RAMAN-SCATTERING FROM DIAMOND PARTICLES

Raman spectra of diamond powders with size less than 2 mum have been m easured as a function of the particle size. The Raman line was found t o become more asymmetric with some tailing towards lower Raman shifts, broader, and weaker with decreasing particle size. The observed resul t can be explained by a phonon confinement effect rather than by a str ain effect. This work predicts that it is very difficult to detect Ram an spectra of diamond particles with size less than approximately 50 a ngstrom. A broad Raman band, whose intensity becomes stronger with dec reasing particle size, was observed around 600 cm-1 in the spectra of diamond powders with particle size less than 2 mum. We hypothesize tha t the broad band arises from transverse acoustic phonons near the Bril louin zone boundary because of the relaxation in the wave vector selec tion rule.