First-Principles Research On Bulk Doping And Surface Adsorption Of TiO₂

Hemocompatibility is a key property of biomaterials that comes in contact with blood, which is affected by their bulk and surface physical and chemical properties. It is very important for the development and application of biomaterials to improve their hemocompatibility. Titanium oxide films are widely studied for their excellent thromboresistance, and how to improve the blood compatibility of Ti-O films is becoming the focus of research. It has been previously proved that hydrogen doped and oxygen deficient titanium oxide films possesse significantly better hemocompatibility than the low temperature isotropic pryolytic carbon (LTIC). Computer simulation can provide more details of atoms geometry and electrons properties than normal experiment methods. Therefore, first principles method has been used in this paper to study the three kinds of defects in bulk rutile TiO2, which are H doped, O deficient and Ti doped. Then, we have calculated the atomic relaxations and electron properties of rutile TiO2 (110) full and oxygen vacancy surfaces, the molecular adsorptions on the surfaces have also been modeled. During the calculations, the defect formation energy, adsorbed configuration, adsorption energy, band structure and electron transfer have been investigated.The results of TiO2 bulk simulation show that, all of these three defects can move Fermi energy level to the bottom of conduction band and form n-type semiconductor structure, only Ti doped defect causes independent state in the band gap. Based the calculation result, we think the improved performance of hydrogen-introduced sputtering Ti-O films is probable related to the hydrogen contained in the films.The calculation results of surface properties are deeply influenced by the surface models chosen by the researcher, our model is considered to be reliable via comparing the calculation result of atomic relaxation with experiment data. Compared with stoichiometric surface, TiO2 (110) oxygen vacancy surface shows n-type semiconductor structure, its band gap increases to 1.99eV and conduction band transferres to-0.13eV. On this oxygen vacancy surface, the molecules of H2O,O2,NH3 will dissociative adsorbed at the site of oxygen vacancy, and the Ti atoms near the vacancy discharge electrons. Water adsorption does not change the n-type semiconductor structure, which is related to the-OH emerging on the surface. But, oxygen adsorption will close the O vacancy, lets valence band and conduction band move up, reduces the band gap to 1.3eV, and thus loses the n-type semiconductor feature. The surface band structure is unchanged after NH3 adsorption.Considered from the electrochemical hypothesis, the electron structures of bulk H doped, bulk O vacancy, O vacancy surface and after water adsorption are likely to prevent charge transfer from fibrinogen into the materials, inhibit the denaturation of fibrinogen, therefore improve the hemocompatibility of Ti-O films. But, the dissociative adsorption of oxygen may cause adverse effect on the anti-thrombotic properties of Ti-O films.