Bent Si Research Articles

Optimization of the bent perfect Si(3 1 1)-crystal monochromator for a residual strain/stress instrument at the HANARO reactor—Part I

Reflectivity and resolution properties of a variety of optimized focusing monochromator performances based on cylindrically bent perfect Si-crystals were tested with the aim of evaluating their possible use in a strain/stress diffractometer. It has been found that the optimized monochromator performances of the curved Si(3 1 1) crystals (for the take-off angle 2 θ M=60°) provide a good luminosity and a sufficiently high resolution (full width at half maximum (FWHM) of the instrumental Δ d/d—profile can be about 2×10 −3 in the vicinity of the lattice spacing d = 0.117 nm for 2 θ S≈90°) of the strain/stress diffractometer with the figure of merit more than one order of magnitude larger than that related to the conventional flat mosaic Ge(2 2 0) monochromator of η = 1 5 ′ .

Optimization of bent perfect Si(2 2 0)-crystal monochromator for residual strain/stress instrument—Part II

Optimized diffractometer arrangements for residual strain measurements employing curved crystal monochromators provide good luminosity and a high Δd/d resolution in the vicinity of usually used scattering angle 2θS≈±90°. Due to a variety of designs of the diffractometers which could be installed at a constant or different take-off angles, except a few attempts, there is a lack of experimental evidence providing a help in a choice of parameters for an optimum performance. In addition to our earlier investigations with curved Si(311) monochromator employed in different diffraction geometries (see paper I [M.K. Moon et al., Physica B, submitted [1]]), the present paper presents the monochromator properties of cylindrically bent perfect Si(220) crystals as another candidate to be used as monochromator in residual strain diffractometers.

Low-energy-channeling surface analysis on silicon crystals designed for high-energy-channeling in accelerators

Channeling of relativistic particles in bent Si crystals is a powerful technique for use with accelerators. Its efficiency can be found to be highly dependent on the state of the surface of the crystal steering the particles. We investigated the morphology and structure of the surface of the samples that have been used with high efficiency for channeling in accelerators. Low-energy channeling of 2MeVα particles or protons was used as a probe. We found that mechanical treatment of the samples leads to a superficial damaged layer, which is correlated to efficiency limitations of the crystal in accelerators. In contrast, chemical etching, which was used to treat the surface of the most efficient crystals, leaves a surface with superior perfection.

Spherically bent analyzers for resonant inelastic X-ray scattering with intrinsic resolution below 200 meV

Resonant inelastic X-ray scattering with very high energy resolution is a promising technique for investigating the electronic structure of strongly correlated materials. The demands for this technique are analyzers which deliver an energy resolution of the order of 200 meV full width at half-maximum or below, at energies corresponding to the K-edges of transition metals (Cu, Ni, Co etc.). To date, high resolution under these conditions has been achieved only with diced Ge analyzers working at the Cu K-edge. Here, by perfecting each aspect of the fabrication, it is shown that spherically bent Si analyzers can provide the required energy resolution. Such analyzers have been successfully produced and have greatly improved the energy resolution in standard spherically bent analyzers.

Strong suppression of nuclear-charge changing interactions for 18 TeV/c In ions channeled through a bent Si crystal

We present experimental results giving evidence for the strong reduction—a factor of more than 20—of nuclear-charge changing interactions for 18 TeV In49+ ions channeled through a silicon crystal bent to 7.5, 11.9 and 19.8 mrad. A very small fraction of the deflected ions suffer electromagnetic or nuclear interactions leading to proton loss while traversing the 60 mm long crystal, even though its thickness corresponds to about 0.13 nuclear interaction lengths for an amorphous material. By considering the deflected ions only, we show experimentally that the nuclear-charge pickup reaction believed to be induced by virtual photons is a short-range phenomenon.

The residual stress instrument with optimized Si(2 2 0) monochromator and position-sensitive detector at HANARO

An upgraded residual stress instrument at the HANARO reactor of the KAERI is described. A horizontally focusing bent perfect crystal Si(2 2 0) monochromator (instead of a mosaic vertical focusing Ge monochromator) is installed in a drum with a tunable (2 θ M=0–60°) take-off angle/wavelength. A specially designed position-sensitive detector (60% efficiency for λ = 1.8 A ) with 200 mm (instead of 100 mm) high-active area is used. There are no Soller type collimators in the instrument. The minimum possible monochromator to sample distance, L MS = 2 m , and sample to detector distance, L SD = 1.2 m , were found to be optimal. The new PSD and bent Si(2 2 0) monochromator combined with the possibility of selecting an appropriate wavelength resulted in about a ten-fold gain in data collection rate. The optimal reflections of austenitic and ferritic steels, aluminum and nickel for stress measurements with a Si(2 2 0) monochromator were chosen experimentally. The ability of the instrument to make strain measurements deep inside the austenitic and ferritic steels has been tested. For the chosen reflections and wavelengths, no shift of peak position (apparent strain) was observed up to 56 mm length of path.

Neutron protein crystallography in JAERI

Neutron diffraction provides an experimental method of directly locating hydrogen atoms in proteins. After developing an original neutron detector (neutron imaging plate) and a novel practical neutron monochromator (elastically bent perfect Si monochromator), BIX-type diffractometers which were equipped with these tools were efficiently constructed at JRR-3 in Japan Atomic Energy Research Institute (JAERI), Japan and they have finished many protein crystallographic measurements and interesting results have come one after another. At the same time a method of growing large protein single crystals and a database of hydrogen and hydration have also been developed. In the near future, a pulsed neutron diffractometer for biological macromolecules has been proposed at J-PARC in JAERI.

Bent Si monochromator—multi-detector neutron diffractometer installed at B4 super-mirror thermal guide tube in KUR

A new multi-detector neutron diffractometer has been installed at B4 thermal supermirror neutron guide in KUR, using a new bent Si monochromator developed by Mikula et al. and Ono et al.. Here we report resolutions of powder diffraction patterns by the multi-detector neutron diffractometer, which mainly depend on a radius of sample. Bragg diffraction optics by bent perfect crystal shows improvement of resolution without loss of luminosity and the multi- detector on the same 2 θ arm can gain the intensity without loosing resolution.

Bragg diffraction optics in neutron diffractometry

A review of recent practical applications of Bragg diffraction optics in neutron diffractometry is presented. Besides examples of a direct comparison of the flat Ge-mosaic and a bent perfect Si crystals for neutron monochromatization, the results of new tests of dispersive monochromator, multiple reflection monochromator and curved TOF analyzer for high- and ultra-high resolution studies as received within a wide collaboration are introduced.

Bragg diffraction optics in neutron diffractometry

A review of recent practical applications of Bragg diffraction optics in neutron diffractometry is presented. Besides examples of a direct comparison of the flat Ge-mosaic and a bent perfect Si crystals for neutron monochromatization, the results of new tests of dispersive monochromator, multiple reflection monochromator and curved TOF analyzer for high- and ultra-high resolution studies as received within a wide collaboration are introduced.

Direct comparison of plastically deformed Ge mosaic crystal and bent perfect Si crystal for neutron monochromatization

The results of direct comparison of some monochromator properties of plastically deformed (mosaic) Ge single crystal with cylindrically bent perfect crystal (BPC) of Si are presented. Using a double-crystal diffractometer and α o=20′ collimation of the incident polychromatic beam we compared monochromatic beam current at the sample position for the take off angles of 40°, 50° and 60°. The comparison was carried out on the diffraction planes (3 1 1) M when the monochromators operated at nearly the same asymmetric diffraction geometry. For the sake of comparison of their resolution properties, Fe(1 1 0) and Fe(2 1 1) diffraction profiles of the beam scattered by a solid and well annealed α-Fe polycrystalline sample are also presented. It has been found that under these specific experimental conditions often used for residual strain scanning, the focusing bent Si crystal is a good cheap alternative to the flat mosaic Ge monochromator.

Combining flat crystals, bent crystals and compound refractive lenses for high-energy X-ray optics.

Compound refractive lenses (CRLs) are effective for collimating or focusing high-energy X-ray beams (50-100 keV) and can be used in conjunction with crystal optics in a variety of configurations, as demonstrated at the 1-ID undulator beamline of the Advanced Photon Source. As a primary example, this article describes the quadrupling of the output flux when a collimating CRL, composed of cylindrical holes in aluminium, is inserted between two successive monochromators, i.e. a modest-energy-resolution premonochromator followed by a high-resolution monochromator. The premonochromator is a cryogenically cooled divergence-preserving bent double-Laue Si(111) crystal device delivering an energy width DeltaE/E approximately 10(-3), which is sufficient for most experiments. The high-resolution monochromator is a four-reflection flat Si(111) crystal system resembling two channel-cuts in a dispersive arrangement, reducing the bandwidth to less than 10(-4), as required for some applications. Tests with 67 and 81 keV photon energies show that the high-resolution monochromator, having a narrow angular acceptance of a few microradians, exhibits a fourfold throughput enhancement due to the insertion of a CRL that reduces the premonochromatized beam's vertical divergence from 29 micro rad to a few microradians. The ability to focus high-energy X-rays with CRLs having long focal lengths (tens of meters) is also shown by creating a line focus of 70-90 micro m beam height in the beamline end-station with both the modest-energy-resolution and the high-energy-resolution monochromatic X-rays.

Hard x-ray imaging using free-standing spherically bent crystals

We report the attempt to prepare free-standing spherically bent Si crystals with radii of curvature as small as 30 cm and large uniform working areas up to several cm2. We also report on the use of these crystals in the Laue geometry to record two-dimensional high spatial resolution x-ray images in the hard x-ray region (λ∼0.5 Å). We discuss how these bent crystals were made, and show how these spherically bent crystals were used in the Laue geometry to obtain hard x-ray images of test objects at the silver K-alpha wavelength at two different magnifications. The mean spatial resolution of this x-ray imaging scheme, determined from the recorded image traces, was found to be better than 10 μm over a field of view of 1.5×1.5 mm. Contributions of possible focusing mechanisms (dynamical and polychromatic) are discussed. Additional theoretical understanding of how such a scheme is working is needed.

On the possibility of using bent perfect crystals in TOF neutron scattering devices

A silicon bent perfect crystal in fully asymmetric diffraction (FAD) geometry in combination with a linear position-sensitive detector can be effectively used for high-resolution analysis of a beam scattered by a sample. The results of the first promising time of flight (TOF) experimental tests of λ scanning carried out with the FAD of cylindrically bent Si slabs of different cuts are presented. The length and the homogeneous curvature of the crystal determine the range of Δλ/λ of about 10-2 that could be investigated with the accuracy of δk/k≈10-4. The obtained experimental results indicate that the FAD geometry of the bent Si slab in combination with a one-dimensional position-sensitive detector could be a good candidate for a high-resolution analyzer at some of the TOF instruments.

Optimization of a focusing monochromator for neutron strain-scanning diffractometer

Comparison of mosaic and elastically deformed crystals as possible candidates for horizontally focusing monochromators at a high-resolution powder diffractometer is presented. The comparison is based on Monte Carlo simulations used to optimize instrument performance for several variants of configuration. The results show that elastically deformed crystals can be optimized better than the mosaic ones in a wide range of wavelengths, except for the case when focusing in momentum space requires a nearly flat monochromator. A set of diffraction profiles measured at a strain-scanning diffractometer configured with an elastically bent Si monochromator is compared with simulations in order to validate the simulations.

Water-Induced Diastereomeric Isomerization of Novel Disiloxane-1,3-diols Separated Manually

Diastereomeric disiloxane-1,3-diols, 1, with two asymmetric silicon centers and intramolecular coordination arms were synthesized and separated manually. They show distinguishing structural features such as a linear or bent Si−O−Si skeleton, a short Si−O bond length, and strong intramolecular hydrogen bonding. A trace of water induced the diastreomeric isomerization of 1 under noncatalytic conditions, while the anhydrous disiloxane-1,3-diols were stereochemically stable.

Cryogenically cooled bent double-Laue monochromator for high-energy undulator X-rays (50-200 keV).

A liquid-nitrogen-cooled monochromator for high-energy X-rays consisting of two bent Si(111) Laue crystals adjusted to sequential Rowland conditions has been in operation for over two years at the SRI-CAT sector 1 undulator beamline of the Advanced Photon Source (APS). It delivers over ten times more flux than a flat-crystal monochromator does at high energies, without any increase in energy width (DeltaE/E approximately 10(-3)). Cryogenic cooling permits optimal flux, avoiding a sacrifice from the often employed alternative technique of filtration - a technique less effective at sources like the 7 GeV APS, where considerable heat loads can be deposited by high-energy photons, especially at closed undulator gaps. The fixed-offset geometry provides a fully tunable in-line monochromatic beam. In addition to presenting the optics performance, unique crystal design and stable bending mechanism for a cryogenically cooled crystal under high heat load, the bending radii adjustment procedures are described.

The Use of Dispersive Double Crystal Monochromator – A Way for High-Resolution Powder Diffractometry

Excellent properties of a dispersive double-crystal monochromator for the use in powder diffractometry, namely for strain/stress measurements are presented. For this purpose a strongly dispersive double crystal setting consisting of a mosaic Ge(331) (mosaicity η of about 16') and bent perfect Si(111) crystal set for diffraction at the neutron wavelength of λ=0.1835 nm, was used. The optimized arrangement provides good luminosity and a sufficiently high resolution (FWHM of the instrumental Δd/d - profile can be about 3x10 -3 in the vicinity of the lattice spacing d =0.13 nm (2θ s ≃ ±90°) for both parallel and antiparallel scattering geometry, simultaneously.

Crystal-assisted extraction of Au ions from RHIC and application of the Au beam for the search of anomalous Cherenkov radiation

It is proposed to perform an extraction of the gold ion beam from Relativistic Heavy Ion Collider at BNL (USA) with the highest energy of 100 A GeV. The beam extraction is to be done by a bent Si crystal. The following scientific program could be performed on the extracted gold ion beam: a search for superluminal particles – tachyons; a study of the Cherenkov double photon radiation; a measurement of the absolute intensity of heavy ion Cherenkov radiation; a study of the ionization loss of the heavy ions; a study of the Cherenkov radiation in anisotropy media.

Highly stressed carbon film coatings on silicon: Potential applications

Highly stressed and strongly adhered nanocrystalline diamond films are grown on Si substrates by providing controlled and continuous bias current density (BCD) in microwave plasma chemical vapor deposition system. The stress and hence the curvature of the films on Si substrates can be varied and controlled by changing the BCD. We propose applications for such stressed films in the areas in which bent crystals are being used for various purposes, i.e., particle physics, x-ray optics, etc. These bent Si substrates can replace crystal benders, a cumbersome mechanical arrangement, used for bending Si in those areas.