Gyöngyi Klupp

Interactions and chemical transformations of coronene inside and outside carbon nanotubes

By exposing flat and curved carbon surfaces to coronene, a variety of van der Waals hybrid heterostructures are prepared, including coronene encapsulated in carbon nanotubes, and coronene and dicoronylene adsorbed on nanotubes or graphite via π-π interactions. The structure of the final product is determined by the temperature of the experiment and the curvature of the carbon surface. While at temperatures below and close to the sublimation point of coronene, nanotubes with suitable diameters are filled with single coronene molecules, at higher temperatures additional dimerization and oligomerization of coronene occurs on the surface of carbon nanotubes. The fact that dicoronylene and possible higher oligomers are formed at lower temperatures than expected for vapor-phase polymerization indicates the active role of the carbon surface used primarily as template. Removal of adsorbed species from the nanotube surface is of utmost importance for reliable characterization of encapsulated molecules: it is demonstrated that the green fluorescence attributed previously to encapsulated coronene is instead caused by dicoronylene adsorbed on the surface which can be solubilized and removed using surfactants. After removing most of the adsorbed layer, a combination of Raman spectroscopy and transmission electron microscopy was employed to follow the transformation dynamics of coronene molecules inside nanotubes.

Static and dynamic Jahn-Teller effect in the alkali metal fulleride salts A4C60 (A=K,Rb,Cs)

We report the temperature dependent mid- and near-infrared spectra of K4C60, Rb4C60, and Cs4C60. The splitting of the vibrational and electronic transitions indicates a molecular symmetry change of C-60(4-) which brings the fulleride anion from D-2h to either a D-3d or a D-5d distortion. In contrast to Cs4C60, low temperature neutron diffraction measurements did not reveal a structural phase transition in either K4C60 and Rb4C60. This proves that the molecular transition is driven by the molecular Jahn-Teller effect, which overrides the distorting potential field of the surrounding cations at high temperature. In K4C60 and Rb4C60 we suggest a transition from a static to a dynamic Jahn-Teller state without changing the average structure. We studied the librations of these two fullerides by temperature dependent inelastic neutron scattering and conclude that both pseudorotation and jump reorientation are present in the dynamic Jahn-Teller state.

Mott localization in the correlated superconductor Cs3C60 resulting from the molecular Jahn-Teller effect

{\mathrm{Na}}_{2}{\mathrm{C}}_{60}

Vibrational spectra of C60·C8H8 and C70·C8H8 in the rotor-stator and polymer phases

is believed to be an electron-hole counterpart of the Mott-Jahn-Teller insulator

Electronic and ionic conductivities in superionic Li4 C60

{A}_{4}{\mathrm{C}}_{60}

Distortions of C604− studied by infrared spectroscopy

salts. We present a study of infrared, ESR, NMR spectroscopy, x-ray diffraction, chemical composition and neutron scattering on this compound. Our spectroscopic results at room temperature can be reconciled in a picture of segregated regions of the size

Infrared spectra of C70 and its alkali salts

3\char21{}10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

Electronic Properties of Air-Sensitive Nanomaterials Probed with Microwave Impedance Measurements

. We observe a significant insulating

Infrared signatures of the dynamic Jahn-Teller effect in fullerene-based materials

{\mathrm{C}}_{60}