PORES IN HYDROGENATED AMORPHOUS-CARBON FILMS ON STAINLESS-STEEL

The aim of this work is to investigate the influence of surface precle aning procedures prior to deposition of hydrogenated amorphous carbon films onto stainless steel. In industrial coating processes the substr ates are first degreased and then Ar-ion sputter-cleaned in the deposi tion chamber just prior to film deposition. This sputter cleaning, whi ch removes the native surface oxide layer as well as unknown contamina tions, is carried out rather thoroughly to assure a good adhesion of t he hard carbon him. In these films holes or pores are found when inspe cted with the scanning electron microscope. We demonstrate that these are not pores in the coating but holes in the stainless steel substrat e at locations of manganese-sulphur inclusions. They are produced duri ng the sputter-cleaning procedure owing to a higher sputter yield of t he manganese-sulphur inclusions with respect to the stainless steel su bstrate. By carefully selecting the surface preparation procedures, th e depth of these holes may be reduced below the surface roughness and can then be neglected. We also show that the Ar-ion sputter etching in creases the surface roughness by less than 2% of the thickness of the removed layer and that the amorphous carbon film growth is extremely u niform, the increase in surface roughness being less than 1% of the fi lm thickness for 100 nm thick coatings.