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Schematic illustration (top) and calculated electronic band structure (bottom) of a monolayer MoS2; b monolayer Mo2C. c Schematic diagram (top) and energy band diagram (bottom) of MoC2/MoS2/Au device

a Schematic diagram of the CVD method to grown Mo2C. In the type I method, copper foil is placed on molybdenum foil to directly grow molybdenum carbide. In the type II method, the molybdenum foil is placed near the copper foil. Copper evaporates at high temperatures and adsorbs on the molybdenum foil for the growth of Mo2C. b Optical image of Mo2C prepared by the type I method with a growth time of 20 min. c Schematic diagram of the type I Mo2C growth process. d Optical image of Mo2C prepared by the type II method. e Schematic diagram of the type II Mo2C growth process. The black line represents graphene

a High-resolution TEM image of Mo2C, with space group Pbcn. b SAED pattern along the [ 00] zone axis. c Raman spectrum of MoS2. d High-resolution TEM image of MoS2, with space group P63/mmc. e SAED pattern along the [0001] zone axis. f Raman spectrum of MoS2

a Optical image of the Mo2C/MoS2/Mo2C device. b Dark (black) and light (red) I-V curves of the Mo2C/MoS2/Mo2C photodetector. The inset image shows the magnified dark I-V curve of the photodetector

a Optical image and schematic illustration of the Mo2C/MoS2/Au device. b |I|-V curves of Mo2C/MoS2/Au devices with (red) and without (black) 80 mW cm-2 white light irradiation. The inset image shows the magnified dark current. c Magnified I-V curves of Mo2C/MoS2/Au devices with a bias voltage range of -0.1 to 0.3 mV. d Photocurrent response of self-powered Mo2C/MoS2/Au (red) and Au/MoS2/Au (black) devices under 80 mW cm-2 white light irradiation. The image in the inset shows the magnified dark current. e Transfer characteristic curves of the photodetector with and without white light irradiation

Schematic band energy diagram of the Mo2C/MoS2/Au device

a Photodetector responses to light with various wavelengths and energy density of 0.5 mW cm-2. b Photodetector responses to 600 nm light of different intensities. c Response and recovery times of the photodetectors. The intensity of the incident light (600 nm) is 0.56 mW cm-2. d Long-term performance of the Mo2C/MoS2/Au photodetector under illumination with 600 nm light