X-ray Standing Waves in X-ray Specular Reflection and Fluorescence Study of Nano-Films

The analysis of the wavefield intensity distribution connected with X-ray standing wave (XRSW) generation above the mirror surface at total reflection (TR) is presented for a vacuum/film/substrate sample along with experimental examples for organic and inorganic films for cases where the refractive index of the film is greater than that of the substrate. The thickness of an ultra-thin film may be estimated from the value of the XRSW period formed above the film/substrate interface at TR. In some cases, the thickness of an ultra-thin film may be roughly obtained just from the form of the X-ray reflection curve at incident angles smaller than the critical angle of the substrate. It is demonstrated that interference phenomena at TR, leading to waveguide mode formation inside the layered structure and responsible for a modulation of the X-ray reflection and fluorescence angular dependence, can be used for characterization of nano-films.