Characterization of diamond film and bare metal photocathodes as a function of temperature and surface preparation Page: 4 of 8
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The photoelectric process in a
semiconductor take place when a photon is
absorbed and converted into a free electron,
i.e., raised from the valance band into the
conduction band. Additionally, to escape
to the vacuum level the electron must have
sufficient energy to overcome the electron
affinity. In semiconductors the electron
scattering loss processes are negligible
relative to losses by phonon scattering or
interaction with the lattice. This process is
much smaller than the electron scattering in
A photocathode test stand (PCTS) (fig.l)
was assembled to conduct scaled
experiments on the subject photocathode
materials. An ArF laser, 193 nm (photon
energy 6.4eV) was selected to illuminate
the photocathodes to achieve a reasonable
quantum efficiency on a bare Al
photocathode used as a baseline reference.
The light beam. normal to the cathode
surface, is able to be varied in intensity by
over one order of magnitude through the
use of multiple, thin quartz attenuating
plates. The photocathode is able to be
radiatively heated from ambient to 200C
The diode vacuum chamber is pumped with
1500 /s cryopump. The planar diode
(fig.2) is configured with an easily
removable cathode. The anode is a >93%
transparent W fine wire mesh screen. The
tubular charge collector contains a defining
to size the illuminating laser beam and
three UV transmissive fiberoptics, at the
aperture, feeding a line filtered photodiode
to sample each light pulse. The photodiode
is calibrated to a laser energy meter with
the cathode removed. The diode operates at
30kV d.c. and has an A-K gap of 6.7mm.
The selection of aluminum as the bare
metal photocathode was made based on
mechanical properties and work function.
The cathode was diamond turned aluminum
alloy with a 1 micron layer of pure
aluminum vapor deposited on the emitting
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Shurter, R.P.; Moir, D.C. & Devlin, D.J. Characterization of diamond film and bare metal photocathodes as a function of temperature and surface preparation, article, July 1, 1996; New Mexico. (digital.library.unt.edu/ark:/67531/metadc667849/m1/4/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.