A New Spin on Photoemission Spectroscopy Page: 49 of 259
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Figure 2.1. Schematic of Hertz's famous experiment demonstrating the photoelectric effect.
Large inductors (a,e) powered by a battery (b) drive spark gaps (d,f). When switch (c) is
open, primary spark at (d) was found to influence the possibility of spark at (f). Influence
of primary spark could be shielded with a metal plate (p). Figure adapted from ref. 31.
most influential contributions was performed by Philipp Lenard, who began his career as
an assistant to Hertz. Lenard began to investigate the velocity distribution of the photo-
electrons, although at the time they were not understood to be electrons, but were referred
to as cathode rays. He wondered if adsorbed gases on the cathode had an influence on his
measurements, and he began doing his photoemission experiments in vacuum tubes, such
as shown in Figure 2.2(a). With such an apparatus, he performed many experiments on the
effect of external electric and magnetic fields on the cathode rays, and used retarding poten-
tials at the anodes to study their velocity distributions. He came to three key conclusions
in 1902 which had no immediate explanation.33 First he noted that the number of cathode
rays depended on the light intensity. Second, he found that cathode ray velocity did not,
however, depend on the light intensity. Finally, he found that the velocity was dependent
on the light frequency. Lenard later received the 1905 Nobel prize for his work with cathode
rays, which he described as "negatively charged quanta of electricity". It is interesting to
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Jozwiak, Chris. A New Spin on Photoemission Spectroscopy, thesis or dissertation, December 1, 2008; United States. (https://digital.library.unt.edu/ark:/67531/metadc1014237/m1/49/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.