Face-to-face transfer of wafer-scale graphene films

High-quality graphene is grown on copper and then transferred to the underlying substrate, typically silicon oxide or quartz, by simply etching away the copper; the graphene is held in place during etching by capillary bridges. Between the sheets with graphene The single-atom-thick layered form of carbon known as graphene has many properties that make it ideal for large-scale technological applications. But first it has to be made available in large quantities and at a realistic price. Until now it has proved impossible to produce a large-area, continuous graphene film that can subsequently be layered onto silicon wafers — highly desirable for electronic applications — without cracks, folds and ridges compromising the end-product. Now a Singapore-based team has developed a process for growing high-quality graphene on a bed of copper that can then be etched away by metal catalysis, depositing an intact graphene film onto a silicon wafer that was beneath the copper. Key to this 'face-to-face' transfer is pretreatment with a surfactant to promote formation of a smooth graphene film and the use of nascent gas bubbles to form capillary bridges so that graphene stays attached to the substrate while copper is removed. The resulting graphene has good electronic properties, and the face-to-face transfer technique should be well suited to the rapid production of graphene devices by batch processing. Graphene has attracted worldwide interest since its experimental discovery 1 , 2 , but the preparation of large-area, continuous graphene film on SiO 2 /Si wafers, free from growth-related morphological defects or transfer-induced cracks and folds, remains a formidable challenge 3 . Growth of graphene by chemical vapour deposition on Cu foils 4 , 5 , 6 , 7 has emerged as a powerful technique owing to its compatibility with industrial-scale roll-to-roll technology 6 . However, the polycrystalline nature and microscopic roughness of Cu foils means that such roll-to-roll transferred films are not devoid of cracks and folds 6 , 7 . High-fidelity transfer or direct growth of high-quality graphene films on arbitrary substrates is needed to enable wide-ranging applications in photonics or electronics, which include devices such as optoelectronic modulators, transistors, on-chip biosensors and tunnelling barriers 3 , 8 , 9 . The direct growth of graphene film on an insulating substrate, such as a SiO 2 /Si wafer, would be useful for this purpose, but current research efforts rem