Figure 6.

Determination of the diffusion coefficient using different time intervals for estimating the slope $dE\left(t\right)/d\sqrt{t}$ by linear fitting. An improper choice of the lower cut time $t_1=9\mathrm{s}$ (e. g. by an automated analysis) leads to an inaccurate diffusion coefficient of $D_{\mathrm{fit}}=0.47·{10}^{-16}{\mathrm{m}}^2{\mathrm{s}}^{-1}$ compared to the exact value of $D_{\mathrm{exa}}={10}^{-16}{\mathrm{m}}^2{\mathrm{s}}^{-1}$ (a). Choosing $t_1=81\mathrm{s}$ and $t_2=900\mathrm{s}$ yields the better result of $D_{\mathrm{fit}}=1.47·{10}^{-16}{\mathrm{m}}^2{\mathrm{s}}^{-1}$ (b). Further parameters: $T=-20{}^{\circ }\mathrm{C}$ , $k={10}^{-7}\mathrm{mol}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ , $x_0=0.9$ , $i_{\mathrm{GS}}=0.01\mathrm{A}{\mathrm{m}}^{-2}$ .