Investigation of the effects of thermal annealing on the structural, morphological and optical properties of nanostructured Mn doped ZnO thin films

The control of the optical properties of ZnO nanostructured thin films by using different dopant elements paves the way for the development of potential materials for photonic and optoelectronic applications. In this work manganese (Mn) doped ZnO thin films were fabricated by rapid thermal evaporation method on a glass substrate having the same Mn content level of ~10% and annealed at different temperatures. XRD analysis showed that the annealed layers have hexagonal wurtzite structure, however, the unannealed layers showed only Zn peaks without any preferential direction. The elemental analysis of the films has been investigated by XPS, which revealed the presence of Mn and oxygen atoms for all layers. In addition, it was observed by FIB-SEM that the morphology of thin films changed with the annealing temperature. For an anneal at 500 °C nanoneedles appeared. Raman spectroscopy showed E1 (TO) mode in the sample annealed at 500 °C which was attributed with the formation of nanoneedles structures. The optical transmission of the annealed films was in the range of 75–77% and the optical bandgap varied from 3.97 to 3.72 eV. These variations are related to the structural and morphological changes of the thin films with annealing temperature

Investigation of the Effect of Substrate Orientation on the Structural, Electrical and Optical Properties of n-type GaAs1-xBix Layers Grown by Molecular Beam Epitaxy

Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep Level Transient Spectroscopy (DLTS), Laplace DLTS, Photoluminescence (PL) and Micro-Raman techniques have been employed to investigate the effect of the orientation of the substrates on the structural, electrically and optically active defects in dilute GaAs1−xBix epilayers structures having a Bi composition x = ~5.4%, grown by Molecular Beam Epitaxy (MBE) on (100) and (311)B GaAs planes. X-ray diffraction results revealed that the in-plane strain in the Ga(As,Bi) layer of the samples grown on (100)-oriented substrate (−0.0484) is significantly larger than that of the samples grown on (311)B-oriented substrate. The substrate orientation is found to have a noticeable impact on the Bi incorporation and the electrical properties of dilute GaAsBi Schottky diodes. The I-V characteristics showed that (100) Schottky diodes exhibited a larger ideality factor and higher barrier height compared with (311)B samples. The DLTS measurements showed that the number of electrically active traps were different for the two GaAs substrate orientations. In particular, three and two electron traps are detected in samples grown on (100) and (311)B GaAs substrates, respectively, with activation energies ranging from 0.12 to 0.41 eV. Additionally, one hole trap was observed only in sample grown on (100) substrates with activation energy 0.24 eV. The observed traps with small activation energies are attributed to Bi pair defects. The photoluminescence (PL) and Raman spectra have evidenced different compressive strain which affects considerably the optical properties. Furthermore, the PL spectra were also affected by different contributions of Bi- related traps which are different for different substrate orientation in agreement with DLTS results

A facile green approach to the synthesis of Bi2WO6@V2O5 heterostructure and their photocatalytic activity evaluation under visible light irradiation for RhB dye removal

Bismuth tungsten oxide and vanadium pentoxide (Bi2WO6/V2O5) heterostructures are produced by a green synthesis approach using Azadirachta indica extract for photocatalytic performance. The hydrothermal method at temperatures between 120 °C and 140 °C is used to synthesize Bi2WO6. Bi2WO6 and V2O5 phases are formed in pure orthorhombic wells according to the XRD pattern. The SEM displays V2O5 nanorods, Bi2WO6 hierarchical microspheres that resemble flowers at 120 °C, and particles with a particle-like character at 140 °C. In V2O5, the asymmetric stretching vibrations of the triplely coordinated oxygen (chain oxygen) bonds and the vibration of the doubly coordinated oxygen (bridge oxygen) bonds are responsible for a peak at 611 cm−1. In FTIR spectra between 600 and 1600 cm−1, the major absorption bands in Bi2WO6 are attributed to the W-O stretching, Bi-O stretching, and W-O-W bridging stretching modes. Bi2WO6@V2O5 at 120 °C has the lowest bandgap energy (2.32 eV) and optical electronegativity (0.62), as well as the highest refractive index (2.57), extinction coefficient (2.21), and dielectric constant (εr = 0.72 and εi = 11.4) among all samples, making it a suitable material for photocatalysis. Rhodamine blue (RhB) dye degradation is used to measure the photocatalytic activity (PCA) of certain materials. The results showed that heterostructure V2O5@Bi2WO6 synthesized at 120 °C is more attractive among all samples due to high degradation of RhB dye under sunlight irradiation in 90 min