Hydrogenated amorphous diamond-like carbon coatings have been deposited on glass and silicon substrates using an r.f. plasma-assisted chemical vapour deposition process. The mechanical properties of these coatings such as stress (bending beam measurements), hardness and Young's modulus (nanoindentation measurements) were studied as a function of the r.f. bias voltage in the range 50-500 V. IR absorption spectroscopy and elastic recoil detection analysis were used to correlate these mechanical properties with the total hydrogen content and the hydrogen bonding configuration. Compressive stress. hardness and Young's modulus are shown to reach their maximum values simultaneously at a bias voltage of about 200 V. At the same time, the hydrogen-bonded sp3:sp2 ratio reaches a local minimum.