cluster and each single K atom. The average BH reduction at the K adsorbed site is -1.9 eV under positive sample bias where the electronic structure of tip has little influence on the BH. According to recent photoemission experiments, the reduction of the work function at the saturation coverage of K is -2.9 eV. The measured BH reduction at K sites is smaller than this value but can be a plausible value since the K-Si bonding at the initial stage of adsorption may be different from that in a K overlayer at the saturation coverage. @FootnoteText@ @footnote 1@ T. Hashizume, K. Motai, Y. Hasegawa, I. Sumita, H. Tanaka, S. Amano, S. Hyodo and T. Sakurai, J. Vac. Sci. Technol. B9, 745 (1991).