I've recently conducted some experiments and used a UV-Vis spectrophotometer to measure absorbance spectra. However, I've noticed that in my measurements, the obtained absorbance values are negative, which has left me puzzled. I'm wondering if this could be due to the influence of thickness.
Sample: PDMS, cross-linking agent ratio 20:1
The PDMS mixture, weighing 6 g, was evenly coated onto a template with a diameter of 2.4 cm using a spin-coater. The spin-coater operated at a rotation speed of 100 rpm, resulting in a thin film with a thickness of 0.8 mm. To solidify the film, the coated template was placed in an oven and heated to 100℃ for 60 minutes.
Has anyone encountered a similar situation before? I would greatly appreciate any advice or insights regarding this issue.
Thank you all!
Can you tell us more about your sample (is it a layer on a substrate?) and the reference sample you use? Also, it would be could if you could show us a spectrum.
Thank you - and what was the reference sample for your measurement? Did you calculate the absorbance according to A = -log10(T/T0), where T is the transmittance of your sample and T0 the transmittance of the reference sample?
This is a very interesting question! In our laboratory, researchers who are not familiar with the equipment often measure negative absorbance values that are unusual. Most of these instances arise because the absorbance spectrum is not set properly. In some UV-Vis absorption spectroscopy devices, when using an integrating sphere for testing, you need to switch the positions of the sample and the reference, like the R/S reverse option in our UV-5700. If the previous user does not reset the settings after using the integrating sphere, then the person conducting the "normal" test will obtain a negative absorbance value
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