Photoelectron emission in the extreme ultraviolet region

Photoelectron emission from solid tungsten, nickel, and semitransparent aluminum cathodes exposed to ultraviolet radiation between 256 A and 1216 A has been studied with planar retarding-potential analyzers. The resulting current-voltage diagrams (CVDs) for these three metal cathodes are essentially identical. The CVDs comparing photoelectron emission from the front and rear surfaces of the semitransparent aluminum cathode are also identical. A retarding-potential analyzer having near-spherical geometry was also used to obtain CVDs for the photoelectrons emitted from the rear surface of a thin-aluminum cathode. The value of retarding potential detectors for limited spectral resolution in the extreme ultraviolet is discussed. A comparison of the CVDs for the thin aluminum cathode indicates that the spectral discrimination achieved with a spherical retarding-potential analyzer is superior to that obtained with a planar one. Both the planar and spherical detectors consisted of a retarding-potential analyzer coupled to an electron multiplier. The CVDs obtained by using the multiplier either as a photoelectron counter or in dc operation were found to be identical. The photoelectric yields of several metal and alkali halide cathodes commonly used in the extreme ultraviolet were also compared. Those of CsI and LiF were found to depend upon cathode thickness and to be sensitive to the time of aging in air. Preliminary data on the absolute yield of tungsten between 31.6 A and 304 A are presented. (Author).