R. Suresh

Effect of solvent and substrate temperature on morphology of cerium oxide thin films by simple nebuliser spray pyrolysis technique

Abstract Cerium oxide thin films are coated on glass substrates by nebuliser spray pyrolysis technique. The crystallographic structures, surface morphology, optical properties and I–V characteristics have been studied as a function of solvent and substrate temperature (300–500°C). X-ray diffraction was used to estimate crystallographic texture, grain size, strain and lattice constant. All films exhibit cubic fluorite structure with different preferred orientations depending on the preparation conditions. Photoluminescence spectra revealed the presence of violet and blue emissions in the visible region. The calculated band gap energy is found to be in the range 3·0 to 3·6 eV. Spherical and lamellar shaped particles with crystallite size 10–41 nm are found in the film surface. X-ray photoelectron spectroscopy analysis confirms the highly non-stoichiometric nature of the films with dominant occurrence of Ce4+ (CeO2) and subsidiary occurrence of Ce3+ (Ce2O3).

Influence of Substrate Temperature on the Properties of Cobalt Oxide Thin Films Prepared by Nebulizer Spray Pyrolysis (NSP) Technique

Cobalt oxide thin films are prepared by the nebulizer spray pyrolysis technique using cobalt chloride as the precursor material. The structural, optical, morphological and electrical properties are investigated as a function of substrate temperature (300–450 °C). The X-ray diffraction (XRD) analysis reveals that all the films are polycrystalline in nature, having cubic structure with preferential orientation along the (111) plane. The optical spectra show that the films are transparent (68 %) in the IR region. The optical band gap values are calculated for different substrate temperature. Photoluminescence (PL) spectra of the films indicate the presence of indigo, blue and green emission peaks with an ultraviolet emission peak centered around 368nm. SEM images reveals small sphere-like structures for the prepared Co3O4 films. The maximum conductivity obtained is 1.48 x 10−3 S/cm at 350 °C. The activation energy varies between 0.039 and 0.138 eV for the substrate temperature variation from 300-450 Q°C.

IDC golf-ball structured thin films: preparation, characterization and photodiode properties

Uniform and well-dispersed IDC (indium doped cerium oxide) films are successfully deposited by Nebulizer Spray Pyrolysis (NSP) technique. Cubic fluorite crystallites are detected by an X-ray diffraction pattern with a preferred orientation along the (200) direction. The In concentration affects the crystallinity and structural parameters like crystallite size, texture coefficient, lattice constant and dislocation density. The transmittance decreases with increasing In concentration up to 15% and then increases due to the presence of covalent bonds between cerium and an oxygen additive at the shortest wavelengths. PL spectra revealed that three consistent sharp and broad peaks are observed at 394 (3.14 eV), 425 (2.91 eV) and 579 nm (2.14 eV), which correspond to near band edge emission (NBE) at the UV region and blue and red deep level emission (DLE) in the visible region, respectively. Large agglomerated ring and white spherical crystallites are obtained with a typical size in the range of 93–128 nm. Satellites are caused by the facilitation of ligand (O 2p) to metal (Ce 4f) charge transfer by primary and main photoionization processes, which indicates that the valance states of Ce3+ (16.7%) and Ce4+ (36.4%) have entered in to the CeO2 lattice sites. I–V characteristics show the rectifying nature of this hetero-junction with a typical forward to reverse current ratio of ∼7 in the range −3 to +3 V. The turn-on voltage of the hetero-junction is found to be ∼1.5 V. The transient photocurrent behavior indicates that the device has good stability and quick response and suggests that the prepared heterojunction device can be used as a white light photodetector and for UV detector applications.