Study of inter-diffusion of gold in copper in the presence of single layer graphene

Abstract

• Graphene acts as a diffusion barrier for interdiffusion of Au in Cu upto 220°C. • From 240°C to 280°C, grain boundary diffusion is dominant in Au/Gr/Cu. • Slower ion beam mixing is observed in Au/Gr/Cu compared to Au/Cu sample. • Disorder is more in graphene upon annealing and amorphization upon irradiation. Rutherford backscattering spectrometry (RBS) has been used to examine the inter-diffusion behaviour in Au thin films (∼30 nm) deposited on CVD grown monolayer Graphene on copper (Au/Gr/Cu) with reference to gold film deposited on copper (Au/Cu), under thermal annealing and ion beam irradiation processes. Graphene is acting as a diffusion barrier in Au/Gr/Cu upto 220 °C for the inter-diffusion of Au in Cu in thermal annealing process, while interdiffusion occurs below 200 °C in Au/Cu. In high temperature regime, bulk diffusion mechanism is dominant in Au/Cu system whereas grain boundary diffusion is dominant in Au/Gr/Cu system. The dominant grain boundary diffusion in Au/Gr/Cu indicates that grain boundary defects in graphene play a major role in inter-diffusion process. Upon 9 MeV Si 6+ ion irradiation, there is no ion beam mixing upto 5 × 10 15 ions/cm 2 and at the ion fluence of 3 × 10 16 ions/cm 2 , ion beam mixing is observed in both Au/Cu and Au/Gr/Cu samples, with lower ion beam mixing rate and mixing efficiency for Au/Gr/Cu sample. This implies that graphene interlayer can prevent ion beam mixing to a certain extent due to its impermeable nature. The blue shift of Raman spectroscopy peaks G and 2D and the splitting of G-peak from graphene barrier layer signifies the compressive strain in Au deposited and thermally annealed Gr/Cu samples. Even though interlayer graphene can reduce the interdiffusion in Au/Cu system modestly, it becomes disordered with the formation of sp 3 carbon bonds with increase in annealing temperatures and ion fluences, thereby loosing its impermeable nature.