Ur answer is so helpful Nikhil. Thank u so much. Can you just help me on this last thing.. The attachment is the UV-Vis spectra of my sample. Is this absorption data acceptable. N as per your advice I will consider taking transmittance data from now on. Thanks again.

Sandip, would you share what your spectrophotometer does actually measure and what the geometry is for that. And how is the quantity "absorbance" exactly defined in your case and how is it determined from measured intensities.

And finally:

a) what information would you like to get about your samples?

b) What do you know about the morphology of your films? It can play a huge role for the optical experiments!

Well thank you so much for your help sir. The spectrometer gives me the data of wavelength and absorbance. I didn't get the second part of your question sir but I guess by absorbance I meant in the UV region. I am using glass as substrate. The spectrometer is first zeroed with only glass then one glass is replaced by the film deposited glass (its a double beam spectrometer).

a) Information I would like to obtain - band gap and thickness of the film (alhough I am not sure how to obtain the thickness from the data)

b) I expect nano-particles below 100nm.

Sir expecting a helpful answer. Thanks in advance.

If the film is discontinuous (you expect particles), then quantitative evaluation is difficult. Also, "thickness" is then probably not a well-defined quantity. It helps then to use conplementary methods for obtaining as much information as you can possibly get.

You did not get my point on "the definition of absorbance". What exactly does the apparatus measure and calculate to yield the "absorbance" numbers? What would it do to give you "transmittance" values? (What exactly are the two curves in your graph above). And you need to learn how the optical properties of a film relate to these measured quantities.

And again, with a discontinuous film it may get difficult, especially when the characteristic dimensions characterizing the morphology are similar to wavelength.

Sir The instrument measures the intensity to yield the absorbance. My graph is the Wavelength VS Intensity curve...

Sandip, please try getting hold of manual(s) and informed opinions. Above you stated "absorbance vs. wavelength", now it is "intensity vs. wavelength". Both cannot probably be true. Of course, intensity is measured somehow and absorbance is derived from that measurement(s). But you need to understand (maybe in detail!) how that is done and achieved in order to assess whether that is meaningful in the case of your samples. Also for an outside person it is almost impossible to help if measurement geometries and procedures are unknown.

Sir by Intensity I meant absorbtion data from intensity.. However thank you for advice sir. I will surely do that.

thanks Nikhil

Dear Sandip, I still haven't understood what the two curves in you plot actually represent and in which manner the data were acquired (and computed) by your apparatus. (They could be the result of a single or two measurements at each wavelength, it could be a single or dual beam instrument, you could be measuring in a setup with or without an integrating sphere etc.... As I said before, details may matter. Nikhil recommends to use "transmittance" data instead of "absorbance" data. Both shall rely in some way to measured intensities with and without your specimen(s), respectively. Either choice of "data type" should be backed with your understanding of how these datasets are generated from intensity measurements.)

Sir its a double beam Spectrophotometer (Model no. Cary 100 Bio UV-Visible spectrophotometer). I have the sample thin film and the substrate (glass without sample deposition) on the two beam paths. So as I thought in the Visible range the wavelength absorbed is zero (so 100% should be transmitted). But in the UV region beyond 300 nm the sample absorbs and transmittance of the incident wavelength decreases.

Sandip, are the intensities collected from the straight beam or does the geometry involve an integrating sphere?

And is the substrate carrying the film covered on the entire surface or is there some area uncovered which you could insert into the beam.

Have you ever measured two such substrates simultaneously to see how well the two light channels match (and then flip positions to see how well the two optical beams match in intensity, this can also be done without a sample in any of the two branches).

Coming back to your figure: do the two lines display then represent two different dual beam measurements or the intensities of the two beams in a single run?

The specification does say it has an integrating sphere. The beam is not straight and there is the use of beam splitter. I assume my sample is covered entirely with the sample. Sir I have done a zero correction by putting two empty substrates (empty in the sense it doesn't contain the deposited film). Although I am not sure about the matching of the two light channels. The figure represents two different runs for two different samples.

So your sample is located at the entrance of that integrating sphere, I guess.

Btw., are you familiar with Lambert's law? (or Lambert & Beer's law, as we like to say in Germany)

Sandip, there is a (small) jump in your data at 350 nm. Is your experiment equipped with two or more detectors and does it switch detectors at this wavelength?

(This is (unfortunately) a very typical shortcoming of many such instruments and is most probably related to (1) different field of views of the detectors in combination with (2) non-ideal Lambertian surfaces in the integrating sphere.)

Yes Sir I do know about Lambert's law.. Sir there is switching of source (UV and Vis sources are different) which I am sure about.

Most probably, your experiment is done in wrong way (the experiment does not fulfil the Lamberet-Beer low what is indicated by the flat part of the spectrum) Also the minus value of the absorbance means that absorbance of the reference is higher than absorbance of the measured sample (Absorbance A= log (intencity of incident light / intensity of the light leaving the sample e.g. log[ I(zero)/ I.]

Have a success. DaW

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