by Professor Wolfgang Bacsa
Scientific research on carbon nanotubes witnessed a large expansion1. The fact that CNTs can be produced by relative simple
synthesis processes and their record breaking properties lead to numerous
demonstration of many different types of applications ranging from building fast
field effect transistors, flat screens, transparent electrodes, electrodes for
rechargeable batteries, conducting polymer composites, bullet proof textiles and
As a result we have seen enormous progress in controlling growth of CNTs.
CNTs with controlled diameter can be grown along a given direction parallel to
the surface or perpendicular to the surface. In recent years we have seen narrow
diameter CNTs with 2 and more walls to be grown at high yield2.
Behind this progress one might forget about the remaining tantalizing
challenges. Samples of CNTs still contain a large amount of disordered forms of
carbon, catalytic metal particles or parts of the growth support are still a
large fraction of the carbon nanotube mass. CNT as produced continue to contain
a relative wide dispersion of diameters and lengths. To disperse CNTs and
control their distribution in a matrix or on a given surface is still a
challenge. There has been enormous progress in size selecting CNTs3,4. However, the often applied techniques
limit application to due to the presence of surfactant molecules or cannot be
applied to larger volumes.
Analytical techniques are playing an important role when developing new
synthesis, purification and separation processes. Screening of carbon nanotubes
is essential for any real world application but is also essential for their
fundamental understanding such as the understanding the effect of tube bundling,
doping and the role of defects5.
At the 'Centre for materials
elaboration and structural studies', Professor Wolfgang Bacsa and Pascal
Puech and have much focused in screening CNTs with optical methods and
developing physical processes for carbon nanotubes working closely with the
materials chemists at different local institutions. We have much focused our
attention on double wall carbon nanotubes grown form the catalytic chemical
vapour deposition technique2.
Their small diameter, high electrical conductivity and their large length as
well as the fact that the inner wall is protected from the environment by the
outer wall, are all good attributes for incorporating them in polymer
composites. Depending on the synthesis process used we find the two walls are at
times strongly or weakly coupled.
By studying their Raman spectra at high pressure6, in acids7, strongly photo
excited or on individual tubes we can observe the effect on the internal and
external walls. A good knowledge of Raman spectra of double wall CNTs gives us
the opportunity to map the Raman signal of the ultra thin slices of composites
and determine the distribution, agglomeration state and interaction with the
|TEM images (V Tishkova CEMES-CNRS) of double wall
(a), industrial multiwall carbon nanotubes (b) and Raman G band of double wall
CNTs at high pressure in different pressure media revealing molecular nanoscal
Working on individual CNTs in collaboration with Anna Swan of Boston
University, gave us the opportunity to work on precisely positioned individual
suspended CNTs. An individual CNT is an ideal point source and this can be used
to map out the focal spot and to learn about the fundamental limitations of high
resolution grating spectrometers8.
The field of carbon nanotube research has grown enormously during the last
decade making it difficult to follow all the new results in this field. It is
quite clear that applications where macroscopic amounts of CNTs are needed,
standardisation of measurement protocols, classification of CNT samples,
combined with new processing techniques to deal with large CNT volumes will be
needed. Applications where only minute quantities on a surface are used, suffer
from the fact that no parallel processing is still limited. This shows further
progress in growing CNT on surfaces is still needed although they have been a
recent break through in growing CNT in a parallel fashion and with preferential
seminconducting or metallic tubes9.
1. Ali Javel, ACNano 2 (2008) 1329
Flahaut, R. Bacsa, A. Peigney, Ch Laurent, Chem. Commun. 12 (2003) 1442
3. M. S. Arnold et al Nature Nanotechnology 1 (2006) 60
4. S. Ghosh, S. M. Bachilo, R. Bruce Weisman, Nature Nanotechnology 9
May 2010, doi:10.1038/nnano.2010.68
5. I. Gerber, P. Puech, A.
Gannouni, W. Bacsa, Phys. Rev. B 79 (2009) 075423
6. P. Puech,
H. Hubel, D. Dunstan, R. R. Bacsa, Ch. Laurent, and W. S. Bacsa, Phys. Rev.
Lett. 93 (2004) 095506
7. P. Puech, E. Flahaut, A. Sapelkin, H.
Hubel, D.J. Dunstan, G. Landa, W.S. Bacsa, Phys Rev B 73 (2006) 233408
8. A. G. Walsh, W. S. Bacsa, A. N. Vamivakas, A. K. Swan, Nano
Letters Vol. 8 (2008) 2215
9. L Ding et al, Nano Letters 9
Copyright AZoNano.com, Professor Wolfgang Bacsa (Center for
Materials Elaboration and Structural Studies (CEMES))