Glancing Angle X-ray Absorption Spectroscopy

The use of glancing angles of incidence enables X-ray Absorption Spectroscopy to be measured as a function of depth from the surface of a material into the bulk. As x-rays rather than photoelectrons are detected, a UHV environment is not required and instead surfaces and interfaces can be examined under realistic operational conditions. Whilst the reflected beam carries the fine structure of concentrated species in the imaginary part of the refractive index, this is obscured by the contribution from the real part for angles greater than ϕc, the critical angle for total external reflection. Measuring the x-ray fluorescence offers more flexibility, particularly for dilute systems. The use of synchrotron radiation in conjunction with a multi-element Solid State Detector enables impurity loadings down to a few 1019 cm-3 to be measured which for ion implants is equivalent to around half-monolayer coverage at the surface. This sensitivity makes it practical to examine impurities in semiconductors at realistic dopant levels.