68
4 Solid and Liquid Skins
Figures 4.4 and 4.5 show the BOLS-TB decomposed 4f 7/2 spectra for the Ir, Al,
and Au(001), (111), and (110) skins [36]. Table 4.1 summarizes the optimal 4f 7/2 (0,
z, 12) component and the bulk shift E 4f5/2 (12) for Au skins under the common z
values for the fcc structures. One can readily derive the local strain, bond length,
bond energy, E coh and E den according to practice discussed in Sect. 5. Figure 4.5d
shows the ZPS 4f 7/2 profiles of gold foil after O 3 oxidation at different stages and at
100 °C [37]. Clearly, oxidation polarizes the skin but over dosage of oxygen creates
H-bond network at the surface, which annihilates the skin dipoles and prevents the
skin from further oxidation [38]. Figure 4.6 shows the BOLS-TB decomposed 3d
spectra for the Ag(100) and Ag(111) skins using the same optimized CN set for the
fcc geometries.
4.3.2 Bcc-Structured W, Mo and Ta
The apparent atomic CN in the bcc bulk is 8 instead of 12 for the fcc standard.
However, one can normalize the CN by applying z = 12×CN bcc /8. The documented
best fit using the B, S 2 , and S 1 components provides reference for fine-tuning in the
present XPS spectral analysis [13, 48–50]. Figures 4.7 and 4.8 show the decomposed
XPS spectra for the bcc (001), (110), and (111) skins of W 4f 7/2 , Ta 4f 7/2 , and Mo
3d 5/2 with derivatives given in Table 4.2.
4.3.3 Diamond-Structured Si and Ge
Figure 4.9 shows the sublayer-resolved XPS Si 2p 3/2 spectra [57, 58] and Ge 3d 5/2
spectra [21, 59] for their (100) and (111) skins. Table 4.3 lists information derived
from the best fit. Fine-tuning results in z 1 = 5.08 instead of 4.0 for the (100) skin
because the diamond structure is an interlock of two fcc unit cells. The layer-resolved
Si 2p [57, 58] and Ge 3d [21, 59] spectra for the (100) and (111) skins show
consistently that atomic undercoordination results in the local quantum entrapment.
4.3.4 The hcp-Structured Be, Re, and Ru
Figure 4.11a–c shows the decomposed 1s spectra for the Be(1010), (0001), and
(1120) skins [9, 11, 63, 64]. The XPS spectrum of Be(0001) surface contains four
components. An S 1 addition to the deeper end of the Be(1010) spectrum represents
the undercoordinated Be atom in the Be(1010) kink edge. Including the B component
that was counted only once, there are a total of n = 12 components for the Be skins
and 55 possible E ν (0) values for averaging.
According to the decomposition criteria, the common B component must exist and
keep constant in all skins of the same substance regardless of geometrical orientation.
4 Solid and Liquid Skins
Figures 4.4 and 4.5 show the BOLS-TB decomposed 4f 7/2 spectra for the Ir, Al,
and Au(001), (111), and (110) skins [36]. Table 4.1 summarizes the optimal 4f 7/2 (0,
z, 12) component and the bulk shift E 4f5/2 (12) for Au skins under the common z
values for the fcc structures. One can readily derive the local strain, bond length,
bond energy, E coh and E den according to practice discussed in Sect. 5. Figure 4.5d
shows the ZPS 4f 7/2 profiles of gold foil after O 3 oxidation at different stages and at
100 °C [37]. Clearly, oxidation polarizes the skin but over dosage of oxygen creates
H-bond network at the surface, which annihilates the skin dipoles and prevents the
skin from further oxidation [38]. Figure 4.6 shows the BOLS-TB decomposed 3d
spectra for the Ag(100) and Ag(111) skins using the same optimized CN set for the
fcc geometries.
4.3.2 Bcc-Structured W, Mo and Ta
The apparent atomic CN in the bcc bulk is 8 instead of 12 for the fcc standard.
However, one can normalize the CN by applying z = 12×CN bcc /8. The documented
best fit using the B, S 2 , and S 1 components provides reference for fine-tuning in the
present XPS spectral analysis [13, 48–50]. Figures 4.7 and 4.8 show the decomposed
XPS spectra for the bcc (001), (110), and (111) skins of W 4f 7/2 , Ta 4f 7/2 , and Mo
3d 5/2 with derivatives given in Table 4.2.
4.3.3 Diamond-Structured Si and Ge
Figure 4.9 shows the sublayer-resolved XPS Si 2p 3/2 spectra [57, 58] and Ge 3d 5/2
spectra [21, 59] for their (100) and (111) skins. Table 4.3 lists information derived
from the best fit. Fine-tuning results in z 1 = 5.08 instead of 4.0 for the (100) skin
because the diamond structure is an interlock of two fcc unit cells. The layer-resolved
Si 2p [57, 58] and Ge 3d [21, 59] spectra for the (100) and (111) skins show
consistently that atomic undercoordination results in the local quantum entrapment.
4.3.4 The hcp-Structured Be, Re, and Ru
Figure 4.11a–c shows the decomposed 1s spectra for the Be(1010), (0001), and
(1120) skins [9, 11, 63, 64]. The XPS spectrum of Be(0001) surface contains four
components. An S 1 addition to the deeper end of the Be(1010) spectrum represents
the undercoordinated Be atom in the Be(1010) kink edge. Including the B component
that was counted only once, there are a total of n = 12 components for the Be skins
and 55 possible E ν (0) values for averaging.
According to the decomposition criteria, the common B component must exist and
keep constant in all skins of the same substance regardless of geometrical orientation.