Studies of Na2KSb(Cs) Photocathodes.

摘要

More than 15 years after its discovery, Na2KSb(Cs) remains an important photocathode material, but control of its formation remains a problem. In these studies Auger electron spectroscopy (AES) was used to determine the atomic species present in the surface region during formation of Na2KSb(Cs) films. It was found that the electron bombardment incidental to the use of the AES technique could cause sample changes, but this problem was eliminated for samples that were heated during or after constituent depositions. Important conclusions derived from these studies are as follows: 1. Heating to temperature greater than 200 C at the 2Na + K3Sb yields 2K + Na2KSb stage of formation is probably required to produce antimony-rich material, if formation is approached from an alkali-rich standpoint. Alkali antimonide photocathodes of high sensitivity are thought to be 'p' type due to an excess of antimony. 2. The relative populations of the constituents are factors in determining which alkali species will leave when an alkali antimonide film is heated. 3. An alkali overlayer can exist on an alkali antimonide sample that is alkali-deficient in the bulk. 4. An alkali overlyaer is probably present on photocathodes of high sensitivity, and Cs is probably present in that overlayer.