Graphite macroparticle filtering efficiency of three different magnetic filter designs used in the filtered cathodic vacuum arc deposition of tetrahedral amorphous carbon films

The graphite macroparticle filtering efficiency of three different magnetic filter designs (straight duct, toroidal duct, and $90°$ free-standing solenoid) used in the filtered cathodic vacuum arc deposition of tetrahedral amorphous carbon (ta-C) films was investigated. The particle contents in the coatings were measured using scanning electron microscopy (SEM) technique. In addition, during the ta-C deposition, long time exposure photographs were taken to see the graphite macroparticle trajectories and thus to qualitatively evaluate the filtering performance of different magnetic filters. The particle density measurements from the SEM images show that the filtering efficiency of the $90°$ free-standing solenoid design is 13 times better than the filtering efficiency of the straight duct design. However, the toroidal duct design had only 3 times higher filtering efficiency compared to the straight duct design.