Differences in surface reactivity in two synthetic routes between HiPIMS and DC magnetron sputtered carbon

Abstract

Diamond-like carbon (DLC) is an amorphous form of carbon with a significant fraction of sp3 bonds. In general, it enjoys high hardness, chemical inertness, and optical transparency. It can be deposited by various chemical (CVD) and physical (PVD) vapor deposition methods, including sputtering, which is an industrially important PVD method. Here we investigate the reactivity of carbon deposited by conventional direct current magnetron sputtering (DCMS) and by the newer high power impulse magnetron sputtering (HiPIMS). Scanning electron microscopy (SEM) showed that HiPIMS produced more compact films. Both types of carbon films were very smooth by atomic force microscopy (AFM): for HiPIMS: 1.20 ± 0.55 nm and for DCMS: 1.55 ± 0.27 nm. X-ray photoelectron spectroscopy (XPS) revealed chemical differences between the two types of carbon surfaces. Two functionalization schemes were investigated. The first consisted of amidation of the surfaces by activation with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy sulfosuccinamide (sulfo-NHS) followed by reaction with a range of water-soluble and insoluble amines, and the second consisted of activation via halogenation with PCl5 or PBr5 followed by subsequent amination. The resulting surfaces were characterized by XPS and wetting. HiPIMS-deposited carbon showed higher levels of amidation. On the other hand, the DCMS surface showed greater functionalization in the halogenation/amination route. These results are consistent with the higher level of oxidized carbon initially found on the HiPIMS surface.