Synthesis and Characterization of Carbynoid Structures in Cluster-Assembled Carbon Films - Polyynes: Synthesis, Properties, and Applications - page 25

FIGURE 2.8 Raman spectra of a 200 nm thick sample exposed to 500mbar of
molecular nitrogen after different exposure times: as deposited (A), after 50min (B),
2.5 h (C), 18.5 h (D) and 44.5 h (E). Gaussian fit of the two components of the
carbyne peak is also reported.

temporal evolution of the Raman spectrum of a film exposed to N 2 . Similar
spectra have been obtained for helium and hydrogen exposure, indicating
that the evolution of the polyyne and polycumulene peaks is substantially
similar for all these gases. Dry air induces a different behavior, which will be
discussed later.
The intensity of the C peak decreases readily following an exponential
law and reaching an asymptotic value after a few hours from gas injection

( Figure 2.7 ) . Table 2.1 presents the results of the analysis of the evolution

of I C rel , fitted with an exponential decay: the time constants and the

percentage R 0 of the nonreacted fraction of sp chains for the different gas
exposures are shown, together with the parameters of the metastable decay
in UHV as discussed above.
The gas exposure slightly affects the sp 2 component of the carbon
network. Since these changes are not relevant as for the C band, I C rel can be
considered a reliable parameter when following the sp component evolution.
The same behavior is qualitatively observed for exposure to helium and
molecular hydrogen, and the analysis of the decay time constants and the
R 0 for hydrogen, helium and nitrogen shows that the values of R 0 vary
of 12-14% for the three gas, while

is substantially different ( N2 ¼ 1h,

He ¼ 11 h). The relative intensity of the polyyne and the poly-

cumulene components remains substantially unchanged during the peak
evolution and only a small blue shift is observed for both peaks.

2h, H2 ¼