5.3 ZPS of Rh, W, and Re Kink Edges
93
40
41
42
43
44
-0.2
0.0
0.2
ΔI (a.u.)
Re(eV)
Re (12-31) 4f
(75
o - 0
o
)
4f 7/2
4f 5/2
B
B
T
T
(a)
42.0
42.5
43.0
43.5
-0.2
0.0
0.2
75
0
-0
0
ΔI (a.u.)
BE (eV)
B S 4 S 3
S 2 S 1
Re(12-31) 4f 7/2
(b)
Fig. 5.10 ZPS of a the kinked Re (12 ¯
31) 4f bands [27]. The B valleys correspond to bulk (B)
components and the T peaks to the kink-induced quantum entrapment. b The ZPS of the 4f 5/2
band with the valley centered at 42.645 eV includes contribution from the B, the S 4 and the S 3
sublayers. The spectral gains at the bottom edge correspond to the quantum entrapment dominated
by the outermost two layers of kink atoms. Reprinted with permission from [57]. Copyright 2011
American Chemical Society
ZPS could therefore separate the kinks from their bulk mixture without needing any
hypothetic assignment of the B or the skin component.
From the spectral bandwidth of the B valley, one can find that the overlap integral β
is indeed negligible compared with the exchange integral α in the TB approximation.
The width of a core band is 2zβ and the shift of the band from that of an isolated atom
is α + zβ. Based on the width of the B valley for both the 4f 7/2 and the 4f 5/2 bands
of ~0.25 eV and the bulk shift of α + zβ = 2.629 eV (β/α ≈ 0.01/2.63 < 0.4%)
only, in the present case.
5.3.5 O-Re (12 ¯
31) Kink Edge and Chemisorbed States
Figure 5.11a, b decompose the 4f 7/2 band for the Re (12 ¯
31) surface with and without
oxygen chemisorption [27]. A direct decomposition of the spectrum for oxygenadsorbed Re (12 ¯
31) surface using the coordination scheme is no longer valid because
of oxide bond formation. The O-Re bond formation will increase the local crystal potential in the adsorbed region, which deepens the surface states, as shown in
Fig. 5.11b [52, 56]. The O-induced Re 4f 7/2 shift is in line with what detected from
oxygen-chemisorbed surfaces [58], in which the O 2p states shift positively by an
amount of ~0.5 eV upon oxide formation.
Figure 5.11c compares the ZPS for the Re (12 ¯
31) surface with and without oxygen
adsorption. A BO valley centered at 40.40 eV is different from the B (40.30 eV) and
the S 4 in the referential ZPS of the clean Re surface. This difference indicates that
the O-Re bond is much stronger and that the synchrotron beam of 90 eV collects
less information from the bulk or the S 4 region. The extra states extend to energy
that is even lower than the energy states of the clean surface. The ZPS has thus
93
40
41
42
43
44
-0.2
0.0
0.2
ΔI (a.u.)
Re(eV)
Re (12-31) 4f
(75
o - 0
o
)
4f 7/2
4f 5/2
B
B
T
T
(a)
42.0
42.5
43.0
43.5
-0.2
0.0
0.2
75
0
-0
0
ΔI (a.u.)
BE (eV)
B S 4 S 3
S 2 S 1
Re(12-31) 4f 7/2
(b)
Fig. 5.10 ZPS of a the kinked Re (12 ¯
31) 4f bands [27]. The B valleys correspond to bulk (B)
components and the T peaks to the kink-induced quantum entrapment. b The ZPS of the 4f 5/2
band with the valley centered at 42.645 eV includes contribution from the B, the S 4 and the S 3
sublayers. The spectral gains at the bottom edge correspond to the quantum entrapment dominated
by the outermost two layers of kink atoms. Reprinted with permission from [57]. Copyright 2011
American Chemical Society
ZPS could therefore separate the kinks from their bulk mixture without needing any
hypothetic assignment of the B or the skin component.
From the spectral bandwidth of the B valley, one can find that the overlap integral β
is indeed negligible compared with the exchange integral α in the TB approximation.
The width of a core band is 2zβ and the shift of the band from that of an isolated atom
is α + zβ. Based on the width of the B valley for both the 4f 7/2 and the 4f 5/2 bands
of ~0.25 eV and the bulk shift of α + zβ = 2.629 eV (β/α ≈ 0.01/2.63 < 0.4%)
only, in the present case.
5.3.5 O-Re (12 ¯
31) Kink Edge and Chemisorbed States
Figure 5.11a, b decompose the 4f 7/2 band for the Re (12 ¯
31) surface with and without
oxygen chemisorption [27]. A direct decomposition of the spectrum for oxygenadsorbed Re (12 ¯
31) surface using the coordination scheme is no longer valid because
of oxide bond formation. The O-Re bond formation will increase the local crystal potential in the adsorbed region, which deepens the surface states, as shown in
Fig. 5.11b [52, 56]. The O-induced Re 4f 7/2 shift is in line with what detected from
oxygen-chemisorbed surfaces [58], in which the O 2p states shift positively by an
amount of ~0.5 eV upon oxide formation.
Figure 5.11c compares the ZPS for the Re (12 ¯
31) surface with and without oxygen
adsorption. A BO valley centered at 40.40 eV is different from the B (40.30 eV) and
the S 4 in the referential ZPS of the clean Re surface. This difference indicates that
the O-Re bond is much stronger and that the synchrotron beam of 90 eV collects
less information from the bulk or the S 4 region. The extra states extend to energy
that is even lower than the energy states of the clean surface. The ZPS has thus