Faradaic currents and ion transfer numbers in electrochemical atomic switches
Final Report Abstract
We have studied the transference numbers of thin film solid electrolytes for atomic switches by combining the solid state cell emf method with impedance spectroscopy and Hebb-Wagner technique. We reported that Ag and Cu dissolve chemically into chalcogenide matrix and the composition equilibrates for at least few days. The transference number of ions were found to be close to 0.8 which is in contrast to the often used assumption tion = 1. We also provided a systematic screening of the thin film deposition conditions and found that we can control the morphology and the chemical composition by variation of the process parameter e.g. pressure, sputter rate and RF power. After current-voltage testing the most appropriate composition was then chosen for further detailed experiments on the kinetics of the resistive switching. The role of the ambient moisture was elucidated and we reported for the first time on the influence of the water partial pressure on the switching characteristics and cell behavior of oxide based atomic switches. Absorbed water molecules were identified by FTIR and incorporation of D was observed by SIMS depth profiling after equilibration in D2 and D2O atmospheres. The kinetics of the electrochemical oxidation of Cu was found to be controlled by the charge transfer in accordance to the Butler-Volmer kinetics and we have calculated the diffusion coefficients for the Cu ions. Using a small amount of Fe doping in RbAg4I5 superionic electrolyte we succeeded to enable STM measurements and have shown for the first time atomically resolved STM image of ionic solid electrolyte. Detailed studies on the surface kinetics have shown that the nucleation is the rate limiting process in the switching and using the atomistic theory of nucleation we were able to offer a microscopic view in the very initial process of the filament formation. The publication of the result on the STM studies has been acknowledged in “Elektronik Praxis” (30.04.2012) and the official press office of Forschungszentrum Jülich (29.04.2012).
Publications
- Phys. Chem. Chem. Phys., Vol. 11, 28, 2009, 5974-5979
C. Schindler, I. Valov, R. Waser
(See online at https://dx.doi.org/10.1039/b901026b) - Appl. Phys. Lett., Vol. 99, 20, 2011, 203103/1-3
S. Tappertzhofen, S. Menzel, I. Valov, R. Waser
(See online at https://dx.doi.org/10.1063/1.3662013) - Advanced Functional Materials, Vol. 22, 1, 2012, 70-77
T. Tsuruoka, K. Terabe, T. Hasegawa, I. Valov, R. Waser, M. Aono
(See online at https://doi.org/10.1002/adfm.201101846) - Nanoscale, Vol. 4, 10, 2012, 3040-3043
S. Tappertzhofen, H. Mündelein, I. Valov, R. Waser
(See online at https://dx.doi.org/10.1039/c2nr30413a) - Nature Materials, Vol. 11, 6, 2012, 530-535
I. Valov, I. Sapezanskaia, A. Nayak, T. Tsuruoka, T. Bredow, T. Hasegawa, G. Staikov, M. Aono, R. Waser
(See online at https://doi.org/10.1038/NMAT3307)
