INFLUENCES OF THE DEPOSITION RATE ON THE MICROSTRUCTURE AND HARDNESS OF COMPOSITE FILMS PREPARED BY REACTIVE ION-ASSISTED COEVAPORATION

The influence of the deposition rate on the microstructure and hardnes s of TiO2-SiO2 and TiO2-MgF2 composites and their single component fil ms prepared by reactive ion-assisted coevaporation in the deposition r ate range 0.14 to 2 nm/s are investigated using an x-ray diffractomete r, a transmission electron microscope, and a microhardness tester, It is found that the hardness of the composite films and their single com ponents increase with a decreasing deposition rate, However, the hardn esses of TiO2-SiO2 and TiO2-MgF2 composite films were generally lower than that of pure SiO2 and MgF2, respectively, at the same component d eposition rate. This indicates that the addition of TiO2 reduces the h ardness of SiO2 and MgF2 films. The ultrahigh hardness of pure MgF, fi lms deposited by ion assistance at the deposition rate of 0.14 nm/s pr obably results from the high packing density, low lattice defects, and the small grain size (<20 nm) with the preferred orientation of [110] . Furthermore, the homogeneous dispersion of these hard nanoscale MgF2 grains within the amorphous TiO2 matrix causes the hardening of the c omposite film.