Mechanism and adjustability of negative differential resistance of 2-phenylpyridine molecular devices by graphene electrode bending

Combining non-equilibrium Green's function with density functional theory, we study the electronic transport properties of the molecular devices constructed by 2-phenylpyridine and zigzag graphene nanoribbon(ZGNR) electrodes. The I-V characteristics and transmission coefficients under external voltage biases are analyzed, the results show that the negative differential resistance(NDR) is effectively adjusted by the bending of ZGNR electrode, which decrease peak voltage(Vp) and increase the peak-valley ratio(PVR) of the device. When the electrode bending angle is 15°, the PVR of device M2 is maximum (12.84) and Vp is 0.1V, which is low enough for practical applications. The transmission spectra, the density of states and the real-space scattering states distribution at Efof device under zero bias explain that the weaker coupling between the molecules and the electrodes is caused by the bending of the ZGNR electrode,which might be responsible for the adjustability of NDR. The analysis shows that the bending of the electrode changes the electronic structure between the 2-phenylpyridine molecule and the ZGNR electrode, and then changes the wave functions overlap between them, the coupling between the molecule and the electrodes gets weaker. An external bias can induce level shift and the transmission coefficients for the weaker coupling between the molecules and the electrodes can fluctuate wildly from level to level, and large NDR effect under very low bias is obtained with the variation of external bias. Therefore, for highly symmetric molecular devices, the electronic transport properties can be effectively adjusted by changing the coupling between the central molecule and the electrodes. Our investigations indicate that 2-phenylpyridine molecular device with ZGNR electrodes may have potential applications in the field of low-power dissipation molecules device.