Carrier injection from gold electrodes into thioacetyl-end-functionalized poly(para-phenyleneethynylene)s

Abstract

Carrier injection from a gold electrode into a thioacetyl-end-functionalized polymer, poly(para-phenyleneethynylene)s (TA-PPE), has been investigated by using sandwich and nanogap electrode devices. The results suggest that carrier injection depends on the organized status of the Au/TA-PPE interface. For sandwich devices with spin-coated TA-PPE films, carrier injection is dominated by a thermal emission mechanism with a barrier height of around 1.16 eV. However, as regards devices with nanogap electrodes, when the Au/TA-PPE interface is poorly organized, the carrier injection is dominated by a mixed mechanism consisting of thermal emission and tunneling. When the Au/TA-PPE interface is well organized, i.e., most of the molecules are connected to the Au electrode by Au-S bonds, and the carrier injection is dominated by tunneling, the tunneling barrier height ${\ensuremath{\Phi}}_{B}$ is estimated to be around 1.33--1.43 eV.