Comparison of Tunneling Barrier Heights among Phenylene Oligomers Adsorbed on Au(111) Using Scanning Tunneling Microscopy

Satoshi Wakamatsu, Uichi Akiba, and Masamichi Fujihira

Department of Biomolecular Engineering, Tokyo Institute of Technology,
4259 Nagatsuta, Midori-ku, Yokohama, 226-8501, Japan

We investigated tunneling barrier heights of phenylene oligomers embedded in self-assembled monolayer (SAM) matrices of shorter phenylene oligomers. The STM topographic height difference between the longer molecule and the matrix does not always reflect the physical height difference, but depends on difference in the tunneling barrier heights between the longer molecule and the matrix. Thus, we prepared three types of two-component SAMs, i.e. a SAM matrix of benzenemethanethiolate (BMT) into which isolated biphenylmethanethiolate (BPMT) or terphenylmethanethiolate (TPMT) molecules were inserted and a SAM matrix of BPMT into which isolated TPMT molecules were inserted. We compared the tunneling barrier heights of the phenylene oligomers using scanning tunneling microscopy.