Analytical Sciences

Local Imaging of an Electrochemical Active/Inactive Region on a Conductive Carbon Surface by Using Scanning Electrochemical Microscopy

Akio UEDA,*^1,*² Dai KATO,*² Naoyuki SEKIOKA,*³ Shigeru HIRONO,*⁴ and Osamu NIWA*^1,*^2,*³

*1 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan
*2 National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan
*3 University of Tsukuba, 1-1-1 Tenno-dai, Tsukuba, Ibaraki 305-8571, Japan
*4 MES-Afty Corporation, 2-35-2 Hyoe, Hachioji, Tokyo 192-0918, Japan

We demonstrated the imaging of local electron transfer-rate differences on a flat conductive carbon substrate, attributed to only surface functional groups, by using a scanning electrochemical microscopy (SECM) technique. These differences were clearly imaged by using a redox mediator with surface state sensitive electron transfer rates, even if the conductivity of each imaging area were almost identical. The carbon electrode surface was masked with a patterned photoresist, and selectively introduced oxygen functional groups using an oxygen plasma treatment. This patterned surface exhibited hardly any topographical features when observed by scanning electron microscopy (SEM), and a height difference of only 1.0 nm was observed with atomic force microscopy (AFM). However, the SECM feedback mode and substrate generation-tip collection (SG-TC) mode are able to distinguish these interfaces with an almost micrometer order resolution by utilizing the difference in the electron transfer rate for the Fe^2+/3+ mediator, and the current ratios for regions rich and poor in oxygen containing groups were 1.5 and 2.0, respectively. This technique could be employed for imaging and monitoring the electron transfer rates on various electrode surfaces, including fluorine and nitrogen terminated surfaces and a monolayer film patterned with micro or nano contact printing techniques.

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