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.

Currently there is a lively discussion concerning Fermi velocity renormalization in twisted bilayers and several contradicted experimental results are reported.Here we study electronic structures of the twisted bilayers by scanning tunneling microscopy (STM) and spectroscopy (STS). The interlayer coupling strengths between the adjacent bilayers are measured according to energy separations of two pronounced low-energy van Hove singularities (VHSs) in the STS spectra.We demonstrate that there is a large range of values for the interlayer interaction in different twisted bilayers. Below the VHSs, the observed Landau quantization in the twisted bilayers is identical to that of massless Dirac fermions in graphene monolayer, which allows us to measure the Fermi velocity directly. Our result indicates that the Fermi velocity of the twisted bilayers depends remarkably on both the twisted angles and the interlayer coupling strengths.This removes the discrepancy about the Fermi velocity renormalization in the twisted bilayers and provides a consistent interpretation of all current data.

RNA interference (RNAi) is a powerful tool to silence gene expression posttranscriptionally. In this study, we evaluated the antiviral potential of small interfering RNA (siRNA) targeting VP1 of foot-and-mouth disease virus (FMDV), which is essential during the life cycle of the virus and plays a key role in virus attachment to susceptible cells. We investigated in vivo the inhibitory effect of VP1-specific siRNAs on FMDV replication in BHK-21 cells and suckling mice, a commonly used small animal model. The results showed that transfection of siRNA-expressing plasmids gave an 80 to 90% reduction in the expression of FMDV VP1 in BHK-21 cells. Moreover, BHK-21 cells transiently transfected with siRNA-expressing plasmids were specifically resistant to FMDV infection when exposed to 100 50% tissue culture infective doses of virus, and the antiviral effects extended to almost 48 h postinfection. Furthermore, subcutaneous injection of siRNA-expressing plasmids in the neck made suckling mice significantly less susceptible to FMDV. In conclusion, our data suggests that RNAi may provide a viable therapeutic approach to treat FMDV infection.

Foot-and-mouth disease virus (FMDV) infection is responsible for the heavy economic losses in stockbreed-

Theoretical research has predicted that ripple of graphene generates effective gauge field on its low energy electronic structure and could lead to Landau quantization. Here we demonstrate, using a combination of scanning tunneling microscopy and tight-binding approximation, that Landau levels will form when effective pseudomagnetic flux per ripple Φ ~ (h 2 /la)Φ 0 is larger than the flux quantum Φ 0 (here h is the height, l is the width of the ripple, a is the nearest C-C bond length). The strain induced gauge field in the ripple only results in one-dimensional (1D) Landau-level quantization along the ripple. Such 1D Landau quantization does not exist in two-dimensional systems in an external magnetic field. Its existence offers a unique opportunity to realize novel electronic properties in strained graphene.

Recent studies show that periodic potentials can generate superlattice Dirac points at energies ±ћν F |G|/2 in graphene (ν F 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 quasi-periodic ripples of nanometer wavelength in the corrugated graphene give rise to weak one-dimensional (1D) 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 demonstrated that the space-dependent superlattice Dirac points is 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.Since the laboratory realization of graphene in 2004 [1], this two-dimensional honeycomb lattice of carbon atoms has motivated intense theoretical and experimental investigations of its properties [2][3][4][5][6][7][8]. It was demonstrated that the electronic chirality (the spinorlike structure of the wavefunction) is of central importance to many of graphene's unique electronic properties [3,[9][10][11][12]. Recently, a number of theoretical studies predicted that the chiral nature of charge carriers results in highly anisotropic behaviours of massless Dirac fermions in graphene under periodic potentials and generates new Dirac points at energies E SD = ±ћν F |G|/2 in graphene superlattice (here ν F is the Fermi velocity of graphene and G is the reciprocal superlattice vector) [13][14][15][16]. Despite these suggestive findings [13][14][15][16] and many other interesting physics [17][18][19][20][21][22] in graphene superlattice, the experimental study of this system is scarce due to the difficulty in fabricating graphene under nano-scale periodic potentials [23]. Until recently, it was demonstrated that graphene superlattice (corrugated graphene or moiré pattern) induced between the top graphene layer and the substrate (or the underlayer graphene) acts as a weak periodic potential, which generates superlattice Dirac points at an energy determined by the period of the potential [24][25][26]. These seminal experiments provide a facile method to realize graphene superlattice and open opportunities for superlattice engineering of electronic properties in graphene.In this Letter, we address the electronic structures of a corrugated graphene monolayer on Rh foil. We show that the quasi-periodic ripples of nanometer wavelength give rise to a weak one-dimensional (1D) electronic potential in graphene. This 1D potential leads to the emergence of the superlattice Dirac points E SD , which are manifested by two dips in the density of states, symmetrically placed at energies flanking the pristine graphene Dirac point E D . The position of E SD is space-dependent and shows a wide distribution of values. Our experimental result demonstrates tha...

The controlled fabrication of single-crystal twelve-pointed graphene grains is demonstrated for the first time by ambient pressure chemical vapor deposition on a liquid Cu surface. An edge-diffusion limited mechanism is proposed. The highly controllable growth of twelve-pointed graphene grains presents an intriguing case for the fundamental study of graphene growth and should exhibit wide applications in graphene-based electronics.

The creation of van der Waals heterostructures based on a graphene monolayer and other two-dimensional crystals has attracted great interest because atomic registry of the two-dimensional crystals can modify the electronic spectra and properties of graphene. Twisted graphene bilayer can be viewed as a special van der Waals structure composed of two mutual misoriented graphene layers, where the sublayer graphene not only plays the role of a substrate, but also acts as an equivalent role as the top graphene layer in the structure. Here we report the electronic spectra of slightly twisted graphene bilayers studied by scanning tunneling microscopy and spectroscopy. Our experiment demonstrates that twist-induced van Hove singularities are ubiquitously present for rotation angles θ less than about 3.5 o , corresponding to moiré-pattern periods D longer than 4 nm. However, they totally vanish for θ > 5.5 o (D < 2.5 nm). Such a behavior indicates that the continuum models, which capture moiré-pattern periodicity more accurately at small rotation angles, are no longer applicable at large rotation angles.Graphene's novel electronic properties are a consequence of its two-dimensional honeycomb lattice [1]. Its electronic spectra are relatively easy to be tuned because graphene is a single-atom-thick membrane of carbon [2][3][4]. Very recently, it was demonstrated that a layer of hexagonal boron nitride (hBN) in contact with graphene can generate a periodic potential felt by graphene and lead to profound changes in graphene's electronic spectrum [5][6][7][8][9][10]. This provides an effective route to control the electronic spectra and properties of graphene via the creation of van der Waals heterostructures [5][6][7][8][9][10]. Graphene placed on top of another graphene monolayer with stacked misorientation forms a unique two dimensional van der Waals structure, i.e., twisted graphene bilayer [11][12][13][14][15][16][17][18][19][20][21], in which the graphene-on-graphene moiré modifies the electronic spectra [16,17,19]. The period of the moiré pattern D is related to the rotation angle θ by D = a/[2sin(θ/2)] with a = 0.246 nm the lattice parameter of graphene. This unique layered structure exhibits many fascinating physical properties beyond that of graphene monolayer due to interlayer coupling [16][17][18][19][20]. For example, the quasiparticles in twisted graphene bilayer are expected to show tunable chirality and adjustable probability of chiral tunneling [20].At small rotation angles electronic spectra of twisted graphene bilayer have been experimentally demonstrated to follow the predictions of the continuum models [11] and show twist-induced van Hove singularities (VHSs) [13][14][15]22,23], which directly arise from the finite interlayer coupling. However, the VHSs were not always observed and several experiments indicate that the electronic properties of the twisted graphene bilayer resemble a single graphene sheet [13,14,[24][25][26][27]. Obviously, the