What parameters could be extracted from Raman spectra of nanopowders

Analytical theory of the optical phonon line broadening in disordered nanoparticles is developed, the disorder is modeled as weak delta-correlated spatially randomized variations of atomic masses. The linewidth dependence on the mean particle size, its shape, the variance of size distribution function, the strength of disorder, as well as on the phonon quantum number is determined for both investigated regimes of separated and overlapped phonon levels, and crossover scales are determined. Analytical results are strongly supported by numerical calculations. The possibility to extract these parameters of a nanopowder of nonpolar crystal from the Raman experimental data is demonstrated and illustrated with the use of the diamond nanocrystallites serving as an example.