Seed-Mediated Growth of Unidirectional Armchair Graphene Nanoribbon Arrays on Germanium

Graphene nanoribbons with sub-10 nm widths and smooth armchair edges exhibit promising electrical and thermal properties and can have bandgaps sufficiently large for semiconductor electronics. However, development of nanoribbons has been hindered by difficulties in producing ribbons with a high degree of structural precision in a scalable manner. It was recently shown that CVD growth on Ge(001) can directly yield long, semiconducting graphene nanoribbons with smooth armchair edges. However, the mechanisms that give rise to the anisotropic crystal growth are not understood, and the nanoribbons stochastically nucleate at random locations and times, causing width and bandgap polydispersity. Here, we study the seed-mediated growth of graphene nanoribbons on Ge(001). We find that high aspect ratio ribbons evolve when the armchair direction of the seeds is parallel to Ge<110>, while the aspect ratio decreases as these two directions become misaligned. We show that seeding enables control over nanoribbon position, reduced polydispersity, and the fabrication of unidirectional, nanoribbon arrays. Provided that dense arrays of sub-10 nm can be fabricated, this seed-mediated growth promises to provide a route toward the scalable integration of nanoribbons into semiconductor electronics.