A new carbon modification: ‘n-diamond’ or face-centred cubic carbon?

Nucleation and growth studies of crystalline carbon phases at nanoscale.

“…Initial theoretical analysis based on local density approximation [24] suggested that, for fcc carbon structure, the cell dimensions for maximum stability should be about 0.356 nm as observed experimentally in the different reports. But later, more complete calculations [58] suggested that the most stable cell dimension would be 0.308 nm.…”

“…n-diamond was initially synthesized by rapid-cooling of graphite sheets shock-compressed to very high temperatures and pressures [19,20]. Later, the ndiamond phase was observed in several other techniques: homogenous nucleation of diamond directly from the gas phase [50], synthesis of diamond from silicon carbide [21], Ru-doped nanostructured carbon films [22], carbon ion-implantation into quartz [23], and hydrogen-plasma etching of CVD grown diamond films [24,25]. Incidentally, in all these methods, perfect diamond-cubic nanocrystals were also found along with ndiamond nanocrystals.…”

“…Electron energy loss spectroscopy (EELS) was carried out on the n-diamond samples to confirm the absence of any chemical contamination [24]. In fact, EELS for ndiamond showed a characteristic edge offset distinguishing it from regular diamond, amorphous carbon, and graphite.…”

“…In addition, based on theoretical calculations, these phases were also shown to have properties different from bulk diamond. F or instance, hexagonal diamond has a higher bulk modulus compared to diamond [60] and hence could surpass diamond in hardness, and n-diamond could be metallic in character, compared to diamond which is electrically insulating [24]. However, the structure of carbon in the fcc crystalline form is not yet known.…”

“…Also, previous attempts to detect other elements in n-diamond samples by use of EELS have not been successful [24,148]. Since hydrogen is the key constituent of the gas phase used for synthesis of these crystals, and that it is the only atom, which cannot be readily detected by EELS, the possibility of H being present in the structure must be considered.…”