Spectroscopic scanning tunnel microscopy of Cl–Si(111)7×7: Determination of Cl–Si σ* resonance line shape

Abstract

Scanning tunnel microscopy (STM) of Cl∕Si(111)7×7 at low coverage has been used to carefully measure a trend with sample bias in height contrast between Cl adsorbates and silicon adatoms. The apparent height of the Cl adsorbate increases monotonically with increasing sample bias. In order to help explain the observed trend a model was developed for the tunnel current between a tungsten tip and the Si(111)7×7 surface. The model uses a tight-binding approach incorporating known local density of states information calculated using density functional theory. Simulation of the clean surface STM topography yields the correct appearance in both positive and negative sample bias. Application of the model to Cl∕Si(111)7×7 allowed for a good fit to the observed contrast trend. Valuable new information on the detailed line shape of the Cl–Si σ* antibonding resonance was obtained. Detailed knowledge of this resonance may well be crucial to future understanding of the unique long-range form of tip-induced diffusion and desorption observed on this system.

Facile Charge-Displacement at Silicon Gives Spaced-out Reaction

“…27 The OPCH pattern is also discernible, in light of the present observations, in the chlorination of the Si(111)-7Â7 surface by trichloroethylene in the STM work of the Patitsas group. 28,29 The exposure was insufficient to reveal the OPCH pattern, but a preference for reaction at corner adatoms leading to a product separation of 30 Å, was observed. The indication from all five chemically different adsorbates (trichloroethylene 28,29 and the four molecules examined here) is that the molecular physisorption of organic halides on Si(111)-7Â7 gives a strong preference for OPCH physisorption and hence, subsequently, OPCH surface-halogenation.…”

Thermodynamically induced particle transport: Order-by-induction and entropic trapping at the nano-scale

“…This is the case, for example, in STM studies of Cl chemisorbed onto Si(111)7 × 7 [49]. Near 3 V bias, the Cl atoms dissociate at a high rate and are imaged as very bright features, approaching 0.2 nm in apparent height [50]. The ∆µ G,qss energy of 2.8 eV is very significant and is large enough to break almost all chemical bonds.…”

“…Towards obtaining an induced potential energy profile for diffusing surface adsorbates near an STM tunnel junction, I invoke the Tersoff-Hamann approach for the tunnel current [66,50]. The result is the form ξ = ξ 0 e α(−L+R) ,…”