8.2 BOLS-TB Formulation of the PES Attributes
167
Subtracting the composed UPS spectrum, I composed = [xI A + (1 − x)I B ], for
instance, from the alloying UPS spectrum I alloy upon spectral peak area normalization
results in the valence ZPS, I = I alloy − I comosed , that distills the effect of alloy
formation. The x is the concentration of A constituent in the AB alloy. The valence
ZPS profiles in Fig. 8.1 reveal that (b) Ag/Pd alloy formation migrates the valence
DOS upwardly and that (c) Cu/Pd alloy shifts the DOS to deeper energy. The opposite
directions of valence DOS polarization distinguish the Cu/Pd (acceptor-like) from
the Ag/Pd (donor-like) in their catalytic performance.
8.3 ZPS: Core Band Entrapment and Polarization
8.3.1 Ag/Pd, Cu/Pd, Zn/Pd and Be/W Interfaces
XPS spectra in Figs. 8.2 and 8.3 show the evolution of the Cu 2p 3/2 , Ag 3d 5/2 , Pd 3d 5/2 ,
Zn 3d 5/2 , Be 1s, and W 4f 7/2 bands upon annealing at transition temperatures [32,
33]. The intensity inversion of the I and the B component indicates the completeness
of interface alloying as summarized in Table 8.1.
The ZPS features allow one to calibrate the potential depth, γ = [E ν (I) −
E ν (B)]/E ν (B), for the respective alloys, as summarized in Table 8.2. ZPS profiles
in Figs. 8.2 and 8.3 reveal the following information:
1. Both the Cu 2p and the Pd 3d bands shift positively from B to I component upon
Cu/Pd alloy formation, which is consistent with the valence band shift. Cu/Pd
alloy formation strengthens the interface Cu–Cu and Pd–Pd bond, resulting in
quantum entrapment.
2. Both the Ag 3d and the Pd 3d bands at the Ag/Pd interface shift upwardly
from B to I, which also agrees with the valence band evolution. The Ag/Pd
alloy formation weakens the interface Ag–Ag and Pd–Pd bond, resulting in
polarization.
3. The Zn 3d, Pd 3d, Be 1s and W 4f bands shift up at the Zn/Pd and the Be/W
interfaces, following the same polarization trend at the Ag/Pd interface.
4. The core and the valence bands evolve consistently in the same direction of the
same alloy. One can infer that the Be/W and Zn/Pd valence bands follow the
same polarization trend of their core bands though it is subject to experimental
verification.
8.3.2 C/Si, C/Ge, Si/Ge, Cu/Si and Cu/Sn Interfaces
Figure 8.4 shows the C 1s, Si 2p, and Ge 3p ZPS for C/Si, C/Ge and Si/Ge alloys
[54–56] and Table 8.3 summarizes the derive information on the interface entities.
Results indicate the following:
167
Subtracting the composed UPS spectrum, I composed = [xI A + (1 − x)I B ], for
instance, from the alloying UPS spectrum I alloy upon spectral peak area normalization
results in the valence ZPS, I = I alloy − I comosed , that distills the effect of alloy
formation. The x is the concentration of A constituent in the AB alloy. The valence
ZPS profiles in Fig. 8.1 reveal that (b) Ag/Pd alloy formation migrates the valence
DOS upwardly and that (c) Cu/Pd alloy shifts the DOS to deeper energy. The opposite
directions of valence DOS polarization distinguish the Cu/Pd (acceptor-like) from
the Ag/Pd (donor-like) in their catalytic performance.
8.3 ZPS: Core Band Entrapment and Polarization
8.3.1 Ag/Pd, Cu/Pd, Zn/Pd and Be/W Interfaces
XPS spectra in Figs. 8.2 and 8.3 show the evolution of the Cu 2p 3/2 , Ag 3d 5/2 , Pd 3d 5/2 ,
Zn 3d 5/2 , Be 1s, and W 4f 7/2 bands upon annealing at transition temperatures [32,
33]. The intensity inversion of the I and the B component indicates the completeness
of interface alloying as summarized in Table 8.1.
The ZPS features allow one to calibrate the potential depth, γ = [E ν (I) −
E ν (B)]/E ν (B), for the respective alloys, as summarized in Table 8.2. ZPS profiles
in Figs. 8.2 and 8.3 reveal the following information:
1. Both the Cu 2p and the Pd 3d bands shift positively from B to I component upon
Cu/Pd alloy formation, which is consistent with the valence band shift. Cu/Pd
alloy formation strengthens the interface Cu–Cu and Pd–Pd bond, resulting in
quantum entrapment.
2. Both the Ag 3d and the Pd 3d bands at the Ag/Pd interface shift upwardly
from B to I, which also agrees with the valence band evolution. The Ag/Pd
alloy formation weakens the interface Ag–Ag and Pd–Pd bond, resulting in
polarization.
3. The Zn 3d, Pd 3d, Be 1s and W 4f bands shift up at the Zn/Pd and the Be/W
interfaces, following the same polarization trend at the Ag/Pd interface.
4. The core and the valence bands evolve consistently in the same direction of the
same alloy. One can infer that the Be/W and Zn/Pd valence bands follow the
same polarization trend of their core bands though it is subject to experimental
verification.
8.3.2 C/Si, C/Ge, Si/Ge, Cu/Si and Cu/Sn Interfaces
Figure 8.4 shows the C 1s, Si 2p, and Ge 3p ZPS for C/Si, C/Ge and Si/Ge alloys
[54–56] and Table 8.3 summarizes the derive information on the interface entities.
Results indicate the following: