Correlation between tip-apex shape and surface modification by scanning tunneling microscopy

The correlation between the shape of a probe tip apex for scanning tunneling microscopy and the surface modification patterns on a Si(111)-7×7 surface is demonstrated by using an in situ tip evaluation technique. The tip apex is inversely imaged by using a very sharp nanoneedle fabricated on the sample surface by applying a high voltage between the tip and the surface. When a large current of 100–300 nA flows between the tip and the surface, silicon atoms on the surface are extracted and a trench pattern is formed. The trench pattern agrees well with the geometry of the tip apex. The correlation between the tip shape and the fabrication pattern is discussed in terms of the electric field under the tip.