R. Vinodkumar

Growth and characterization of molybdenum oxide nanorods by RF magnetron sputtering and subsequent annealing

High-densely packed and uniformly distributed molybdenum oxide nanorods have been grown onto glass substrates by RF magnetron sputtering and subsequent annealing in an oxygen atmosphere. A two-step growth mechanism (sputtering redeposition and enhanced rearrangement during annealing) for the formation of MoO3 nanorods has been proposed. The morphological, structural, optical and electrical properties of the nanorods have been investigated systematically using atomic force microscopy, scanning electron microscopy, x-ray diffraction, micro-Raman, UV–visible, photoluminescence (PL) spectroscopy and dc resistivity studies. The nanorods in the as-sputtered film and the film annealed at 473 K are amorphous in nature. However, the nanorods in the films annealed at 573 and 673 K exhibit the presence of monoclinic Mo8O23 and orthorhombic MoO3, respectively. Vibrational analysis of the molybdenum and oxygen atoms in the nanorods is carried out by micro-Raman spectra. The nanorods show room temperature PL in the UV–visible region. The PL emission is found to be strongly enhanced by post-deposition annealing. The low temperature resistivity measurement is done on the as-deposited film; the activation energy and polaron hopping energy for electrical conduction are calculated. The MoO3 nanorods are expected to exhibit enhanced functionality, particularly in nanoscale, photochromic and gas sensing applications.

Transparent and low resistive nanostructured laser ablated tungsten oxide thin films by nitrogen doping: II. Substrate temperature

Nitrogen incorporated tungsten oxide thin films are deposited onto fused quartz substrates at various substrate temperatures (Ts) in nitrogen ambient (pN2) of 12 Pa by pulsed laser deposition. The structural, optical and electrical properties of the deposited films are found to depend on the substrate temperature/nitrogen doping concentration. Compositional analysis by energy dispersive x-ray spectra confirms the incorporation of nitrogen into the films, with maximum nitrogen incorporation for films deposited at Ts = 973 K. X-ray diffraction analysis reveals an orthorhombic crystalline phase for the WO3 : N films deposited at Ts = 300, 873 and 973 K, with a nanocrystalline structure for the films prepared at intermediate growth temperatures. Morphology investigation of WO3 : N films in relation to substrate temperature/nitrogen doping is done by scanning electron microscopy and atomic force microscopy. Vibrational properties of the WO3 : N films are measured using micro-Raman spectroscopy. Bandgap of WO3 : N films decreases from 3.31 ± 0.04 to 2.85 ± 0.03 eV and room temperature resistivity decreases from 1.77 × 103 to 4.3 × 10−2 Ω m with change in substrate temperature/nitrogen content. Analysis of optical and electrical properties reveals that the incorporated nitrogen acts as an electronic dopant in WO3. Narrow bandgap, low dc resistivity at room temperature and average transmittance in the visible range, observed for the films deposited at higher substrate temperatures (873 and 973 K), make very interesting prospects for technological transfer, especially as novel solar cell materials.

Preparation and characterization studies of nanostructured silicon thin films using rf magnetron sputtering

High quality Silicon thin films are prepared using planar RF magnetron sputtering technique. GIXRD and Raman spectra of the films show broad peaks of Si indicating that they are either amorphous or nanostructured in nature consisting of particles of very small size. The optical band gap energy estimated from the Tauc plot for the films prepared RF powers at 200, 250 and 300 W is found to be 2.87, 3.21 and 2.33 eV respectively. The enhanced band gap energy for the films compared to the bulk silicon supports the presence of quantum confinement in the films due to the presence of nanoparticles. Grain size and root mean square (rms) surface roughness of the deposited films are determined from the AFM analysis and are found to be increases with increase in RF power. The films exhibit strong photoluminescence emission in the visible region.

Growth of MoO3 nanorods on glass substrates by R F magnetron sputtering

Uniformly distributed MoO3 nanorods of length ~1.2 μm and diameter ~200 nm have been grown onto glass substrates by RF magnetron sputtering technique. A sputtering—redeposition mechanism and enhanced rearrangement during subsequent annealing has been proposed for the growth of MoO3 nanorods on glass substrates. The surface morphological, structural and optical properties of nanorods are investigated systematically using atomic force microscopy (AFM), X-ray diffraction (XRD) and UV-vis spectroscopy. The AFM images exhibit the distribution of nanograins and nanorods. The XRD studies reveal the presence of monoclinic Mo8O23 and orthorhombic MoO3 in the films annealed at 573 and 673 K respectively. The optical band gap energy is found to increase with increase in annealing temperature and particle size. The MoO3 nanorods are expected to exhibit enhanced functionality particularly in nanoscale, photochromic and gas sensing applications.

Laser ablated nanostructured zinc sulphide thin films for optoelectronics device applications

ZnS thin films are prepared by pulsed laser deposition and the effect of annealing temperature on the structural and optical properties of ZnS films is investigated systematically using techniques like X-ray diffraction (XRD), Atomic force microscopy (AFM), UV-VIS spectroscopy and Photoluminescence spectroscopy (PL). The XRD pattern of the film annealed at 600 °C show a less intense XRD peak of hexagonal ZnO. In the photoluminescence spectra, an orange emission is observed for the films with 325 nm excitation.

Laser ablated nanostructured tin oxide thin films for optoelectronic device applications

Nanostructured tin oxide (SnO2) thin films are prepared by pulsed laser deposition technique and the films are annealed at different temperatures viz. 300, 400, 500 and 600 °C. The as-deposited and annealed films are characterized by X-ray diffraction, Micro-Raman spectroscopy, Atomic force microscopy, UV-visible spectroscopy and Photoluminescence spectroscopy. The films annealed at higher temperature exhibit more intense and sharper X-ray diffraction peaks compared to other annealed films showing their enhanced crystallinity. Raman spectra of nanocrystalline tin oxide exhibits very broad spectral feature extending from 400– 700 cm−1. All the films exhibit a broad luminescence band centered on 376 nm and a blue emission at 450 and 470 nm.

Effects of the Eu3+ concentration on the structural, optical and morphological properties of cubic Gd2O3 nanostructured thin films

Nanostructured Gd2O3: Eu3+ thin films were prepared by pulsed laser ablation technique. The dependence of structural, morphological and optical properties of these films on photoluminescence was systematically studied by varying the Eu3+ incorporation concentration. Micro-Raman and XRD analysis indicate that Eu3+ incorporation strongly perturbs the cubic Gd2O3 structure and suppresses the grain growth. For 0.10 mol Eu3+ doped Gd2O3 films deposited under a vacuum of 10-6 mbar when subjected to annealing at 1173 K give transparent films exhibiting intense photoemission at 612 nm due to 5D0-7F2 transition. The Eu3+ incorporation concentration above 10 mol %, decreased the luminance intensity may be due to concentration quenching effect.