141 research outputs found
Probing high pressure properties of single wall carbon nanotubes through fullerene encapsulation
The high pressure behavior of bundled 1.35±0.1nm diameter single wall carbon nanotubes (SWNT) filled with C70 fullerenes (usually called peapods) has been investigated by Raman spectroscopy and compared with the corresponding behavior of the nonfilled SWNT. We show experimentally that two reversible pressure-induced transitions take place in the compressed bundle SWNT. The first transition, in the 2–2.5GPa range, is in good correspondence with predictions of the thermodynamic instability of the nanotube circular cross section for the studied tube diameter. An interaction between the fullerenes and the tube walls is then observed at about 3.5GPa, which evidences a progressive deformation of the tube cross section. The second transition takes place at pressures between 10 and 30GPa, and is evidenced by two effects by a strong frequency downshift of the Raman transverse modes and the concomitant disappearance of the fullerenes Raman modes in peapods. The pressure at which the second transition takes place is strongly dependent on the nature of the pressure transmitting medium. We also report irreversible effects at high pressure as the shortening of the tubes, the formation of nanostructures and the disappearance of the C70 Raman signal in some cases. Transmission electron microscopy studies are also reported supporting these transformations
Structural phase stability and homogeneity enhancement of electrochemically synthesized Mn2V2O7 by nanocarbon networks
Structural phase stability and homogeneity of the electrochemically synthesized Mn2V2O7 (MVO) on nanocarbon network structures are investigated. The cup-stacked multi-walled carbon nanotubes (CNTs) and electrolytic graphene oxide (eGO) are the networks exploited in present work. It is shown that co-electrodeposition of carbonaceous network and V2O5.nH2O followed by electro-insertion of Mn2+ cations results in the formation of intermixed β-Mn2V2O7 nano-structures. The morphology and surface chemistry of the synthesized nano-structures is studied via high-resolution electron transmission and scanning X-ray photo-emission microscopies as well as Raman spectroscopy. The synthesized MVO on carbon fiber surface in the absence of the nanocarbon network shows a non-uniform phase formation and uneven coating distribution. The nanocarbon networks assisted MVO demonstrate uniform phase formation and distribution. The dominant MVO structural phase product present in these samples differs with different type of carbonaceous networks. The possible effect of the catalytic activity of the carbonaceous network as well as their hydrophilicity on the final structural and phase formation is discussed. The present study establishes new possibilities on catalytic assisted metal alloy oxide deposition for advanced applications
Quantifying defects in graphene via Raman spectroscopy at different excitation energies.
We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity
Raman spectroscopy as a versatile tool for studying the properties of graphene.
Raman spectroscopy is an integral part of graphene research. It is used to determine the number and orientation of layers, the quality and types of edge, and the effects of perturbations, such as electric and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp(2)-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential physical processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminology that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene
An Anomalous Enhancement of the A(g)(2) Mode in the Resonance Raman Spectra of C-60 Embedded in Single-Walled Carbon Nanotubes during Anodic Charging
The effect of electrochemical charging on C60 fullerenes embedded in single-walled carbon nanotubes (peapods) has been studied. The Raman Ag(2) mode of C60 fullerene has been used as a probe. The spectra were measured using seven different laser excitation energies. For cathodic charging we observed bleaching of the Ag(2) mode independent of laser excitation energy. On the other hand for anodic charging the behavior of the Ag(2) mode was dependent on laser excitation energy. The intensity of the Ag(2) mode decreased only for the 1.16 eV laser excitation energy. In the case of other laser excitation energies (2.70, 2.60, 2.54, 2.41, 2.33, 2.18 eV) an increase of intensity has been observed. The dependence of the slope of the intensity on the electrode potential has been found to be a function of laser excitation energy. Observation of the upshift of the Ag(2) frequency supported by first principles calculations suggests that only a small amount of charge penetrates the nanotube, resulting in partial charge on the encapsulated fullerenes
Effect of Bundling on the Tangential Displacement Mode in the Raman Spectra of Semiconducting Single-Walled Carbon Nanotubes during Electrochemical Charging
Raman Spectroscopy as a Tool to Address Individual Graphene Layers in Few-Layer Graphene
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