Inducing Desorption of Organic Molecules with a Scanning Tunneling Microscope: Theory and Experiments

A scanning-tunneling microscope has been used to induce efficient local desorption of benzene from Si(100) at low currents ( $<100\mathrm{pA}$), sample biases ( $\sim -2.4\mathrm{V}$) and temperatures (22 K). A theoretical model based upon first principles electronic structure calculations and quantum mechanical wave packet dynamics describes this process as occurring via transient ionization of a $\pi$ state of the adsorbed molecule. This model accounts for the unexpected efficiency and sharp threshold of the yield.