MECHANISM OF ELECTRICAL CONDUCTION THROUGH SINGLE OLIGOTHIOPHENE MOLECULES

The temperature dependence of electrical conductance of oligothiophene molecules with the length of 2.2 nm (5-mer), 5.6 nm (14-mer) and 6.7 nm (17-mer) was measured by break junction method with a scanning tunneling microscope to clarify the charge transport mechanisms. The conductance of 17-mer molecule increased exponentially with temperature whereas the conductance of 5-mer and 14-mer molecules did not change. These results indicate that the dominant charge transport mechanism changed from tunneling to thermally activated hopping at molecular length around 6.7 nm (17-mer).