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Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. University of Oslo, Norway.ORCID-id: 0000-0002-9050-5445
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2013 (engelsk)Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 20, s. 205502-Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
2013. Vol. 25, nr 20, s. 205502-
Emneord [en]
Microscopic Surface-Roughness, Augmented-Wave Method, Tungsten-Oxide, Phase-Transitions, Crystal-Structure, Smart Windows, Trioxide, Electrochromics, Photoemission, Dependence
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Identifikatorer
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, id: diva2:628535
Forskningsfinansiär
Swedish Research CouncilSwedish Energy Agency
Merknad

QC 20130614

Tilgjengelig fra: 2013-06-14 Laget: 2013-06-13 Sist oppdatert: 2017-12-06bibliografisk kontrollert

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