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Title: Electron beam induced coloration and luminescence in layered structure of WO{sub 3} thin films grown by pulsed dc magnetron sputtering

Abstract

Tungsten oxide thin films have been deposited by pulsed dc magnetron sputtering of tungsten in argon and oxygen atmosphere. The as-deposited WO{sub 3} film is amorphous, highly transparent, and shows a layered structure along the edges. In addition, the optical properties of the as-deposited film show a steplike behavior of extinction coefficient. However, the electron beam irradiation (3.0 keV) of the as-deposited films results in crystallization, coloration (deep blue), and luminescence (intense red emission). The above changes in physical properties are attributed to the extraction of oxygen atoms from the sample and the structural modifications induced by electron bombardment. The present method of coloration and luminescence has a potential for fabricating high-density optical data storage device.

Authors:
;  [1]
  1. Semiconductor Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai-600036 (India)
Publication Date:
OSTI Identifier:
20979414
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 11; Other Information: DOI: 10.1063/1.2737957; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; AMORPHOUS STATE; ARGON; ATMOSPHERES; CATHODOLUMINESCENCE; COLOR; COLORATION; CRYSTALLIZATION; ELECTRON BEAMS; KEV RANGE 01-10; MAGNETRONS; MEMORY DEVICES; OPACITY; OXYGEN; SPUTTERING; SURFACE COATING; THIN FILMS; TUNGSTEN; TUNGSTEN OXIDES

Citation Formats

Karuppasamy, A., and Subrahmanyam, A. Electron beam induced coloration and luminescence in layered structure of WO{sub 3} thin films grown by pulsed dc magnetron sputtering. United States: N. p., 2007. Web. doi:10.1063/1.2737957.
Karuppasamy, A., & Subrahmanyam, A. Electron beam induced coloration and luminescence in layered structure of WO{sub 3} thin films grown by pulsed dc magnetron sputtering. United States. doi:10.1063/1.2737957.
Karuppasamy, A., and Subrahmanyam, A. Fri . "Electron beam induced coloration and luminescence in layered structure of WO{sub 3} thin films grown by pulsed dc magnetron sputtering". United States. doi:10.1063/1.2737957.
@article{osti_20979414,
title = {Electron beam induced coloration and luminescence in layered structure of WO{sub 3} thin films grown by pulsed dc magnetron sputtering},
author = {Karuppasamy, A. and Subrahmanyam, A.},
abstractNote = {Tungsten oxide thin films have been deposited by pulsed dc magnetron sputtering of tungsten in argon and oxygen atmosphere. The as-deposited WO{sub 3} film is amorphous, highly transparent, and shows a layered structure along the edges. In addition, the optical properties of the as-deposited film show a steplike behavior of extinction coefficient. However, the electron beam irradiation (3.0 keV) of the as-deposited films results in crystallization, coloration (deep blue), and luminescence (intense red emission). The above changes in physical properties are attributed to the extraction of oxygen atoms from the sample and the structural modifications induced by electron bombardment. The present method of coloration and luminescence has a potential for fabricating high-density optical data storage device.},
doi = {10.1063/1.2737957},
journal = {Journal of Applied Physics},
number = 11,
volume = 101,
place = {United States},
year = {Fri Jun 01 00:00:00 EDT 2007},
month = {Fri Jun 01 00:00:00 EDT 2007}
}
  • In this work, we present the pulsing frequency induced change in the structural, optical, vibrational, and luminescence properties of tungsten oxide (WO{sub 3}) thin films deposited on microscopic glass and fluorine doped tin oxide (SnO{sub 2}:F) coated glass substrates by pulsed dc magnetron sputtering technique. The WO{sub 3} films deposited on SnO{sub 2}:F substrate belongs to monoclinic phase. The pulsing frequency has a significant influence on the preferred orientation and crystallinity of WO{sub 3} film. The maximum optical transmittance of 85% was observed for the film and the slight shift in transmission threshold towards higher wavelength region with increasing pulsingmore » frequency revealed the systematic reduction in optical energy band gap (3.78 to 3.13 eV) of the films. The refractive index (n) of films are found to decrease (1.832 to 1.333 at 550 nm) with increasing pulsing frequency and the average value of extinction coefficient (k) is in the order of 10{sup −3}. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (E{sub d}) parameters, dielectric constants, plasma frequency, oscillator strength, and oscillator energy (E{sub o}) of WO{sub 3} films were calculated and reported for the first time due to variation in pulsing frequency during deposition by pulsed dc magnetron sputtering. The E{sub o} is change between 6.30 and 3.88 eV, while the E{sub d} varies from 25.81 to 7.88 eV, with pulsing frequency. The Raman peak observed at 1095 cm{sup −1} attributes the presence of W-O symmetric stretching vibration. The slight shift in photoluminescence band is attributed to the difference in excitons transition. We have made an attempt to discuss and correlate these results with the light of possible mechanisms underlying the phenomena.« less
  • The optical properties of tungsten trioxide thin films prepared by DC magnetron sputtering, with different oxygen vacancy (V{sub o}) concentration, have been studied by spectrophotometry and photoluminescence (PL) emission spectroscopy. Absorption and PL spectra show that the films exhibit similar band gap energies, E{sub g} ≈ 2.9 eV. The absorption spectra of the films show two pronounced absorption bands in the near-infrared region. One peak (P1) is located at approximately 0.7 eV, independent of V{sub o} concentration. A second peak (P2) shifts from 0.96 eV to 1.16 eV with decreasing V{sub o} concentration. Peak P1 is assigned to polaron absorption due to transitions betweenmore » tungsten sites (W{sup 5+} → W{sup 6+}), or an optical transition from a neutral vacancy state to the conduction band, V{sub o}{sup 0} → W{sup 6+}. The origin of peak P2 is more uncertain but may involve +1 and +2 charged vacancy sites. The PL spectra show several emission bands in the range 2.07 to 3.10 eV in the more sub-stoichiometric and 2.40 to 3.02 eV in the less sub-stoichiometric films. The low energy emission bands agree well with calculated optical transition energies of oxygen vacancy sites, with dominant contribution from neutral and singly charged vacancies in the less sub-stoichiometric films, and additional contributions from doubly charged vacancy sites in the more sub-stoichiometric films.« less
  • The authors examined the photocatalytic activity of WO{sub 3} films (thickness 500-600 nm) deposited on a fused quartz substrate heated at 350-800 deg. C by dc reactive magnetron sputtering using a W metal target under the O{sub 2} gas pressure from 1.0 to 5.0 Pa. Films deposited at 800 deg. C under 5.0 Pa have excellent crystallinity of triclinic, P1(1) structure and a large surface area, as confirmed by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Exposure of acetaldehyde (CH{sub 3}CHO) adsorbed onto the film surface to ultraviolet, visible, or standard fluorescence light induces oxidative photocatalytic decomposition indicatedmore » by a decrease in CH{sub 3}CHO concentration and generation of CO{sub 2} gas. For all three types of irradiation, concentration ratio of decreased CH{sub 3}CHO to increased CO{sub 2} is about 1:1, suggesting the possible presence of intermediates. The sputter-deposited WO{sub 3} film can be a good candidate as a visible light-responsive photocatalyst.« less
  • DC magnetron sputtering was used to deposit molybdenum boride thin films for potential low-friction applications. The films exhibit a nanocomposite structure with ∼10 nm large MoB{sub 2−x} (x > 0.4) grains surrounded by a boron-rich tissue phase. The preferred formation of the metastable and substoichiometric hP3-MoB{sub 2} structure (AlB{sub 2}-type) is explained with kinetic constraints to form the thermodynamically stable hR18-MoB{sub 2} phase with a very complex crystal structure. Nanoindentation revealed a relatively high hardness of (29 ± 2) GPa, which is higher than bulk samples. The high hardness can be explained by a hardening effect associated with the nanocomposite microstructure where the surrounding tissuemore » phase restricts dislocation movement. A tribological study confirmed a significant formation of a tribofilm consisting of molybdenum oxide and boron oxide, however, without any lubricating effects at room temperature.« less