Fine-structure of soft X-ray absorption edges - I—Li, Mg, Ni, Cu metals

Abstract

The borderland region between ultra-violet light and X-rays, particularly from about 100 to 300 A, is very suitable for obtaining spectroscopic information regarding the electronic structure of metals, or solids generally. The first step towards this problem consists in the determination of the intensity distribution in the soft X-ray emission bands, which represent transitions from the filled conduction-electron levels of a metal into a vacant inner shell. We thus obtain information relating to the distribution with energy of these filled levels. The most complete experimental investigations of the emission bands are those of Siegbahn and Magnusson (1934) and of O’Bryan and Skinner (1934) for the metals Li, Be, Na, Mg, Al, Si. Subse­quent work showed that the extension of these results to heavier metals is very difficult, because the Auger effect reduces the intensity of the emission by a large factor. The complementary problem is that of absorption, in which we are dealing with transitions from an inner shell of the metal into one of the unoccupied conduction-electron levels of the metal. The probability of such an absorption process is closely connected with the density of the unoccupied levels as a function of energy. The experimental problem therefore consists of the determination of the variation in the absorption coefficient of radiation by electrons of a given inner shell as a function of wave-length; or, as it may be called, the determination of the fine-structure on the short wave-length side of an X-ray absorption edge of a metal.