Effect of vacancy defects on transport properties of

The effect of vacancy defects on electrons transport behavior of the alpha-armchair graphyne nanoribbons has been studied by density-functional tight-binding and non-equilibrium Green’s function methods. Three different widths of the nanoribbons with 6, 7 and 8 atoms and four types of vacancy defects contain one, two, three and four missing atoms were selected in this study. In relaxed structures, the structural changes around the defects are observed. Some of the free hands form new atomic chains containing 6 or 7 atoms. Comparing with perfect devices, the current decreases at the defective devices with 8 atoms width, whereas, it increases for devices with 6 atoms width. By calculating the density of states, transmission spectrums and molecular energy spectrums for devices with 6-atoms widths, there is a resonance state for DDOS and T(E) peaks in the QV device, while the peak of the density of states and transmission spectrums does not match in the SV1 device. Also, the results show that HOMO-LUMO gap energy in the SV1 device is much more than the perfect and QV devices. For devices with 8 atoms width, the transmission spectrums are reduced for all defects due to the lower density of the energy level of molecular energy. However, the orbital distribution of LUMO state in the device with the defect is localized but for the perfect structure, both the LUMO and the HOMO orbital distribution are quite delocalized

Electronic and optical properties of CuGaS

In this work we study the electronic and optical properties of fully relaxed CuGaS2 nanowires using the pseudo-potential density functional method. In our calculations we have investigated nanowires with two shapes of hexagonal and triangular with their corresponding diameters in the order of 8 to 15 Å in (1–10) growth direction. For CuGaS2 bulk, the geometrical parameters such as anion displacement and equilibrium lattice constant agree well with other theoretical and experimental results. We have shown that for the CuGaS2 nanowires, there is an important contraction of the Cu-S and Ga-S bond lengths in the wires of 2.1% and 1.24% of the bulk value. In addition, in this manuscript the electronic properties such as band structures and atom-projected density of states have been examined. Our results show that while the nanowire diameter increases, the band gap decreases. From partial density of states we found that the greatest valence bands involve atoms which are placed at the surface. The optical constants, the dielectric function, reflectivity, refractive index and absorption of the nanowires have been analyzed. The results show that compared to the CuGaS2 bulk, the corresponding peaks of dielectric functions of CuGaS2 nanowires are blue-shifted. The calculations reveal that the dielectric functions of the nanowires augment while the nanowires’ size increases. It is also found that the peaks related to optical parameters of nanowires are affected by the diameter of the nanowire

Effect of point defects on the electronic density states of SnC nanosheets: First-principles calculations

In this work, we investigated the electronic and structural properties of various defects including single Sn and C vacancies, double vacancy of the Sn and C atoms, anti-sites, position exchange and the Stone–Wales (SW) defects in SnC nanosheets by using density-functional theory (DFT). We found that various vacancy defects in the SnC monolayer can change the electronic and structural properties. Our results show that the SnC is an indirect band gap compound, with the band gap of 2.10 eV. The system turns into metal for both structure of the single Sn and C vacancies. However, for the double vacancy contained Sn and C atoms, the structure remains semiconductor with the direct band gap of 0.37 eV at the G point. We also found that for anti-site defects, the structure remains semiconductor and for the exchange defect, the structure becomes indirect semiconductor with the K-G point and the band gap of 0.74 eV. Finally, the structure of SW defect remains semiconductor with the direct band gap at K point with band gap of 0.54 eV. Keywords: SnC nanosheets, Density-functional theory, First-principles calculations, Electronic density of states, Band ga