Next, the valve to a "roughing" vacuum pump is opened to take the load lock down to a pressure of less than one millionth of an atmosphere (10-6).
The bottom of the load lock (which also serves as a vacuum seal) is then lowered. The pressure falls to that of the center chamber, which is generally at a vacuum of lower than 10-12 atmospheres (!).
This sounds excessive, but at 10-12 atmospheres there are still 1010 air atoms per cubic liter running around. Any more and MBE really doesn?t work.
