Current-driven desorption at the organic molecule-semiconductor interface: Cyclopentene on Si(100)

The current-driven dynamics of cyclopentene desorption from the Si(100) surface are studied using scanning tunneling microscopy (STM) measurements and electronic structure, transport, and reaction dynamics calculations. Cyclopentene is shown to desorb from n-type and p-type Si(100) surfaces with clear turn-on behavior at modest (+/- 3 V) sample biases. The yield of the desorption process for this saturated hydrocarbon is found to be 500-1000x lower than for previously studied unsaturated hydrocarbons, and measurements of the desorption rate as a function of tunneling current indicate a single-electron desorption mechanism. Electronic structure calculations point to low-lying resonant states resulting from partial hybridization of the cyclopentene with the silicon dimer, and ionic state equilibrium geometries show substantial distortion with respect to the neutral state. Transport calculations confirm the presence of electronic states lying within 2-3 eV of the Fermi level that possess relatively long electronic lifetimes (90-250 fs). Detailed reaction dynamics calculations indicate poor coupling between the excited modes and the desorption mode, consistent with the low desorption yields observed for cyclopentene. Since cyclopentene possesses a bonding geometry that is shared with many other organic adsorbates on silicon, the work outlined here is expected to have broad applicability to other moleculesemiconductor systems.