Summary: Computational study of interstitial hydrogen atoms
in nano-diamond grains embedded in an amorphous
Amihai Silverman1, Alon Hoffman2, and Joan Adler3,
1 Taub Computer Center, Technion-IIT, Haifa 32000, Israel.
2 Schulich Faculty of Chemistry, Technion-IIT, Haifa 32000, Israel.
3 Department of Physics, Technion-IIT, Haifa 32000, Israel.
Abstract. The properties of hydrogen atoms in a nano-diamond grain surrounded
by an amorphous carbon shell are studied with Tight Binding computer simulations.
Our samples model nano-diamond grains, of a few nanometers in size, that nucleate
within an amorphous carbon matrix, as observed in deposition from a hydrocarbon
rich plasma. The calculations show that the average hydrogen interstitial formation
energy in the amorphous region is lower than in the nano-diamond core, therefore
hydrogen interstitial sites in the in the amorphous region are more stable than in the
nano-diamond core. This formation energy difference is the driving force for the dif-
fusion of hydrogen atoms from nano-diamond grains into amorphous carbon regions.
An energy well was observed on the amorphous side of the nano-diamond amorphous
carbon interface: hydrogen atoms are expected to be trapped here. This scenario agrees
with experimental results which show that hydrogen retention of diamond films in-
creases with decreasing grain size, and suggest that hydrogen is bonded and trapped