Phase ID with 1D & 2D Detectors
Phase ID with Linear/Area Detectors
Comparison of geometry and data from 0D/1D/2D
Bob B. He Topics discussed in the ICDD 1D and 2D Detector Task Group Meeting XOptics and Geometry XDefocusing and resolution XPreferred orientation and relative intensity
Page .1 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
Comparison of 0D, 1D and 2D Detectors
scintillation detector
small spot measured scan necessary long measuring time
PSD
large 2θ range measured
simultaneously medium measuring time
GADDS
large 2θ and chi range
measured simultaneously measurement of oriented samples very short measuring times intensity versus 2θ by
integration of the data
Page .2 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
1D2D: Soller slits can be used for 0D and 1D
In cases of 0D and 1D, the intensity is a superposition of slices from diffraction ring, all same geometry condition. All within diffractometer plane and same Lorentz polarization and absorption correction. Page .3 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
No soller slits can be used for 2D - point beam is required
Smearing effect from line focus beam
Diffraction rings from point focus beam Page .4 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
Phase ID: γ-integration with merged frames
γ
γ
Out of diffractometer plane and different Lorentz polarization and absorption correction at different γ angle. Page .5 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors Bragg-Brentano Geometry Conventional X-ray Diffraction
Page .6 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
2D detector for phase ID at various 2θ angles
Diffraction pattern is measured at different detector swing angle α to cover different 2θ range. Page .7 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors XRD2: Data Collection: Acetaminophen powder 5 second data collection
30 second data collection
Lin (Cps)
2
1
0
9
10
20
30
40
2-Theta - Scale Page .8 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
Defocusing with 1D or 2D detectors Capillary smaller than beam size
Reflection mode
Transmission mode Page .9 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2: No slits or monochromator in front of the detector to stop air scatter or fluorescence Air scatter from the incident beam
Open incident beam path
Air scatter from the diffracted beam Page .10 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2 : Defocusing at low incident angle in reflection
Lower resolution when θ2 or (2θ-ω) → 90°
B sin θ 2 sin(2θ − ω ) = = b sin θ1 sin ω Page .11 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
Defocusing effect with reflection sample depends on detector and data collection strategy
Cylinder detector with 5° incident angle for 5°~80° 2θ
Flat detector with several (5°,15°,25°,35°) incident angles for 5°~80° 2θ Page .12 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
Defocusing effect with reflection sample depends on detector and data collection strategy 12
Defocusing vs. Detectors
Defocusing Factor
10 8
Cylinder detector may collect large 2θ range, but with large defocusing effect at high 2θ angle Flat Cylinder BB
6 4
Defocus effect can be minimized with data collection strategy
2 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 T wo T heta
Page .13 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors XRD2: reflection vs. transmission
Reflection mode frame from corundum at 5° incident angle.
Transmission mode frame with perpendicular incident beam. Page .14 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with Reflection and Transmission Collection: 1D & 2D Data Detectors Ibuprofen powder 10 second overall data collection 1.5
1.4
1.3
1.2
1.1
Lin (Cps)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
R
0.3
0.2
TT
0.1
0 3
10
20
30
2-Theta - Scale Page .15 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
0D/1D/2D: Samples with preferred orientation
Bragg-Brentano Configuration. Diffraction vector parallel to sample normal
Same 2θ with unsymmetrical incident and diffracted angles
1D detector with one incident angle but a range of diffracted angles
Page .16 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
0D1D2D: Samples with preferred orientation
Random powder sample with same relative intensity at all χ angles
Sample with preferred orientation (fiber texture), relative intensity varies with χ angles Page .17 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
1D: Relative intensity with preferred orientation 15%
The relative intensities from NIST 1976 are measured with 6 line detectors.
Relative Intensity from Linear Detectors)
10% 5%
The vertical scale is the deviation from the relative intensities measured with Bragg-Brentano system
0% -5% -10% -15% -20% 25.576
35.149
88.993
95.249
127.68
136.08
The 6 detectors show consistent deviations due to preferred orientation in NIST 1976. Page .18 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
0D/1D/2D:
2θ resolution between 0D/1D/2D XRD
In BB system, the resolution can be changed
with incident and receiving slits. No slits can be used in front of 1D/2D to
improve the resolution. In addition to the condition of the incident X-ray
beam, the resolution is determined by the detector spatial resolution and distance. The spatial resolution depends on the point
spread function and the pixel size.
Page .19 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
1D/2D: Point Spread Function and Resolution
Consider a very small diffraction spot (blue linedelta function)
A perfect detector - dashed blue line. A real detector - intensity in a spread distribution.
An adjacent spot – red line
Can be measured if the separation is larger than FWHM. Page .20 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 2D detector resolution: -Kα2 split 1D & 2DKα1Detectors at 35° 2θ with NIST1976 (measured with VÅNTEC-2000)
∆λ (Kα2-Kα1) →∆2θ=0.06º→ 210 µm on the detector (20 cm) Page .21 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
Summary
Many advantages of 1D and 2D detectors, such as
high speed, high sensitivity and angular coverage in γ direction, have been recognized by XRD users.
The discrepancy between diffraction patterns from
conventional Bragg-Brentano system and diffractometers with 1D and 2D detectors can be analyzed and corrected.
The instrument parameters for systems with 1D and
2D detectors should be investigated and considered in qualitative and quantitative phase analysis.
Page .22 © Bob He, 2004 Bruker AXS All Rights Reserved
Phase ID with 1D & 2D Detectors
XRD2:
References
Philip R. Rudolf and Brian G. Landes, Two-dimensional X-ray
diffraction and scattering of microcrystalline and polymeric Materials, Spectroscopy, 9(6), pp 22-33, Jul/Aug, 1994
B. B. He and U. Preckwinkel, X-ray optics for two-dimensional
diffraction, Advances in X-ray Analysis, Vol. 45, 2001.
B. He, Satish Rao, and C.R. Houska, A simplified procedures
for obtaining relative x-ray intensities when a texture and atomic displacements are present, J. Appl. Phys. Vol. 75, No 9, May 1994.
B. B. He, Introduction to two-dimensional X-ray diffraction,
Powder Diffraction, Vol. 18, No 2, June 2003.
Page .23 © Bob He, 2004 Bruker AXS All Rights Reserved
