X-Ray Ellipsometry: A Surface Sensitive Technique to Characterize Thin Films and Layered Materials

Abstract

As polarization sensitive experiments are an important trend in x-ray physics nowadays, a strong demand has arised for producing various polarization states and for measuring them, therefore, calling for polarizers for the x-ray domain. Intense x-ray sources exist or are under development; such as the ones produced by a laser plasma or by synchrotron radiation. In the latter case, the radiation is essentially linearly polarized on axis with an electric field parallel to the plane of the electron. If another state of polarization is desirable one can use either quarter and half wave plates[1] or exotic insertion devices, such as a crossed undulator[2], a planar/ helical undulator,[3] or an asymmetric wiggler. It is always important to know the amount of unpolarized light that is present. Quarter and half wave plates can be made of perfect crystals[4] and have effectively been used at energies higher than 7 keV[5]. In the soft x-ray region the property of phase retardation between s and p components were recently proven for multilayers both in the reflection[7,8] and the transmission[6][10] geometries. However, an upper energy limit of application seems to be about 400 eV when accounting for the minimum d-spacing that can be produced at present without sacrifying the multilayer performance. Other authors[7] have mentioned the carbon K-edge as an upper limit because of an increase in the absorption contribution.