Hydrogen Stabilization of {111} Nanodiamond
- PDF / 333,959 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 57 Downloads / 177 Views
I3.4.1
Hydrogen Stabilization of {111} Nanodiamond A.S. Barnard1, N.A. Marks2, S.P. Russo1 and I.K. Snook1 1 Department of Applied Physics, RMIT University, Melbourne, Victoria, 3001, Australia 2 Department of Applied Physics, School of Physics, University of Sydney, Sydney, New South Wales, 2006, Australia ABSTRACT Presented here are results of ab initio Density Functional Theory (DFT) structural relaxations performed on dehydrogenated and monohydrogenated nanocrystalline diamond structures of octahedral {111} and cuboctahedral morphologies, up to approximately 2nm in diameter. Our results in this size range show a transition of dehydrogenated nanodiamond clusters into carbon onion-like structures, with preferential exfoliation of the C(111) surfaces, in agreement with experimental observations. However, we have found that this transition may be prevented by hydrogenation of the surfaces. Bonding between atoms in the surface layers of the relaxed structures, and interlayer bonding has been investigated using Wannier functions. INTRODUCTION With the advent of nanotechnology related research in recent years, many studies have sought to understand the formation of the carbon clusters, and the dynamic phase changes and stability relationship between graphite and nanodiamond clusters. It has been observed experimentally [1-3], that upon annealing nanodiamond particles transform into onion-like carbon, from the surface inward (with the transformation temperature dependant on the size of the particle). Such observations reveal preferential graphitization and exfoliation of the diamond C(111) surfaces over other lower index surfaces, and the transformation of complete dehydrogenated nanodiamonds into onion carbon. This transition has also been modelled theoretically using semi-empirical [2,4-7] and ab initio methods [8,9]. Presented here are structural relaxations of hydrogenated nanodiamonds with octahedral and cuboctahedral morphologies. It is anticipated that saturation of the nanodiamonds surfaces with hydrogen will passivate the surfaces and stabilize the structures and preserve the diamond structure. AB INITIO METHOD The hydrogenated nanodiamonds have been relaxed using the Vienna Ab initio Simulation Package (VASP)[11,12]. We used ultra-soft, gradient corrected Vanderbilt type pseudopotentials [13] as supplied by Kresse and Hafner [14], and the valence orbitals are expanded in a plane-wave basis up to a kinetic energy cut-off of 290eV. The crystal relaxations were performed in the framework of DFT within the Generalized-Gradient Approximation (GGA), with the exchange-correlation functional of Perdew and Wang (PW91)[15]. A detailed description of this technique may be found in references [16,17]. We have successfully applied this technique to the relaxation of dehydrogenated [8-10], hydrogenated [18] and doped [10] nanodiamond structures in the past, with results showing excellent agreement with experiment and all-electron methods [19].
I3.4.2
Figure 1. The C35H36, C84H64 and C165H100 octahedral nanodiamond cryst
Data Loading...
