Positive SECM feedback vs. tunneling glass NP O R - e A +e- -e- B Pt tip Schematic representation of the SECM feedback at the floating metal NP (A) and tunnelling experiment (B) in which the overall charge-transfer process involves diffusion of redox species to the NP, faradaic reaction at its surface, and tunnelling between the tip and NP

Pt tip approaching a Au NP in 1 mM FcMeOH solution and zoom in of the tunneling region glass Fc Fc+ Au glass Fc Fc+ a = 30 nm, rp = 50 nm tunneling feedback zoom-in solid line – experiment symbols - simulations

Tunneling mode image of a Pd cube edge length 14 nm; tip radius, 10 nm