6.2. Edwards 306 Vacuum Operating Instructions

Please sign in the log book whenever you use this instrument.

6.2.1. Start-Up from Either Cold Status or Partially Warm Status:

  1. To turn the instrument on from a cold start, first check the positions of the following controls:

    • The valve handle should be in the valves closed position and the rotary pump should be off. If the rotary pump is on and the valve handle is in the backing position, then begin at section"B" below.

    • The high vacuum gauge should be off.

    • The rotary pump, oil diffusion pump and air admit push-buttons should be off (not depressed).

    • The low tension (LT) and high tension (HT) push-buttons should be off (not depressed).

    • Wall circuit breaker should be off.

    • Cooling water should be off.

6.2.2. Turning the Instrument On:

  1. Turn the cooling water on by turning the valve (located right and to the rear of the evaporator) fully counterclockwise.

  2. Switch the circuit breaker on.

  3. Switch rotary pump on by depressing the rotary pump push-button.

  4. Turn the valve handle clockwise to the backing position.

  5. Switch the thermocouple gauge on and select the back position. When the vacuum is 50 millitor you can continue.

  6. Turn the oil diffusion pump on by depressing the difussion pump push-button. (Not necessary for glow discharging.)

  7. You must now wait approximately 20 minutes for the diffusion pump to reach operating vacuum. While waiting, fill the liquid nitrogen trap using the chrome funnel to the left of the vacuum chamber (two complete fills is usually adequate).

6.2.3. Start-Up from Partially Warm Status

  1. Make sure the high vacuum gauge is off.

  2. Depress the air admit push-button. Air will now enter the chamber through the silica gel air dryer to the left of the vacuum chamber. When the hissing noise stops (3-5 minutes) and the bell jar lifts approximately 1 mm off the base plate, the vacuum chamber is at atmospheric pressure.

  3. Very gently and slowly guide the bell jar up with the aid of the counter-weight mechanism. Take care not to hit the electrode posts to avoid chipping the bell jar. If the bell jar is accidently chipped, please notify a staff member as it will have to be replaced before any more evaporations can be made.

  4. Release the air admit push-button.

  5. Load your samples and metals to be evaporated into the vacuum chamber. Please remember that finger grease is a source of contamination. Wear gloves whenever possible. Remove flakes of carbon and dust from carbon gun assembly with a can of compressed air. You may want to place a piece of filter paper near your sample to indicate the thickness of the evaporated metals. Note that there are three different types of carbon rods currently in use. The very shiny rods (ultra high purity carbon) are the most resistant to heating. The medium shiny rods (high purity with a coarser surface texture than the ones mentioned above) are medium in resistance to heating. The very black, dull looking rods are the least resistant to heating. When choosing rods for your evaporation, be sure to choose two rods of the same type (same resistance). When preparing the rods for the evaporator, wear the white cotton gloves located in the drawer where the supplies for the evaporator are located.

    Important: If you are glow discharging grids, remove the carbon gun and affix the glow discharge collar onto the three support posts and the HT posts. Make sure the platinum leads that connect to the HT posts do not contact the metal of the glow discharge collar.

  6. Wipe the O-ring on the bell jar with your hand (no gloves) or Ross optical tissue. Observe the base plate, where the bell jar seals, for evidence of particles which may induce leaks.

  7. Check to make sure the protective O-rings at the base of the chamber are properly positioned to protect the bell jar from possible damage.

  8. Check to make sure the air admit button is not depressed.

  9. Slowly and carefully lower the bell jar and center it on the base plate.

  10. For metal shadowing: while holding the bell jar in position, push the valve handle in and turn it counterclockwise to the roughing position. When the thermocouple gauge reaches 90 microns (TC gauge switch set to rough position), you may continue. If 90 microns pressure is not obtainable in 5 minutes of rough pumping, there may be a leak at the base of the bell jar or you have introduced materials into the chamber that are too wet and they are outgassing. If this is the case, return the valve handle to backing and ask a staff memeber for assitance or vent the chamber (steps 3-16 from Section 6.2.3) and clean the bell jar O-ring and base plate.

    Important: Do not leave the valve handle in the "roughing" position for more than 5-10 minutes when the oil diffusion pump is hot.

    For glow discharging: Rough the chamber to approximately 150 microns (TC gauge set to rough position). Remove the rubber stopper from the glow discharge air inlet port and open the needle valve to maintain a roughing pressure of 150 microns. Switch HT on and turn power control to setting 20 on meter. Glow discharge sample for desired amount of time (1-2 minutes will make carbon coated grids hydrophilic). When finished, turn the power control 0 and switch HT off and trip green reset button. Close needle valve and replace rubber stopper. Turn valve handle to backing. Following instructions under "Venting the Chamber to Remove your Sample and Leaving the Instrument in Stand-by for the Next User."

  11. Turn the valve handle clockwise to the backing position and read the backing pressure on the TC gauge. Do not continue until it indicates a vacuum of 80 microns.

  12. Turn the valve handle counterclockwise to the roughing position and read the pressure on the TC gauge. Wait until the gauge reads 90 microns or lower.

  13. When the roughing and backing pressures are adequate (at least 90 microns on roughing and 80 microns on backing), it is possible to connect the oil diffusion pump to the vacuum chamber. To do this, turn the vacuum handle clockwise to the fine pumping position. The poppet valve (high vacuum valve) below the specimen stage will open slightly. (This may take several minutes.) When this occurs, open the valve fully by continuing to turn the valve handle clockwise to the open position. (Watch the thermocouple gauge while doing this; if the vacuum detriorates more than 20 microns with the TC gauge set to backing, you are opening the valve too quickly or the liquid nitrogen trap needs to be refilled.)

  14. Switch the high vacuum (ionization) gauge on. At first only ".10" will appear on the readout. After 30 seconds, a complete reading will be indicated. Allow a few minutes for the gauge to stabilize. If the reading on the gauge seems erratic, it may require a short period of degas. If necessary, switch to the degas position for approximately 3-5 minutes. Return the switch to the on position. The reading should now be stable.

  15. When the HV gauge reads less than 1 X 10^-5 Torr, you may continue. (Better: 2 x 10^-6 Torr.) (This may take 15-60 minutes depending on the size and type of sample being shadowed).

6.2.4. Vacuum Evaporation of Metals:

  1. Select the carbon (position 2) or filament (position 3) of the LT selector switch.

  2. Push the green reset button (located below the power control knobs).

  3. Push the LT push-button.

  4. Heat the carbon or filatment using the power control (variable resistor) until evaporation is complete.

  5. Release the LT push-button.

  6. Release the green reset button by depressing the red trip button.

  7. Return the power control to its full counterclockwise position.

6.2.5. Venting the Chamber to Remove Your Samples and Leaving the Instrument in Stand-by for the Next User:

  1. Follow steps 1-5 from Section 6.2.3.

  2. Remove samples from the vacuum chamber. Remove the filament from the chamber but leave the carbon gun in the chamber. In order to keep the carbon electrode assembly clean and dry, it is recommended that it remain under vacuum in the bell jar. The user that follows you will be responsible for cleaning it and reloading fresh carbon rods. As rotary shadowing is less frequently used, it is requested that the rotary stage be removed from the chamber, cleaned and returned to its storage place.

  3. Evacuate the chamber to low vacuum by following steps 9-12 from Section 6.2.3.

  4. If someone is going to use the instrument after you, leave the diffusion pump on and make sure the valve handle is in the backing position, the high vacuum and TC guages are off, and the cooling water is on.

6.2.6. To Shut the Instrument Off:

  1. Before shutting the instrument off, check to make sure the roughing pressure is 60 millitor and the backing pressure is 50 millitor.

  2. Turn the diffusion pump off and allow it to cool for at least 1 hour while pumping in the backing position.

  3. When the diffusion pump is cool, turn the cooling water off by turning the valve clockwise. (Stand-by.)

  4. The liquid nitrogen cold trap must be warm before you can continue. This will take approximately 8 hours from the time its last filling, so if you used the cold trap just leave the instrument in backing overnight to allow the trap to come to room temperature.

  5. When the liquid nitrogen cold trap is warm, push the valve handle in and turn it counterclockwise to valves closed.

  6. Turn the rotary pump off by releasing the rotary pump push-button.

  7. Switch the wall circuit breaker off.

  8. Vent the pump: flip the valve on left side of the unit to vertical for 5 seconds, then flip it back.

  9. Before leaving, please remember to return all supplies to their proper storage locations.