Abstract
Scattering experiments on xenon nanoclusters with high-intensity soft x-ray laser pulses from the Free-Electron LASer in Hamburg (FLASH) are performed to investigate different cluster morphologies in the gas phase. Three different types of scattering patterns can be identified. The most frequent pattern of concentric rings reflects the event of a single spherical cluster in focus. Fine interference rings similar to Newton rings appear when two clusters are illuminated at μm distance, revealing three-dimensional information about the location of the clusters. Between 10 and 30% of all hits show a previously unknown twin cluster configuration with two clusters in direct contact. Simulations of scattering patterns for twin clusters with different sizes of the two particles, degree of fusion and orientation in space allow us to explain all the observed patterns.
Highlights
For the studies of this paper, a new experimental setup for the single-shot imaging of nanometersized samples at the Free-Electron LASer in Hamburg (FLASH) was designed combining a spectroscopy approach and an imaging approach
The optical path is given in figure 1(a) and a schematic layout of the interaction region is presented in figure 1(b)
The soft x-ray pulses are focused by a multilayer mirror into a focal spot of about five microns diameter
Summary
For the studies of this paper, a new experimental setup for the single-shot imaging of nanometersized samples at the Free-Electron LASer in Hamburg (FLASH) was designed combining a spectroscopy approach and an imaging approach. We use an off-axis backfocusing geometry with an angle of 2.5◦ between the incident and reflected beams in order to cover small scattering angles without blocking the incoming beam. By using this geometry the incoming beam does not cross the interaction region, which greatly reduces the background from the fluorescent light. The cluster beam is generated by supersonic expansion of xenon through a cryogenically cooled and pulsed conical nozzle with a diameter of 200 μm and a half-cone angle of 4◦. With the scattering detector covering angles up to 47◦, a maximal detectable momentum transfer of q = 4π/λ · sin(θ/2) = 0.36 nm−1 limits the resolution to 2π/q = 17 nm
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