AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS1+NS-ThM

Paper SS1+NS-ThM9
STM Study of Ultrathin NaCl(111) Layers on Aluminum

Thursday, November 5, 1998, 11:00 am, Room 308

Session: Growth and Thin Films
Presenter: W. Hebenstreit, TU Vienna, Austria
Authors: W. Hebenstreit, TU Vienna, Austria
J. Redinger, TU Vienna, Austria
R. Podloucky, University Vienna, Austria
M. Schmid, TU Vienna, Austria
P. Varga, TU Vienna, Austria
Correspondent: Click to Email
Polar surfaces like NaCl(111) are electrostatically unstable and cannot be found as terminating surfaces of crystals. But we can grow NaCl islands with (111) surface orientation on Al(111) and Al(100) single crystals. The (111) structure is revealed by atomically resolved Scanning Tunneling Microscopy (STM). The maxium coverage we could achive was 0.3 monolayer. The islands are triangular shaped, located at the lower side of substrate step edges and in the case of the Al(111) substrate alinged with the closed packed directions of the substrate. The islands consist of two Na layers with one Cl layer in between. We performed ab initio calculations with the FLAPW (full potential lineraized augumented plane waves) method of the electronic structure of a free standing Na-Cl-Na sandwich structure. These calculations reveal that the Na 3s level is filled with half an electron. The sandwich consists of two +0.5 charged Na metallic layers with a -1 charged ionic Cl layer in between, so the whole film ist neutral, free of dipoles, and electrostatically stable. The film is 4.6% laterally contracted and 5.3% expanded in vertical direction with respect to NaCl bulk distances.