nanoscopy - attocube

Photoluminescence. Fluorescence
selected applications for cryogenic confocal microscopy
The requirements of the microelectronic and semiconductor industry
for producing increasingly smaller, faster and more powerful
electronic devices drives the quest for new approaches where
the conventional semiconductor components can be replaced by
materials of superior properties. Due to the remarkable features
of semiconductor quantum dots and improvements in designing
quantum dot structures these “artificial atoms” are gateways to an
enormous array of possible applications in the fields of quantum
computing, quantum cryptography and single electron / single
photon devices.
pioneers of precision
Particularly, the observation of the optical transitions is the main
tool to the basis for the application of quantum dots as laser
emitters, storage devices or for quantum information processing.
Semiconductor quantum dots have also been found to be attractive
for the realization of spin quantum bits, as they can be controllably
positioned, electronically coupled and embedded into active
devices. These quantum bits represent the fundamental logical
unit in a quantum computer. By using single electron spins in
semiconductor quantum dots with a well-defined orientation, it
is possible to directly measure the intrinsic spin-flip time and its
dependence on magnetic fields.
Photocurrent Measurements on Graphene Devices using the Fiber based attoCFM
Spatially resolved photocurrent measurements on a graphene field-effect device in the QHE regime
are presented to study the distribution of Landau levels and its relation with macroscopic
transport characteristics. The exceptional stability and the ease of use of the attoCFM microscope
greatly facilitated these measurements and allowed for measuring working devices in magnetic
fields from -9 to +9 T.
G. Nazin, Y. Zhang, L. Zhang, E. Sutter, P. Sutter, Nature Physics, 6, 870–874 (2010) .
Optical Emission from a Charge-tunable Quantum Ring
The dispersion of the photoluminescence from singly-, doubly-, and triply-charged excitons (X 1- ,
X 2- , and X 3- , all on the same spot) was monitored under the influence of an altering magnetic field
(-9 to +9 Tesla). While X 1- and X 2- show typical photoluminescence behaviour of localized excitons,
the X 3- develops at high fields a remarkable series of oscillations in addition to a diamagnetic
shift. Furthermore, a gradual collapse around 1 Tesla of the two low field lines was observed. (K.
Karrai et al.)
K. Karrai, R. J. Warburton, C. Schulhauser, A. Högele, B. Urbaszek, E. J. McGhee, A.O. Govorov, J. M. Garcia, B.
D. Gerardot, P. M. Petroff, Nature (2004) 247, 8, 135.
laser energy (eV)
laser energy (eV)
1.2983 1.2983
1.2982
1.2981 1.2981
1.29812
1.29810
1.29808
1.29806
1.29804
delay time, τd [ns]
70
56
42
28
14
0
X 1- 50mK
0 20 40 60 80 100
gate voltage (mV)
15 30 45
gate voltage (mV)
∆E [µeV]
13 26 39 52 65
second pulse length, τp [µs]
"
laser energy (eV)
laser energy (eV)
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0
1.29808 1.29808
1.29806 1.29806
1.29804
-6
1.2983
1.2982
1.2981
1.29810 1.29810
laser energy (eV)
1.29812
X 1- 50mK
0 20 40 60 80 100
gate voltage (mV)
15 30 45
gate voltage (mV)
gate voltage (mV)
Confocal Microscopy on Quantum Dots at 50 mK
A confocal microscope was manufactured for the detailed investigation of quantum dots in an
ultra low temperature environment (< 44 mK) by using photoluminescence and transmission
measurement techniques inside a magnetic field of up to 7 Tesla. For this purpose, a
customized attoCFM II module was implemented into a dilution refrigerator with a cooling
power of 400 μW at 120 mK on the cold finger and a base temperature on the sample plate of
less than 44 mK.
Figure 1 shows differential transmission measurements of a InAs quantum dot embedded in
a GaAs matrix at 50 mK. The pronounced deviation from the lineshape as expected from the
quantum confined stark effect is due to many-particle interaction.
C. Latta et al, Nature, Vol 474, 627 (2011)
Realization of Fast Arbitrary Rotations of Nuclear Spin Polarization in a Dot
The graph demonstrates fast rotation on the micro-second scale of nuclear polarization in
a single GaAs/AlGaAs interface quantum dot controlled with two rf pulses. The first pulse is
π/2, and the length of the second pulse (horizontal axis) and its phase with respect to the first
(vertical axis) are varied. The colour scale of the figure to the left shows the changes in the
Overhauser shift on the dot, as a result of excitation with the rf pulses. The shift is measured
optically using PL from the probed QD. Previously, similar experiments were only possible in
macroscopically large quantum well structures. Using attocube’s confocal microscope this experiment
has become possible in single dots. Such experiments greatly benefit from versatility
of the optical and mechanical parts of the microscope, and as always rely on exceptional stability
of the whole system.
M. N. Makhonin et al., Nature Materials (2011), doi:10.1038/nmat3102, published online 28th August 2011.
Observation of Many-Body Exciton States using the attoCFM I
The graph on the left shows a 3D map of the photoluminescence of a single InAs/GaAs
quantum dot in a charge-tunable device. It was found that the coupling between the
semiconductor quantum dot states and the continuum of the Fermi sea gives rise to new
optical transitions, manifesting the formation of many-body exciton states. The experiments
are an excellent proof for the stability of the attoCFM as the measurements took
more than 15 hours without the need for re-alignment.
[1] N. A. J. M. Kleemans et al. Nature Physics 6, 534 - 538 (2010).
nanoSCOPY
Scanning Probe Microscopes for Extreme Environments