Recent research on hydrogen storage
in metal–organic frameworks focuses on how to achieve increased
hydrogen binding energies by using doped metal, using unsaturated
metal ions, or forming composites comprising Pt-doped carbon materials.
In particular, noticeable progress using MOFs and Pt-doped carbons
has been achieved to enhance the hydrogen storage capacity near room
temperature. A three-component composite material, Pt-MWCNT-MOF5 (PMM5),
which is a metal–organic framework (MOF-5) hybridized with
Pt nanoparticles on multiwalled carbon nanotubes (MWCNT), stores 0.22
wt % hydrogen at 320 K and 30 bar, which is larger than 0.13 wt %
at 300 K and 30 bar. Although the increased quantity is small, it
is possible to detect the origin of uptake increase based on various
analyses. In situ neutron diffraction experiments of deuterium-sorbed
PMM5 with a temperature cycling process (D2 loading at
50 K → 4 K → 320 K, 2 h → 50 K → 4 K)
result in a significant background increase owing to both chemisorbed
deuterium atoms and a local deformation of the MOF-5 framework. Hydrogen
loading in PMM5 induces significant binding energy shifts in C 1s
and Zn 2p3/2 electrons in the X-ray photoelectron spectra,
suggesting the chemical environment change in Zn4O(COO)6 coordination sphere in MOF-5. All accumulated experimental
data support the fact that the hydrogen receptor is the oxygen atoms
of benzene-1,4-dicarboxylates of MOF-5, which is facilitated by the
embedded Pt-MWCNT.
The PERCIVAL detector is a CMOS imager designed for the soft X-ray regime at photon sources. Although still in its final development phase, it has recently seen its first user experiments: ptychography at a free-electron laser, holographic imaging at a storage ring and preliminary tests on X-ray photon correlation spectroscopy. The detector performed remarkably well in terms of spatial resolution achievable in the sample plane, owing to its small pixel size, large active area and very large dynamic range; but also in terms of its frame rate, which is significantly faster than traditional CCDs. In particular, it is the combination of these features which makes PERCIVAL an attractive option for soft X-ray science.
In this work, single-shot ptychography was adapted to the XUV range and, as a proof of concept, performed at the free-electron laser FLASH at DESY to obtain a high-resolution reconstruction of a test sample. Ptychography is a coherent diffraction imaging technique capable of imaging extended samples with diffraction-limited resolution. However, its scanning nature makes ptychography time-consuming and also prevents its application for mapping of dynamical processes. Single-shot ptychography can be realized by collecting the diffraction patterns of multiple overlapping beams in one shot and, in recent years, several concepts based on two con-focal lenses were employed in the visible regime. Unfortunately, this approach cannot be extended straightforwardly to X-ray wavelengths due to the use of refractive optics. Here, a novel single-shot ptychography setup utilizes a combination of X-ray focusing optics with a two-dimensional beam-splitting diffraction grating. It facilitates single-shot imaging of extended samples at X-ray wavelengths.
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