Theoretical analysis of the graphitization of a nanodiamond

Abstract

We report on a theoretical analysis of the graphitization of a nanosize diamond (nanodiamond) in the metastable state. A nanodiamond annealed at a relatively lower temperature suffers morphological transition into a nanodiamond–graphite core–shell structure. Thermodynamic stability analysis of the nanodiamond showed that the phase diagram (relationship between the annealing temperature and radius) of the nanodiamond–graphite has three regimes: smaller nanodiamond, nanodiamond–graphite, and larger nanodiamond. These regimes of nanodiamond–graphite are due to an additional phase boundary from finding the maximum size of the nanodiamond which can be graphitized. In the theoretical analysis, the most probable and the maximum volume fractions of graphite in the nanodiamond were 0.76 and 0.84 respectively, which were independent of the annealing temperature and the initial radius of the nanodiamond. Therefore, the nanodiamond is not completely transformed into graphite by simple annealing at relatively lower process temperature and pressure. The highest graphitization probability decreased with increasing annealing temperature. Raman spectra for the F2g vibration mode of nanodiamond were also calculated, and we found that the variation in properties of the spectral line was strongly dependent on the graphitization temperature and the initial size of the nanodiamond.

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10–30 nm grain size prepared by chemical vapor deposition

“…2 Graphitization mechanism of diamond and the preferential energetic stability of nanodiamond crystallites over graphitic particles of the same size has been the subject of rigorous research in the past decades. [2][3][4][5][6][7][8][9][10][11] The size, surface termination, and intergranular phase and chemical composition of the diamond crystallites affect the physical and electronic film properties, including the dielectric constant, 12,13 electron and field emission 14,15 and tribological properties, 16 etc. Elevated temperatures were also found to improve the field emission, 17 thermionic emission, 18 and secondary electron emission properties.…”

The scattering and extinction properties of nanodiamonds

“…Iatı et al (2008) report triple‐layered grains with silicate, sp 2 and sp 3 carbonaceous material and Yastrebov & Smith (2009) report nanodiamonds enveloped in glassy carbon shells. Considering that the surface graphitization of nanodiamonds leads to a core–mantle‐like shell structure (Kwon & Park 2007; Li et al 2008), extinction efficiency calculations are reported for spherical nanodiamonds inside a graphite ellipsoidal mantle.…”

“…Partial graphitization of nanodiamonds due to heat (Le Guillou & Rouzaud 2007) or pressure conditions (Davydov et al 2007) is suggested on the basis of some experimental studies. Theoretical analysis by Kwon & Park (2007) show that the surface graphitization of nanodiamonds under a strong radiation field can lead to a core–mantle‐like shell structure with up to 80 per cent graphitization. Thus nanodiamonds are possible within ISM carbonaceous matter and would modify the optical properties of dust.…”

Self-assembly of InAs quantum dots on GaAs(001) by molecular beam epitaxy

“…At the critical size of about n 3rd cri (C) ∼ 300 carbon atoms (or a diameter of ∼ 1.3 nm), the carbon cluster becomes an octahedral nanodiamond [420]. At a critical linear size ranging from 1.5 nm to 5 nm, the C cluster should be a spherical diamond; above this range, the cluster spreads into a graphene sheet or becomes a three-dimensional graphite crystallite [421]. InAs is isoelectronic to Si and C, and an InAs cluster may exhibit the same behavior as the atomic clusters of these elements.…”