Procedures for the Preparation of Carbon Support Films
Back to Techniques Back to E6300/6700
A. Preparation of normal carbon support films
1. Copper grids should be pre-cleaned by sonicating for 10 seconds in acetone
followed by 10 seconds of sonication in ethyl alcohol. Allow grids to dry on
filter paper in a dust-free environment before use.
2. Add 0.12g of Formvar powder to 50 ml of ethylene dichloride and mix well
on a magnetic stirrer until dissolved. Pour the solution into a clean coplin
jar.
3. Clean a glass slide with water and detergent. Rinse well to make sure that
all of the detergent is removed and finally rinse in de-ionized water before
drying with a paper towel. Blow off any lint on the slide with compressed air.
Place the slide in a dry, dust-free environment such as on filter paper under
an upturned beaker. If there are problems in getting the plastic film to be
released from the slide (Step 5), using a slide that has not been as thoroughly
cleaned might help.
4. Dip the cleaned slide into the Formvar solution (Fig. 1-1) and touch edge
to filter paper to drain off the excess fluid (Fig 1-2). Dry upright in a dust-free
environment (this requires 5 to 10 minutes.).
5. Score the edges of the Formvar film with an acetone-cleaned razor blade
(Fig. 1-3). Breathe on the slide to loosen the film, and slowly slide off onto
a clean water surface by immersing the slide into the water at a ~15° angle
(Fig. 1-4). Place grids, dull/rough surface down, onto good (uniform, grey
colour, un-wrinkled, etc.) areas of the film. Place a small piece of clean,
white office paper onto the surface of the grids and film and allow the paper
to soak up water. Pick up the paper, grids and film and place in a covered
petri dish to dry.
6. Carbon coat film according to directions (see Section C) to desired thickness
(A light-brown colour indicates a thickness of <100Å.).
7. Place the paper and coated grids onto a piece of filter paper that is soaked
with ethylene dichloride in a covered petri dish. One half hour should be sufficient
time to dissolve the Formvar film and not damage the carbon support. Remove
the grids and paper and allow them to dry in a dust-free area.
B. Preparation of perforated carbon support films
1. Copper grids should be pre-cleaned by sonicating for 10 seconds in acetone
followed by 10 seconds of sonication in ethyl alcohol. Allow grids to dry on
filter paper in a dust-free environment before use.
2. Add 0.17 g of Formvar powder to 50 ml of chloroform and mix well on a magnetic
stirrer until dissolved. Pour the solution into a clean coplin jar.
3. Clean a glass slide with water and detergent. Rinse well to make sure that
all of the detergent is removed and finally rinse in de-ionized water before
drying with a paper towel. Blow off any lint on the slide with compressed air.
Place the slide in a dry, dust-free environment such as on filter paper under
an upturned beaker. If there are problems in getting the plastic film to be
released from the slide (Step 6), using a slide that has not been as thoroughly
cleaned might help.
4. Add about 50 drops of a 50% glycerol/water solution to the surface of the
Formvar solution. Place the tip of a probe sonicator onto the surface of the
solution and sonicate until mixed. Sonication intensity should be great enough
to "violently" cause the solution to bubble. This often requires
not much more than about 5 seconds. This should produce numerous holes that
are 1-2 µm in diameter and suitable for use with frozen-hydrated samples. Sonicating
for longer periods of time produces smaller holes in the film.
5. Immediately after sonicating, dip the cleaned slide into the Formvar solution
(Fig. 1-1) and touch edge to filter paper to drain off the excess fluid (Fig
1-2.). Dry upright in a dust-free environment for about 5 to 10 minutes.
6. Score the edges of the Formvar film with an acetone-cleaned razor
blade (Fig. 1-3). Breathe on the slide to loosen the film, and slowly
slide off onto a clean water surface by immersing the slide into the
water at a ~15° angle (Fig. 1-4). Place grids, dull/rough surface down,
onto good (uniform, grey colour, unwrinkled, etc.) areas of the film.
Place a small piece of clean, white office paper onto the surface of
the grids and film and allow the paper to soak up water. Pick up the
paper, grids and film and place in a covered petri dish to dry.
7. Place the paper with the film and grids onto a methanol-soaked piece of
filter paper in a covered petri dish for about 30 minutes. This should perforate
any pseudo-holes (these occur when a small drop of glycerol was present but
it was not enough to perforate the film) that may be in the films. After allowing
the paper and film to dry, the grids may be examined in a light microscope
under phase contrast to determine the quality of the films.
8. Carbon coat film according to directions (see Section C) to desired thickness
(A light-brown colour indicates a thickness of < 100Å.).
9. Place the paper and coated grids onto a piece of filter paper that is soaked
with ethylene dichloride in a covered petri dish. One half hour should be sufficient
time to dissolve the Formvar film and not damage the carbon support. Remove
the grids and paper and allow them to dry in a dust-free area.
C. Use of a shadow evaporator for carbon coating plastic films
1. Turn shadow evaporator on: Turn both the main and mechanical pump switches
on. Move the black-knobbed, manifold valve handle downwards to "backing" position.
Open the air inlet valve and CAREFULLY remove the implosion shield and bell
jar. Set the bell jar upside down on the rest on the adjacent cabinet
2. Set up carbon coating apparatus: Plug one lead to ground ("E")
and the other to "1" (See lower diagram). Remove the cylindrical
glass shield. Release the tension spring that holds the right carbon rod in
place and remove the rod. File the edge of the left carbon rod flat with a
piece of emery cloth. Replace the right rod with a fresh one or sharpen it
by the procedure described below.
3. Carbon rod sharpening procedure: Place the carbon rod in the chuck of the
sharpener. Pull the rod out until its edge is aligned with the edge of the
aligning arm and then tighten the chuck. Turn on the sharpener and run the
first sharpener tool against the rod until a conical point is formed. Then
run the other sharpener tool against the rod until a narrow point is formed.
Turn off the sharpener and clean off all carbon dust. Put the newly sharpened
rod in the chuck of the carbon coater and tighten. Replace the tension spring
and then the glass shield.
4. Set up grids: Place the grids and paper support on a piece of filter paper
on top of the base of the carbon coating apparatus (See diagram below). Place
a thumbtack along side the slide. This provides a "shadow" on the
filter paper and helps you determine the relative thickness of the carbon coating.
5. Diffusion pump warm up: Replace the bell jar and the implosion shield. Close
the air inlet, and move the manifold valve handle slowly upwards to the roughing
position. Allow the vacuum to reach 0.04 Torr on the bell jar gauge and then
move the handle downwards to backing. IMPORTANT: Turn on the water supply.
The water supply-line valve is located on the wall behind the shadow evaporator.
Turn on the diffusion pump switch and allow the pump to warm up for 15 minutes
before continuing.
6. Obtaining a high vacuum: Move the manifold valve handle slowly upwards to
the roughing position and allow the vacuum to reach 0.04 Torr on the bell jar
gauge. While waiting for the vacuum to recover, fill the baffle with liquid
nitrogen. When the bell jar vacuum has reached 0.04 Torr, move manifold valve
handle down to the backing position. Depress the metal guard beneath the red
mains valve knob and move the knob handle upwards to the open position Allow
the vacuum to reach a minimum of 2x10-5 Torr or better.
7. Carbon coating: Turn the electrode selector to #1. Turn the electrode switch
on. Slowly turn the electrode current control knob until there is a slight
glow at the point where the two carbon rods meet. Slowly increase the current
until the rods become white hot. The proper current setting should be just
before the point where the carbon starts to sputter. Frequently monitor the
thickness of the carbon by turning down the current, checking the darkening
of the filter paper and then turning the current back up again.
8. Diffusion pump cool down: Turn down the electrode current control knob and
turn off the electrode switch. Make sure the manifold valve is set to the backing
position and close the mains valve. Open the air inlet, remove the implosion
shield and bell jar and remove the grids. Then replace the bell jar and implosion
shield, close the air inlet and move the manifold valve handle to the roughing
position. Allow the vacuum to reach 0.04 Torr on the bell jar gauge, move the
manifold valve handle to the backing position, turn off the diffusion pump,
and allow the pump to cool for 20 minutes.
9. Turn Shadow Evaporator off: Close the manifold and turn off the mechanical pump and main power switches. Turn off the cooling water.
D. Glow discharging carbon films
1. Note: Place the very edge of your carbon coated grids along the edge of a piece of double-sided tape on a glass slide. This will help to prevent your grids from flying around inside the shadow evaporator when the air release switch is opened.
2. Turn shadow evaporator on: Turn the main power switch on, turn on the mechanical pump and move the manifold valve handle (black knob) downwards to the backing position. Open the air inlet. CAREFULLY remove the implosion shield and bell jar.
3. Set up glow discharge unit: Plug the lead into the proper receptacle (BNC connector). Place the glass slide with your grids on the unit and replace the bell jar and implosion shield. Close the air inlet, turn the butterfly switch by the current gauges to glow discharge and move the manifold valve handle slowly upwards to the roughing position. Allow the vacuum to reach 0.2-0.15 Torr on the bell jar gauge. The manifold valve may be turned to the closed position if the vacuum rises above 0.10 Torr.
4. Glow discharging: Turn the electrode selector to position #1 and turn the electrode switch on. Slowly turn up the electrode current until there is a bright purple glow surrounding the glow discharge unit. Maintain this setting for approximately 10 seconds while monitoring vacuum. Turn off the electrode current control knob and the electrode switch. Move the manifold valve handle to the backing position. Turn the butterfly switch back to the evaporator setting.
5. Turn shadow evaporator off: Slowly open the air inlet to prevent your grids from being blown around the bell jar. Remove the grids, replace the shields and then close the air inlet. Move the manifold valve to the roughing position. Allow the vacuum to reach 0.04 Torr on the bell jar gauge before moving the manifold valve handle to the horizontal (closed) position. Turn off the mechanical pump and the main switch.
Acknowledgement: Quorum Technologies would like
to thank Norman Olson at Purdue University for
permission to reproduce is article.
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