No abstract

Emerging free-electron lasers (FELs) at short wavelengths open a new possibility for ultrafast microscopy of transient phenomena at high spatial resolution due to the ultrashort pulse duration. As a first step, we performed sub-picosecond snapshot imaging with extreme ultraviolet FEL by adopting a recently proposed holographic technique, holography with extended reference by autocorrelation linear differential operation (HERALDO). We point out that HERALDO enables efficient single-shot phase-contrast imaging by carefully designing the aperture size of the reference without sacrificing spatial resolution. The successful reconstruction of a test pattern from a single-shot hologram demonstrates an effective method of taking phase-contrast sub-picosecond snapshots.

X‐ray reflectivity (XR) and scanning probe microscopy (SPM) were used to examine the structures, polymorphic transitions, and surface morphologies of triacylglycerol (TAG), 1,3‐stearin‐2‐olein (SOS) and 1‐palmitin‐2‐olein‐3‐stearin (POS) thin films supported on Si substrates. The structural parameters: thickness, electron density, and surface/interface roughnesses of TAG thin films were determined by the nonlinear least‐squares regression of XR profiles to reveal their temperature dependences. In the lower temperature regimes, we observed Bragg peaks without significant interference fringe patterns in the XR profiles. SPM at room temperature displayed isolated islands on TAG thin films with surface undulations. Whereas in the higher temperature regimes in which the Bragg peaks disappeared, the interference fringe patterns became prominent. The analyses of the XR profiles indicated the structural change in thin films from three layers to single layer on Si substrates with increasing temperature. However, the temperatures at which the structural change occurred were obviously different between SOS and POS thin films.

Natural cocoa butter is known to exhibit five structural phase transitions. In situ observation on these phase transitions in surface region has been perfonned by a combination of grazing incidence X-ray diffraction and X-ray Reflectivity (XR) to compare the phase transitions in bulk. A surface-induced preferred orientation of constituent oil molecules is found, of which origin is the same as the diffuse scattering observed in bulk samples. A novel double-layer to single-layer phase transition is found by XR of Si-supported ultrathin films with thickness of several nm, indicating the anisotropic nature of inter molecular interactions.