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Title: Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique

Abstract

Nanocrystalline ZnS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction and selected area electron diffraction studies confirmed the formation of nanocrystalline cubic phase of ZnS in the films, although the target material was hexagonal ZnS. The particle size, calculated from the XRD patterns of the thin films was found in the range 2.06-4.86 nm. TEM micrographs of the thin films revealed the manifestation of ZnS nanoparticles with sizes in the range 3.00-5.83 nm. UV-vis-NIR spectrophotometric measurements showed that the films were highly transparent ({approx}90%) in the wavelength range 400-2600 nm with a blue shift of the absorption edge. The direct allowed bandgaps have been calculated and they lie in the range 3.89-4.44 eV. The particle size, calculated from the shift of direct bandgap, due to quantum confinement effect lying in the range 3.23-5.60 nm, well support the TEM results. The room temperature photoluminescence spectra of the films showed two peaks centered around 315 and 450 nm. We assigned the first peak due to bandgap transitions while the latter was due to sulfur vacancy in the films. The composition analysis by energy dispersive X-rays alsomore » supported the existence of sulfur deficiency in the films. The dielectric property study showed high dielectric constant (85-100) at a higher frequency (>5 kHz)« less

Authors:
 [1];  [1];  [1];  [2]
  1. Thin Film and Nanoscience Laboratory, Department of Physics, Jadavpur University, Kolkata 700 032 (India)
  2. Thin Film and Nanoscience Laboratory, Department of Physics, Jadavpur University, Kolkata 700 032 (India). E-mail: kalyan_chattopadhyay@yahoo.com
Publication Date:
OSTI Identifier:
21000606
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 42; Journal Issue: 3; Other Information: DOI: 10.1016/j.materresbull.2006.06.019; PII: S0025-5408(06)00261-3; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRYSTALS; ELECTRON DIFFRACTION; GLASS; MAGNETRONS; NANOSTRUCTURES; PARTICLE SIZE; PERMITTIVITY; PHOTOLUMINESCENCE; RADIOWAVE RADIATION; SEMICONDUCTOR MATERIALS; SPECTROPHOTOMETRY; SPUTTERING; SUBSTRATES; SULFUR; THIN FILMS; TRANSMISSION ELECTRON MICROSCOPY; VACANCIES; X-RAY DIFFRACTION; ZINC SULFIDES

Citation Formats

Ghosh, P.K., Jana, S., Nandy, S., and Chattopadhyay, K.K. Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique. United States: N. p., 2007. Web. doi:10.1016/j.materresbull.2006.06.019.
Ghosh, P.K., Jana, S., Nandy, S., & Chattopadhyay, K.K. Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique. United States. doi:10.1016/j.materresbull.2006.06.019.
Ghosh, P.K., Jana, S., Nandy, S., and Chattopadhyay, K.K. Thu . "Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique". United States. doi:10.1016/j.materresbull.2006.06.019.
@article{osti_21000606,
title = {Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique},
author = {Ghosh, P.K. and Jana, S. and Nandy, S. and Chattopadhyay, K.K.},
abstractNote = {Nanocrystalline ZnS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction and selected area electron diffraction studies confirmed the formation of nanocrystalline cubic phase of ZnS in the films, although the target material was hexagonal ZnS. The particle size, calculated from the XRD patterns of the thin films was found in the range 2.06-4.86 nm. TEM micrographs of the thin films revealed the manifestation of ZnS nanoparticles with sizes in the range 3.00-5.83 nm. UV-vis-NIR spectrophotometric measurements showed that the films were highly transparent ({approx}90%) in the wavelength range 400-2600 nm with a blue shift of the absorption edge. The direct allowed bandgaps have been calculated and they lie in the range 3.89-4.44 eV. The particle size, calculated from the shift of direct bandgap, due to quantum confinement effect lying in the range 3.23-5.60 nm, well support the TEM results. The room temperature photoluminescence spectra of the films showed two peaks centered around 315 and 450 nm. We assigned the first peak due to bandgap transitions while the latter was due to sulfur vacancy in the films. The composition analysis by energy dispersive X-rays also supported the existence of sulfur deficiency in the films. The dielectric property study showed high dielectric constant (85-100) at a higher frequency (>5 kHz)},
doi = {10.1016/j.materresbull.2006.06.019},
journal = {Materials Research Bulletin},
number = 3,
volume = 42,
place = {United States},
year = {Thu Mar 22 00:00:00 EDT 2007},
month = {Thu Mar 22 00:00:00 EDT 2007}
}
  • Cadmium oxide (CdO) thin films were deposited on glass substrate by r.f. magnetron sputtering technique using a high purity (99.99%) Cd target of 2-inch diameter and 3 mm thickness in an Argon and oxygen mixed atmosphere with sputtering power of 50W and sputtering pressure of 2×10{sup −2} mbar. The prepared films were characterized by X-ray diffraction (XRD), optical spectroscopy and scanning electron microscopy (SEM). The XRD analysis reveals that the films were polycrystalline with cubic structure. The visible range transmittance was found to be over 70%. The optical band gap increased from 2.7 eV to2.84 eV with decrease of filmmore » thickness.« less
  • A spectroscopic ellipsometry compatible approach is reported for the optical study of Si quantum dots (QDs) in Si-rich nitride/silicon nitride (SRN/Si{sub 3}N{sub 4}) superlattice, which based on Tauc-Lorentz model and Bruggeman effective medium approximation. It is shown that the optical constants and dielectric functions of Si QDs are strongly size dependent. The suppressed imaginary dielectric function of Si QDs exhibits a single broad peak analogous to amorphous Si, which centered between the transition energies E{sub 1} and E{sub 2} of bulk crystalline Si and blue shifted toward E{sub 2} as the QD size reduced. A bandgap expansion observed by themore » TL model when the size of Si QD reduced is in good agreement with the PL measurement. The bandgap expansion with the reduction of Si QD size is well supported by the first-principles calculations based on quantum confinement.« less
  • ZnO thin films were epitaxially grown on Al{sub 2}O{sub 3} (0001) substrates in a radio-frequency (rf) magnetron sputtering chamber. The surface morphology of ZnO was remarkably affected by the incorporation of a low-temperature grown ZnO buffer as well as the changes in rf-power. X-ray diffractions, combined with the surface micropits, revealed strain relaxations in the ZnO epilayers grown with higher rf-powers, which in turn caused a redshift to the intrinsic exciton absorption peak. Strain relaxations were also observed in the ZnO epilayers upon thermal annealing, which led to a redshift in the E{sub 2}{sup high} Raman mode. A factor ofmore » approx0.7 cm{sup -1} GPa{sup -1}, i.e., a biaxial stress of 1 GPa can shift the E{sub 2}{sup high} mode by 0.7 cm{sup -1}, was obtained. The point defects related absorptions and the exciton localizations were suppressed by annealing, which, in conjunction with the strain-relaxation induced redshift in the intrinsic-exciton absorptions, steepened the absorption edge and increased the optical bandgap energy of the ZnO epilayer.« 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
  • ZrO{sub 2} samples with 0, 7, 9, 11, 13 % Gd doping have been prepared by RF magnetron sputtering deposition technique for solid oxide fuel cell application. The optical properties of the samples have been studied by transmission spectrophotometry and spectroscopic ellipsometry while the local structure surrounding Zr sites has been characterized by extended x-ray absorption fine structure (EXAFS) measurement at Zr K edge with synchrotron radiation. It has been observed that beyond 11% Gd doping, band gap decreases and refractive index increases significantly and also oxygen and Zr coordinations surrounding Zr sites increase which indicates the formation of Gdmore » clustering in ZrO{sub 2} matrix beyond this doping concentration.« less