W0141

Neutron Reflectometry Methods in the Study of Biological Membranes. C.F.Majkrzak, Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899 USA

Scattering length density profiles along a direction normal to the surface of a flat substrate supporting biological films and multilayers can be obtained by measurement of the specular neutron reflectivity. Overall film thicknesses can be deduced with an accuracy of the order of one Angstrom whereas more detailed features of the profile can be determined with a spatial resolution of several Angstroms, taking advantage of selective deuteration to accentuate specific segments of the structure.

By employing a buried reference layer, it is now possible to exactly determine the phase of the reflectivity for the "unknown" biological layers of interest, even in the dynamical scattering regime at low wavevector transfers. As a consequence, the scattering length density profiles can be obtained by direct inversion using the Gel'fand-Levitan-Marchenko formalism rather than by conventional fitting procedures. The ability to do this is of considerable importance since it yields a unique potential.

A description of the methodology which allows the phase to be determined as well as actual experimental results on thin film biological systems will be presented.