The Controllable Phase Structure and Related Properties of NbN-NbB2 Nanocomposite Films at Different Bias Voltages

摘要

Nanocomposite NbN-NbB2 films were prepared on Si (100) substrates by using multi-target magnetron co-sputtering system with different bias voltages (Vb). The effects of the substrate bias voltage on the phase transition and hardness of the obtained films were investigated via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM) and nano-indentation measurement. The results revealed that the best crystallization appeared at -160 V, where are the face-centered cubic (fcc) NbN and hexagonal close-packed (hcp) NbN coexisted in the films and fcc-NbN with (111) preferred orientation was a major phase. The films became much denser and more compact with increasing substrate bias. Meanwhile, hardness and elastic modulus were correspondingly elevated, which can be attributed to the amorphous NbB2 embedded in the crystals of NbN and the amorphous NbB2 were surrounded by crystalline of NbN. The maximum hardness and elastic modulus of films with applied bias -160 V were 26.542 GPa and 291.154 GPa, respectively, and the films also showed the better thermal stability and oxidation resistance properties. The further increase of the substrate bias voltage led to a phase transition from (fcc) NbN (111) to (hcp) NbN (110). This work also demonstrated that the decreased crystallinity induced at higher bias voltage led to the decrease in the mechanical properties.