Figure 6.

Optical activity of WS₂ nanopores in 1 M KCl solution. (a) Schematic of the optical measurement setup. A 532 nm (green) laser is focused onto a nanopore device using an objective lens (4×) and 3-axis micromanipulator stage. The positions of the laser and SiN_x window are monitored with a CMOS camera, while its power is controlled through a variable neutral density filter and the laser driving voltage. All measurements were performed in 1 M KCl solution. (b) Change in ionic current through WS₂ and SiN_x nanopores with laser exposure. Ionic current (I_B) measurements at V_B = 100 mV were obtained for two WS₂ nanopores of effective diameters (d_eff) of (i) 11.1 nm (pore C) and (ii) 43.2 nm (pore D) and a SiN_x nanopore with (iii) d_eff = 4.8 nm. Periods when the laser (power density = 3 W/cm²) is turned on (light) and off (dark) are represented in green and black, respectively. The spikes in I_B correspond to the capacitive noise from switching the laser on or off. (c) Change in effective diameter of pore C with time. The effective diameter (d_eff) was plotted against the experiment time, t. The regions with the laser on (green) were extracted and concatenated into a single plot (inset) as a function of exposure time, t_L. The resulting exponential fit for the relation between effective nanopore diameter and laser exposure time is given by α = 55.1 nm, β = 43.5 nm, and γ = 249.5 s. An illustration of the expansion of the pore is shown on the top left. (d) STEM observation of the laser-induced expansion of nanopores. STEM images were obtained of WS₂ nanopores (outlined in yellow) with initial diameters (d_TEM) of (i) 4.6, (iii) 4.0, and (v) 4.0 nm. Images after laser exposure (t_L ~ 5s) to power densities of (ii) 5400, (iv) 90, and (vi) 3 W/cm² at V_B = 0 V show expansion of pores. Corresponding conductance values before and after exposure are also provided.