Evaluation of diffusion parameters and phase formation between tungsten films and glassy carbon

Abstract

Thin films of tungsten (W) were deposited on glassy carbon (C) substrates using a magnetron sputtering system. The as-deposited samples were annealed isothermally under vacuum at temperatures ranging from 673 to 1273 K. The structural changes due to thermal annealing were monitored by Rutherford backscattering spectrometry (RBS) and grazing incidence X-ray diffraction (GIXRD). RUMP software was used to simulate the RBS spectra. The thickness of W thin films deposited, atomic composition of deposited layer and the intermixed layer growth were deduced from the RUMP simulation results. The GIXRD analysis showed that carbide formation was first observed at annealing temperature of 1173 K. The kinetics of the solid-state interaction was found to be diffusion controlled at the interface between W and C. The activation energy for the diffusion of C in W was estimated as 2.23 eV. The XRD results showed that the average crystallite size of the as-deposited W film was 9.77 nm. It increased with annealing temperature up to 18.05 nm at 1173 K. The first carbide phase observed was W2C in the sample annealed at 1173 K, while WC was the dominant carbide phase at 1273 K. The stability of W/C system under heat treatments below 1073 K suggests that this system has a promising application for long-term structural integrity of dry cask storage devices.