Graphene destruction by metal-carbide formation: An approach for patterning of metal-supported graphene

Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single layer graphene with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. We also developed graphene film transfer processes to arbitrary substrates, and dual-gated field-effect transistors fabricated on Si/SiO2 substrates showed electron mobilities as high as 4050 cm2V-1s-1 at room temperature.

We investigate electronic transport in lithographically patterned graphene ribbon structures where the lateral confinement of charge carriers creates an energy gap near the charge neutrality point. Individual graphene layers are contacted with metal electrodes and patterned into ribbons of varying widths and different crystallographic orientations. The temperature dependent conductance measurements show larger energy gaps opening for narrower ribbons. The sizes of these energy gaps are investigated by measuring the conductance in the non-linear response regime at low temperatures. We find that the energy gap scales inversely with the ribbon width, thus demonstrating the ability to engineer the band gap of graphene nanostructures by lithographic processes.

Graphene has significant potential for application in electronics1-5, but cannot be used for effective field-effect transistors operating at room temperature because it is a semimetal with a zero bandgap6,7. Processing graphene sheets into nanoribbons with widths of less than 10nm can open up a bandgap that is large enough for room temperature transistor operation8-19, but nanoribbon devices often have low driving currents or transconductances18,19. Moreover, practical devices and circuits will require the production of dense arrays of ordered nanoribbons, which is of significant challenge20,21. Here we report the production of a new graphene nanostructure - which we call graphene nanomesh - that can open up a band gap in a large sheet of graphene to create a semiconducting thin film. The nanomeshes are prepared with block copolymer lithography and can have variable periodicities and neck widths down to 5 nm. Graphene nanomesh field-effect transistors can support currents nearly 100 times greater than individual graphene nanoribbon devices, and the on-off ratio - which is comparable with the values achieved in individual nanoribbon devices - can be tuned by varying the neck width. The block copolymer lithography approach used to make the nanomesh devices is intrinsically scalable and could allow for the rational design and fabrication of graphene-based devices and circuits with standard semiconductor processing.