On the Origin of Damped Electrochemical Oscillations at Silicon Anodes (Revisited)

Abstract

Electrochemical oscillations accompanying the formation of anodic silica have been shown in the past to be correlated with rather abrupt changes in the mechanical stress state of the silica film, commonly associated with some kind of fracture or porosification of the oxide. To advance the understanding on the origin of such oscillations in fluoride-free electrolytes, we have revisited a seminal experiment reported by Lehmann almost two decades ago. We thereby demonstrate that the oscillations are not stress-induced, and do not originate from a morphological transformation of the oxide in the course of anodisation. Alternatively, the mechanical features accompanying the oscillations can be explained by a partial relaxation of the field-induced electrostrictive stress. Furthermore, our observations suggest that the oscillation mechanism more likely results from a periodic depolarisation of the anodic silica.

In Situ Monitoring of Electrochemical Oscillations during the Transition between Dense and Porous Anodic Silica Formation

“…This refractive index spectrum is in agreement with the index spectra of dense anodic silica grown in acetic acid. 15,28 For the experiments performed at higher current, the ellipsometric spectrum acquisition is not possible in-situ due to the high generation of gas bubbles. Instead, ex-situ measurements are performed on samples taken out of the electrolyte and rinsed with ultrapure water in less than 3 seconds.…”

“…The different electrochemical oscillations regimes at the silicon anode have been extensively described and commented over the last decades. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Under specific conditions, the electrodissolution of silicon in dilute fluoride electrolytes leads to sustained electrochemical oscillations. In galvanostatic (potentiostatic) regimes the associated voltage (current) oscillates along with the interfacial silica properties (e.g.…”

“…In the latter case, the silica grown without dissolution exhibit several periodic transitions which are similar to the sustained oscillation in fluoride electrolyte in terms of voltage, stress and thickness evolutions. [13][14][15] One open question concerns the need for an external resistance. The first hypothesis was proposed by Chazalviel's group and considers the oscillations as the macroscopic outcome of the synchronization of self-oscillating domains composing the anode surface.…”

“…Our results show that the oscillations associated with dense silica formation share several key features with the damped oscillation in fluoride-free electrolytes. 15 Then, we use a model of artificial coupling to demonstrate that the self-oscillating mechanism is the same in the two regimes. The similarities between the oscillatory regimes and the persistence of sustained oscillations during the formation of thicker porous silica indicate that all oscillations arise from a same growth mechanism.…”

Electro-oxidation of p-silicon in fluoride-containing electrolyte: a physical model for the regime of negative differential resistance

“…When a silicon electrode is electrochemically dissolved in a fluoride containing electrolyte, it is covered by a layer of silica which can change its thickness in peculiar spatio-temporal patterns [1,2,3,4,5,6,7,8]. (For a comprehensive overview of the work until 2003 see Chapter 5 in [9].)…”