Modeling of magnesium-decorated graphene quantum dot nanostructure for trapping AsH3, PH3 and NH3 gases

A magnesium-decorated graphene quantum dot (C₂₄H₁₂-Mg) surface has been examined theoretically using density functional theory (DFT) computations at the ωB97XD/6-311++G(2p,2d) level of theory to determine its sensing capability toward XH₃ gases, where X = As, N and P, in four different phases: gas, benzene solvent, ethanol solvent and water. This research was carried out in different phases in order to predict the best possible phase for the adsorption of the toxic gases. Analysis of the electronic properties shows that in the different phases the energy gap follows the order NH₃@C₂₄H₁₂-Mg < PH₃@C₂₄H₁₂-Mg < AsH₃@C₂₄H₁₂-Mg. The results obtained from the adsorption studies show that all the calculated adsorption energies are negative, indicating that the nature of the adsorption is chemisorption. The adsorption energies can be arranged in an increasing trend of NH₃@C₂₄H₁₂-Mg < PH₃@C₂₄H₁₂-Mg < AsH₃@C₂₄H₁₂-Mg. The best adsorption performance was noted in the gas phase compared to the other studied counterparts. The interaction between the adsorbed gases and the surfaces shows a non-covalent interaction nature, as confirmed by the quantum theory of atoms-in-molecules (QTAIM) and non-covalent interactions (NCI) analysis. The overall results suggest that we can infer that the surface of the magnesium-decorated graphene quantum dot C₂₄H₁₂-Mg is more efficient for sensing the gas AsH₃ than PH₃ and NH₃.

Influence of Carrier Gas Pressure on the Physical Properties of CdO Thin Films

Conducting cadmium oxide (CdO) thin film samples were deposited on amorphous glass substrates at the optimized substrate temperature (200 °C) as a function of carrier gas pressure (10.8, 12.7, 14.7, 16.7 and 18.6 × 104 N m−2 respectively) by spray pyrolysis technique using nebulizer. XRD results showed that all the CdO thin films were polycrystalline in nature along with cubic structure. The scanning electron microscopy (SEM) images revealed that all the thin films had a sphere like grains without any cracks. The elemental composition of the film is analyzed with EDAX spectrum formed in stochiometric range. Direct energy gap values were found to be had decreased from 2.46 to 2.42 eV as the function of carrier gas pressure had increased from 10.8 to 14.7 × 104 (N m−2) and the energy gap increased further. All the as deposited samples of Cd–O vibration bond (690 cm−1) were confirmed by FTIR spectrum. PL emission spectra revealed that all the CdO thin films exhibit a strong emission (green) peak at 520 nm. High carrier concentration (2.88 × 1019 cm−3), low resistivity (4.76 × 10−3 Ω cm) and high figure of merit (25.0 × 10−3) were observed for 14.7 × 104 (N m−2) carrier gas pressure of CdO thin film.