Figure 2.

Finite-element method calculations of the tip-plane geometry. (A) Magnitude (colors, logarithmically scaled) and direction (white arrows, also logarithmically scaled) of ∇|E|² for 10 V potential and 50 μm electrode gap. (B) Magnitude of ∇|E|² plotted along the black solid (z direction at x = 0 nm) and dotted (x direction at z = 5 nm below the tip) arrows in (A). (C) Electric field gradient as a function of the distance between the tip and the counter electrode (ITO). The experiments were performed in the region (black dotted circle) spanning over 50–70 μm. The inset shows the modeling design with gold tip and ITO counter electrode separated by an electrode gap, d.