Energy Level Spectroscopy of Individual Quantum Dots by Electric Force Detection with Atomic force Microscopy

Abstract

We present an experimental technique for probing the charge state and electronic level structure of individual quantum dots (QD) which is based on the sensitive electric force detection using atomic force microscopy (AFM). An oscillating AFM tip positioned above a QD modulates the energy of the QD with respect to the back electrode and causes single electrons to tunnel back and forth between the QD and back electrode. The resulting periodically oscillating electric force changes the resonance frequency and damping of an AFM cantilever, enabling electric charge sensing with single-electron charge sensitivity. The technique enables quantitative energy level spectroscopy of individual QD and spatial mapping of the charge state of coupled QDs from which the interaction between QD can be extracted.