Ld ec epiplan neofluar dic

For the PL time traces of excitonic emission of the Au-WS₂-Au junctions and the corresponding PL spectra for the bright or dark states under AC bias (Figs. 2c–f, 3), a confocal PL imaging system (WITEC Alpha300 R) was used with a 532 nm CW laser (WITEC-532) as the excitation source. During the measurements, the laser was focused on the sample by an objective (Zeiss LD EC Epiplan-Neofluar Dic, 50×, NA = 0.55) and its power was kept as 50 μW. While for monolayer WSe₂ and MoS₂ based junctions (Fig. 4), the 633 nm CW laser (WITEC-633) was used with a power of 500 μW.

To determine the local pH on the electrode surface under CO₂RR working conditions, in situ Raman spectra were acquired using a confocal Raman microscope (WITec Alpha 300R). The excitation source was a 633 nm laser with the power of 3 mW and grating of 600 grooves/mm, and a 50× objective (Zeiss LD EC Epiplan-Neofluar Dic) was used. Each spectrum was obtained with an acquisition time of 10 s and 3 times of accumulation. The electrochemical reactor for in situ Raman measurements was a C031-4 CO₂RR flow cell purchased from Wuhan Gaoshi Ruilian Technology Co., Ltd, and ER-CuNS or F-CuNS catalyst was loaded on the carbon paper GDE and integrated into the flow cell. Details to calculate the local pH based on the Raman signal of HCO₃⁻ and CO₃²⁻ ions at the electrode surface can be found in Supplementary Information Note S1.