Fig. 2
SKPM-based imaging and analysis of tribocharge distribution. a AFM image of the PDMS nanocup array’s surface topography. b SKPM image of the surface potential VCPD at the same spot. (Scale bars: 1 μm) c Superimposed cross-sectional profiles of the surface topography and potential along the scan lines in a, b. The pattern overlap clearly indicates that the inner cavity of the nanocup is negatively charged. d A schematic diagram of the surface potential computation setup. Ltot and Lch represent the arc lengths measured from the nanocup’s rim to the bottom and the end point of the surface charge distribution, respectively. Ho is the vertical gap maintained between the probe tips and the PDMS surface. The white dots represent the probing points for the surface potential measurement and evaluation. e The computed surface potentials for different charge distributions. They clearly show that the center peak rises within the potential well as the charge distribution becomes concentrated around the rim. In contrast, a dome charge (Lch = Ltot) produces negligible center peak. The gray dots represent the experimental data in c within the 1.2 μm < x <1.8 μm range
