Synthesis and Characterization of Carbynoid Structures in Cluster-Assembled Carbon Films - Polyynes: Synthesis, Properties, and Applications - page 21

FIGURE 2.4 (a) TEM image of a cluster assembled carbon film showing an
amorphous matrix with small closed shell particles and bundles of graphene sheets.
(b) Tapping mode AFM topographies at different magnifications of a cluster assem-
bled carbon film with nominal thickness of 700 nm. The scan size is 1000 1000 nm,
the vertical color scale is 50 nm.

Transmission electron microscope (TEM) analysis of nanostructured
carbon films shows that, at this scale, the morphology is reminiscent of the
precursor clusters. TEM micrographs show the presence of an amorphous
matrix with small closed shell particles and bundles of graphene sheets
(Figure 2.4a). Large onion-like and tubular particles have also been
observed.
Surface morphology of nanostructured carbon films has been investi-
gated by atomic force microscopy (AFM) in air (Digital Nanoscope IIIA)
operating in tapping mode to avoid scratching of the samples. Figure 2.4b
shows typical morphologies of nanostructured carbon films. The observed
grains are larger than single clusters in the beam and they result from an
aggregation mechanism. The grain size depends on precursor size, and their
mean diameter value ranges between 10 and 15 nm.

2.3.2 R AMAN C HARACTERIZATION OF THE A S -D EPOSITED
C ARBON F ILMS

Raman spectra of cluster-assembled carbon films grown in our apparatus
and then kept under ambient conditions are characterized by the presence
of the so-called G and D bands in the 1300-1600 cm 1 spectral region [36].
Their position and shape can be related to the degree of structural disorder
of the film and to the distribution of bond lengths and angle distortions [37].
A weak feature in the 2000-2200 cm 1 spectral region is also present [31].
This feature can be interpreted a posteriori as due to sp chains protected
from oxidation by the sp 2

carbon matrix (see Figure 2.5 ).