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The MRSEC Facilities Network is a nationwide partnership of NSF supported MRSEC centers designed to provide support to researchers in the broad area of Materials Research in academic, government and industrial laboratories around the world.
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Description:
The Panalytical X'Pert Diffractometer is a highly advanced, versatile materials
characterization system. Interchangeable PreFIX incident and diffracted
beam optics can be configured for optimal measurement of high resolution scans,
reflectivity experiments, or for in-plane diffraction.
High Resolution X-ray Diffraction: High resolution x-ray
diffraction is generally applied to highly ordered crystals. It is
useful to examine nearly lattice matched materials or the structural perfection
of materials. The system can be used to accurately measure the width
of Bragg diffraction peaks from nearly perfect single crystals over the range
of a few seconds of arc. In order to obtain the high resolution, the
angular divergence of the incident x-ray beam must be very small with little
or no peak broadening due to spectral dispersion and the goniometer must be
capable of very accurate stepping. Special incident and diffracted beam
conditioning makes this possible. This system can also map regions in
reciprocal space around the Bragg reflections which can be useful to
characterization relaxation of strained epitaxial films.
Reflectometry: Reflectometry is an analytical technique for
investigating thin layers. In reflectivity experiments, the X-ray reflection
of a sample is measured around the critical angle. Below the critical
angle of total external reflection, X-rays penetrate only a few nanometers
into the sample. Above this angle the penetration depth increases
rapidly. At every interface where the electron density changes, a part
of the X-ray beam is reflected. The interference of these partially
reflected X-ray beams creates the oscillation pattern observed in reflectivity
experiments. From these reflectivity curves, layer parameters such as
thickness and density, interface and surface roughness can be determined
through modeling.
In-plane diffraction: In-plane diffraction is a diffraction
technique in which both the incident and diffracted beams are nearly parallel
to the sample surface. Because the beam is incident at a grazing angle,
the penetration depth of the beam is limited to within about 100 nm of the
surface. The in-plane diffraction technique measures diffracted beams
nearly parallel to the sample surface and hence measures lattice planes that
are (nearly) perpendicular to the sample surface. These planes are
inaccessible by other techniques.
Equipment
- Selectable line or point focus 1.8kW sealed ceramic copper x-ray
tube source.
- Choice of PreFIX incident beam optics include a graded parabolic x-ray
mirror with automatic attenuator, four-bounce Ge(220) monochromator, hybrid
four-bounce monochromator with mirror and automatic attenuator, fixed divergence
slits, or x-ray lens.
- High resolution goniometer with optically encoded sample positioning
enables a minimum step size of 0.0001°.
- 1/2 circle Eulerian cradle with motorized sample stage enables
sample tilts of +/- 90°, in-plane rotation of 360°, in-plane X
and Y translations of 100 mm, and vertical Z displacement of 11 mm.
- Sample holder accommodates samples up to 4 inches in diameter.
- Choice of PreFIX diffracted beam optics include triple axis/rocking
curve optics or parallel plate collimator.
- Triple axis setup utilizes a three bounce (022) channel cut Ge crystal
to provide an acceptance angle of 12 arc seconds.
- The rocking curve optics utilize interchangeable slits to control
the background and detector resolution.
- The parallel plate collimator has a 0.27° acceptance angle with an
optional 0.1 mm collimator slit to improve the resolution at 2Θ angles
less than 4°.
- 2 sealed proportional detectors with a large dynamic range.
Accessories:
Applications:
- High Resolution
- Rocking curves.
- Superlattice scans.
- Reciprocal space maps.
- Substrate offcut.
- Epitaxial layer tilt.
- Layer relaxation.
- Epitaxial layer mismatch.
- Reflectometry
- Composition analysis structure of grain boundaries in ceramics.
- Magnetic films on chromium.
- Identification of precipitates in materials.
- Analysis of nanoparticle sizes.
Capabilities:
- Samples up to 4 inches in diameter may be analyzed.
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