80
4 Measurement of Work Function
the threshold of the photoelectron emission yield is equal to φ. If the free electron
approximation is employed, the shape of the DOS near the Fermi level is represented
by a quadratic function. Therefore, the photoelectron emission yield is proportional
to (hν − φ)
2 . In practice, the photoemission current should be divided by the photon
intensity at each photon energy to obtain the photoelectron emission yield. By plotting the square root of the photoelectron emission yield as a function of the photon
energy, as schematically shown in Fig. 4.11, the threshold photon energy, which is
equal to the work function, is obtained. In Fig. 4.12, plots for polycrystalline Pt and
Al measured in air are shown as examples. Because measurements are performed
Fig. 4.11 Schematic
illustration of plot of square
root of photoelectron
emission yield versus photon
energy to obtain work
function (see text for
explanation)
Fig. 4.12 Plots obtained by
photoelectron emission yield
spectroscopy for
polycrystalline Pt and Al
measured in air