1. USAXS/USANS and slit smeared instruments in general
11/2/2019
USAXS/USANS and slit smeared instruments in general
Jan Ilavsky
Advanced Photon Source, Argonne national Laboratory, Argonne, IL, USA
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2. Presentation purpose…
11/2/2019
Presentation purpose…
USAXS/USANS instruments
Show differences, advantages and disadvantages of these instruments
Problem of slit smearing
Absolute calibration standard from USAXS instrument
SAS is premier method for size characterization of nanoscale density inhomogeneities
“statistically representative”
Determine volume fraction and number density
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3. APS Bonse-Hart camera (USAXS)
11/2/2019
APS Bonse-Hart camera (USAXS)
Instrumentation availability USAXS:
Desktop instrument (Rigaku/MSC)
Synchrotron based :
APS
ESRF
USANS instruments NIST and other neutron sources.
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4. ESRF USAXS camera
Rigaku USAXS

5. USANS instrument - NIST
11/2/2019
USANS instrument - NIST
A perfect crystal diffractometer (PCD) for ultra-high resolution small-angle neutron scattering (USANS) measurements is in operation at the thermal neutron beam port, BT-5. The PCD increases the maximum size of features accessible with the NCNR's 30-m long, pinhole collimation SANS instruments by nearly two orders of magnitude, from ~102 nm to 104 nm.
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6. Basic cameras - differences
11/2/2019
Basic cameras - differences
Camera
Pros
Cons
Pinhole
“Small beam”
Simple design
Can use area detector
time-resolved studies
adjust collimation with slits
no slit smearing
Qmin > Å-1
can’t reject fluorescence
long detector distance needed for high resolution
limited Q range unless changing distance
USAXS
“Large beam”
reaches very small Q (10-4 – 10-5 A-1)
compact size
large Q range measured at once (4 decades)
absolute cross-section
rejects fluorescence
examine larger sample volume without compromising resolution
must use step-scan
if slit smeared geometry - must correct for slit collimation or include slit smearing in data analysis
More complex operation
Adjust collimation by changing crystal optics
Note: 2D collimated variation of USAXS is available at both APS and ESRF.
ESRF is actually running only in 2D collimation, at APS we select appropriate setup for each application.
2D collimation has also some disadvantages…
Myths about Bonse-Hart cameras:
High background (Bragg reflection is background) – not always true, ESRF instrument has lower background than their pinhole camera. Depends on crystals and design.
Unreliable operation – today design collects reliably data for 24 hours/day, 7 days a week.
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7. USAXS/SAXS/USANS capabilities comparison
11/2/2019
USAXS/SAXS/USANS capabilities comparison
Varies wildly from instrument to instrument, X-ray (neutron) energy and source… This is ONLY orientation
1-D collimated USAXS:
8 x 10-5 < Q < 1 Å-1
Intensity range up to 9 decades
Beam size up to
0.4 mm x 3 mm horizontal
0.04 mm x 0.4 mm vertical
Slit smeared data (need for numerical desmearing) – limited to isotropic scatterers
Slow data collection (20 minutes)
Pinhole camera SAXS:
~1 x 10-3 < Q < 1 Å-1, at less than 2 decades at one time
Intensity range usually about 3.5 decades
Beam size up to
smaller than 0.5 mm x 0.5 mm
Generally fast data collection (< second) sometimes ultrafast
USANS:
3 x 10-5 < Q < 0.01 Å -1
Intensity range up to 3 decades
Beam size up to
up to 50 mm x 50 mm
Slit smeared data
Very slow data collection (~8 hours)
2-D collimated USAXS:
8 x 10-5 < Q < 0.1 Å -1
Intensity range up to 8 decades
Beam size up to
0.4 mm x 1 mm horizontal
0.04 mm x 0.4 mm vertical
Pinhole collimated data – studies of anisotropic scatterers possible
Slow data collection (20 minutes)
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8. Examples of USAXS data

9. 11/2/2019
Example of data - Glassy carbon measurement comparison of different SAS cameras
Comparison:
Different Q range
Different Intensity range
Different DQ for each point
Different noise levels
Note: the exposure times are _very_ different:
DND (pinhole, synchrotron): <1s
ARL (pinhole, desktop): ~ 240s
USAXS (synchrotron): ~20 minutes
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10. Slit smeared data & desmearing
11/2/2019
Slit smeared data & desmearing
Slit smearing by detector geometry (Bonse-Hart camera, Kratky camera)
Various of methods developed to desmear the data….
We prefer by J. A. Lake; ACTA CRYST 23 (1967)
Basically, possible for isotropic structures
Best is to slit smear model and evaluate slit smeared data! (“Irena” will do it in most cases).
General Collimation Broadening Formula
Rectangular Slit Collimation in USAXS
Desmearing routines (for slit smeared data) available in either Irena package (see later) or for download as self standing code:
(note : ONLY finite slit)
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11. Absolute Calibration - SAS Cross-Section d/d
11/2/2019
Absolute Calibration - SAS Cross-Section d/d
R. W. Hendricks, J Appl Cryst 5 (1972)
T. P. Russell, J Appl Cryst 16 (1983)
P. R. Jemian, Acta Metall Mater (1991)
I(Q) : intensity, arbitrary units
I0 : apparent source intensity, arbitrary units
W : solid angle subtended by detector
t : sample thickness
m : absorption coefficient
e-mt : sample transmission
d(Q)/d : differential scattering cross-section per unit volume per unit solid angle
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12. Absolute Calibration methods
11/2/2019
Absolute Calibration methods
Standard-less method (USAXS, NIST SANS)
Absolute intensity calibration from first principles (measure I0, calculate rest)
Standard based methods
Measure “known” sample
Absolute intensity standards can be water, glassy carbon, silica, or any other “known” sample
Water often used for SANS since the SAS can be calculated – but it is weak scatterer
Generally, good instrument should provide the absolute intensity standard. Ask for it.
NIST is considering development of SAS absolute intensity standard – but market has not been proven yet.
If interested, we at APS (contact me: provide glassy carbon sample and measured intensity curves at this time.
Jan, I’d definitely like to get a calibrated glassy carbon sample from you. That would be great!
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13. accessible energy range
11/2/2019
APS SAXS instruments
Nine different small-angle X-ray scattering (SAXS) beam lines are accessible to the APS general user. The combined capabilities of these beam lines span a broad range of reciprocal space and X-ray photon energy allowing for investigations from many disciplines of science including biology, materials science, environmental science, chemistry, medicine, and physics. Coupled with a high data throughput and fast time-resolved measurement capabilities, these instruments enable an efficient use of the high intensity and high brilliance APS X-ray source.
accessible Q range
accessible energy range
32ID
32ID
Q, Å-1
Energy, keV
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