Controlling organic reactions on silicon surfaces with a scanning tunneling microscope: Theoretical and experimental studies of resonance-mediated desorption

The dynamics of tip-induced, resonance-mediated bond-breaking in complex or ganic adsorbates is studied theoretically and experimentally. Desorption of benzene from a Si(100) surface is found to be efficient and sensitive to v oltage, the measured yield rising from below 10(-10) to ca. 10(-6) per elec tron within a ca. 0.8 V range at low (< 100 pA) current. A theoretical mode l, based upon first principles electronic structure calculations and quantu m mechanical wavepacket simulations, traces these observations to multi-mod e dynamics triggered by a transition into a cationic resonance. The model i s generalized to provide understanding of, and suggest a means of control o ver, the behaviour of different classes of organic adsorbates under tunneli ng current.