Synthesis And Property Investigation Of Si-NO Thin Films

Improving the blood compatibility of cardiovascular biomaterials is an essential problem in biomaterials field. Surface modification is regarded as a significant means to improve the blood compatibility of cardiovascular biomaterials. Currently, no one kind of inorganic materials could replace the application of low temperature isotropic pyrolytic carbon (LTIC) in clinic. Si-NO thin films, as a kind of novel biomaterials, have just attracted much attention of researchers. However, current research results show that Si-NO thin films have potential advantages in blood compatibility compared with LTIC.In this thesis, unbalanced magnetron sputtering technic was used to synthesize Si-NO thin films by adjusting N₂ flux and other parameters, such as the distance between target and substrates and the deposition pressure. Their chemical composition and structural information were determined using X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS) and Fourier transform infrared spectroscopy (FTIR), and the results were shown as follows.As N₂ flux was increased from 0 to 40sccm, the excessive N ions in the vacuum chamber caused Si target poisoning, leading to the reduction of film thickness and deposition rate. The reduction of the distance between target and substrates enhanced the N ions arrived to the substrates, which means more N ions were incorporated into the films.The chemical composition of obtained Si-NO thin films varied in the range of SiN_0.04O_0.45～SiN_0.7O_0.27 with the increment of N₂ flux. Obtained Si-NO films in this thesis could be described to random mixing model (RMM) and random bonding model (RBM). In RMM, the a-SiO₂ and a-Si₃N₄ components uniformly existed in the matrix of abundant Si⁰, and in RBM, the Si2p existed in the form of a-Si₃N₄ and SiN_vO_4-v (v=0,1,2,3,4) components. The amount of related components existing in the films depended on the varied deposition parameters.The optical bandgap of the Si-NO films increased from 1.41eV to 4.14eV. The increment was corresponding to the reduction of Si⁰ component in RMM films, and the increment of N and O atom concentration in RBM films.The hydrophilic property of RMM films decreased as the ratio of N to O atom concentration (N/O) increased. On the other hand, the hydrophilic property of RBM films increased as the ratio of N to O atom concentration (N/O) increased.The blood compatibility of Si-NO films-was-investigated by systematic in vitro tests. The correlativity of film synthesis parameters, chemical composition and structural information, film properties and blood compatibility was discussed in the thesis.The RMM Si-NO films with lower N/O ratio showed favorable blood compatibility. The RBM films with higher N/O ratio also showed favorable blood compatibility. The blood compatibility of these Si-NO films was better than LTIC. The improvement of blood compatibility was closely related to the favorablehydrophilic property, the increase of polar component, the ratio ofγ_s^p/γ_s^d and thealkaline component.The hydrophilic property was the most significant factor to influence the blood compatibility of Si-NO films. The film properties, especially the hydrophilic property, adjusted by the film composition, structural information and micro-structure, had great effect on blood compatibility.