Dependence of Structure and Haemocompatibility of Amorphous Carbon Films on Substrate Bias Voltage

Tetrahedral amorphous hydrogenated carbon (ta-C:H) films on Si(100) substrates were prepared by using a magnetic-field-filter plasma stream deposition system. Samples with different ratios of sp³-bond to sp²-bond were obtained by changing the bias voltage applied to the substrates. The ellipsometric spectra of various carbon films in the photon energy range of 1.9--5.4eV were measured. The refractive index n and the relative sp³ C ratio of these films were obtained by simulating their ellipsometric spectra using the Forouhi--Bloomer model and by using the Bruggeman effective medium approximation, respectively. The haemocompatibility of these ta-C:H films was analysed by observation of platelet adhesion and measurement of kinetic clotting time. The results show that the sp³ C fraction is dependent on the substrate bias voltage, and the haemocompatibility is dependent on the ratio of sp³-bond to sp²-bond. A good haemocompatibility material of ta-C:H films with a suitable sp³ C fraction can be prepared by changing the substrate bias voltage.