Atomistic simulations are used to study thin-film growth through the deposition of beams of adamantane molecules on hydrogen-terminated diamond (111) surfaces. A range of incident velocities from 13 to 17 km/s (corresponding to kinetic energies of 119-204 eV/molecule) are considered that fall in the hyperthermal energy region for particle deposition on surfaces. The forces on the atoms in the simulations are calculated using a many-body reactive empirical potential for hydrocarbons. During the deposition process the adamantane molecules react with one another and the surface to form hydrocarbon thin films that are primarily polymeric with the amount of adhesion depending strongly on incident energy. Despite the fact that the carbon atoms in the adamantane molecules are fully sp(3) hybridized, the films contain primarily sp(2) hybridized carbon with the percentage of sp(2) hybridization increasing as the incident velocity goes up. These results are compared with the predictions of simulations that examine the deposition of ethylene molecular and cluster beams.