CVD-grown ultralong graphene nanoribbons for high-performance electronics

Graphene nanoribbons (GNRs) with widths of a few nanometers are promising candidates for future nano-electronic applications due to their structurally tunable bandgaps, ultrahigh carrier mobilities, and exceptional stability. However, the direct growth of micrometer-long GNRs on insulating substrates, which is essential for the fabrication of nano-electronic devices, remains an immense challenge. Here, we report the growth of GNRs on an insulating hexagonal boron nitride (hBN) substrate through nanoparticle-catalyzed chemical vapor deposition (CVD). The as-grown GNRs exhibit highly desirable features being ultra-long (micrometers), ultra-narrow (a few nm), and atomically smooth edges. Remarkably, the as-grown GNRs are crystallographically aligned with the hBN substrate, forming one-dimensional (1D) moiré superlattices. The ultranarrow nature and bandgaps are revealed by high-resolution microscopic techniques and spectroscopy. Fully atomistic computational simulations support the experimental results and reveal a competition between the formation of GNRs and carbon nanotubes (CNTs) during the nucleation stage, and van der Waals sliding of the GNRs throughout the growth stage. Using the grown structures, we demonstrate the transfer-free fabrication of GNR field-effect devices that exhibit excellent performance at room temperature. Our study provides a scalable, single-step method for growing micrometer-long narrow GNRs on insulating substrates, thus opening a route to explore the performance of high-quality GNR devices and the fundamental physics of 1D moiré superlattices.