Contact engineering for graphene nanoribbon devices

Graphene nanoribbons (GNRs), when synthesized with atomic precision by bottom-up chemical approaches, possess tunable electronic structure, and high theoretical mobility, conductivity, and heat dissipation capabilities, which makes them an excellent candidate for channel material in post-silicon transistors. Despite their immense potential, achieving highly transparent contacts for efficient charge transport-which requires proper contact selection and a deep understanding of the complex one-dimensional GNR channel-three-dimensional metal contact interface-remains a challenge. In this study, we investigated the impact of different electron-beam deposited contact metals-the commonly used palladium (Pd) and softer metal indium (In)-on the structural properties and field-effect transistor performance of semiconducting nine-atom wide armchair GNRs. The performance and integrity of the GNR channel material were studied by means of a comprehensive Raman spectroscopy analysis, scanning tunneling microscopy (STM) imaging, optical absorption calculations, and transport measurements. We found that, compared to Pd, In contacts facilitate favorable Ohmic-like transport because of the reduction of interface defects, while the edge structure quality of GNR channel plays a more dominant role in determining the overall device performance. Our study provides a blueprint for improving device performance through contact engineering and material quality enhancements in emerging GNR-based technology.