Platform Integration – Example
Tuning-fork-based AFM for Scanning
Gate Microscopy in Top-loading DR
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For this project, we have developed a mK tuning-fork
AFM for a dry top-loading DR in close collaboration
with Bluefors. The DR has a cooling power of ~300
μW at 100 mK and a base temperature of 8 mK.
The cooling power at the sample location on the
top-loading insert is 100 μW at 100 mK. Thanks
to the top-loading probe, the turnaround time is
typically 9-11 hours, hence tip and sample exchange
can be achieved within a reasonable timeframe
without warming up the whole DR including the
superconducting magnet.
The customized attoAFM III has been carefully adapted
for the mK environment in terms of wiring and
thermalization, and the whole configuration has
been tested and optimized at mK temperatures. The
microscope is intended to be used for scanning gate
microscopy (SGM), where the wire-type AFM tip on the
tuning fork serves as a mobile local gate.
This allows for characterization of electrical
transport properties in mesoscopic samples on
the nanoscale as a function of gate position and
tip potential.Previous implementations of such
mK microscopes [1] have involved heavy spring
isolation of the microscope inside the DR, which
yielded good results. However, it makes the design
and practical use much more complicated, since
any material shows a finite susceptibility and hence
undesired motion in strong magnetic fields.
Despite the top-loading probe design, and despite
having no spring isolation on the microscope module,
the tuning-fork AFM system reaches 2.9 nm rms z-noise.
This is of the same order of magnitude as previously
reported [1], where a heavy 6 kg damping stage inside
the DR was used. At typical tip-sample distances of
a few tens of nanometers, this is well suited for SGM
experiments.
[1] M. Pelliccione et al., Rev. Sci. Instrum. 84, 033703 (2013)
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Customer
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Prof. Alexander Hamilton
(University of New South Wales, Australia)
Project
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Top
Loader
Setup:
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01 Bluefors dry dilution refrigerator
02 top-loading insert
03 superconducting magnet
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attoAFM III microscope for mK
tuning fork with AFM tip
chip carrier sample holder with thermalization
positioners and scanners for sample motion
mK AFM III for SGM
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Top-loading
DR Bluefors
mK attoAFM III
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Bottom
Loader
mK Positioners