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FSM setup. The cantilever is always driven on resonance using a PLL controlled bimorph. We measure and of the cantilever through a lock-in amplifier and a frequency counter, respectively. The CNT is locally gated by the AFM tip or globally gated by the Si backgate. For technical convenience, we sometimes bias the electrodes as well.
Frequency shift imaging of quantum dots formed on CNTs. (a) A CNT with two electrodes. , , tip height . (b) Coulomb oscillations of two neighboring quantum dots formed on a CNT. , , tip height . Each contour represents the addition of one electron onto the enclosed dot. Location of CNT indicated by a white line. (c) FS detection of charge hopping among quantum dots formed on an isolated CNT. , , tip height .
Charging energy of a quantum dot. (a) dependent charge addition spectra of the quantum dot. AFM tip is centered above the dot at different heights as indicated in the figure. . The arrows mark the addition of the second hole to this dot. (b) as a function of the tip height . (c) Integration of the FS signal through the Coulomb oscillation. Background is subtracted before the integration. The width of the dip (full width at half ) is mainly due to the motion of the AFM tip . (d) FS area vs at different tip heights. The slope of the graph yields an average . Inset: Image of this dot with hole occupancy number. , , .
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