Carbon Material with a Highly Ordered Linear-Chain Structure - Polyynes: Synthesis, Properties, and Applications - page 216

confirmed by electron spectroscopy including electron energy loss spectro-
scopy (EELS) and atomic emission spectroscopy (AES) with x-ray exci-

tation (see Section 11.4.1 ) . The spectroscopic results provide clear evidence

that the Tetracarbon TM films were composed of carbon chains with sp 1
hybridization.
The data obtained permitted us to propose the model of atomic arrange-
ment of the film structure, which is similar to that published before [2]. The

structure shown in Figure 11.1(g) is multi-layered with each layer consisting

of carbon atom chains in the sp 1 -hybridization state. These chains are
densely packed into a hexagonal lattice. According to the diffraction pattern
and atomic force microscopy (AFM) images the distance between the chains
is in the range of 0.490 to 0.503 nm.
According to the results on attenuation of the higher-order electron
diffraction reflections, the layers are randomly shifted with respect to each
other. In other words, the film structure is composed of identical kinked
chains with the kinks randomly oriented with respect to the chain axis. The
presence of the kinks is well correlated with the Raman peak at 1552-
1583 cm 1
The kinks of the neighboring chains are presumably correlated and
positioned in the same plane and at the same direction. When taking into
account the length of sp 1 hybridized carbon bounds (0.128 nm in cumulene)
and the possible inter-chain distances of 0.480 to 5.00 nm, the density of
Tetracarbon TM having a hexagonal crystal lattice is calculated to lie between
1.54 and 1.18 g/cm 3 . This is in good agreement with the density value
determined from the EELS measurement (1.35 g/cm 3 ) described below (see
By means of the linear combination of atomic orbitals
(LCAO) method the density of valence electron states (DOVS) of infinite sp 1
carbon chains with periodic kinks as a function of the kink angle

in the Raman spectrum shown in Figure 11.2 and Figure 11.11 .

Section 11.4.2 ).

was also
calculated. The possibility of decreasing the total energy of the chains is
found to have a maximum at 55 . The phonon spectrum of infinite sp 1

carbon chain with periodic kinks was also calculated.
The anisotropic structure of the films obtained on the basis of the
proposed model of its crystal and atomic structure is in agreement with the
anisotropy of its physical properties described below.
The new results on experimental and theoretical investigations of the
linear chain-like structure presented below confirm the proposed model
of its atomic and crystal structure. The major question still remains: is
sp 1 -hybridized chain-like carbon stable or unstable with respect to the
formation of cross-linkages among carbon chains? The viewpoint that
sp 1 -hybridized chain-like carbon is unstable is based on studies of free,
randomly oriented sp 1 carbon chains, which can simply be cross-linked. In
the case when the chain ends are strongly fixed on the surface of substrate,
the substrate plays an important role of a ''command'' surface [8]. This
means that the surface controls the orientation of the chains and keeps
them at a distance apart from cross-linking. However, the substrate can

¼