Kirkpatrick-Baez (KB) mirrors consist of two individual mirrors: one vertical focusing mirror and one horizontal
mirror at separate positions. Nested (Montel) KB mirrors consist of two mirrors arranged perpendicularly to each
other and side-by-side. We report our results from the fabrication and tests of the first set of nested KB mirrors for a
synchrotron hard x-ray micro/nano-focusing system. The elliptically shaped nested Platinum KB mirrors include
two 40 mm long mirrors fabricated by depositing Platinum on Silicon substrates using the magnetron sputtering
technique. Hard x-ray synchrotron tests have been performed at 15 keV and 2D focal spots of approximately 150 nm
x 150 nm (FWHM) were achieved from both monochromatic and polychromatic beams at the 34 ID beamline of the
Advanced Photon Source (APS) at Argonne National Laboratory. The side-by-side arrangement of nested KB
mirrors requires them to have good surfaces and low figure errors at the intersection of the two mirrors' surfaces. It
is very challenging to fabricate substrates that fit the nested KB mirror's arrangement and to deposit thin films to
ideal elliptical shapes at the edge of the mirrors. Further research and development will be performed in the areas of
fabrication and testing with respect to nested KB mirrors used in micro/nano-focusing systems. In particular,
substrate processing and deposition techniques should be examined to improve the performance of the mirrors.
Montel (nested) Kirkpatrick-Baez mirrors can focus X-ray and neutron beams with larger divergences into small beams
than is possible with standard (sequential) Kirkpatrick-Baez optics. They also provide for a more compact focusing
system and higher fluxes into small beams than with current alternatives. These attributes make Montel optics critically
important for both achromatic neutron and X-ray focusing. Here we describe design rules that optimize mirror
performance under various constraints, including diffraction-limited, and flux-limited focusing. We also describe first
tests of optical designs that employ nesting as a way to improve neutron microfocusing optics and suggest future
directions for X-ray nanofocusing optics.
VESPERS beamline is a hard X-ray microprobe beamline dedicated to micro-diffraction and micro-fluorescence analysis at the Canadian Light Source; it requires multi-bandpass X-ray beams for different types of samples and experiments. A specially designed double crystal/multilayer monochromator was built for this purpose with three
different bandpasses: 0.01%, 1.6% and 10%. The diffraction elements used for the monochromator have a triple-stripe design using Si(111) crystal as a single substrate with two differing stripes of Mo/B4C multilayers deposited thereon. The uncovered Si(111) section provides a 0.01% bandpass, while the periodic and depth-graded Mo/B4C multilayers provide 1.6% and 10% bandpasses, respectively. This paper outlines the requirements and specifications of the diffracting elements as well as the design, deposition and optimization of the multilayers. The performance of the deposited multilayer structures has been tested using Cu-Kα radiation line with a Huber diffractometer.
We describe x-ray Kirkpatrick-Baez mirror designs with the potential to produce hard x-ray beams of 40 nm or smaller. The x-ray quality mirrors required to achieve the desired performance can be fabricated by differential deposition on ultra-smooth surfaces, or by differential polishing. Various mirror systems designed for nanofocusing to ~40 nm and below are compared. The performance limits of total-external-reflection mirrors are compared with the limits of multilayer mirrors that can potentially focus to an even smaller spot size. The advantages of side-by-side Kirkpatrick-Baez mirrors are evaluated and more advanced, four-mirror systems with significantly greater geometrical demagnification are discussed. These systems can potentially reach 5 - 20 nm focal spot sizes for multilayer and total-external-reflection optics respectively.
For microfocusing x-ray mirrors, an ellipse shape is desirable for aberration-free optics. However, it is difficult to polish elliptical mirrors to x-ray quality smoothness. A differential coating method to convert a cylindrical mirror to an elliptical one has been previously reported The differential coating was obtained by varying the sputter source power while the mirror was passed through. Here we report a new method of profile coating to achieve the same goal more effectively. In the profile coating, the sputter source power is kept constant, while the substrate is passed over a contoured mask at a constant speed. The mask is placed very close to the substrate level (within 1.0 mm) on a shield-can over the sputter gun. Four-inch-diameter Si wafers were coated through a 100-mm-long by 152-mm-wide aperture on the top of the shield-can. The thickness distribution was then obtained using a spectroscopic ellipsometer with computer-controlled X-Y translation stages. A model has been developed to fit the measured thickness distribution of stationary growth. The relative thickness weightings are then digitized at every point 1 mm apart for the entire open area of the aperture. When the substrate is moving across the shield-can during a deposition, the film thickness is directly proportional to the length of the opening on the can along the moving direction. By equating the summation of relative weighting to the required relative thickness at the same position, the length of the opening at that position can be determined. By repeating the same process for the whole length of the required profile, a contour can be obtained for a desired thickness profile. The contoured mask is then placed on the opening of the shield-can. The number of passes and the moving speed of the substrate are determined according to the required thickness and the growth-rate calibration. The mirror coating profile is determined from the ideal surface figure of a focus ellipse and that obtained from a long trace profiler on the substrate. Preliminary test results using Au as a coating material are presented.
Nanofocused x-ray beams provide a powerful tool for studying materials at the submicron level. One approach to achieve such a small-sized focused beam is to use a pair of mirrors, in the Kirkpatrick Baez (KB) arrangement. Each mirror focuses the beam in one direction and has an elliptical profile. To focus hard x-rays generated from high-brilliance third-generation synchrotron sources to nanometer spots, it is necessary that the mirror figure errors, defined as the deviation of the surface from the ideal ellipse, be in the submicroradian range, or about an order of magnitude smaller than those presently in use.
In this paper, the advances in deterministic figuring of extreme ultraviolet (EUV) lithography optics is discussed and is proposed as a technique for developing elliptical mirrors. Such elliptical mirrors with slope errors under 0.2 μrad rms are expected to provide nanometer-focused beams at third-generation synchrotron radiation facilities. The minimum focal size will then be governed by diffraction limit rather than optics quality.
An alternative approach to developing an elliptically surface is to use flat or spherical mirrors of the same surface quality, and bend or differentially coat them to attain elliptical profiles. These additional steps would be unnecessary if an elliptical profile is directly polished into the substrate. In any case, the substrate is finally coated with a thin layer (< 400 Å) of a high-atomic-number metal to increase the total external reflection critical angle and thereby increase the aperture.
X-ray mirrors for synchrotron radiation beamlines must have low roughness and small figure errors to preserve source brilliance. Gravitationally-induced slope errors can be particularly detrimental for large vertically-deflecting mirrors on ultra-high brilliance third-generation beamlines. Although mirror support can greatly reduce gravitational distortions, in some cases mirror support can complicate dynamic bending. We discuss techniques for controlling gravitational distortions with particular emphasis on removing gravitational distortions from simple bendable mirrors. We also show that in beamlines with parallel mirrors, gravitation induced slope errors can be cancelled through the mirror pair; gravitation induced slope errors of the first mirror can be cancelled by matching slope errors with opposite signs on the second mirror.
For some x-ray experiments, only a fraction of the intense central cone of x-rays generated by high-power undulator sources can be used: the x-ray source emittance is larger than the useful emittance for the experiment. For example with microfocusing optics, or for coherence experiments, x- ray beams with cross sections less than 0.1 mm2 are desirable. With such small beams, the total thermal load is small even though the heat flux density is high. Analyses indicate that under these conditions, rather simple crystal cooling techniques can be used. We illustrate the advantages of a small beam monochromator, with a simple x-ray monochromator optimized for x-ray microdiffraction. This monochromator is designed to achieve negligible distortion when subjected to a narrow (0.1 mm wide) beam from a APS undulator A operating at 100 mA. It also allows for rapid and repeatable energy scans and rapid cycling between monochromatic and white beam conditions.
For some x-ray experiments, only a fraction of the intense central cone of x-rays generated by high-power undulator sources can be used; the x-ray source emittance is larger than the useful emittance for the experiment. For example with microfocusing optics, or for coherence experiments, x- ray beams with cross sections less than 0.1 mm2 are desirable. With such small beams, the total thermal load is small even though the heat flux density is high. Analyses indicate that under these conditions, rather simple crystal cooling techniques can be used. We illustrate the advantages of a small beam monochromator, with a simple x-ray monochromator optimized for x-ray microdiffraction. This monochromator is designed to achieve negligible distortion when subjected to a narrow beam from an APS undulator A operating at 100 mA. It also allows for rapid and repeatable energy scans and rapid cycling between monochromatic and white beam conditions.
Sagittal focusing of undulator radiation is shown to be compatible with the proposed inclined double-crystal monochromator geometry for heat load reduction. The focusing aberrations are shown to be negligible for typical undulator-beam divergences over a range of magnifications from 1:2 to 6:1 and energies from 3 to 40 keV. The inclined geometry reduces the required sagittal curvature of the focusing crystal compared to focusing with conventional symmetric crystals; hence, focusing is possible at higher X-ray energies and with less anticlastic bending. In addition, anticlastic stiffening ribs project a smaller footprint to the beam so that the achievable focal spot size is potentially better than with conventional symmetrically cut crystals.