Atomic force microscope

X-ray photoelectron spectrometer (ThermoFisher ESCALAB250X) was used to analyze the composition and valence states of the films under room temperature. The laser Raman spectrometer (HORIBA Jobin Yvon LabRAM HR Evolution) was used for measurement, and the wavelength and raster of the laser were 532 nm and 1800 gr·nm⁻¹, respectively. The scanning image of MoS_x was obtained using an atomic force microscope (Bruker). The spectral response curve of the solar cells was tested using the IPCE testing system (CROWNTECH) of the solar cells. The current density–voltage (J–V) was measured using the semiconductor device parameter analyzer (Agilent B1500A).

SEM images of the swimming microrobots were acquired with a double-beam electron microscopy (Scios2, Thermo Fisher Scientific, USA) at an operating voltage of 10 keV. The samples were coated with a 5-nm carbon layer to improve the conductivity (Leica EM ACE600 Carbon Evaporator). The bright-field and fluorescence microscopic images of swimming microrobots were captured at 25 frame·s⁻¹ by an inverted optical microscope (Olympus, IX73, Japan) coupled with a Point Grey CCD camera (FLIR, GS3-U3-51S5C/M-C, USA). These video data were analyzed using ImageJ to obtain the trajectories of swimming microrobots. The magnetic hysteresis curve of samples was obtained using a vibrating sample magnetometer (Lake Shore Cryotronics 7404, USA). The viscous force between swimming microrobots and the inner wall of vein was measured by an atomic force microscope (Bruker Instruments, Innova, USA).