Pattern Formation at the Semiconductor/Liquid Interface

We are interested in principles governing pattern formation at the semiconductor/electrolyte interface. Currently we are focusing on electrodissolution of Si.

Although being of great importance, the electrochemistry of Si in aqueous electrolytes is still only poorly understood. This is especially true for the occurrence of dynamic instabilities, such as current oscillations at high anodic voltage. They have been known to occur for more than half a century, yet the underlying mechanism lies still in the dark. Fig. 1 below shows different oscillation types that are frequently encountered during the electrodissolution of Si.

Fig.1: Different oscillation types occurring during the electrodissolution of Si in fluoride containing electrolyte solution. Taken from ref. [3].

The goals of this project are (a) to uncover the electrochemical mechanism leading to the oscillations, (b) to investigate spatial pattern formation in the oscillatory regime using ellipsometric imaging (Fig. 2) and (c) to extract the universal laws that lead to the observed, unusual patterns from the point of view of nonlinear dynamics. Fig. 3 gives an example of a labyrinthine pattern in the oxide thickness that forms  in a subharmonic mode only. More information about subharmonic patterns, which we typically find in our experiments, can be found in refs. [1,4].

Fig. 2: Scheme of the ellipsometric imaging set-up used to monitor in-situ the thickness of the oxide layer at the Si|electrolyte interface.
Fig. 3: Amplitude of a subharmonic oscillation obtained from a Fourier Analysis of the local time series of the ellipsometric images during electrodissolution of Si in fluoride-containing electrolyte solution. Taken from ref. [1]

 

This project is funded by the DFG.

 

References

[1] I. Miethe, V. García-Morales, K. Krischer, Phys. Rev. Lett. 102, 194101 (2009)

[2] I. Miethe, K. Krischer, J. Electroanal. Chem. 666, 1 (2012)

[3] K. Schönleber, K. Krischer, ChemPhysChem 13, 2989 (2012)

[4] V. García-Morales, A. Orlov, K. Krischer, Phys. Rev. E 82, 065202(R) (2010)

[5] L. Schmidt, K. Schönleber, K. Krischer, V. García-Morales, Chaos 24, 013102 (2014)