Synchrotron And Beamline
STOE MULTI-MYTHEN2 R nK DETECTOR – THE SOLUTION IF ONE MYTHEN IS NOT FAST ENOUGH
Though the combination STOE STADI P diffractometer and DECTRIS MYTHEN 1K detector enables the user to collect high resolution powder data over a large 2Theta region in very short time, some experiments, especially in the wide field of non-ambient methods, require the possibility to take “snapshot patterns”.
In combination with their MYTHEN2, DECTRIS launched the DCS4 which offers the possibility to process the data of up to four MYHTEN2 modules simultaneously. Consequently the installation of two, three or four MYTHEN2 R modules on one detector arm for the STOE STADI P has been obvious and the result is the STOE MULTI-MYTHEN2 R nK (n = 2, 3 or 4).
In combination with STOE’s high temperature attachments or with an Oxford Cryostream, the STOE MULTI-MYTHEN 2 R nK offers the user the optimized detector for temperature depending measurements. Highly time resolved observations as in battery cells are possible as well as data collection for PDF calculations in a reasonable time scale. The STOE MULTI-MYTHEN 2R nK is available with all actual chip thicknesses (320, 450 or 1000µm).
Left to right: MYTHEN2 R 2K, MYTHEN 2 R 3K and, ideal for PDF-data collection, MYTHEN2 R 4K
Linked with the arrangement of more than one MYTHEN2 R module on a detector arm is the question how to treat the resulting gaps. To cover the full 2Theta range of a STOE STADI P with a modicum of modules, the MULTI-MYTHEN2 nK has gaps only a little smaller than the width of the detector window (approximately 18.5 degrees 2Theta) and offers two different measurement strategies:
Following both modes are explained for the MULTI-MYTHEN2 R 3K:
MYTHEN2 3K – STATIONARY MODE
In the stationary mode, the 3K doesn‘t move but takes one pattern with two gaps. After the shutter closed, the pattern taken with the low angle module is folded by the software in the gap between the two modules yielding a pattern of 55° 2Theta.
MYTHEN2 3K – MOVING MODE
Collecting data in the moving mode, the 3K takes one pattern (with 2 gaps), then the shutter closes and the detector arm makes an 18.25°-step. The shutter opens again and the 3K takes a 2nd pattern (again 2 gaps). These 2 patterns are combined by the software to one pattern (with no gaps) of 109.75°.
ULTRA FAST MEASUREMENTS WITH EXCELLENT DATA QUALITY
To prove the data quality of a pattern measured in the moving mode, particularly with regard to the 2Theta range close to the joints of the single module patterns, a glass capillary of 0.5mm diameter was filled with NIST 660b LaB6 standard material and mounted on a STOE STADI P in Debye-Scherrer geometry using a STOE MULTI MYTHEN2 R 3K detector (450µm chip thickness) and Mo Ka1 radiation.
The sample was measured from 2 to 110° 2Theta in 120 s (2x60s, moving mode) and the data taken to refine the cell. The first 40° 2Theta of the fit are magnified in the upper right corner of the figure. The impressive results of the refinement are listed below.
File title: LaB6
Wavelength: 0.709300
Number of accepted peaks: 68
2Theta window: 0.050
2Theta zeropoint: 0.0023 (refineable)
Symmetry: Cubic P
Spacegroup: P m-3m (No. 221)
Initial cell parameters: Cell_A: 4.1569
Refined cell parameters :
Cell_A: 4.15698(11)
Cell_Volume: 71.834(3)
Number of single indexed lines: 68
Number of unindexed lines: 0
2Theta zeropoint: 0.0014(23)
Average delta(2Theta) = 0.005
Figure of Merit F(30) = 460.4 ( 0.002, 31 )
THE STOE TRANSMISSION GEOMETRY
The STOE Transmission geometry is a hybrid of the Scherrer (left) and the Guinier camera (right) using the sample position centered in the detector circle from the first and the focusing optic from the latter.
A (111)-cut Ge monochromator (Johann-type) provides pure Ka1-radiation. It focuses primary and diffracted beam on the detector circle yielding highest resolution in 2q (FWHM<0.03° for a LaB6 (110) reflection and Mo Ka1-radiation).
CONSTANT SAMPLE VOLUME
With a constant sample volume in the beam, the Transmission-/Debye-Scherrer geometry provides reliable intensities over the full 2q scale (appr. 0.3 to 140°) while the variable amount of unaffected beam as a function of the q-value in a reflection setup yields false intensities up to at least 10° 2q if not corrected by variable slits!
NO HEIGHT DISPLACEMENT
Reflection data often yields a zero shift in 2q if the sample thickness varies and cannot be corrected by an automated z-translation. An aligned capillary is always in the center of the goniometer.
NO LINE BROADENING FOR WEAK ABSORBERS
In reflection geometry the difference in the depth penetration as a function of the absorption factor yields a remarkable peak broadening for weak absorbers. Powder diffraction in Transmission-/ Debye-Scherrer geometry avoids this phenomenon.
LESS AFFECTED BY PREFERED ORIENTATION
The statistical distribution of the particles in a capillary yields a pattern less affected by the effects of preferred orientation than the periodic stacking sequence of the planes in reflection mode.
The properties of thin films affect their reflection and interference characteristics. The two most common ways to measure these are reflectometry and ellipsometry. The STOE thin film attachment uses the total scattering method and detects the reflected amount of X-ray radiation from a thin film. It allows analyzing the thickness of layers in the nanometer scale. For example, single-layer or multilayer films of semiconductor process films can be analyzed.
With STOE’s evaluation program Layer, up to six layers can be specified in a film stack on a buffer and a substrate. The various films and substrate materials can be metallic, dielectric, amorphous or crystalline semiconductors.
As misalignment of the sample strongly affects the quality of the results in reflectometry experiments, STOE’s reflectometry sample holder has been specifically designed for accurate alignment.
The data have been collected on a STOE STADI MP diffractometer with a scintillation counter as point detector and Cu Ka1 radiation. The usage of the focusing position allows a quasi-parallel beam at the sample space. The adjustment blade also serves as a slit suppressing undesirable parts of the beam.
The sample has been a Silicon wafer coated with Tantalum and polycrystalline Silicon. The data have been analyzed with the program Layer, part of the STOE WinXPOW software suite.
1. Experimental Setup
All measurements were performed on a STOE STADI P COMBI (Mo-Kα1 radiation 0.70930(9) Å) using the STOE INSITU HT2 high temperature reaction chamber. This chamber was designed to study solid state and solid state – gas reactions in capillaries in a temperature range between RT and 1600˚C on a vertically mounted transmission diffractometer, e.g. the STOE STADI P or STADI MP.
The high temperature chamber consists of a cylindrical double walled, water cooled body with an entrance collimator for the primary beam and an exit window with 90° opening for the diffracted X-rays (covered with Kapton® foil). The heating element consists of a coiled graphite rod, which is clamped between the lid and base plate and contacted by a thermocouple directly. To reduce effects of preferred orientation the sample can be oscillated by a motor. The STOE IN SITU HT2 is fully computer-controlled in the newest WinXPow software version.
2. Results
a. Measurements with Mo-Kα1 in the HT2 in-situ measurement cell under ambient conditions.
The HT2 in-situ measurement cell uses capillaries with 2.0 mm outer and 1.0 mm inner diameter made from silica or sapphire depending on the temperature of the heating experiment. The HT2 has to be mounted on a vertically installed STOE diffractometer and can provide temperatures up to 1600 °C with a measurement range of 90° 2θ. The system works best with fast MYTHEN1K detectors and, in case of Fe containing samples, Mo-Kα1 radiation. Figure 2 shows diffraction pattern measured with 3 sec and 10 sec measurement time. As there is no read-out time for MYTHEN1K detectors, the measurement time is equal to the exposure time in this case. It is possible to collect evaluable data in a 3 sec diffraction experiment and after 10 sec the results are satisfactory for phase analysis. If more precise data is needed, perfect measurements are done in ~1 to 10 min (c.f. Figure 3). If data up to higher 2θ angles is needed measurements in a two-step measurement mode covering a 2θ range between ~2° and ~77° are possible (c.f. Figure 4). The data shown in both figures simulates a Multi-MYTHEN1K detector using 2 MYTHEN1K modules, which is under development by STOE right now. STOE will provide also the possibility to upgrade Single-MYTHEN1K detectors to Multi-MYTHEN1K detectors.
3. Conclusion and Outlook
Using Mo-Kα1 radiation and a (Multi-)MYTHEN1K detector, fast measurements of a nano-crystalline Fe2O3 sample are possible using the STOE HT2 in-situ measurement cell already under ambient conditions, and it is most likely to observe also fast reactions or phase transitions in this sample when performing non-ambient measurements with that set-up.
HE ULTRA PRECISE FOUR CIRCLE X-RAY DIFFRACTOMETER
INSTALLATION OF THE FIRST STADIVARI IN VERTICAL SET-UP ON THE HIGH PRESSURE BEAMLINE 12.2.2 AT THE ADVANCED LIGHT SOURCE IN BERKELEY, CALIFORNIA, FOR SINGLE CRYSTAL HIGH PRESSURE RESEARCH
Beamline 12.2.2 at the Advanced Light Source is a Synchrotron-based Hard X-ray Diffraction beamline specifically aimed at samples under high pressure within diamond anvil cells. The beamline photon energy range is 6-35keV with an x-ray spot size down to 10 x 10 μm. This research plays an important role in the fields of Earth sciences, materials science, construction materials, chemistry and energy and is funded by the DOE (Department of Energy) and COMPRES (the Consortium for Materials Properties Research in Earth Sciences).
The STADIVARI was selected by Dr. Christine Beavers for 12.2.2 due to its ability to easily mount the heavy high pressure cells (up to 2 kg) and yet maintain its high precision and accuracy. The STADIVARI four circle XRDs have a sphere of confusion of less than 10 μm in diameter / 5 μm in radius. In addition,’s powerful user-friendly software makes high quality data acquisition and analysis remarkably fast.