I dispersed my sample in IPA and dropped onto Si wafer. I wonder if this is the right way to prepare sample?
When I check UV-Vis spectrometry, I used reflectance mode and convert it to absorption, But the value is negative, I am curious why?
Dear Lingling,
for me this seems anything but the right way. I wonder, how you obtained what you refer as absorption? For me it seems that you show Absorbance.
I suspect the negative values you obtained are due to the reflectance values higher than 1 (or 100 %). However, in contrast with my statement above, what you show is not the Absorbance, but Optical density. Your spectrometer software just made a negative logarithm of values it measured.
TH
Thanks for your answer.@ Tomáš Halenkovič sorry for my ambiguous explanation in the question.
As you said that the reflectance value is higher than 100%, so when I converted it to Abs, the value became negative. however, it is this phenomena that confuses me, how could the absorbance be negative? it looks abnormal to me.
And I wonder if it is because of my wrong handling of sample or machine problem?
Dear Lingling Wang ,
values of reflectance higher than 100 % means, that your sample reflects more than your reference. There can be other reasons, but I don't know your spectrometer and your measurement conditions.
TH.
Use the best solvent for the powder sample, then place the dissolved sample into the holder of the UV machine
Thanks for all the answers, I have solved the problems. Here I want to share my experience, it may be helpful to someone who faces similar issue. I borrowed the reference sample from my friend at first time, but the surface was not very clean and flat. Then I made a new reference sample again, just simply pressed the BaSO4 into a holder(I used the holder we check for XRD...), everything works fine after that. I also compared the data with different sampling method (dropping onto Si wafer vs scattering onto BaSO4 reference), seems doesn't really matter in my case. So make sure the reference surface CLEAN AND FLAT.
Grind the solid sample , and you can choose the best solvent for your solid sample
You can take the best solvent like distilled water .Also, put very little weight of solid state sample
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