Results Of Electronic Band Structure Research Articles

Electronic and optical properties of Janus-like hexagonal monolayer materials of group IV-VI

We report $ab\phantom{\rule{4pt}{0ex}}initio$ calculations of the electronic and optical response properties of Janus-like hexagonal monolayers materials of group IV-VI. By combining phonons spectra calculations and ab initio molecular dynamics simulations, we verify that some two-dimensional (2D) group IV-VI hexagonal materials are dynamically unstable. Our results of electronic band structure based on both density functional theory (DFT) with Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and ${\mathrm{G}}_{0}{\mathrm{W}}_{0}$ formalisms indicate that the dynamically stable materials exhibit indirect band gaps. The calculations clearly reveal that the hexagonal crystal structure of the group IV-VI monolayers plays a crucial role not only in determining the width of the band gap but also on the electron-hole screening effect, and consequently the strength of the exciton binding energy. Despite their strong binding, exciton binding energies in these nanomaterials are found to be in agreement with a 2D Mott-Wannier model. We also show that most of the stable 2D materials exhibit strong optical absorbance in the visible range, being promising materials for ultra-thin-film photovoltaic applications. Thus, our systematic analysis on electronic and optical properties of hexagonal monolayer materials of group IV-VI will complement forthcoming experimental measurements and can pave the way for technological applications of those materials.

Investigation into the photoluminescence and energy levels in bismuth-doped Sr3MgSi2O8 through first principles calculations

In this paper, influences of Bi3+ doping on the crystal structure and electronic band structure of Sr3MgSi2O8, and charge transfer process from the valence band to Bi3+ (CT) and from Bi3+ to the conduction band in Sr3MgSi2O8 (MMCT) have been investigated through first principles calculations. The total energy calculations make clear the location of the doped Bi3+ in Sr3MgSi2O8 that the doped Bi3+ preferred to take up the Mg2+ sites and form BiO6. The calculated results of electronic band structure and density of states reveal the constituents that make up the conduction band and valence band of Sr3MgSi2O8 and Sr3Mg0.875Bi0.125Si2O8, respectively. In addition, a defect level appears in the band gap of Sr3Mg0.875Bi0.125Si2O8, which is originated from the p orbit of the doped Bi3+. Also, the calculated absorptions of Sr3MgSi2O8 and Sr3Mg0.875Bi0.125Si2O8 show a gradually shifted absorption band from deep UV region to the blue area with increasing absorption intensity. The above results make clear of the fact that first principles calculations can be useful in investigating the properties of Bi3+ doped luminescent materials and designing new kinds of luminescent host materials.

Electronic, optical and magnetic characteristics of V doped BeS

Electronic, magnetic and optical features of V doped BeS compound are obtained with FP-LAW technique. A comparative investigation is performed among electronic band structure (BS), total and partial density of states (PDOS) is presented with 6.25, 12.5, 18.75 and 25% concentration of V. The results of electronic BS and density of states (DOS) show half metallic ferromagnetic (HMF) behavior with direct band gap (Eg). The calculated Eg are 2.8, 2.9, 3.3 and 3.7 for Be0.9375V0.0625S, Be00875V0.125S, Be0.8125V0.1875S and Be0.75V0.25S, respectively. For the optical feedback of TM doped BeS material, the imaginary and real part of dielectric function has been studied with the absorption coefficient, extinction coefficient, reflectivity, optical conductivity, and refractive index up to 15 eV. It is noted that with the increment of Eg, the static dielectric constant increases. Furthermore, the magnetic characteristics of resultant compound are examined. The HMF nature of TM doped BeS in electronic and magnetic properties may makes resultant compounds a potential candidate for optical and spintronic appliances.

Adsorption performance of SO2 gases over the transition metal/P‒codoped graphitic carbon nitride: A DFT investigation

The adsorption performance of SO2 on the P‒doped and transition metal (TM)/P‒codoped graphitic carbon nitride (gCN) systems (TM = Co, Rh, and Ir elements) were studied by DFT methods. The adsorption energy (Eads) results demonstrated that the interaction energy between SO2 and TM/P‒codoped gCN systems are stronger than that of the pristine gCN. Furthermore, it was found that SO2 molecule prefers to adsorbed on the Ir/P‒codoped gCN with superior Eads of −3.52 eV. Hence, the Ir/P‒codoped gCN is a suitable candidate for removing and detecting SO2 molecules from the atmosphere, in comparison with that of the other adsorbents. Besides, the results revealed that the presence of SO2 molecules over surface of doped and codoped gCN systems led to considerable changes in the magnetic, and structural characteristics of these systems. Furthermore, the Lowdin charges analysis demonstrated that with adsorption of SO2 over the TM/P‒codoped gCN systems, electrons remarkable transfer from the TM/P‒codoped systems to SO2 gas molecules owing to the strong adsorption of this gas. The results of electronic band structure displayed that with adsorption of SO2 gas and also codoping of TM/P elements, the electrical conductivity of gCN systems significantly decreased owing to the induced new impurity energy states near the Fermi energy level (Ef). The results of partial density of states (PDOS) plots for the P‒doped, TM/P‒codoped, and SO2‒adsorbed gCN systems revealed that the sharp peak are localized near the Ef in SO2‒adsorbed Ir/P‒codoped system, which confirmed the strong interaction between SO2 gas molecules and this system. Thus, it can be deduced that the Ir/P‒codoped system with the highest Eads can be efficiently used for the removing and sensing of SO2 gas from the environment.

Direct band gaps in group IV-VI monolayer materials: Binary counterparts of phosphorene

We perform systematic investigation on the geometric, energetic and electronic properties of group IV-VI binary monolayers (XY), which are the counterparts of phosphorene, by employing density functional theory based electronic structure calculations. For this purpose, we choose the binary systems XY consisting of equal numbers of group IV (X = C, Si, Ge, Sn) and group VI elements (Y = O, S, Se, Te) in three geometrical configurations, the puckered, buckled and planar structures. The results of binding energy calculations show that all the binary systems studied are energetically stable. It is observed that, the puckered structure, similar to that of phosphorene, is the energetically most stable geometric configuration. Our results of electronic band structure predict that puckered SiO and CSe are direct band semiconductors with gaps of 1.449 and 0.905 eV, respectively. Band structure of CSe closely resembles that of phosphorene. Remaining group IV-VI binary monolayers in the puckered configuration and all the buckled monolayers are also semiconductors, but with indirect band gaps. Importantly, we find that the difference between indirect and direct band gaps is very small for many puckered monolayers. Thus, there is a possibility of making these systems undergo transition from indirect to direct band gap semiconducting state by a suitable external influence. Indeed, we show in the present work that seven binary monolayers namely SnS, SiSe, GeSe, SnSe, SiTe, GeTe and SnTe become direct band gap semiconductors when they are subjected to a small mechanical strain (<= 3 %). This makes nine out of sixteen binary monolayers studied in the present work direct band gap semiconductors. Thus, there is a possibility of utilizing these binary counterparts of phosphorene in future light-emitting diodes and solar cells.

Aluminene as highly hole‐doped graphene

Monolayer structures made up of purely one kind of atom are fascinating. Many kinds of honeycomb systems including carbon, silicon, germanium, tin, phosphorus and arsenic have been shown to be stable. However, so far the structures are restricted to group-IV and V elements. In this work we systematically investigate the stability of monolayer structures made up of aluminium, in four different geometric configurations (planar, buckled, puckered and triangular), by employing density functional theory‐based electronic structure calculation. Our results on cohesive energy and phonon dispersion predict that only the planar honeycomb structure made up of aluminium is stable. We call it ‘aluminene’ according to the standard naming convention. It is a metal. Results of electronic band structure suggest that it may be regarded as a highly hole-doped graphene. We also present the tight-binding model and the Dirac theory to discuss the electronic properties of aluminene.

Electronic structure and thermoelectric properties ofn- andp-type SnSe from first-principles calculations

We present results of electronic band structure, Fermi surface and electron transport properties calculations in orthorhombic $n$- and $p$-type SnSe, applying Korringa-Kohn-Rostoker method and Boltzmann transport approach. The analysis accounted for temperature effect on crystallographic parameters in $Pnma$ structure as well as the phase transition to $CmCm$ structure at $T_c\sim 807 $K. Remarkable modifications of conduction and valence bands were notified upon varying crystallographic parameters within the structure before $T_c$, while the phase transition mostly leads to jump in the band gap value. The diagonal components of kinetic parameter tensors (velocity, effective mass) and resulting transport quantity tensors (electrical conductivity $\sigma$, thermopower $S$ and power factor PF) were computed in wide range of temperature ($15-900 $K) and, hole ($p-$type) and electron ($n-$type) concentration ($10^{17}-10^{21}$ cm$^{-3}$). SnSe is shown to have strong anisotropy of the electron transport properties for both types of charge conductivity, as expected for the layered structure. In general, $p$-type effective masses are larger than $n$-type ones. Interestingly, $p$-type SnSe has strongly non-parabolic dispersion relations, with the 'pudding-mold'-like shape of the highest valence band. The analysis of $\sigma$, $S$ and PF tensors indicates, that the inter-layer electron transport is beneficial for thermoelectric performance in $n$-type SnSe, while this direction is blocked in $p$-type SnSe, where in-plane transport is preferred. Our results predict, that $n$-type SnSe is potentially even better thermoelectric material than $p$-type one. Theoretical results are compared with single crystal $p$-SnSe measurements, and good agreement is found.

Ab-initio studies of thermal and superconducting properties of HfX2 alloys (X = Tc, Re, and Os)

Abstract A systematic study of thermal properties such as the Debye temperature, specific heat coefficient, Grüneisen constant, electron-phonon coupling constant and transition temperature have been carried out using the results of electronic band structure and related characteristics, for hafnium superconducting alloys, namely, HfTc2, HfRe2 and HfOs2. Computation of the electronic band structure and associated properties has been carried out using the tight-binding-linear-muffin-tin-orbital (TBLMTO) method within atomic sphere approximation (ASA). The calculated values have been compared with the available results of literature data.

1,3‐Bis(2‐thienylmethylene)1‐1H,3H1‐thieno[3,4‐c]thiophene: A Precursor for a New Low Band Gap Polymer

AbstractA new precursor, 1,3‐bis(2‐thienylmethylene)1‐1H,3H1‐thieno‐[3,4‐c]thiophene(9), for polyarenemethylenes (PAM), which are predicted to be low band gap polymers, is obtained by a Knoevenagel‐type condensation of 1H,3H1‐thieno[3,4‐c]thiophene 2‐oxide (7) with 2‐thiophenecarbaldehyde followed by reduction of the intermediate sulfoxide 8 with 2‐chloro‐1,3,2‐benzodioxaphosphole. Several investigations with cyclic voltammetry and UV‐Vis‐NIR spectroelectrochemistry (SEC) are carried out on 9. The experimental data are compared with the results of electronic band structure calculated on the basis of an MNDO‐optimized geometric structure by VEH pseudopotential method.