M. Tegze

Dynamics in a cluster under the influence of intense femtosecond hard X-ray pulses

Abstract.In this paper we examine the behavior of small cluster of atoms in a short (10-50 fs) very intense hard X-ray (10 keV) pulse. We use numerical modeling based on the non-relativistic classical equation of motion. Quantum processes are taken into account by the respective cross-sections. We show that there is a Coulomb explosion, which has a different dynamics than one finds in classical laser driven cluster explosions. We discuss the consequences of our results to single molecule imaging by the free electron laser pulses.

Imaging light atoms by X-ray holography

We demonstrate here the imaging of light atoms by hard X-ray holography. Using intense synchrotron radiation for the excitation, the oxygen and nickel atoms in a nickel oxide sample are imaged in three dimensions with high resolution inside a volume of about 1,000 cubic ångströms. These remarkable characteristics mean that X-ray holography bridges the gap between diffraction, which relies on long-range order, and extended X-ray absorption fine structure, which gives information on the local environment of atoms.

Structure and stability of crystalline C60 · n-pentane clathrate

Abstract Clathrate type single crystals with the composition of C60(n-C5H12)0.88(C7H8)0.05 were grown from C60-toluene- petroleum ether solution. The structure of the crystals, determined by X-ray diffraction is b-face centered orthorhombic. No phase transition, corresponding to the orientational ordering is observed at 250 K by differential scanning calorimetry. Around 420 K the solvent molecules are released from the clathrate as determined by thermogravimetry-mass spectrometry. An irreversible phase transition is observed simultaneously with the evolution of solvents, resulting in the face centered cubic structure of pure C60.

Atomic structure of a single large biomolecule from diffraction patterns of random orientations

The short and intense pulses of the new X-ray free electron lasers, now operational or under construction, may make possible diffraction experiments on single molecule-sized objects with high resolution, before radiation damage destroys the sample. In a single molecule imaging (SMI) experiment thousands of diffraction patterns of single molecules with random orientations are recorded. One of the most challenging problems of SMI is how to assemble these noisy patterns of unknown orientations into a consistent single set of diffraction data. Here we present a new method which can solve the orientation problem of SMI efficiently even for large biological molecules and in the presence of noise. We show on simulated diffraction patterns of a large protein molecule, how the orientations of the patterns can be found and the structure to atomic resolution can be solved. The concept of our algorithm could be also applied to experiments where images of an object are recorded in unknown orientations and/or positions like in cryoEM or tomography.

Common arc method for diffraction pattern orientation

Very short pulses of X-ray free-electron lasers opened the way to obtaining diffraction signal from single particles beyond the radiation dose limit. For three-dimensional structure reconstruction many patterns are recorded in the objects unknown orientation. A method is described for the orientation of continuous diffraction patterns of non-periodic objects, utilizing intensity correlations in the curved intersections of the corresponding Ewald spheres, and hence named the common arc orientation method. The present implementation of the algorithm optionally takes into account Friedels law, handles missing data and is capable of determining the point group of symmetric objects. Its performance is demonstrated on simulated diffraction data sets and verification of the results indicates a high orientation accuracy even at low signal levels. The common arc method fills a gap in the wide palette of orientation methods.

Infrared and raman spectra of C60·n-pentane clathrate crystals

We used infrared and Raman spectroscopy to investigate single crystals of the compound C60(C5H12)0.88(C7H8)0.05. We observed the signatures of the individual components C60 and pentane in the infrared spectrum with minimal changes when compared to solvent-free solid or solution spectra. The corresponding Raman spectrum shows that while the molecular C60 frequencies remain unchanged, there are some additional lines, probably due to symmetry effects of the solid state. We conclude that the material is a true clathrate with no electronic interaction between the constituents. Unlike the infrared spectrum pentane lines are not observed in Raman spectra.

Shift of the Optical Absorption Edge in C60 Clathrate Single Crystals

We measured the transmission between 1.6–2.2 eV of pure C60 and three clathrate single crystals containing different aliphatic guest molecules. The absorption edge in the clathrates shows a blue shift of 0.1 eV irrespective of the guest molecule, indicating that C60 is electronically isolated in these compounds.

Enthalpies of phase transformations in the alkali fulleride RbC60

Abstract Phase transformations in the alkali fulleride RbC60 between the polymeric, dimeric and metastable fcc phases are investigated by differential scanning calorimetry (DSC) and x-ray diffraction in the ∼215 to 500 K range. The transformation enthalpies of the polymer→monomer and dimer→monomer transitions (25.8 and 10.5 kJ/mol, respectively) are less than expected for covalent interfullerene bonding which suggests substantial contributions from Madelung and deformation energies. Stability of the polymer phase depends on the temperature and duration of polymerization. In samples quenched from 500 to 273 K a transformation from an fcc phase with hindered rotation of the C60 monomers to another fcc phase in which C60− ions are freely rotating is observed at 290 K. The relative Gibbs free energies of the stable and metastable phases are estimated from the measured transformation temperatures and enthalpies. The polymer is the most stable phase at low temperatures.

Structure and stability of C60Xy clathrates

Abstract A series of novel single crystalline C60Xy clathrates were prepared with various guest materials by crystallization from organic solvent-precipitant systems. Four different stoichiometric compositions ( y = 1, 3 4 , 2 3 and 1 2 ) were found. The stability of the clathrates was studied by thermoanalytical methods. The crystal structures were determined by X-ray diffraction. Based on the stoichiometry and structure, the clathrates are classified as members of two related homologous series with compositions of (C60)m+2X3 and (C60)n+1X2. The first observations of birefringence and phase transitions corresponding to orientational ordering are demonstrated.

X-ray holography: theory and experiment

A detailed description of x-ray fluorescent holography is given using the formalism of classical electrodynamics. Effects of the wavefront curvature are calculated. It is shown that neglecting these effects might cause large errors especially in the forward direction. The model calculation is compared with experimental data. It is shown that for the model system of NiO the experiment agrees well with theoretical images.