I have a light absorbing metal oxide deposited on FTO coated glass. I want to perform a diffuse reflectance measurement and determine the %R for our light absorber only and not the underlying FTO. We are using an Agilent Cary 5000
The way I was taught by a student in another lab is as follows:
1) Get baseline spectrum with BaSO4 standard
2) Perform DRS measurement on the FTO substrate by itself and obtain the %R of the FTO substrate
3) Perform DRS measurement on the sample (light absorber on FTO) and obtain the %R of the sample
4) Obtain the %R of light absorber only by the operation: (%R Sample)/(%R FTO)*100. To this Kubelka-Munk can be applied and F(R) obtained for the light absorber only
Is this the correct way to obtain F(R) for my light absorbing material?
I get results that I expect but I very much want to be sure I am doing this correctly.
Thank you
I use a Cary 5000 for transmission & absorbance measurements. I've only assisted others in using an older Diffuse Reflectance Accessory (DRA) for reflectance, so I can't speak to the details of your calculations after collecting reflectance data, but the little bit of literature I've seen on it appears consistent with your procedure. Maybe some others here on researchgate can address that. However, I have become very familiar with the Cary 5000 and its software, so I am curious...
I notice that there is no mention of collecting a "zero" -- basically a scan of the detector noise, with no standard or sample in place on the reflectance accessory. Are you using the "baseline/zero" correction option in the software settings? I don't know what range of wavelengths you are measuring, but if your detector noise is very low across that range, perhaps it is not much of an issue to not collect a "zero" along with the baseline. Here, I have noticed a small amount of noise with the NIR detector in our own Cary 5000 (not surprising for NIR under ambient air conditions). The noise is quite low for the measurement ranges we have typically used, but there is the possibility that the detector noise could affect the data for certain samples measured across specific wavelengths. So it's something I keep in mind when setting up measurements, and I typically choose the "baseline/zero" option for any measurement I make.
Of course, you may be using a different (older/newer/other) Cary accessory for reflectance than the DRA we use, so your actual procedure could differ because of that, too.
Thanks for your response.
I do use the baseline/zero option. Should have mentioned it in the original post.
I scan from 2000 nm to 300 nm for my current set of samples. The band edge is around 470 nm for my metal oxide and the defect that I am interested in shows up in the N-IR at around 1200 nm.
Update for people in the future who find this through a search engine.
We found that trying to remove the FTO background by dividing out the FTO signal (step 4 in original post) will not work. There were cases where we were getting impossible results. We decided to leave the FTO NIR signal in our spectra as that was the most accurate depiction of the data.
It was decided that if we want data without the FTO signal, then we must grow films thick enough that all the light in the DRS experiment is scattered before it reaches the FTO or simply scrape off the film and perform a measurement on the powder.
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