A low-cost and effective approach to large-quantity freestanding graphene sheets through selective solid-phase chemical reactions between Ni and poly-crystalline SiC powders at the temperature of 1000 °C was reported. High-resolution transmission electron microscopy (HRTEM) investigations indicated that single- and multi-layered graphene sheets in microns of size were obtained. The proposed mechanism for our approach shows that Ni silicides produced from the interface reactions might act as a blockade to slow down further diffusion and cystallization of precipitated carbon. The average yield of carbon reached up to 94 wt.%. Real-time measurement of the gas sensor shows graphene synthesized by taking this approach exhibited a sensible and repeatable response to hydrogen with low concentration.Highlights► Our results provide a low-cost and effective approach to large-quantity freestanding graphene sheets preparation through solid-phase chemical reactions. ► 1–3 layer graphene sheets of micron in size were prepared with an average yield up to 94 wt.%. ► Ni silicides produced from the interface reactions might act as a blockade to slow down further diffusion and cystallization of precipitated carbon. ► The synthesized graphene has sensible and repeatable response to hydrogen with low concentration.

The interfacial reactions between a Ta/Ni bilayered film and SiC single-crystal substrate during annealing at 650–1,100 °C were investigated. It was found that H-Ni2Si (hexagonal Ni2Si) and TaC formed at the interface as a result of thermal annealing. A small amount of free C atoms diffused outwards the surface, leading to the formation of carbon vacancies that could act as electron donors. The electrical properties of the contacts showed that ohmic behavior was observed for the sample annealed above 800 °C. The specific contact resistivity was determined to be as low as 4.4 × 10−4 Ω cm2 at 1,100 °C.