Raman scattering from diamond particles

Raman spectra of diamond powders with size less than 2 μm have been measured as a function of the particle size. The Raman line was found to become more asymmetric with some tailing towards lower Raman shifts, broader, and weaker with decreasing particle size. The observed result can be explained by a phonon confinement effect rather than by a strain effect. This work predicts that it is very difficult to detect Raman spectra of diamond particles with size less than ∼50 A. A broad Raman band, whose intensity becomes stronger with decreasing particle size, was observed around 600 cm−1 in the spectra of diamond powders with particle size less than 2 μm. We hypothesize that the broad band arises from transverse acoustic phonons near the Brillouin zone boundary because of the relaxation in the wave vector selection rule.