I would like to illustrate the above question with XRD technique. For example, width of the Bragg’s peak in XRD is inversely proportional to crystallite size, hence one I can expect increase in line width for nano material (compared to micro crystal). Up to my knowledge, Raman line width is directly proportional to degree of crystallinity. Then why nano crystal shows broader Raman line width? Kindly help me to understand this.
Dear Rajaji,
I think, the broadening of Raman modes for nanostructures is because of the phonon confinement in the system.
Please find the article for more details
https://www.researchgate.net/publication/229532197_Raman_Spectroscopy_of_Optical_Phonon_Confinement_in_Nanostructured_Materials
Article Raman Spectroscopy of Optical Phonon Confinement in Nanostru...
If the broadening is asymmetric towards the lower frequency region, we can interpret the broadening to phonon confiment, otherwise many other reason could be responsible for that such as defects and difference in electron phonon coupling.
Hello Rajaji,
While photon confinement could be a reason for peak broadening, there could be other reasons like defects, nanoparticle size etc like Sanjay mentioned. Check this paper where they study line broadening of porous silicon(attached). Also try
Modified Confinement Model for Size Dependent Raman Shift and Linewidth of Silicon Nanocrystals by Sanjeev K. Gupta and Prafulla K. Jha.
Best,
Buddini
Please have a look at the link below
https://www.researchgate.net/post/Why_do_we_get_broadened_peaks_in_Raman_Spectroscopy
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