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Carbon Coating Formvar-covered Grids with the Emitech K950XPDF

The instructions here do not go into all of the available parameters on the Emitech equipment but should show what is needed by most users. Also, different labs have slightly different techniques for making carbon films. This procedure is used by researchers in the Baker Lab. If you need other functions not listed in these instructions, such as the Film Thickness Monitor, please see Norm Olson.

Needed Materials:

  • Emitech K950X
  • Carbon rods
  • Pre-cleaned glass slides
  • "Scotch" tape
  • Formvar-covered grids on paper
  • Fine-grit sand paper
  • Paper towels
  • Nitrile or latex gloves
  • 95% ethanol for cleaning the bell jar
Preliminary Procedures (Click on each thumbnail for a larger image. Click on the large image to close.):
  1. Put on latex or nitrile gloves. Do not touch anything in the chamber with your bare hands.
  2. Turn on the K950X main unit (Fig. 1). The switch is above the power plug in the back on the right side.
  3. Tip back the carbon coating unit that sits on top of the bell jar. Place a paper towel on top of the open bell jar to prevent carbon dust or specs from getting into the chamber.
  4. Take a piece of fine-grit sand paper and smooth the surface of the flat-end of the carbon rod (anvil) in the right-hand electrode (Fig. 2). If the rod is too short loosen the chuck and pull out more of the rod or replace it .
  5. Replace the rod (spigot) in the left-hand chuck or sharpen the one that is there. The rod can be sharpened with either the electric or the manual rod sharpener. The sharpened end should be at least 4-5 mm long. During the evaporation process, the sharpened end should never be so short that the anvil and spigot touch. This can cause a fuse to blow out. Smooth the tip of the spigot with the sand paper. When tightening the carbon rods make sure that there is enough spring tension in the chucks so that the rods will remain in contact during evaporation. The quality of the connection and the length of the sharpened spigot are important to achieve reproducible results.
  6. Remove the paper towel from the top of the bell jar. For routine carbon coating leave the cap on the crystal of the FTM (Fig. 3).
  7. Tape the piece of paper with your grids to a glass slide. Use the minimum amount of tape necessary. Too much tape is difficult to remove and could cause you to dislodge your grids on its removal. Place the slide into the slide-shaped recess on the stage. Run a finger around the periphery of the rubber seal on the bell jar and the contact point on the coating assembly to remove any dust that may prevent a good vacuum. Carefully lower the coating assembly onto the top of the bell jar.
K950X Menu Items:
  1. From the initial startup menu, hit the ENTER button on the K950X twice to pass through the parameters menu and get into the Evaporating submenu. The STOP button can be hit any time to escape back to the initial menu (Fig. 4).
  2. The display will show Evaporating Mode: Single Pulse. If it shows anything other than single pulse hit the UP or DOWN buttons in the Evaporating mode until you see Single Pulse. Hit ENTER.
  3. The next submenu item is Outgas Time 00:00:20 H:M:S. Leave it as is. Hit ENTER.
  4. The following submenu item will show Evaporate Time and the amount of time that was previously entered. Hit the UP or DOWN buttons to increase or decrease the time until you get to your desired time of evaporation. For example, a time of 200 milliseconds may be good for standard carbon films and 400 milliseconds for perforated carbon films. Figure 5 shows an example of evaporation times, resultant densities of carbon on white paper, and the film thickness as measured by the FTM. Hit ENTER when you reach your desired time.
  5. No. Evap. Pulses: 1. Hit ENTER.
  6. Variable Evap. Time 00:03:00 H:M:S. Hit ENTER. This should get you back to the initial startup menu.
  7. Hit ENTER then DOWN once and ENTER to get into the Pump Cycle menu. Pump Hold Enabled: will show either Yes or No. Hit UP or DOWN to get to No and select by hitting Enter. Hit Enter to bypass the remaining parameters.
  8. Hit ENTER then DOWN twice and ENTER to get into the FTM menu.
  9. FTM Enabled: No. If you see anything else hit UP or DOWN until it is set to NO then ENTER.
  10. Hit ENTER repeatedly until you leave the FTM menu.
  11. Hit ENTER to get into the parameters menu and then DOWN three times until you get to the Miscellaneous submenu. Then hit ENTER.
  12. Check to make sure that Stage Rotate Enabled is No. If it is not use the UP or DOWN buttons to set it that way. Then hit ENTER until you get back to the main menu.
Evaporation Procedures:
  1. Hold the top down onto the bell jar and Hit START. The vacuum reading will change from Vacuum: No Vacuum to a vacuum reading and the Turbospeed value should increase. If it does not you have an air leak that will need to be corrected.
  2. Shortly after the Turbospeed reads 100% the Vacuum should read High Vacuum. Wait until the five-minute, timed setting runs out before proceeding. The menu will then read Press UP to outgas or DOWN to evaporate.
  3. Outgas the carbon rods. To do this press UP then slowly turn up the CURRENT dial until you see that the rods become white hot. Leave it that way for 5 secs. and then turn the CURRENT back down. After the time runs out the menu will read Press UP to outgas or DOWN to evaporate.
  4. Press DOWN. The rest of the process is automatic. You will see a warning on the screen ***About to Evaporate***. Look away from the rods until you see the flash reflected on the back wall. You will then be returned to the previous menu.
  5. Check the darkness of the coating. If you need repeat the process you may do so or else hit STOP. You will not be able, however, to change the parameters until the jar comes to atmosphere which then allows you to enter into the main menu.
  6. Air will be let into the chamber in pulses. This prevents your grids from being blown around the chamber. When the chamber comes to atmosphere remove your grids.
  7. If the bell jar is getting too dark to see through it is your responsibility to clean it. Protect your clothing from the carbon in the jar by wearing a lab coat. Remove the rubber seals. Clean the jar with paper towels, 95% ethanol and elbow grease. Be very careful. The bell jar is very slippery when wet and you could drop and break it. Rinse the jar with clean water, dry it with paper towels, replace the seals and put it back into position on the K950X. Lower the evaporating unit onto the jar. It is not necessary to re-pump the chamber.
  8. Turn off the power on the unit and clean up whatever mess there is in the area.
Obtaining Finer Grain Carbon Films:

The above procedures work well for holey carbon films and for continuous carbon films that are used for quickly checking the quality of your preparation. If image data is to be collected from particulate samples over carbon it is desirable that the carbon film grain be as fine as possible to reduce the noise in the images from the carbon. When the procedures listed under the "K950X Menu Items" paragraph above are followed the vacuum in the chamber is only about 3X10-4mbar when the display reads High Vacuum. At this vacuum you may get some sputtering of the carbon instead of an even evaporation. For finer grain carbon films modify the above procedures as described here:
  1. From the initial startup menu press ENTER to get into the parameters menu and then ENTER to get into the Evaporating submenu. The display will show Evaporating Mode:. Some individuals prefer to use Single Pulse (see instructions above) and others prefer the Variable mode which allows the user to increase the current manually. Use the UP or DOWN buttons to change the option and hit ENTER to make your selection. Hit ENTER to accept the remaining parameters.
  2. Hit ENTER then DOWN once and ENTER to get into the Pump Cycle menu. Pump Hold Enabled: will show either Yes or No. Hit UP or DOWN to get to Yes and select by hitting Enter. Hit Enter to bypass the remaining parameters.
  3. Hit the Start button to begin pumping. Follow the directions under Evaporation Procedures above. The Time Remaining: will countdown from 5 minutes, and after awhile, the display will show Vacuum: High Vacuum. After the initial five minute period the vacuum display will show the actual vacuum. Allow the evaporator to pump anywhere from a half an hour to over an hour until you achieve approximately 9X10-5mbar. A better vacuum produces finer grained films.
  4. The display now shows Press a key to continue. When you have achieved your desired vacuum hit a key to suspend the timing process. Then go into the evaporation procedure as described above. If you have set your Evaporating Mode: to Variable you can now slowly increase the current with the CURRENT knob. This must be done extremely slowly to prevent sputtering and carbon rod burnout which will increase the grain of your film.
  5. Continue your process as described above.

K950X
Fig. 1. Front of the main unit (K950X) displaying the initial startup menu.

Carbon rods in chucks
Fig. 2. Carbon coating unit showing the two carbon rods.

Chamber
Fig. 3. Inside the evaporation chamber. The recess where the slide sits and the FTM crystal are marked.

Menu
Fig. 4. Parameters menu on the K950X


Densities of carbon
Fig. 5. Example of the density of carbon coating on white office paper at various lengths of Evaporate Time (milliseconds). The thickness of the resultant carbon film (nanometers) is shown.

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