Scratch testing for micro- and nanoscale evaluation of tribocharging in DLC films containing silver nanoparticles using AFM and KPFM techniques

Scratch testing is a fast and effective method for the measurement of critical loads in order to determine the adhesion properties of coatings and their behavior in tribological applications. Kelvin probe force microscopy (KPFM) provides a means of monitoring electrostatic charging on the surfaces of materials. In this paper, we describe the use of a combination of scratch testing and KPFM analysis to evaluate the electrostatic effect induced by silver nanoparticles incorporated as clusters in diamond-like carbon (DLC) films, as well as its correlation with the rubbing process. KPFM was used for mapping of the potentials on the surfaces of DLC-Ag films subjected to nanoscale scratching. The procedure was also conducted at the microscale in order to analyze the way in which silver nanoparticles were spread in the track. After scratching, the track was analyzed using backscattered electrons (BSE) and energy dispersive X-ray diffraction (EDX). The BSE images highlighted bright domains of metallic nanoparticles dispersed in the amorphous coating and EDX confirmed the presence of silver nanoparticles in the scratched track. Micro Raman spectroscopy was used to check the DLC signature. The electric potentials of DLC films with and without silver nanoparticles were also analyzed. The results indicated that the incorporation of silver nanoparticles in amorphous materials could offer new option for electrostatic energy storage on the surfaces of materials.