Transition from tunneling to point contact investigated by scanning tunneling microscopy and spectroscopy

STM has been extensively employed to study topographic and spectroscopic properties of surfaces at approximately constant gap separation (Rt typically ∼106-108 Ω). The purpose of the present work is to explore the effects of varying the tip-sample gap separation, s, in a controlled manner over an extended range. Using a newly developed variation of STM (I-z) where the "gap" is scanned (corresponding to a variation in Rt of 105) the transition from tunneling to point contact is observed. Monitoring of tip-sample excursions beyond the tunneling regime enables key elements of reversible and irreversible local surface modifications to be identified dynamically. In the case of permanent deformation, the resulting nanostructures can be characterized both topographically and spectroscopically. This technique shows promise for the investigation of adhesion, tribology and interface formation on the nanometer scale. © 1987 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division).