Low-dimensional thermoelectric materials

The promise of low dimensional thermoelectric materials for enhanced performance is reviewed, with particular attention given to quantum wells and quantum wires. The high potential of bismuth as a low-dimensional thermoelectric material is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 755–758 (May 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Phonons in carbon nanotubes

A broad review of the unusual one-dimensional properties of phonons in carbon nanotubes is presented, including phonons in isolated nanotubes and in crystalline arrays of nanotubes in nanotube bundles. The main technique for probing the phonon spectra has been Raman spectroscopy and the many unique and unusual features of the Raman spectra of carbon nanotubes are reviewed. Also included is a brief review of the thermal properties of carbon nanotubes in relation to their unusual phonon dispersion relations and density of states.     

News and Views: Perspectives on Graphene and Other 2D Materials Research and Technology Investments

With the actual experimental realization of graphene samples, it became possible not only to exploit the special physical properties of graphene but also to exploit its technological applications. As the field developed, the discovery of other 2D materials occurred and this opened up access to a plethora of combinations of a large variety of electrical, optical, mechanical, and chemical properties. Now there are large investments being made around the world to develop the graphene research area and to boost graphene use in technology. Here, we discuss current research and some future prospects for this area of layered nanomaterials.     

Raman study on electrochemical lithium insertion into multiwalled carbon nanotubes

We have carried out in situ Raman studies during the electrochemical insertion of lithium ions (Li⁺) into pristine and thermally treated multiwalled carbon nanotubes (MWNTs). We found an improved structural integrity as well as the removal of defects in the thermally treated tubes. The different Li⁺ insertion behaviors above 0.5 V in as‐grown and thermally treated tubes could be explained by the presence of defects on the outer surface of the tubes. No change of Raman spectra from 2.8 to 0.8 V is characterized by the coverage of Li⁺ on the outer surface of tubes, whereas the upshift of G band and the absence of a separated G band below 0.75 V indicate the formation of diluted graphite intercalation below the stage‐2 phase (LiC₁₂). Copyright © 2008 John Wiley & Sons, Ltd.     

Magnetoreflection study of graphite intercalated with bromine

We report here the first observation of interband Landau level transitions in graphite intercalation compounds. Magnetoreflection measurements are reported for residue compounds of graphite intercalated with up to 1.2 at.% Br. The observed magnetoreflection resonances show evidence for domains in which the electronic band structure and Fermi energy are only slightly dependent on bromine concentration. These conclusions are in general agreement with recently reported de Haas-van Alphen results for these compounds.     

Application of X-ray structure factor measurements to graphite intercalation compounds

We report here two new applications of (00l) X-ray scattering intensity data for graphite intercalation compounds, yielding the structure of sandwich intercalates, as in metal chloride compounds, and an estimate of the state index via the l-value at maximum scattering intensity.     

Phenomenological theory of Raman scattering in europium chalcogenides

First-order Raman scattering from phonons in the magnetic phases of the europium chalcogenides is analyzed in terms of symmetry for both electric-dipole and electric-quadrupole virtual electronic transitions. The magnetic ordering increases the size of the unit cell and lowers the point group symmetry of the various phases. The magnetic symmetry is used to derive the allowed Raman transitions and polarization selection rules. A phonon dispersion curve for EuSe along the [111] axis is inferred from recent experimental data by applying the selection rules derived on the basis of the magnetic symmetry.     

Observation of superlattice-induced Raman modes in graphite-potassium-amalgam compounds

The first definitive observation is reported of zone-folded Raman modes associated with in-plane superlattice ordering for the stage 1 graphite-potassium-amalgam intercalation compounds. Raman spectra for stages 2 and 3 are also reported and show only staging effects, consistent with spectra previously reported for donor compounds.     

Raman scattering from one-dimensional carbon systems

Although the Raman effect was discovered nearly 80 years ago, it is only recently that the special characteristics of Raman scattering for one-dimensional systems have been seriously considered. This review focuses on the special interest of the Raman effect for one-dimensional systems that is of particular relevance to carbon nanostructures. Two examples of Raman scattering in one-dimensional systems are given. The first illustrates the use of Raman spectroscopy to reveal the remarkable structure and properties of carbon nanotubes arising from their one-dimensionality. Some of the recent advances in using Raman spectroscopy to study doping and intercalation to modify nanotube properties are reviewed, in the context of a one-dimensional system. The second example is the Raman spectra of a linear chain of carbon atoms and the special properties of this interesting system. New approaches toward applying Raman spectroscopy to carbon nanostructures are also emphasized.