Site- and energy-selective intramolecular manipulation of polychlorinated biphenyl (PCB) molecules

Non-local atomic manipulation on semiconductor surfaces in the STM: the case of chlorobenzene on Si(111)-7×7

Control over individual atoms with the scanning tunnelling microscope (STM) holds the tantalising prospect of atomic-scale construction, but is limited by its "one atom at a time" serial nature. "Remote control" through non-local STM manipulation-as we have demonstrated in the case of chlorobenzene on Si(111)-7×7-offers a new avenue for future "bottom-up" nanofabrication, since hundreds of chemical reactions may be carried out in parallel. Thus a good understanding of the non-local manipulation process, as provided by recent experiments, is important. Comparison of scanning tunnelling spectroscopy (STS) measurements of the bare Si(111)-7×7 surface and chemisorbed chlorobenzene molecules with the voltage dependence of the non-local STM-induced desorption of chlorobenzene proves particularly instructive. For example, the chlorobenzene LUMO appears at +0.9 V with respect to the Fermi level, whereas non-local manipulation thresholds are found at +2.1 V and +2.7 V. This difference supports a picture in which the voltage thresholds for non-local electron-induced desorption depend principally on the energies of the electronic states of the surface. Furthermore, the demonstration that the non-local process is largely insensitive to surface steps up to five layers in height suggests that either the electron transport in this process is subsurface in character or surface charge transport is responsible but is in some way unaffected by the steps.

Preparing and regulating a bi-stable molecular switch by atomic manipulation

We present a scanning tunneling microscopy (STM) investigation into the influence of the STM tip on the adsorption site switching of polychlorinatedbiphenyl (PCB) molecules on the Si(111)-7 × 7 surface at room temperature. From an initially stable adsorption configuration, atomic manipulation by charge injection from the STM tip prepared a new bi-stable configuration that switched between two bonding arrangements. No switching rate bias dependence was found for +1.0 to +2.2 V. Assuming a thermally driven switching process we find that the measured energy barriers to switching are influenced by the exact location of the STM tip by more than 10%. We propose that this energy difference is due the dispersion interaction between the tip and the molecule.