Eliminating Parasitic Slit Scattering in Small Angle X-ray Diffractometers

Cyrus R. Safinya, UC Santa Barbara, DMR 0619171

Our instrumentation development effort has led to a new hybrid design of x-ray aperture slits, which has been demonstrated to almost completely eliminate the detrimental parasitic slit scatterings in small angle x-ray scattering (SAXS) instruments. Parasitic slit scattering is one of the most difficult-to-overcome resolution-limiting factors in current SAXS instrument design. The simple, yet effective hybrid slit design combines a highly polished single crystalline (Si) slit edge bonded to a Tungsten base (inset in C). By using a polished (1 0 0) Si slit edge that generates no SAXS signal, most of the parasitic slit scattering due to the polycrystallinity of the slit material can be eliminated, as shown in the experimental data (A, B, C) collected and analyzed by our 2007 summer RISE (Research In Science and Engineering) intern Thomas Huang (Grinnell College, Iowa) mentored by Co-PI Y. Li (UCSB MRL Summer RISE Intern Report, 2007)

This broadly applicable design concept represents a very cost-effective way to significantly upgrade the performance of a large number of existing and future SAXS instruments, which are essential tools used widely for nanoscale characterization in broad areas of research.

Figure (A, B) Slit scattering images from a traditional Tungsten slit (A) and a Si-W hybrid slit (B). The intensity profiles (C) across the beam stop (centered at X=0) show the dramatic reduction of parasitic scattering to the background level with the hybrid Si-W slit (inset)

F ig . 7: S c attering P rofile of the Hybrid S lit in C omparis on with B ac kg round and T ung s ten S lit

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MRI: Development of an Ultra-High Resolution Small Angle X-Ray Scattering Instrument for Characterizing Supramolecular Assemblies

Cyrus R. Safinya, UC Santa Barbara, DMR-0619171

Education: Multidisciplinary teams comprised of undergraduate and graduate students, and postdocs, with backgrounds in materials, physics and engineering, are educated in x-ray instrumentation science and SAXS methods for nanoscale characterization of supramolecular assemblies. These skills are essential to successful careers in a broad range of areas including nanoscience and nanotechnology, polymer physics and chemistry, chemical and biomedical engineering.

Outreach: The PI’s actively participate in multiple outreach programs at UCSB for undergraduate and high school teacher research internships. Thomas (Tuo) Huang (Top photo, presenting at UCSB summer research interns conference), a MRL RISE Intern (2007) from Grinnell College, Iowa, worked directly with mentor and Co-PI Dr. Youli Li to develop the scatter-free hybrid x-ray slit (see research highlights). Thomas worked closely with UCSB mechanical engineering undergraduate students Nicholas Judy (bottom photo, left), Eric Walsh, and staff research associate Morito Divinagracia (bottom photo, right), who are actively working on the MRI project together with other graduate students and postdoctoral researchers.