289 research outputs found
Interaction between concentric Tubes in DWCNTs
A detailed investigation of the Raman response of the inner tube radial
breathing modes (RBMs) in double-wall carbon nanotubes is reported. It revealed
that the number of observed RBMs is two to three times larger than the number
of possible tubes in the studied frequency range. This unexpected increase in
Raman lines is attributed to a splitting of the inner tube response. It is
shown to originate from the possibility that one type of inner tube may form in
different types of outer tubes and the fact that the inner tube RBM frequency
depends on the diameter of the enclosing tube. Finally, a comparison of the
inner tube RBMs and the RBMs of tubes in bundles gave clear evidence that the
interaction in a bundle is stronger than the interaction between inner and
outer tubes.Comment: 6 pages, 7 figures, submitted to Eur. Phys. J.
Low temperature fullerene encapsulation in single wall carbon nanotubes: synthesis of N@C@SWCNT
High filling of single wall carbon nanotubes (SWCNT) with C and
C fullerenes in solvent is reported at temperatures as low as 69
C. A 2 hour long refluxing in n-hexane of the mixture of the fullerene
and SWCNT results in a high yield of C,C@SWCNT, fullerene peapod,
material. The peapod filling is characterized by TEM, Raman and electron energy
loss spectroscopy and X-ray scattering. We applied the method to synthesize the
temperature sensitive (N@C:C)@SWCNT as proved by electron spin
resonance spectroscopy. The solvent prepared peapod samples can be transformed
to double walled nanotubes enabling a high yield and industrially scalable
production of DWCNT
Low frequency Raman studies of multi-wall carbon nanotubes: experiments and theory
In this paper, we investigate the low frequency Raman spectra of multi-wall
carbon nanotubes (MWNT) prepared by the electric arc method. Low frequency
Raman modes are unambiguously identified on purified samples thanks to the
small internal diameter of the MWNT. We propose a model to describe these
modes. They originate from the radial breathing vibrations of the individual
walls coupled through the Van der Waals interaction between adjacent concentric
walls. The intensity of the modes is described in the framework of bond
polarization theory. Using this model and the structural characteristics of the
nanotubes obtained from transmission electron microscopy allows to simulate the
experimental low frequency Raman spectra with an excellent agreement. It
suggests that Raman spectroscopy can be as useful regarding the
characterization of MWNT as it is in the case of single-wall nanotubes.Comment: 4 pages, 2 eps fig., 2 jpeg fig., RevTex, submitted to Phys. Rev.
Separation of VUV/UV photons and reactive particles in the effluent of a He/O2 atmospheric pressure plasma jet
Cold atmospheric pressure plasmas can be used for treatment of living tissues
or for inactivation of bacteria or biological macromolecules. The treatment is
usually characterized by a combined effect of UV and VUV radiation, reactive
species, and ions. This combination is usually beneficial for the effectiveness
of the treatment but it makes the study of fundamental interaction mechanisms
very difficult. Here we report on an effective separation of VUV/UV photons and
heavy reactive species in the effluent of a micro scale atmospheric pressure
plasma jet (-APPJ). The separation is realized by an additional flow of
helium gas under well-defined flow conditions, which deflects heavy particles
in the effluent without affecting the VUV and UV photons. Both components of
the effluent, the photons and the reactive species, can be used separately or
in combination for sample treatment. The results of treatment of a model plasma
polymer film and vegetative Bacillus subtilis and Escherichia coli cells are
shown and discussed. A simple model of the He gas flow and reaction kinetics of
oxygen atoms in the gas phase and at the surface is used to provide a better
understanding of the processes in the plasma effluent. The new jet
modification, called X-Jet for its appearance, will simplify the investigation
of interaction mechanisms of atmospheric pressure plasmas with biological
samples.Comment: 10 pages, 7 figures, submitted to Journal of Physics D: Applied
Physic
Electronic and Magnetic Properties of Nanographite Ribbons
Electronic and magnetic properties of ribbon-shaped nanographite systems with
zigzag and armchair edges in a magnetic field are investigated by using a tight
binding model. One of the most remarkable features of these systems is the
appearance of edge states, strongly localized near zigzag edges. The edge state
in magnetic field, generating a rational fraction of the magnetic flux (\phi=
p/q) in each hexagonal plaquette of the graphite plane, behaves like a
zero-field edge state with q internal degrees of freedom. The orbital
diamagnetic susceptibility strongly depends on the edge shapes. The reason is
found in the analysis of the ring currents, which are very sensitive to the
lattice topology near the edge. Moreover, the orbital diamagnetic
susceptibility is scaled as a function of the temperature, Fermi energy and
ribbon width. Because the edge states lead to a sharp peak in the density of
states at the Fermi level, the graphite ribbons with zigzag edges show
Curie-like temperature dependence of the Pauli paramagnetic susceptibility.
Hence, it is shown that the crossover from high-temperature diamagnetic to
low-temperature paramagnetic behavior of the magnetic susceptibility of
nanographite ribbons with zigzag edges.Comment: 13 pages including 19 figures, submitted to Physical Rev
Unconventional magnetism in all-carbon nanofoam
We report production of nanostructured carbon foam by a high-repetition-rate,
high-power laser ablation of glassy carbon in Ar atmosphere. A combination of
characterization techniques revealed that the system contains both sp2 and sp3
bonded carbon atoms. The material is a novel form of carbon in which
graphite-like sheets fill space at very low density due to strong hyperbolic
curvature, as proposed for ?schwarzite?. The foam exhibits ferromagnetic-like
behaviour up to 90 K, with a narrow hysteresis curve and a high saturation
magnetization. Such magnetic properties are very unusual for a carbon
allotrope. Detailed analysis excludes impurities as the origin of the magnetic
signal. We postulate that localized unpaired spins occur because of topological
and bonding defects associated with the sheet curvature, and that these spins
are stabilized due to the steric protection offered by the convoluted sheets.Comment: 14 pages, including 2 tables and 7 figs. Submitted to Phys Rev B 10
September 200
Anisotropic Condensation of Helium in Nanotube Bundles
Helium atoms are strongly attracted to the interstitial channels within a
bundle of carbon nanotubes. The strong corrugation of the axial potential
within a channel can produce a lattice gas system where the weak mutual
attraction between atoms in neighboring channels of a bundle induces
condensation into a remarkably anisotropic phase with very low binding energy.
We estimate the binding energy and critical temperature for 4He in this novel
quasi-one-dimensional condensed state. At low temperatures, the specific heat
of the adsorbate phase (fewer than 2% of the total number of atoms) greatly
exceeds that of the host material.Comment: 8 pages, 3 figures, submitted to PRL (corrected typo in abstract
Genital ulcer severity score and genital health quality of life in Behçet's disease
Background: Behçet's Disease (BD) is a chronic auto-inflammatory, multisystem relapsing/remitting disorder of unknown aetiology. Oro-genital ulceration is a key feature of the disease and has a major impact on the patients' quality of life. Other clinical manifestations include ocular inflammation, rheumatologic and skin involvement, while CNS and vascular complications can lead to considerable morbidity. The availability of a valid monitoring tool for BD activity is crucial in evaluating the impact of the disease on daily life activity. The aims of this study were to validate a novel tool for monitoring genital ulceration severity in BD and to assess the impact of genital ulcers on the Genital Health Quality of Life (GHQoL). Methods: Genital Ulcer Severity Score (GUSS) was developed using six genital ulcer characteristics: number, size, duration, ulcer-free period, pain and site. A total of 207 BD patients were examined, (137 females: mean age∈±∈SD: 39.83∈±∈13.42 and 70 males: mean age∈±∈SD: 39.98∈±∈11.95) from the multidisciplinary Behçet's Centre of Excellence at Barts Health NHS Trust. GUSS was used in conjunction with Behçet's Disease Current Activity Form (BDCAF). Results: The over-all score of GUSS showed a strong correlation with all genital ulcer characteristics, and the strongest correlation was with the pain domain (r∈=∈0.936; P∈2: 0.600; P∈<∈0.0001). Conclusions: This study established the practicality of GUSS as a severity monitoring tool for BD genital ulcers and validated its use in 207 patients. Genital ulcers of BD have a considerable impact on the patients GHQoL
Coupling of Raman Radial Breathing Modes in Double-Wall Carbon Nanotubes and Bundles of Nanotubes
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