K/Si(100) 2 × 1: A Case Study for the Transfer of Charge between Alkali Metals and Semiconductor Surfaces

Experimental data and theoretical calculations for K/Si(100) 2 × 1 provide a picture of the interface interaction essentially similar to the one established for adsorption of alkali metals on metals in contradiction with recent calculations. In particular, the transfer of charge from K to Si decreases with coverage and it is far from being complete at saturation coverage. The K-Si bond length and the charge transfer indicate that the bonding has a substantial covalent character.