Hou Shi-Min

Field emission from an array of free-standing metallic nanowires

Arrays of single crystalline gold nanowires were synthesized electrochemically in porous polycarbonate membranes. The polycarbonate membrane was then removed to obtain free-standing nanowires for field emission measurements. The turn-on electric field strength for field emission is found to be lower than 2V/µm. The actual electric field that extracted electrons out of the gold nanowires is estimated to be about 103 times higher than the field directly expected in the model of a parallel plate condenser. The availability of the field emission is therefore attributed to the strong electric field at the tips resulting from small curvature radius of the gold nanowires.

Single wall carbon nanotubes and their electrical properties

Single-wall carbon nanotubes (SWCNTs) were synthesized and purified. A water colloid of SWCNTs was prepared and used to assemble SWCNTs onto a gold film surface. Scanning tunneling microscopy (STM) images showed that short SWCNTs stood on gold film surfaces. Using STM tips made of SWCNTs, a crystal grain image of a gold thin film and an atomic resolution image of highly oriented pyrolytic graphite were successfully obtained. The electrical properties of short SWCNTs, which stood on the surface of gold film, were measured using STM. That SWCNTs stand on gold thin films is a promising technique for studying structures and properties of carbon nanotubes, as well as assembling and fabricating high-intensity coherent electron sources, field emission flat panel display, tips for scanning probe microscopes, new nanoelectronic devices, etc.

Structure and Electrical Properties of Gold Nanowires Grown with Electrochemical Deposition

The effect of Al substitution for Fe on the structure, magnetostriction, anisotropy and spin reorientation of a series Of Tb-0.3 Dy-0.7 (Fe1-xAlx)(1.95) alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature has been investigated. It was found that all the compositions of Tb-0.3 Dy-0.7 (Fe1-xAlx)(1.95) substantially retained the MgCu2-type C-15 cubic Laves phase structure and the lattice constant increases with increasing x. The substitution of Al increases slightly the magnetostriction in low magnetic field ( H less than or equal to 40kA.m(-1)) when x 0.15. The intrinsic magnetostriction lambda(111) decreases sharply also with incresasing x. The Mossbauer spectra show that for 0 less than or equal to x 0.15. The measurements of relative susceptibility indicate that the temperature of spin reorientation decreases with increasing x.

Field-ion microscopy observation of single-walled carbon nanotubes

Field-ion microscopy (FIM), a tool for surface analysis with atomic resolution, has been employed to observe the end structure of single-walled carbon nanotubes (SWCNTs). FIM images revealed the existence of open SWCNT ends. Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them. Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles. Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends.

First-principles Calculation of the Conductance of the Al-C 60 -Al Junction

The conductance of an Al-C60-Al molecule junction is calculated using a density functional theory combined with Greens function method. When the molecule is connected to the electrodes and allowed to relax, resonant conductance is the main feature of the transport properties of the Al-C60-Al molecule junction. The conductance around the Fermi level is determined to be about 1.14G0 (G0=2e^2/h). Analysis of the density of states projected onto the frontier molecular orbitals of the C60 molecule shows that electron transport occurs primarily through the lowest unoccupied molecular orbital (LUMO) and the second lowest unoccupied molecular orbital (LUMO+1) of C60. The dependence of the junction conductance on the distance between the C60 molecule and the electrodes is also discussed.

Electronic Transport Properties through Gold–Dithiol-Molecule–Gold Junctions in Equilibrium

We consider the electronic transport through gold–dithiol-molecule–gold junctions. We used an atomically-contacted extended molecule model for the description of such systems. The calculations are based on the matrix Green function method combined with the hybrid tight-binding density functional theory. In order to determine the position of Fermi level, we referenced the experimental results from ultraviolet photoelectron spectroscopy. Our calculation of molecular conductance near the Fermi level qualitatively reproduces the experimental values measured previously [Science 301 (2003) 1221; J. Am. Chem. Soc. 125 (2003) 16164; Nano Lett. 4 (2004) 267]. In addition, we discuss the relationship between different molecular electronic structures and transport properties.

Reversible, electrical and optical switching on silver 3-phenyl-1-ureidonitrile complex thin films

We report on the reversible, electrical and optical switching on silver 3-phenyl-1-ureidonitrile complex thin films. The films can switch from a high impedance state to a low impedance state with an applied electric field at the threshold of 3.5x10(7)V/m. Furthermore, the films can be switched back to the original state by treating the samples at about 80degreesC. The optical recording is fulfilled using a semiconductor laser with a wavelength of 780 nm. Erasure can be accomplished by bulk heating or by the laser working with the power beneath the threshold. No loss of the organic was found in the experiments. This material may have a potential application in ultrahigh data density storage.