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FIGURE 13.3
Transmittance IR spectra at room temperature of: (a) a cluster
assembled carbon thin film after exposure to air (about 20min); (b) after ion
irradiation (3.8
10
13
200 keV Ar
þ
cm
2
); and (c) after ion irradiation (1.5
10
14
200 keV Ar
þ
cm
2
). Spectra have been vertically shifted for clarity.
13.4.1 A
SPHALTITE
Asphaltite samples used in this work are from Izhem, Timano-Pechora
Basin, Russia and have been analyzed by Moroz et al. [17]. Compared to
most other solid oil bitumens, asphaltite is rich in H and has a relatively
disordered structure. Its polycyclic aromatic structural units are relatively
small. It is rather bright and transparent in the infrared due to a large
optical gap (the energy gap between valence and conduction bands) [18].
Moreover, asphaltite is very dark in the visible range due to a broad
complex electronic absorption feature typical of PAHs [18-21]. To obtain
asphaltite samples suitable for ion irradiation and contemporary transmit-
tance IR spectroscopy, we deposited some drops of asphaltite diluted in
chloroform on a IR-transparent Si substrate. We allowed the mixture to
evaporate and leave uniform asphaltite layers whose thickness was of the
order of 1
m
m, as evaluated by an optical microscope.
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