First-Principles Study of Rectification in Bis-2-(5-ethynylthienyl)ethyne Molecular Junctions

Electron Transport of the Nanojunctions of (BN) n (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 (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 (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.

Structural and electronic transport properties of a SiC chain encapsulated inside a SiC nanotube: first-principles study

Silicon carbide (SiC) chains and silicon carbide nanotubes (SiCNTs), as promising one-dimensional nanostructures, have potential applications in more controllable nanoelectronic devices. In this paper, we design a completely new hybrid structure with encapsulation of a linear SiC chain inside a SiCNT, using first-principles calculation and the non-equilibrium Green's function formalism to systematically investigate the structural stability and electronic properties, particularly the quantum transport properties. It is found that, due to the nanotube-chain interaction, the stability of this structure is mainly provided by the charge transfer from the hosting tube to the guest chain. Furthermore, the transport properties of the hybrid structure confirm that encapsulation of a SiC chain within a SiCNT can significantly enhance the electronic transport of the component system in a wide range of high voltage. The distance and the unique coupling configuration between the encapsulated system and the electrodes are demonstrated to be other important factors that affect the transport behaviours. We hope that our study of encapsulation may offer a significant starting point for the design of new materials related to low-dimensional SiC nanostructures and possibly open a novel path towards stability and conductivity enhancement.