Tuning and Tracking of Coherent Shear Waves in Molecular Films

We have determined the time-dependent displacement fields in molecular sub-micrometer thin films as response to femtosecond and picosecond laser pulse heating by time-resolved X-ray diffraction. This method allows a direct absolute determination of the molecular displacements induced by electron–phonon interactions, which are crucial for, for example, charge transport in organic electronic devices. We demonstrate that two different modes of coherent shear motion can be photoexcited in a thin film of organic molecules by careful tuning of the laser penetration depth relative to the thickness of the film. The measured response of the organic film to impulse heating is explained by a thermoelastic model and reveals the spatially resolved displacement in the film. Thereby, information about the profile of the energy deposition in the film as well as about the mechanical interaction with the substrate material is obtained

Effect of Phospholipid Composition and Phase on Nanodisc Films at the Solid–Liquid Interface as Studied by Neutron Reflectivity

Nanodiscs are disc-like self-assembled structures formed by phospholipids and amphipatic proteins. The proteins wrap like a belt around the hydrophobic part of the lipids, basically producing nanometer-sized patches of lipid bilayers. The bilayer in the nanodisc constitutes a native-like model of the cell membrane and can act as a nanometer-sized container for functional single membrane proteins. In this study, we present a general nanodisc-based system, intended for structural and functional studies of membrane proteins. In this method, the nanodiscs are aligned at a solid surface, providing the ability to determine the average structure of the film along an axis perpendicular to the interface as measured by neutron reflectivity. The nanodisc film was optimized in terms of nanodisc coverage, reduced film roughness, and stability for time-consuming studies. This was achieved by a systematic variation of the lipid phase, charge, and length of lipid tails. Herein, we show that, although all studied nanodiscs align with their lipid bilayer parallel to the interface, gel-phase DMPC nanodiscs form the most suitable film for future membrane protein studies since they yield a dense irreversibly adsorbed film with low roughness and high stability over time. This may be explained by the appropriate matching between the thickness of the hydrophobic lipid core of gel phase DMPC and the height of the belt protein. Moreover, once formed the gel-phase DMPC nanodiscs film can be heated up to melt the lipid bilayer, thus providing a more biologically friendly environment for membrane proteins

Hard X-ray phase-contrast imaging with the Compact Light Source based on inverse Compton X-rays

First X-ray phase-contrast imaging results recorded at the Compact Light Source, a laboratory-based inverse Compton X-ray source, are reported

Fast Strain Mapping of Nanowire Light-Emitting Diodes Using Nanofocused X-ray Beams

X-ray nanobeams are unique nondestructive probes that allow direct measurements of the nanoscale strain distribution and composition inside the micrometer thick layered structures that are found in most electronic device architectures. However, the method is usually extremely time-consuming, and as a result, data sets are often constrained to a few or even single objects. Here we demonstrate that by special design of a nanofocused X-ray beam diffraction experiment we can (in a single 2D scan with no sample rotation) measure the individual strain and composition profiles of many structures in an array of upright standing nanowires. We make use of the observation that in the generic nanowire device configuration, which is found in high-speed transistors, solar cells, and light-emitting diodes, each wire exhibits very small degrees of random tilts and twists toward the substrate. Although the tilt and twist are very small, they give a new contrast mechanism between different wires. In the present case, we image complex nanowires for nanoLED fabrication and compare to theoretical simulations, demonstrating that this fast method is suitable for real nanostructured devices