Synthesis of Carbynoid Structures by the Combustion Flame Method - Polyynes: Synthesis, Properties, and Applications - page 92

in the incident angle at the intersection of the flame front and the substrate.
By observing the flame during deposition, we found that in the central zone
the incident flame jet is perpendicular to the surface. The incident angle
decreases with increasing distance from the center, and the flame forms a
toric swirling flow at the periphery. These parameters are an important
factor affecting the crystallites carbyne growth. The non-uniformity of the
flame can lead to the formation of different lengths of linear carbon chains
and to different allotropic forms of carbon in the same film.
From the surface point of view and from experimental observation, the
initial growth of carbyne on a carbide tungsten substrate is always an island
growth. In this growth mode, the equilibrium state is obtained when all
the deposited carbon atoms are in one large island. The driving force to
approach this equilibrium is the reduction of the surface energy. Some
carbyne crystallites of approximately equal size can be closely packed in
a mosaic crystal, as seen in the figures. Comparable dimensions of crys-
tallites can in turn be determined by similar growth conditions of the crystal
nuclei [39].

5.4 CONCLUSIONS

In this paper we have presented the synthesis of carbynoid structures by the
combustion flame method and investigated the influence of the ratio
acetylene/oxygen on the morphology and quality of the carbon film
deposited. Under our deposition conditions, the following conclusions can
be drawn:

Linear carbon chains with variable crystal lattice parameters could be
obtained. The carbon film is composed of a mixture of sp 3 - and sp-
hybridized carbon atoms. Therefore we are dealing with carbynoid
structures. Carbynoid crystals of 1 m m size were obtained.
Decreasing the ratio acetylene/oxygen from

1.1 causes
a decrease in the content of sp-carbon atoms in the films but
increases the chain length of sp-hybridized carbon.
At a low ratio of acetylene/oxygen (

¼ 1.15 to ¼

¼ 1.05) only crystalline diamond

is obtained.
The structure of the carbyne deposited is multilayered.

REFERENCES

[1] Kudryavtsev, Yu.P. The discovery of carbyne. In: Carbyne and Carbynoid
Structures. Kluwer Academic Publishers: Dordrecht /Boston/London, 1999;
1-6.