Markus Simon

X-ray full field microscopy at 30 KeV

In our X-ray full field microscopy experiments, we demonstrated a resolution better than 260 nm over the entire field of view of 80 μm × 80 μm at 30 keV. Our experimental setup at PETRA III, P05, had a length of about 5 m consisting of an illumination optics, an imaging lens and a detector. For imaging, we used a compound refractive lens (CLR) consisting of mr-L negative photo resist, which was fabricated by deep X-ray lithography. As illumination optics, we choose a refractive rolled X-ray prism lens, which was adapted to the numerical aperture of the imaging lens.

X-ray prism lenses with large apertures

Existing refractive X-ray lenses are characterized by either small apertures due to high absorption in the border areas. They can only be used with synchrotron sources, offering high brilliance. By increasing transparency and aperture the range of applications will expand, common X-ray tubes might turn out to be reasonable X-ray sources in an application with X-ray lenses. A basic concept that meets the demands is an X-ray Fresnel lens. But, Fresnel X-ray lenses are hard to fabricate, since the smaller lens structures need to be produced with extremely high aspect ratios. As an alternative, the Fresnel structures can be replaced by an array of prism-shaped structures. In particular equilateral triangular structures are easier to fabricate and additionally give a higher surface-volume-ratio, increasing transparency. At the Institute for Microstructure Technology the development of such prism lenses is under way. Due to the physical properties of X-rays, several thousands of precisely arranged prisms with large aspect ratio and smooth sidewalls are needed for a single X-ray lens. Therefore, direct X-ray lithography is used to fabricate the SU-8 microstructures. The length of one single prism edge is of the order of 10 μm. One single prismatic X-ray lens consists of up to 60.000 prisms. With the appropriate X-ray mask, refractive X-ray lenses with an aperture of up to 2 mm, for a source distance of 350 mm and a working distance of 350 mm are being produced, assuming a point-shaped source. These X-ray prism lenses are not optimized for smallest focal diameter, but designed to illuminate samples in X-ray optical systems. Most important in this application is an as high transparency as possible.

Large-aperture refractive lenses for momentum-resolved spectroscopy with hard X-rays

Large-aperture focusing lenses have been evaluated for momentum-resolved and flux-limited spectroscopy with hard X-rays.

Rolled-up tubes and cantilevers by releasing SrRuO3-Pr0.7Ca0.3MnO3 nanomembranes

AbstractThree-dimensional micro-objects are fabricated by the controlled release of inherently strained SrRuO3/Pr0.7Ca0.3MnO3/SrRuO3 nanometer-sized trilayers from SrTiO3(001) substrates. Freestanding cantilevers and rolled-up microtubes with a diameter of 6 to 8 μm are demonstrated. The etching behavior of the SrRuO3 film is investigated, and a selectivity of 1:9,100 with respect to the SrTiO3 substrate is found. The initial and final strain states of the rolled-up oxide layers are studied by X-ray diffraction on an ensemble of tubes. Relaxation of the sandwiched Pr0.7Ca0.3MnO3 layer towards its bulk lattice parameter is observed as the major driving force for the roll-up of the trilayers. Finally, μ-diffraction experiments reveal that a single object can represent the ensemble proving a good homogeneity of the rolled-up tubes. PACS: 81.07.-b; 68.60.-p; 68.37.Lp; 81.16.Dn.

Transmission hard X-ray microscope with increased view field using planar refractive objectives and condensers made of SU-8 polymer

Planar X-ray refractive lenses in crossed geometry providing 2D focusing are fabricated from SU-8 polymer using tilted deep X-ray lithography. The profiles of the objective lens elements are parabolic. The lens elements for the condensers were designed with a power of the surface function of 1.5, 1.7 and 2 to vary the field of views for a transmission X-ray microscope (TXM). With these lenses a TXM was set up at the ESRF beamline BM-5 for a photon energy of 15 keV. Different test nanostructures were imaged with this TXM using inline phase-contrast, with X-ray magnification factors of 29, demonstrated spatial detail resolution of 100 nm (half-period of lines and spaces) and exposure times around 10 s. Further improvement of a TXM based on the SU-8 lenses using refractive condensers with large apertures is considered with the aim to reduce exposure times.

Low-cost Rolled X-ray Prism Lenses to increase photon flux density in diffractometry experiments

At the Institute of Microstructure Technology (IMT) of the Karlsruhe Institute of Technology (KIT), a new type of refractive X-ray optics has been developed. Owing to its comparably easy fabrication method and the large aperture, the so-called Rolled X-ray Prism Lenses (RXPL) have the potential to be used with X-ray tubes in an industrial environment as a low-cost alternative to existing optics. The lens itself is built out of a micro-structured foil which is cut into shape and rolled around a winding core to form a refracting element for X-rays. The resulting refractive structure can be used as illumination optics. Diffractometry experiments with an NIST 1976a sample were performed and showed up to an 18-fold enhanced integrated intensity compared to that acquired with a steel tube collimator.

Refractive X-ray Optics made from Polymer Microstructures

Refractive X-ray lenses can be used effectively, to focus or collimate X-rays with photon energies clearly above 10 keV. On the one hand parabolic Compound Refractive Lenses (CRLs) are suitable as imaging optics in high resolution X-ray microscopy. The most recent developments are nanofocusing refractive X-ray lenses (NFLs). These show focal spot sizes of less below 100 nm. On the other hand refractive X-ray lenses can provide a high photon flux when used as large aperture condenser optics. Two types of refractive condenser optics made out of structures with triangular profile have been developed at the Institute for Microstructure Technology (IMT) at the Karlsruhe Institute of Technology (KIT) and have been tested at synchrotron sources in recent years. One type of special interest is the Rolled X-ray Prism Lens (RXPL). These lenses are made of a rolled polymer foil structured with micro grooves with triangular profile. The combination of such condenser optics and NFLs provides a basis for future hard X-ray microscopes.

Achromatic x-ray focusing using diffractive and refractive elements

We develop a new type of X-ray lens system which is achromatic in a limited energy range. For such achromats we combine different types of refractive and diffractive elements. For example, Fresnel zone plates and planar parabolic concave SU-8 lenses are combined with lenses with a biconvex parabolic shape and with Fresnel lenses, respectively. We present numerical results from a theoretical study of such optical systems. We determine the focal spot size for an energy range of about E ± ΔE with ΔE/E ≈ 17%. Amongst other results we find that, compared with conventional lens systems, the spot size can be reduced by several tens of percent by using such achromatic lens systems.

Numerical simulations of achromatic X-ray lenses

Over the last decade refractive lenses for monochromatic X-ray radiation have been realized for many different materials by microfabrication technology. All these lens systems are successfully working only for one discrete energy, i.e. the lenses are chromatic. Thus each discrete energy within a certain energy range has a different focal length. While the focal spot size is smaller than a micron for a particular energy at the corresponding focal distance, it increases up to several tens of microns for a larger energy range. We present results of numerical simulations for a new type of lens system which addresses this problem. We are developing achromats by combining different refractive elements of different materials. Via ray-tracing we determine the parameters of the lenses by minimizing the focal spot size for an energy range of about E ± ΔE with ΔE = 15%. Thus the spot size of an energy range can be noticeably reduced compared with conventional refractive (chromatic) lens systems.

Refractive Optics for Hard X‐ray Transmission Microscopy

For hard x‐ray transmission microscopy at photon energies higher than 15 keV we design refractive condenser and imaging elements to be used with synchrotron light sources as well as with x‐ray tube sources. The condenser lenses are optimized for low x‐ray attenuation—resulting in apertures greater than 1 mm—and homogeneous intensity distribution on the detector plane, whereas the imaging enables high‐resolution (<100 nm) full‐field imaging. To obtain high image quality at reasonable exposure times, custom‐tailored matched pairs of condenser and imaging lenses are being developed. The imaging lenses (compound refractive lenses, CRLs) are made of SU‐8 negative resist by deep x‐ray lithography. SU‐8 shows high radiation stability. The fabrication technique enables high‐quality lens structures regarding surface roughness and arrangement precision with arbitrary 2D geometry. To provide point foci, crossed pairs of lenses are used. Condenser lenses have been made utilizing deep x‐ray lithographic patterning of ...