USAXSUSANS and slit smeared instruments in general Jan

USAXS/USANS and slit smeared instruments in general Jan Ilavsky Advanced Photon Source, Argonne national Laboratory, Argonne, IL, USA

Presentation purpose… ü ü 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 2

APS Bonse-Hart camera (USAXS) Instrumentation availability USAXS: Desktop instrument (Rigaku/MSC) Synchrotron based : APS ESRF USANS instruments NIST and other neutron sources. 3

ESRF USAXS camera Rigaku USAXS 4

USANS instrument - NIST A perfect crystal diffractometer (PCD) for ultra-high resolution small-angle neutron scattering (USANS) measurements is in operation at 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. http: //www. ncnr. nist. gov/instruments/usans/ 5

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 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 USAXS “Large beam” Qmin > 0. 001 Å-1 can’t reject fluorescence long detector distance needed for high resolution limited Q range unless changing distance 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: 2 D collimated variation of USAXS is available at both APS and ESRF is actually running only in 2 D collimation, at APS we select appropriate setup for each application. 2 D 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. 6

USAXS/USANS capabilities comparison n Varies wildly from instrument to instrument, X-ray (neutron) energy and source… This is ONLY orientation 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 50 mm x 50 mm Slit smeared data Very slow data collection (~8 hours) 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) 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) 7

Examples of USAXS data 8

Example of data - Glassy carbon measurement comparison of different SAS cameras n Comparison: – Different Q range – Different Intensity range – Different DQ for each point – Different noise levels n Note: the exposure times are _very_ different: – DND (pinhole, synchrotron): <1 s – ARL (pinhole, desktop): ~ 240 s – USAXS (synchrotron): ~20 minutes 9

Slit smeared data & desmearing n Slit smearing by detector geometry (Bonse-Hart camera, Kratky camera) n Various of methods developed to desmear the data…. – We prefer by J. A. Lake; ACTA CRYST 23 (1967) 191 -194 – Basically, possible for isotropic structures n 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: http: //www. uni. aps. anl. gov/~jemian/sas. html (note : ONLY finite slit) 10

Absolute Calibration - SAS Cross-Section d /d R. W. Hendricks, J Appl Cryst 5 (1972) 315 -324 T. P. Russell, J Appl Cryst 16 (1983) 473 -478 P. R. Jemian, Acta Metall Mater 39. 11 (1991) 2477 -2487 I(Q) : intensity, arbitrary units I 0 : apparent source intensity, arbitrary units : 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 11

Absolute Calibration methods n Standard-less method (USAXS, NIST SANS) – Absolute intensity calibration from first principles (measure I 0, calculate rest) n 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 n Generally, good instrument should provide the absolute intensity standard. Ask for it. n NIST is considering development of SAS absolute intensity standard – but market has not been proven yet. n If interested, we at APS (contact me: ilavsky@aps. anl. gov) provide glassy carbon sample and measured intensity curves at this time. 12

APS SAXS instruments http: //small-angle. aps. anl. gov 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 Xray 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 32 ID accessible energy range 32 ID Q, Å-1 Energy, ke. V 13