Density and microstructure of a-C thin films

Abstract In this work, we studied amorphous carbon ( a -C) thin films deposited using direct current (dc) and high power-impulse magnetron sputtering (HiPIMS) techniques. The microstructure and electronic properties reveal subtle differences in a -C thin films deposited by two techniques. While films deposited with dcMS have a smooth texture typically found in a -C thin films, those deposited with HiPIMS consist of dense hillocks surrounded by a porous microstructure. The density of a -C thin films is a decisive parameter to judge their quality. Often, x-ray reflectivity (XRR) has been used to measure the density of carbon thin films. From the present work, we find that the determination of density of carbon thin films, especially those with a thickness of few tens of nm, may not be accurate with XRR due to a poor scattering contrast between the film and substrate. By utilizing neutron reflectivity in time of flight mode, it has been shown that the density of carbon films can be measured more accurately. Prime novelty statement In this work, we have studied amorphous carbon ( a -C) thin films prepared by direct current and high power impulse magnetron sputtering (dcMS and HiPIMS). We did precise density measurements using time of flight (ToF) neutron reflectivity (NR), a technique seldom used to study carbon thin films. We amply demonstrate limitation of x-ray reflectivity technique generally used for determination of density of thin carbon films. It is expected that our demonstration of NR in density determination of carbon thin film will turn out to be landmark for carbon film community and will certainly be helpful in enriching the related research work.