In the trenches

Nat. Commun. 8, 14703 (2017)

In spite of graphene's exciting electronic and thermal properties, it is unsuitable as a transistor for future digital devices, due to the absence of a bandgap between the conduction and valence bands. This makes it impossible to switch between on and off states with respect to electron flow. Scaling things down, graphene nanoribbons of less than 10 nm in width do exhibit electronic bandgaps and are therefore potential candidates for digital devices. Precise control over their dimensions, and hence electronic properties, however, represents a challenging goal, and the ribbons typically possess rough edges that are detrimental to their performance.

Now, Chen et al. report on a strategy to grow graphene nanoribbons with controlled widths and smooth edges directly onto dielectric hexagonal boron nitride (h-BN) substrates. The team use nickel nanoparticles to etch monolayer-deep, nanometre-wide trenches into h-BN, and subsequently fill them with graphene using chemical vapour deposition. Modifying the etching parameters allows the width of the trench to be tuned to less than 10 nm, and the resulting sub-10-nm ribbons display bandgaps of almost 0.5 eV. Integrating these nanoribbons into field-effect transistor devices reveals on–off ratios of greater than 10⁴ at room temperature, as well as high carrier mobilities of ∼750 cm² V⁻¹ s⁻¹. While gaining control over the length and specific placements of the ribbons will be the focus of future work, this method could offer a platform to access digital integrated circuitry based on ultra-narrow graphene nanoribbons.