Quantum Dot Spectroscopy
We have 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 ac-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.
Schematic of the cantilever over the sample. An optical fiber shines 1550 nm light onto the backside of the cantilever for position detection (interferometry).
800nm image of InAs self assembled quantum dots on an InP surface of heights between 2-4 nm.
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 (Grutter Lab)
- FIB (Laboratoire de microfabrication)
- SEM (McGill University)
- Antoine Roy-Gobeil (MSc Student)
- Lynda Cockins (PhD Student)
- Yoichi Miyahara (Research Associate)
- Steven Bennett (McGill University)
- Aashish Clerk (McGill University)
- Andrew Sachrajda (National Research Council of Canada)
- Philip Poole (National Research Council of Canada)
- Sergei Studenikin (National Research Council of Canada)
- Hanadi Sleiman (McGill University)