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Experiment 1 features a custom designed
UHV, variable temperature scanning tunneling microscope.
Features:
Vibration Isolation:
With a tip-sample separation of about 10 angstroms, eliminating vibrations
is a necessity. We have gone to great lengths to reduce potential vibrations
including supporting our experiment on a two ton granite table top,
using air springs to float the table during measurements, using concrete
table legs which extend 45 ft. into the terrain below the lab to support
the air springs, and finally employing an in situ spring system for
the microscope itself.
Electronic Noise Reduction:
We work with a tunneling current of ~ picoamps. Any possible external
electrical noise (e.g. signal pickup, ground loops, etc.) will severely
affect the signal to noise ratio of our spectral measurements. For this
reason the experiment is in an RF shielded room, all electronic equipment
used in the experiment is housed in a separate room from the experiment,
and a number of “noisy” instruments run through isolation
transformers.
Atomic Resolution and Spectroscopic Stability:
Both of these are achieved through vibration damping and electronic
noise reduction. Atomic resolution is imperative to pinpoint a location
of interest and understand spatial variations in spectroscopic measurements.
Variable Temperature:
We have the ability to vary the microscope and sample temperatures from
3K to over 100K. This allows for studies above and below critical temperatures.
In addition, we have overcome drift issues which have plagued other
variable temperature STMs and are able to follow the same atomically
resolved region as a function of temperature. With this new ability,
we can see changes at specific atom sites as we pass through critical
temperatures.
Below shows our entire Experiment 1
setup (left) as well as our custom built STM (right).
Experiment 2 features the same custom STM,
but adapted for room temperature biological applications.
Features:
Vibration Isolation:
Similar to Experiment 1, vibration damping is of paramount concern.
However, due to the smaller vacuum chamber and peripheries for this
experiment, vibrationally isolating the system to the extent of Experiment
1 is not needed. Here we support our experiment on a concrete mass which
is hung from the ceiling using bungee cords. We have a separate in situ
spring system for further isolation, but we have not yet had a need
to employ this.
Acoustic Isolation:
This experiment is conducted at atmospheric pressure. Hence, unlike
in Experiment 1 where we work in vacuum, acoustic transmissions can
cause further vibration to the experiment. We have taken care to line
the experimental walls with bass traps to absorb low frequency audio.
Electronic Noise Reduction:
Very similar precautions were taken in this experiment to that in Experiment
1.
Atomic Resolution and Spectroscopic Stability:
Both of these are achieved through vibration damping and electronic
noise reduction. Atomic resolution is imperative to pinpoint a location
of interest and understand spatial variations in spectroscopic measurements.
Variable Temperature:
We again have the ability to vary the temperature of the experiment,
but this time the temperature range is from about 0°C to 100°C.
The built in temperature variability is done to aid in the study of
biological molecules.
Below shows our Experiment 2 setup.
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