Study of carbon doped cobalt mononitride thin films

Abstract

In this work, we address the issue of N diffusion in cobalt mononitride (CoN) thin films. The diffusivity of N in CoN is the highest among 3d-transition metal nitrides, causing a gradient in N concentration across the depth. In order to reduce N-diffusion and to improve the thermal stability, we doped various amounts of C in CoN. The long-range ordering of samples was investigated using x-ray diffraction. Elemental depth profiles were investigated using secondary ion mass spectroscopy, exhibiting a gradient in the depth profile towards the surface of undoped CoN film and the gradient decreases with an increase in C-doping. The local structure of samples was studied using x-ray absorption near-edge spectroscopy at N and Co K-edges and extended x-ray absorption fine structure (EXAFS) at Co K-edge. Defects and vacancies due to N-diffusion can also be seen from the EXAFS spectra of the undoped sample which minimizes at some optimum amount of C-doping. The thermal stability also gets improved at this optimum amount of C-doping. The obtained results can be utilized in the energy sector in which CoN finds many applications such as a high capacity electrode for Li-ion batteries, non-aqueous supercapacitors, and solar cells.