Diamond-like carbon is a promising material for MEMS and opto-electronic systems applications. There is a notion that the hybridised sp<sup>3</sup> (diamond-like) fraction controls the mechanical properties and the sp<sup>2</sup> 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 C<sub>1s</sub> 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 sp<sup>3</sup> constituent, whereas the configuration of the sp<sup>2</sup> fraction was different. The sp<sup>2</sup> fraction of both aromatic rings and olefinic chains in examined films. We found that Tauc gap E<sub>t</sub>, was controlled by the perturbation of the π tail states of the sp<sup>2</sup> fraction. The Tauc gap E<sub>t</sub>, was determined by N-IR and surface conduction band E<sub>oi</sub>, 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 sp<sup>3</sup> bonding but also are determined by the degree of the sp<sup>2</sup> bonding arrangement.