Niobium layers on graphite: Growth parameters and thermal annealing effects

Thin films of niobium (∼8 μm thick) were deposited on an ATJ graphite substrate by radio-frequency magnetron sputtering at low temperatures (420±50 K) under argon pressure of 0.67 Pa. After deposition, the layers were thermally annealed in a vacuum of 6.67×10−4 Pa at temperatures of 1073–2073 K for 10 to 480 min. Nb2C and NbC phases were identified by X-ray diffraction after the thermal annealing, scanning electron microscopy and wavelength dispersive analyses. The carbide layer thicknesses were measured and the growth rate constants were determined at different temperatures. It was found that the activation energies are 190 kJ/mol for Nb2C, 164 kJ/mol for NbC, and 169.4 kJ/mol for the combined carbide layers. This study also presents the specific features of phase formation, adhesion and microhardness of the carbide layers.