Dear Colleagues!
I am currently measuring the absorption of "absorbing thin films on non-absorbing substrate" type samples. The semiconductor material has a gap in the visible region and I am using a spectrophotometer. By comparing the measurement using 3 different manufacturers (Jasco, Scinco) I realize that the "critical information" (Band-Gap, absorption coefficient) comes out rather similar but the instruments differ quite much in terms of noise, baseline, shape of the baseline, etc.
I am therefore wondering if someone could recommend a more suitable setup for measuring the absorption that (at least partially) is less sensitive to the scattering. For example, photothermal deflection spectroscopy seems to suffer just as much from scattering in the lower end of the onset of absorption (in terms of energy), making it hard to properly determine the slope of the signal in this region (critical for the disorder energy - Urbach energy).
ideally the setup would be able to better distinguish between scattering and absorption than commercial spectrophotometer do.
Your comments are very appreciated!
Yours,
Chris
Photoacoustic detection could be a method.
Otherwise, I'd recommend to go for a setup where you can (but not need to) use a (very high quality) integrating sphere, i.e. one built from "spectralon" (a special type of teflon, I think). You can then do different experiments:
a) transmission and reflection with the "normal", directed beam.
b) diffuse (angle integrated) transmission and reflection
With some modeling one can (try to) disentangle reflectivity, absorbance and scattering. It requires a good optical design of the instrument (there are caveats with using integrating spheres well) and results in an instrument far from a kind of "i-put-my-sample-push-the-button-and-out-comes-my-publication-ready-result" of scientific instrument.
Dear Christoph Wolf,
Have a nice time and good day.
You can use a computerized SHIMADZU UV-1100 double beam spectrophotometer with 10 nm steps. to measure Transmittance, T and reflectance, R at normal incidence In case of measuring R you may use reference material instead of reference glass in the position of reference on the holder.
Like Kai mentionned already, a good approach would be to use an integrating sphere (labsphere is the company making them). I think that Jasco sells an integrating sphere accessory for their instrument (I saw that on their website). That way, the effect of scattering on the absorption estimation will be reduced (for that, the larger the sphere, the better).
You could also use photothermal deflection spectroscopy which avoids the effect of scattering. You can find details with a quick Google search.
Dear all!
Thank you for your ideas and comments! I will have a more detailed look into photothermal deflection and the photoacoustic method, which I am not familiar with.
Kai and Daniel, thank you for bringing the integrating sphere to my attention. I must have totally forgotten about it and since I have one at hand I will try that as soon as possible.
Yours,
Chris
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