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Title: X-ray Absorption Spectroscopy of Vanadium Dioxide Thin Films Across the Phase-Transition Boundary

Abstract

X-ray absorption spectroscopy (XAS) and x-ray photoemission spectroscopy of the V L edge and O K edge were performed on VO{sub 2} thin films rf sputtered at various conditions. The spectra give evidence of the changes in the electronic structure depending on the film quality. XAS of the O K edge shows a decrease of the spacing between 3d{sub {pi}} and 3d{sub {sigma}} bands by 0.8 eV with concurrent broadening of both bands for the sample sputtered at lower substrate temperature and consequently having more polycrystalline and disordered character. 3d{sub {sigma}} band position appears to be more sensitive to the sample quality, indicating that the cation-ligand interaction is mostly affected likely due to the distortion of the local O coordination surrounding a V ion. The observed variation of the spectra in films of different morphologies may reflect the changes of the density of states responsible for the considerable variation of the metal-insulator transition (MIT) properties reported for VO{sub 2} thin films synthesized at different conditions. The study of the temperature dependence of the XAS spectra including repeated measurements across the MIT revealed both reversible and irreversible V L-edge and O K-edge changes. The thermal cycling of the VO{sub 2} filmsmore » through the MIT shows irreversible shifts of the conduction bands toward lower photon energies apparently caused by the sample deterioration due to the lattice transformations at the MIT. The signature of a phase transition in a VO{sub 2} film at MIT temperature (T{sub MIT}) is clearly seen in the XAS O K-edge spectra which show reversible switches of the 3d{sub {pi}} and 3d{sub {sigma}} bandwidths by approximately 20% depending on the sample being above or below T{sub MIT}.« less

Authors:
; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930664
Report Number(s):
BNL-81159-2008-JA
Journal ID: ISSN 0163-1829; PRBMDO; TRN: US0900016
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B: Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 19
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ABSORPTION SPECTROSCOPY; ELECTRONIC STRUCTURE; PHOTOEMISSION; PHOTONS; SPECTRA; SPECTROSCOPY; SUBSTRATES; SWITCHES; TEMPERATURE DEPENDENCE; THERMAL CYCLING; THIN FILMS; TRANSFORMATIONS; VANADIUM; national synchrotron light source

Citation Formats

Ruzmetov,D., Senanayake, S., and Ramanathan, S. X-ray Absorption Spectroscopy of Vanadium Dioxide Thin Films Across the Phase-Transition Boundary. United States: N. p., 2007. Web. doi:10.1103/PhysRevB.75.195102.
Ruzmetov,D., Senanayake, S., & Ramanathan, S. X-ray Absorption Spectroscopy of Vanadium Dioxide Thin Films Across the Phase-Transition Boundary. United States. doi:10.1103/PhysRevB.75.195102.
Ruzmetov,D., Senanayake, S., and Ramanathan, S. Mon . "X-ray Absorption Spectroscopy of Vanadium Dioxide Thin Films Across the Phase-Transition Boundary". United States. doi:10.1103/PhysRevB.75.195102.
@article{osti_930664,
title = {X-ray Absorption Spectroscopy of Vanadium Dioxide Thin Films Across the Phase-Transition Boundary},
author = {Ruzmetov,D. and Senanayake, S. and Ramanathan, S.},
abstractNote = {X-ray absorption spectroscopy (XAS) and x-ray photoemission spectroscopy of the V L edge and O K edge were performed on VO{sub 2} thin films rf sputtered at various conditions. The spectra give evidence of the changes in the electronic structure depending on the film quality. XAS of the O K edge shows a decrease of the spacing between 3d{sub {pi}} and 3d{sub {sigma}} bands by 0.8 eV with concurrent broadening of both bands for the sample sputtered at lower substrate temperature and consequently having more polycrystalline and disordered character. 3d{sub {sigma}} band position appears to be more sensitive to the sample quality, indicating that the cation-ligand interaction is mostly affected likely due to the distortion of the local O coordination surrounding a V ion. The observed variation of the spectra in films of different morphologies may reflect the changes of the density of states responsible for the considerable variation of the metal-insulator transition (MIT) properties reported for VO{sub 2} thin films synthesized at different conditions. The study of the temperature dependence of the XAS spectra including repeated measurements across the MIT revealed both reversible and irreversible V L-edge and O K-edge changes. The thermal cycling of the VO{sub 2} films through the MIT shows irreversible shifts of the conduction bands toward lower photon energies apparently caused by the sample deterioration due to the lattice transformations at the MIT. The signature of a phase transition in a VO{sub 2} film at MIT temperature (T{sub MIT}) is clearly seen in the XAS O K-edge spectra which show reversible switches of the 3d{sub {pi}} and 3d{sub {sigma}} bandwidths by approximately 20% depending on the sample being above or below T{sub MIT}.},
doi = {10.1103/PhysRevB.75.195102},
journal = {Physical Review B: Condensed Matter and Materials Physics},
number = 19,
volume = 75,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • X-ray absorption spectroscopy (XAS) and x-ray photoemission spectroscopy of the V L edge and O K edge were performed on VO{sub 2} thin films rf sputtered at various conditions. The spectra give evidence of the changes in the electronic structure depending on the film quality. XAS of the O K edge shows a decrease of the spacing between 3d{sub {pi}} and 3d{sub {sigma}} bands by 0.8 eV with concurrent broadening of both bands for the sample sputtered at lower substrate temperature and consequently having more polycrystalline and disordered character. 3d{sub {sigma}} band position appears to be more sensitive to themore » sample quality, indicating that the cation-ligand interaction is mostly affected likely due to the distortion of the local O coordination surrounding a V ion. The observed variation of the spectra in films of different morphologies may reflect the changes of the density of states responsible for the considerable variation of the metal-insulator transition (MIT) properties reported for VO{sub 2} thin films synthesized at different conditions. The study of the temperature dependence of the XAS spectra including repeated measurements across the MIT revealed both reversible and irreversible V L-edge and O K-edge changes. The thermal cycling of the VO{sub 2} films through the MIT shows irreversible shifts of the conduction bands toward lower photon energies apparently caused by the sample deterioration due to the lattice transformations at the MIT. The signature of a phase transition in a VO{sub 2} film at MIT temperature (T{sub MIT}) is clearly seen in the XAS O K-edge spectra which show reversible switches of the 3d{sub {pi}} and 3d{sub {sigma}} bandwidths by approximately 20% depending on the sample being above or below T{sub MIT}.« less
  • Optical properties and valence band density of states near the Fermi level of high-quality VO2 thin films have been investigated by mid-infrared reflectometry and hard-UV (h = 150 eV) photoemission spectroscopy. An exceptionally large change in reflectance from 2 to 94% is found upon the thermally driven metal insulator transition (MIT). The infrared dispersion spectra of the reflectance across the MIT are presented and evidence for the percolative nature of the MIT is pointed out. The discrepancy between the MIT temperatures defined from the electrical and optical properties is found and its origin is discussed. The manifestation of the MITmore » is observed in the photoemission spectra of the V 3d levels. The analysis of the changes of the V 3d density of states is done and the top valence band shift upon the MIT is measured to be 0.6 eV.« less
  • Chemical solution deposited (CSD) complex oxide thin films attract considerable interest in various emerging fields as for example, fuel cells, ferroelectric random access memories or coated conductors. In the present paper the results of soft-x-ray spectroscopy between 100 eV and 500 eV on the amorphous to crystalline phase transition of ferroelectric PbZr{sub 0.3}Ti{sub 0.7}O{sub 3} (PZT) thin films are presented. Five CSD samples derived from the same wafer coated with a PZT film pyrolyzed at 350 C were heat treated at different temperatures between 400 C and 700 C. At first the sample were morphologically and electrically characterized. Subsequently themore » soft-x-ray absorption and emission experiments were performed at the undulator beamline 8.0 of the Advanced Light Source of the Lawrence Berkeley National Laboratory. Soft-x-ray absorption spectra were acquired for the Ti L{sub 2,3-}, O K-, and C K-edge thresholds by using simultaneously the total electron yield (TEY) and total fluorescence yield (TFY) detection methods. For two samples, annealed at 400 C and 700 C, respectively, the resonant inelastic soft-x-ray spectroscopy (RIXS) was applied for various excitation energies near the Ti L-, O K-edges. We observed clear evidence of a rutile phase at untypically low temperatures. This rutile phase transforms into the perovskite phase upon increasing annealing temperature. These results are discussed in the framework of current microscopic models of the PZT (111) texture selection.« less
  • No abstract prepared.