Atomic Manipulation at Room Temperature

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Atomic manipulation with the scanning tunneling microscope (STM) is the extreme limit of nanotechnology. The experiments to date have generally been done at low temperatures, where the thermal energy is low enough that the atoms do not move around randomly. Atomic manipulation at room temperature is a new ball game. One approach is to anchor a molecule to the surface through a chemical bond, such that a particular target group is presented to the tip of the STM, which can be used as a molecular-scale source of electrons. The aim is to achieve bond-selective molecular manipulation - one of the frontiers of nanoscale science. Our understanding of the mechanisms of such manipulation (e.g., coupling between the electrons and the vibrations of the molecule, energy dissipation, symmetry rules, etc) is however in its infancy. The aim of this project is to investigate single molecule excitation and bond-selective dissociation with the STM, at room temperature, in carefully selected molecular systems, building on our previous work published in Nature last year. In the case of chlorobenzene and the related family of polychlorinated biphenyl (PCB) molecules, we will test a model we proposed for two-electron dissociation of the C-Cl bond, which involves symmetry-breaking, by vibrational excitation, which couples together otherwise disconnected ( orthogonal ) molecular orbitals. PCB's are environmentally harmful and we may in the process cast some light on how to break them down.In the case of small molecules chosen to present the S-S (disulphide) group, we will investigate the stability of the bond to charge injection, the competing ( non-adiabatic ) dynamical channels expected to arise as a result of resonance formation and the mechanism of S-S bond fission. This is relevant to the response of biological molecules, notably proteins, to ionising radiation (which generates low energy electrons), since different chains in a folded protein are often connected by S-S bonds between cysteine amino acids.Our recent experiments have established the Birmingham group amongst the leading atomic manipulation groups in the world. The purpose of the present grant proposal is to build on this foundation with a new generation of high impact, room temperature STM manipulation experiments designed to take the work on to the next level.