developed cryogenic electrostatic force microscopy (EFM) to determine the shell
structure of self-assembled quantum dots. Back-action of a quantum mechanical
system on a macroscopic AFM cantilever is at the heart of this unique method
that allows energy level spectroscopy of quantum systems without the need of
attaching contact leads. We operate at temperatures T which are low enough so
that the Coulomb blockade energy of the system is large compared to kT. This
allows us to charge the dot electron-by-electron and detect the resultant
change in force by EFM techniques. A dc-bias voltage between oscillating tip
and sample leads to an effective ac-voltage between a quantum dot and the
backelectrode. This a
c-voltage modulates the alignment of energy levels between
the dot and backelectrode, causing the electron to tunnel into and out of the
dot. The motion of the cantilever is damped by the electron tunnelling back and
forth, allowing us to perform quantitative energy level spectroscopy.
The upper figure is a schematic of the cantilever over the sample. An optical fiber shines 1550 nm light onto the backside of the cantilever for position detection (interferometry).
The middle figure is an 800nm image of InAs self assembled quantum dots on an InP surface of heights between 2-4 nm.
In the lower figure, the number, n, of electrons loaded in the dot is labeled on the dissipation-voltage spectra and compared to theory written by S. D. Bennett and A. A. Clerk [PNAS 2010]. From a detailed analysis of the line shape one can deduce the details of the energy levels in the dot. Data taken at 30K.
- Home-built cryogenic 4.5-300K AFM (Grutter Lab)
- Nanoscope AFM
- FIB (Laboratoire de microfabrication)
- SEM (McGill University)
- Antoine Roy-Gobeil (MSc Student)
- Lynda Cockins (PhD
- Yoichi Miyahara
- Steven Bennett (McGill
Clerk (McGill University)
(National Research Council of Canada)
Philip Poole (National
Research Council of Canada)
- Sergei Studenikin (National Research
Council of Canada)