154
7 Carbon Allotropes
The angle-resolved C 1s spectra show a slight positive shift while the defectresolved C 1s spectra exhibit tails at both spectral ends. The spectra collected at
larger (off normal) emission angles or from higher defect densities weaken their
overall intensities due to scattering loss [121].
The spectrum collected from the defect-free surface at the least emission angle
(25°) serves as the reference for the ZPS processing upon all spectral peak area
normalization and background correction. The skin ZPS is the difference between
spectra collected at highest and lowest emission angles. The defect ZPS is the difference between a defected spectrum and this reference as well, as compared in
Fig. 7.5c, d.
The ZPS in Fig. 7.5c, d purifies the energy states of the (a) defect-free monolayer
skin and (b) the vacancy defects at graphite skin. The peaks above the x-axis are
the DOS gain due to defects or the monolayer skin while the DOS loss under the
axis is the bulk/skin components. According to the BOLS-TB notion, the separation
between the specific spectral features and the E 1s (0) = 282.57 eV is proportional to
the C–C bond energy at the particular atomic site.
[E 1s (z) − E 1s (12)]
[E 1s (5.335) − E 1s (12)] =
C z
C 5.335
−2.56
The lateral axis is gridded with the effective atomic CN. The valley at 284.20 eV
in (c) corresponds to graphite bulk (z = 5.335). The valley at 284.40 eV in (d) is
a mixture of the bulk and the skin (z = 4). In addition to the spectral valleys, one
entrapped peak (T S ) presents at the bottom edge of the C 1s band corresponding to
the skin with z ~ 3.1. The T S moves to energy even deeper and evolves into the T D
component with effective CN of 2.2–2.4, as defects generate. The shift from T S to T D
is accompanied surprisingly by an emergence of both the P component at the upper
edge of the C 1s band and the DFs at the E F as probed using STM/S [43–45, 47–49,
87]. The T D is deeper than the T S means that the defect bonds are indeed shorter and
stronger than that of the monolayer skin.
As the defect density is increased, the intensity of the T D component grows but
remains its energy. In contrast, the P component moves up in both energy and intensity. The atomic CN has reached and stabilized at the lowest value (2.2 for the nearest
and 2.4 for the next nearest neighbors) and that the extent of polarization increases
with defect density. The T S energy depends only on the atomic CN but polarization
on both the density and the CN of undercoordinated atoms. Only one neighbor short
makes a great difference in the bond length and binding energy!
Figure 7.6 summarizes the ZPS spectra of graphite monolayer skin and vacancy
defect. The skin ZPS differentiates two spectra collected at 75° and at 25°. The
defect ZPS differentiates two spectra collected at 75° from the surface after and
before high-density defect generation. Insets illustrate color zones contributing the
excessive states in each case. The atomic CN for the skin is about 3.1, which is
close to the ideal case of 3.0 of graphene interior. The atomic CN for the vacancy
extends from 2.2 to 2.4, which indicates that the next nearest neighbors contribute
to broadening the ZPS identity of the vacancy.
7 Carbon Allotropes
The angle-resolved C 1s spectra show a slight positive shift while the defectresolved C 1s spectra exhibit tails at both spectral ends. The spectra collected at
larger (off normal) emission angles or from higher defect densities weaken their
overall intensities due to scattering loss [121].
The spectrum collected from the defect-free surface at the least emission angle
(25°) serves as the reference for the ZPS processing upon all spectral peak area
normalization and background correction. The skin ZPS is the difference between
spectra collected at highest and lowest emission angles. The defect ZPS is the difference between a defected spectrum and this reference as well, as compared in
Fig. 7.5c, d.
The ZPS in Fig. 7.5c, d purifies the energy states of the (a) defect-free monolayer
skin and (b) the vacancy defects at graphite skin. The peaks above the x-axis are
the DOS gain due to defects or the monolayer skin while the DOS loss under the
axis is the bulk/skin components. According to the BOLS-TB notion, the separation
between the specific spectral features and the E 1s (0) = 282.57 eV is proportional to
the C–C bond energy at the particular atomic site.
[E 1s (z) − E 1s (12)]
[E 1s (5.335) − E 1s (12)] =
C z
C 5.335
−2.56
The lateral axis is gridded with the effective atomic CN. The valley at 284.20 eV
in (c) corresponds to graphite bulk (z = 5.335). The valley at 284.40 eV in (d) is
a mixture of the bulk and the skin (z = 4). In addition to the spectral valleys, one
entrapped peak (T S ) presents at the bottom edge of the C 1s band corresponding to
the skin with z ~ 3.1. The T S moves to energy even deeper and evolves into the T D
component with effective CN of 2.2–2.4, as defects generate. The shift from T S to T D
is accompanied surprisingly by an emergence of both the P component at the upper
edge of the C 1s band and the DFs at the E F as probed using STM/S [43–45, 47–49,
87]. The T D is deeper than the T S means that the defect bonds are indeed shorter and
stronger than that of the monolayer skin.
As the defect density is increased, the intensity of the T D component grows but
remains its energy. In contrast, the P component moves up in both energy and intensity. The atomic CN has reached and stabilized at the lowest value (2.2 for the nearest
and 2.4 for the next nearest neighbors) and that the extent of polarization increases
with defect density. The T S energy depends only on the atomic CN but polarization
on both the density and the CN of undercoordinated atoms. Only one neighbor short
makes a great difference in the bond length and binding energy!
Figure 7.6 summarizes the ZPS spectra of graphite monolayer skin and vacancy
defect. The skin ZPS differentiates two spectra collected at 75° and at 25°. The
defect ZPS differentiates two spectra collected at 75° from the surface after and
before high-density defect generation. Insets illustrate color zones contributing the
excessive states in each case. The atomic CN for the skin is about 3.1, which is
close to the ideal case of 3.0 of graphene interior. The atomic CN for the vacancy
extends from 2.2 to 2.4, which indicates that the next nearest neighbors contribute
to broadening the ZPS identity of the vacancy.