First-principles molecular dynamics study of alkali-metal adsorption on a Si(001) surface

Abstract

The alkali-metal (Li, Na, K) adsorption on a Si(001) surface is studied for a wide range of coverage ( θ = 1 6 −2.0 ). The optimized configuration and their electronic structures are obtained by using the first-principles molecular dynamics method. For Na and K adsorption, the double-layer model proposed by Abukawa and Kono [Phys. Rev. B 37 (1988) 9097] is strongly supported by our theoretical calculation. Most of the available experimental data are consistent with our results. In particular, the charge density analysis based on the double-layer model can explain the seemingly contradictory STM image successfully. Li adsorption is very different from Na and K adsorption. Li can be adsorbed beyond 1.0 monolayer (ML) and breaks the Si-Si dimerization at 2.0 ML. It is suggested that the coverage where the experimental work function starts to saturate with Li adsorption may be 2.0 ML.