The etching step is preferably followed by a polishing step which comprises providing a thin film of a second acidic aqueous etchant solution containing an alkaline earth salt; then contacting said electrode tip to the thin film: and then etching {HEAD ~ the tip} at {TAIL ~ about 2 volts rms} ac to thereby polish the tip 
The etching step is preferably followed by a polishing step which comprises providing a thin film of a second acidic aqueous etchant solution containing an alkaline earth salt ; then contacting said electrode tip to the thin film : and then etching { HEAD ~ the tip } at { TAIL ~ about 2 volts rms } ac to thereby polish the tip
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