No abstract

No abstract

Gallium oxide (Ga2O3) is a promising wide-band-gap semiconductor material for UV optical detectors and high-power transistor applications. The fabrication of p-type Ga2O3 is a key problem that hinders its potential for realistic power applications. In this paper, pure α-Ga2O3 and Ca-doped α-Ga2O3 band structure, the density of states, charge density distribution, and optical properties were determined by a first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. It was found that calcium (Ca) doping decreases the bandgap by introducing deep acceptor energy levels as the intermediate band above the valence band maximum. This intermediate valence band mainly consists of Ca 3p and O 2p orbitals and is adequately high in energy to provide an opportunity for p-type conductivity. Moreover, Ca doping enhances the absorptivity and reflectivity become low in the visible region. Aside, transparency decreases compared to the pure material. The optical properties were studied and clarified by electrons-photons interband transitions along with the complex dielectric function’s imaginary function.

No abstract

The crystal structure, electron charge density, band structure, density of states, and optical properties of pure and strontium (Sr)-doped β-Ga2O3 were studied using the first-principles calculation based on the density functional theory (DFT) within the generalized-gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE). The reason for choosing strontium as a dopant is due to its p-type doping behavior, which is expected to boost the material’s electrical and optical properties and maximize the devices’ efficiency. The structural parameter for pure β-Ga2O3 crystal structure is in the monoclinic space group (C2/m), which shows good agreement with the previous studies from experimental work. Bandgap energy from both pure and Sr-doped β-Ga2O3 is lower than the experimental bandgap value due to the limitation of DFT, which will ignore the calculation of exchange-correlation potential. To counterbalance the current incompatibilities, the better way to complete the theoretical calculations is to refine the theoretical predictions using the scissor operator’s working principle, according to literature published in the past and present. Therefore, the scissor operator was used to overcome the limitation of DFT. The density of states (DOS) shows the hybridization state of Ga 3d, O 2p, and Sr 5s orbital. The bonding population analysis exhibits the bonding characteristics for both pure and Sr-doped β-Ga2O3. The calculated optical properties for the absorption coefficient in Sr doping causes red-shift of the absorption spectrum, thus, strengthening visible light absorption. The reflectivity, refractive index, dielectric function, and loss function were obtained to understand further this novel work on Sr-doped β-Ga2O3 from the first-principles calculation.

No abstract

Extracts from plant materials have great potential as alternatives to inorganic corrosion inhibitors, which typically have harmful consequences. Experimental and theoretical methodologies studied the effectiveness of agricultural waste, namely, date palm seed extract as a green anti-corrosive agent in 0.5 M hydrochloric acid. Experimental results showed that immersion time and temperature are closely related to the effectivity of date palm seed as a corrosion inhibitor. The inhibition efficiency reduced from 95% to 91% at 1400 ppm when the immersion time was increased from 72 h to 168 h. The experimental results also indicated that the inhibition efficiency decreased as the temperature increased. The presence of a protective layer of organic matter was corroborated by scanning electron microscopy. The adsorption studies indicated that date palm seed obeyed Langmuir adsorption isotherm on the carbon steel surface, and Gibbs free energy values were in the range of −33.45 to −38.41 kJ·mol−1. These results suggested that the date palm seed molecules interacted with the carbon steel surface through mixture adsorption. Theoretical calculations using density functional theory showed that the capability to donate and accept electrons between the alloy surface and the date palm seed inhibitor molecules is critical for adsorption effectiveness. The HOMO and LUMO result indicated that the carboxyl (COOH) group and C=C bond were the most active sites for the electron donation-acceptance type of interaction and most auxiliary to the adsorption process over the Fe surface.

We are the first to report Bi–Co co-doped zinc oxide nanowires (ZnO NWs) to investigate theoretically and experimentally the alignment of relative spin and the location of Bi3+ and Co2+ as the primary cause of magnetism. In the present study, we carefully performed theoretical and experimental studies of ZnO NWs prepared by the hydrothermal method and obtained exciting outcomes. The x-ray diffraction findings show that the NWs have a wurtzite crystal structure and high intensity at the (002) peak, indicating that most of the reflection comes from the hexagonal surface of the NWs. This means that the extended NWs are mainly aligned along the c-axis. The field-emission scanning electron microscope results show that, due to its anisotropic crystal existence, the grown NWs have a preferred path along the c-axis in the (001) direction. X-ray photoelectron spectroscopy studies established the presence of both Bi and Co in all the Bi–Co co-doped samples. They also showed that OH− groups exist on the surface of ZnO NWs, and increasing Co content tends to increase the O-deficient region in the ZnO matrix. UV–vis analysis showed a decreased optical band gap upon doping, which is probably due to the sp-d exchange interaction between localized d-electron bands of dopants. Optical studies also suggested that the doping induced an increase in electron concentration. The Raman results indicate that the ZnO NWs contain crystallization with few defects after Bi–Co-doping. From the magnetic studies, it was observed that the ferromagnetism probably originates from the defect-rich regions, i.e. NW surface and Bi and Co sit at ZnO’s substitutional site. In contrast, the core of the NWs remains under the other magnetic state. Our density functional theory studies are in line with the experimental results.