Chapter 4
Solid and Liquid Skins
Abstract Decomposition of the XPS profiles into components of sublayers derives
information on the local bond length, bond energy, atomic cohesive energy, binding
energy density, and the energy levels E ν (0) of an isolated atom and its shift with the
coordination environment. The E ν (0) and E ν (12) remain constant and the atomic CN
varies only with the layer order and surface registry, regardless of the skin chemical
constituent. Atomic undercoordination induced bond contraction drives relaxation
and reconstruction of the surface of a crystal.
Highlights
• BOLS-TB-XPS not only quantifies the E ν (0) and E ν (12) but also the CN-resolved
d z , E z , E den , and E coh .
• Atomic CN varies only with the sublayer order and the surface registry regardless
of chemical composition.
• Atomic undercoordination shortens the skin bonds and densely entraps core
electrons, deepens the CL.
• The skin of a substance is generally denser, stiffer, yet chemically and thermally
more active than the bulk.
4.1 XPS Derivatives
It has long been controversial regarding the skin CLS that may be in a positive,
a negative, or a mixed order. Rules are lacking for such order assignment despite
intuitive or calculation derivative using the “final-initial” state relaxation scheme.
Nb(100) [1, 2], graphite [3], Tb(0001) [4], Ta(100) [5], Ta(110) [6], Mg(1010) [7],
and Ga(0001) [8] skins follow the positive CLS order (E F , B, …, S 2 , S 1 ) with E F
as the reference point. Be(0001) [9], Be(1010) [7, 10, 11], Ru(1010) [12], Mo(110)
[13], Al(100) [14], W(110) [15], W(320) [16], and Pd(110), (100) and (111) [17]
skins follow the negative CLS order (E F , S 1 , S 2 , …, B). However, Si(111) [18],
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
C. Q. Sun, Electron and Phonon Spectrometrics,
https://doi.org/10.1007/978-981-15-3176-7_4
59
Solid and Liquid Skins
Abstract Decomposition of the XPS profiles into components of sublayers derives
information on the local bond length, bond energy, atomic cohesive energy, binding
energy density, and the energy levels E ν (0) of an isolated atom and its shift with the
coordination environment. The E ν (0) and E ν (12) remain constant and the atomic CN
varies only with the layer order and surface registry, regardless of the skin chemical
constituent. Atomic undercoordination induced bond contraction drives relaxation
and reconstruction of the surface of a crystal.
Highlights
• BOLS-TB-XPS not only quantifies the E ν (0) and E ν (12) but also the CN-resolved
d z , E z , E den , and E coh .
• Atomic CN varies only with the sublayer order and the surface registry regardless
of chemical composition.
• Atomic undercoordination shortens the skin bonds and densely entraps core
electrons, deepens the CL.
• The skin of a substance is generally denser, stiffer, yet chemically and thermally
more active than the bulk.
4.1 XPS Derivatives
It has long been controversial regarding the skin CLS that may be in a positive,
a negative, or a mixed order. Rules are lacking for such order assignment despite
intuitive or calculation derivative using the “final-initial” state relaxation scheme.
Nb(100) [1, 2], graphite [3], Tb(0001) [4], Ta(100) [5], Ta(110) [6], Mg(1010) [7],
and Ga(0001) [8] skins follow the positive CLS order (E F , B, …, S 2 , S 1 ) with E F
as the reference point. Be(0001) [9], Be(1010) [7, 10, 11], Ru(1010) [12], Mo(110)
[13], Al(100) [14], W(110) [15], W(320) [16], and Pd(110), (100) and (111) [17]
skins follow the negative CLS order (E F , S 1 , S 2 , …, B). However, Si(111) [18],
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
C. Q. Sun, Electron and Phonon Spectrometrics,
https://doi.org/10.1007/978-981-15-3176-7_4
59