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Abstract Diamond-like carbon films/coatings (DLC) can be employed in a wide range of applications, but the film quality and performance are strongly dependent on the deposition conditions. In this paper, we attempted to clarify the structural and compositional alterations induced by substrate bias voltage (SBV) variation in DLC films by employing different spectroscopic analyses and to correlate them with the variations of two important film properties, hardness and adhesion energy. A series of DLC films fabricated by unbalanced magnetron sputtering with changing substrate bias voltage were investigated by Raman, FTIR and X-ray photoelectron spectroscopies. The results revealed the presence of sp2 and sp3 carbon chains and rings and various types of hydrocarbon in the tetrahedral amorphous carbon films due to incorporation of hydrogen and oxygen. The reduction in hydrogen content together with a generation of sp2 hydrocarbon rings in response to SBV increase were responsible for increases in Young's modulus and hardness, and, concurrently, for a decrease in film adhesion energy. Graphical abstract Unlabelled Image Highlights • Structure & composition of DLC films/Metal grown by UBM were explicitly analyzed. • Applying substrate bias altered DLC microstructures, decreasing sp3 carbon content. • Various types of hydrocarbon were produced by H-incorporation but changed by SBV. • Oxygen incorporation depended on SBV and modified DLC structures and performance. • Modification of hydrocarbon content and structure by SBV determined film adhesion. [ABSTRACT FROM AUTHOR]