ABSTRACT

Small-angle X-ray scattering (SAXS) was first observed at end of the 1920s by many researchers fairly simultaneously, but it was the work of A. Guinier in the 1930s which started a rapid development of this new phenomenon into a useful method. During his PhD work which was related to diffraction of metal alloys, Guinier quantified the intense scattering in the centers of his diffraction patterns, at small angles, to be related to the nano meter scale structures in the samples [1,2]. In the following decades, plenty of SAXS studies that were made using laboratory X-ray tubes contributed to the development of the theoretical concepts relevant to SAXS. Later, the emergence of synchrotron sources made it possible to study weakly scattering samples and to make time-resolved studies due to the high flux of the synchrotron radiation. The first synchrotron SAXS studies were made already in the 1970s from muscle fibers at the DESY storage ring in Hamburg [3]. By the end of the decade, time-resolved SAXS studies of contracting muscle fibers with 10 ms time resolution were possible [4]. Nowadays, most synchrotrons in the world have dedicated SAXS beamlines. With synchrotrons becoming readily available, completely new SAXS techniques were developed in the 1980s. H.B. Stuhrmann was the first to extend the concept of anomalous scattering to small angles and used ASAXS to make element-specific measurements of nanometerscale structures [5]. The ASAXS method would not be feasible without the possibility of tuning the photon energy continuously. At the end of the decade, also the surface-sensitive GISAXS method was invented [6], and soon it became a popular method to complement microscopy studies. While electron microscopy techniques and atomic force microscopy are excellent tools for studying the local structure of surfaces, GISAXS can give statistically averaged information about structures on surfaces without worries about possible artifacts arising from sample preparation. In this chapter, a basic introduction to SAXS is given. More complete presentations can be found in these three books: Small Angle Scattering of X-Rays (1955) by Guinier and Fournet, Small Angle X-Ray Scattering (1982) edited by Glatter and Kratky, and Structure Analysis by Small-Angle X-Ray and Neutron Scattering (1987) by Feigin and Svergun.