Theoretical design of molecular diode based on thiol- and amino- terminated molecules

Utilizing density functional theory (DFT) and non-equilibrium Green’s function, we systematically studied the electrical transport and rectification properties of thiol- and amino-terminated molecules embedded in graphene nanoribbons. We firstly found the thiol-terminated molecules show better electron transport properties compared to the amino-terminated, which can be attributed to the strong electronwithdrawing ability and favorable coupling effects. Secondly, the symmetrical molecules show almost symmetrical current-voltage (I-V) curves and exhibit negligible rectification effects. On the other hand, the asymmetrical molecules exhibit asymmetrical I-V curves and better rectification performance. The rectification effect is closely related to molecular asymmetry degrees. For example, the rectification ratio of asymmetric N6 ((E)-Nl-(3-aminopropyl)-but-2-ene-1,4-diamine) molecule is much smaller than the N4 (5-phenylthiazole-2,4-diamine) and N5 (2,6-diaminohexane-1,1,5-triol) molecules. Furthermore, we found the rectification ratio of the asymmetrical amino-terminated molecules can reach 400, while the biggest rectification ratio of the thiol-terminated molecule can only reach 45. These findings offer crucial insights for future graphene molecular electronic device design.