Rui-Fen Dou

Strain and curvature induced evolution of electronic band structures in twisted graphene bilayer

It is well established that strain and geometry could affect the band structure of graphene monolayer dramatically. Here we study the evolution of local electronic properties of a twisted graphene bilayer induced by a strain and a high curvature, which are found to strongly affect the local band structures of the twisted graphene bilayer. The energy difference of the two low-energy van Hove singularities decreases with increasing lattice deformation and the states condensed into well-defined pseudo-Landau levels, which mimic the quantization of massive chiral fermions in a magnetic field of about 100 T, along a graphene wrinkle. The joint effect of strain and out-of-plane distortion in the graphene wrinkle also results in a valley polarization with a significant gap. These results suggest that strained graphene bilayer could be an ideal platform to realize the high-temperature zero-field quantum valley Hall effect.

Quantum confinement effect in ZnO thin films grown by pulsed laser deposition

High quality crystalline nanostructured ZnO thin films were fabricated by pulsed laser deposition on (0001) sapphire substrates. The films were investigated by x-ray diffraction, scanning electron microscopy, and optical absorption spectroscopy. The exciton peak energy from absorption spectra was used to determine the band gap energy Eg, which was found to increase systematically with the decrease in the mean grain size and ranged from 3.388to3.647eV. This is consistent with the quantum confinement model and, up until now, not observed in a convincing manner in the ZnO thin films.

Hierarchy of graphene wrinkles induced by thermal strain engineering

Here, we study hierarchy of graphene wrinkles induced by thermal strain engineering and demonstrate that the wrinkling hierarchy can be accounted for by the wrinklon theory. We derive an equation λ = (ky)0.5, explaining evolution of wrinkling wavelength λ with the distance to the edge y observed in our experiment by considering both bending energy and stretching energy of the graphene flakes. The prefactor k in the equation is determined to be about 55 nm. Our experimental result indicates that the classical membrane behavior of graphene persists down to about 100 nm of the wrinkling wavelength.

Superlattice Dirac points and space-dependent Fermi velocity in a corrugated graphene monolayer

Recent studies show that periodic potentials can generate superlattice Dirac points at energies

Strain-induced one-dimensional Landau level quantization in corrugated graphene

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Grain size dependence of electrical and optical properties in Nb-doped anatase TiO2

in graphene (where

Angle-dependent van Hove singularities and their breakdown in twisted graphene bilayers

\ensuremath{\hbar}

d carrier induced intrinsic room temperature ferromagnetism in Nb:TiO2 film

is the reduced Planck constant,

Landau quantization and Fermi velocity renormalization in twisted graphene bilayers

{\ensuremath{\nu}}_{\mathrm{F}}

Electronic structures of graphene layers on a metal foil: The effect of atomic-scale defects

is the Fermi velocity of graphene, and G is the reciprocal superlattice vector). Here, we perform scanning tunneling microscopy and spectroscopy studies of a corrugated graphene monolayer on Rh foil. We show that the quasiperiodic ripples of nanometer wavelength in the corrugated graphene give rise to weak one-dimensional electronic potentials and thereby lead to the emergence of the superlattice Dirac points. The position of the superlattice Dirac point is space dependent and shows a wide distribution of values. We demonstrate that the space-dependent superlattice Dirac points are closely related to the space-dependent Fermi velocity, which may arise from the effect of the local strain and the strong electron-electron interaction in the corrugated graphene.