i have deposited TiO2 with pulse laser deposition system at room temperature and 10 e -6 pressure infact thin film was fabricated but the target has changed colour from white to steel grey where laser was incident.Can anyone suggest the reason for it? the laser wavelength was 532.
Vacuum has reducing property. Your target's stoichiometry changed due to formation of oxygen vacancies. Now you have TiyOx non stoichiometric TiO2. Reduced Tio2 can have blue, grey and even very dark colors.
FTIR will give you peaks on certain wavelength, which can vary with standard data, you can compare them
The change of color in grey after PLD may be an indicative of metal-rich layer.
In case of oxygen presence into the deposition chamber, this can also influence the color of the film due to oxygen vacancies in the deposited film.
Please see also:
L.M. Doeswijk,G. Rijnders,D.H.A. Blank
Pulsed laser deposition:metal versus oxide ablation
Appl. Phys. A 78, 263–268 (2004)
and
Jaewon Park et al.
Optical Reactivity of Epitaxially Grown Nitrogen-Doped
Titanium Oxide (TiO2) Films
Journal of the Korean Physical Society, Vol. 49, No. 5, November 2006, pp. 21472150
Most oxide targets unless they are very dense, l would always change color from light brown to dark brown with repeated ablation. It is unavoidable, as stated in earlier answers, they become reduced. therefore one removes the target scrapes it after a few ablation runs, and then sticks thetarget bck again, and tries to deposit a film with a fresh target surface.
this is a typical problem faced while sputtering with oxide targets also, and the problems are similar to pulsed laser ablation.
K. Sreenivas
Dear Asma,
I agree with Amir Abidov , the change in stoichiometry lead to formation of oxygen vacancies and you have TiyOx .Increase oxygen content lead to more dark .
Ghaleb Al-Dahash
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