Raman Spectra and Bulk Modulus of Nanodiamond in a Size Interval of 2-5 nm

Nanodiamond in a 2-5-nm size interval (which is typical for an appearance of quantum confinement effect) show Raman spectra composed of 3 bands at 1325, 1600, and 1500 cm^-1 (at the 458-nm laser excitation) which shifts to 1630 cm^-1 at the 257-nm laser excitation. Contrary to sp²-bonded carbon, relative intensities of the bands do not depend on the 458- and 257-nm excitation wavelengths, and a halfwidth and the intensity of the 1600 cm^-1 band does not change visibly under pressure at least up to 50 GPa. Bulk modulus of the 2-5-nm nanodiamond determined from the high-pressure study is around 560 GPa. Studied 2-5-nm nanodiamond was purified from contamination layers and dispersed in Si or NaCl.