A DFT study on molecular junction devices with cyclic disulfide anchors: Effect of anchor oxidation on electron transport

Abstract

A molecular-scale electronic device can be built with programmable molecular switches sandwiched between two electrodes. A cyclic disulfide, 1,2-dithiolane, is a promising anchor group for attaching molecules to gold electrodes in such molecular junction devices, since its dithiol-Au linkage (with the disulfide bond broken) can provide added stabilities and reduced current fluctuations. However, operations of the molecular switches under redox conditions might lead to redox processes involving the AuAS bonds at the contact. Formation of the disulfide linkage can be induced, and the dithiolate group (AuS) can be converted into disulfoxide (AuSO) or disulfone (AuSO 2 ) groups. Coexistence of these various oxidation states at the contact or the conversion between them can be a potential source of current fluctuation in the junction. However, our nonequilibrium Green's function calculations combined with the density functional theory show that the molecular junctions with different oxidation states of the 1,2-dithiolane alligator clips to two gold electrodes exhibit essentially the same insulating current-voltage characteristics at moderate bias voltages. Therefore, the robustness of the molecular junctions would not be affected by the state change of the disulfide alligator clips at the contact.