C.G. Schroer

A MICROSCOPE FOR HARD X RAYS BASED ON PARABOLIC COMPOUND REFRACTIVE LENSES

We describe refractive x-ray lenses with a parabolic profile that are genuine imaging devices, similar to glass lenses for visible light. They open considerable possibilities in x-ray microscopy, tomography, microanalysis, and coherent scattering. Based on these lenses a microscope for hard x rays is described, that can operate in the range from 2 to 50 keV, allowing for magnifications up to 50. At present, it is possible to image an area of about 300 μm in diameter with a resolving power of 0.3 μm that can be increased to 0.1 μm. This microscope is especially suited for opaque samples, up to 1 cm in thickness, which do not tolerate sample preparation, like many biological and soil specimens.

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.

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.

Dislocation density analysis in single grains of steel by X-ray scanning microdiffraction

Abstract A new set-up for X-ray micro-diffraction has been developed on the ESRF beamline ID22. It allows microscopic characterization of materials with micrometer resolution. This facilitates the measurement of material quantities as average size of the coherently diffracting volume, local dislocation density, residual stress, local fluctuation of the residual stress, and intragranular misorientation from single grains of a polycrystalline material. The first application on an IF-Ti steel after different thermo-mechanical treatments is presented.

Recent developments in hard X-ray tomography

A new technique for magnified hard X-ray tomography using compound refractive lenses (CRLs) has been tested. A full-field X-ray microscope was included into a conventional microtomography setup at a synchrotron undulator beamline. Experiments were carried out at 19.7 keV with a monochromatic beam as well as with the so-called ‘‘pink’’ beam using a larger energy bandwidth. During this pilot experiment a resolution of about 1mm was already achieved, which corresponds to the best resolution obtained with phase-contrast enhanced microtomography. The technique has the potential to increase the spatial resolution of hard-X-ray microtomography to a scale of several hundred nanometers. # 2001 Elsevier Science B.V. All rights reserved.

Multimode transport in a T-shaped quantum transistor

This article presents numerical studies on multimode transport in a T-shaped quantum transistor geometry. Solving the time independent Schrodinger equation with adequate boundary conditions we model the current for up to six one-dimensional modes in the T structure. It is found, that independent of the number of modes periodic features dominate the conductivity as a function of gate voltage. Their origin is explained in terms of mode coupling in the stub region of the transistor for which the electron velocity in the waveguide is essential. The results are compared with experimental data.

2D imaging by X-ray fluorescence microtomography

First experimental results of fluorescence microtomography in “pencil-beam” geometry with 6 μm resolution obtained at the ESRF/1D 22 are described. Image reconstructions are based on either a simplified algebraic reconstruction method (ART) or the filtered back-projection method (FBT). Simple cylindrical test objects are accurately reconstructed.

A X-ray microscope for stored energy in single grains of cold-rolled steel

A new set-up for X-ray microdiffraction has been developed on the ESRF beamline ID22. This set-up allows microscopic characterization of materials in diffraction mode, the size of the focused beam being only of a few microns. This facilitates the measurement of material quantities as average size of the coherently diffracting volume, local dislocation density, residual stress, local fluctuation of the residual stress, and intragranular misorientation from single grains of a polycrystalline material. The first application on an IF-Ti steel after different thermomechanical treatments (recrystallization, cold-rolling, annealing) is presented.

Compound refractive lenses for X-ray microanalysis

We describe parabolic compound refractive X-ray lenses made of aluminum that are genuine imaging devices, similar to glass lenses for visible light. When used to image a synchrotron radiation source onto a sample in a strongly demagnifying setup, these lenses allow to produce a small pencil beam of high intensity that can be used for (scanning) microprobe experiments, such as microdiffraction and microfluorescence. The aluminum lenses are most effective above 10 keV and are particularly suited for hard x-rays up to at least 60 keV. The pencil beam has a typical lateral size in the micrometer range with a gain in intensity of two to three orders of magnitude. The small beam convergence in the spot (typically Δk/k<10−4) is ideal for microdiffraction and micro-SAXS experiments. We give examples of microprobe experiments including microdiffraction, microfluorescence, and fluorescence microtomography.