First principles study on the structure and STM image of acetylene adsorption on Ge(0 0 1)

The adsorption of acetylene on Ge(0 0 1) is investigated by first-principles calculations. The calculations of total energy and simulations of scanning tunneling microscopic images consistently show that the two binding features observed experimentally are di-σ and paired-end-bridge configurations, instead of p-bridge structure. In addition, the bias-dependent STM images and the electronic states from the adsorbed molecule and bare Ge atoms above the surface have been calculated to clarify what cause the adsorbed molecule appear darker than the bare Ge atoms. Particularly, we caution that all features in STM imaging have been adequately simulated by the Tersoff-Hamann theory except tip-sample interactions.