The Photoelectric Properties of the (100) and (111) Faces of a Single Copper Crystal

The two faces were cut from the same single crystal, and etched to remove the broken surface pieces and to expose only crystal facets which were parallel to the geometric boundaries in question. Care was taken to prevent any contacts between the prepared planes and foreign objects. The two specimens were heated simultaneously by electronic bombardment at various red-heat temperatures for over 1500 hours in a good vacuum. The photoelectric thresholds were measured by the use of filters as the outgassing proceeded. During readings, the pressure was less than 5×{}10^-8 mm Hg. After 500 hours of outgassing the threshold wavelengths were approximately 2540A for the (111) face and 2200A for the (100) face. The results show that the etching produced by evaporation should be avoided in such an experiment.