Matko Mužević; Maja Varga Pajtler; Sanjeev Kumar Gupta; Igor Lukačević
Abstract
Optical properties of 2D materials can be effectively modulated by employing multilayer structures with different number of layers. Using the theoretical approach based on density functional theory we simulated relevant optical spectra of antimony and indium mono- and multilayers. We showed that the ...
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Optical properties of 2D materials can be effectively modulated by employing multilayer structures with different number of layers. Using the theoretical approach based on density functional theory we simulated relevant optical spectra of antimony and indium mono- and multilayers. We showed that the electronic band structures of antimonene and indiene possess numerous tracking bands enhancing the transition probability. Therefore, high absorption coefficients are found. Modelled multilayer nanostructures of antimonene and indiene experience a red-shift of absorption bands. Antimonene exhibits an optical directional anisotropy regarding the absorbance coefficient and reflectance spectrum for different nanolayer thicknesses. Indiene possesses very high reflectance and refractive index in the visible and IR spectrum which can be effectively modulated by the number of layers. Our work shows that antimonene and indiene multilayers harbour untapped potential for the optical applications at the nanoscale.
Jiban Kangsabanik; Aftab Alam
Abstract
Hybrid perovskites (CH3NH3PbI3) is one of the most promising novel materials for solar harvesting. Toxicity of lead (Pb), however, has always remained a concern. We investigated the electronic structure of complete replacement of Pb by alkaline earths (Ca, Sr, Ba) and found them to be wide band gap (Eg) ...
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Hybrid perovskites (CH3NH3PbI3) is one of the most promising novel materials for solar harvesting. Toxicity of lead (Pb), however, has always remained a concern. We investigated the electronic structure of complete replacement of Pb by alkaline earths (Ca, Sr, Ba) and found them to be wide band gap (Eg) semiconductors (band gap ~ 3.7 to 4.0 eV), and hence not suitable as absorber material. This opens up a new avenue to explore these materials as transparent conductor (TC). We doped CH3NH3BaI3 (largest Eg) with La, which shifts its Fermi level (EF) at conduction band bottom and induces states at EF for conduction. This is precisely what is required for a transparent conductors. Optical and transport properties simulated from linear response (within Density Functional Theory (DFT)) calculations suggested it to be a very good TC material with a high figure of merit (s/a), where s is the electrical conductivity and a is the optical absorption coefficient. This claim is also supported by our calculated results on density of states at EF, effective mass, carrier concentration etc. at various La-doping. We propose CH3NH3(Ba1-xLax)I3 (x£12.5%) to be a good TC material to be used in an all perovskite solar cell.
Venu H. Mankad; Sanjeev K. Gupta;Prafulla K. Jha
Abstract
The size dependent vibrational and thermodynamical properties of Zinc Oxide Nanowire (ZnO NWs) along with its bulk counterparts has been studied using the first principles calculations within density functional theory. The thermodynamical parameters such as specific heat at constant volume, entropy, ...
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The size dependent vibrational and thermodynamical properties of Zinc Oxide Nanowire (ZnO NWs) along with its bulk counterparts has been studied using the first principles calculations within density functional theory. The thermodynamical parameters such as specific heat at constant volume, entropy, internal energy and Helmholtz energy as function of temperature for the different size of nanowires are obtained and compared with the bulk ZnO in wurtzite phase. We address the effects of structural confinement on the phonon dispersion, vibrational density of states and qualitatively on the sound velocities and thermal conductance. The phonon dispersion curves for considered ZnO nanowires and its bulk counterpart indicates dynamical stability. The band gap increases from bulk to nanowire and an inverse size dependency in the case of nanowires arising due to quantum confinement. The analysis of bands character in context of growth characteristics and thermodynamical properties are also discussed. Our findings will give some reference to the insight understanding of the electronic, vibrational and thermodynamical properties of size orientation dependent ZnO nanowire.
A. Nouri; M. Mirzaei; T. Tayebi; Z. Alipanah
Abstract
In this work, density functional theory (DFT) calculations at the BLYP/6-31G* level was performed to investigate doping and functionalizing effect on the graphene in according geometric, NMR parameters and electronic properties. In the considered models, the energy gap is decreased in doped and functionalized ...
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In this work, density functional theory (DFT) calculations at the BLYP/6-31G* level was performed to investigate doping and functionalizing effect on the graphene in according geometric, NMR parameters and electronic properties. In the considered models, the energy gap is decreased in doped and functionalized models in respect to the pristine model but there are not significant changes between energy gap of the pristine model and functionalized models. Furthermore, results show the high and low sensitivity of the electronic properties of doped and functionalized models towards pristine model respectively. The results indicate that the formation energies of functionalized models are smaller than doped models ones. The NMR parameters follow the results of structural properties. It was found that for production of electronic devices doped models is better than functionalized models and nitrogen atom is a better choice for this purpose respect to the boron atom. All DFT calculations are performed by the Gaussian 98 package.
Ritu Gaba; Mamta Bhandari; Rita Kakkar
Abstract
The present work deals with the adsorption of acetaldehyde, one of the most harmful volatile organic compounds (VOCs), on the TiO2 anatase nanosurface. The research was undertaken due to environmental concerns, as the TiO2 nanosurface serves as an excellent catalyst for the adsorption and decomposition ...
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The present work deals with the adsorption of acetaldehyde, one of the most harmful volatile organic compounds (VOCs), on the TiO2 anatase nanosurface. The research was undertaken due to environmental concerns, as the TiO2 nanosurface serves as an excellent catalyst for the adsorption and decomposition of VOCs. The chemistry of aldehydes on metal oxides is complex and elaborate, as it can result in a variety of reactions, such as selective oxidation, alcohols disproportionation, etherification and reductive coupling to higher olefins. The structural properties of the various nanosurfaces were first examined and finally adsorption studies were made on the (TiO2)17 cluster, as it shows least reconstruction and offers all kinds of coordination sites for the study. It is found that a myriad of different adsorption products are formed on the TiO2 nanosurface, depending upon the coordination site. The low coordination (3c) sites are highly reactive and form stronger bonds with the acetaldehyde molecule, whereas adsorption at the four coordination site leads to the reconstruction of the nanosurface. Acetaldehyde chemisorbs onto the surface producing zwitterionic four-membered rings, in which the carbonyl C=O bond is considerably weakened, or it adsorbs on the TiO2 surface in a H-bridge bonded form. The most feasible mode of adsorption on the TiO2 nanosurface is found to be methyl hydrogen migration resulting in the formation of [CH2-C(H)O] species, which may further undergo transformation by β-aldolization to yield crotonaldehyde and butane. Other products investigated in this work include oxidation to acetate and reduction to ethoxy species. The results obtained in this work can be of significant help in deciding the fate of reaction of acetaldehyde on the TiO2 nanosurface, and using it for decomposition of acetaldehyde to benign products.
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