Yufeng Guo

Mechanical and electrostatic properties of carbon nanotubes under tensile loading and electric field

Coupled mechanical and electronic behaviours of single walled open carbon nanotubes (CNTs) under applied electric field and tensile loading are investigated by the use of quantum mechanics as well as quantum-molecular dynamics techniques based on the Roothaan–Hall equations and the Newton motion laws. Different failure mechanisms and mechanical properties are found for CNTs subjected to electric fields and that subjected to tensile load. The electric field induced breaking in CNT begins from the outmost carbon atomic layers while the tensile load breaks the nanotube near its middle at 300 K. Electronic polarization and mechanical deformation induced by an electric field can significantly change the electronic properties of a CNT. Under electric field, the CNT can be stretched but the toughness is much lower than that under mechanical loading. Applied tensile loading causes no electronic polarization even in a metallic tube but it indeed changes the energy gap of the tube, thus exhibits influence on field-emission properties of CNTs. When a tube is tensioned in an electric field, the critical tensile strength of the tube may decrease significantly with increasing intensity of electric field. The coupling of mechanical and electrical behaviours is an important characteristic of CNTs.

Tuning field-induced energy gap of bilayer graphene via interlayer spacing

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.

Structural transformation of partially confined copper nanowires inside defected carbon nanotubes

The encapsulated copper atoms inside a defected single-walled carbon nanotube escape from the tube through the defect hole as the temperature increases. This causes the partially confined copper nanowires (CNWs) to undergo special structural transformations from a solid to a distinguishable helical layered structure and finally to the liquid state. The defect has a vital function in automatically adjusting the internal pressure and copper atom density. The critical structural transformation temperature of the CNW is significantly influenced by the confinement conditions of the carbon nanotube.

Tunable electronic and magnetic properties of two‐dimensional materials and their one‐dimensional derivatives

Low‐dimensional materials exhibit many exceptional properties and functionalities which can be efficiently tuned by externally applied force or fields. Here we review the current status of research on tuning the electronic and magnetic properties of low‐dimensional carbon, boron nitride, metal‐dichalcogenides, phosphorene nanomaterials by applied engineering strain, external electric field and interaction with substrates, etc, with particular focus on the progress of computational methods and studies. We highlight the similarities and differences of the property modulation among one‐ and two‐dimensional nanomaterials. Recent breakthroughs in experimental demonstration of the tunable functionalities in typical nanostructures are also presented. Finally, prospective and challenges for applying the tunable properties into functional devices are discussed. WIREs Comput Mol Sci 2016, 6:324–350. doi: 10.1002/wcms.1251

Electrostrictive effect on electronic structures of carbon nanotubes

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.

Electronic and transport properties of T-graphene nanoribbon: Symmetry-dependent multiple Dirac points, negative differential resistance and linear current-bias characteristics

Based on the tight-binding method and density functional theory, band structures and transport properties of T-graphene nanoribbons are investigated. By constructing and solving the tight-binding Hamiltonian, we derived the analytic expressions of the linear dispersion relation and Fermi velocity of Dirac-like fermions for armchair T-graphene nanoribbons. Multiple Dirac points, which are triggered by the mirror symmetry of armchair T-graphene nanoribbons, are observed. The number and positions of multiple Dirac points can be well explained by our analytic expressions. Tight-binding results are confirmed by the results from density functional calculations. Moreover, armchair T-graphene nanoribbons exhibit negative differential resistance, whereas zigzag T-graphene nanoribbons have linear current-bias voltage characteristics near the Fermi level.

CrO2 thin films epitaxially grown on TiO2 (001): Electronic structure and magnetic properties

CrO2 thin films epitaxially grown on the rutile TiO2 (001) substrate are studied via density function theory. Due to the strain from the substrate, a semiconductor to half-metal transition with the film growth is observed. It is found that, as the film is thicker than three atomic layers, the half-metallic property can be retained with an antiferromagnetic feature which reduces the total magnetic moment. With the help of ionic and the double exchange picture, the physics behind the half-metallic rebuilding process is revealed.

Strength, Plasticity, Interlayer Interactions and Phase Transition of Low-Dimensional Nanomaterials Under Multiple Fields

Atoms are hold together to form different materials and devices through short range interactions such as chemical bonds and long range interactions such as the van der Waals force and electromagnetic interactions. Quantum mechanics is powerful to describe the short range interactions of materials at the nanometer scale, while molecular mechanics and dynamics based on empirical potentials are able to simulate material behaviors at much large scales, but weak in handling of processes including charge transfer and redistributions, such as mechanical-electric coupling of functional nanomaterials, plastic deformation, fracture and phase transition of nanomaterials. These issues are also challenging to quantum mechanics which needs to be extended to van der Waals distance and larger spatial as well as temporal scales. Here, we make brief review and discussions on such kind of mechanical behaviors of some important functional nanomaterials and nanostructures, to probe the frontier of nanomechanics and the trend to multiscale physical mechanics.

Mechanical and electronic coupling in few-layer graphene and hBN wrinkles: a first-principles study

Wrinkle engineering is an important pathway to develop novel functional devices of two-dimensional materials. By combining first-principles calculations and continuum mechanics modelling, we have investigated the wrinkling of few-layer graphene and hexagonal boron nitride (hBN) and provide a way to estimate their bending stiffness. For few-layer wrinkles under the same strain, the magnitude of structural deformation of each constituent layer gradually decreases from bottom to top layers, while interlayer interaction increases with increasing layer number. Comparing with monolayer wrinkles, the electronic properties of few-layer wrinkles are more sensitive to bending deformation as mechanical and electronic coupling induce charge redistribution at the wrinkles, making few-layer graphene and hBN wrinkles suitable for electromechanical system application.

Multiple negative differential resistance and the modulation in a nanotubelike fullerene D5h(1)-C90

We have preformed a first-principle calculation on the electronic transport properties of a recently synthesized nanotubelike fullerene D5h(1)-C90. One finds three negative differential resistance regions in the I-V curve, which could be modulated by gate voltage and contact configuration. Further analysis showed that, the charge transfer and molecule-electrode coupling, induced by both bias and gate voltages, are responsible for the observed phenomena.