Читать книгу Amorphous Nanomaterials - Lin Guo - Страница 31

X-ray absorption fine structure spectroscopy (XAFS) is a unique tool for studying the local structure around the selected elements that are contained within a material, at the atomic and molecular scale. Owing to its element-specific and short-range nature, the core-level XAFS is now routinely used to elucidate the local structural, vibrational, and other physical properties of complex, aperiodic materials. The XAFS encompasses both the extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge spectra (XANES). The XANES refers to the structure in the X-ray absorption spectrum at high and low energies relative to the absorption edge with the crossover typically at about 20–30 eV above the edge. However, EXAFS refers to the oscillations at energies above the XANES region. The extraordinary capabilities of these spectroscopies come at a price: they depend on the comparisons with quantitative simulations of the spectra. However, theories of X-ray spectra have become increasingly accurate and sophisticated, generally overcoming this limitation.

In this chapter, we will start with a brief introduction of XAFS, including the conceptions and classifications of XAFS. Then, two branches of XAFS, EXAFS and XANES, and their corresponding theories, mechanisms, and scope of applications will be discussed in detail. Finally, attention will be focused on the application of XAFS for amorphous material characterization. XAFS can be applied not only to crystals but also to the materials that possess little or no long-range translational order: amorphous systems, glasses, quasicrystals, disordered films, membranes, solutions, liquids, metalloproteins, and even molecular gases. In the last section, a series of researches on amorphous materials based on the data gathered and analyzed from XAFS will be reviewed.