Seminars and thesis defenses
Graphene effect on mechanical response of copper film
By Farzaneh Bahrami (iMMC / IMAP)
This research has investigated the effect of the presence of single-layer graphene on the development of the contact plasticity inside a copper underlying substrate. As a matter of fact, a film of copper (deposited on a quartz wafer) is the substrate used in the CVD process for graphene production, there is no need for transferring graphene which avoids any possible artifacts. Moreover, the adhesion between CVD-grown graphene and the underlying Cu film is larger than transferred graphene, since transfer cause wrinkles and ripples form, thus weakening the interaction between graphene and the substrate. Nanoindentation was performed on the Cu-film with and without graphene. The analysis of the force-displacement curves indicates that the presence of graphene modifies the onset of plasticity, which appears in the form of a burst which is called pop-in. The first pop-in occurs at lower loads with smaller lengths for the system with graphene in comparison to the bare Cu-film. In order to understand the root causes of these effects of the presence of graphene on the plastic flow, transmission electron microscopy is used to compare samples after nanoindentation in terms of dislocation structures. 3D discrete dislocation dynamics simulations are performed to analyze the long-range back stress that is generated by the dislocation arrangements with and without graphene. To further extend this research and investigate the known effect of hardening by graphene insertion into metals, another system has been addressed which involves the deposition of a Cu film on top of the graphene layer, lying on top of the annealed Cu substrate. The presence of graphene caused marked effects on the indentation response in this case, even larger than in the first configuration.