4.3 Registry and Sublayer-Order Resolution
63
4.3 Registry and Sublayer-Order Resolution
4.3.1 Fcc-Structured Al, Ag, Au, Ir, Rh, and Pd
Data sourced from the literature has been corrected by removing background and
noises. Including the B component that counts only once, there are a total of l = 7
components for these fcc(100), (110), and (111) skins, as each peak contains the S 1
and S 2 components [32, 33]. There will be C(7, 2) = 21 different E ν (0) values for
averaging. The decomposition refines the effective CN of atoms in each sublayer.
Figure 4.3, 4.4, 4.5 and 4.6 show the decomposed spectra for Rh, Pd, Al, Ag, Au, and
Ir skins of different orientations. Table 4.1 summarizes the decomposition outcome.
Derivatives include the effective CN, bond strain ε z , bond energy E z , energy density
E den , and atomic cohesive energy E coh , relative to their bulk values. These elemental
quantities determine the performance of the skin. For instance, E den determines the
mechanical strength and elasticity and the E coh determine the diffusivity and thermal
stability such as the critical temperature for phase transition [31].
Figure 4.3 displays that the Pd 3d 5/2 spectra exhibit one symmetric convoluted
peak but the Rh 3d 5/2 spectra display two majors. The asymmetry at the deeper
edge indicates the possible presence of defects or adatoms that induce quantum
entrapment of binding energy. Electronic configurations of Pd(5s
0 4d
10 ), Rh(5s
1 4d
8 ),
and Ir(6s
2 5d
7 ) may affect their spectral patterns as they are in the same geometry
and similar atomic cross-section area for scattering [24]. Atoms at the sharp edges
may retain partly their discreted orbital nature in isolation.
Results indicate indeed that the amount of the CLS for the (110) skin is greater
than that for the (001) and the (111) skins because of its lower atomic CN of the
(110). The CLS of the (111) skin shifts least because of its highest effective CN
among them [17]. Bonds in the outermost layer are shortest and strongest than those
in the subsequent sublayers, which agrees with what discovered by Matsui et al. [35]
from Ni surface. They resolved that the Ni 2p levels of the outermost three atomic
layers shift positively to deeper BE, with the outermost layer shifting the most.
It is clear now that atomic undercoordination creates the local strain and stress
(gradient of bond energy) that reconstructs laterally and relaxes inward vertically the
skin, which is intrinsically unavoidable. The skin of the fcc-structured metals consisting of at most three atomic layers or two interatomic spacings performs differently
from the bulk. Therefore, the concept of skin is more meaningful and practical than
the concept of surface without thickness being involved [31].
63
4.3 Registry and Sublayer-Order Resolution
4.3.1 Fcc-Structured Al, Ag, Au, Ir, Rh, and Pd
Data sourced from the literature has been corrected by removing background and
noises. Including the B component that counts only once, there are a total of l = 7
components for these fcc(100), (110), and (111) skins, as each peak contains the S 1
and S 2 components [32, 33]. There will be C(7, 2) = 21 different E ν (0) values for
averaging. The decomposition refines the effective CN of atoms in each sublayer.
Figure 4.3, 4.4, 4.5 and 4.6 show the decomposed spectra for Rh, Pd, Al, Ag, Au, and
Ir skins of different orientations. Table 4.1 summarizes the decomposition outcome.
Derivatives include the effective CN, bond strain ε z , bond energy E z , energy density
E den , and atomic cohesive energy E coh , relative to their bulk values. These elemental
quantities determine the performance of the skin. For instance, E den determines the
mechanical strength and elasticity and the E coh determine the diffusivity and thermal
stability such as the critical temperature for phase transition [31].
Figure 4.3 displays that the Pd 3d 5/2 spectra exhibit one symmetric convoluted
peak but the Rh 3d 5/2 spectra display two majors. The asymmetry at the deeper
edge indicates the possible presence of defects or adatoms that induce quantum
entrapment of binding energy. Electronic configurations of Pd(5s
0 4d
10 ), Rh(5s
1 4d
8 ),
and Ir(6s
2 5d
7 ) may affect their spectral patterns as they are in the same geometry
and similar atomic cross-section area for scattering [24]. Atoms at the sharp edges
may retain partly their discreted orbital nature in isolation.
Results indicate indeed that the amount of the CLS for the (110) skin is greater
than that for the (001) and the (111) skins because of its lower atomic CN of the
(110). The CLS of the (111) skin shifts least because of its highest effective CN
among them [17]. Bonds in the outermost layer are shortest and strongest than those
in the subsequent sublayers, which agrees with what discovered by Matsui et al. [35]
from Ni surface. They resolved that the Ni 2p levels of the outermost three atomic
layers shift positively to deeper BE, with the outermost layer shifting the most.
It is clear now that atomic undercoordination creates the local strain and stress
(gradient of bond energy) that reconstructs laterally and relaxes inward vertically the
skin, which is intrinsically unavoidable. The skin of the fcc-structured metals consisting of at most three atomic layers or two interatomic spacings performs differently
from the bulk. Therefore, the concept of skin is more meaningful and practical than
the concept of surface without thickness being involved [31].