Oscillatory electrochemical reactions at corroding silicon surface

摘要

The paper analyses the nature of chaotic and well-ordered oscillations of the anodic potential and open circuit potential of silicon immersed in aqueous electrolytes. These oscillations are observed when experimental conditions are fine tuned in what corresponds to the current flowing through the system, composition of electrolyte, its viscosity, etc. It is assumed that the oscillations are due to the accumulation of mechanical stress in the thin (50-80 nm) oxide film formed at the surface of silicon as a result of electrochemical anodic reaction. The stress is released by local etching of the oxide and its lifting-on from the Si surface. The process repeats again and again yielding long-lasting oscillations of the anodic potential value (amplitude around 10-15 V, period 20-150 s) or of the open circuit potential (several hundreds milli-volts). Along with temporal ordering of the process (oscillations of potential) there occurs a spatial ordering in the system - the surface of corroding Si sample is covered with hexagonally ordered semi-spherical cells (diameter about 700 nm). The effect is well-fit by the general phenomenology of chaos-order transitions in chemical systems (bifurcationss, strange attractors are the intrinsic features of these oscillations) and its kinetics is very similar to that of the Belousov-Zabotinsky reaction. However, oscillatory processes on the corroding Si surface are caused by quite specific physical and chemical mechanisms, which are not well understood presently. We present the microscopic model for the oscillatory behavior which involves, generation of local mechanical stress at the Si/electrolyte interface, non-linear electrochemical etching of Si, localization of the electric field at the etched surface, etc.