Ion-enhanced adhesion of Ni films on glassy carbon: III. Si intermediate layer and 84Kr + implantation

Abstract

The adhesion of 30 nm Ni films on glassy carbon (GC) was examined as a function of 84Kr + implantation through a 7 nm Si intermediate layer. The Ni/Si/GC specimens were held at 100°C and implanted with 170 keV 84Kr + at doses of 5 × 10 15, 1 times; 10 16 and 5 times; 10 16 Kr/cm 2. The implantation had only a small influence on the surface topography, but had a tremendous influence on the depth distribution of the elements. Auger electron spectroscopy (AES) depth profiling showed that the as-deposited Ni/Si/GC specimens consisted of a rather sharp Ni/GC interface with the Si dispersed into both the Ni and GC. 84Kr + implantation caused the Si intermediate layer to be mixed extensively into both the Ni film and the GC substrate. Ni from the film was mixed into the substrate to approximately the same depth that the Si was intermixed. The C from the substrate was mixed into the Ni layer, and segregated at the surface. In this way, the interface between the Ni and the GC was graded (up to 2.5 times its original width) by the implantation. X-ray photoelectron spectroscopy (XPS) revealed that the Si in the as-deposited specimens was composed primarily of Ni-Si bonding in the Ni-rich region of the interface, Si-O bonding in the middle of the interface, and Si-C bonding in the C-rich region of the interface. After 84Kr + implantation, the types of Si chemical bonding were very similar (Ni-Si, Si-C, and Si-O), but they were no longer segregated to the interfaces. Instead, the types of chemical bonding were more extensively intermixed. The interfacial chemistry of the implanted specimens showed a gentle gradient from Ni-Si-rich regions near the Ni film to Si-C-rich regions near the GC substrate. The XPS results showed no indication of any Ni-C bonding in the interfacial region. The adhesion of the Ni/Si/GC specimens was examined using a scratch test in conjunction with SEM and AES analysis. The as-deposited films were removed at forces less than 1 N. In contrast, after the 5 times; 10 15 and 1 times; 10 16 Kr/cm 2 implants the critical force for film removal was increased to approximately 23 N. When the implant dose was increased to 5 times; 10 16 Kr/cm 2, the films could only be removed at forces (approximately 45 N) sufficient for catastrophic substrate failure. This adhesion increase was primarily attributed to the graded interfacial bonding produced by the ion implantation.