Synthesis and characterization of carbon-silicon-titanium-aluminum nanostructures doped with nitrogen

The purpose of this work was to create varied types of nanostructured thin films using four materials of interest: graphite, titanium, silicon, and aluminum, with the inclusion of nitrogen, on the Si substrate, by Thermionic Vacuum Arc (TVA) technology. In this respect they were used three separate anode-cathode plasma sources, where the anode was made of the coating material and the cathode was a thermoemissive tungsten wire. The N2 flux was maintained at a constant 10 sccm during the deposition process. Into another series of synthesis, the N₂ flux was varied between 5,10, 15 sccm during the deposition process. The final thickness of C/Ti/C/Al/C/Si multilayer and C+Ti/C+Al/C+Si composite thin films thus obtained was 300 nm. Also, for each type of samples were varied substrates temperature (room temperature, 200°C, 300°C, 400°C) and bias voltage applied on substrates (-400V). TDS analysis reveal that nitrogen desorption seems to keep the same shape for each sample, despite the deposition conditions used. SEM, STEM, HRTEM, XPS and EDX characterizations of C/Ti/C/Al/C/Si multilayer thin films and C+Ti/C+Al/C+Si composite thin films were performed. EDX measured spectra in the case of C/Ti/C/Al/C/Si/+N samples and C+Ti/C+Al/C+Si/+N reveal, in all cases, the presence of nitrogen. XPS spectra reveal the peaks of the three materials Si, Al and Ti are well defined. The O concentration is much lower, due to the high working temperature. Elemental composition at different deposition substrate temperatures reveal that Atomic % of O, Al, Si, and Ti register significant changes depending on the deposition temperature. The Raman spectra shows that the nitrogen treatment of the films leads to the formation of nitrides for each compound, i.e. aluminum, carbon and silicon nitrides. Thermal treatment of the substrates leads to an increase in the concentration of nitrides in the films. However, in general they do not have a well-defined crystallographic structure, being more quickly an agglomeration of particles. The infrared absorption spectra are dominated by the formation of C-N bonds exactly as in Raman spectra, whose concentration increases with the increase of the substrate temperature. They are predominant in layer type samples where nitriding is performed on the carbon layer. Al-N and Si-N vibrations are also observed. In the case of aluminum nitride, heating the substrate leads to a slight increase in the concentration of AlN. More prominent is the increase in the concentration of Si-N in the substrate heated to 400°C. Based on nanoindentation measurements, Young modulus and Hardness were measured. The data obtained reveal that the values of the Hardness in the case of N-doped thin films are generally bigger compared with the values in the case of undoped samples (especially in the case of composite samples). The tribology data shows that the values of the friction coefficient in the case of N-doped thin films are generally smaller compared with the values in the case of undoped samples (especially in the case of composite samples), in relation with the growth of Hardness. We suppose the measured values of friction coefficient are associated with the occurrence of atomic diffusion process at interfaces.