Marion Kuhlmann

Small-angle options of the upgraded ultrasmall-angle x-ray scattering beamline BW4 at HASYLAB

We present the upgrade and present status of the ultrasmall-angle x-ray scattering (USAXS) beamline BW4 at the Hamburg Synchrotronstrahlungslabor. In order to extend the accessible scattering vector range, new small-angle setups have been established, making use of the high flux and small divergence of BW4. In standard transmission geometry using a beam size of B=400×400μm2 (horizontal×vertical), typical small-angle resolution ranges from dmax=90to650nm, depending on sample-to-detector distance. Additionally a new microfocus option has been established. This microfocus option allows reducing the sample size by one order of magnitude. Using parabolic beryllium compound refractive lenses, a new standard beam size of B=65×35μm2 (horizontal×vertical) can be provided. The μ-SAXS resolution is as high as dmax=150nm. Using μ-SAXS in combination with grazing incidence (μ-GISAXS) on a standard noble metal gradient multilayer, we prove the feasibility of μ-GISAXS experiments at a second generation source.

Nanofocusing parabolic refractive X-ray lenses

Parabolic refractive x-ray lenses with short focal distance can generate intensive hard x-ray microbeams with lateral extensions in the 100 nm range even at a short distance from a synchrotron radiation source. We have fabricated planar parabolic lenses made of silicon that have a focal distance in the range of a few millimeters at hard x-ray energies. In a crossed geometry, two lenses were used to generate a microbeam with a lateral size of 380 nm by 210 nm at 25 keV in a distance of 42 m from the synchrotron radiation source. Using diamond as the lens material, microbeams with a lateral size down to 20 nm and below are conceivable in the energy range from 10 to 100 keV.

Refractive x-ray lenses

Parabolic refractive x-ray lenses are novel optical components for the hard x-ray range from about 5 keV to about 120 keV. They are compact, robust, and easy to align and to operate. They can be used like glass lenses are used for visible light, the main difference being that the numerical aperture is much smaller than 1 (of the order of 10−4–10−3). They have been developed at Aachen University and are made of beryllium, boron, aluminium and silicon. Their main applications are in micro- and nanofocusing, in imaging by absorption and phase contrast. In combination with tomography they allow for three-dimensional imaging of opaque media with sub-micrometre resolution. Finally, they can be used in speckle spectroscopy by means of coherent x-ray scattering. References to a number of applications are given.

Mapping the chemical states of an element inside a sample using tomographic x-ray absorption spectroscopy

Hard x-ray absorption spectroscopy is combined with scanning microtomography to reconstruct full near-edge spectra of an elemental species at each location on an arbitrary virtual section through a sample. These spectra reveal the local concentrations of different chemical compounds of the absorbing element inside the sample and give insight into the oxidation state, the local atomic structure, and the local projected free density of states. The method is implemented by combining a quick scanning monochromator and data acquisition system with a scanning microprobe setup based on refractive x-ray lenses.

Mapping the local nanostructure inside a specimen by tomographic small-angle x-ray scattering

Small-angle x-ray scattering is combined with scanning microtomography to reconstruct the small-angle diffraction pattern in the direction of the tomographic rotation axis at each location on a virtual section through a specimen. These data yield information about the local nanoscale structure of the sample. With rotational symmetry present in the diffraction patterns, e.g., for isotropic or fiber-textured scatterers, the full reciprocal space information in the small-angle scattering regime can be reconstructed at each location inside the specimen. The method is illustrated investigating a polymer rod made by injection molding.

Nanotomography based on hard x-ray microscopy with refractive lenses

Based on parabolic refractive x-ray lenses we have built a hard x-ray microscope that allows one to image the interior of opaque samples with submicrometer resolution. We have combined magnified imaging with tomography to obtain the three-dimensional structure of the sample at a resolution well below 1 μm. Using an aluminum lens to record a magnified tomogram of a test sample (microprocessor), a resolution of slightly above 400 nm was found for the three-dimensional reconstruction. Lenses made of beryllium are expected to improve this resolution to well below 100 nm. The resulting challenges concerning instrumentation and numerical methods are discussed.

Combinatorial investigation of the isolated nanoparticle to coalescent layer transition in a gradient sputtered gold nanoparticle layer on top of polystyrene

Within a combinatorial investigation, a gradient sputtered gold layer on top of polystyrene on silicon substrate is addressed. Results from a real-space inspection by transmission electron microscopy are compared with surface-sensitive microbeam grazing incidence small-angle x-ray scattering. The combinatorial approach allows distinguishing different morphologies prepared under exactly the same environmental conditions on one single substrate. The transition of a coalescent layer to an isolated nanoparticle layer is determined as a function of sputter rate. Though optical spectra show only slight differences, the morphology and structure are distinctly different from evaporated layers prepared with same mass thickness.

Parabolic refractive X-ray lenses: a breakthrough in X-ray optics

Refractive X-ray lenses, considered for a long time as unfeasible, have been realized with a rotational parabolic profile at our institute: The main features of the new lenses are: they focus in two directions and are free of spherical aberration. By varying the number of individual lenses in the stack the focal length can be chosen in a typical range from 0.5 to 2 m for photon energies between about 6 and 60 keV. The aperture of the lens is about 1 mm matching the angular divergence of undulator beams at 3d generation synchrotron radiation sources. They cope without problems with the heat load from the white beam of an undulator. Finally, they are easy to align and to operate. Refractive X-ray lenses can be used with hard X-rays in the same way as glass lenses can be used for visible light, if it is taken into account that the numerical aperture is small (of the order 10 � 4 ). Being high-quality optical elements, the refractive X-ray lenses can be used for generating a focal spot in the mm range with a gain of a factor 1000 and more, or for imaging purposes as in a hard X-ray microscope. Recent examples from microanalysis, microtomography, fluorescence tomography, X-ray microscopy will be shown to demonstrate the state of the art. Possible new developments will be discussed. # 2001 Elsevier Science B.V. All rights reserved. PACS: 41.50; 07.85.T

Beryllium parabolic refractive x-ray lenses

Recently, we have been able to fabricate high quality parabolic refractive x-ray lenses made of beryllium. We report first experimental results in both full field microscopy and microbeam production using these new lenses. In full field microscopy, undistorted images of test patterns were recorded in a field of view of 450 μm full width half maximum at 12keV with 10 fold magnification. A significant improvement of the lateral resolution as compared to imaging with aluminium refractive lenses was achieved. Microbeam characteristics were determined at 12keV demagnifying a high β undulator source 82 times. The lateral beam size was measured by fluorescence knife-edge. Microbeam characteristics, such as flux, lateral beam size, and low intensity background are discussed.

High resolution imaging and lithography with hard x rays using parabolic compound refractive lenses

Parabolic compound refractive lenses are high quality optical components for hard x rays. They are particularly suited for full field imaging, with applications in microscopy and x-ray lithography. Taking advantage of the large penetration depth of hard x rays, the interior of opaque samples can be imaged with submicrometer resolution. To obtain the three-dimensional structure of a sample, microscopy is combined with tomographic techniques. In a first hard x-ray lithography experiment, parabolic compound refractive lenses have been used to project the reduced image of a lithography mask onto a resist. Future developments are discussed.