Ion Irradiation of Solid Carbons - Polyynes: Synthesis, Properties, and Applications - page 269

the same optics and it is collimated into a parallel beam that is reflected
back along the same path of the laser, in the optical axis of the confocal
illuminator. A small fraction of this beam is intercepted by the micro-prism,
while the rest is focused on the entrance slit of the spectrometer. A CCD
camera is used as detector in the range 400-1000 nm. The spectral resolution
is about 3 cm 1 and the positioning reproducibility is about 1 cm 1 .
The carbon thin films have been irradiated with 200 keV Ar þ ions and
their IR spectrum obtained in situ before, during and after irradiation, by an
FTIR spectrometer (Bruker Equinox 55).
The vacuum chamber is interfaced to an ion implanter (200 kV) from
which ions with energy up to 200 keV (400 keV for double ionizations) can
be obtained. The IR spectrometer is positioned (by a moveable optical
bench) in a way such that the IR beam is transmitted, through a hole of the
sample holder, by the substrate. The sample holder is mounted at an angle
of 45 both with the ion beam and with the incoming IR beam and spectra
can be acquired in situ without tilting the sample. Samples can also be put in
thermal contact with a closed-cycle helium cryostat whose temperature can
be varied between 10 and 300K. The spectra shown in this work have been
taken with a resolution of 2 cm 1 and a sampling of 0.5 cm 1 .
The ion beam produces a spot larger than the hole in the sample holder
and currents in the range of 100 nA cm 2 to tens of m Acm 2 . The integrated
ion flux (fluence in ions cm 2 ) is measured, by a charge integrator, from the
ion current monitored during irradiation. For further details on the

experimental apparatus see [ 15 ] .

The results are shown in Figure 13.3 . The as prepared cluster assembled

carbon film exhibits the typical band of carbynoid materials at 2097 cm 1
[16] that appears quite broad, perhaps due to the superposition with
cumulene bands. In addition, the films exhibit C-H stretching bands, in
particular in the aliphatic region (3000-2800 cm 1 ), and also an aromatic
feature at 3071 cm 1 . These features have to come from contaminations,
either in the vacuum chamber during the preparation of the samples, or
most likely after their exposure to air. In any case, before irradiation, there
are clear evidences both from Raman and IR spectroscopy of the survival of
carbynoid structures along with a component of hydrogenated amorphous
carbon. After irradiation (Figure 13.3 spectra b and c) the intensity of the
C C band at 2097 cm 1 increases, the intensity C-H stretching bands

progressively decreases due to an hydrogen loss and a carbonization of the
sample. A new band at about 3300 cm 1 appears, as indicated by an arrow,
that is easily attributed to C-H stretching in R-(C C)-H.

13.4 ION IRRADIATION OF RELATED MATERIALS

In this paragraph we report some results obtained after ion irradiation of
asphaltite, a natural bitumen, and benzene frozen at low T (16K).