Nanoscale fabrication of well-defined molecular assemblies would give insight into the effect of through-space interactions of molecules. The intermolecular interaction and correlation effect of the neighboring molecules may give rises to novel or enhanced structural and functional properties of materials. The versatility and exactitude of the scanning tunneling microscope (STM) has been used as a main tool for manipulating individual molecules to fabricate molecular assemblies. Controlled manipulation of individual molecules by means of an STM tip has been achieved by using mainly the " tip-molecule interaction ", such as pushing, pulling, sliding and picking up the molecules with a tip. And, the technique has been extended to a wide variety of systems including relatively large fullerenes and molecular clusters, medium-size lander molecules and small substituted benzenes. However, the method by using the tip-molecule interaction is not always possible for the manipulation of adsorbate. Indeed, the lateral manipulation of an isolated CH3S molecule on Cu(111) by the pushing method was not applicable.
A different method for molecular manipulation has been developed by utilizing the molecular vibration through inelastic electron tunneling. However the vibrationally-enhanced molecular motion has been usually governed by the stochastic nature, therefore it is difficult to definitely control the molecular motions. In our previous study, it has been shown that the lateral hopping motion of an isolated CH3S on Cu(111) is induced by the injection of tunneling electrons to manipulate it. In this study, we reveal that the hopping motion of an isolated CH3S on Cu(111) is induced not only by the injection of tunnel electrons into the center of the molecule, but also by the extraction of the electrons from it. Moreover, we show that the direction of the hopping motion can be controlled by the electron injection into (or extraction from) the off-center position of the molecule.
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