Molecular and atomic manipulation mediated by electronic excitation of the underlying Si(111)-7x7 surface

Abstract

We report the local atomic manipulation properties of chemisorbed toluene molecules on the Si(111)-7x7 surface and of the silicon adatoms of the surface. Charge injected directly into the molecule, or into its underlying bonding silicon adatom, can induce the molecule to change bonding site. The voltage dependence of the rates of these processes match closely with scanning tunnelling spectroscopy of the toluene and adatom species. The branching ratio between toluene molecules which are moved to a neighbouring site, or those that travel further is invariant to voltage, suggesting a common final manipulation step for both injection into the molecule and into the bonding adatom site. At low temperatures the rate of silicon adatom manipulation matches that of toluene manipulation, further suggesting that all these manipulation processes are driven by electronic excitation of the underlying silicon surface. Our results therefore suggest that a common non-adiabatic process mediates atomic and molecular manipulation induced by the STM on the Si(111)-7x7 surface and may also mediate similar manipulation induced by the laser irradiation of the Si(111)-7x7 surface.

Common source of light emission and nonlocal molecular manipulation on the Si(111)−7 × 7 surface

“…As we demonstrated in an earlier work the actual molecular displacement is in fact driven by excitation of the underlying silicon surface [27]. It is possible to manipulate the silicon adatoms of the surface in exactly the same fashion as reported here for the toluene adsorbates [40,41].…”

“…The U 3 state centred at (+2.3±0.5) eV has a clear amplitude at each adatom site. The minimum energy required to manipulate a toluene molecule is +1.4 eV [22,27], and the energy range of photons detectable by our camera is ≈1.4 to 3.1 eV. Thus, we would be insensitive to any transition between the bottom of the U 3 state and next state, U 2 , observed at +1.3 V in the STS (ΔE=0.7 eV).…”

“…To prepare a partially toluene covered surface (∼3 molecules per unit cell) the Si(111)−7×7 surface was dosed through a computer-controlled leak valve. Automated drift tracking combined with a feature locking technique was used to ensure stability during charge carrier injection [22,23,27,28]. Typical values of the drift compensation ranged from 100 fm s −1 up to 2 pm s −1 in all three directions.…”

Local resonances in STM manipulation of chlorobenzene on Si(111)-7×7: performance of different cluster models and density functionals

“…In addition to the diffusive hole transport, a region near to the injection site (<15 nm) was identified where a ballistic hole transport leads to a substantial reduction of the reaction probability, which one would expect from a purely diffusive model. Furthermore, it was demonstrated that the hole-induced desorption is connected to a surface silicon adatom excitation [31]. For the thermally activated electron-induced desorption of chlorobenzene in Ref.…”

Desorption induced by low energy charge carriers on Si(111)‐7 × 7: First principles molecular dynamics for benzene derivates

“…Thresholds for the bias voltage of 1.4 eV (electrons) and −1.2 eV (holes) have been determined. Further, it was found that the electron induced process is most probably connected to an excitation of the so called silicon ad‐atom . This is in line with earlier experiments reporting an ad‐atom displacement on the Si(111)‐7 × 7 surface for positive bias voltages in the STM manipulation.…”