Beamline responsible 

Jean Susini, tel. +33 4 76 88 27 85 
Phone on beamline +33 4 76 88 21 59, fax: +33 4 76 88 27 85

Scientific applications

Micro-Fluorescence, Imaging and Diffraction (Micro-FID)

High Beta-section with two undulators: U42 standard, minimal gap 16 mm, and U23 in-vacuum, minimal gap 6 mm (operational 2002)
 

Optics

Flat Si mirror with 2 coatings

Horizontal deflection: 2.6 mrad

Cut-off energies:

Si strip: 12 keV

Pd strip: 24 keV

Pt strip: 32 keV

Vertical double flat crystal monochromator, fixed exit cam system (Kohzu)

Angular range: 3-30 deg.

Energy range:

4-37 keV for Si[111] crystals

7-72 keV for Si[311] crystals

Micro-focusing elements:

Bragg-Fresnel lenses (BFL)

Fresnel zone plates (FZP)

Compound refractive lenses (CRL)

Size of beam at the sample location (V x H): 0.85 mm x 1.5 mm @ 40 m (EH1) and 1.2 x 2.2 @ 60 m (EH2).

Detectors:

Si(Li) detector

Si drift diode detector

PIN diodes, ionization chambers

High resolution CCD cameras

Medium resolution CCD camera

gas filled (position sensitive) detector

Beamline control

SUN (Solaris) Ultra-Sparc 5, SPEC control software for optics and experimental setup with TCP/IP and GPIB network connection in experimental hutches

Introduction

The micro-FID (Fluorescence, Imaging and Diffraction) beamline is dedicated to elemental concentration determination (including trace analysis), absorption spectroscopy, imaging, tomography, holography and diffraction studies of samples with micrometer spatialresolution using hard X-rays.

The beamline uses the synchrotron beam from an undulator located at the insertion device port ID22 (high beta section).

A classical layout has been chosen in order to provide a flexible and easy-to-use device and to keep it open for further evolutions: the beamline can be operated either with the direct beam from the undulator (white) or with a flatmirror (pink) and/or a fixed-exit double crystal monochromator (4-70 keV).

Different X-ray focusing elements are be available for different experimental set-ups: Bragg-Fresnel optics and Fresnel Zone plates areused with high demagnification factors (20 to 100). Compound Refractive lenses (CRL) allow either pre-focusing of the beam - frontend location - or focusing - experimental hutch location. The machine provides a low emittance beam (0.04 nm.rad vertically) and the particularly low divergence of the beam in the high-beta section is an advantage considering the small acceptance of the focusing elements.

Micro-analysis

The beamline provides a microprobe facility for micro-fluorescence, micro-XAS and micro-diffraction. At the sample location, the beam can be focused on a spot of few microns size with 10⁹ -10¹² phot/sec. Using the monochromator in the range 4-35 keV, measurement of all elements can be carried out with very high sensitivity(> ppb or 10^-15 g): K edges up to xenon (Z = 54, B_K = 34.6 keV),L and M edges and lines up to uranium (Z = 92, B_L1 = 21.8 keV, B_M1 =5.5 keV).

The recently commissioned PINK beam mode uses high intensity, high energy bandwidth beams obtained directly from the undulator and mirror. These beams span several full undulator harmonics and can be focused with high efficiency by CRL lenses located in the experimental hutches. The flux thus obtained is one to two orders of magnitude higher than the monochromatic one.

At high energy, the undulator flux is still strong ; for example, it is possible to use 90 keV radiation to analyze Pt, Au, Hg or Pb at the K edges.

Recently, a novel type of elemental mapping has been commissioned: fluorescence tomography. This allows the 2D reconstruction (vertical/horizontal slice) of internal elemental concentrations of volumes. So far, homogenous samples have been analyzed successfully - the method will be extended to non-homogenous samples.

X-ray fluorescence detection can be coupled with either XAS measurements, topography, diffraction or small angle scattering.

Imaging and tomography

The coherent properties of the X-ray beam delivered by the ESRF allow the observation of very weak perturbations of the wave front passing through a non-absorbing sample. Therefore, it is possible to get phase contrast projections of the 3D topology of a sample almost transparent to hard X-raysin order to perform the reconstruction of the shape of sample with high resolution.Using high energy X-rays presents many advantages like the possibility to investigate thick samples, the reduction of the absorbed dose and large objet-to-detector distance that gives the possibility to install special sample environments (high pressure cells, furnaces or cryostats for example).

In this framework, the micro-FID beamline is design to perform coherence measurements for different applications:

Phase-contrast imaging:

Phase-contrast images of dry and wet samples can be taken on high-resolution film or by means of a high-resolution CCD camera. Typical exposure times are 10 ms to 5 s.

Phase-contrast microtomography:

Collecting a set of phase contrast images from different orientations of a sample in a parallel beam, it is already possible to perform 3D reconstruction (back-projection algorithm) by tomography at the micrometer scale.

Micro-topography:

The high contrast and high resolution achievable is used on the micro-FID beamline to observe details of the very fine topography of exotic or modified crystals used in microelectronics or laser technology.

Holography and interferometry:

Gabor in-line holography (planar reference wave) or Fourier holography (spherical reference wave) are feasible. The fine interference pattern obtained can be used for the high accuracy determination of optical density and refraction index.

To preserve the beam coherence, all the optical components of the beamline have been carefully optimized (e.g. polished Be windows and non-polycrystalline filters, mirror with low micro-roughness). The experiments can be performed in a straightforward setup: the sample stands directly in a parallel monochromatic beam and images are recorded by a CCD camera within a field of a few millimeter squared.

Optics

The spectrum available at the micro-FID beamline is limited down to ~5 keV due to the beryllium windows between the storage ring and the experimental hutches. Direct beam can be provided at the experiment location but the beam can be filtered by using the flat mirror, the double-crystal monochromator, absorption filters or any combination thereof.

The mirror produces a reduction of intensity of the high energy harmonics from the undulator. It gives a horizontal deflection (at a fixed angle of 0.15 degrees) in order to preserve the vertical coherence of the beam. Two different coated strips Pt, Pd and the Si substrate provide an energy cut-off respectively at 32, 24 and 12 keV.

The monochromator is based on a so-called CAM system wich provides avery high stablity of the beam along all the spectral range. The parallelism between the two crystals is better than few microradians and the exit beam is maintained in less than 15 mrad over the full angular range (3-30 deg.). Recent measurements over a range of 200 eV at 6.5 keV achieved a fixed exit of better than 2 ?m on the sample. Further corrections using piezo actuators of the crystals angle can improve the fixed-exit capabilities to sub-micron range for Xanes measurements.

Using Si[111] and Si[113] at first order of diffraction, the monochromator will cover the energy range 4-70 keV but it is also possible to reach up to 100 keV with higher orders of diffraction.

The direct beam is at a height of 1400 mm from the floor and the monochromatic beam is delivered 12.5 mm lower than the direct beam.

End Station

Two large experimental hutches (~30m² each) accept different set-ups:

• The microprobe facility is located in the first experimental hutch on a 2.5 x 1.2 m² granite optical table. The set-up includes a focusing stage, a pinhole stage, a sample scanning stage with 2 sample holders (goniohead or slide holder), a video microscope, fluorescence, diffraction and normalization detectors as well as a high/medium resolution CCD camera stage. The optical table can be remotely moved in the vertical plane.
• A 6 circle diffractometer, featuring a 3 ?m sphere of confusion is installed in the first experimental hutch and is operated jointly with the Univ. of Karlsruhe.
• The imaging and tomography set-up located in the second hutch includes a high resolution rotation sample stage, a CCD X-ray camera standing on an optical bench and an optical microscope for alignment.

Typical distance between the beam path and the surface of the table is 38 cm. The experiment is currently operated in air but special sample chambers can be mounted for in vacuum measurements.

Detectors

The micro-FID beamline is provided with different detectors for X-rays:

• The beam is monitored by current integration detectors (silicon PIN diodes), a scintillator counter or proportional counters (ionization chambers).
• Spatial sensitive detectors are used for microdiffraction and X-ray imaging by absorption or phase contrast: two dynamic (16 bits) CCD cameras for X-rays with less than 1 micron resolution will be commissioned before the end of 1998.
• A multiple wire gas filled detector is available for time resolved small-angle scattering experiments.
• X-ray fluorescence measurements are carried out with either a Si(Li) solid state detector or a Si drift detector.
• Further developments of the micro-spectroscopy setup will provide a wavelength dispersive system for high spectral resolution (WD-XRF) and high counting rate and a high resolution scanning sample stage using piezo motors.

Current Status

The Micro-FID beamline is operational.

Further Information...

can be found at the

micro-FID₂₂ homepage and beamline manual

General view of the beam layout with relevant dimensions