NANOWELDING - TIP RESPONSE DURING STM MODIFICATION OF AU SURFACES

We have studied the response of the tunnel current and the feedback ci rcuit during surface modification by an STM tip. Our studies show that several classes of events occur when ''writing'' by applying voltage pulses. We have studied W and Au tips on Au surfaces and PtRh tips on Pt surfaces. Strong correlation is found between the tunnel current re sponse and the kind of surface change that occurs. One dramatic discov ery is the formation of a wire between the tip and surface, which is c haracterized by an electrical shorting of the tip to the surface until the feedback circuit of the tip retracts enough to break the wire. Us ing a sophisticated graphics display system and allowing pulse placeme nt by pointing at the desired location, we are able to distinguish eas ily between changes in surface morphology and changes in tip shape and length.