Scanning Tunneling Microscopy Observation of Apparent Molecular Motion Induced by Polarity Change of Electric Fields

We observed apparent molecular motion induced by the polarity change of electric fields by scanning tunneling microscopy (STM), when small amounts of asymmetrical disulfides including susceptible terphenyl moiety to an electric field were embedded into dodecanethiol self-assembled monolayers (SAMs). By taking the direction of the dipole moment into account, the thickness of embedded molecular parts should become larger at the positive bias. However, STM experiments revealed that the thickness of both the molecular protrusions was larger at the negative bias, contrary to this prediction. As a result of scanning tunneling spectroscopy (STS), we concluded that this apparent molecular motion of the embedded asymmetrical disulfides was caused by higher rectification property (or conductance change) of the electrically active terphenyl moiety in mixed SAMs.