Coulomb diamond

A blocked region in a source-drain-voltage versus gate-voltage diagram of a small charge island. Gate widths, edge slopes and tip heights encode gate coupling, junction capacitance ratios and addition energies; extracting named source/drain values requires a bias convention.

With source biased and drain grounded, a constant-interaction island has diamond edge slopes $s_{-}=-C_g/C_s$ and $s_{+}=C_g/(C_{\Sigma }-C_s)$. The latter includes the gate capacitance. A gate period for charging without an orbital gap is $\Delta V_g=e/C_g$. Combining widths and slopes determines capacitances only under a stated bias and single-island model; shell gaps must not be mistaken for a universal gate period.