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Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. University of Oslo, Norway.ORCID iD: 0000-0002-9050-5445
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2013 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 20, 205502- p.Article in journal (Refereed) Published
Abstract [en]

The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (P-tot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low P-tot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies E-g approximate to 3.1 eV, which increase with increasing P-tot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic delta-WO3, and monoclinic gamma- and epsilon-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The delta-WO3 and gamma-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that E-g in epsilon-WO3 is higher than in the delta-WO3 and gamma-WO3 phases, which provides an explanation for the P-tot dependence of the optical data.

Place, publisher, year, edition, pages
2013. Vol. 25, no 20, 205502- p.
Keyword [en]
Microscopic Surface-Roughness, Augmented-Wave Method, Tungsten-Oxide, Phase-Transitions, Crystal-Structure, Smart Windows, Trioxide, Electrochromics, Photoemission, Dependence
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-123618DOI: 10.1088/0953-8984/25/20/205502ISI: 000318556100013Scopus ID: 2-s2.0-84877635597OAI: oai:DiVA.org:kth-123618DiVA: diva2:628535
Funder
Swedish Research CouncilSwedish Energy Agency
Note

QC 20130614

Available from: 2013-06-14 Created: 2013-06-13 Last updated: 2017-12-06Bibliographically approved

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