Larger and heavier instruments for dedicated use in a laboratory.
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A powder or polycrystalline sample is irradiated with a beam of x-rays and the resulting powder diffraction pattern is recorded with a detector - photographic film, CCD, image plate, PSD, etc. The powder method is the most widely applied technique in the field of x-ray diffraction analysis for the identification of phases or compounds and the measurement of lattice spacings. A Powder Diffraction FileTM exists with over a hundred thousand characteristic diffraction patterns ("fingerprints") for elements, alloys, minerals and organic compounds ( http://www.icdd.com/ ).
Diffraction patterns from a single crystal are produced using a beam of white, x-ray radiation. The range of wavelengths in the white x-ray radiation assures that diffracting conditions will be met.
In the rotating crystal method, a single crystal is rotated and irradiated with monochromatic x-ray beam. As the crystal rotates a series of lattice planes are brought into diffracting conditions and the diffraction pattern is collected with film or detectors. The method is utilized in determining the structure of unknown materials (no matching fingerprints) and to provide an unequivocal determination of unit cell dimensions.
Variations or the basic methods (Lang, Borrman, rocking curves, diffractometer, etc.) can be applied for crystal quality/perfection, topographic, texture or residual stress studies.
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Rotary positioning tables and sample holders utilized to orient a sample to specific angles to produce a diffraction pattern and to reposition the sample to the desired crystallographic orientation.
Rotary positioning units where the axis of rotation is located outside the body of unit. The cradles consist of an open cylindrical design where the sample or a goniometer is mounted to the inner surface of the cradle. A combination of a cradle and goniometer can produce a 4-circle diffractometer.
Simple stages or sample holders for powder method or robotic positioners.
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Laue, Debeye-Scherrer, Buerger Precession, Gunier and Weisenberg cameras using photographic film for the collection of x-ray diffraction patterns. Cameras represent the oldest type of diffraction instrument and their use has been largely supplanted by diffractometers.
Imaging Plates or foils are a new film-like radiation image sensor based on the photo stimulated luminescence (PSL). They are comprised of specifically designed phosphors that trap and store the radiation energy. The stored energy is stable until scanned with a laser beam, which releases the energy as luminescence signal which is collected with a photodetector (e.g., photomultiplier tube).
A type of proportional counter that utilizes gas ionization and a localized electron avalanche process to amplify the signal from the detected x-ray. Both linear (1-D) and area (2-D) type position sensitive detectors are available. Linear position-sensitive detectors use a fine wire to collect intensity over an angular range simultaneously, offering speed advantages up to one hundred times that of a point detector (scintillation and solid-state). These detectors may be held fixed over a 5 to 10 degree 2-theta range or scanned like a point detector over a larger range. The speed of this detector is advantageous for high sample throughput, time resolved studies, weakly diffracting materials and the detection of minor phases.
Solid-state or semiconductor detectors collect diffracted intensity from one angle at a time and are scanned through the angular range of interest. These detectors provide the energy resolution of a diffracted-beam monochromator without the associated intensity loss and offer a three- to fourfold speed advantage over a scintillation detector and monochromator. Various types of solid state detectors exist such as Germanium, Si(Li) (lithium drifted silicon), CCD (charge coupled device), PDA (photo diode array), PIPS (passivated implanted planar silicon) and SSB (silicon surface barrier). The semiconductor detectors typically require cryogenic cooling to improve the signal to noise ratio.
Scintillation detectors consist of a fluorescent crystal (e.g., NaI, plastic scintillators) bonded to the end of a photo-multiplier tube. Scintillation detectors collect diffracted intensity from one angle at a time and are scanned through the angular range of interest. They may be used with Kbeta filters or with diffracted-beam monochromators.
Geiger counters or gas flow proportional counters.
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Monochromating crystals or monochromators utilize the diffraction conditions of a crystal to produce a monochromatic x-ray beam. Crystals with different lattice spacings and tilts (lattice planes) are used to provide the desired beam of the desired wavelength. The monochromators can be used on the incident beam to produce the monochromatic beam required to produce a diffraction pattern in the sample and to filter out undesirable white or Bremsstrahlung radiation from the diffracted beam.
A series of slits, soller slits, divergence slits, etc, produce a collimated beam with less angular divergence. They may be utilized on the incident or diffracted beam.
Absorption filters utilize the x-ray absorption edge characteristics of a material to filter out the K-beta peak and some white radiation from an incident beam to produce a more monochromatic beam of radiation.
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2-Theta Angular Range. The range of diffracted beam (2-theta) angles that can be measured.
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The maximum specimen width or diameter that can be analyzed in the x-ray diffraction instrument. This feature is important in selecting an instrument for mapping or quality studies on silicon wafers.
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Texture or preferred crystal orientation of individual grains (crystallites) in a polycrystalline sample is commonly measured through the determination and analysis of pole figure plots.
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Residual stress produces strain or a lattice deformation in a sample and a corresponding change in lattice spacing. The change in lattice spacing will cause a shift or broadening of the diffraction lines or spots.
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Techniques that allow the determination of the orientation of the crystallographic planes in a single crystal sample. The method is important for the semiconductor industry which utilizes single crystal silicon substrates (wafers) of known crystallographic orientation. Material properties such as hardness and etching rate change with orientation.
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Rocking curves, reflectometry, topography, reciprocal space mapping, microdiffraction or other methods are utilized to crystal quality assessments or other high resolution studies. X-ray topography or microscopy utilized to examine defects within a crystal structure. Crystal defects or imperfections reflect more strongly and therefore produce dark regions on the x-ray topograph or reflection image. Rocking curves provide an indication of sub-grains and surface roughness in a crystal. Microdiffraction utilize a small incident x-ray beam with a diameter less than 100 microns for investigation of small samples or a particular region of larger sample. Reflectometry utilizes the refractive index of thin film or semiconductor materials to provide density, surface roughness, composition variation, interfacial thickness, and total film thickness with depth profiling capability through the film.
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Interfaces to a computer for operation of the unit and display of diffraction patterns. The interface may facilitate data storage and/or data analysis.
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Software for automated identification or matching of diffraction data to standard library data or quantification of parameters such as lattice spacings.
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This is the full required range of ambient operating temperature.
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This is the full required range of ambient operating humidity.
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