Carbon Material with a Highly Ordered Linear-Chain Structure - Polyynes: Synthesis, Properties, and Applications - page 222

FIGURE 11.8 Calculated total electron energy of the chain as a function of kink
angle.

band and the maximum found experimentally at 12 eV now corresponds to

the bottom of the forbidden gap ( Figure 11.6(b) ). Thus, the periodic kinks

in a carbon chain are an example of a deformation wave decreasing the
total energy of the chain where the linear sp 1 carbon chains are regularly
separated by carbon atoms in p 2 states. The kink angle

was varied from

zero (for cumulene) to 90 .

11.4.2 EELS M EASUREMENTS

The EELS results provide reliable information about the density of electrons
in the valence band of solids, electron excitations in solids, and volume den-
sity of the material. The EELS spectrum was obtained from the spectrum of
the 1s carbon photoemission line corresponding to the electron energy of
about 1 keV. We have followed the procedure described in ref. [15] and
removed the elastic 1s line to obtain the loss function in order to evaluate

the energy losses as shown in Figures 11.9 and 11.10(a) .

Figure 11.9 shows the EELS spectrum of diamond (dash dotted line)
[16], graphite (dashed line) [17], polyacetylene (dotted line) [15] and oriented
carbon film (solid line). Energy losses were recorded in a low energy region
from zero to 40 eV, which corresponds to both one-particle excitation
and collective excitation modes (plasmons). The loss function is S(E)

¼

" " ¼ " 1 (E) þ " 2 (E) is a complex dielectric function. The

Im(1/ (E)) where (E) i

maximum of S(E) at the energy E 3.7 eV corresponds to one particle inter-

bend excitation enhanced by the p -plasmon in carbon films. The broad
maximum at energy of 21.8 eV is the

¼

þp -plasmon excitation energy.