Photocathodes shall be used in the strongest possible electrical fields. The work function of these solids should be sufficiently low to enable effective photoelectric effect but also not too low because of said strong electric Fields, field emission occurs which rapidly destroys the cathode . The desired measurement allows us to characterize the cathode in this regard.
The ultra-high vacuum compatible vibrating capacitor method ("Kelvin Probe") are used in this instance. A corresponding device is present and installed in a vacuum apparatus, the samples are positioned with vacuum manipulators in front of the Kelvin detector. The method is first tested on reference samples with a known work function (metallic surfaces such as gold).