Publikationsserver der RWTH Aachen University
Schaltbare optische Schichten : vom atomistischen Verständnis des gasochromen Schaltens von Wolframoxid zur industriellen Anwendung
Abstract
dc:descriptionCatalyst covered (few nanometers of Platinum or Palladium) tungsten oxide films of some hundred nanometers color in hydrogen containing atmosphere blue because of an absorption with a maximum in the infrared region. In oxygen containing atmosphere the films bleach. This coloration and bleaching is reversible and shows remarkable potential for industrial applications. Main goal of the thesis is the identification of the atomistic switching process. Two different models describing the switching effect on an atomic level are known. The model of hydrogen-intercalation predicts the building of tungsten bronzes by the intercalataion of hydrogen atoms into the film during coloration in hydrogen containing atmosphere. This reduces the tungsten atoms. Small polarons are build which generate an absorption in the infrared region. During bleaching in oxygen containing atmosphere the intercalated hydrogen atoms reach the pores of the tungsten oxide films, where they build water with oxygen atoms out of the gas-atmosphere. The second model describes that oxygen vacancies are build during coloration under hydrogen containing atmosphere. So this model is named oxygen-vacancies model. Tungsten is reduced from oxidation state VI+ to V+. Again polaron absorption is generated. The oxygen atoms form water in the pores of the tungsten oxide film with the hydrogen atoms out of the atmosphere. Oxygen containing atmosphere generates the reverse reactions. Oxygen vacancies are filled again by oxygen atoms. Tungsten atoms are oxidized from V+ to VI+ and the film bleaches. Optical in-situ analysis of tungsten oxide films during coloration and bleaching give important hints to the atomistic process. The oxygen vacancies model can describe the results: Transmission spectroscopy and ellipsometric spectroscopy were performed at the same time for the same tungsten oxide sample. The simulation of these spectra results in a variation of the film thickness. During coloration in hydrogen containing atmosphere the thickness is reduced by around one percent. In oxygen containing atmosphere the thickness reaches after bleaching that film thickness of the bleached film before coloration again. In-situ XRR-analysis confirmed this result for the variation of the film thickness. Spectroscopic in-situ analysis in the near infrared region detect a strong increase of the amount of water during coloration in hydrogen containing atmosphere. It does not during bleaching in oxygen containing atmosphere. Variation of the tungsten oxide film thickness of around one percent and the development of the amount of water during coloration and bleaching could be explained by the oxygen vacancies model only. The hydrogen intercalation model is not able to explain the results.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2005
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Salinga, Christian Lothar
- Contributors dc:contributor
-
- Wuttig, Matthias
Subjects
dc:subject × 8Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger
Identifiers
dc:identifier.*- OAI identifier oai:identifier
- oai:publications.rwth-aachen.de:61894