Structure and spectroscopic properties of C-Ni and CN x -Ni nanocomposite films

Magnetron-sputtered carbon-nickel and carbon-nitride-nickel thin films were investigated by high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy, electron-energy-loss spectroscopy (EELS), and scanning tunneling microscopyspectroscopy (STMSTS) to clarify the relationship between the structure and the spectroscopic properties. The films were deposited in argon or nitrogen plasma at temperatures from 25 to 800 °C. The microstructures can be described as a nanocomposite, built from Ni or Ni3 C nanocrystals in a carbonC Nx matrix. The nanocomposite shows columnar structure up to 200 °C deposition temperature, and above this temperature gradually changes to globular morphology. The CC Nx matrix also grows thicker as the deposition temperature increases. The matrix is amorphous at high nitrogen content and low deposition temperature and it is ordered into 3-5 layer thick graphitic shells around the Ni3 C or Ni crystallites at higher temperatures. The surface roughness of the nanocomposite ranges between 0.7 and 2.3 nm, increasing with increasing deposition temperature. EELS measurements confirm the expected chemical interaction between nickel and carbon. EELS suggests that the nitrogen is incorporated only into the matrix in C Nx -Ni samples, mainly with s p1 bonds for deposition temperature below 500 °C. STS investigations show that the conductivity increases with increasing deposition temperature. A conductivity gap of 1-2 V exists in the nanocomposite films. A structural model based on the HRTEM investigation is given that can describe the spectroscopic properties and their behavior with the deposition temperature.