164
8 Hetero-Coordinated Interfaces
As the first wall material in a nuclear fusion device, Be/W alloying easily occurs
in the processes of plasma interaction within the wall for radiation protection [11,
12]. However, understanding the energetics and electronics of the interface alloy is
crucial to engineering such functional materials. Due to the electronic structures of
W (6s
2 5d
4 , delocalized d electrons dominate) and Be (2s
2 states dominate), a strong
influence of the alloying on both the core and the valence electrons is apparent, but
insofar, it remains poorly understood.
Another example is the catalytic nature and ability of alloys. Ag and Cu often form
alloys with Pd because their interactions typically result in improved heterogeneous
catalysts [16–18] that behave quite differently in reactions—reduction or oxidation
[19, 20]. Cu/Pd is more active for the CO and alkene oxidation, CO, NO, benzene,
toluene, and 1,3-butadiene hydrogenation and ethanol decomposition [21]. Ag/Pd is
a good candidate for hydrogenation and permeation [22, 23]. Si, Ge, Sn, C and Cu
are also used as constituent for the electrode of Li-ion batteries [24].
In the process of catalytic reaction, the direction and the ability of charge flow
between the catalyst and the gaseous adsorbate are the key concern. The reactivity
depends on the filling degree of the empty anti-bonding states of the catalyst by the
reactant electrons. The reactivity also depends on the ability of the catalyst donating
its valence electrons to the specimen. The catalyst and the adsorbate having orbits
of similar energies should overlap for charge transportation during reaction [25, 26].
Although the catalytic behaviors of Cu/Pd and Ag/Pd alloys have been intensively
investigated [14, 19, 27–31], laws governing the energetic behavior of the core and
the valence electrons and their catalytic nature and ability are yet to be established.
Upon reacting with electronegative elements such as oxygen, nitrogen and fluorine
with lone pair production, the core levels of metals also shift accordingly associated
with excessive valence DOS features due to charge polarization and transportation
[35, 36]. For instance, oxygen adsorption deepens the bulk and the skin 3d 5/2 components of a clean Ru(0001) surface simultaneously by up to 1.0 eV [37]. Oxidation
also deepens the Rh 3d 5/2 level and its satellite by 0.40 eV further [38]. These observations confirm that both surface bond relaxation and new bond formation could
shift the core-level positively in a superposition way by an amount that varies not
only with the original E ν (0) but also with the extent of reaction [39]. However, the
polarization due to lone pair production is unapparent in the energy shift of deeper
levels but the lone pairs create polarized energy states in the upper conduction and
valence band. The polarized states may screen and split the local crystal potential,
which in turn influence the CLS [40].
Hetero-junction bond formation shifts the XPS features positively or negatively,
depending on the local potentials. For instances, Ag/Pd [41], Zn/Pd [42], and Be/W
[32, 43] alloy formation shift the core and the valence bands upwardly but Cu/Pd [41,
44] alloy formation deepens all bands simultaneously, as summarized in Table 8.1.
For alloy containing N constituent elements, there will be C(N, 2) terms of interactions such as the A-A, B-B, and A-B interaction for an AB alloy instance. The
additional A-B type exchange interactions contribute to the overall potentials of an
8 Hetero-Coordinated Interfaces
As the first wall material in a nuclear fusion device, Be/W alloying easily occurs
in the processes of plasma interaction within the wall for radiation protection [11,
12]. However, understanding the energetics and electronics of the interface alloy is
crucial to engineering such functional materials. Due to the electronic structures of
W (6s
2 5d
4 , delocalized d electrons dominate) and Be (2s
2 states dominate), a strong
influence of the alloying on both the core and the valence electrons is apparent, but
insofar, it remains poorly understood.
Another example is the catalytic nature and ability of alloys. Ag and Cu often form
alloys with Pd because their interactions typically result in improved heterogeneous
catalysts [16–18] that behave quite differently in reactions—reduction or oxidation
[19, 20]. Cu/Pd is more active for the CO and alkene oxidation, CO, NO, benzene,
toluene, and 1,3-butadiene hydrogenation and ethanol decomposition [21]. Ag/Pd is
a good candidate for hydrogenation and permeation [22, 23]. Si, Ge, Sn, C and Cu
are also used as constituent for the electrode of Li-ion batteries [24].
In the process of catalytic reaction, the direction and the ability of charge flow
between the catalyst and the gaseous adsorbate are the key concern. The reactivity
depends on the filling degree of the empty anti-bonding states of the catalyst by the
reactant electrons. The reactivity also depends on the ability of the catalyst donating
its valence electrons to the specimen. The catalyst and the adsorbate having orbits
of similar energies should overlap for charge transportation during reaction [25, 26].
Although the catalytic behaviors of Cu/Pd and Ag/Pd alloys have been intensively
investigated [14, 19, 27–31], laws governing the energetic behavior of the core and
the valence electrons and their catalytic nature and ability are yet to be established.
Upon reacting with electronegative elements such as oxygen, nitrogen and fluorine
with lone pair production, the core levels of metals also shift accordingly associated
with excessive valence DOS features due to charge polarization and transportation
[35, 36]. For instance, oxygen adsorption deepens the bulk and the skin 3d 5/2 components of a clean Ru(0001) surface simultaneously by up to 1.0 eV [37]. Oxidation
also deepens the Rh 3d 5/2 level and its satellite by 0.40 eV further [38]. These observations confirm that both surface bond relaxation and new bond formation could
shift the core-level positively in a superposition way by an amount that varies not
only with the original E ν (0) but also with the extent of reaction [39]. However, the
polarization due to lone pair production is unapparent in the energy shift of deeper
levels but the lone pairs create polarized energy states in the upper conduction and
valence band. The polarized states may screen and split the local crystal potential,
which in turn influence the CLS [40].
Hetero-junction bond formation shifts the XPS features positively or negatively,
depending on the local potentials. For instances, Ag/Pd [41], Zn/Pd [42], and Be/W
[32, 43] alloy formation shift the core and the valence bands upwardly but Cu/Pd [41,
44] alloy formation deepens all bands simultaneously, as summarized in Table 8.1.
For alloy containing N constituent elements, there will be C(N, 2) terms of interactions such as the A-A, B-B, and A-B interaction for an AB alloy instance. The
additional A-B type exchange interactions contribute to the overall potentials of an