36
3 Modification of the Work Function
Fig. 3.1 Schematic illustration of cross-sectional atomic arrangements for three main strategies of
work function modification
of binary compounds using this trend, the relationship between the work function
and Pauling’s electronegativity, and the representation of Pauling’s electronegativity
using the effective radius and the number of valence electrons.
As we saw in Sect. 2.3, the work function of a polycrystalline pure metal has a
strong correlation with Pauling’s electronegativity χ . Pauling’s electronegativity has
been found to also have a strong correlation with the number of electrons per atom
that participate in the bonding, n, and the effective radius of the atom in the bonded
state, r [2].
χ = 0.31
n + 1
r
+ 0.50
(3.1)
The relationship between
n+1
r
and Pauling’s electronegativity is shown in Fig. 3.2,
which was prepared using data in Table 1 in Ref. [2]. Except for Ag, Au, and Cu,
the points roughly lie on a straight line. The large deviation for Ag, Au, and Cu is
explained in Ref. [2] as follows: “Ag, Au, and Cu are known to form compounds
Fig. 3.2 Relationship
between (n + 1)/r and
Pauling’s electronegativity
for many elements (see text
for explanation of n and r)
Ag Cu
Au
(n+1)/r