Platinum/iridium tips with controlled geometry for scanning tunneling microscopy

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Abstract
An electrochemical etching procedure using a saturated CaCl2/H2O/concentrated HCl (60%/36%/4% by volume) solution has been developed to fabricate platinum/iridium tips with controlled geometry for scanning tunneling microscopy (STM). These tips, which have a high aspect ratio (5°–10° cone half angle) and a small radius of curvature (∼500 Å), are particularly useful for the imaging and metrology of precision-engineered surfaces. Initial attempts to use the tips showed them to be unreliable for STM imaging. Auger electron spectroscopy indicated the presence of a carbon contamination layer. By eliminating CO2 from the etching environment, the contamination was reduced and the reliability of the resulting tips improved dramatically. The imaging versatility of these tips is demonstrated for sputter-deposited gold on silicon, for a gold-coated polymethylmethacrylate lithographic test pattern, and for highly oriented pyrolytic graphite.

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