Evaporating Thin Films of Carbon60 Content from the guide to life, the universe and everything

Evaporating Thin Films of Carbon60

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This is a short guide on how to evaporate Carbon60 (or C60). C60 is an graphitic allotrope of Carbon (like diamond and graphite) which is shaped just like a soccer ball.

For this you will need:

  • A vacuum evaporator
  • C60
  • Patience

But first, you may be asking 'Why one would want to evaporate a film of C60?' Well, there are many reasons, but the main ones are:

  • To make spectroscopy (the study of chemicals using light) of the material easier.

  • C60 behaves differently in a thin film than it does as a powder or a single crystal.

C60 is usually supplied in the form of a crystalline powder. For best results the C60 should be 99.5% pure or better. A small amount of the powder (a fraction of a gram or less) should be ground to a fairly fine powder. The powder should then be transferred to a receptacle (or 'boat') made of Tungsten. Try not to waste it, it's expensive.

The boat is then connected to a power supply capable of delivering between 0 and 10 amps. The aim is to eventually get the boat glowing red hot, so the current required will depend on the resistance of the boat. The surface you want to evaporate onto (the substrate) is then placed about 10cm above the boat.

The evaporator should then be pumped down to about 10^-6 mbar (that's one millionth of a millibar) for a good hard and even film, the lower the pressure the better. Once the pressure is low enough the current should be applied to the boat.

This is the tricky (and most important) bit. If the current is applied too quickly then the C60 will jump around and hop out of the boat; while this is fun to watch, it makes a mess, and scientists are not messy people1. The current should be increased by about 0.2 amps every two to three minutes or even slower if you can manage it. Eventually there will be a slight increase in pressure; this signifies the start of evaporation. At this point all the impurities and CRAP (Carbon Related Amorphous Product) will be coming off and it is best to shield the substrate with a shutter for 10 minutes while all the CRAP is coming off.

The current may be increased further to speed up the process but a better film is obtained if the process is slow.

When finished turn off the current to the boat and allow the substrate to cool to near room temperature before letting the air back into the chamber and removing it.

1Not while sober anyway.

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