J. Kürti

Raman spectra of titanium dioxide (anatase, rutile) with identified oxygen isotopes (16, 17, 18)

Six representative isotope-labeled samples of titanium dioxide were synthesized: Ti(16)O(2), Ti(17)O(2) and Ti(18)O(2), each in anatase and rutile forms. Their Raman scattering was analyzed at temperatures down to 5 K. Spectral assignment was supported by numerical simulation using DFT calculations. The combination of experimental and theoretical Raman frequencies with the corresponding isotopic shifts allowed us to address various still-open questions about the second-order Raman scattering in rutile, and the analysis of overlapping features in the anatase spectrum.

Fine tuning the charge transfer in carbon nanotubes via the interconversion of encapsulated molecules

Tweaking the properties of carbon nanotubes is a prerequisite for their practical applications. Here we demonstrate fine-tuning the electronic properties of single-wall carbon nanotubes via filling with ferrocene molecules. The evolution of the bonding and charge transfer within the tube is demonstrated via chemical reaction of the ferrocene filler ending up as secondary inner tube. The charge transfer nature is interpreted well within density functional theory. This work gives the first direct observation of a fine-tuned continuous amphoteric doping of single-wall carbon nanotubes.

Iron(III) complexes of sugar-type ligands

Abstract A series of iron(III) complexes formed with sugartype ligands (aldoses, ketoses, polyalcohols, sugar acids, di- and trisaccharides) was prepared. The composition of the complexes was determined by standard analytical methods. It was shown that deprotonated alcoholic hydroxy groups participate in the complex formation and polynuclear species are formed. Mossbauer spectra reflected the presence of high spin iron(III) central atoms. EPR spectra showed antiferromagnetic interactions between the iron(III) centres in the complexes indicating dimeric or oligomeric complex structures. The ratio of interacting and isolated iron(III) atoms depend on the nature of the ligand and on the preparation mode of the complexes (metal-to-ligand ratio, pH, diamagnetic dilution, etc.).

Electronic transitions in KxC60 (0 ⩽ x ⩽ 6) from in situ absorption spectroscopy

Abstract In situ optical absorption measurements at room temperature are reported for K x C 60 (0 ⩽ x ⩽ 6). The main results are a strong bleaching of the peak at 3.5 eV, an increase and line broadening in the spectral range between 2 and 2.7 eV, an increase of a new structure around 1.3 eV and a strong change for the absorption at 0.47 eV with increasing potassium concentrations. From a fit of the absorption spectra of the three stable phases C 60 , K 3 C 60 and K 6 C 60 with a Kramers-Heisenberg dielectric function a definite assignment of the electronic transitions was found, which is in excellent agreement with LHS and LDA calculations. The line broadening in the C 60 metallic phase is explained as resonating valence fluctuations.

Quinoid vs aromatic structure of polyisothianaphthene

We show that the optimum structure of polyisothianaphthene strongly depends on the chain length. Short oligomers have an aromatic structure, while chains consisting of more than 9 monomers exhibit an aromatic to quinoidal transition along the chain.

Electron spin resonance signal of Luttinger liquids and single-wall carbon nanotubes

A comprehensive theory of electron spin resonance (ESR) for a Luttinger liquid state of correlated metals is presented. The ESR measurables such as the signal intensity and the linewidth are calculated in the framework of Luttinger liquid theory with broken spin rotational symmetry as a function of magnetic field and temperature. We obtain a significant temperature dependent homogeneous line broadening which is related to the spin-symmetry breaking and the electron-electron interaction. The result crosses over smoothly to the ESR of itinerant electrons in the noninteracting limit. These findings explain the absence of the long-sought ESR signal of itinerant electrons in single-wall carbon nanotubes when considering realistic experimental conditions.

Resonance Raman investigation of single wall carbon nanotubes

Resonance Raman scattering for the radial breathing mode of single wall carbon nanotubes was investigated experimentally and theoretically. 14 different Raman lines were identified as a fine structure of the mode response. The strongest lines were assigned to achiral and chiral tubes. The metallic tubes were suggested to give the strongest contribution.

The physical meaning of the conjugation length in polymers

Abstract Raman scattering experiments were performed on pristine trans-polyacetylene, on polymer samples where defects had been accomodated systematically along the chains, and on polydiacetylene. The results show that the dispersion of the satellite line strongly depends on the concentration of the defects. A calculation showed the sp3 carbons to be the most effective interruptions of the conjugation. Other physical and chemical properties like electrochemical doping, linewidth of e.s.r. signals and conductivity after doping are strongly related to the dispersion.

High Tc superconductivity of a TlBaCaCuO compound

Abstract A TlBaCaCuO 4.5+ x compound has been investigated from the point of view of superconductivity. Depending on the heat treatment, one part of the samples exhibits superconductivity with an onset of 121 K and a zero resistivity of 106 K, while the other part of them shows only a sharp drop in resistivity at 130 K which hints at the existence of superconducting domains. This picture was confirmed by magnetic and ESR measurements giving possibility for estimation of the critical magnetic fields.

Design of small gap conjugated polymers

Abstract Design of small energy gap conjugated polymers rests on the understanding of the geometric and electronic structure of prototypical systems followed by calculations and predictions of closely related derivatives and modifications. Calculations employed use periodic boundary condition and are based on geometry optimization, since the energy levels around the Fermi level are strongly coupled to the geometry. We consider prototypes, based on thiophene derivatives and silicon containing polymers.