40
3 Modification of the Work Function
(a)
(b)
Fig. 3.7 a Phase diagram and work function in Nb–Mo system (the bottom figure is replotted from
the figure in Ref. [4]). b Phase diagram and work function [5] in Ag–Au system. c Phase diagram
and work function [6] in Ag–Pd system. d Phase diagram and work function [7] in Cu–Pd system.
e Phase diagram and work function [8] in Cu–Ni system
but in a concave manner rather than linearly (Fig. 3.7b) [5]. The deviation from
a straight line agrees with the trend that the work function of a binary compound
tends to be closer to that of the element with the lower work function of the two
constituent elements [1], as mentioned at the beginning of Sect. 3.1. For Ag–Pd, a
similar composition dependence has been reported (Fig. 3.7c) [6]. For Cu–Pd [7] and
Cu–Ni [8], where a solid solution is formed at a high temperature but a compound
is formed at a low temperature, a slight concave deviation from a linear relationship
has been reported (Fig. 3.7d, e, respectively).
3.1.2 Interstitials (Metal Carbides and Nitrides)
When the second element mixed with the mother metal is a small nonmetal atom
such as carbon or nitrogen, the second element is not substituted at the position of