B3b. Glow Discharging PDF Format

Carbon coated grids are exposed to ions to change the surface charge of the film. Many macromolecules have positive charges exposed at their surface. Exposing the carbon film to a reduced atomosphere under a high voltage renders the films hydrophilic and negatively charged. This allows the sample to spread more evenly and adhere to the surface of the grid.

Procedure Outline:
  1. Mount grids
  2. Insert grids into vacuum evaporator
  3. Replace bell jar but do not close lid
  4. Prepare glow discharge unit
  5. Open both nitrogen valves
  6. Begin vacuum cycle
  7. Set desired vacuum
  8. Glow discharge
  9. Stop glow discharge and vent chamber
  10. Retrieve grids
  11. Shut down procedure
 Materials needed to glow discharge support films:
  • Emitech K950 vacuum evaporator (room B421)
  • Glow discharge head (w/ Emitech K950)
  • Glass slides (precleaned)
  • Double sticky tape
  • Nitrile or Latex Gloves
In Depth Procedure: (Click on each thumbnail for a larger image. Click on the large image to close.)
1) Mount a few grids to a clean glass slide.
a) Mount a piece of double sided tape on the slide.

b) Attach a few carbon coated grids to it by touching just the very edge of each grid to the edge of the tape (Fig. 1).

c) Glow discharge only enough grids for immediate use.
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Fig. 1.
2) Place grids in vacuum evaporator.
a) Tip the lid back that contains the carbon coating unit.

b) Place slide with grids on the specimen stage (Fig. 2).
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Fig. 2. Note: The glow discharge unit is in place on top of the bell jar and the carbon coating unit is tipped back.
3) Prepare the glow discharge head.
a) Take the glow discharge unit, which is normally stored in the stainless-steel container behind the evaporator, and place it in position on top of bell jar (Note Fig. 2).
b) Close the needle valve on the glow discharge head (Fig. 3).
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Fig. 3.
4) Open both of the nitrogen valves on the wall behind the evaporator by turning them CCW.

5) Begin the vacuum cycle.
a) Switch ON both the vacuum evaporator and the glow discharge control units. The switches are in the back of each unit on the right, just above the power cord.
b) Press the "Start" button on vacuum evaporator (Fig. 4).
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Fig. 4.

c) Wait for turbomolecular pump to reach 100% speed as observed on the screen of the vacuum controller unit. There is no need to wait for the bell jar to reach high vacuum. A high vacuum is undesirable when glow discharging.
6) Set the desired vacuum.
a) When the turbomolecular pump reaches 100%, crack open the needle valve on the glow discharge head slightly. Observe the change in bell jar vacuum.

b) Continue to open the needle valve to raise the pressure in the bell jar until the vacuum gauge reads 2x10-1 torr.
7) Begin glow discharge.
a) Set the timer on the glow discharge unit (20-30 sec is sufficient).

b) Push the "Start" button on glow discharge unit.
c) Check for a purple-orange glow emanating from the glow discharge cathode (Fig 5). If necessary, turn the rheostat knob on the glow discharge unit clockwise until the glow appears. The timer will shut off the power automatically.
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Fig. 5.
8) Stop the glow discharge and vent the chamber.

a) Push the "Stop" button on the vacuum evaporator main unit.

b) Close the needle valve.

c) Wait until the chamber is vented.

d) If the chamber does not come fully to atmosphere, hit the "Stop" button again.
9) Retrieve the grids
a) Remove the glow discharge head and replace it in the storage container.

b) Retrieve your grids.
10) Shut down procedure
a) Close the carbon-coating apparatus lid.

b) Shut off the power to both units.

c) Close both nitrogen valves by turning them CW.
Last edited August 18, 2004