The main objective of this set-up is to provide a large variety of X-ray diffraction experiments for the Spanish scientific community, as well as for foreign scientists around the world. An important aspect, which has been one of the major goals of the end-station during the design, start-up and upgrade periods, is the adaptability and flexibility for different sample environment set-ups that must be easily installed to allow for a high throughput of users. It is conceived to carry out X-Ray Reflectivity (XRR), Surface X-Ray Diffraction (SXRD), Single Crystal Diffraction (SCD), Reciprocal Space Maps (RSM), Grazing Incidence X-Ray Diffraction (GI-XRD) and Grazing Incidence High Resolution Powder Diffraction (GI-HRPD) experiments. Thus, the multipurpose character of the end-station is reflected on the huge variety of experiments carried out in the last years, showing multidisciplinary work areas, from surfaces and thin films to liquid crystal materials.

Figure below shows a scheme and a picture of the multipurpose X-ray diffraction set-up. It is mainly composed of a six-circle diffractometer in vertical geometry equipped with a 2x2 Maxipix detector on the diffractometer arm and a large area CCD detector mounted on an independently motorized stage. The six-circle instrument is a very flexible diffractometer due to its six (or seven in the case of single crystal configuration) degrees of freedom. Three circles are dedicated to the sample motion (χ, φ and θ), two circles are dedicated to the detector motion (Γ, δ) and finally a rotation (μ) coupled to the sample and detector motion is present. The θ-circle rotates the sample around the direction normal to the sample surface and the (χ, φ)-circles are used only for the sample alignment. The μ-circle sets the beam incident angle, which can be varied between 0.0o and 5.0o. The Γ-detector circle performs out-of-plane measurements while the δ-circle, when Γ=0, performs in-plane measurements. The diffractometer sphere of confusion for all axis  circles is 50 μm.

The diffractometer has its main axis in the vertical and is able to house loads up to 50 kg. In this way UHV baby chambers, magnets, cryostats and reactor cells are easily accommodated. In addition to the standard circles for orienting the sample and the detector, additional motions to align the surface normal along predefined directions (vertical or horizontal) are required for interface scattering experiments, as it is customary in surface diffraction.

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For high-resolution experiments, a θ−2θ set-up together with a goniometer head is installed on the detector arm in order to use a crystal analyser. An angular resolution of 0.002o has been obtained in a θ−2θ scan for the Si (400) reflection by using Si(111) as a crystal analyser. Two pairs of slits are located on the detector arm. A pair of slits is placed near the detector (750 mm from the sample) defining the angular acceptance while a pair of slits is placed near the sample (200 mm from the sample) defining the area seen by the detector.

The detector arm incorporates an additional rotation (ν) around its axis for polarization analysis. Three translations movements (x, y, and z) are used for the sample positioning and two translations movements (x, z) perpendicular to the beam direction are used for the diffractometer alignment. An extra ω circle (spindle), which is mounted in a removable pseudo-kappa stage, is used for the single crystal measurements. The sphere of confusion of the ω circle is smaller than 10 µm (Wobble). The diffractometer is controlled using the SPEC software, which includes all the equations for the angular motions for the six-circle geometry. The SPEC software imposes the names of the angles.

The experimental station incorporates, also,  a large 2D detector (CCD type) that can be used simultaneously to pixel detector located at the detector arm. The CCD detector is a high-resolution large area X-ray camera (Photonic Science VHR 3x1 X-ray camera). It is composed of three independent 11 Mega-pixel sensors, consecutively placed, forming a full 33 Mega-pixel array with a final active area of 250x125 mm2. The final image resolution is 7651x3825 pixels with a pixel size of 32.8 microns square. The scintillator is made of Gadolinium oxysulphide, which is optimized for the acquisition of high-resolution images in the energy range between 5 and 35 keV. Flat field, dark field and offset subtraction corrections are available for the users for photon energies between 5 and 35 keV (with 1 keV of energy step). The 2D detector is mounted on a motorized stage with 4 degrees of freedom (three translations x, y, z and a tilt Θccd). The y translation, which is along the beam direction, is used to change the detector-sample distance and hence the angular resolution of each pixel. It can be varied between 1.5 m and 0.25 m. The maximum angular range is varied with the x translation, which is perpendicular to the X-ray beam. The detector can be rotated in a circle around the sample with the simultaneous combination of the z translation (height), y translation (beam direction) and the Θccd tilt. The 2D detector can be also manually rotated around its axis (beam direction axis) in order to improve/adapt the angular acceptance either vertically or horizontally to the experiment requirements. Two configuration are possible either large side along the vertical scattering geometry or along the horizontal scattering geometry.

Photonic Science CCD:

  • 3 x 11 MegaPixel CCD's
  • Final image resolution: 7651 x 3825 pixels
  • Pixel size: 32.8 microns square
  • Input active area: 250 x 125 mm.

 

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