The Fabrication And Properties Of Tantalum Oxide And Tantalum Nitride Films

Interaction between the biomaterials and organism is keeping on a few atoms layer, and so the antithrombogenic properties of the biomaterials is affected by their surface properties, such as composition, microstructure, morphology, water contact angle, surface energy and surface conductibility, etc. The surface modification of the biomaterials is the main method to control the surface properties of the biomaterials and its biological properties.Tantalum, tantalum oxides and tantalum nitrides are biologic nontoxic. They were already applied in biomaterials, such as vascular stents and bone substitutes. In order to research the relationship between materials properties and antithrombogenic properties, tantalum oxide and tantalum nitride films with different surface properties were synthesized by different processing parameters.Tantalum oxide and tantalum nitride films with different composition, microstructure, physical and mechanical properties fabricated by unbalanced magnetron sputtering were investigated in this paper. The composition, microstructure and properties of the films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), four-point probe sheet resistance measurement, UV-visible spectrophotometer and platelet adhension test, etc. The effect of the gas inlet ratio between reactive gas (O₂ or N₂) and working gas (Ar) on film microstructure and properties was studied.The Ta-O films deposited by unbalanced DC magnetron sputtering were amorphous. Oxide content of the films was increased and the sub-stoichiometric, stoichiometric and supersaturative Ta₂O₅ were in turn fabricated with the increasing O₂:Ar flow ratio. This is the reason that the electricial properties of Ta-O films change from conductor to semi-conductor and then to insulator. Optical band-gap ofthe semi-conductive and insulative Ta-0 films was in the range of 3.6eV to 4.0eV. The surface energy of the Ta-0 films was in the range of 40mJ/m2 to 45mJ/m2 which is close to the surface energy of low tempreture isotropic pryolytic carbon (LTIC). The hardness of Ta-0 films was increasing to maximum firstly and then decreasing with the increasing 02iAr flow ratio. The results of the platelet adhension test indicated that Ta-0 films with higher band-gap, lower surface energy and low ratio of dispersive energy and polar energy (yd /yp) had better blood compatibility, its blood compatibility was similar with LTIC.Increasing N2:Ar flow ratio, hexagonal y-T&2N, face-centered cubic (fee.) 8 -TaN* and body-centered tetragonal (bet.) TaN, was grown in turn in Ta-N films deposited by unbalanced DC magnetron sputtering at different N2:Ar flow ratio. The metastable single-phase fee. <5-TaNx(x is ¹) was formed while the wide N2:Ar flow ratio from 0.2 to 0.8. The &TaN* and bet. TaN* were coexisting in Ta-N films at N2:Ar flow ratio larger than 1. Resistivity of the Ta-N films was increasing with the increasing N2:Ar flow ratio because that the nitrogen content and the amount of the Ta vacancies were increased with the increasing N2:Ar flow ratio. Optical band-gap of the Ta-N films was low, and range from 0.6eV to 1.5eV. The surface energy of Ta-N films ranged from 40mJ/m2 to 45mJ/m2 which is close to the surface energy of LTIC. The blood compatibility of the Ta-N films, which blood compatibility is similar with LTIC, synthesized at lower N2:Ar inlet ratio were better than that deposited at the higher N2:Ar inlet ratio.