This puzzle can lead to a lesson(s) that connect the rate of gas removal the vacuum pump has to the rate of gas appearing in the chamber because of a leak (gas entering the chamber from the outside) or from a fixed amount of gas trapped in the materials within the vacuum environment (outgassing). This connection uses the mass transport and energy balance STEM concepts. The energy (power if normalized with time) available from the single stage pump to remove the gas from the chamber walls established a steady state vacuum (value defined by the flat part of the blue triangle plot) in the chamber. The two-stage pump has a greater pumping speed (more energy per second) thus; this pump can pull more material faster from the walls. (Students can use the two plots to calculate and then compare the two pumping speeds.) Thus, if outgas type material exists, the pressure in the sputter deposition chamber will start to drop sooner when the two-stage pump is used. The natural technology extension to these science and mathematics concepts is a review of the mechanical construction of a single and double stage pump to see why the two stage pump has a higher pumping speed. Ask if the pumping speed for the 2-stage pump after outgassing will be the same as before outgassing began. This is a good way to push student STEM knowledge as it relates to pump mechanics and gas behavior.
The Tech now knows that the vacuum system is “outgassing”.YES
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