3.1 Mixing Elements
51
Fig. 3.15 a DOS near the
Fermi level for HfCx without
vacancies and with vacancies
both in the bulk and at the
surface [13]. b Density of
states of each component at
the Fermi level for HfC [14]
Fermi level
Hf-derived
(b)
Fermi level
(a)
hand, for WC and PtC, vacancy introduction will affect the surface term, and the
change in the work function will be more complicated, although if the structure of
WC is hexagonal, there is almost no involvement of carbon-derived electrons in the
Fermi level and the surface term will not be affected by carbon vacancies. Although
examples of calculations for nitrides are limited, similar schematic pictures of the
DOS near the Fermi level can be deduced from previous studies and are shown in
Fig. 3.18a [9] for 4d transition metal nitrides and Fig. 3.18b [9] for 5d transition
metal nitrides. It is speculated that for 4d metal nitrides the surface terms of the