Four probe electron transport characteristics of porphyrin phenylacetylene molecular devices

Abstract

We examine the transport properties of multi-channels of a porphyrin phenylacetylene (PPA) molecule by changing gate and source voltages at its two terminals. Density functional theory (DFT) within the non-equilibrium Green's function framework (NEGF) is employed to calculate the four probe PPA device by connecting with four Au electrodes using S linkages. Two gate voltages are chosen as 0.6 V (denoted as PPA-0.6) and 1.0 V (denoted as PPA-1.0), respectively. At each certain gate voltage, source voltages are applied in the range of 0.0 V to 1.0 V at a step of 0.2 V. It is found that the magnitude of the gate voltage plays a significant role in the whole transport property. No matter in PPA-0.6 or in PPA-1.0, evident NDR behavior is observed for lead currents. Moreover, a smaller gate voltage could induce a more prominent NDR effect. On the other hand, the relative magnitude of the gate voltage and the source voltage determines the current directions of the gate and source leads. Furthermore, input/output current switches can be achieved for the gate lead at the critical voltage of V_gate = V_source. These interesting transport characteristics are further analyzed from the transmission spectra and the local density of states (LDOS). This presentation provides a clue for exploring novel functional nano-electronic molecular devices based on PPA by tuning gate voltages and source voltages as well as changing lead-to-lead channels.