Hello,
I have been attempting to grow barium titanate thin films with sputtering by using 99.95% pure separate Barium and Titanium targets and varying oxygen flow rates to my sputtering chamber. After growth of my films, I take them out of my chamber, and I notice within a few minutes the color of my thin film begins to "grow" other colors or polka-dots, which grow larger and larger over my film. It makes me think my films are not stable, but I am using the same sputtering parameters as our collaborator to produce these films. What would cause my films to do this when exposed to ambient air? Are they oxidizing? Are they hydrating? Do I need to provide more Oxygen to my films during deposition?
I think that most probable is the you do not have a stochiometric compound of barium titanate. In the sputtering, the substrate is kept cold. I think you need to heat up the substrate such that the sputtered species react with each other forming barium titanite. Un this way you stabilize also the sputtered film.
Best wishes
Dear Derek Rosdahl ,
if there is, locally[1,2], high relative environmental humidity, the films might soak up water, along the time (t-t0) from the opening of the chamber (t0), changing color[1].
Transfer your samples in a 'dry[3,4] environment', the soon the possible (t-t0 < minutes)[5].
1. Device soaks moisture from air and produces energy https://www.cambridge.org/core/journals/mrs-bulletin/news/device-soaks-moisture-from-air-and-produces-energy
2. Check if there is low(er) relative humidity at the place of your collaborator (?).
3. Vacuum Atmospheres NexGen Inert Atmosphere Glovebox System
4. Glove Box - operation https://www.youtube.com/watch?v=IpTc-qcNPgY
5. Transfer your samples in a GB's environment, to protect them from humidity in storage and measure later in an Ar-filled GB[3,4].
Dear Derek Rosdahl,
You could compare the temperature inside and out of the chamber. By reading the pages 4 and 5 in the thesis in the link below, I hope you could find a reason for the changing in the color of barium titanate thin film
https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=6028&context=rtd
By itself, in its crystalline forms, Ba Titanate is not susceptible to chemical modification due to environment that may change its color. From your question I deduce that some collaborator of yours managed to get a better performing film by using your recipe... I think that the difference might be in the affinity to humidity uptake of your own film (differently from films produced by others) as Ioannis Samaras suggested, perhaps due to the surface micromorphoogly, namely porosity, or surface distribution of defects (including impurities) centers where such water uptake is favored. If you heat your sample at, say, 90-110 degC, you could possibly restore the originally dry surface and its correct appearance. Just try this heating, in inert environment (N2, Ar) if possible, and see what happens.
If my hypothesis is correct, then the problem is not of chemical nature, but rather of morphology, so depending also on the substrate you have used, how it was pre-treated, and the same deposition thermal/geometrical setup.
Hope having given you some useful ideas.
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