Fig. 1: On-chip integrated Cherenkov radiation emitter in the THz frequency region.
a Schematic diagram of the THz radiation chip. An HMM (alternating graphene/hBN 4-6 layer structure with a thickness of 100–200 nm and an area of 30 × 30 μm) is adopted to generate broadband THz CR when excited by a free-electron beam. The field-emission Mo cathode and anode, with a thickness of ~350 nm and a distance of 50 μm, serve as the planar free-electron emitter and collector. A metallic grating with a period of p = 2–6 μm is applied to extract the CR in the HMM into free space along the −x-direction, with a frequency related to the electron energy and grating period. b 3D sketch of the wavevector matching of the evanescent field surrounding the free-electron beam (black line, ω = u0·|kz|) to the CR mode in the HMM (blue arrow) and then to the free space wave. The red and blue surfaces represent the dispersion surface (kx-kz-ω) of the modes in the HMM and the isofrequency plane (namely, ω = ω0), respectively. c Optical microscope image of the radiation chip with cathode-anode and a four-layer graphene/hBN HMM transferred onto a gold grating.
