Initiating and imaging the coherent surface dynamics of charge carriers in real space

Abstract

The tip of a scanning tunnelling microscope is an atomic-scale source of electrons and holes. As the injected charge spreads out, it can induce adsorbed molecules to react. By comparing large-scale ‘before' and ‘after' images of an adsorbate covered surface, the spatial extent of the nonlocal manipulation is revealed. Here, we measure the nonlocal manipulation of toluene molecules on the Si(111)-7 × 7 surface at room temperature. Both the range and probability of nonlocal manipulation have a voltage dependence. A region within 5–15 nm of the injection site shows a marked reduction in manipulation. We propose that this region marks the extent of the initial coherent (that is, ballistic) time-dependent evolution of the injected charge carrier. Using scanning tunnelling spectroscopy, we develop a model of this time-dependent expansion of the initially localized hole wavepacket within a particular surface state and deduce a quantum coherence (ballistic) lifetime of ∼10 fs.

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

“…In recent works diffusion models for holes and electrons have been successfully applied to the nonlocal STM‐induced desorption of benzene derivates, that is, the electron induced desorption of benzene, toluene, and chlorobenzene and the hole driven desorption of toluene . Here, nonlocal means the actual desorption occurs up to several nm away from the STM‐tip.…”

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

“…We show that the voltage threshold of +2.0 V for such STM electron induced nonlocal molecular manipulation matches the voltage threshold for STL electron induced light emission. Building on our prior nonlocal manipulation work [21][22][23] and other group's STL work [20,24], we suggest a common mechanism for these electron induced events. Namely, a fast inelastic relaxation of the injected charge to the bottom of a high-lying electronic surfaceresonance, followed by elastic diffusive transport away from the injection site and eventual inelastic decay to a lower lying surface state with possible outcomes of molecule displacement, or of light emission.…”

“…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.…”

“…We have previously reported on nonlocal manipulation of chlorobenzene and toluene from the Si(111) −7×7 surface [21][22][23]32]. See [33] for a general review of nonlocal manipulation.…”

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

“…Furthermore, one sees that A and B have about 1.0 and 0.8 eV smaller EAs than C Although these numbers are only rough estimates, they nevertheless indicate, that the charged clusters could be at least a reasonable model for localised 'hot' charge carriers with an excess energy in the range of the experimentally observed thresholds, i.e. bias voltages of 1.4 V (electrons) [29] and -1.2 V (holes) [30]. Nevertheless, the estimated energies seem to be more sensitive to the choice of the cluster and/or the quantum chemistry method than most other quantities (see below).…”