I have used an annealed MXene sample and non-annealed sample. 785 nm laser was used. I see a significant reduction in peak intensity of resonance peak for annealed sample. What information do we get from resonance peak and what actually happen when its intensity get reduced.
You spectrum seems to be incomplete, there are only wavenumbers 1-100 included. Please reupload.
I just wanted to know about the first peak which is a resonance peak.
Are you sure this is a resonance peak? Some Raman spectrometers have narrow notch filters and let through some backscattered light for highly reflective samples. You can check this by tilting the sample mildly with respect to your spectrometer so that the directly reflected beam is no longer seen.
I concur with Dr. Weippert's concern. What type of monochromator are you using? Are you using micro-Raman imaging machine? If so, quite typically they use a single monochromator. In such a case, laser light rejection efficiency is poor. Iin order to protect the detector being harmed from the Rayleigh line, the filter is adjusted in such a way that you can start recording a Raman spectrum starting from say around 150 cm-1 and above. However, your Raman spectrum starts with 0 cm-1.
If you have a double monochromator, the way ordinary Raman spectrometer is (not the imaging Raman spectrometer), then you can go close to the excitation line, say to several cm-1, but still not 0 cm-1. Using this spectrometer, and using unreasonably narrow slit width, you can obtain a spectrum starting from practically 0 cm-1, but in such a setting, you will not observe a Raman spectrum. All you observe is laser lines, if you ever see the lines.
Assuming everything you did was spectroscopically correct, the reduction of the resonance Raman line is due to the changes in the electronic absorption spectrum of the material upon annealing. The absorption peak may be shifting away from the excitation laser frequency, or band width of the electronic absorption peak is broadening, or both. Resonance excitation efficiency depends on the difference between the electronic excitation peak and your excitation laser frequency, and the hand with at half height of the electronic absorption peak (the sharper the band the stronger the resonance effect, in general). But, you should make sure that you are recording the spectrum correctly first as your Raman spectrum does not look like acceptable norm.
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