Diamond like carbon (DLC) films have attracted increasing attention in a variety of industries due to their excellent mechanical and chemical properties. To meet the demands from the emerging industries, such as micro electro mechanical systems (MEMS), a considerable number of research studies have been conducted to advance the technology for thin DLC films fabrication. However, it has been reported that the properties of DLC films vary with thickness, which necessitate further understanding of the mechanism of initial film growth. To elucidate the mechanism of carbon film growth, the present study employs X-ray photoelectron spectroscopy (XPS) to characterize two types of amorphous carbon films fabricated by cathodic vacuum arc discharge and radio-frequency magnetron sputtering. The results indicated that wide range of energy distribution of carbon ions in the cathodic arc discharge caused a decline in the sp³ ratio with decreasing thicknesses. [DOI: 10.1380/ejssnt.2006.129]