CONDENSED MATTER SEMINAR


Speaker: Prof. Ajay Gupta, Center Director, Indore Center, University Campus,
         Indore, INDIA

Title:  "Depth Resolved Structural Studies in Multilayer Nanostructures
         Using X-ray Standing Waves"

Place and time: Room 223, Physics Building, Friday, August 25, 2006,
                3:30 p.m. Refreshments served in Room 242 at 3:00

Abstract: 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 the
          interface structure. Since the width of the interfacial region
          ranges from a fraction of a nm to a few nms, 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,
          XAFS (x-ray absorption fine structure), 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
          measurements , ii) measurement of concentration profile of a specific
          isotope (e.g. Fe57) by making use of 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.