Local bond breaking via STM-induced excitations: the role of temperature

We discuss the influence of temperature on local bond breaking through multiple vibrational excitations induced by inelastic tunneling in the STM. We focus on hydrogen desorption from the H-Si(lll) and H-Si(100) systems, but the results are general. The substrate temperature affects the desorption yield in two important ways: first, lowering the temperature increases the H-Si vibrational energy relaxation time, resulting in a higher effective adsorbate temperature and an increased desorption yield. Second, lowering the substrate temperature decreases the dephasing rate of the H-Si modes (manifested by a decrease of the infrared absorption linewidth), which then reduces the rate of incoherent (Forster) vibrational energy transfer away from the Stark-shifted K-Si mode under the tip. This increases the localization of the vibrational energy and enhances the probability for multiple vibrational excitation and desorption. Finally, we discuss the possible implications of our findings on the mechanism of MOS device degradation by hot electrons. (C) 1997 Elsevier Science B.V.