The effect of hydrogen on the electronic and bonding properties of amorphouscarbon

Abstract

A series of amorphous carbon and hydrogen-containing amorphous carbon structures hasbeen generated, by using classical Monte Carlo and molecular dynamics simulationtechniques, respectively. The Brenner empirical bond order potential is used to generatehydrogenated amorphous carbon while that by Tersoff is used for amorphous carbon. Theresulting structures are relaxed further using the density functional theory approach.Structures containing 15 at.% hydrogen are generated for various mass densitiesin order to investigate the effect of pressure changes on the properties of thehydrogenated amorphous carbon. The structures are analysed in terms of theirsp3/sp2 ratio. The density of states (DOS), energy-loss near-edge structure (ELNES)and x-ray photoelectron spectroscopy (XPS) calculations are performedwithin the first-principles methodology on the generated carbon systems. TheELNES and the C 1s energy calculations are performed taking into accountthe core–hole effect. Our calculations show that depending on the densityρ,hydrogenated amorphous carbon can be classified into three categories: polymeric at low densities(ρ≤2.0 g cm−3), graphitic at intermediatedensities (2.0 g cm−3<ρ≤2.4 g cm−3) and diamond-likeat high densities (ρ>2.4 g cm−3).