Research: Instrumentation

We currently have two running scanning tunneling microscopy experimental setups:

  • Experiment 1 is dedicated to studying low temperature phenomena in 2D systems such as the cuprates.
  • Experiment 2 is a room temperature STM focused on biological applications.

Details of both experimental setups are given below.

Experiment 1

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.

 

Our entire Experiment 1 setup (left) and custom built STM (right) are shown below. Click the images for a more detailed view.


Experiment 2

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 and is achieved using multiple layers of peltier chips attached to the STM and the STM support system. The built in temperature variability is done to aid in the study of biological molecules.

 

Our Experiment 2 setup is shown below. Click the image for a more detailed view.