Observation of metallic adhesion using the scanning tunneling microscope

The interaction between an Ir tip and an Ir sample was investigated during normal tunneling operation of the scanning tunneling microscope. Force gradients compatible with metallic adhesion were observed within a range of 2 before making contact. Based on the theory of metallic adhesion, a scaling relation is derived which allows the tip geometry and the characteristics of the interaction to be accounted for in a systematic manner. © 1990 The American Physical Society.