Measuring negative growth rates

Negative "growth rates" can only be measured if the initial amplitude of the corresponding mode is excited strongly enough. To enforce this situation we prepared a textured electrode that stimulates the initial growth at a wave length of 1 mm. Figure 1 gives an example of the resulting growth: islands of growing deposit evolve at the tips of the copper stripes and amalgamate after some time. Figure 2 shows the exponential decay of the Fourier mode with a wave length of 1 mm. Fourier modes with longer wave length exhibit at the same time exponential growth.

Figure 1
Growing deposit at the textured electrode.

Figure 2
Temporal evolution of two Fourier amplitudes measured with the textured electrode. The data belong to the experiment displayed in Figure 1. Data points represented by filled symbols were included in the exponential fits.