Walking around the right hand side of laser table, we see the beam machine in full glory. The main chamber is in the foreground with the interconnected second and first differential pumping stages and the molecular beam source chamber extending to the left. The differential pumping stages serve two purposes. First, they reduce the amount of gas in the molecular beam that reaches the main chamber. Second, collimating apertures between the differential stages ensure that nearly all molecules interacting with the nickel surface in the main chamber originate from the supersonic expansion, and not from background gases that may be present in the molecular beam source.
Surface chemistry is highly sensitive to the presence of contaminants on the surface of interest.
This level of vacuum minimizes the number of gas-phase species that may interact with, stick to, and contaminate the surface under study. The manipulator allows the nickel crystal to be rotated about a vertical axis and translated in three dimensions within the UHV environment. The QMS is located on the machine's beam axis. It is mounted on the end of the main chamber by the small flange visible just above the RF box. The DPs are backed by direct drive mechanical pumps that are located in a separate pump room behind the white wall.