Etching and narrowing of graphene from the edges

Large-scale graphene electronics requires lithographic patterning of narrow graphene nanoribbons for device integration. However, conventional lithography can only reliably pattern ~20-nm-wide GNR arrays limited by lithography resolution, while sub-5-nm GNRs are desirable for high on/off ratio field-effect transistors at room temperature. Here, we devised a gas phase chemical approach to etch graphene from the edges without damaging its basal plane. The reaction involved high temperature oxidation of graphene in a slightly reducing environment in the presence of ammonia to afford controlled etch rate (≲1 nm min−1). We fabricated ~20–30-nm-wide graphene nanoribbon arrays lithographically, and used the gas phase etching chemistry to narrow the ribbons down to <10 nm. For the first time, a high on/off ratio up to ~104 was achieved at room temperature for field-effect transistors built with sub-5-nm-wide graphene nanoribbon semiconductors derived from lithographic patterning and narrowing. Our controlled etching method opens up a chemical way to control the size of various graphene nano-structures beyond the capability of top-down lithography. Usable electronic devices exploiting the attractive properties of graphene will require narrow ‘nanoribbons’ of the atom-thin carbon sheets. Ribbons narrower than 5 nm are desirable for effective devices, but conventional lithography is limited to 20 nm. Now, a gas-phase chemical approach for etching graphene from the edges has produced graphene nanoribbons below 5 nm.