A New Spin on Photoemission Spectroscopy Page: 53 of 259
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2.2 Energy resolution
The decades after the explanation of the photoelectric effect continued to see a huge
amount of effort, both experimental and theoretical, aimed at understanding the photo-
electric effect more thoroughly. Instrumental improvements in magnetic and electrostatic
electron energy analyzers, various semi-monochromatic light sources, and improving vac-
uum pressures aided in the precision that photoelectron energies could be measured. Ex-
perimental effort was matched by the rapid progression in the theoretical understanding of
atomic, molecular, and solid state structure with quantum theory. These advances allowed
photoelectric experiments to evolve into a technique for studying the electronics of these
Due to conservation of energy in the photoemission process, it was realized that mea-
suring the kinetic energy of a photoemitted electron in vacuum allows the calculation of its
binding energy in the solid if a well-monochromatized light source is used. This is expressed
EK =hv - ( - JEB (2.2)
where EK is the kinetic energy of the photoelectron in vacuum, measured with respect
to the vacuum level, (F is the work function, hv is the photon energy, and EB is the
binding energy (a negative value measured with respect to the Fermi level, EF). If electrons
emitted at all angles are collected together (an angle-integrated experiment), or equivalently
a polycrystalline sample is used, the distribution of photoelectrons in kinetic energy can then
effectively map the density of states (DOS) of the sample's electronic structure. This idea
is shown schematically in Figure 2.4. A sample has a certain DOS (N(E) in the figure)
which includes the so-called "core levels" of distinct inner-shell electron energy states, as
well as a valence band at Ep dictated by the energy bands formed by the delocalized
valence electrons. An incident photon can promote an electron in this DOS upwards in
the energy diagram by an amount Lw. Electrons promoted above the sample's vacuum
level can physically escape the sample and can be detected by an energy resolving electron
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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/m1/53/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.