-3000 V dc bias Ti oxidation by inductively coupled plasma

Broadening the outer oxidized layer of titanium by means of plasmas commands considerable interest in the biomedical research area due to its potential in human biocompatibility enhancement. Some early results of titanium substrate superficial oxidation experiments which have been conducted in a cylindrical vessel inductively coupled to a 13.56 MHz RF generator with a 500 W output are presented. The oxidation process was carried out in a 20 % oxygen and 80 % argon mixture at work pressures in the 5×10^-3-1 mbar range, while the samples were dc biased down to -3000 V. The substrate temperature appears to be directly dependent on this voltage, reaching 685°C at the maximum bias when a diffusive oxidation process gives rise to the TiO₂ and α-TiO rutile phases. These were characterized by means of x-ray diffraction and scanning electron microscopy revealing atomic percentage concentrations of oxygen, with respect to those of titanium, between 68 and 13 at.%. The optimum modified layer depth reached 5 μm at a 5×10^-2 mbar work pressure.