Fig. 2: Experimental detection of the charged state.
a–c, d–f A simultaneously taken series of the constant-height frequency shift and dissipation images taken at the same tip-sample distance at three different bias voltages: U = −3.3 V, U = −2.5 V and U = 0 V (corresponding to double positively charged molecule, once positively charged molecule and neutral molecule). The scanning area is 3 × 3 nm2, oscillation amplitude A = 40 pm for each image, temperature 5 K. g, h Simultaneously taken frequency shift and dissipation x-z images of the characteristic sharp (“singularity”) line (once positively charged molecule). The vertical cut is 2 × 0.9 nm2 with the gap of 0.1 nm between the base image and perpendicular image of the singularity line. The perpendicular image is taken with a bias voltage U = −2.5 V. The base image of bisFc is a constant height frequency shift and dissipation image, taken with a bias voltage U = −2.5 V (once positively charged molecule). The scanning area is 2 × 2 nm2. i Δf(z) charging curves taken at three different positions, see the red, green, and purple lines marked in g and h. All curves are shown after background subtraction and tip-height alignment, as described in Supplementary Methods. j Dissipation signal Ediss(z) corresponding to Δf(z) spectroscopies. Background dissipation was subtracted. k Effective transfer rates kET obtained from experiments at two different temperatures, various bias voltages and different tips.
