Electronic tunneling through a single molecule embedded in self-assembled monolayer matrices

In studies of molecular devices, it is very important to estimate the electric conductivity of single molecules. This subject has recently been studied in various ways. Weiss and co-workers (J. Am. Chem. Soc. 120 (1998) 2721) estimated transconductance of a single molecule embedded in a self-assembled monolayer (SAM) using scanning tunneling microscopy (STM). In the present work, we studied the transconductance of various single molecules embedded in SAM matrices such as alkanethiolate and biphenylmethanethiolate derivatives. We formed one-component SAMs of decanethiolate (DT) and biphenylmethanethiolate (BPMT) on Au(111), and then inserted 4-carboxyterphenyl-4′-methanethiol (CTPMT) in the one-component SAMs of DT and BPMT. In addition, BPMT used as one of the matrices above was inserted as isolated single molecules in the other one-component SAM of DT. These SAMs enabled us to measure the transconductance of the isolated single molecules using STM. All the STM images of these three types of the mixed SAMs showed that the isolated single molecules were scattered in the one-component SAMs. The STM topographic height differences between the isolated single molecules and the matrices depended on differences in their electronic tunneling conductivities.