Autonomous Oscillations and Pattern Formation with Zero External Resistance during Silicon Electrodissolution

We report the existence of small autonomous amplitude oscillations without the presence of an external series resistor during electrodissolution of both p- and highly illuminated n-type Si electrodes in a 60 mM NH₄F electrolyte at pH 1. This finding enabled us to study possible emergence of patterns without the presence of the global coupling induced by an external resistance. While with p-type electrodes we could not find a spatial bifurcation upon varying the parameters, stable domain-type patterns with distinct dynamics formed spontaneously when lowering the illumination intensity. Their emergence could be linked to the lateral coupling through valence band holes. Experiments where only part of the electrode was illuminated gave further insight into the role of the hole dynamics for the formation of spatio-temporal dissipative structures.