2. Scanning tunneling microscope

2.1 Introduction

As a consequence of wave-corpuscle duality, the tunnel effect occurs when a particle must cross a region of space where its total energy is less than its potential energy. Such a region constitutes a potential barrier that the particle cannot cross. However, if the wave associated with the particle extends over dimensions comparable to the extension of this barrier, quantum mechanics predicts that the particle can tunnel through this potential barrier, which is forbidden in the sense of classical mechanics. Since the predictions of quantum mechanics, numerous manifestations of the tunneling effect have been observed in atomic and nuclear physics.

It was in the late 1920s that electron tunneling through the potential barrier formed by the empty...