Abstract
Many disparate methods of compositional analysis of materials are underpinned by the same fundamental atomic processes: the excitation of the electronic system of the atoms followed by its subsequent relaxation. These methods include the electron spectroscopies (XPS, AES) used for surface studies, the electron microscopies used for elemental and structural characterisation (SEM using EDS and WDX; TEM using EELS), the X-ray methods (XRF, XAS) and ion beam analysis (PIXE) used for elemental and chemical characterisation. All rely on measuring the characteristic energy absorbed or emitted by the unknown target atom when its electronic system is excited by ionisation due to charged particles or electromagnetic radiation. This excitation is defined by the energy levels of the atomic electrons, determined primarily by the atomic number of the atom. (Atoms can also be excited without ionisation, as in optical and infra-red spectroscopy: this is outside the scope of this article.) The theoretical description of the electronic structure of atoms is a major intellectual triumph of the twentieth century and this body of knowledge is exploited in the theoretical description of each of these methods, but the treatment of any particular method is usually presented by specialists in that method in isolation from all others. In this chapter we present a brief synthetic overview of materials analysis using atomic excitation, highlighting those features and physical concepts which underpin all these apparently disparate analysis methods. We hope to encourage modern analysts to appreciate the truly complementary nature of the powerful methods at their disposal.