Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Th-1200
Mechanism of Dissipative Interaction by Tunneling Single-Electrons
Yoichi Miyahara 1 , L. Cockins 1 , S. D. Bennett 1 , A. A. Clerk 1 , S. A. Studenikin 2 ,
P. Poole 2 , A. Sachrajda 2 and P. Grutter 1
1 Department of Physics, McGill University, Montreal, Canada
2 Institute for Microstructural Science, National Research Council of Canada, Ottawa, Canada
The frequency modulation mode atomic force microscopy (FM-AFM) can be used as a
sensitive electrometer which can detect the motion of a single electron. An oscillating
AFM tip with an applied dc-bias voltage (Vbias) can allow a single electron to tunnel back
and forth between a quantum dot (QD) and a back-electrode by oscillating the chemical
potential of the QD around that of the back-electrode, owing to Coulomb blockade effect.
The resulting electron motion in turn modulates the electrostatic force acting on the tip
and causes the dissipation as well as the resonance frequency shift (Δf) of the cantilever.
Both dissipation and Δf images taken in constant-height mode show characteristic
concentric rings around the QD, each of which reflects the above-mentioned single-
electron tunneling. The corresponding features also appear as peaks (dips) in the
dissipation (Δf) versus Vbias spectra taken above the QD. These spectra can be interepreted
as addition energy spectra which enable us to investigate the electronic structure of a
single QD.
In this contribution, we present the mechanism of the dissipative electrostatic
interaction due to the tunneling single-electrons in detail. In essence, this dissipative
interaction arises from the delayed response of a single tunneling electron to the
oscillating chemical potential induced by the oscillating tip. The delay is due to the finite
tunneling rate which is determined by the tunnel barrier.
We developed a theoretical model for this dissipation process and obtained a very
good agreement between the theoretical dissipation versus Vbias curve and the
experimental one (Fig. 1). We also discuss the effect of the tip oscillation amplitude and
temperature and the relation between Δf and dissipation signal.
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Figure 1: Theoretical (solid) and
experimental (dashed) dissipation versus
bias voltage curves. (T = 30 K, A=0.5 nm,
Tip-QD distance = 15 nm)