The research group of Professor Hiromichi Ohta from Research Institute for Electronic Science at Hokkaido University and Associate Professor Hyoungjeen Jeen from Physics department at Pusan National University, Korea, has succeeded in visualizing the electrochemical oxidation reaction in materials for current and magnetic information storage devices. This is an epoch-making result that accelerates the development of advanced information storage devices. Since around 2013, the research group has been working on the development of devices that store information using current and magnetism using the redox reactions of strontium cobalt oxide (SrCoO_x) thin film called oxygen sponge. However, the operating speed was slow. In order to overcome the problems in electrochemical reactions, it is necessary to visualize the redox reactions of materials on a macroscopic scale, not on an atomic scale. Although transmission electron microscopy observation is generally used in the field of materials science, it  cannot be applied to SrCoO_x. In this study, the electrochemical oxidation reaction of SrCoO_x thin films was macroscopically visualized by a newly developed visualization method that combines the measurement of thermoelectric properties (electrical resistivity and thermopower) and observation with a conductive atomic force microscopy. Steep decrease of both resistivity and the absolute value of thermopower of electrochemically oxidized SrCoO_x epitaxial films indicate the columnar oxidation first occurred along with the surface normal and then spread in the perpendicular to the normal. Further, the phenomena are directly visualized using the conductive atomic force microscopy. The present results not only accelerates the development of advanced information storage devices using SrCoO_x thin films, but also enables to visualize electrochemical redox reactions of materials that cannot be applied to transmission electron microscopy.

Original article

Qian Yang, Hai Jun Cho, Hyoungjeen Jeen*, and Hiromichi Ohta*, “Macroscopic Visualization of Fast Electrochemical Reaction of SrCoO_x Oxygen Sponge”, Adv. Mater. Interfaces 6, 1901260 (2019). (DOI: 10.1002/admi.201901260) (October 23, 2019)  arXiv Outside Back Cover

Funding information

This research was supported by Grants-in-Aid for Scientific Research A (17H01314) and Innovative Areas (19H05791) from the JSPS. Hyoungjeen Jeen and Hiromichi Ohta are supported by the Korea-Japan bilateral program funded from following programs of each country (NRF-2018K2A9A2A08000079 for H.J. and JSPS for H.O.). A part of this work was supported by Dynamic Alliance for Open Innovation Bridging Human, Environment, and Materials, and by the Network Joint Research Center for Materials and Devices.

Contacts

Professor Hiromichi Ohta

Research Institute for Electronic Science,

Hokkaido University

Email: hiromichi.ohta[at]es.hokudai.ac.jp

https://functfilm.es.hokudai.ac.jp/english/