Metallic adhesion and tunnelling at the atomic scale

Abstract

We simultaneously measured the distance dependence of the force and the tunnelling current between a W(111) tip and a Au(111) sample in an ultrahigh vacuum at T = 150 K. The tip was characterized by field ion microscopy. Even at atomically close contact no evidence of structural instabilities was found. The scaling of the force curves show an unexpectedly long distance scaling parameter of λ = 0.2 nm. We conclude that not only the apex atoms contribute to the adhesion forces, but the first three layers play an almost equal role. Using a model that correlates the force and the tunnelling current, we are able to extract the tip density of states. Possible reasons for the long scaling length are discussed.