Diamond-like carbon is a promising material for MEMS and opto-electronic systems applications. There is a notion that the hybridised sp3 (diamond-like) fraction controls the mechanical properties and the sp2 fraction (graphite-like) determines the electro-optical properties. We investigated amorphous hydrogenated diamond-like carbon (a-C:H) films synthesised using an inductively coupled hydrocarbon plasma reactor under varying bias. The films were characterised using UV Raman, X-ray C1s photoelectron, N-IR spectroscopy, scanning probe microscopy (SPM) and nano-indentation measurements. We found that all examined samples displayed essentially the same amount of the sp3 constituent, whereas the configuration of the sp2 fraction was different. The sp2 fraction of both aromatic rings and olefinic chains in examined films. We found that Tauc gap Et, was controlled by the perturbation of the π tail states of the sp2 fraction. The Tauc gap Et, was determined by N-IR and surface conduction band Eoi, measured by SPM changed inversely with an increase of bias. Results obtained using nanoindentation measurements show that mechanical properties such as hardness and Young's modulus increased with an increase of bias for all films studied. These results indicate that mechanical properties of a-C:H films (hardness and Young's modulus) not only controlled by the amount of the sp3 bonding but also are determined by the degree of the sp2 bonding arrangement.