Quantum Confinement and Fullerenelike Surface Reconstructions in Nanodiamonds

Abstract

We present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addition, our calculations show that the surface of nanodiamond particles larger than approximately 1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features observed in measured absorption spectra.

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

“…This issue may be explained in terms of high energy surface atoms rearrangement and the lack of volume constraint effects on the film's surface. It was previously found that at 927°C ͑1200 K͒ nanocrystalline diamond prepared by a detonation method transforms into bucky diamond, 14 and raising the annealing temperature to 1227°C ͑1500 K͒, led to a cluster with graphitic shells and a diamond core. A high resolution transmission electron microscopy study has shown that graphitization starts from the surface of individual ND crystallites.…”

“…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.…”

Carbon-based nanostructured composite films: Elastic, mechanical and optoelectronic properties derived from computer simulations

“…Using both the MC and TBMD, one is able to combine higher statistical precision with higher accuracy and bridge the gap between classical and first-principles calculations. Both the Tersoff potential, as well as the two hamiltonians have been used to successfully model the interatomic interactions in various crystalline and amorphous carbon forms [19,20,21,22,23] The TBMD simulations are carried out in the canonical (N, V, T ) ensemble. The volume V and the number of particles (atoms) N are constant.…”

Structural Stability of Clean, Passivated, and Partially Dehydrogenated Cuboid and Octahedral Nanodiamonds Up to 2 Nanometers in Size

“…However, for a sufficiently small carbon cluster, nanodiamond can be more stable than nanographite because of the small molar volume of diamond compared to that of graphite. 19 As particle size falls deeper into the nanoscale, graphite and diamond phases can sometimes co-exist with, or even be co-opted by, other forms of pure carbon, particularly (A) onion-like carbon or OLC (multi-shelled nested fullerenes) 20 and (B) "bucky-diamond" (a diamond core up to a few nanometers wide surrounded by a partially or completely delaminated fullerenic outer shell), 21 an intermediary between nanodiamond and OLC. There appear to be three distinct thermodynamic regimes for pure carbon nanoparticles as a function of size: 19 22 (1) The size range above 5-10 nm is most likely the graphitic regime wherein the graphite phase is thermodynamically preferred and the nanodiamond phase is metastable relative to graphite, but where nanodiamond, once formed (e.g., from sp 3 -bonded amorphous carbon clusters), 23 will not readily transform into graphite at moderate or low temperatures in any practical time period.…”