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Accueil du site > Divers > equipes de recherche > Cristallographie > Instrumentation > Diffractomètre Nonius Kappa CCD > Nonius Kappa CCD

Nonius Kappa CCD

4-circle monocrystals

3 novembre 2010

The 4-circle Bruker (Nonius) diffractometer is dedicated to the monocrystal studies. However it is also possible to make texture analyses on polycrystalline phases in reflexion and transmission modes, of thin films for example. This instrument is equipped by a kappa goniometer, a traditional source of x-rays (Mo anode) and a two-dimensional CCD detector.

Figure 1 : Kappa CCD diffractometer

The diffractometer is equipped by a low temperature system : a Cryostream Cooler Oxford 600 (100K with 373K) and a high temperature system : a Gas Blower GSB 1300 allowing to work until 1200K.

Goniometer :

The crystal is in the optical center of three rotation axes : φ, ω and κ. Thanks to the rotations combination around these axes, it is possible to give all the possible orientations to the crystal. The respective position of these three axes is indicated on the following figure :

Figure 2 : Kappa CCD goniometer

Goniometer characteristics are presented in the following table :

 

Angles

Scanning

Speed

Résolution

Phi

± 180°  0.0012-3000°/min ± 0.0015°

Kappa

± 175° 0.009-2000°/min ± 0.0010°

Oméga

± 210°  0.009-2000°/min ± 0.0010°

Thêta

-10° à +66°  0.009-2000°/min ± 0.0010°

DX

25 - 170 mm 2000 mm/min ±0.5mm

 

X-rays source :

A x-rays tube equipped by an anticathode of Ag, Mo or Cu generates a monochromatic x-ray beam lie to a graphite blade which then collimated. The section of the beam is in the mm2 order of magnitude. This section is a limiting factor to the sample size because the crystal must be completely insolated by the x-ray beam. 

 

Detector :

The ponctual detectors were replaced into major part by two-dimensional detectors which make it possible to record whole parts of reciprocal space (figure 3) : 

Figure 3 : diffraction pattern obtained with a Kappa CCD diffractometer

This new generation of detector to which belonged CCD instrument (Charges Coupled Device) relegate the photographic chamber instruments, until here essential to the comprehension of complex diffraction patterns (macles, modulations) to the row of museum pieces. Let us note that on Kappa, CCD detector is motorized : it is possible to bring it or to move away it from the crystal in function to the desired resolution (25mm < Dx < 165mm). On figure 4, a schematic section of a CCD camera is presented.

Figure 4 : Schematic section of CCD camera

Detector caracteristics are described in the table below :

Screen 63.5 x 63.5 mm
Pixels 621 x 576
Distorsion < 2%
Phosphore 25mg/m² Gd2O2S, optimisé pour Mo
Detector size
20 x 15 x 15 cm (l x p x h)