N. M. Nemes

Electrical and thermal transport properties of magnetically aligned single wall carbon nanotube films

Dense, thick films of aligned single wall carbon nanotubes and nanotube ropes have been produced by filtration/deposition from suspension in strong magnetic fields. Electrical resistivity exhibits moderate anisotropy with respect to the alignment axis, while the thermopower is the same when measured parallel or perpendicular to this axis. Both parameters have identical temperature dependencies in the two orientations. Thermal conductivity in the parallel direction exceeds 200 W/mK, within a decade of graphite.

Encapsulation of metallofullerenes and metallocenes in carbon nanotubes

We encapsulate a number of fullerenes inside single-walled carbon nanotubes (SWNTs) including C60, La2@C80 and ErxSc3−xN@C80(x=0–3). In addition, a number of metallocenes are seen to form hybrid structures with SWNTs, filling the lumen. Ferrocene is used to show that a particular molecule can be induced to fill the lumen of nanotubes from either the liquid or vapor states. The structural properties of these nanoscopic hybrid materials are described using high-resolution transmission electron microscopy (HRTEM) and electron diffraction. It is found that the encapsulated fullerenes self-assemble into long, one-dimensional chains. In the case of C60@SWNT, room-temperature electron diffraction and HRTEM results are consistent with close-packed 1-D chains of equally-spaced monomers.

Single Wall Carbon Nanotubes Filled with Metallocenes: a First Example of Non-Fullerene Peapods

We report the synthesis and analysis of metallocenes (ferrocene, chromocene, ruthenocene, vanadocene, tungstenocene-dihydride) encapsulated in single wall carbon nanotubes (SWNTs). In the case of ferrocene, efficient filling of the SWNTs was accomplished from both the liquid and the vapor phase. The other two metallocenes were filled from the vapor phase. High resolution transmission electron microscopy reveals single molecular chains of metallocenes inside SWNTs. Molecules move under the electron beam in the SWNTs indicating the absence of strong chemical bonds between each other and the SWNT wall. Their movement freezes after short illumination as a result of irradiation damage. Energy dispersive X-ray spectrometry confirms the presence of iron, chromium, ruthenium, vanadium and tungsten.

Electronic and structural properties of alkali doped SWNT

Comprehensive experiments on structural and transport properties of alkali intercalated single walled carbon nanotubes (SWNT) are presented. The increasing electron density was measured as a shift of the Drude‐edge in optical reflectivity in‐situ with progressive doping. In saturation‐doped samples the Drude‐edge shifts into the visible (to 25,000 – 30,000 cm−1 for potassium and rubidium doped samples) and the samples have a golden‐brown color, similar to stage I graphite. X‐ray diffraction reveals a crystalline rope structure with expanded lattice constant, similar to results of Duclaux et al.. The change in the low temperature divergence of the resistivity after degassing at high temperature and high vacuum and after K‐doping is studied in‐situ.

Conduction electron spin resonance in the superconducting state of K3C60

The conduction electron spin resonance (CESR) of K3C60 single crystal and powder samples was studied from temperatures well below the superconducting transition (Tc=19 K) to 800 K. Several ESR frequencies were used with corresponding magnetic fields up to 8 T. We observed an anomalous change of the g factor with temperature in the superconducting state which may arise from an anisotropy of the superconducting energy gap. We proved that the change of the g factor is not caused by diamagnetic screening.