Realization of highly asymmetric hydrogenated graphene in the van der Waals confined space

The van der Waals (vdW) confined space provides a distinct environment from free space, enabling the production of two-dimensional Janus materials, like highly asymmetric hydrogenated graphene (AH-Gr). Here, we develop a vdW confined space assisted hydrogenation method to produce AH-Gr. The confined space between graphene and the substrate aggregates hydrogen radicals, making the bottom-side of graphene more prone to hydrogenation. The dense and homogeneous confined spaces between adjacent vdW crystals promote rapid and uniform distribution of carbon-hydrogen (C-H) bonds. The hydrogen-to-carbon atomic (H/C) ratios can be quantitatively controlled by adjusting the permeated proton dose. All AH-Gr, regardless of H/C ratios, remain vacancy-free. The spatial distributions of C-H bonds significantly influence the electrical and magnetic properties of AH-Gr. Asymmetric hydrogenation transforms graphene from a semi-metal to a semiconductor, suppresses the quantum Hall effect, and reduces the phase coherence length. This study provides new insights into the preparation and characteristics of hydrogenated graphene, broadening the applications of vdW confined space.