Single Electrons, Contacts and Forces – What Afm Can Do for Nanoelectronics

In this talk I will give an overview of our attempts to understand electrons in nanoscale structures using various scanning probe techniques. I will first concentrate on our recent attempts to measure single-electron charging in an individual InAs quantum dot with a 4.5 K atomic force microscope (AFM) [1]. The resonant frequency shift and the dissipated energy of an oscillating AFM cantilever were measured as a function of the tip-back electrode voltage, and the resulting spectra show distinct jumps when the tip was positioned above the dot. The observed jumps in the frequency shift, with corresponding peaks in dissipation, are attributed to a single-electron tunneling between the dot and the back electrode governed by the Coulomb blockade effect, and are consistent with a model based on the free energy of the system (fig. 1). The observed phenomenon may be regarded as the ‘‘force version’’ of the Coulomb blockade effect. The peaks in dissipation are essentially due to a single electron back action effect on a micromechanical transducer.