Christoph Ollinger

Collective Dynamics of Lipid Membranes Studied by Inelastic Neutron Scattering

We have studied the collective short wavelength dynamics in deuterated 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine (DMPC) bilayers by inelastic neutron scattering. The corresponding dispersion relation variant Plancks over 2pi omega(Q) is presented for the gel and the fluid phase of this model system. The temperature dependence of the inelastic excitations indicates a phase coexistence between the two phases over a broad range and leads to a different assignment of excitations from that reported in a preceding inelastic x-ray scattering study [Phys. Rev. Lett. 86, 740 (2001)]]. As a consequence, we find that the minimum in the dispersion relation is actually deeper in the gel than in the fluid phase. Finally, we can clearly identify an additional nondispersive (optical) mode predicted by molecular dynamics simulations [Phys. Rev. Lett. 87, 238101 (2001)]].

Collective dynamics in phospholipid bilayers investigated by inelastic neutron scattering: exploring the dynamics of biological membranes with neutrons

We present the first inelastic neutron scattering study of the short wavelength dynamics in a phospholipid bilayer. We show that inelastic neutron scattering using a triple-axis spectrometer at the high-flux reactor of the ILL yields the necessary resolution and signal to determine the dynamics of model membranes. The results can quantitatively be compared to recent Molecular Dynamics simulations. Reflectivity, in-plane correlations and the corresponding dynamics can be measured simultaneously to gain a maximum amount of information. With this technique, complete dispersion relations can be measured with a high-energy resolution. Structure and dynamics in phospholipid bilayers, and the relation between them, can be studied on a molecular length scale.

Front-coupling of a prefocused x-ray beam into a monomodal planar waveguide

A hard x-ray beam of photon energy E=12.5keV has been focused by a Kirkpatrick–Baez mirror system and coupled into the front side of a single-mode x-ray waveguide. The beam dimensions of 3.8×2.5μm2 in the focus of the mirror system have thus been reduced in one direction to 32nm, corresponding to the guiding layer thickness of the waveguide. At the same time the waveguide acts as a coherence filter and leads to a well-defined intensity distribution with steep tails in the near- and far-field regions. The total flux transmitted by the waveguide exceeded 108 photons/s while no significant contributions of radiation transmitted through the absorbing waveguide cladding have been observed.

X-ray waveguide nanostructures : Design, fabrication, and characterization

Two dimensionally confining x-ray channel waveguide structures are fabricated and used for the delivery of nanoscopic x-ray beams. The waveguides can be combined with a high gain Kirkpatrick-Baez-prefocusing mirror system yielding hard x-ray beams with a cross section down to 25nm (full width at half maximum). The incoming synchrotron x-ray beam is coupled in from the front side of the waveguide. Here we address the general design of the x-ray optical devices and their fabrication by e-beam lithography methods.

Electric field unbinding of solid-supported lipid multilayers

Abstract. We studied by X-ray reflectivity the behaviour of fully hydrated solid-supported lipid multilayers under the influence of a transverse electric field, under conditions routinely used in the electroformation process. The kinetics of sample loss (unbinding) was measured as a function of the amplitude and frequency of the applied field by monitoring the integrated intensity of the Bragg peaks. We also performed a time-resolved analysis of the intensity of the first Bragg peak and characterized the final state of the sample.

Object localization with 10nm accuracy by x-ray phase contrast projection imaging

The present work focuses on the question of localizing single object by hard x-ray phase contrast projection imaging. The authors present a setup where an x-ray channel waveguide defines a “quasi-point source” used to illuminate and image an object in a highly coherent cone beam. Knife edge fluorescence scans revealed a beam diameter of 75nm at a distance of 30μm behind the guide. The recorded image corresponds to an in-line hologram of the object which can be reconstructed numerically. Object translations and associated shifts in the hologram allow for the 10nm localization accuracy.

Coherent propagation of white X-rays in a planar waveguide.

The far-field diffraction pattern of a front-coupled planar waveguide supporting two guided modes has been measured using a white X-ray beam. Interference of the guided modes leads to a characteristic variation of the far-field diffraction pattern for different photon energies. The experiment verifies the predicted properties of the guided modes, shows that these modes superpose coherently, and demonstrates that the electromagnetic field downstream of the waveguide is significantly different from that expected for a hypothetical small slit of the same size.

Parabolic Capillary Optics with less than 50 μm Focus and Large Focal Distance for Synchrotron Radiation Scattering

We report the design and performance of a unique parabolic focusing optics for a general purpose materials research station at the bending magnet BM20 (ROBL‐CRG) at ESRF. The measured gain between 8–12 keV was >1000, the focal spot <40 μm at a focal length of 235 mm (8 keV) and 244 mm (11.5 keV), respectively, which allows the use of special sample environments around the focus spot. The low divergence of <0.15° especially permits the in situ characterization of stress states in copper dual inlaid interconnect micro‐structures as well as the measurement of far‐field diffraction patterns of planar waveguides. First test results will be shown and the advantages of the parabolic focusing optics discussed.