Ion-enhanced adhesion of Ni films on glassy carbon: I. 28Si + implantation

Abstract

The adhesion of 30 nm Ni films on glassy carbon (GC) was examined as a function of the interface modification produced by 28Si + implantation through the interface. The Ni/GC specimens were held at 100°C and implanted with 55 keV 28Si + at doses ranging from 1 × 10 16 to 5 × 10 17 Si/cm 2. The ion implantation had very little influence on the surface topography, but had a tremendous influence on the depth distribution of the elements. Auger electron spectroscopy (AES) depth profiling revealed that the as-deposited films formed rather sharp interfaces with the GC substrates. Following ion implantation, the Ni/GC interface was substantially graded. This interfacial grading increased with the ion dose. The implanted Si reached a maximum concentration (15 at% for the 1 × 10 17 Si/cm 2 implant) in the Ni layer and then extended deep into the GC substrate. X-ray photoelectron spectroscopy (XPS) analysis of the interfaces of the specimens implanted with high doses of 28Si + (> 5 × 10 16 Si/cm 2) showed that it was composed of a mixture of Ni-Si, Si-C, Si-O and C-O chemical bonding. The XPS results showed no evidence of chemical bonding between Ni and C at the Ni/GC interfaces. Adhesion testing, using a scratch tester in conjunction with SEM/AES analysis, showed a dramatic increase in adhesion for the 28Si + implanted specimens. The as-deposited specimens were readily removed at forces less than 1 N. In contrast, the films implanted with doses of 5 × 10 16 Si/cm 2 or greater could not be removed short of catastrophic substrate failure (at approximately 45 N). This adhesion increase was attributed to a combination of enhanced interfacial bonding, mechanical interlocking, and stress relief through interfacial grading.