Physics Room 120, Lecture Hall
The MU Physics & Astronomy Department's O. M. Stewart Colloquium Series presents, "What can the reflection of neutrons reveal about the structure of hard and soft condensed matter?" by Dr. Charles Majkrzak, National Institute of Standards and Technology, Monday, April 23, 4:00 p.m. Refreshments will be served beginning at 3:30 p.m. in Rm. 223A, Physics Library.
Dr. Majkrzak writes, "In general, direct imaging methods such as optical, atomic force, and electron microscopy are powerful and of wide-ranging application for obtaining information about the shapes of materials on micron, nanometer, and atomic length scales, respectively. Nonetheless, as is well known, there are limitations to what can be discerned by such techniques and complementary scattering measurements are often necessary to obtain a more detailed compositional picture. In particular, for studies of materials possessing multi-layered lamellar morphologies, diffraction measurements with x-rays and neutrons at glancing angles of incidence can yield unique quantitative structural information on a nanometer length scale. Diffraction at relatively low values of wavevector transfer Q -- where the scattering potential of a material object can be treated as being continuous and associated with a corresponding refractive index (as in ordinary light optics) -- has come to be referred to specifically as reflectometry. From measurements of the reflectivity as a function of Q in the specular condition (in which the angles of incidence and reflection are of equal magnitude), the depth profile of the scattering potential density along the nominal surface normal can be reconstructed and subsequently related to the actual material composition distribution. Neutron reflectivity studies of a number of hard and soft condensed matter systems of current interest -- including examples in magnetism, polymer science, and biology -- will be examined. Possible future advances in neutron reflectometry as a probe to investigate the structure of materials will also be discussed. The presentation will be directed toward a broader audience of scientists, including students, and not intended primarily for scattering experts."