Computational Study of Interstitial Hydrogen Atoms in Nano-Diamond Grains Embedded in an Amorphous Carbon Shell

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 diffusion 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 increases with decreasing grain size,and suggest that hydrogen is bonded and trapped in nano-diamond grain boundaries and on internal grain surfaces.

Morphological Similarities between Single-Walled Nanotubes and Tubelike Structures of Polymers with Strong Adsorption Affinity to Nanowires

In their tubelike phase,nanowire-adsorbed polymers exhibit strong structural similarities to morphologies known from single-walled carbon(hexagonal)and boron(triangular)nanotubes.Since boron/boron nitride tubes require some disorder for stability the triangular polymer tubes provide a closer analog to the carbon tubes.By means of computer simulations of both two and three dimensional versions of a coarse-grained bead-spring model for the polymers,we investigate their structural properties and make a detailed comparison with structures of carbon nanotubes.