Tip-Sample Distance Control and Image Recording

Commonly used methods to control the nanometer distance between the tip-apex and the sample surface are based on the shear-force feedback [24] and the electron tunneling [25] for conducting samples. 

For producing tips the following procedure proved to be reliable. The tips are produced by electrochemical etching the end of a 125 M-m gold wire in concentrated hydrochloric acid (HCl, 37%], see Fig. 9.6. 

As counter electrode a platinum wire formed as a ring is used to generate a circular constant field on the gold wire. A frequency 

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