Search

Introducing sp3 bonds in carbon nanotubes can significantly modify their electronic properties but need high pressure at room temperature. Here we show by molecular dynamics simulations that sp2 to sp3 bond transition can be realized through bending manipulation at the buckling location, resembling that of nanoindented carbon nanostructures but with more convenient operation technique. The capability of sp3 bond formation is sensitive to the thickness and diameter of the carbon nanotubes. This bending induced sp3 structures can serve as tunneling junction for electrons, thus bending manipulation could be a route to tailoring nanocircuits. [ABSTRACT FROM AUTHOR]

Tunable electromagnetic properties of pristine two-dimensional boron phosphide (h-BP) nanosheet and its semihydrogenated structure were studied by density functional theory computations. In sharp contrast to previously reported tensile strain-induced red shift in two-dimensional semiconductors, the direct gap of h-BP undergoes blue shift under biaxial tensile strain. Once semihydrogenated, the h-BP not only transform from the nonmagnetic semiconductor into metal which is spin-resolved but also exhibits linear response between the magnetic moment and biaxial strain with a slope up to 0.005 iB/1%. These findings provide a simple and effective route to tune the electronic and magnetic properties of μ-BP nanostructures in a wide range and should inspire experimental enthusiasm. [ABSTRACT FROM AUTHOR]

We show by density functional theory calculations that asymmetric hetero-stacking of Bi2Te3/Sb2Te3 films can modulate the topological surface states. Due to the structure inversion asymmetry, an intrinsic Rashba-like splitting of the conical surface bands is aroused. While such splitting in homogeneous Bi2Te3-class topological insulators can be realized in films with more than three quintuple layers under external electric fields, the hetero-stacking breaks the limit of thickness for preserving the topological nature into the thinnest two quintuple layers. These results indicate that the hetero-stacking can serve as an efficient strategy for spin-resolved band engineering of topological insulators. [ABSTRACT FROM AUTHOR]

We find experimentally that gas-flow-induced voltage in monolayer graphene is more than twenty times of that in bulk graphite. Examination over samples with sheet resistances ranging from 307 to 1600 Ω/sq shows that the induced voltage increases with the electric resistance and can be further improved by controlling the quality and doping level of graphene. The induced voltage is nearly independent of the substrate materials and can be well explained by the interplay of Bernoulli's principle and the carrier density dependent Seebeck coefficient. The results demonstrate that graphene has great potential for flow sensors and energy conversion devices. [ABSTRACT FROM AUTHOR]

We predict by first-principles calculations a spontaneous charge carrier separation mechanism in pristine [0001]-oriented ZnO nanowires. We find that the shrinking strain induced by surface reconstruction causes electrons and holes to separate and move toward the core and surface region, respectively. Such separation can be enhanced by axially applied tensile strain as a result of the enhancement of surface strain induced by the Poisson effect, and be suppressed by compressive axial strain. Similar carrier separations are found in IIB-sulfides. This intrinsic charge separation and tensile strain induced enhancement are expected to shed light on solar cell designs. [ABSTRACT FROM AUTHOR]

We show by first-principles calculations that H-terminated armchair BC2N nanoribbons (a-BC2NNRs) have exceptional electronic and magnetic properties. In particular, a-BC2NNRs with the B and N atoms uncoordinated can be either p- or n-doped semiconductors, and the wide ones own spontaneous magnetization. It is shown that the magnetism is induced by the localization of acceptor or donor levels from unpaired B or N atoms, and the magnetic moment increases with further increasing ribbon width. The a-BC2NNRs with B and N atoms coordinated have band gaps decreasing with increasing ribbon width. [ABSTRACT FROM AUTHOR]

We show by first-principles calculations that the electronic properties of zigzag graphene nanoribbons (Z-GNRs) adsorbed on Si(001) substrate strongly depend on ribbon width and adsorption orientation. Only narrow Z-GNRs with even rows of zigzag chains across their width adsorbed perpendicularly to the Si dimer rows possess an energy gap, while wider Z-GNRs are metallic due to width-dependent interface hybridization. The Z-GNRs can be metastably adsorbed parallel to the Si dimer rows, but show uniform metallic nature independent of ribbon width due to adsorption-induced dangling-bond states on the Si surface. [ABSTRACT FROM AUTHOR]

By semiempirical molecular dynamics simulations and ab initio total energy calculations, the freestanding (3,0) boron nitride nanotube (BNNT) with a diameter of 2.7 Å is expected to be stable well over room temperature with remarkably higher stability than the experimentally reported (2,2) carbon nanotube. We elucidate the underlying physics by examining the variation in surface dipole and charge reordering driven by geometrical relaxation. In addition, the (3,0) BNNT can become globally stable when encapsulated in a larger BNNT. [ABSTRACT FROM AUTHOR]

Our first-principles calculations reveal surprisingly high sensitivity of the field-induced energy gap of bilayer graphene to changes in its interlayer spacing. Small adjustments in the interlayer spacing near its equilibrium value produce large modulations in the gap over a wide range of field strength. We elucidate the mechanism for the extremely effective gap tuning by examining the interlayer charge redistribution driven by the coupled electric field and nanomechanical effect. [ABSTRACT FROM AUTHOR]

The size dependence of the piezoelectricity in ZnO nanofilms is investigated using ab initio density-functional theory calculations. The effective piezoelectric constant of ZnO nanofilms increases monotonically with increasing film thickness in the nanoscale simulated in the present work, and surprisingly, exceeds that of the bulk ZnO when the thickness is greater than 2.4 nm. The enhancement over the bulk value reaches 11% when the film thickness is 2.9 nm. [ABSTRACT FROM AUTHOR]

The effect of axial electrostrictive deformation on the electronic properties of single walled carbon nanotubes (SWCNTs) is studied by the density functional theory. We find that the band structures of SWCNTs change in electric fields, and the change can be significantly enhanced by the electrostrictive deformation. The polarization of the orbital charge densities and the variation of the dipole moment are also enhanced by the electrostriction. The influence of chirality and size effect on these properties are also analyzed. [ABSTRACT FROM AUTHOR]

Uniformly cold-compressed nanographite sheets in diamond anvil cells (DAC) are found to transform from soft into hard phase at about 17 GPa using molecular dynamics simulations. The hard phase can reach the compressive strength of about 150 GPa. Finite element analyses show that high stress concentrations occur along the boundary of interface on the diamond-anvil culets contacted with the nanographite sheets. The concentrated compressive stress can exceed the strength of diamond in a ring region with the width about 0.2 μm, when the average pressure in the graphite sample is 17 GPa as in [W. L. Mao et al., Science 302, 425 (2003)]. Within the narrow ring, superhard carbon phase can be formed from the nanographite sheets, which leads to cracking of the DAC near the contact edge. [ABSTRACT FROM AUTHOR]