Effects of atomic-scale contacts on transport properties through single molecules - ab initio study

Using the RTM/NEGF method, which is a first-principles calculation tool for the quantum transport through nanostructures between electrodes, we study the effects of atomic-scale contacts on the transport properties through single molecules. Electronic states and current-voltage (I-V) characteristics are investigated in various contact conditions with and without single molecules between electrodes. We find that similar nonlinear behaviors appear in the I-V characteristics. Such nonlinear behaviors are determined not only by the HOMO-LUMO electronic states of single molecules between electrodes, but also by the atomic-scale contact conditions. We show that the transitions from tunneling to ballistic regimes affect the I-V characteristics significantly.     

无机固体功能材料的水热合成化学

综述了无机固体功能材料的水热合成化学进展。重点强调强关联系固体、无机-有机杂化材料、缺陷与混合价态固体、三重价态与原子尺度p-n结以及水热生物化学。     

Molecular dynamics investigation on the atomic-scale friction behaviors between copper(0 0 1) and diamond(1 1 1) surfaces

Classical molecular dynamics (MD) simulations are conducted to examine the atomic-scale friction behavior of an infinite flat-flat contact between copper(0 0 1) and diamond(1 1 1) surfaces. Two types of diamond surface, namely H-free and hydrogenated, are constructed and on each of them the copper counterface is brought to slide along the [1 1 −2] and [1 −1 0] crystallographic directions with a variety of loads. The simulation results demonstrate that the hydrogen atoms chemisorbed to the diamond surface can to large extent eliminate the directional dependency of its friction behavior with copper. Under pressures less than 30 GPa, the sliding between copper and hydrogenated is wearless. In this period, the shear stress of them just slightly increases to 0.6 GPa. Between 30 GPa and 32 GPa, copper atoms near the interface begin to be worn and incorporate into the diamond substrate and this causes a sharp shift from 0.6 GPa to 2.7 GPa in their shear stress. In contrast, the sliding process between copper and H-free diamond is always wearless even under pressure beyond 40 GPa. The H-free [1 −1 0] model exhibits much higher shear stress than H-free [1 1 −2] under pressures less than 35 GPa. Beyond 35 GPa, they present nearly consistent shear stress evolution. Moreover, the simulations for hydrogenated diamond models suggest that their friction behavior is independent on sliding velocity only under wearless sliding regime.