Small Angle X-ray Scattering for Materials Science

Introduction
Small-angle X-ray scattering (SAXS) is a well-established characterization method for microstructure investigations in various materials. It can probe structural inhomogeneities (really electron density differences) from the near atomic scale (1nm) to the micron scale (1000nm). The method involves measuring the scattered X-ray intensity as a function (typically small) scattering angle angles and is generally performed in transmission. SAXS is used to characterize the size scale of inhomogeneities (e.g, pores, inclusions, second phase regions) in polymer blends, microemulsions, geological materials, bones, cements and ceramics.

Instrumentation
SAXS measurements can be done at either beamlines 1-4 or 4-2. Beamline 7-2 can also be used for certain SAXS experiments, such as anomalous SAXS. There is also a now ultra small angle (uSAXS) facility on 4-2, for measurements of Q to below 0.0001 Å^-1.

Analysis
Some details on data reduction can be found here (see new developments link). In general SAXS analysis is model dependent, and will, in general, depend on the material under investigation (e.g., degree of order, nature of the inhomogeneities, concentration of the inhomogeneities). Some details can be found here and in the references below.

Recently, we have developed a novel method of analyzing SAXS data from random or suitably disordered two-phase materials {Hedstrom].

Applications of SAXS for materials science
An application of SAXS on beamline 1-4 shows how to tailor plastics at a molecular level to improve manufacturability of these materials.

SAXS has been used to determine the morphology of highly porous thin films, using a novel analysis method. Representative morphologies as a function of porosity are shown in the figure below. Details are given here; contact Mike Toney for more information.

Further General Reading:

• Modern Aspects of Small Angle Scattering, Brumberger, H., ed., (Kluwer, Amesterdam, 1995).
  
• "Small Angle X-ray Scattering from Polymers", B. Chu and B.S. Hsiao, Chem. Rev. 101, 1727 (2001).
  
• "Pore Size Distributions in Nanoporous Methylsilsesquioxanes (MSSQ) Films as Determined by Small Angle X-Ray Scattering", E. Huang et al., Appl. Phys. Lett. 81, 2232-2234 (2002).