Hard X-ray shearing interferometry

We have developed a hard x-ray interferometer known in visible and EUV optics as shearing interferometer. In contrast to the well known Bonse-Hart interferometer, the interfering beams are not completely separated into object and reference beams, but they are merely sheared by a small angle, so that both beams pass through the sample. We used silicon phase gratings generated by electron beam lithography and wet chemical etching as beam splitter and analyzer elements. The technique was tested successfully at 2.4 keV and 24.8 keV photon energies by using polystyrene spheres as low absorbing test objects. The interferometer proved to be insensitive to mechanical vibrations and drift. We obtained micrographs with Moire patterns of good visibility. The local distortions of the interference pattems result from the local gradient in phase shift caused by the test objects. For a pcrfoetly aligned and divergence compensated setup, the phase map of low absorbing objects can bc rctrieved by using a simple numerical integration

Arrays of nanoscale magnetic dots: Fabrication by x-ray interference lithography and characterization

X-ray interference lithography (XIL) was employed in combination with electrodeposition to fabricate arrays of nanoscale nickel dots which are uniform over 40 µm and have periods down to 71 nm. Using extreme-ultraviolet light, XIL has the potential to produce magnetic dot arrays over large areas with periods well below 50 nm, and down to a theoretical limit of 6.5 nm for a 13 nm x-ray wavelength. In the nickel dot arrays, we observed the effect of interdot magnetic stray field interactions. Measuring the hysteresis loops using the magneto-optical Kerr effect, a double switching via the vortex state was observed in the nickel dots with diameters down to 44 nm and large dot separations. As the dot separations are reduced to below around 50 nm a single switching, occurring by collective rotation of the magnetic spins, is favored due to interdot magnetic stray field interactions. This results in magnetic flux closure through several dots which could be visualized with micromagnetic simulations. Further evidence of the stray field interactions was seen in photoemission electron microscopy images, where bands of contrast corresponding to chains of coupled dots were observed

Diffractive soft and hard X-ray optics

The Laboratory for Micro- and Nanotechnology provides the essential technologies necessary for the design and fabrication of diffractive x-ray optics for a wide range of applications. Over the past years, a large variety of optics has been fabricated and tested in collaboration with a large number of partners. To ensure good performance of the devices, they have to be tailored to the specific needs of a specific x-ray optical experiment in terms of photon energy and spatial coherence of the source, as well as required spatial resolution, working distance and diffraction efficiency. We report on a selection of such developments including transmission Fresnel phase zone plates for microscopy or microprobe applications at photon energies ranging from the EUV to the multi-keV region. For photon energies beyond 10 keV transmission zone plates are very rarely used. Our recent development of linear optics with ultra high aspect ratio structures has opened up a way to extend the applications of diffractive optics at least to the 30 keV range. Besides focusing elements, other diffractive optics such as decoherers or beam splitters for interferometric applications are presented