Surface Tamm States of 2-5 nm Nanodiamond via Raman Spectroscopy.

We observed resonance effects in the Raman scattering of nanodiamonds with an average size of 2-5 nm excited at a wavelength of 1064 nm (1.16 eV). The resonant Raman spectrum of the 2-5 nm nanodiamonds consists of bands at wavelengths of 1325 and 1600 cm, a band at 1100-1250 cm, and a plateau in the range from 1420 to 1630 cm.

The Effect of Shear Deformation on C-N Structure under Pressure up to 80 GPa.

We studythe effect of shear deformation on graphitic -CN under pressures of up to 80 GPa at room temperature. -CN samples are transformed from initial amorphous flakes into onion-like structures, in which the nitrogen content in the quenched samples decreases with increasing pressure (from 42% in the initial conditions to 1% at 80 GPa). The concentration of the bonds also decreases from 1 (the initial sample) to 0.

Transformation of diamond to fullerene-type onions at pressure 70 GPa and temperature 2400 K.

We report the observation of a phase transition of diamond to denser than diamond carbon phase composed from 2 to 3 fullerene-type shells of onions. Raman spectra indicate the fullerene-type of the onions shells. The onions phase is a stable phase in a diamond instability zone of a phase diagram of carbon at pressure 70 GPa and temperature 2400 K.

Phase diagram of carbon and the factors limiting the quantity and size of natural diamonds.

Phase diagrams of carbon, and those focusing on the graphite-to-diamond transitional conditions in particular, are of great interest for fundamental and applied research. The present study introduces a number of experiments carried out to convert graphite under high-pressure conditions, showing a formation of stable phase of fullerene-type onions cross-linked by sp-bonds in the 55-115 GPa pressure range instead of diamonds formation (even at temperature 2000-3000 K) and the already formed diamonds turn into carbon onions. Our results refute the widespread idea that diamonds can form at any pressure from 2.

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 (at the 458-nm laser excitation) which shifts to 1630 cm at the 257-nm laser excitation. Contrary to sp-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 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.