An energetic particle collision analysis of the effect of Ar~+ ion bombardment on tetrahedral carbon hybridization (sp~3) in amorphous carbon (a-C) thin films is presented for nonmagnetron radio-frequency sputtering. The analysis is based on sequential surface events involving the collision of Ar~+ ions with carbon atoms on the surface of the growing film and subsequent collision cascades between excited carbon atoms and other surface carbon atoms, which promote the formation of sp~3 carbon bonding. The model is validated by transmission electron and electron energy loss spectroscopy results that confirm the existence of a two-layer film structure consisting of an ultrathin interface layer and a continuous a-C film. Analytical results for the sp~3 carbon content are shown to be in good agreement with similar experimental results obtained from the analysis of the C1s core level spectra of the sputtered a-C films.
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