Inelastic Electron Tunnelling Spectroscopy

Abstract

Inelastic electron tunnelling spectroscopy (IETS) is fast becoming established as a useful technique for the study of vibrational modes of surface adsorbates. It owes its existence to some observations in the middle 1960^’s at the Ford Motor Company Laboratories by R. C. JAKLEVIC and J. LAMBE [1, 2]. They noted anomalies in the current-voltage characteristic of a metal-insulator-metal thin film tunnel sandwich. These anomalies showed up more clearly in the first and particularly the second derivative of the characteristic and were identified as being due to the onset of an inelastic process in which organic impurities in the sandwich were being stimulated to higher vibrational states by the tunnelling electrons. The impurity in question was a hydrocarbon pump oil (Fig. l) and the interpretation was subsequently confirmed through deliberate doping with other molecules and correlating the tunnelling results with known infrared data (Fig. 2) .