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 {HEAD ~ electrode tip} to {TAIL ~ the thin film}: and then etching the tip at about 2 volts rms ac to thereby polish the tip 
to
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 { HEAD ~ electrode tip } to { TAIL ~ the thin film } : and then etching the tip at about 2 volts rms ac to thereby polish the tip
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