Considering the potential applications of transition metal doped nanostructured materials and the advantages of novel, cost-effective and environmental friendly biosynthesis methods, Ni-doped SnO2 nanomaterials have been synthesized using remnant water (ideally kitchen waste) collected from soaked Bengal gram beans (Cicer arietinum L.) extract. The structural and optical properties of the Ni-doped SnO2 nanostructures were studied using various techniques such as UV/visible spectroscopy, FT-IR spectroscopy, X-ray powder diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The SEM, TEM images and XRD of biosynthesized Ni-SnO2 nanoparticles reveal uniform size distribution with the average size of 6 nm and confirmed the formation of rutile structure with space group (P42/mnm) and nanocrystalline nature of the products with spherical morphology.Subsequently, Ni-doped biosynthesized SnO2 nanoparticles were coated onto the glass substrate using doctor blade method to form thin films. The NO2 sensing properties of the materials have been studied in comparison with other gases.The reported gas sensing results are promising, which suggest that the Ni-dopant is a promising noble metal additives to fabricate low cost SnO2 based sensor.
Leaky mode analysis of luminescent thin films: The case of ZnO on sapphire J. Appl. Phys. 112, 063112 (2012) ZnO/ZnSxSe1−x core/shell nanowire arrays as photoelectrodes with efficient visible light absorption Appl. Phys. Lett. 101, 073105 (2012) Study of the photoluminescence emission line at 3.33eV in ZnO films J. Appl. Phys. 112, 013528 (2012) Optical analysis of doped ZnO thin films using nonparabolic conduction-band parametersWe investigated the effects of post-growth annealing in the temperature range of 873 to 1273 K on the spectral features of photoluminescence (PL) vis-à-vis the crystalline and compositional native defects of ZnO thin films grown at 773 K by pulsed laser deposition (PLD) on sapphire substrates. It is found in the PL spectra at 10 K that the deep level emission (DLE) shifted from red-orange spectral region of $1.8-2.4 eV to yellow-green region of $2.4-2.9 eV with the increasing temperature of annealing. We propose that the PL in red-orange region originating from the singly ionized oxygen vacancies diminished due to increased replenishment of oxygen with increasing annealing temperature and that in the yellow-green region originating from the oxygen interstitials and/or zinc vacancies increased due to enhanced concentration of these point defects. As the annealing temperature was increased, the overall intensity of PL in the DLE region increased slightly up to 973 K but beyond that it increased steeply and made a quantum leap at 1073 K. In contrast to that, intensity of PL due to the near band-edge emission (NBE) in UV region of $3.15 to 3.45 eV increased very steeply up to the annealing temperature of 973 K, which is found to be due to improvement in the crystalline and compositional qualities of the films and beyond that it dropped drastically due to deteriorations of these qualities. The high resolution PL spectra at 10 K in the NBE region mainly consisted of peaks due to the recombinations of neutral donor bound excitons' complexes (D 0 X) at $3.36 eV, free excitons (FX A ) at $3.38 eV with their conspicuous LO phonon replicas and some other features such as exciton complexes bound to surface states or transitions of conduction band electrons to acceptor levels located in stacking faults and recombination of neutral acceptor bound excitons. The relative intensities of these individual features were strongly dependent on the annealing temperature of the films and the ensuing crystalline and compositional qualities. The 10 K PL spectra from the interfacial region of the annealed ZnO films and the sapphire substrates observed from the backside of the samples showed that the annealing temperature affected the crystalline and compositional qualities at the interface in a complex manner. Particularly, the features corresponding to the interface deteriorations resulting from the diffusion of Al into the ZnO films and the crystalline defects at the interface caused by the sputtering due to the PLD plume were prominently present in these PL spectra. These studies provide deeper insight...
We study the structural and electronic properties of Fe doped (4–8 at. %) and undoped TiO2 thin films deposited by pulsed laser deposition on Si(111) substrate. The films grow in single phase anatase structure of TiO2 as revealed by x-ray diffraction and Raman spectroscopy measurements. The Fe doped films reveal room temperature magnetic hysteresis behavior. We have probed the electronic environment of Fe in TiO2 matrix and its coupling to the cations, using photoelectron spectroscopy measurements. Photoelectron spectroscopic studies reveal the ionic state of Fe in TiO2, precluding the formation of Fe metal clusters. Valence band spectra of these films suggest that it primarily consists of O-2p derived state, however, Fe derived state is also observed in Fe doped films. Resonance photoelectron spectroscopy studies indicate that Fe ions are hybridized with Ti3+ defect states.
We investigate the resistive switching behavior of Ba-doped BiFeO3 (BBFO) films grown on single crystalline SrTi0.99Nb0.01O3 substrates. Observation of diode like I-V behavior and reduction in VC with Ba-content in BBFO films have been understood in the context of modifications in its energy band diagram. Also, I-V curves exhibit hysteresis which has been explained on the basis of migration and recombination of oxygen vacancies under field conditions. Furthermore, increment in Ba-content improves the retention property and ON/OFF switching ratio in BFO films which makes them suitable for applications in switching devices.
We report the growth of undoped and Fe (2 and 5 at%) doped molybdenum oxide thin films on c-plane of sapphire substrate using pulsed laser ablation. X-ray diffraction results show that the films are oriented in (100) direction and have monoclinic structure based on MoO 2 phase as also supported by Raman spectroscopy. The x-ray photoelectron spectroscopy reveals chemical state of Fe is +2, which favors the substitutional occupancy of Fe ion in the MoO 2 matrix.The room temperature resistivity of all the films are very low (~100 µΩcm). The Fe doped samples show ferromagnetic behavior at room temperature.
The effect of 5% Fe doping at Mn site, on the valence band structure of La0.7Sr0.3MnO3 has been investigated. Polycrystalline samples of La0.7Sr0.3MnO3 and La0.7Sr0.3Mn0.95Fe0.05O3 have been prepared by the solid-state reaction route. The phase purity of these samples was confirmed using x-ray diffraction. Core-level x-ray photoelectron spectroscopy measurements were performed to study the changes in the chemical composition. The valence band spectroscopy measurements on these samples, using a synchrotron radiation source, show a considerable change in the density of states (DOSs) at the Fermi level with 5% Fe doping. The results are correlated with room temperature resistivity and magnetization data on these samples. These results suggest that though the DOSs at the Fermi level increase on Fe doping, the conduction in LSMO gets hampered. This may be a result of changes in the hybridization of the orbitals due to Fe doping which modifies the MnO6 octahedra and hence the Mn3+–O–Mn4+ network.
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