What can we learn from Raman spectra of nanopowders
Analytical theory of the optical phonon line broadening in disordered nanoparticles is developed, the disorder is modelled 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 parameters of a nanopowder from Raman experimental data is demonstrated and illustrated with the use of concrete example.