Contact mode: 6 nm constant gap between the trace and the retrace line?

stsolong posted on Thu, Jul 12 2012 2:43 AM

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Hi everyone,

I scan over a flat Si wafer surface by contact mode(Conductive-AFM) with tip SCM-PIC. There is always a gap between  the trace and the retrace line, around 6 nm. Is it a water film? The deflection setpoint is 0.3 V, but i have to pull the tip out of surface by setting the ´deflection setpoint´= -0.5 V, instead of  0V.

The worse thing is that the trace and retrace lines sometime don´t have the similar sharp. For example, a small high feature in trace line becomes the small indentation(low feature) in the retrace line. The 6 nm gap is always existing while scanning some flat surface.

What is the reason for that? How can I eliminate or reduce it? Thanks a lot!!