Determination of structural differencies of different types of carbon using
TEM and electron diffraction
R.O.Grasin, J.L. Lábár, G. Radnóczi
Research Institute for Technical Physics and Materials Science,
Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary
Carbon can form a vast number of natural or synthetically generated compounds including the
highly anisotropic hexagonal phase graphite, tetrahedrally bonded diamond, BuckmintserFullerenes and bucky-tubes, glassy carbon and many disordered forms. Whilst the microstructure
of highly crystalline forms of carbon may be deduced by careful crystallographic analysis, the
average microstucture of disordered forms poses quite a challenge [1]. In this poster, the short
and medium range order is compared for different carbon structures as determined from
measured electron diffraction patterns.
The used microscope is a Philips CM 20 – TEM operating at 200 kV accelerating voltage.
Selected area electron diffraction (SAED) patterns were recorded on DITABIS imaging plates.
This image is processed with the Process Diffraction program [2]. The Q(i)Q reduced
interference function and its Fourier transform, the pair correlation function (G(r)) was
determined by applying a self consistent empirical correction to the baseline of the measured
diffraction, ensuring that the pair correlation function becomes physically meaningful [2]. From
the normalized pair correlation function (g(r)) we can determine the distribution of the atomic
distances in the material. The radial distribution function which yields the coordination numbers
can also be obtained from G(r). Because the coordination numbers are sensitive to the density, it
is necessary to determine the plasmon energy, from which the density of the material is defined.
Using these techniques we studied five amorphous carbon samples. The first two amorphous
carbon thin film samples are produced by different PVD techniques. These materials and their
diffraction patterns are shown in Fig.1a and Fig. 1b. The third sample is an ion milled glassy
carbon which is presented in Fig. 1c. Glassy carbon is a turbostratic (disordered layer stacking)
form of carbon that is produced by carbonizing a polymer under carefully controlled conditions
of temperature and pressure. Glassy carbon is made from a resin that is carbonized at a very low
heating rate [3]. The last two samples are multiwall carbon nanotubes. The microscopic images
of these nanotubes and their diffraction patterns are shown in Fig. 1d and Fig. 1e. A nanotube can
be considered as a single sheet of graphene that has been rolled up into a tube. The multiwall
nanotube represents more single wall tubes pulled one into another.
We show similarities and also differences in g(r) of these materials. The g(r) of the first two
samples are almost identical. This function is presented in Fig. 2a. The glassy carbon is more
structured then the PVD carbon films. Fig. 2b shows the g(r) of the glassy carbon. The g(r) of the
multiwall carbon nanotubes are similar to the g(r) function of the glassy carbon and are presented
in Fig. 2c. In the first two samples we defined a short range order until a 0,4 nm, but the glassy
carbon is more ordered and it shows a medium range order until 0,7 nm distance. The nearest
neighbour distances are in good agreement with the literature [4]. In case of the multiwall carbon
nanotubes a better structural order is present. This material shows a medium range order until
around 1 nm.
100 nm
a) PVD 1
b) PVD 2
1000 nm
1000 nm
50 nm
20 nm
c) Glassy carbon
d) MWCNT-S1
e) MWCNT-S2
Fig. 1 The microscopic images of the studied materials and their diffraction patterns
Glassy carbon
Intensity / a.u.
Intensity / a.u.
DC magnetron sputtered C
DC arc deposited C
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
Atomic distances / nm
Intensity / a.u.
0,2
0,3
0,4
0,5
0,6
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
b) g(r) of glassy carbon
MWCNT-S2
MWCNT-S1
0,1
0,1
Atomic distances / nm
a) g(r) of PVD carbons
0,0
0,0
0,7
0,8
0,9
1,0
As we expect in case of the
multiwall carbon nanotubes the
nearest
neighbor
distance
correspond with the nearest
neighbor distance in a graphite,
but the other interatomic
distances are changed in the
rolled up graphene sheet, the
MWCNT.
Atomic distances / nm
c) g(r) of MWCNT-S1 and S2
Fig. 2 Normalized pair correlation functions of the studied materials, bars indicate the interatomic
distances of graphite.
Acknowledgements
This work was supported in part by the EC´s Human Potential Programme under contract HPRN-CT-2002-00209,
(New Fullerene-like Materials). R. O. Grasin acknowledges the financial support provided through the same project.
The support of the Hungarian National Scientific Found (OTKA) through grants M M041689 and T043437 is
acknowledged.
References
[1] T. Petersen, I. Yarovsky, I. Snook, D. G. McCulloch, G. Opletal, Carbon 41, 2403-2411 (2003)
[2] Lábár JL, Kovács A, Barna BP, Hanada T, Ishimaru M, Hirotsu Y, Bae IT, Proc. 6th Multinational Congress on
Electron Microscopy, Pula, 2003, 469-470
[3] W.V. Kotlensky, D.B. Fischbach, JPL Technical Report No. 32-842 (1965)
[4] B.O’Malley and I. Snook, D. McCulloch, Phys. Rev B, 57, No. 22, 14148-14157 (1998)