Enhancement of weak anti-localization signatures in the magneto-resistance of bismuth anti-dot thin films

Anti-dot array thin films of bismuth were prepared by the e-beam deposition of this semi-metal on nano-porous substrates. The magneto-resistance measurements of bismuth thin films deposited under identical conditions on various substrates displayed signatures from both classical magneto-resistance and weak anti-localization effects. The relative intensity of the two effects could be altered by the choice of the substrate, with the anti-dot array morphology suppressing the classical magneto-resistance, and enhancing the weak anti-localization contribution to the measured magneto-resistance. As a result, the weak anti-localization effect can be traced to higher magnetic field strengths and higher temperatures than is possible in non-patterned films, improving the accuracy of the parameters extracted from the data. PACS 73.20.Fz; 73.23-b; 73.61.At     

Magnetoreflection studies of ion implanted bismuth

The effect of the implantation of Sb ions on the electronic structure of the semimetal bismuth is studied by the magnetoreflection technique. The results show long electronic mean free paths and large implantation-induced increases in the band overlap and L-point band gap. These effects are opposite to those observed for Bi chemically doped with Sb.     

Raman spectroscopy of graphene and carbon nanotubes

This paper reviews progress that has been made in the use of Raman spectroscopy to study graphene and carbon nanotubes. These are two nanostructured forms of sp² carbon materials that are of major current interest. These nanostructured materials have attracted particular attention because of their simplicity, small physical size and the exciting new science they have introduced. This review focuses on each of these materials systems individually and comparatively as prototype examples of nanostructured materials. In particular, this paper discusses the power of Raman spectroscopy as a probe and a characterization tool for sp² carbon materials, with particular emphasis given to the field of photophysics. Some coverage is also given to the close relatives of these sp² carbon materials, namely graphite, a three-dimensional (3D) material based on the AB stacking of individual graphene layers, and carbon nanoribbons, which are one-dimensional (1D) planar structures, where the width of the ribbon is on the nanometer length scale. Carbon nanoribbons differ from carbon nanotubes is that nanoribbons have edges, whereas nanotubes have terminations only at their two ends.     

X-ray characterization of graphite intercalation compounds

The understanding of electronic and lattice properties of graphite intercalation compounds depends critically on the model describing the structural properties. We report here results showing that well-staged as-grown samples do not exhibit the expected in-plane intercalant density, and that careful analysis of the 00? x-ray diffractograms reveals important information on the in-plane occupation probability.     

The temperature variation of the thermal conductivity of benzene-derived carbon fibers

The temperature variation of the in-plane thermal conductivity of benzene-derived carbon fibers (BDF) measured from 5 to 300 K is reported and discussed. Very high thermal conductivity values — comparable to that of the best HOPG heat treated at the same temperature — are found. The data confirms the high structural order previously reported for BDF.     

Landau levels in graphite intercalation compounds

The first calculation of the magnetic energy level structure of a graphite intercalation compound is presented. The calculational technique exploits the staging symmetry through the k_z-axis zone folding of the magnetic energy levels of the graphite π-bands. The results are applicable to the interpretation of the magnetoreflection and de Haas-van Alphen type experiments in intercalated graphite.     

Anisotropy of the Raman spectra of nanographite ribbons

A polarized Raman study of nanographite ribbons on a highly oriented pyrolytic graphite substrate is reported. The Raman peak of the nanographite ribbons exhibits an intensity dependence on the light polarization direction relative to the nanographite ribbon axis. This result is due to the quantum confinement of the electrons in the 1D band structure of the nanographite ribbons, combined with the anisotropy of the light absorption in 2D graphite, in agreement with theoretical predictions.     

The growth of carbon nanostructures on cobalt-doped carbon aerogels

By carbonizing cobalt-doped aerogel precursors directly at various temperatures, or by carbon monoxide decomposition of cobalt-doped carbon aerogels, different carbon nano-features such as carbon nano-filaments and graphitic nano-ribbons were grown on cobalt-doped carbon aerogel samples. Transmission electron spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction characterization results showed that metallic cobalt nano-particles form when heating the cobalt-doped aerogel samples over 500 °C. At low heating temperature, many highly oriented carbon thin films can be found on metallic cobalt nano-particles. When heating the samples at 850 °C, some carbon nano-filaments are obtained. While heating the samples at 1050 °C, many graphitic nano-ribbons are grown and the framework of the interconnected carbon particles of the sample is changed. Graphitic nano-ribbons can also be grown by CO decomposition of the cobalt-doped carbon aerogels. We can therefore control and modify the nanostructures of cobalt-doped carbon aerogels by heating them at different temperatures or by using CO decomposition.