The diffusion pump is an oil-based vacuum pump, that is used for obtaining different levels of vacuum – even high vacuum of 10 powered -9 Pascal. In this system the oil is boiled by a heating with a heater. Next, the jets of vaporized oil grab the gas molecules in the chamber and transport them to the colder chambers walls where oil condensates and moves down. At this stage the captured gas molecules are released and removed from the system with a pre-vacuum pump. The #diffusionpump has very high pumping speeds and it can even be used for the pumping of corrosive gases. The downside however, is the possibility of contaminating the vacuum system with oil and therefore oil traps are highly recommended.
Vacuum can be understood as space from where matter (for example air) has been removed. It naturally exists in outer space but for certain applications, like materials characterization techniques, it needs to be achieved artificially. The desired level of vacuum is obtained with the help of a suitable vacuum pump. For example low vacuum (low quality vacuum with higher pressure) can be generated with a diffusion pump, scroll compressor pump, rotary vane pump, diaphragm pump or a sorption pump. High vacuum (high quality vacuum with very low pressures) however, can be obtained with high vacuum pumps such as the turbomolecular pump, ion pump, titanium sublimation pump and cryopump. The level of vacuum is measured with devices called vacuum gauges (vacuum meters) like the thermocouple gauge, pirani gauge, penning ionization gauge and the quadrupole mass spectrometer (analyzer). The working principle of vacuum pumps and vacuum gauges is explained with 3D animations in the video lecture above.