Nanocomposite thin films of the niobium-carbon system. An in-depth study from 0 to ~100 at% carbon

Nb-C nanocomposite thin films with carbon content ranging from 0 to ~100 at.% were deposited at room temperature by non reactive magnetron sputtering from pure Nb and C targets without applying bias voltage or additional temperature to the substrates. XPS analysis showed the co-existence of NbC and free C-C phases with different proportions while complementary Raman analysis showed that the carbon changes from graphite like to amorphous like as the Nb content of the films increased. XRD analyses showed the evolution of the crystalline structure of the samples from amorphous/nanostructured to cubic NbC with a relatively high crystallinity. HRTEM images confirmed the nanocomposite structure with NbC nanocrystals of different sizes embedded in the carbon matrix. The nanohardness of the films showed a strong dependence on the amount of the carbon matrix, with a maximum hardness of 23 GPa for the film with ~8-10% percent of the free carbon. The same film showed a four-point probe electrical conductivity of 2.2x106 S/m at 22C. The fact that the substrates do not need to be heated to obtain relatively hard, elastic and electrically conductive nanocomposite structures opens the possibility for a wide range of applications for temperature sensitive flexible substrates such as polymers and plastics.