A position sensitive X-ray diffraction (XRD) detector is designed to gather powder data, by distributing its detection elements/strips throughout the goniometer scattering plane and then scanning it across the measurement range. The LYNXEYE XE Energy-Dispersive 0D/1D/2D-mode detector is the latest generation compound silicon strip detector, which can fulfill all of these functions. It not only offers high-speed data acquisition, but also features the highest level of energy discrimination which results in high peak to background, without using any monochromators or filters.
Besides scanning 1D mode, the detection strips or elements of this detector can be programmed to characterize the same 2theta position, allowing the detector to be used in “0D” mode for high-resolution parallel-beam geometries.
A patented 0/90 degree mount from Bruker allows the detector to be rapidly re-oriented, with the strips perpendicular to the scattering plane (Figure 1). In this direction the scattering angle is established by a physical slit located at the front of the detector, and the intensity can be spread throughout the detector strips allowing a very high dynamic range 0D mode.
Figure 1. LYNXEYE XE in 0 degree and 90 degree orientations. The relationship of active area to scanning direction and scattering plane is shown.
If the LYNXEYE XE strips are configured to preserve their position sensitivity in this 90 degree orientation, a 2D scattering pattern can be built by scanning the detector along the length of the 2θ direction (Figure 2). This novel, 2D-mode of operation, supported by DIFFRAC.EVA and DIFFRAC.MEASUREMENT, allows access to scattering data that is basically unavailable to other 0D/1D detectors.
Figure 2. LYNXEYE XE 2D-mode data collection in DIFFRAC.MEASUREMENT. 2D data is integrated to 1D in real-time.
Scattering maxima from polycrystalline samples happens at precise diffraction angles as defined by Bragg’s Law. In 2D scattering space, the scattering maxima emerge as Debye cone, which intersect a conventional 2D detector to form rings as illustrated in Figure 3.
Figure 3. (Left) Illustration of 2D diffraction geometry, here shown in transmission geometry. (Right) Examples of Debye rings exhibiting intensity distributions due to stress, texture, particle size, and number of particles. The red outline represents the region that can be scanned and displayed in 2D-mode.
The scattering intensity along the rings is known as the gamma (γ) direction, and contains extra data regarding the sample including; texture, particle size, stress, and phase type, such as single crystal, few crystal, or polycrystalline.
Application Example: Phase ID using 2D-mode
The 2D mode was used to examine a rock obtained from a mine in Wausau, Wisconsin. Figure 4 and 5 illustrate the results of this examination. By examining the gamma profile of the 2D data, it is apparent that the sample comprises of a minimum of two crystalline phases. The first phase is fine grained and textured (blue arrows), and is specified by the nonstop, but uneven, intensity distribution along gamma. The second phase is large grained (red arrows) and is indicated by the spotty and uneven intensity along gamma. This data facilitates peaks to be cautiously assigned to a range of phases before the 1D search/match even starts. The search/match process is simple and fast, and offers a comprehensible theory for the relative intensity deviations between reference patterns and raw data.
Figure 4. A measured rock from a mine in Wausau, WI.
Figure 5. (Top) 2D-mode scan and real-time 1D integration of Wausau, WI mine rock. Based on gamma scattering profile, the peaks are grouped into phase 1 (red arrows) and phase 2 (blue arrows). (Bottom) DIFFRAC.EVA Search/Match results in phase identification of Quartz for phase 1 and Biotite for phase 2. Relative intensity differences can be explained by referencing the 2D data
A key benefit of utilizing the LYNXEYE XE for this application is the excellent energy resolution, which out performs the capabilities of conventional 2D detectors, that help to acquire 2D images without sample fluorescence. Although this approach could raise the background and limit trace phase sensitivity (Figure 6).
Figure 6. Fluorescence Filtering. 2D-mode scan (bottom) with resulting integrated 1D data (top) of Iron sample with Copper Ka primary radiation. Fluorescence filtering set of OFF to simulate a traditional 2D detector and ON showing results from LYNXEYE XE standard setting.
With the combination of a 0/90 degree detector mounting system and an advanced scan type, the LYNXEYE XE, energy discriminating detector offers a new and powerful mode of operation - 2D-mode. In this mode, 2D scattering images can be generated which disclose sample information, not possible with basic 0D/1D detectors.
The major benefits of using LYNXEYE XE in 2D-mode are listed below:
- Anti-scatter slits decrease background by blocking air-scatter
- Variable positioning to improve gamma and 2θ
- Modifiable resolution through scan and slit settings
- Prevents defocusing issues by applying symmetrical scanning mode
- No compromise 0D/1D performance with same detector
- Operation with all regular wavelengths, including hard radiation
- Sample fluorescence removed through excellent energy discrimination
This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.
For more information on this source, please visit Bruker AXS Inc.