Carbon Material with a Highly Ordered Linear-Chain Structure - Polyynes: Synthesis, Properties, and Applications - page 236

materials [27], as the work function of the films appears to be relatively

small (see Section 11.4.10 ) . This is important for the fabrication of electro-

luminescent devices, which require electric currents of both electrons and
holes, recombination of which results in light emission. One of the inter-
esting aspects of this issue is the possibility of obtaining oriented sp 1 -carbon
films, which can be used as a command surface for deposition of different
organic molecules on the surface of a substrate [8]. This property permits
luminescent layers consisting of organic molecules of different types to be
obtained. At the same time the electron injector serves as a supporting
command surface.

11.4.12 T HE D EPENDENCE OF A TOMIC S TRUCTURE OF
sp 1 -H YBRIDIZED C ARBON F ILMS ON THEIR T HICKNESS
It is well known that the ensemble of sp 1 -carbon chains is unstable and used
to form cross-bonds between the neighboring chains. This results in the
formation of sp 2 and sp 3 chemical bonds between carbon atoms. However,
on the substrate surface the situation is radically changed due to the
interaction of carbon chains with the surface. In this case the growth of well-
oriented carbon chains was observed in [9]. The film orientation is found to
be strongly dependent both on the film thickness and deposition conditions.
For thicker films the influence of the substrate surface becomes negligible
and the films are not purely sp 1 .
The mean size of the crystallites of linear-chain carbon films calculated
from the width of their electron diffraction maximums depends on the film

thickness ( Table 11.1 ). As can be seen from Table 11.1 the mean crystal size

of the films is comparable with the film thickness if that thickness is about
4.0 nm. In this case, the films become highly oriented and there are sharp

reflections in their diffraction pattern ( Figure 11.1(a) ) . If the thickness of the

films increases to 16.0 nm, the orientation still takes place. In films with a
thickness greater than 60 nm amorphization is observed, with the formation
of inter-chain bounds. This is clearly seen by increasing the intensity of
diffraction maximums corresponding to the three-dimensional amorphous
carbon phase and finally by the complete disappearance of diffraction
maximums corresponding to the sp 1 phase.

TABLE 11.1
The Dependence of Crystal Mean Size on Film Thickness

Thickness (nm) 4.0 6.0 8.0 16.0 32.0 >64

Crystal mean size (nm) 3.5 2.5 2.3 2.0 1.7 <1.0