Effects of defect density on ultrathin graphene-based metal diffusion barriers

Abstract

The authors investigated the effects of defect density on the performance of monolayer graphene as a barrier to metal diffusion. The defects were introduced to the graphene by controlled ultraviolet-ozone irradiation. The barrier performance of pristine graphene was found to be superior to that of defective graphene at temperatures up to 700 °C. Changes in surface morphology were more prevalent in the defective graphene-based films than in the pristine graphene-based film; the thermal stability of graphene films depends on their defect density. Defect density was found to be a determining factor in the barrier performance of graphene.

Passivation of Germanium by Graphene for Stable Graphene/Germanium Heterostructure Devices

“…These data may also indicate that minimizing the graphene defect density is important for reducing oxidation of Ge and that oxidation of Ge preferentially occurs at defects in graphene, similar to previous results for graphene on metal surfaces. − For example, the reduction in oxidation of Ge(001) and Ge(111) with increasing H 2 :CH 4 (Figure ) directly correlates with a decrease in the total defect density in graphene (Figures –). Moreover, at least for the growth conditions used here, these results indicate that atomic-scale defects contribute to oxidation of Ge to a much greater extent than the relatively sparse pinhole defects, as oxidation of Ge is reduced by increasing the H 2 :CH 4 ratio (Figure ) despite an increase in ρ pinhole (Figure ).…”

“…Figure indicates that passivation of Ge by graphene can be enhanced by growing graphene with a high H 2 :CH 4 ratio, and thus low growth rate, and that passivation is most effective on Ge(110). It has been shown that oxidation of metal surfaces preferentially occurs at defects in graphene − and critically depends on the graphene/substrate interaction strength . We therefore hypothesize that the oxidation behavior in Figure can be explained by the effect of H 2 :CH 4 and Ge surface orientation on the (1) density of pinhole defects in graphene, (2) density of atomic-scale defects in graphene, (3) graphene/Ge interaction strength, or (4) degradation of graphene after exposure to air.…”

“…Furthermore, the Ge surface orientation can affect the graphene/substrate interaction strength . Surface orientation and H 2 :CH 4 ratio can also affect the shape and size of graphene crystals that comprise the continuous film, factors that impact the density and structure of grain boundaries. ,− As passivation of metal substrates is strongly influenced by the graphene/substrate interaction and defects in graphene, − we hypothesize that the H 2 :CH 4 ratio and Ge surface orientation can be tuned to modify oxidation of the Ge surface.…”

“…Previous studies on passivation of metal surfaces coated with graphene have shown that to reduce oxidation, it is critical to achieve a strong graphene/substrate interaction and to minimize defects in the graphene film. While the pristine sp 2 graphene lattice is impermeable to species as small as He atoms, defects can be selectively permeable sites for oxidants to access the underlying substrate. − Consequently, oxidation of metal surfaces preferentially occurs at point defects, grain boundaries, and pinholes (i.e., relatively large voids that are at least several angstroms in diameter) in graphene. − Furthermore, strong coupling between graphene and the metal substrate is critical to reduce intercalation and lateral diffusion of oxidants at the graphene/substrate interface, preventing oxidation from spreading to regions under pristine graphene . For example, on metal surfaces that interact strongly with graphene, oxidation can be localized near defects in graphene, and thus, most of the surface can be passivated for several weeks even if graphene is relatively defective or discontinuous.…”

Quantifying Mn diffusion through transferred versus directly-grown graphene barriers

“…The use of nonnative substrates often requires post-synthesis graphene layer transfers, which can damage the graphene and create tears, wrinkles, and point defects. The impacts of this transfer process on effectiveness as a diffusion barrier have not been quantified, although the impacts of other intentional defects have been studied [9].…”