Growth mechanism of hydrogenated amorphous carbon films: Molecular dynamics simulations

The microstructure and growth mechanism of hydrogenated amorphous carbon films, deposited from different hydrocarbon sources and at various incident energies, are investigated by molecular dynamics (MD) simulations. At low energies, molecular adsorption dominates the process of the film growth, so the incident molecules tend to preserve their original molecular structures. As the incident energy rises, film density increases firstly and then becomes stabilized, while hydrogen content decreases because of molecular fragmentation and the increase in sputtering yield of hydrogen atoms. Hydrogen atoms play an important role in the growth of hydrogenated amorphous carbon films. The formation of sp³ structures at low energies, for example, mainly attributes to the hydrogen adsorption and the formation of C-H bonds; while at high energies the subplantation of carbon atoms and formation of C-C bonds are most responsible to the formation of sp³ structures. An increase of hydrogen content in source gas could lead to lower film density, higher hydrogen content in film and a general increase of sp³ fraction. The existence of dangling bonds in incident radicals facilitates easier adsorption than neutral molecules at low energies, resulting in higher deposition yield and sp³ fraction. This trend, however, diminishes at high energies when extensive molecular fragmentation occurs.