Accurate density functional theory prediction of low-dimensional yttrium nitride: From 2D hexagonal and square monolayers to 1D zizag single walled nanotubes

Through this contribution, we aim to highlight the structural stability of low dimensional YN structures ranging from the 3D bulk to the 2D square and hexagonal monolayers and their corresponding 1D zigzag single walled nanotubes. For all arrangements, geometry optimization is achieved at the DFT/B3LYP level of theory using a Gaussian basis set. Then, the coupled perturbed Kohn-Sham and Hartree-Fock (CPKS/HF) computational approach is used to simulate Raman and IR spectrum. Rolling, cohesive and relaxation energies, electronic and vibrational contributions to the polarizability and equilibrium lattice parameters are also reported. Insights into their structural stability are provided by combining optimized parameters and vibrational phonon spectra. For the optimized 3D bulks, 2D monolayers and 1D square nanotubes, no imaginary frequency has been recorded in their vibrational spectra which reveals a dynamic stability. Likewise, imaginary frequencies appeared only for relatively large YN (n,0) single walled hexagonal nanotubes (n > 6) indicating that the optimized structures are not a real global minimum and implying a dynamic instability. A scaning mode procedure along the largest imaginary vibrational mode has been adopted to obtain the equilibrium geometry of (22,0) YN hexagonal nanotube. Therefore, it must be emphasized that the obtained potential energy surface presents two minima between a saddle point. These minima corresponds to a stable structures slightly distorted compared to the initial one. The absence of imaginary phonon frequencies in the Raman and IR spectra of the optimized (22,0) YN hexagonal nanotube confirms its structural stability.

Methylammonium lead triiodide perovskite-based solar cells efficiency: Insight from experimental and simulation

This work deals with the growth investigation of the methylammonium lead triiodide (MAPbI₃) thin films prepared by the spin coating technique. Firstly, MAPbI₃ films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and UV-Visible spectroscopy as well as photoluminescence techniques are used to calculate the band gap energy. Indeed, the high-quality MAPbI₃ perovskite films were obtained by using Chlorobenzene as an antisolvent with good crystallinity, large grain sizes, and higher absorption compared to MAPbI₃ treated by toluene. Secondly, the performance of FTO/TiO₂/MAPbI₃/Spiro OMeTAD/Au perovskite solar cell was evaluated using a numerical simulation of the Solar Cell by SCAPS simulator. The effect of the structural and physical parameters of MAPbI₃ absorber layer and HTL with the different antisolvents, including thickness, defect density, total charge density, donor density and electron affinity. Obtained results are: Jsc of 25.96 mA/cm², PCE of 30.70%, Voc of 1.259 V, FF of 88.93% of MAPbI₃-based solar cells when MAPbI₃ is treated by toluene. However, for MAPbI₃- Chlorobenzene, the I-V characteristics are rather: Jsc of 28.18 mA/cm², PCE of 31.81%, FF of 88.19% and Voc of 1.200 V. It is pointed out that the use of chlorobenzene may be of interest to improve the perovskites solar cells performances.

Enhanced photocatalytic activity against crystal violet dye of Co and In doped ZnO thin films grown on PEI flexible substrate under UV and sunlight irradiations

This work is focused on the photocatalytic activities of undoped ZnO, Co (1%) doped ZnO (CZO) and In (1%) doped ZnO (IZO) thin films grown on flexible PEI (Polyetherimide) substrate by spray pyrolysis. The photodegradation of crystal violet dye was investigated under UV and sunlight irradiations. Doping and excitation energy effects on photocatalytic efficiencies are discussed. All ZnO thin films show high photocatalytic efficiency up to 80% under either UV or sunlight irradiations for 210 min. However, CZO has the higher photocatalytic performance under UV irradiation. While, the photodegradation efficiency of IZO was enhanced under sunlight irradiation due to the narrowing of its optical gap. These results are discussed based on structural, morphological and optical investigations. The photocatalytic stability of ZnO films was studied as well. So, after three photocatalysis cycles, all ZnO thin films still effective. The obtained results are promising for the use of doped ZnO/PEI as talented photocatalysts for applications in large surfaces with various geometries for photodegradation of hazardous pollutants.

Temperature dependence of Raman spectra and first principles study of NiMn2O4 magnetic spinel oxide thin films. Application in efficient photocatalytic removal of RhB and MB dyes

Magnetic spinel oxide NiMn₂O₄ thin films were grown on glass substrates using the spray pyrolysis deposition technique at 350 °C. First, structural optimization, electronic structure and vibrational properties were obtained for NiMn₂O₄ by density functional theory (DFT) with an all electron basis set and the hybrid functional B3LYP implemented in the CRYSTAL14 code. Our DFT results show good agreement with previous experimental and theoretical data. Second, Raman spectra of as-prepared thin films have been measured over the temperature range from 100 K to 620 K. We report on the temperature dependence of their dominant first-order scattering F_2g and A_1g phonons modes. The phonon dynamic behavior is well described by a model taking into account explicit lattice anharmonicity associated to both cubic and quartic phonon decay processes and thermal expansion related quasiharmonicity. Finally, the photocatalytic activities of the obtained thin films were evaluated through the photocatalytic degradation of Rhodamine B (RhB) and methylene blue (MB) solutions under solar light irradiation as a function of time. All the results indicate that NiMn₂O₄ thin film can be used as a potential solar-light-driven photocatalyst.

An attempt to study (111) oriented NiO-like TCO thin films in terms of structural, optical properties and photocatalytic activities under strontium doping

This work covers some physical properties of Sr-doped NiO sprayed thin films at various concentrations (0 to 4%) prepared on glass substrates. Structural properties by using X-ray diffraction (XRD) show that all films have a cubic structure with (111) orientation. The stress, estimated by adjusting the XRD diffraction peaks increases with the doping concentration. Also, the grain size decreases with the doping concentration. On the other hand, the stacking fault probability has been discussed in terms of Sr doping level. The surface morphology of NiO:Sr thin films were examined by AFM observations. The optical constants (refractive index and extinction coefficient) were obtained by reflectance and transmittance measurements. This optical measurements show that the optical band gap is around 3.8 eV. PL measurements show mainly the transition band in UV blue and green domains related to the band-to-band transition and some defects in these prepared thin films. Finally, the advances in the actively studied photocatalysts that are emerging as effective alternate for nickel oxide based photocatalysts is also discussed.

An enhancement of photoluminescence property of Ag doped La2O3 thin films at room temperature

Metal transition doped oxide thin films or nanocomposites have recently emerged at the forefront of potentials research. With the focus mainly on efficiency, the aspect of stability against optical irradiation of such materials has so far not been thoroughly addressed. This work covers the synthesis of silver doped lanthanum oxide thin films (La₂O₃:Ag) which have been prepared by the spray pyrolysis technique on glass substrates at 460°C. Then, Ag thin films were grown on lanthanum oxide thin films by thermal evaporation. The present work aims to reach the synthesis of La₂O₃:Ag thin films using both the spray pyrolysis and thermal evaporation techniques. First, X-ray diffraction analysis shows that undoped and Ag doped films crystallize in a mixture of hexagonal and cubic phase with crystallites oriented along (001) direction. Raman spectroscopy shows the bands positions corresponding to hexagonal and cubic phases. On the other hand, an attempt regarding their optical properties has been carried out by means of photoluminescence measurements. Second, from electrical conductivity measurements, the activation energy decreases from 1.42 to 1.09eV with the increase of annealing time and the charge carriers are following the CBH model as dominant charge transport mechanism. Finally, the annealing time influences the surface wettability property and transforms La₂O₃ character from hydrophobic (θ>90°) to hydrophilic (θ<90°).

High Zr doping effects on the microstructural and optical properties of Mn3 O4 thin films along with ethanol sensing

Transition metal oxides as transparent conducting oxides (TCOs) films, with high optical transparency (≥82%), various valence states and p-type conductivity are used in a several physical domains. This work covers the physical study of Zr doped Mn₃O₄ semiconductor thin films using a spray pyrolysis method where Zr content varies in starting solutions from 0 to 20at.%. The impact of this work is to offer some understanding of microscopic effects of relatively high doping Zr and then correlate these effects with the macroscopic properties for interesting applications especially gas sensor. In fact, the addition of Zr ions pointed out the reduction of crystallite size (24.1 (nm)) with 20at.% doping allowing a better adsorption of gas molecules. In addition, it promotes the increase of optical gap (2.92eV) with 6at.% doping which is a useful parameter for some optical devices. X-ray diffraction (XRD), Raman spectroscopy, FTIR spectroscopy, atomic force microscopy (AFM) and EDAX techniques were used. It is found that these films crystallized in spinel type tetragonal hausmmanite structure. The gas sensing activity of these thin films (0, 6, 12 and 20at.% Zr) was examined with Ethanol. The performances of these last four sensing layers were compared. All the tests were performed at different working temperatures T_work=125, 150, 175 and 225°C and under two gas concentrations: 0.1% and 0.5% ethanol using dry air as carrier gas. The films exhibited noticeably ethanol sensing especially the sample doped with 6% of zirconium exhibits the most excellent sensing performance since it showed a clear response already at a low ethanol concentration of 0.1%.