In a planar capacitively coupled RF reactor we deposited DLC films from the mixture of methane and argon. The self biased electrode was in a poor thermal contact with walls of the reactor, neither water cooled nor electrical heated by a special external circuit. The temperatures were continuously increasing even during the longest deposition time of 120 min and differed for the electrode and the silicons of different specific resistances correlated to their emissivities. Ellipsometric and reflectance measurements of films deposited on two different silicon substrates of different emissivities were carried out. Their deposition rate depended significantly on the silicon emissivities because of the different temperatures. The influence of the silicon substrate emissivity on the mechanical properties of DLC films were studied by means of Vickers microhardness tester.