MICRO- AND NANOPATTERNING USING THE SCANNING ELECTROCHEMICAL MICROSCOPE

MICRO- AND NANOPATTERNING USING THE SCANNING ELECTROCHEMICAL MICROSCOPE 

1 Schematic representation of the direct (A) and the feedback mode (B) of the SECM. 

This mode of operation was primarily developed by Bard and coworkers in the early days of SECM. The direct mode is based on approaching a conducting substrate with a biased UME. The substrate acts as the auxiliary electrode, which means that if a reduction process occurs at the UME, an oxidation reaction must take place at the substrate. The latter reduction is the driving force for the patterning process. Because the whole substrate is biased, localization of the process on the substrate is caused by the distribution of the electrical field between the UME and the substrate (2). Accordingly, the resolution of the patterns chiefly depends on the distance between the UME and the substrate. Therefore, in most cases where the direct mode has been applied, care has been taken to minimize the distance between the UME and the substrate. 

The only system that employs the direct mode for semiconductor etching was reported by Lin et al. (3). n-GaAs was photoetched by holding a sharp metallic tip, insulated in glass, in close proximity ( 1 /xm) to a positively biased (4 V) n-GaAs while illuminating the substrate. The formation of etched patterns with line widths of 0.3-2 /xm was attributed to the nonuniform spatial current distribution. Nonetheless, some etching also occurred across the whole surface because there was no attempt to focus the illumination on the area beneath the UME. 

One of the critical problems of the previous system was the lack of a mechanism for controlling the distance between the UME and the substrate using 

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D. Mandler, Micro- and nanopatterning using the scanning electrochemical microscope. In A.J. Bard and M.V. Mirkin (Eds.), Scanning Electrochemical Microscopy, Marcel Dekker, New York, Basel, 2001, pp. 593-627. 

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