ADSORPTION OF K ON CLEAN AND HYDROGENATED SI(100)2X1

This paper presents a study of K adsorption on clean and hydrogen covered Si(100)2 × 1 surfaces (n-type). The experiments were performed in an uhv system equipped with LEED, AES, TDS and WF measurements. Deposition of K on clean Si(100)2 × 1 surfaces at room temperature gives the typical WF curve of an alkali on metal, which goes through a minimum value, min, and a subsequent maximum, max, at saturation alkali coverage. Preadsorption of hydrogen on Si(100)2 × 1 does not change the sticking coefficient and so the maximum coverage of K. However, it causes (i) an increase of the initial dipole moment (ii) a lowering of the min for K on Si(100)2 × 1 : H, monohydride phase, and a rise of the min for alkali on Si(100)2 × 1 : 2H, dihydride phase (iii) a shift of min to smaller θk and (iv) an increase of max. These are attributed to an increase in the K{single bond}Si interlayer distance caused by the preadsorbed hydrogen, which prevents electronic communication between K and the Si substrate, resulting in early and increased metallization in the K overlayer, in agreement with recent theoretical calculations. This is also consistent with the TDS measurements. The latter suggests that the presence of a hydrogen underlayer changes the binding states of the K on Si(100)2 × 1. © 1990 Pergamon Press plc.