Figure 2: Pb NCs in the regime of Coulomb blockade.

(a–c) 30 nm × 30 nm Laplacian Δ_xyz(x,y) topographic images (30 pA, 1 V) of NCs of decreasing size, labelled I to III, where the hexagonal shape of the (111) facets is visible, as shown by the dash line in c. The scale bars correspond to 10 nm. The insets show the corresponding topographic STM images. (d) DC measured at the centre of NC I and II, indicated by dots in b,c. The addition voltages δV_odd and δV_even can be identified for each curve. The black arrows indicate the local maxima in the density of states due to quantum well states. The coloured symbols identify the corresponding data points in f,h, and Fig. 5. (e) DC map as function of sample bias and distance measured on NC III along the red arrow shown in a. The black arrows indicate the Coulomb peak lines. (f) Capacitance C_sub extracted from the Coulomb gap at zero bias. It scales linearly with the NC area. (g) Simulation of the DC for NC II using the weak coupling model²⁶. (h) Normalized Coulomb peak amplitude A_norm=(A_peak–A_base)/A_base, this value decreases at the approach of the area π/4. (i) Sketch of electron occupation of NC II.