An efficient nonequilibrium Green's function formalism combined with density functional theory approach for calculating electron transport properties of molecular devices with quasi-one-dimensional electrodes.

An efficient self-consistent approach combining the nonequilibrium Green's function formalism with density functional theory is developed to calculate electron transport properties of molecular devices with quasi-one-dimensional (1D) electrodes. Two problems associated with the low dimensionality of the 1D electrodes, i.e., the nonequilibrium state and the uncertain boundary conditions for the electrostatic potential, are circumvented by introducing the reflectionless boundary conditions at the electrode-contact interfaces and the zero electric field boundary conditions at the electrode-molecule interfaces. Three prototypical systems, respectively, an ideal ballistic conductor, a high resistance tunnel junction, and a molecular device, are investigated to illustrate the accuracy and efficiency of our approach.

First-principles calculation on the conductance of a single 1,4-diisocyanatobenzene molecule with single-walled carbon nanotubes as the electrodes.

The conductance of a single 1,4-diisocyanatobenzene molecule sandwiched between two single-walled carbon nanotube (SWCNT) electrodes are studied using a fully self-consistent ab initio approach which combines nonequilibrium Green's function formalism with density functional theory calculations. Several metallic zigzag and armchair SWCNTs with different diameters are used as electrodes; dangling bonds at their open ends are terminated with hydrogen atoms. Within the energy range of a few eV of the Fermi energy, all the SWCNT electrodes couple strongly only with the frontier molecular orbitals that are related to nonlocal pi bonds. Although the chirality of SWCNT electrodes has significant influences on this coupling and thus the molecular conductance, the diameter of electrodes, the distance, and the torsion angle between electrodes have only minor influences on the conductance, showing the advantage of using SWCNTs as the electrodes for molecular electronic devices.

Synthesis of methane in nanotube channels by a flash.

Inorganic synthesis of organic molecules is a significant step for the primordial life. Generally, inorganic synthesis of methane necessitates, in addition to catalyst, a high-temperature and high-pressure environment. Here we will show that such an environment could be locally and instantly realized in the channels of single-walled carbon nanotubes (SWNTs) even under room temperature and ultrahigh vacuum conditions just by a visible-light flash, owing to the ultra-photothermal effect of nanomaterials. As a result, methane signals were definitely detected by using a quadrupole mass spectrometer and an optical fiber spectrometer. The mechanisms were interpreted as Fischer-Tropsch synthesis. Our results provide an alternative explanation of abiogenic methane origin.

Visible-light-induced water-splitting in channels of carbon nanotubes.

The visible-light-induced split of water confined in channels of single-walled carbon nanotubes (SWNTs) was experimentally studied. Arc-discharging synthesized SWNTs were used to adsorb water vapor and then were irradiated in a vacuum by using light from a camera flash. It was found that a great amount of hydrogen-rich gases could be repeatedly produced under several rapid flashes of light, occasionally accompanying evident charge emission phenomena. A quantitative method was developed to estimate the relative amount of gas components on the basis of the data acquired with an ion gauge and a quadrupole mass spectrometer. The results indicated that hydrogen occupied about 80 mol % of the photogenerated gases, with other components such as carbon oxides, helium, methane and trace of ethane, and the total gas yield in one flash (0.1-0.2 J/cm2, 8 ms) reached 400-900 ppm of the mass of the SWNTs. Such a yield could be repeatedly obtained in serial flashings until the adsorbed water was depleted, and then, by sufficiently adsorbing water vapor again, the same phenomena could be reproduced.

Atomically resolved field emission patterns of single-walled carbon nanotubes.

The electron emission and structural properties of single-walled carbon nanotubes (SWCNTs) were investigated by using field emission microscopy (FEM). The transmission electron microscopy micrograph confirmed the existence of an SWCNT bundle on the W tip. Under appropriate experimental conditions, an FEM image with an elliptic ring-like structure composed of separated bright dots was obtained, a reasonable interpretation of it is that it was produced from the open end for a zigzag (16,0) SWCNT protruding from the SWCNT bundle, each bright dot corresponding to a single atom at the open end. And, if true, this means that the FEM demonstrated 0.2nm resolution, which was theoretically possible for the assumed geometry. The calculated value of the magnification of the pattern was also consistent with the measured value if the value of the compression factor beta was set at 1.76.