ZrB2 Thin Films : Growth and Characterization
Abstract: Zirconium diboride, ZrB2, is a ceramic material with bulk properties such as high melting point (3245 °C), high hardness (23 GPa), and low resistivity (~8 μΩcm). Thin film growth of ZrB2 using physical vapor deposition has suffered from problems with films deviating from stoichiometry and with high levels of contaminants, especially high oxygen content. The homogeneity range of ZrB2 is very narrow, and consequently it is vital to achieve the correct stoichiometry to grow films with high crystalline order.This thesis describes a direct current magnetron sputtering process to grow stoichiometric ZrB2 thin films with a low degree of impurities. Growth of epitaxial ZrB2 films was achieved on 4H-SiC(0001), Si(111) and Al2O3(0001) substrates. The effect of deposition temperature and power applied on the sputtering target was investigated and showed that high power density (8.77 Wcm-2) and high temperature (900 °C) resulted in films with the best composition and the highest crystal quality. ZrB2 films on GaN(0001) templates exhibit an amorphous layer at the film-substrate interface and the resulting films are either polycrystalline or textured.Resistivity measurements showed that the ZrB2 thin films exhibit typical resistivity values of ~100-250 μΩcm and that the resistivity decreased with increasing deposition temperature.Nanoindentation was applied to assess the mechanical properties of the films. The epitaxial ZrB2 films exhibit high elastic recovery and a hardness of ~45-50 GPa, twice as high as the literature bulk value. In addition, evaluation of the mechanical properties was performed at high temperatures of up to 600 °C and showed that the epitaxial films retained a higher hardness, compared to textured ZrB2 films and bulk, also at these temperatures.
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