I have seen a red shift with decreasing size of Si nanoparticles in Raman spectra. For bulk, I am having peak at 520 cm-1 and for 40 nm particle, the peak is shifted to 510 cm-1 and become broader. I think stress accumulation could be there but how to be sure that the broadening , I am seeing is only contributed by optical phonons not by acoustic phonons.
Dear Ankit,
can you short explain, which experiment you are carring out? Raman, absorption or luminescence experiment? What means peak?
R. Mitdank
Dear Rudiger,
Its Raman spectroscopy. Sorry, I forgot to mention earlier. It would be great to have an explanation for it.
Regards
Ankit
What you are seeing there is the "textbook" behavior.
For smaller particle sizes the peaks shift to lower frequencies (compared to the corresponding bulk frequency) and becomes assymetric towards the lower frequency side.
This is explained in the model of phonon confinement, which leads to a relaxation of selection rules. The confiment of phonons in space leads to contributions of non-zone center phonons (which always have lower frequencies than the zone center "bulk" phonon). This explains the assymetry. The shape of the spectrum can be simulated and in principle you can use it to extract the particle sizes.
There are many nice reviews on it out there, which can serve you as a starting point.
Article Raman Spectroscopy of Optical Phonon Confinement in Nanostru...
Article Raman Spectroscopy of Nanomaterials: How Spectra Relate to D...
Regards,
Michael
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