Neutron and X-ray Non-Specular Reflectivity

The theory and analysis of INTERFACIAL ROUGHNESS using NON-SPECULAR NEUTRON and X-Ray REFLECTIVITY is a major research interest in the NIST Center for Neutron Research.
  • Neutron and X-Ray Reflectometry Studies of Rough Interfaces in a Langmuir-Blodgett Film
    H. Kepa, L. J. Kleinwaks, N. F. Berk, C. F. Majkrzak, V. I. Troitsky, R. Antolini, and L. A. Feigin, Proc. Int. Conf. on Neutron Scattering, Toronto (1997). To be published in Physica B.

    Neutron and x-ray reflectometry are used to study interlayer roughness and islanding in a 20-bilayer barium stearate Langmuir-Blodgett film with alternating hyrogenated and deuterated bilayers. The interlayer roughness is highly conformal, and analysis of the diffuse x-ray peak widths suggest it is approximately self-affine with a roughness exponent approximately 0.8. This exponent describes the film in all directions, even though steps on the Si substrate interrupt the correlation of the film across the steps. The neutron and x-ray specular reflectivities have modulated Kiessig fringes, indicating the presence of islands on the top of the film. Odd Bragg peaks in the neutron specular reflectivity are broadended, implying long-range disorder in the H-D bilayer structure. These data suggest that the islands arose from incomplete coverage during the film preparation.

    This work was presented as an invited paper to ICNS by Henryk Kepa, a guest researcher at NIST from Oregon State University. The study is a collaboration between scientists at NIST and the from the Center for Materials and Medical Biophysics, Povo, Italy (Antonlini), Technobiochip, Marciana, Italy (Berzina, Troitsky),and the Institute of Crystallography, Moscow, Russia (Feigin).

    Logan J. Kleinwaks contributed to this study while a senior at Thomas Jefferson High School for Science and Technology in Alexandria, VA.

    Values of the self-affine roughness exponent have been published which range from 0.2 to 0.8 (the value found here). Such a span, if reliable, is likely the result of several distinct physical process at work during L-B film fabrication. Values near 1 are consistent with models of random crumpling, as during drying; e.g., Tzschichholz, Hansen, and Roux.

NIST Center for Neutron Research

Last modified: September 30, 1997