Vacuum Evaporation
John Collins

In the study of physics as well as in industry the use of thermal deposition to lay down thin films of metal is pervasive. At SSU our system consists of a bell jar, mechanical and diffusion pumps, a high current low voltage circuit and a plasma generator.

The substrate (the material to coat) is held in place in the bell jar by tooling of our own design. Then the chamber is pumped down to less than 5E-5 torr. With the two pumps in tandem we routinely reach pressures as low as 1E-5 torr. A plasma is then generated by introducing a small amount of inert gas such as argon or nitrogen and applying 5000 volts. This ionized gas does a good job of releasing contaminants that cling to surfaces inside the bell jar. The coating material must be heated to evaporative temperatures by passing 120 amps through the material. The evaporating metal then coats the substrate.

We use our vacuum evaporation equipment to produce mirrors of very specific reflectance for use in fiber optics sensor experiments. Currently we are tooling up our machine to coat optic fibers. Operating, designing and optimizing the system for a given application are very useful skills in research and industry.