MMR Low Temperature Measurement

Venting/Mounting your sample

A cylinder of industrial nitrogen is used to vent the system to atmosphere. Whenever you are flowing nitrogen into the chamber and the window is in place, hold your gloved hand over the window.
  1. Open the vent valve all the way.
  2. Open the main tank valve on the industrial nitrogen cylinder. DO NOT adjust the tank regulator; it has already been adjusted to 40 psi. While this may seem like a low pressure for compressed gas, it's more than enough to pop the window off if you're not careful.
  3. Use an allen wrench to slowly open the vent regulator valve for the argon adjacent to the vent valve. You should be able to hear the gas entering the system. Make sure to hold a gloved hand over the window as the positive pressure inside the chamber may unexpectedly pop the window off. (Ask Tim Wisleder if you don't believe this can happen.)
  4. With nitrogen flowing into the chamber, remove the window by screwing in the nylon screws to push the window up.
  5. Once you've removed the window, you can turn up the flow of argon to keep the chamber free of moisture.
  6. Mount the sample:
    1. The sample stage is made of glass and is supported only at the entry point to the chamber. Do not apply pressure to the sample stage.
    2. Move the probes away from the stage.
    3. Remove old sample (if present):
      • Carefully remove sample with tweezers.
      • Use a cotton swab soaked in isopropanol to remove the thermal grease from the sample stage.
      • If desired, use the hot air gun on low setting for 10-15 seconds to dry the sample stage. Be sure to move the gun around continuously.
    4. Apply thermal grease to the stage using a cotton swab.
      • Use only Dow Corning Thermal Grease #340. This should be wrapped in a clean wipe in the drawer beneath the probe station. Please store the grease in this manner.
      • You only need a tiny amount to mount the sample to the stage. Excessive grease may get on the probe tips or on the front of your sample.
      • It's easiest to apply the grease with the wooden end of a cotton swab. There should be a supply of wooden end cotton swabs (as opposed to q-tips) in the drawer beneath the probe station, either in a bag or wrapped in a clean wipe, next to the thermal grease.
      • Do not get thermal grease on parts of the J-T refrigerator other than the gold rectangle.
      • Carefully place your sample on the stage. The gold rectangle is the only part that changes temperature; keep this in mind when you position your sample.


  1. Place the window in the opening, making sure that the holes for the nylon screws ARE NOT aligned with the holes beneath the window.
  2. Close the main tank valve on the industrial nitrogen cylinder.
  3. After the pressure reading on the vent regulator valve gauge (next to the vent valve) goes to 0, close the vent regulator valve and the vent valve.
  4. Make sure the turbo pump is set to low speed operation; this is important as we no longer have a house vacuum connection to rough out the pumping station. Pressing the low speed button toggles between the regular and low speed operation modes; the low speed mode is indicated by "LS" on pumping station display.
  5. The window should seal; if the window does not seal, repeat the vent and evacuation procedures, realigning the window with the opening.

Purging the J-T Refrigerator

Once the chamber pressure has reached 10mTorr:
  1. Make sure the high pressure nitrogen (HPN) tank regulator is closed.
  2. Open the HPN main tank valve.
  3. Set the HPN regulator to 500 PSI.
  4. Record the tank pressure in the "before" column of the log book.
  5. Purge the system for at least 3-5 minutes (20 minutes if the system has been clogging). If you're going to cool down to 80K it's advisable to purge the system for at least 10 minutes; if you're planning on doing some high temperature measurements before your low temperature measurements, 3-5 minutes is sufficient.

Using the System

  1. Turn on the K20 temperature controller.
  2. The temperature range of the current refrigerator is 80K to 730K.
  3. If you want to cool, increase the HPN to 1500-1800 PSI.
  4. If you want to heat, leave the HPN at 500 PSI.

Venting after Using the System

  1. Turn off the K20.
  2. Record the HPN tank pressure in the "after" column of the log book.
  3. Close the HPN main tank valve.
  4. When the HPN regulator read 0, close it..
  5. Turn off the turbo pump. Let it spin down completely.
  6. Follow venting procedure above.
  7. Remove sample and clean off the thermal grease with a cotton swab and isopropanol.
  8. Replace the window.
  9. Turn on the turbo pump station at its low speed setting to evacuate the chamber and seal the window.
  10. Clean up after yourself.
  11. Fill in the log book.
Revision History:
Original: 09/24/1996 Robert D. Underwood
Revised: 09/24/1999 Robert D. Underwood
Revised: 02/23/2000 Robert D. Underwood
Revised: 01/23/2002 Nadia Pervez
Mangled: 07/15/2002 someone else
Revised: 06/25/2003 Nadia Pervez
Revised: 07/03/2003 Nadia Pervez