Condensed Matter and Biological Physics Seminars

Thin films and multilayers have emerged as an important class of nanostructured materials with immense possibilities of tailoring their properties in order to achieve the desired functionality. Interfacial region plays a dominant role in determining the properties of multilayers. Therefore, it is important to elucidate the interface structure in multilayers in order to understand their novel properties as well as to tailor the same through tailoring the interface structure. Since the width of the interfacial region ranges from a fraction of a nm to a few nm, it is necessary to use experimental techniques with a depth resolution of 1 nm or better. X-ray based techniques like fluorescence, x-ray diffraction, x-ray absorption fine structure (XAFS), and Nuclear Resonance Scattering are powerful techniques for structural characterization. In general, x-rays being highly penetrating radiation, these techniques lack depth resolution. However, X-ray standing waves (XSW) formed by the superposition of two coherently coupled X-ray beams, make it possible to localize the X-ray intensity into anti-nodal regions of an XSW field, and thereby attain a spatially localized periodic probe with a length scale equivalent to the period of XSW. In the present talk the use of XSW will be demonstrated in: i) determining elemental concentration profiles through fluorescence measurement, ii) measurement of concentration profile of a specific isotope (e.g. 57Fe) by making use of nuclear resonance fluorescence, iii) depth resolved XAFS and nuclear forward scattering. The examples taken include, i) study of the effects of swift heavy ion irradiation on metal/silicon systems, ii) characterization of magnetic multilayers, and iii) measurement of self-diffusion of Fe in amorphous and nanocrystalline alloys.