In our previous works, TiC based nanocomposites have been deposited between 25 °C and 800 °C. As it has been showed, the nanocomposite film deposited at 200 °C ex­hibited the best mechanical properties (nanohardness 18 GPa and elastic modulus 205 GPa) 53,54 The film consisted of TiC crystallites separated by thin carbon matrix (Fig. 2.16a) as showed by TEM investigations. The crystallites have columnar structure with average width around 10-15 nm (Fig. 2.4.2b). The mechanical properties of films, namely hardness and elastic modulus may be compare with mechanical proper­ties of bulk Ti implants (Table 2.6). In the case of TiC film, the 18GPahardness and 205 GPa elastic modulus value was measured53,54. TiC phase was the reinforcing phase to enhance the hardness of films. Highest H/E ratio ~ 0.094 and elastic recovery ~ 0.634 indicate that the deformation of the TiC nanocomposites arises mainly from elastic deformation of the C matrix which determines the elasticity of the asperities in a tribological contact.

Selected area electron diffraction (SAED) confirmed the stable cubic TiC phase (Fig. 2.17. JCPSFWIN 32-1383). According to Balden et al.,55 the optimal content from the structure (crystallites separated by thin carbon matrix) of the doped C films is one with a low metal concentration within 1-20 at.%. EDS elemental analysis of the film composition resulted in ~62-72 at.% C and 23-26 at.% Ti composition of the films (Table 2.7).

FIGURE 2.17 SAED of TiC/A:C thin film.

The film prepared at argon-contained ~30 at% Ti and ~70 at% C according to the EDS. The Auger Electron Spectroscopy (AES) depth profiling was applied to deter­mine the in-depth compositions. This surface sensitive analysis obviously gave the concentration values in the surface close region as well, which might play a role in the interaction with the biological substances. To minimize the ion bombardment induced roughening Ar+ ions of 1 keV with angle of incidence (with respect to the surface normal) of 78° were applied, and the sample was rotated during sputtering. The mor­phology of films was studied by atomic force microscopy (AFM AIST-NT, Smart SPM 1010), in semicontact mode. AES analysis gave somewhat higher C and lower Ti concentrations, which can be accepted considering the difficulties of the C analysis56. The concentration of oxygen according to the EDS was below than the detectability limit, while AES detected oxygen in all of the 300 nm thickness of TiC film as shown in Fig. 2.18. The oxygen concentration was constant, around 2%, inside the layer, while it strongly increased at the outer surface as well as at the TiC/SiO2 interface.

The carbon concentration followed similar trend; it was constant inside the layer, while it changed at the outer and inside interface. The carbon concentration, however, decreased at the surface (Fig. 2.18b). Thus the surface of the film consists Fig. 2.18b. AES spectra of carbon in TiC film of amorphous carbon, titanium carbide and tita­nium oxide.