GALAXI : Gallium anode low-angle x-ray instrument Forschungszentrum Jülich

The high brilliance laboratory small angle X-ray scattering instrument GALAXI, which is operated by JCNS, Forschungszentrum Jülich, permits the investigation of chemical correlations in bulk materials or of structures deposited on a surface at nanometre and mesoscopic length scales. The instrument is capable to performGISAXS experiments in re ection at grazing incidence as well as SAXS experiments in transmission geometry. The X-ray ux on sample is comparable or higher than the one obtained at a comparable beamline at a second generation synchrotron radiation source.


Introduction
Small Angle X-ray Scattering (SAXS) permits the investigation of chemical correlations in bulk materials at nanometre and mesoscopic length scales.When the X-ray beam is sent under grazing incidence on a at surface, re ectometry and Grazing Incidence Small Angle X-ray Scattering (GISAXS) can be performed, allowing the determination of the chemical depth-pro le of multilayer thin lms and the in-plane correlations at nanometre and mesoscopic length scales.The di ractometer of GALAXI is based on the JUSIFA anomalous SAXS instrument formerly installed at the beamline B1 of the DORIS storage ring at HASYLAB, DESY Hamburg, Germany.After the shutdown of DORIS, the instrument has been moved to the Research Centre of Jülich and has been reinstalled with a new X-ray source and a new position sensitive detector.
Figure 1: Schematic drawing of GALAXI with its main components.The beam direction is from right to left.
As X-ray source we use the METALJET source built by Bruker AXS.This source utilizes a liquid metal jet of a GaInSn alloy as anode.An electron beam of 20 µm height x 80 µm width at 70 keV energy and 200 W power hits the liquid metal jet and X-rays are produced.Parabolic Montel-type optics are used to parallelize the beam and monochromatize it by allowing only the Ga K α radiation (E = 9243 eV photon energy) to pass.Due to the small source size, the intrinsic divergence of the X-ray beam is only 0.3 mrad at a maximum size of 2.4 x 2.4 mm 2 .After the optics, a collimation with two 4-segment slits separated by 4.0 m distance can be used to de ne the size and the collimation of the beam at the sample position.A third slit is used to reduce the background.At the sample position we receive a ux of 1•10 9 photons/mm 2 •s at 0.3 mrad divergence.At the sample position, the sample can be adjusted by two rotational and two translational degrees of freedom.A second sample holder contains several reference samples for calibration purposes.The detector distance can be adjusted between 835 mm and 3535 mm in 5 steps.The X-ray ight path is fully evacuated between the X-ray source and the detector.As detector, we use a Pilatus 1M 2D position sensitive detector with 169 x 179 mm 2 active area.The X-ray source is isolated from the di ractometer area in a separate room for radiation protection.The di ractometer room is freely accessible in all operation states.All parts of GALAXI are controlled by a computer system according to the "Jülich-Munich" standard based on a Linux workstation.The computer system as well as the software are identical with the ones used at the JCNS outstation at MLZ Garching.This allows a exible and e cient remote control with automatic scan programs.

Typical applications 2.1 Hard matter applications
A typical application of GALAXI is the determination of the size and size distribution of nanoparticles in solutions or deposited on surfaces as well as the ordering between those nanoparticles.Those nanoparticles are often magnetic for applications in information technology or spintronics (see Fig. 3).The di ractometer can also be used to measure re ectivity from layered thin lms, in order to determine the thickness of the layers and the interfacial pro les.

Soft matter applications
The application range of GALAXI includes di erent kinds of polymer-based systems, in particular nanocomposite materials, polymers with di erent topology (ring, comb, branched polymers).Due to medium ux density, undesired radiation damage of biological substances is prevented.At the same time, high beam stability allows one to obtain reasonable quality data also for lower concentrations.
The instrument was successfully used for structural studies of proteins in crowded environment and also fragments of DNA.
Figure 2: GALAXI di ractometer with the longest detector distance available.The X-ray source is located behind the wall, the detector is at the left hand side.

Sample environment
The samples are located in the main vacuum system of the x-ray ight path.Standard sample holders are available for sealed capillaries (for liquids and paste-like samples) with outer diameter from 1.5 to 2.1 mm, powders and thin lm samples on substrates.In the case of transmission geometry, up to 11 samples can be mounted at the same time.For capillaries, we o er a heater / cooler setup that can be operated in the temperature range from 4 -70°C.

Figure 3 :
Figure 3: GISAXS measurement from an assembly of magnetic nanoparticles of cubic shape deposited on a substrate.From the positions of the peaks, one can deduce a body centred tetragonal ordering between nanoparticles.(Courtesy of E. Josten, Helmholtz-Zentrum Dresden-Rossendorf)