Substrate surface temperature as a decisive parameter for diamond-like carbon film adhesion to polyethylene substrates

摘要

Protective diamond-like carbon coatings (DLCs) deposited on polymer substrates represent a promising means for modification of the substrate surface. Application of strong DLCs on these substrates is rendered difficult due to a large difference in their thermal expansion coefficients, and also to the low heat resistance and thermal conductivity of most polymers. Vacuum pulsed sputtering of graphite is among the methods which show greatest promise for creation of DLCs on such substrates. In this method it is possible to adjust, within broad limits, the mean sputtering rate, and consequently control the thermal load on the substrate during sputtering. We measured the temperature distribution in bulky high-density polyethylene (PE) substrates depending on the pulse repetition rate and the number of pulses in the carbon source. The data were used to determine optimal conditions for deposition of DLCs on PE. DLCs almost 0.1 μm thick were deposited in two stages. In the first stage, when the best adhesion was provided, the source power was a maximum. In the second stage the source power was an order of magnitude lower. Adhesion of the DLCs to the substrates was evaluated using the standard adhesive tape test and by resistance to thermal cycling in the intervals from 77 to 287 K and 77 to 373 K. Adhesion of the DLCs to PE was shown to be strongly dependent on the substrate temperature at the start of sputtering. The best result was achieved when the substrate temperature was nearly equal to, but did not exceed, the PE melting point.