Synthesis of Carbynoid Structures by the Combustion Flame Method - Polyynes: Synthesis, Properties, and Applications - page 86

energy allows sp 3 sites to be excited with a cross section comparable to sp 2
sites. In another study, Evsyukov [38] has shown that the peak in the Raman
spectra near 1100 cm 1 is likely to result from C-O-C stretching vibrations.
This structure can arise in the reaction products due to combustion of oxy-
acetylene. The peak at 1332 cm 1 due to diamond was also detected in the
spectrum.
It is not possible to assess the ratio of carbon-carbon double bonds
(polycumulene)/triple bonds (polyyne) in the film solely by Raman spectro-
scopy. Theoretically the quantum-chemical simulation shows that both
isomers have very similar Raman spectra [39].
The equation given by Kastner et al. [40],

C ¼ C ð N Þ¼ 1750 þ 3980 = N,

allows the number of carbon atoms, N, in the chain to be calculated:

N ¼ 3980 =ð C ¼ C 1750 Þ ,

C ¼ C is the wavenumber (cm 1 ) that was obtained in the Raman
spectra.
For the carbyne film obtained at

where

1.15, a chain length of only 8
carbon atoms can be calculated (2253 cm 1 ). For the carbyne film obtained
at

¼

1.1 there are two types of chain: the acetylenic chains having 8 carbon
atoms (2248 cm 1 ) and allenic or, better, cumulenic chains of unknown
length.
From the cross section of the SEM image, the growth rate of a carbon
film could be calculated. It grows by increasing the ratio of acetylene to
oxygen. The growth rate is about 100 m m/h at

¼

¼ 1.15 and decreased to

60 m m/h at 1.1 but the quantity of the carbyne in the film was increased.

The quantity of carbyne content present in the sample can be estimated by
the intensity of the carbyne band relative to the lines of carbonaceous
byproducts I c /I bypr [41].
Raman spectra of the carbon sample obtained by combustion flame are
in agreement with Raman spectra reported in literature [42]. The results
were also in agreement with the results obtained by shock-quenched
graphite of Heimann et al. [43]. The ''carbyne'' obtained by this method was
also surrounded by tetragonal disordered diamond grains.
In 2000, Donnet et al. [44], during synthesis diamond by shock-wave
compression, also found the crystalline carbyne in the sample. The
crystalline structure of this film was examined by x-ray. The results
obtained show that the film is composed of a mixture of diamond and
carbyne.

¼