Fluence and thermal threshold for an effective self-healing in high-energy-neutron-irradiated Al2O3/QFS-graphene/6H-SiC(0001) system

This article reveals a unique self-healing ability of the amorphous-aluminum-oxide-passivated p-type hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene on semi-insulating vanadium-compensated nominally on-axis 6H-SiC(0001) system, exposed for 166 h to a destructive flux of 3.3 × 10 11 cm −2 s −1 of mostly fast-neutrons (1–2 MeV), resulting in an accumulated fluence of 2.0 × 10 17 cm −2 . Post-irradiation room-temperature Hall effect characterization proves that the a -Al 2 O 3 /QFS-graphene/6H-SiC(0001) is n-type, which implies the loss of the quasi-free-standing character of graphene and likely damage to the SiC(0001)-saturating hydrogen layer. Micro-Raman spectroscopy suggests an average defect density in graphene of n D = 3.1 × 10 10 cm −2 with an L D = 32-nm inter-defect distance. Yet, a thermal treatment up to 623 K eliminates defect-related Raman peaks and restores the original p-type conductance. At the same time, 623 K is not enough to recover the initial transport properties in a sample irradiated for 245 h with a total fluence of 2.0 × 10 18 cm −2 . A Density Functional Theory model explains the self-healing phenomenon and restoration of the quasi-free-standing properties through thermally-activated lateral diffusion of the remaining population of hydrogen atoms and re-decoupling of the graphene sheet from the SiC(0001) surface. The thermal regime of 623 K fits perfectly into the operational limits of the a -Al 2 O 3 /QFS-graphene/6H-SiC(0001) system, defined as 300 K to 770 K. The finding constitutes a milestone for two-dimensional, graphene-based diagnostic and control systems designed for operation in extreme environments. • Neutron fluences shift the initial p-type conductance of the graphene to an n-type. • The full self-healing of the neutron-damaged a-Al2O3/QFS-GR@SiC is possible. • Post-irradiation annealing up to 623 K triggers the effective self-healing effect. • There is a neutron fluence threshold for the occurrence of the self-healing effect.