As a function of increasing self-bias voltage across the plasma, the following changes are observed in the grown amorphous hydrogenated carbon thin films: the photoluminescence intensity decreases while the peak position shifts only silightly to lower energy; the optical bandgap decreases; the hydrogen concentration decreases; and the carbon dangling bond electron spin resonance signal increases. We explain all these trends in terms of increased number of electron collisions in the plasma that break more carbon-hydrogen bonds in precursor ions and molecules, leading to larger clusters of graphite-like cores coated with hydrogen in the grown films.