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Carbon Nanotubes. Basis Concepts and Physical Properties

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Angewandte
Books
Chemie
Carbon Nanotubes
Basis Concepts and
Physical Properties.
By Stefanie Reich,
Christian Thomsen,
and Janina
Maultzsch. WileyVCH, Weinheim
2004. ix + 215 pp.,
hardcover
E 99.00.—ISBN
3-527-40386-8
With advances in the area of carbon nanotubes progressing exponentially over the
past decade, there has been an increasing
need for comprehensive surveys and texts
that can serve both as introductions for
newcomers to the field and as reference
materials for the already established
investigator. There is no doubt that this
timely and interdisciplinary work will
emerge as an important milestone and
will make a significant impact.
The first chapter covers structure
and symmetry aspects of carbon nanotubes. The authors explain how to construct the atomic structure and the reciprocal lattice of carbon nanotubes based
on a given chiral vector. Experimental
techniques, such as electron microscopy,
electron diffraction, and scanning probe
microscopy,
are
introduced
and
reviewed as valuable aids in determining
the chiral indices of the tubes. The linegroup symmetry of single-walled carbon
nanotubes is developed to demonstrate
that any state of a (quasi-)particle can
be characterized by a set of quantum
numbers: those describing the linear
momentum k, the angular momentum
m, and, at special points in the Brillouin
zone only, parity quantum numbers. On
the other hand, it is shown that achiral
Angew. Chem. Int. Ed. 2004, 43, 5877 – 5879
tubes possess additional vertical and
horizontal mirror planes. By applying
this line-group symmetry one can calculate selection rules. In the final part of
this first chapter, the authors highlight
all infrared and Raman-active phonon
modes, and derive the displacement patterns of Raman-active phonons for armchair-shaped and zig-zag tubes.
In the next chapter Reich, Thomsen,
and Maultzsch derive the electronic
band structure of carbon nanotubes
from the graphene band structure in
the zone-field approximation, in which
the graphene(s electronic energies
along the allowed k-vectors are used.
Conversely, the electronic dispersion in
the p bands in graphene is obtained by
nearest-neighbor and third-neighbor
tight-binding calculations. The resulting
electronic density of states in singlewalled carbon nanotubes shows the typical features of a one-dimensional
system, with singularities that follow an
E 1/2 form. Whereas armchair nanotubes preserve their metallic character,
other nanotubes with integral values of
(n1 n2)/3 develop a small band gap of
the order of 10 meV. The authors demonstrate that the higher-lying states are
shifted towards the Fermi level in the
rolled-up nanotubes. The final part of
this chapter deals with the effects of
the bundling of the nanotubes into
ropes. Probably the most profound
impact is seen in the electronic band
structure of the nanotube bundles,
which differs significantly from the
band structure of the isolated tube.
A comprehensive description of optical experiments follows in the next chapter. By comparing absorption and emission properties it was possible to verify
the calculations of the electronic band
structure. Particularly important is the
section that deals with the strong, but
long-missed, luminescence when debundling the nanotubes. Debundled nanotube carriers have a lifetime in the first
excited state that is longer by an order
of magnitude than that in bundles. This
opens up possibilities for using isolated
nanotubes as light emitters.
Transport properties in single-walled
carbon nanotubes are described in
Chapter 5. Ballistic conductance over
lengths of 100 nm to several mm is
found in armchair tubes. In semiconducting tubes, on the other hand, the
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mean free path for elastic scattering
seems to be shorter, with quasi-ballistic
transport over a mean free path of
around 100 nm. The authors show that
the resistance of nanotubes depends linearly on the applied voltage along the
tube—accelerating electrons to high
energies causes emission relaxation.
Furthermore, it is illustrated that in the
low-temperature domain Coulomb
blockade was observed in experiments.
In this context, the authors point out
that tunneling into the nanotubes is suppressed until an additional energy is provided, thus helping to overcome the
charging energy.
Next, in order to understand the
elastic and vibrational properties of
carbon nanotubes, Reich, Thomsen,
and Maultzsch approximate the tube as
a hollow graphene cylinder with finite
wall thickness and closed ends. They
explain that, in line with expectations,
the linear modulus in the circumferential or radial directions is about two to
three times greater than in the axial
direction. Different pressure slopes for
axial and circumferential vibrations as
well as Raman experiments, which
show uniform pressure dependencies of
all high-energy modes, evolve from
phonon eigenvectors with mixed characters in chiral nanotubes. Also the
authors discuss the degenerate E-eigenvectors, which show a “wobbling” of the
displacement direction when going
around the circumference. This sixth
chapter concludes with some considerations regarding the micromechanical
applications of nanotubes based on
their elastic properties.
Chapter 7 deals with Raman scattering and its selection rules. The authors
give insights into how the symmetry of
the Raman modes can be determined
on unaligned samples from linearly and
circularly polarized measurements. An
important part of this chapter is concerned with double resonance, which
dominates the entire Raman spectrum
of carbon nanotubes more than in
other solids. This explains, both qualitatively and quantitatively, many phenomena in their Raman spectra.
The final chapter is devoted to vibrational properties. Here Reich, Thomsen,
and Maultzsch provide a brief guide to
what can and what cannot be concluded
from the Raman spectrum of a tube. Of
* 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5877
Books
course, most important are the radial
breathing mode and the double-peak
structure just below 1600 cm 1, which
together confirm the presence of nanotubes in any given sample. However,
the radial breathing mode alone is not
sufficient evidence for nanotubes.
Next, the authors consider the orientation of isolated tubes or aligned samples,
and describe how these properties can
be determined from the Raman signal,
since the signal is strongest when the
incoming light is polarized parallel to
the nanotube axis. The authors also conclude that diameters can be estimated
from the frequency of the radial breathing mode. As far as chiral angle and indices are concerned, it is found that the
uncertainty in diameter is too large to
assign n1 and n2 on the basis of the
Raman data alone. A different situation
exists for defect concentrations, which
can be deduced from the ratio of the
intensities of the D and D* peaks.
Whereas the broad peak around
1540 cm 1 is a good indicator for metallic
nanotubes, the identification of semiconducting nanotubes still remains controversial. Finally, the strain of nanotubes
can be determined from a shift in
phonon frequency (at fixed excitation
energy), which results from a change in
the bond lengths and/or angles. Although
in principle possible, the authors decide
that the determination of the band gap
fails, since the typical band gaps below
1 eV are too small for standard lasers.
In summary, all the chapters of
Carbon Nanotubes are solid, comprehensive discussions of the basis concepts
and physical properties of this form of
carbon. Each chapter begins with an
excellent introduction to the topic concerned, which is followed by a good
overview of the subject and more details
for the expert in the area. The chapters
should prove very useful to both students and researchers in the different
areas. I would recommend this book to
practicing chemical physicists and physical chemists as well as to readers
broadly interested in nanoscience.
Dirk M. Guldi
Institut f3r Physikalische Chemie
Friedrich-Alexander-Universit7t Erlangen
(Germany)
DOI: 10.1002/anie.200385171
5878
Life Sciences for the 21st Century
Edited by Ehud
Keinan, Israel
Schechter, and
Michael Sela. WileyVCH, Weinheim
2003. 356 pp.,
hardcover
E 44.90.—ISBN
3-527-30588-2
This book is the second in a threevolume series that started with a
volume on chemistry and will be completed by one on physics and mathematics. In this volume Ehud Keinan, Israel
Schechter, and Michael Sela (of Technion—the Israel Institute of Technology,
and the Weizmann Institute of Science)
have asked scientists to review their
achievements and give their views of
the prospects in their areas of the life
sciences.
The 16 reviews cover a selection of
topics that reflect recent discoveries in
life science. Starting with RNA, which
is suggested to have been the origin of
all life, the book discusses recent advances in basic scientific research, on topics
such as protein synthesis, protein degradation by the proteasome, cell signaling,
and protein interactions. It also includes
novel genetic approaches to the development of medical therapies, and plant
biotechnology based on research
during the 20th century.
After 50 years of research concentrated on DNA, which culminated in
the sequencing of the human genome,
in the 21st century the focus has shifted
to RNA as the nucleic acid species of
particular interest. One review by
Gerald Joyce discusses the synthesis,
modulation, and self-replication capability of RNA, which gives it the potential to act as the carrier of information
for the origin of replicating life on
earth. There is strong evidence that
RNAs thereby served as synthase ribozymes to synthesize their own building
blocks. Some of those reactions, including activation and ligation of the building blocks to form oligomers, have
already been proven in vitro to be possible. Furthermore, it is well known that
different RNA species are capable of
* 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
performing a variety of chemical reactions, including peptide-bond formation.
A remnant of this RNA world in our
cells is certainly the ribosome, a protein
synthesis machinery that consists mainly
of catalytic RNA, tRNAs, and ribozymes. Ada Yonath summarizes the
amazing progress that has been made
during the last 20 years on the structural
and functional determination of such a
large biological complex.
Moving on from the world of RNA
and its role in protein synthesis, other
chapters focus on the mechanism by
which proteins are prepared for their
subsequent intracellular degradation,
and the ubiquitin–proteasome pathway
is explained. Until the late 1980s, the
subject of protein degradation was
more or less neglected, since no organelle had been identified as being responsible for the degradation of cytoplasmic
proteins. We now know that this is a
complicated pathway, which starts with
the labeling of the proteins with ubiquitin, a small polypeptide of 76 amino
acids, thus guiding them to the proteasome, a large protein complex bearing
many protease activities. The chapters
by Aaron Ciechanover and Michael
Glickman describe in detail the structural requirements and the function of
this pathway. Besides its function in the
degradation of endogenous proteins, as
determined by their turnover, the proteolysis pathway is also very important
in the degradation of antigens and
their recognition by our immune
system. In general, protein modifications occurring after their synthesis
often change the cellular fate of the protein or trigger a variety of signaling cascades, such as the phosphorylation process described in Chapter 6 by
Edmond Fischer, and that described in
Chapter 8 by Tony Hunter. It is now
known that communication between
cells, or between cells and their environment, occurs by signaling processes or
cascades that require the rapid modification of transmembrane and intracellular proteins that cross-talk with each
other to transfer a signal from the outside of the cell into the inside, where it
will start a response mechanism. From
results of research in the last 20 years,
this communication pathway has
turned out to be very sophisticated and
complex. Even though many aspects of
Angew. Chem. Int. Ed. 2004, 43, 5877 – 5879
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