Procedures are described for insulating metal scanning tunneling microscope (STM) tips with either glass or polymer coatings. In solutions containing 0.10 M of a reversible redox couple, Fe(CN)−3/−46, the faradaic limiting current to polymer coated tips was 200–500 pA and that for glass coated tips was <10 pA. For polymer insulated tips, steady‐state currents of 10–100 pA were observed at tip‐sample displacements less than 0.3 μm. The suppression of faradaic current achieved by these coating procedures enabled the collection of the first atomic resolution STM images of highly ordered pyrolytic graphite electrodes in contact with redox‐active electrolytes. Preliminary data for the insitu electrochemical characterization of these tips are also discussed.

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Pt(70%)‐Ir(30%) wire (diam. = 0.5 mm, Engelhard Ind.) was electrochemically etched in aqueous 6 M NaCN, 2 M KOH to yield sharp conical tips.
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7.
Poly (α‐mefhylstyrene) MW = 60 000 g/mol, from Aldrich Chemical Co. was dissolved in CH2Cl2, and the solution was supported by a wire loop at room temperature.
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Pt(111) single crystals were polished with 1.0, 0.3, and 0.05 μm alumina powders prior to use.
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The exposed metal area was calculated from the hemispherical diffusion equation: i1 = nFDC(2πA)1/2, where F = 96487C/eq.,D = 8×10−6cm2/s,C is the concentration, and n−1 eq.−1:
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