Investigations of Solid State Dynamics at the NRSSR Beamline at PETRA II. An Overview

The present status of the new nuclear resonance beamline PETRA 1 at HASYLAB, DESY, Hamburg is described. Besides an overview of the experimental setup some examples of recent experiments are given. Those cover the main applications, i.e., inelastic scattering from iron alloys and quasielastic scattering from glass-forming liquids. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ab initio analysis of electron-phonon coupling in molecular devices

We report a first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. Using a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two aluminum leads as an example, we analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. We find that the low-lying modes are most important. As a function of bias voltage, the electron-phonon coupling strength can change drastically while the vibrational spectrum changes at a few percent level.     

Tin–DNA complexes investigated by nuclear inelastic scattering of synchrotron radiation

Nuclear inelastic scattering (NIS) of synchrotron radiation has been used to investigate the dynamics of tin ions chelated by DNA. Theoretical NIS spectra have been simulated with the help of density functional theory (DFT) calculations using 12 models for different binding sites of the tin ion in (CH₃)Sn(DNA_Phosphate)₂. The simulated spectra are compared with the measured spectrum of the tin–DNA complex.     

Confined phonons in glasses

The European Physical Journal E - We have applied nuclear inelastic absorption (NIA) to the molecular glass former dibutyl phthalate/ferrocene, both in bulk and in nanoporous matrices having pore...     

Identification of a rotator phase of octamethyl ferrocene and correlations between its structural and dynamical properties

The low- and high-temperature phases of octamethyl ferrocene were studied in detail, using high-resolution X-ray powder diffraction, differential scanning calorimetry and nuclear resonant scattering, in particular the novel technique of synchrotron radiation perturbed angular correlations (SRPAC). Much as in the case of an analogous but more unsymmetrical molecule, octamethyl ethinyl ferrocene, the high-temperature phase possesses the space group with lattice parameters , , which in the rhombohedral setting correspond to , α=104.79^°. An increase of the volume per formula unit of about 12% across the phase transition is observed.The rotation of the electric field gradient, which can be identified with the rotation of the entire molecule within the lattice, follows Arrhenius behaviour with a high activation energy of . Whereas precursor effects and a change in activation energy were observed for octamethyl ethinyl ferrocene, no such effects are observed for octamethyl ferrocene. We relate this difference to the absence of the ethinyl substituent in octamethyl ferrocene.     

Vibrational properties of nanograins and interfaces in nanocrystalline materials

The vibrational dynamics of nanocrystalline Fe(90)Zr(7)B(3) was studied at various phases of crystallization. The density of phonon states (DOS) of the nanograins was separated from that of the interfaces for a wide range of grain sizes and interface thicknesses. The DOS of the nanograins does not vary with their size and down to 2 nm grains still closely resembles that of the bulk. The anomalous enhancement of the phonon states at low and high energies originates from the DOS of the interfaces and scales linearly to their atomic fraction.     

Confined phonons in glasses. A study by nuclear inelastic absorption and Raman scattering

We have applied nuclear inelastic absorption (NIA) to the molecular glass former dibutyl phthalate/ferrocene, both in bulk and in nanoporous matrices having pore sizes of 50 and 25 A. The quantity g(E)/E(2), where g(E) is the vibrational density of states (VDOS) of the iron atoms, exhibits a pronounced maximum around 2 meV. Confinement in pores leads to a suppression of the VDOS below 1.5 meV, independent of the pore size. The influence of local interactions at the pore wall was assessed using Raman scattering. Our observations are discussed in the light of experimental and theoretical results on nanoparticles and for the Boson peak.     

Phonons in Confinement and the Boson Peak Using Nuclear Inelastic Absorption

Hyperfine Interactions - We have applied nuclear inelastic absorption (NIA) to the molecular glass former dibutylphthalate/ferrocene, both in bulk and in nanoporous matrices having pore sizes of 50...     

The sapphire backscattering monochromator at the Dynamics beamline P01 of PETRA III

We report on a high resolution sapphire backscattering monochromator installed at the Dynamics beamline P01 of PETRA III. The device enables nuclear resonance scattering experiments on Mössbauer isotopes with transition energies between 20 and 60 keV with sub-meV to meV resolution. In a first performance test with ¹¹⁹Sn nuclear resonance at a X-ray energy of 23.88 keV an energy resolution of 1.34 meV was achieved. The device extends the field of nuclear resonance scattering at the PETRA III synchrotron light source to many further isotopes like ¹⁵¹Eu, ¹⁴⁹Sm, ¹⁶¹Dy, ¹²⁵Te and ¹²¹Sb.     

Nuclear forward scattering for high energy mössbauer transitions

We have studied nuclear forward scattering of synchrotron radiation for the 67.41 keV resonance of 61Ni using a silicon crystal monochromator with low-index reflections and a multielement detector. This approach can be extended to other high-energy M?ssbauer transitions and does not pose any restrictions on the sample environment. Under conditions of large sample thickness and short nuclear lifetime, typical for work with high-energy nuclear resonances, the nuclear decay follows a universal dependence where both thickness effects and hyperfine interactions are taken into account by time scaling.