Molecular switch modifications by single atom manipulation

The operation of a single molecule as a molecular nanomachine requires controlling the interaction between the molecule and its surrounding with an atomic scale precision. Recently, it has been demonstrated that a single biphenyl molecule adsorbed on a Si(001) surface behaves as bistable molecule at low temperature. By means of ab-initio calculations, we study the underlying physics of this system. A variety of configurations for the adsorbed biphenyl molecule have been investigated [1]. We show that, during its adsorption on Si(001), one hydrogen atom dissociates from one phenyl and bonds to a neighbouring surface silicon atom. After desorbing this hydrogen with a STM tip, the dynamics of the adsorbed biphenyl molecule is strongly modified: it becomes a multistable molecule having four stable states. Local density of states calculations have been performed and compared to the experimental STM topographies. A good agreement has been observed, allowing a deeper understanding of this system [2]. Our study emphasizes that, by means of a single atom manipulation, one expect to be able to control the intrinsic performance of molecular device. [1] M. Mamatkulov et al., Phys. Rev. B 73 (2006) 035321 [2] M. Martin et al., Phys. Rev. Lett (accepted)