Fig. 1. Schematic diagram of the fabrication process of suspended graphene/hexagonal boron nitride heterojunction devices. (a) Cleaning the silicon wafer; (b) Spin-coating AZ photoresist; (c) Photolithographic patterning of AZ photoresist; (d) Evaporation of Cr/Au metal electrodes; (e) Lift-off electrodes; (f) Graphene/hexagonal boron nitride heterojunctions are directly transferred to electrodes to prepare suspended structure devices

Fig. 2. [in Chinese]

Fig. 2. Characterization of mechanically exfoliated monolayer graphene and multilayer hexagonal boron nitride. (a) Optical microscope image of monolayer graphene, the red cross marks the focus position of Raman spectroscopy; (b) Raman spectrum of monolayer graphene, in which the G peak intensity is significantly lower than the 2D peak intensity, proving it is a monolayer graphene; (c) Optical microscope image of a multilayer hexagonal boron nitride, the white solid line marks the measurement position of atomic force microscope; (d) The thickness of multilayer hexagonal boron nitride is about 36 nm

Fig. 3. Microscopy characterizations of suspended graphene devices. (a) Optical microscopy image of graphene devices suspended after the completion of the fabrication process; (b)-(c) Corresponding scanning electron microscopy images of different magnifications; (d) Optical microscopy image of graphene devices collapsed after the completion of the fabrication process; (e)-(f) Corresponding scanning electron microscopy images of different magnifications

Fig. 4. Comparison of electrical properties of suspended graphene devices before and after annealing. (a) Comparison of I-V_b curves before and after annealing; (b) Comparison of field effect I-V_g curves before and after annealing (black is before annealing, red is after annealing)

Fig. 5. Raman spectra and infrared radiation spectra of suspended graphene devices under bias voltage. (a) Evolution of graphene Raman G peak position at different ambient temperatures, the red solid line is the linear fitting; (b) Evolution of graphene Raman spectrum under different bias voltages, the black dotted line marks the G peak and 2D peak positions; (c) Infrared radiation spectra of different focus positions for graphene (Gr), hexagonal boron nitride (h-BN), gold electrode (Au) and silicon dioxide (SiO₂) at a bias voltage of 6 V; (d) Infrared radiation spectra of graphene under different bias voltages, with logarithmic coordinates on the Y axis and linear coordinates on the X axis