Diffuse X-ray scattering from polished silicon: application of the distorted wave Born approximation.

Measured diffuse X-ray scattering data for a `smooth' as well as for a `rough' silicon sample were fit to theoretical expressions within the distorted wave Born approximation (DWBA). Data for the power spectral density (PSD) for both samples were also obtained by means of atomic force microscopy and optical interferometry. The Fourier transforms of trial correlation functions were fit to the PSD data and then applied to the DWBA formalism. The net correlation functions needed to fit the PSD data for each sample comprised the sum of two terms with different cutoff lengths and different self-affine fractal exponents. At zero distance these correlation functions added up to yield net values of σ2 = (2)2 and (71)2 Å2 for the smooth and rough samples, respectively. X-ray scattering data were obtained at beamline 1-BM of the Advanced Photon Source. Data and fits at values of qz = 0.05 and 0.10 Å-1 for the smooth sample are reported. Good fits for the smooth sample were obtained at both qz values simultaneously, that is, identical fitting parameters were applied at both values of qz. The smooth sample also exhibited weak Yoneda wings and a clear distinction between the strong specular scattering and the weak diffuse scattering. Data for the rough sample were qualitatively different and exhibited very weak scattering at the specular condition in contrast to extremely large Yoneda wings. Fits for the rough sample are reported for qz = 0.04, 0.05, and 0.06 Å-1. Although the large Yoneda wings could be fit quite well in both position and amplitude, scattering near the specular condition could not be equally well fit by applying the same fitting parameters at all values of qz. Albeit imperfect, best-fitting results at the specular condition were obtained by invoking only diffuse scattering, that is, without including a separate theoretical expression for specular scattering.

Spherical analyzers and monochromators for resonant inelastic hard X-ray scattering: a compilation of crystals and reflections.

Resonant inelastic X-ray scattering (RIXS) experiments require special sets of near-backscattering spherical diced analyzers and high-resolution monochromators for every distinct absorption-edge energy and emission line. For the purpose of aiding the design and planning of efficient RIXS experiments, comprehensive lists of suitable analyzer reflections for silicon, germanium, α-quartz, sapphire and lithium niobate crystals were compiled for a multitude of absorption edges and emission lines. Analyzers made from lithium niobate, sapphire or α-quartz offer many choices of reflections with intrinsic resolutions currently unattainable from silicon or germanium. In some cases these materials offer higher intensities at comparable resolutions. While lithium niobate, sapphire or α-quartz analyzers are still in an early stage of development, the present compilation can serve as a computational basis for assessing expected and actual performance. With regard to high-resolution monochromators, bandpass and throughput calculations for combinations of double-crystal, high-heat-load and near-backscattering high-resolution channel-cuts were assembled. The compilation of these analyzer and monochromator data is publicly available on a website.

Hard x-ray monochromator with milli-electron volt bandwidth for high-resolution diffraction studies of diamond crystals.

We report on design and performance of a high-resolution x-ray monochromator with a spectral bandwidth of ΔE(X) ≃ 1.5 meV, which operates at x-ray energies in the vicinity of the backscattering (Bragg) energy E(H) = 13.903 keV of the (008) reflection in diamond. The monochromator is utilized for high-energy-resolution diffraction characterization of diamond crystals as elements of advanced x-ray crystal optics for synchrotrons and x-ray free-electron lasers. The monochromator and the related controls are made portable such that they can be installed and operated at any appropriate synchrotron beamline equipped with a pre-monochromator.

Achromatic nested Kirkpatrick-Baez mirror optics for hard X-ray nanofocusing.

The first test of nanoscale-focusing Kirkpatrick-Baez (KB) mirrors in the nested (or Montel) configuration used at a hard X-ray synchrotron beamline is reported. The two mirrors are both 40 mm long and coated with Pt to produce a focal length of 60 mm at 3 mrad incident angle, and collect up to a 120 µm by 120 µm incident X-ray beam with maximum angular acceptance of 2 mrad and a broad bandwidth of energies up to 30 keV. In an initial test a focal spot of about 150 nm in both horizontal and vertical directions was achieved with either polychromatic or monochromatic beam. The nested mirror geometry, with two mirrors mounted side-by-side and perpendicular to each other, is significantly more compact and provides higher demagnification than the traditional sequential KB mirror arrangement. Ultimately, nested mirrors can focus larger divergence to improve the diffraction limit of achromatic optics. A major challenge with the fabrication of the required mirrors is the need for near-perfect mirror surfaces near the edge of at least one of the mirrors. Special polishing procedures and surface profile coating were used to preserve the mirror surface quality at the reflecting edge. Further developments aimed at achieving diffraction-limited focusing below 50 nm are underway.

Sectioning of multilayers to make a multilayer Laue lens.

We report a process to fabricate multilayer Laue lenses (MLL's) by sectioning and thinning multilayer films. This method can produce a linear zone plate structure with a very large ratio of zone depth to width (e.g., >1000), orders of magnitude larger than can be attained with photolithography. Consequently, MLL's are advantageous for efficient nanofocusing of hard x rays. MLL structures prepared by the technique reported here have been tested at an x-ray energy of 19.5 keV, and a diffraction-limited performance was observed. The present article reports the fabrication techniques that were used to make the MLL's.