Electron Transport of the Nanojunctions of (BN) (n = 1-4) Linear Chains: A First-Principles Study

We applied the density functional theory and nonequilibrium Green's function method (DFT + NEGF) to investigate the relationship between the conductance and chain length in the stretching process, the asymmetric coupling of contact points, and the influence of positive and negative biases on the electron transport properties of the nanojunctions formed by the coupling of (BN) (n = 1-4) linear chains and Au(100)-3 × 3 semi-infinite electrodes. We find that the BN junction has the lowest stability and the (BN)₂ junction has the highest stability. Under zero bias, the equilibrium conductance decreases as the chain length increases; p_x and p_y orbitals play a leading role in electron transport. In the bias range of -1.6 to 1.6 V, the current of the (BN) (n = 1-4) linear chains increases linearly with increasing voltage. Under the same bias voltage, (BN)₁ has the largest current, so its electron transport property is the best. The rectification effect reflects the asymmetry of the structure of BN linear chains themselves and the asymmetry of coupling with the Au electrode surfaces at both ends. With the chain length increasing, the transmission spectrum near E _f is suppressed, the tunneling current decreases, and the rectification ratio increases. (BN)₄ molecular junctions have the largest rectification ratio, reaching 13.32 when the bias voltage is 1.6 V. Additionally, the Au-N strong coupling is more conducive to the electron transport of the molecular chain than the Au-B weak coupling. Our calculations provide an important theoretical reference for the design and development of BN linear-chain nanodevices.