title: Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2nanoparticles on a Si substrate.
abstract: Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO2nanoparticles (NPs) on Si substrates. The NPs are bound into the film byp-toluenesulfonic acid (PTSA) and the film is made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon substrate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Urmas
authors.initials: U
authors.lastname: Joost
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia; Laboratory of Functional Materials Technologies, Riga Technical University, Paula Valdena 3/7, 1048 Riga, Latvia.
authors.forename: Andris
authors.initials: A
authors.lastname: Šutka
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Meeri
authors.initials: M
authors.lastname: Visnapuu
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Aile
authors.initials: A
authors.lastname: Tamm
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Meeri
authors.initials: M
authors.lastname: Lembinen
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Mikk
authors.initials: M
authors.lastname: Antsov
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Kathriin
authors.initials: K
authors.lastname: Utt
authors.affiliation: Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga LV-1063, Latvia.
authors.forename: Krisjanis
authors.initials: K
authors.lastname: Smits
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Ergo
authors.initials: E
authors.lastname: Nõmmiste
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
authors.forename: Vambola
authors.initials: V
authors.lastname: Kisand
keywords: TiO2 nanoparticles; colorimetric gas sensing; p-toluenesulfonic acid (PTSA)