X-Ray Reflectivity

TLDR: In this article, the basic principles of X-ray specular reflectivity are presented starting with the definition of the index of refraction of a material for X-rays, and the influence of interface roughness is described.

Abstract: The basic principles of X-ray specular reflectivity are presented starting with the definition of the index of refraction of a material for X-rays. Applying the boundary conditions to the electric field and its derivative, one can express the reflectivity of a surface with respect to the incident angle and the index of refraction. This naturally yields the so-called Fresnel reflectivity valid for flat surfaces. The reflectivity of more complex structures such as thin layers deposited on a substrate or multilayers can be handled by the matrix technique that is then developed. The influence of interface roughness is described. When some approximations concerning refraction and multiple reflections at interfaces are made, one can extract from the so-called kinematical Born approximation a master formula which can be used for low electron density films. Experimental conditions are then discussed before finishing this chapter by a presentation of X-ray reflectivity by selected samples.