Atomically controlled electrochemical nucleation at superionic solid electrolyte surfaces


Electrochemical equilibrium and the transfer of mass and charge through interfaces at the atomic scale are of fundamental importance for the microscopic understanding of elementary physicochemical processes. Approaching atomic dimensions, phase instabilities and instrumentation limits restrict the resolution. Here we show an ultimate lateral, mass and charge resolution during electrochemical Ag phase formation at the surface of RbAg4I5 superionic conductor thin films. We found that a small amount of electron donors in the solid electrolyte enables scanning tunnelling microscope measurements and atomically resolved imaging. We demonstrate that Ag critical nucleus formation is rate limiting. The Gibbs energy of this process takes discrete values and the number of atoms of the critical nucleus remains constant over a large range of applied potentials. Our approach is crucial to elucidate the mechanism of atomic switches and highlights the possibility of extending this method to a variety of other electrochemical systems.

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Figure 1: Schematic presentation of the distribution of the electrochemical (), chemical (μe) and electrical (φ) potentials (related by ) at three boundary situations.
Figure 2: STM imaging of RbAg4I5 surfaces.
Figure 3: Current–time dependence at an applied voltage of −100 mV.
Figure 4: Voltage and temperature dependence of the switching time.
Figure 5: STM observations of Ag clusters formation and stability.


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The authors would like to thank the German Research Foundation (DFG) and the Japan Science and Technology Agency (JST) for the financial support of the projects W A908/22-1 in Germany and that in Japan. I.S. was supported by the ‘Studienstiftung des deutschen Volkes’. The assistance of T. Pössinger with the graphical layout is gratefully acknowledged.

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I.V. conceived the idea, supervised the measurements, performed the data interpretation and wrote the manuscript. I.S. prepared the samples, performed the measurements and the data evaluation, and contributed to the interpretation. A.N. and T.T. supported the STM measurements and contributed to the interpretation. T.B. performed the DFT calculations, T.H. supervised the STM measurements and contributed to the interpretation. G.S. contributed to the interpretation, M.A and R.W. contributed to the concept of the study and supervised the research. All authors discussed the results and implications at all stages and contributed to the improvement of the manuscript text.

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Correspondence to Ilia Valov.

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Valov, I., Sapezanskaia, I., Nayak, A. et al. Atomically controlled electrochemical nucleation at superionic solid electrolyte surfaces. Nature Mater 11, 530–535 (2012).

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