On-Chip Rolling Design for Controllable Strain Engineering and Enhanced Photon-Phonon Interaction in Graphene.

On-chip strain engineering is highly demanded in 2D materials as an effective route for tuning their extraordinary properties and integrating consistent functionalities toward various applications. Herein, rolling technique is proposed for strain engineering in monolayer graphene grown on a germanium substrate, where compressive or tensile strain could be acquired, depending on the designed layer stressors. Unusual compressive strains up to 0.30% are achieved in the rolled-up graphene tubular structures. The subsequent phonon hardening under compressive loading is observed through strain-induced Raman G band splitting, while distinct blueshifts of characteristic peaks (G(+), G(-), or 2D) can be well regulated on an asymmetric tubular structure with a strain variation. In addition, due to the strong confinement of the local electromagnetic field under 3D tubular geometry, the photon-phonon interaction is highly strengthened, and thus, the Raman scattering of graphene in rolled-up tubes is enhanced. Such an on-chip rolling approach leads to a superior strain tuning method in 2D materials and could improve their light-matter interaction in a tubular configuration, which may hold great capability in 2D materials integration for on-chip applications such as in mechanics, electronics, and photonics.