Fig. 2: Structure and characterization of the device.

a Schematic diagram of the device structure and SEM spectrums of each part, b XRD spectrums of CN and P-CN, c FTIR spectrums of CN and P-CN, d, e XPS spectrums of P-CN. The high-resolution C1s spectrum shows three peaks at 284.8 eV (C-C), 286.36 eV (C-NH), 288.16 eV (N-C=C), and the N1s spectrum shows three peaks at 398.57 eV (C-N=C), 388.62 eV (N-(C)3), 401.04 eV (C-NH). The source data are available in the “Data availability” section.