Carbon Material with a Highly Ordered Linear-Chain Structure - Polyynes: Synthesis, Properties, and Applications - page 240

The I-V curve is found to have Schottky-type dependence under forward
biased conditions. This means that a semiconducting diode can be success-
fully fabricated using the sp 1 /sp 3 junction in the carbon-based structure.
This result opens up a promising route to the creation of carbon electronics
on the basis of using junctions consisting of carbon films with various types
of electron hybridization with the aid of different dopants.

11.5 THE NEW CARBON MATERIAL TETRACARBON TM

A new carbon material, Tetracarbon TM , was developed on the basis of
1
Tetracarbon TM consists of densely packed linear chains of sp 1 -hybridized
carbon, oriented perpendicularly to the substrate surface. An analogy could
be velvet, where linear carbon chains project perpendicularly to the sub-
strate surface.
Thus, inter-atomic distances and the atomic state in Tetracarbon TM are
fundamentally different from all the known forms of carbon. The differ-
ences between clear and hard diamond on the one hand, and soft and black
graphite on the other hand, illustrate the differences among Tetracarbon TM
and other forms of carbon. The distance between the neighboring sp 1 -
carbon atoms within the Tetracarbon TM chain is about 1.3A ˚ , whereas the
distance between the carbon chains is 4.80-5.03 A ˚ . It is interesting to note
that in some respects Tetracarbon TM is similar to tubulenes, as it can be
considered as tubulene in the limit when the diameter of the tube approaches
the diameter of carbon atom. Nevertheless, in Tetracarbon TM the hybri-
dization state of carbon atoms changes from sp 2 to sp 1 . It is basically a new
purely one-dimensional sp 1 -carbon modification with one-dimensional
electron band structure, whereas tubulene is a quasi-one-dimensional
material in which the number of one-dimensional electron bands increases
with increasing tubulene diameter. Tetracarbon TM and tubulene are also
similar in that the carbon chains in Tetracarbon TM are oriented normally to
the surface of the film, similar to the orientation in tubulene.
The sp 1 modification carbyne briefly described below is characterized by
a different intrinsic structure and can be obtained only in the form of very
small particles. Another analogous example is the sp 1 molecular crystals
which are composed of short sp 1 -carbon chains with organic caps on the
ends of the chains, which prevents them from collapsing into the amor-
phous state [28]. These crystals are not composed of pure sp 1 -hybridized
carbon and are stacked into a cross-linked crystal structure, which is easily
dissolved in many organic solvents and is completely different

sp -hybridized highly oriented carbon films. Figure 11.1(g) indicates that

from

Tetracarbon TM .
Numerous tests of Tetracarbon TM have shown a number of its valuable
features. The Tetracarbon TM coating process is performed at low tempera-
ture (20-200 C), so it can be used for coating polymers (polyethylene,