Interface formation of alkali metals on si (111) surfaces

The nature of interfaces formed between alkali metals and silicon (111) surfaces have been investigated with photoemission techniques. The Si(111) 7 × 7-Cs surface is found to exhibit an adatom dangling bond derived surface state with > 0.4 eV downward dispersion. The metallization of this surface upon continued evaporation beyond the saturation of the Cs4d photoemission intensity and the minimum of the workfunction is confirmed through the appearance of a Fermi level cutoff and an asymmetric broadening of the Cs 4d level. The latter shows that the Cs overlayer becomes metallic. Adsorption of K and Cs on the Si(111) 2 × 1 surface is found to be far from equivalent systems. Potassium donates charge to the unoccupied π* dangling bond band resulting in a crossing of the Fermi level of this band and, consequently, a metallic state of the underlying silicon surface of Si(111) 2 × 1-K. Caesium, on the other hand, induces a reconstruction of the 2 × 1 surface into a Si(11 l)√3 × √3R30°-Cs surface. On the latter surface, one empty and three filled surface states have been found, and their dispersions are presented. These results are discussed in connection with theoretical predictions. © 1992 Taylor & Francis Group, LLC.