117 research outputs found
Incidence of the Tomonaga-Luttinger liquid state on the NMR spin lattice relaxation in Carbon Nanotubes
We report 13C nuclear magnetic resonance measurements on single wall carbon
nanotube (SWCNT) bundles. The temperature dependence of the nuclear
spin-lattice relaxation rate, 1/T1, exhibits a power-law variation, as expected
for a Tomonage-Luttinger liquid (TLL). The observed exponent is smaller than
that expected for the two band TLL model. A departure from the power law is
observed only at low T, where thermal and electronic Zeeman energy merge.
Extrapolation to zero magnetic field indicates gapless spin excitations. The
wide T range on which power-law behavior is observed suggests that SWCNT is so
far the best realization of a one-dimensional quantum metal.Comment: 5 pages, 4 figure
Stabilization of carbon nanotubes by filling with inner tubes: An optical spectroscopy study on double-walled carbon nanotubes under hydrostatic pressure
The stabilization of carbon nanotubes via the filling with inner tubes is
demonstrated by probing the optical transitions in double-walled carbon
nanotube bundles under hydrostatic pressure with optical spectroscopy.
Double-walled carbon nanotube films were prepared from fullerene peapods and
characterized by HRTEM and optical spectroscopy. In comparison to single-walled
carbon nanotubes, the pressure-induced redshifts of the optical transitions in
the outer tubes are significantly smaller below 10 GPa, demonstrating the
enhanced mechanical stability due to the inner tube already at low pressures.
Anomalies at the critical pressure P12 GPa signal the onset of the
pressure-induced deformation of the tubular cross-sections. The value of P
is in very good agreement with theoretical predictions of the pressure-induced
structural transitions in double-walled carbon nanotube bundles with similar
average diameters.Comment: 6 pages, 4 figures; to appear in Phys. Rev.
Synthesis and Characterization of Gadolinium Oxide Nanocrystallites
Lanthanide oxide nanocrystallites have gained a lot of attention due to their diverse use for potential applications and for this reason it is very important to find a suitable preparation method that would be economically inexpensive and easy to implement. The chapter describes the preparation of gadolinium oxide nanocrystallites (nano Gd2O3) through thermal decomposition of a complex formed by Gd(NO3)3·6 H2O and glycine. Decomposition of the complex occurs at temperatures about (250 ± 10)°C. An ultrafine white powder of the gadolinium oxide nanocrystallites was obtained. The resulting nanocrystallites were characterized by X‐ray powder diffraction analysis, which revealed the size of the gadolinium oxide nanocrystallites equal to 10 nm. The morphology of the gadolinium oxide nanocrystallites was examined by scanning electron microscopy. The elemental composition of the product was confirmed by EDS analysis
Synthesis of carbon nanotubes with and without catalyst particles
The initial development of carbon nanotube synthesis revolved heavily around the use of 3d valence transition metals such as Fe, Ni, and Co. More recently, noble metals (e.g. Au) and poor metals (e.g. In, Pb) have been shown to also yield carbon nanotubes. In addition, various ceramics and semiconductors can serve as catalytic particles suitable for tube formation and in some cases hybrid metal/metal oxide systems are possible. All-carbon systems for carbon nanotube growth without any catalytic particles have also been demonstrated. These different growth systems are briefly examined in this article and serve to highlight the breadth of avenues available for carbon nanotube synthesis
Linear plasmon dispersion in single-wall carbon nanotubes and the collective excitation spectrum of graphene
We have measured a strictly linear pi-plasmon dispersion along the axis of
individualized single wall carbon nanotubes, which is completely different from
plasmon dispersions of graphite or bundled single wall carbon nanotubes.
Comparative ab initio studies on graphene based systems allow us to reproduce
the different dispersions. This suggests that individualized nanotubes provide
viable experimental access to collective electronic excitations of graphene,
and it validates the use of graphene to understand electronic excitations of
carbon nanotubes. In particular, the calculations reveal that local field
effects (LFE) cause a mixing of electronic transitions, including the 'Dirac
cone', resulting in the observed linear dispersion
Electron-beam induced synthesis of nanostructures: a review
As the success of nanostructures grows in modern society so does the importance of our ability to control their synthesis in precise manners, often with atomic precision as this can directly affect the final properties of the nanostructures. Hence it is crucial to have both deep insight, ideally with real-time temporal resolution, and precise control during the fabrication of nanomaterials. Transmission electron microscopy offers these attributes potentially providing atomic resolution with near real time temporal resolution. In addition, one can fabricate nanostructures in situ in a TEM. This can be achieved with the use of environmental electron microscopes and/or specialized specimen holders. A rather simpler and rapidly growing approach is to take advantage of the imaging electron beam as a tool for in situ reactions. This is possible because there is a wealth of electron specimen interactions, which, when implemented under controlled conditions, enable different approaches to fabricate nanostructures. Moreover, when using the electron beam to drive reactions no specialized specimen holders or peripheral equipment is required. This review is dedicated to explore the body of work available on electron-beam induced synthesis techniques with in situ capabilities. Particular emphasis is placed on the electron beam-induced synthesis of nanostructures conducted inside a TEM, viz. the e-beam is the sole (or primary) agent triggering and driving the synthesis process
Investigating the Outskirts of Fe and Co Catalyst Particles in Alumina-Supported Catalytic CVD Carbon Nanotube Growth
CVD growth of carbon nanostructures from zirconia: mechanisms and a method for enhancing yield.
By excluding metals from synthesis, growth of carbon nanostructures via unreduced oxide nanoparticle catalysts offers wide technological potential. We report new observations of the mechanisms underlying chemical vapor deposition (CVD) growth of fibrous carbon nanostructures from zirconia nanoparticles. Transmission electron microscope (TEM) observation reveals distinct differences in morphological features of carbon nanotubes and nanofibers (CNTs and CNFs) grown from zirconia nanoparticle catalysts versus typical oxide-supported metal nanoparticle catalysts. Nanofibers borne from zirconia lack an observable graphitic cage consistently found with nanotube-bearing metal nanoparticle catalysts. We observe two distinct growth modalities for zirconia: (1) turbostratic CNTs 2-3 times smaller in diameter than the nanoparticle localized at a nanoparticle corner, and (2) nonhollow CNFs with approximately the same diameter as the nanoparticle. Unlike metal nanoparticle catalysts, zirconia-based growth should proceed via surface-bound kinetics, and we propose a growth model where initiation occurs at nanoparticle corners. Utilizing these mechanistic insights, we further demonstrate that preannealing of zirconia nanoparticles with a solid-state amorphous carbon substrate enhances growth yield.This material is based upon work supported by the National
Science Foundation under Grant No. 1007793 and was also
supported by Airbus group, Boeing, Embraer, Lockheed Martin,
Saab AB, Hexcel, and TohoTenax through MIT’s Nano-
Engineered Composite aerospace STructures (NECST) Consortium.
This research was supported (in part) by the U.S. Army
Research Office under Contract W911NF-13-D-0001. This work
was performed in part at the Center for Nanoscale Systems
(CNS), a member of the National Nanotechnology Infrastructure
Network (NNIN), which is supported by the National
Science Foundation under NSF Award No. ECS-0335765. CNS
is part of Harvard University. This work was carried out in part
through the use of MIT Microsystems Technology Laboratories.
Stephan Hofmann acknowledges funding from EPSRC under
grant EP/H047565/1. Piran Kidambi acknowledges the
Lindemann Trust Fellowship.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/ja509872y
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