X-ray phase-contrast radiography and tomography enables to increase contrast for weakly absorbing materials.
Recently, x-ray grating interferometers were developed which extend the possibility of phase-contrast imaging
from highly brilliant radiation sources like third-generation synchrotron even to non-coherent sources. Here,
we present a setup of an x-ray grating interferometer designed and installed at low-coherence wiggler source
at the GKSS beamline W2 (HARWI II) operated at the second-generation synchrotron storage ring DORIS at
the Deutsches Elektronen-Synchrotron (DESY, Hamburg, Germany). The beamline is dedicated to imaging in
materials science. Equipped with the grating interferometer, it is the first synchrotron radiation beamline with
a three-grating setup combining the advantages of phase-contrast imaging with monochromatic radiation with
very high flux and a sufficiently large field of view for centimeter sized objects. Examples of radiography on
laser-welded aluminum and magnesium joints are presented to demonstrate the high potential of the new gratingbased
setup in the field of materials science. In addition, the results of an off-axis phase-contrast tomography of
a human urethra with 15 mm in diameter are presented showing internal structures, which cannot be resolved
by the conventional tomography in absorption mode.
In this paper we describe the design of different X-ray Talbot interferometers that have been built at the tomography
beamline ID19 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, and give a short review of
performance characteristics, of current developments, and of the results obtained with these instruments so far. Among the
applications so far, soft-tissue imaging has been a particular focus, as demonstrated in a recent paper by Schulz et al. (J.
Roy. Soc. Interface, in press).
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.
X-ray prism lenses have been defined with the aim to collimate X-ray radiation emitted from an X-ray tube working as a
condenser lenses. Such a lens must have a large aperture as low absorption as possible. X-ray prism lenses combine low
absorption and large apertures. They are made up of a large array of equilateral triangular prismatic microstructures. The
intent by using these structures is to obtain as many refracting surfaces as possible in the smallest volume. The higher
surface-volume-ratio in comparison to standard lenses reduces absorption significantly at the expense of focus quality.
A first lens has been fabricated by X-ray lithography out of PMMA, with a designed aperture of up to 1.4 mm working
distances of 325 mm to the point source and X-ray energy of 9 keV. The edge-length of the prismatic microstructures is
10 μm. The lenses have been tested at the ESRF in (Grenoble, France) and at ANKA (Karlsruhe, Germany). The results
show an influence of the imperfections of the lens structures (bended prismatic microstructures) on the focal spot along
the focal line. The measured gain was 28 at a focal width of 8 μm at full width at half maximum. Due to these
imperfections the relevant aperture is currently limited to 500 μm.
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.
We report the results on experimental study of optical properties of Ni refractive lenses made by deep X-ray lithography and LIGA techniques. One- and two-dimensional lenses were tested at the ESRF ID15 beamline using wide energy spectrum from 40 keV to 220 keV. The focusing properties in terms of focal length, size of the focal spot/line and gain were studied. Sub micrometer focusing was measured in the energy range from 40 to 150 keV. The measured lens parameters were compared with ray-tracing analysis.
We present results on comprehensive studies of high resolution SU-8 planar refractive lenses. Lens optical properties were investigated using coherent high energy X-ray radiation. Resolution of about 270 nm was measured for the lens consisting of 31 individual lenses at energy 14 keV. Coherent properties of the set-up permit to resolve near-focus fine structure, which is determined by tiny aberrations caused by lens imperfections close to the parabola apex. This study allows understanding as far SR deep lithography as possible can maintaine to close tolerances for lens parameters. Two-dimensional focusing crossed lenses were tested and imaging experiments in projection and imaging mode were conducted. Radiation stability test was performed and conclusions on the applicability of SU-8 lenses were done.
Sets of planar SU-8 cross lenses focusing in two directions have been fabricated by tilted deep X-ray lithography using an X-ray mask with tilted absorber structures. The profile of the absorber structures on the mask take into account the lithographic peculiarities of SU-8 resist to reproduce the designed profile of the lens elements exactly. The cross lenses are placed on one substrate and have identical focal distances, which allow to scan the spectral range from 5 keV to 30 keV by stepping the lens substrate from one lens to the next. Another set of cross lenses was developed with different quasi-parabolic profiles to obtain a large focus depth (up to several centimeters) with uniform intensity distribution in the micron focal spot. This together with the stepping possibilities between lenses satisfies the requirement of static spectroscopy experiments. For the truncated parabolic profile, these cross lenses consist of separate segments arranged in a new mosaic form. In comparison with the known “fern”-like kinoform profile, the lenses have been developed with smaller gain loss. The testing of the new sets have been performed at the undulator ID-18F and ID-22 beamlines (ESRF, Grenoble, France) and the experimental results are compared to simulations.
Compound refractive lenses printed in Al and Be are becoming the key X-ray focusing and imaging components of beamline optical layouts at the 3rd generation synchrotron radiation sources. Recently proposed planar optical elements based on Si, diamond etc. may substantially broaden the spectrum of the refractive optics applicability. Planar optics has focal distances ranging from millimeters to tens of meters offering nano- and micro-focusing lenses, as well as beam condensers and collimators. Here we promote deep X-ray lithography and LIGA-type techniques to create high aspect-ratio lens structures for different optical geometries. Planar X-ray refractive lenses were manufactured in 1 mm thick SU-8 negative resist layer by means of deep synchrotron radiation lithography. The focusing properties of lenses were studied at ID18F and BM5 beamlines at the ESRF using monochromatic radiation in the energy range of 10 - 25 keV. By optimizing lens layout, mask making and resist processing, lenses of good quality were fabricated. The resolution of about 270 nm (FWHM) with gain in the order of 300 was measured at 14 keV. In-line holography of B-fiber was realized in imaging and projection mode with a magnification of 3 and 20, respectively. Submicron features of the fiber were clearly resolved. A radiation stability test proved that the fabricated lenses don't change focusing characteristics after dose of absorbed X-ray radiation of about 2 MJ/cm3. The unique radiation stability along with the high effficiency of SU8 lenses opens wide range of their synchrotron radiation applications such as microfocusing elements, condensers and collimators.
The X-ray lithography with synchrotron radiation at the VEPP-3 storage ring was applied for fabrication of polymer microstructures with submicron sizes of elements and with rather high aspect ratio (up to 20). The microstructures are the regular microporous membranes with pores of 0.3-0.5 micrometers in diameter arranged with a 1 micrometers spacing. The membranes were fabricated on a base of 2.5, 3, 6 and 10 micrometers thick mylar films. In contrast to the commercial track membranes with random pore locations, the regular membranes have no dispersion of pore sizes caused by confluence of adjoining pores. The fabricated membranes have a porosity of 10-20 percent and this value can be increased up to 50 percent and higher by using an X-ray mask with an appropriate pattern. The results of the membrane examination by different techniques are presented. Possible improvements of the membrane parameters and some potential applications of the membranes are discussed as well.
The use of laser-induced chemical vapor deposition (LCVD) of chromium and rhenium film patterns for reporting of photomask defects and LCVD of rhenium, gold and platinum film pattern for repairing similar defects of X-ray masks was demonstrated. Initial compounds were Cr(CO)6, Re2(CO)10, Me2Au(dpm) and Pt(hfa)2. The high marginal sharpness and the thickness uniformity of deposited films was provided by the use of powerful nanosecond pulse laser, the protective system for a delineation of a irradiation zone and the laser beam microscanning in limits of this zone. The scheme of the set for the direct laser deposition of film micropatterns was presented.
The influence of synchrotron radiation on the vacuum-deposited layers of copper and aluminum phthalocyanines was investigated. For creation of patterns in these layers the x-ray radiation exposing and vacuum thermal development were used. It was established that the layers of copper phthalocyanine possess the properties of both positive and negative vacuum x- ray resist upon radiation exposure of 5 kJ/cm3 and 35 kJ/cm3 accordingly. The layers of aluminum phthalocyanine possess the properties of only negative vacuum x-ray resists. The possibility of creating submicron topology in layers of metal phthalocyanines has been demonstrated.