The effects of the electric field in the STM on excitation localization. Implications for local bond breaking

We discuss the effects of the electric field present in the STM on the frequency and spatial localization of (vibrational) excitations induced by inelastic electron tunneling. We show that, depending on its direction and size, the field can produce either a weakening or a strengthening of chemical bonds. The resulting vibrational frequency shifts could lead to the localization of the excitation under the STM tip, reducing energy transfer rates to surrounding sites by several orders of magnitude. This localization gives the STM the ability to locally activate surface dynamical processes, and induce atomic-scale modification of materials.