Parametrized Tight-binding Model Research Articles

Effects of a magnetic field on the optoelectronic properties of mono- and bi-layer transition metal dichalcogenides

We report a theoretical study on the effects of an external magnetic field on the electronic and optical properties of mono- and bi-layer MoS2, and bilayer MoS2/WS2 heterostructures. The direction of an applied magnetic field determines (i) the strength of the coupling between the atomic orbital moments of the structure and the field, and (ii) Zeeman contribution to the splitting of the VB and CB levels with the amplitude of the applied field. Whereas for a magnetic field applied perpendicular to the structure, calculated real part of optical conductivity reveals optical transitions red-shifted compared to zero magnetic field case, conductivity is unaffected by the the amplitude of an in-plane applied magnetic field. We show that through modifying atomic d-orbitals conduction and valence band states by an applied electric field, we can determine and control the impact of a magnetic field on the optical response of these materials. We employ our parametrized tight-binding model with non-orthogonal sp3d5 orbitals and spin–orbit coupling, which was advanced to include the effects of an external magnetic field through Peierls substitution in the wave vector and the Zeeman energy term.

Influence of band offset, nanostructuring, and applied electric field on the optoelectronic properties of vertically stacked MoS2/WS2 materials

We theoretically investigate the electronic and optical properties of multilayer vertically stacked ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$ heterostructures, focusing on the role of the ${\mathrm{MoS}}_{2}\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ band offset, number of monolayers in the heterostructure, effects of an applied electric field, and size reduction in lateral direction, leading to ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$-based nanowires and nanoplatelets. Given that different values of the ${\mathrm{MoS}}_{2}\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ band offset have been reported, we show that the band offset determines the ordering of the energy levels in the valence band and spin projections at the $K$ point of the Brillouin zone. These variations as function of the value of the band offset are suppressed in an external electric field. For multilayer ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$-based nanostructures, our calculations reveal nanowires and nanoplatelets with S-atom edges exhibit a metallic character, but nanowires with one S-atom and other Mo/W edge show the band gap with electrons located in ${\mathrm{MoS}}_{2}$ and holes in ${\mathrm{WS}}_{2}$ layer. The band gap can be controlled by the size of the nanowire in lateral direction and number of layers. The calculated real part of optical conductivity show that the lowest optical transitions originate from the optical transitions in ${\mathrm{MoS}}_{2}$ layers. The electronic structure is obtained from a parametrized tight-binding model that includes nonorthogonal ${sp}^{3}{d}^{5}$ orbitals and spin orbit coupling. Our results are gauged with respect to those extracted from density functional theory and $GW$ methods to ensure the high quality of our predictions.

Electronic Structure and Charge Transport in Nanostripped Graphene

An attractive strategy to generate semiconducting graphene layers is delineating rows of sp3 defects along the armchair direction that disrupt the π-conjugation and result in the formation of nanostripped structures with tunable band gap. This is investigated here using density functional theory (DFT) calculations, where we have assessed how much the electronic structure of the nanostructured graphene layers is affected by the density and structure of sp3 defects. A parametrized tight-binding model is then mapped onto the DFT results, thereby allowing for extending the calculations to much larger system sizes (up to 106 atoms). We have next applied the real-space Kubo–Greenwood formalism to investigate the charge transport characteristics in graphene with various percentages of sp3 defects. The calculations show that although incomplete saturation of the sp3 defects density lines leads to the appearance of localized states within the otherwise band gap, those states do not participate in electron transpor...

A tight-binding model for calculations of structures and properties of graphitic nanotubes

A parameterized tight-binding model is applied to calculate the equilibrium structures, energies, band gaps and elastic properties of graphitic nanotubes with various helicities and radii. The structures, energies and band gaps for the tubes of large radii are in agreement with more accurate calculations. The elastic moduli depend only on the tube radius and follow the continuum model predictions.

Tight-binding study of hydrogen on the C(111), C(100), and C(110) diamond surfaces.

The band structure, total energies, and relaxed geometries are calculated for the C(111), C(100), and C(110) surfaces using a parametrized tight-binding model for carbon. The method and addition of C-H parameters to the model are described in detail. Results for the bare and hydrogenated C(111) surfaces are used to compare the accuracy of the method with ab initio techniques. A stable hydrogenated (2\ifmmode\times\else\texttimes\fi{}1) \ensuremath{\pi} reconstructed surface is found, which resembles the C(110) surface. Removal of one H atom from the dihydride C(100) results in a 3/2 hydride surface, where the odd hydrogen is bonded equally to two surface carbons. Although the fully H-covered C(100)(2\ifmmode\times\else\texttimes\fi{}1) surface has a clean gap, the partially covered surface has a half-filled state, consistent with photoemission data. The geometries and H vibrations are also presented for the C(110) surface. The surface chains on the bare C(110) have bond lengths close to graphite and dimerize from a Peierls distortion. Addition of H to this surface restores the bond lengths to approximately that of bulk diamond. Comparison of the band structures and H vibrations with experiment helps identify the nature of the hydrogen coverage on the surfaces.

Spin-Polarization in Ultrathin Rh Layers on Fe (001)

ABSTRACTThe origin of the Rh polarization at the interface with Fe is discussed within a self-consistent mean-field parameterized tight-binding model. Since experimentally it is not yet known how Rh grows on Fe (001), in this paper we consider both fee and bec growth. When Rh grows in the fee structure, it expands its lattice parameter and a polarization is present up to 3 layers, whereas in the bec case only the Rh atoms at the interface are polarized. The results obtained are compared to recent spin- and angle-resolved photoelectron spectroscopy experiments. Good agreement with experiment is obtained in the case of a fee Rh configuration.