1.1 Overview
11
information on the electron binding energy for skins of liquid water and sized droplet
[148, 149].
However, what one can measure using a PES are the convoluted peaks of the
core bands contributed by intra-atomic trapping, interatomic binding, crystal orientation, defect vacancy, surface relaxation, nanosolid formation, surface passivation
and adsorption, with the mixture of bulk information. An XPS spectral peak often
contains multiple components of energy shift with uncertainty of their separation,
direction, component integral and width, and the reference point from which these
shifts proceed.
Based on the conventional exercises of spectral decomposition analysis, for
instance, one can hardly discriminate the contribution of adatoms from that of the
skin or the bulk to the PES spectrum with little information regarding the relaxation
dynamics of the local bonds and the energetic electrons pertaining to adatoms [132,
150]. Combining the most advanced laser cooling and XPS technologies, one can
only measure the energy separation between two levels of the slowly moving gaseous
atoms of lower bulk meting point [151]. Therefore, discriminating contributions of
different sublayers or oriented crystals from those of the bulk, and separating the
contribution of the interatomic interaction from that of the intra-atomic interaction
to the spectrum is still a challenge. Determination of the individual energy level of
an isolated atom and its shift with coordination and chemical environment remains
as a “bottle net” in study [2].
The valence DOS profile provides direct information about charge transportation during reaction from one constituent to the other (ionization), polarization and
entrapment of valence charge, which evolves the interatomic potentials from the
initial form due to potential screening and splitting effect [45]. Understanding the
evolution of the valence DOS needs proper models to relate the valence DOS change
to the dynamics of bond formation and relaxation. Analyzing the valence DOS
shift is much more complicated than analyzing the core-band shift, as the latter simply fingerprints the binding energy change of a particular energy level of a specific
element by interatomic interaction [45].
Quantum computation using density function theory (DFT) resolves the local
valance DOS and core-level shift (CLS) with optimization of crystal geometries and
interatomic distances [152, 153]. However, the accuracy and reliability of the computational derivatives are often algorithm and boundary-condition sensitive [154].
Employing the ideally periodic or the free boundary condition deviates the calculation
outcome from the true situations to a certain extent. Structural distortion happens at
boundaries associated with local strain, charge densification, polarization, and quantum entrapment. These happenings in turn modify the local potentials that shift the
electronic binding energy accordingly [9].
11
information on the electron binding energy for skins of liquid water and sized droplet
[148, 149].
However, what one can measure using a PES are the convoluted peaks of the
core bands contributed by intra-atomic trapping, interatomic binding, crystal orientation, defect vacancy, surface relaxation, nanosolid formation, surface passivation
and adsorption, with the mixture of bulk information. An XPS spectral peak often
contains multiple components of energy shift with uncertainty of their separation,
direction, component integral and width, and the reference point from which these
shifts proceed.
Based on the conventional exercises of spectral decomposition analysis, for
instance, one can hardly discriminate the contribution of adatoms from that of the
skin or the bulk to the PES spectrum with little information regarding the relaxation
dynamics of the local bonds and the energetic electrons pertaining to adatoms [132,
150]. Combining the most advanced laser cooling and XPS technologies, one can
only measure the energy separation between two levels of the slowly moving gaseous
atoms of lower bulk meting point [151]. Therefore, discriminating contributions of
different sublayers or oriented crystals from those of the bulk, and separating the
contribution of the interatomic interaction from that of the intra-atomic interaction
to the spectrum is still a challenge. Determination of the individual energy level of
an isolated atom and its shift with coordination and chemical environment remains
as a “bottle net” in study [2].
The valence DOS profile provides direct information about charge transportation during reaction from one constituent to the other (ionization), polarization and
entrapment of valence charge, which evolves the interatomic potentials from the
initial form due to potential screening and splitting effect [45]. Understanding the
evolution of the valence DOS needs proper models to relate the valence DOS change
to the dynamics of bond formation and relaxation. Analyzing the valence DOS
shift is much more complicated than analyzing the core-band shift, as the latter simply fingerprints the binding energy change of a particular energy level of a specific
element by interatomic interaction [45].
Quantum computation using density function theory (DFT) resolves the local
valance DOS and core-level shift (CLS) with optimization of crystal geometries and
interatomic distances [152, 153]. However, the accuracy and reliability of the computational derivatives are often algorithm and boundary-condition sensitive [154].
Employing the ideally periodic or the free boundary condition deviates the calculation
outcome from the true situations to a certain extent. Structural distortion happens at
boundaries associated with local strain, charge densification, polarization, and quantum entrapment. These happenings in turn modify the local potentials that shift the
electronic binding energy accordingly [9].