J. M. Feldkamp

Hard x-ray nanobeam characterization by coherent diffraction microscopy

We have carried out a ptychographic scanning coherent diffraction imaging experiment on a test object in order to characterize the hard x-ray nanobeam in a scanning x-ray microscope. In addition to a high resolution image of the test object, a detailed quantitative picture of the complex wave field in the nanofocus is obtained with high spatial resolution and dynamic range. Both are the result of high statistics due to the large number of diffraction patterns. The method yields a complete description of the focus, is robust against inaccuracies in sample positioning, and requires no particular shape or prior knowledge of the test object.

Hard X-ray nanoprobe at beamline P06 at PETRA III

We describe the hard X-ray scanning microscope planned for the new synchrotron radiation source PETRA III at DESY in Hamburg, Germany. It is based on nanofocusing refractive X-ray lenses and is designed for two-dimensional mapping and scanning tomography. It supports X-ray fluorescence and (coherent) diffraction contrast, yielding elemental and structural information from inside the sample. Spatial resolutions down to well below 50 nm are aimed for in direct space. A further increase in spatial resolution is expected by applying ptychographic scanning schemes. The optical scheme with a two-stage focusing optic is described.

Grazing incidence small-angle X-ray scattering microtomography demonstrated on a self-ordered dried drop of nanoparticles.

We combine grazing-incidence small-angle X-ray scattering (GISAXS) with scanning X-ray microtomography to investigate the nanostructure in a dried gold/polystyrene nanocomposite drop. Local GISAXS structure factors are reconstructed at each position on the surface of this two-dimensionally heterogeneous sample with 30 microm pixel size. Evidence for four types of self-assembled colloidal crystalline structures is provided by the reconstructed data of the drop demonstrating the feasibility of the method.

Structure and flow of droplets on solid surfaces

The structure and flow of droplets on solid surfaces is investigated with imaging and scattering techniques and compared to simulations. To access nanostructures at the liquid-solid interface advanced scattering techniques such as grazing incidence small-angle x-ray scattering (GISAXS) with micro- and nanometer-sized beams, GISAXS and in situ imaging ellipsometry and GISAXS tomography are used. Using gold nanoparticle suspensions, structures observed in the wetting area due to deposition are probed in situ during the drying of the droplets. After drying, nanostructures in the wetting area and inside the dried droplets are monitored. In addition to drying, a macroscopic movement of droplets is caused by body forces acting on an inclined substrate. The complexity of the solid surfaces is increased from simple silicon substrates to binary polymer brushes, which undergo a switching due to the liquid in the droplet. Nanostructures introduced in the polymer brush due to the movement of droplets are observed.

Nanofocusing refractive X-ray lenses: Fabrication and modeling

Nanofocusing refractive x-ray lenses (NFLs) form the basis of a hard x-ray scanning microscope. They are characterized by their short focal length (~ 10 mm at 15 keV to 25 keV) and large numerical aperture, allowing for the generation of hard x-ray nanobeams even at short distances from a synchrotron radiation source. These optics, made out of silicon by electron beam lithography and subsequent deep reactive ion etching, have been shown to focus hard x-rays down to 50 nm. We have modeled these optics, allowing us to characterize slight aberrations and the wave-field properties in the focus by analyzing the beam profile in the far field.

Hard X‐Ray Nanoprobe based on Refractive X‐Ray Lenses

At synchrotron radiation sources, parabolic refractive x‐ray lenses allow one to built both full field and scanning microscopes in the hard x‐ray range. The latter microscope can be operated in transmission, fluorescence, and diffraction mode, giving chemical, elemental, and structural contrast. For scanning microscopy, a small and intensive microbeam is required. Parabolic refractive x‐ray lenses with a focal distance in the centimeter range, so‐called nanofocusing lenses (NFLs), can generate hard x‐ray nanobeams in the range of 100 nm and below, even at short distances, i. e., 40 to 70 m from the source. Recently, a 47 × 55 nm2 beam with 1.7 ⋅ 108 ph/s at 21 keV (monochromatic, Si 111) was generated using silicon NFLs in crossed geometry at a distance of 47m from the undulator source at beamline ID13 of ESRF. This beam is not diffraction limited, and smaller beams may become available in the future. Lenses made of more transparent materials, such as boron or diamond, could yield an increase in flux of o...

Hard X-ray scanning microscopy with fluorescence and diffraction contrast

Based on nanofocusing parabolic refractive x-ray lenses we have developed and built a hard x-ray scanning microscope that was tested and put to use at beamline ID13 of the ESRF. It can provide a monochromatic hard x-ray nanobeam with lateral extension below 100 nm (down to 50 nm) and a flux up to 109 ph/s in the energy range from 15 to 25 keV. The microscope exploits transmission, fluorescence, and diffraction contrast to obtain local elemental and nanostructural information from the sample. Tomographic scanning yields high resolution elemental maps from the inside of an object. Coherent x-ray diffraction imaging with nanofocused illumination yields images of objects with highest spatial resolution, e. g., 5 nm in a given example.

Development of SAXS microtomography and related methods

Small-angle x-ray scattering (SAXS) is a standard method for non-destructive structure analysis on the nanometer scale with synchrotron radiation. Many soft condensed matter materials (e.g. natural fibers, polymer fibers, wood, polymer parts) are nanostructured, and their macroscopic properties are a result of this structure. Frequently the nanostructure varies across the specimen under investigation. For these samples the combination of SAXS with microtomography opens up new possibilities for non-destructive studies of complex materials. The result is a mosaic of SAXS patterns, which are associated with defined volume elements in the specimen. These reconstructed patterns can be analyzed in order to track the variation of nanostructure inside the sample. Experimental details and results are illustrated in various examples.