Fig. 5: Tunable plasmons in 2M-WS₂ through ion-intercalation.

a An illustration of the infrared spectrum measurement of an ion intercalated sample. V_g represents the electrochemical intercalation voltage applied between the ion gel and the sample. The voltage between source and drain V_ds serves to monitor the sample resistance. b The evolution of the plasmon spectrum in a 0.6 μm wide c-axis oriented ribbon array with different resistances under gate-controlled Li⁺ intercalation. Due to the strong absorption of the ion-gel below 1500 cm⁻¹ and the other region with shade of gray in the figure, these frequency regimes are not displayed. c Reversible resistance-dependent plasmon frequency extracted from b. The red line is a guide to the eye. d, e The evolution of the plasmons with increasing intercalation duration \({t}_{{{{{{\rm{intercalation}}}}}}}\) in ribbon arrays along the b- and c-axis under gate-controlled deionized water, respectively. f Resistance-dependent plasmon frequencies extracted from d and e. The red and blue lines are guides to the eye. g Extracted Drude weights of a film along the b- and c-axis at different intercalation durations. They are proportional to each other. h Calculated loss function using the extracted film parameters after intercalation. i Calculated intercalation-dependent isofrequency contours at the frequency of 3000 cm⁻¹.