B. Alkan

First principle and tight-binding study of strained SnC

Abstract We study the electronic and optical properties of strained single-layer SnC in the density functional theory (DFT) and tight-binding models. We extract the hopping parameters tight-binding Hamiltonian for monolayer SnC by considering the DFT results as a reference point. We also examine the phonon spectra in the scheme of DFT, and analyze the bonding character by using Mulliken bond population. Moreover, we show that the band gap modulation and transition from indirect to direct band gap in the compressive strained SnC. The applied tensile strain reduces the band gap and eventually the semiconductor to semimetal transition occurs for 7.5% of tensile strain. In the framework of tight-binding model, the effect of spin-orbit coupling on energy spectrum are also discussed. We indicate that while tensile strain closes the band gap, spin-orbit gap is still present which is order of ∼ 40 meV at the Γ point. The substrate effect is modeled through a staggered sub-lattice potential in the tight-binding approximation. The optical properties of pristine and strained SnC are also examined in the DFT scheme. We present the modulation of real and imaginary parts of dielectric function under applied strain.

Atomic and electronic structures of the group-IV elements on Si(111)-(?3 ? ?3) surface

We have examined the Si(111) surface with 1/3 monolayer of group-IV elements within the ab initio density functional theory. We have considered two possible threefold-coordinated sites for the atom adsorption: (i) H3 site (this site is directly above a fourth-layer Si atom and (ii) T4 site (directly above a second-layer Si atom). For the atoms Ge, Sn, and Pb, the T4 position always gives the most stable configuration, comparing with the H3 site. The calculated energy difference between T4 and H3 for Pb, Ge, and Sn, is 0.32 eV, 0.59 eV, and 0.41 eV, respectively. We have also presented electronic band structure and orbital character of the surface states of the Sn/Si(111)-(√3 × √3) surface.