arXiv subjects

Hui Tang

Publications and source records attributed to Hui Tang.

76 records · Page 5Linked to original sources

arXiv2008

Raman and Infra-red properties and layer dependence of the phonon dispersions in multi-layered graphene

The symmetry group analysis is applied to classify the phonon modes of $N$-stacked graphene layers (NSGL's) with AB- and AA-stacking, particularly their infra-red and Raman properties. The dispersions of various phonon modes are calculated in a multi-layer vibrational model, which is generalized from the lattice vibrational potentials of graphene to including the inter-layer interactions in NSGL's. The experimentally reported red shift phenomena in the layer number dependence of the intra-layer optical C-C stretching mode frequencies are interpreted. An interesting low frequency inter-layer optical mode is revealed to be Raman or Infra-red active in even or odd NSGL's respectively. Its frequency shift is sensitive to the layer number and saturated at about 10 layers.

cond-mat.mtrl-sci↗

arXiv2007

Novel Precursors for Boron Nanotubes: The Competition of Two-Center and Three-Center Bonding in Boron Sheets

We present a new class of boron sheets, composed of triangular and hexagonal motifs, that are more stable than structures considered to date and thus are likely to be the precursors of boron nanotubes. We describe a simple and clear picture of electronic bonding in boron sheets and highlight the importance of three-center bonding and its competition with two-center bonding, which can also explain the stability of recently discovered boron fullerenes. Our findings call for reconsideration of the literature on boron sheets, nanotubes, and clusters.

cond-mat.mtrl-sci↗

arXiv2007

A lattice dynamical treatment for the total potential energy of single-walled carbon nanotubes and its applications: relaxed equilibrium structure, elastic properties, and vibrational modes of ultra-narrow tubes

In this paper, we proposed a lattice dynamic treatment for the total potential energy for single-walled carbon nanotubes (SWCNT's) which is, apart from a parameter for the non-linear effects, extracted from the vibrational energy of the planar graphene sheet. Based upon the proposal, we investigated systematically the relaxed lattice configuration for narrow SWCNT's, the strain energy, the Young's modulus and Poisson ratio, and the lattice vibrational properties respected to the relaxed equilibrium tubule structure. Our calculated results for various physical quantities are nicely in consistency with existing experimental measurements. Particularly, we verified that the relaxation effect brings the bond length longer and the frequencies of various optical vibrational modes softer; Our calculation provides the evidence that the Young's modulus of armchair tube exceeds that of the planar graphene sheet, and the large diameter limits of the Young's modulus and Poisson ratio are in agreement with the experimental values of the graphite; The calculated radial breathing modes for the ultra narrow tubes with diameter range between 0.2 - 0.5 nm coincide the experimental results and the existing {\it ab initio} calculations with satisfaction; For narrow tubes of diameter 2 nm, the calculated frequencies of optical modes in tubule tangential plane as well as those of radial breathing modes are also in good agreement with the experimental measurement. In addition, our calculation shows that various physical quantities of relaxed SWCNT's can actually be expanded in terms of the chiral angle defined for the correspondent ideal SWCNT's.

cond-mat.mtrl-sci↗

arXiv2006

Chiral symmetry analysis and rigid rotational invariance for the lattice dynamics of single-wall carbon nanotubes

In this paper, we provide a detailed expression of the vibrational potential for the lattice dynamics of the single-wall carbon nanotubes (SWCNT) satisfying the requirements of the exact rigid translational as well as rotational symmetries, which is a nontrivial generalization of the valence force model for the planar graphene sheet. With the model, the low frequency behavior of the dispersion of the acoustic modes as well as the flexure mode can be precisely calculated. Based upon a comprehensive chiral symmetry analysis, the calculated mode frequencies (including all the Raman and infrared active modes), velocities of acoustic modes and the polarization vectors are systematically fitted in terms of the chiral angle and radius, where the restrictions of various symmetry operations of the SWCNT are fulfilled.

cond-mat.mtrl-sci↗