Electron transport in semiconducting carbon nanotubes with hetero-metallic contacts

We present an atomistic self-consistent study of the electronic and transport properties of semiconducting carbon nanotube in contact with metal electrodes of different work functions, which shows simultaneous electron and hole doping inside the nanotube junction through contact-induced charge transfer. We find that the band lineup in the nanotube bulk region is determined by the effective work function difference between the nanotube channel and source/drain electrodes, while electron transmission through the SWNT junction is affected by the local band structure modulation at the two metal-nanotube interfaces, leading to an effective decoupling of interface and bulk effects in electron transport through nanotube junction devices.Comment: Higher quality figures available at http://www.albany.edu/~yx15212

Superconductivity in pure and electron doped MgB2: Transport properties and pressure effects

The normal state and superconducting properties of MgB2 and Mg1-xAlxB2 are discussed based on structural, transport, and high pressure experiments. The positive Seebeck coefficient and its linear temperature dependence for Tc<T<160 K provide evidence that the low-temperature transport in MgB2 is due to hole-like metallic carriers. Structural and transport data show the important role of defects as indicated by the correlation of Tc, the residual resistance ratio, and the microstrain extracted from x-ray spectra. The decrease of Tc with hydrostatic pressure is well explained by the strong-coupling BCS theory. The large scatter of the pressure coefficients of Tc for different MgB2 samples, however, cannot be explained within this theory. We speculate that pressure may increase the defect density, particularly in samples with large initial defect concentration.Comment: Presented at NATO Advanced Research Workshop "New Trends in Superconductivity", Yalta (Ukraine) 16-20 September, 200

Scaling analysis of Schottky barriers at metal-embedded semiconducting carbon nanotube interfaces

We present an atomistic self-consistent tight-binding study of the electronic and transport properties of metal-semiconducting carbon nanotube interfaces as a function of the nanotube channel length when the end of the nanotube wire is buried inside the electrodes. We show that the lineup of the nanotube band structure relative to the metal Fermi-level depends strongly on the metal work function but weakly on the details of the interface. We analyze the length-dependent transport characteristics, which predicts a transition from tunneling to thermally-activated transport with increasing nanotube channel length.Comment: To appear in Phys.Rev.B Rapid Communications. Color figures available in PRB online versio

Water Content and Superconductivity in Na0.3CoO2*yH2O

We report here the correlation between the water content and superconductivity in Na0.3CoO2*yH2O under the influences of elevated temperature and cold compression. The x-ray diffraction of the sample annealed at elevated temperatures indicates that intergrowths exist in the compound at equilibrium when 0.6 < y < 1.4. Its low-temperature diamagnetization varies linearly with y, but is insensitive to the intergrowth, indicative of quasi-2D superconductivity. The Tc-onset, especially, shifts only slightly with y. Our data from cold compressed samples, on the other hand, show that the water-loss non-proportionally suppresses the diamagnetization, which is suggestive of weak links.Comment: 10 pages, 10 figures; submitted to Physica C (August 13, 2003

DLC2 modulates angiogenic responses in vascular endothelial cells by regulating cell attachment and migration.

Deleted in liver cancer 1 (DLC1) is a RhoGTPase activation protein-containing tumor suppressor that associates with various types of cancer. Although DLC2 shares a similar domain structure with that of DLC1, the function of DLC2 is not well characterized. Here, we describe the expression and ablation of DLC2 in mice using a reporter-knockout approach. DLC2 is expressed in several tissues and in endothelial cells (ECs) of blood vessels. Although ECs and blood vessels show no histological abnormalities and mice appear overall healthy, DLC2-mutant mice display enhanced angiogenic responses induced by matrigel and by tumor cells. Silencing of DLC2 in human ECs has reduced cell attachment, increased migration, and tube formation. These changes are rescued by silencing of RhoA, suggesting that the process is RhoA pathway dependent. These results indicate that DLC2 is not required for mouse development and normal vessel formation, but may protect mouse from unwanted angiogenesis induced by, for example, tumor cells

Unusual Field-Dependence of the Intragrain Superconductive Transition in RuSr2EuCu2O8

A narrow intragrain phase-lock transition was observed in RuSr2EuCu2O8 under a magnetic field H up to a few Tesla. The corresponding transition temperature, T2, decreases rapidly (about 100 K/T at low fields) with H indicating that the grains of RuSr2EuCu2O8 behave like a Josephson-junction-array instead of a homogeneous bulk superconductor. Our data suggest that the bulk superconducting transition may occur on a length scale well below the grain size of 2 to 6 micrometer