טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentOren Ofer
SubjectComputational Study of Hydrogen in Nanodiamond
DepartmentDepartment of Physics
Supervisors Dr. Adler Joan
Full Professor Hoffman Alon


Abstract

In this study, we investigated the diffusion and effect of interstitial hydrogen (H) atom(s) in bulk diamond and in amorphous carbon and diamond composites. The locations, electronic energy levels and motion of hydrogen are investigated through a tight binding molecular dynamics.

In bulk diamond, H has been found to have a sixfold degenerate site known as an ET site. The H atom gives rise to new energy states in the middle of the diamond density of states (DOS) bandgap. This ET site has been found to be at two-thirds of the distance between the diamond hexagonal planes, resulting in a deformation of the diamond lattice. In samples with a surface bounded by a vacuum, the H has been found to have a tendency to migrate to the surface layer of the diamond, resulting in a deformation of the lattice, as seen experimentally. This configuration has new energy states above and below the Fermi energy in the bandgap of the diamond DOS.  These results can be correlated to SWNTs and MWNTs.

Molecular hydrogen, H2, was shown to have little effect on the diamond lattice due to its energetic and thermodynamic stability. However we note that the final configuration of H2 in the diamond bulk has characteristics familiar to orientational order in solid H2.

The amorphous carbon and diamond composite was simulated by the melting of pure diamond and subsequent quenching of the sample. Then, hydrogen atoms were implanted in the diamond core. As H concentration was increased, sp2 bonds were transformed to sp3 bonds in the vicinity of the diamond core, until saturation of H in the composite was reached. This increase stabilizes the diamond core and increases its size, resulting in the growth of the diamond regime.