Direct growth of globally aligned graphene nanoribbons on reconstructed sapphire substrate using PECVD

Graphene nanoribbons (GNRs) are regarded as an ideal candidate for beyond-silicon electronics. However, synthesis of aligned GNR arrays on insulating substrates with high efficiency is challenging. In this work, we develop a facile strategy, involving KOH pre-treatment and high-temperature annealing, to construct parallel steps on the two-fold symmetry a-plane sapphire substrate. Horizontal GNRs as narrow as 15.1 nm with global alignment across a region of 20 mm² are then grown on the step edge-enriched substrate through plasma enhanced chemical vapor deposition (PECVD) method. GNRs align well along the atomic steps on sapphire ([ $1\overline{1}00$] direction) with their widths and densities swiftly adjustable by step morphology modification on substrate surface. A step-edge confined growth mechanism is proposed, attributing the constraint on the nanoribbon broadening to a relatively low growth temperature in PECVD, which restrains the activation energy to suppress GNRs across step edges on sapphire and prevents detrimental nanoribbon widening. The results provide a new perspective for scalable synthesizing well aligned nanoribbons of other two-dimensional materials.