Catalyst-free growth of readily detachable nanographene on alumina

We have grown graphene directly on alumina (Al₂O₃) substrates without catalysts using conventional thermal chemical vapor deposition. By choosing Al₂O₃ as a growth substrate, the polycrystallinity of graphene was enhanced to form nanometer-size dome-like grains, which ensured a statistically homogeneous electrical property of graphene over a large area. As-grown bilayer, the nanographene (nGr) film showed a sheet resistance of ∼3 kΩ □^-1 with a standard deviation of ∼2.3% over 15 mm × 15 mm. Top- and bottom-gate nGr thin film transistors (TFTs) fabricated directly on the Al₂O₃ substrate exhibited field-effect mobilities of 89 and 41 cm² V ^-1 s^-1, respectively. Moreover, the grown nGr could be easily detached from the Al₂O₃ substrate due to weak adhesion between the nGr and Al₂O₃, which has abundant fixed charges. Dry-transfer of the grown nGr from the Al₂O ₃ substrate was realized via spin-coating a polyimide (PI) or poly(4-vinylphenol) film and subsequently detaching the film together with the nGr film. The recycled substrates provided the nGr films with reproducibility. The nGr devices on a 3 μm-thick PI film were stable upon bending with a bending diameter of down to 6 mm.