Probing Interfaces in Metals Using Neutron Reflectometry

Abstract

Solid-state interfaces play a major role in a variety of material properties. They are especially important in determining the behavior of nano-structured materials, such as metallic multilayers. However, interface structure and properties remain poorly understood, in part because the experimental toolbox for characterizing them is limited. Neutron reflectometry (NR) offers unique opportunities for studying interfaces in metals due to the high penetration depth of neutrons and the non-monotonic dependence of their scattering cross-sections on atomic numbers. We review the basic physics of NR and outline the advantages that this method offers for investigating interface behavior in metals, especially under extreme environments. We then present several example NR studies to illustrate these advantages and discuss avenues for expanding the use of NR within the metals community.

Spreading of macromolecules at the air/water interface

“…Indeed, NR has been successfully used for the characterization of the structure and the composition of different materials, ranging from metal layers ,132 to magnetic films 133 ; from semiconductors 131 to soft organic interfaces 102,103,127 and atmospheric chemistry 134 .…”

Metals Challenged by Neutron and Synchrotron Radiation

“…When these depths are scanned by varying the incident angle to the surface, or more quantitatively by varying the scattering vector, accurate depth profiles are obtained. Demkowicz and Majewski [22] review the basic scattering theory and concepts behind this method, starting from the very basic concepts of diffraction, the definition of scattering vector, evanescent wave functions, and interaction potential expressed by atomic scattering lengths. Both neutron and X-ray scattering theories are very similar, differing mostly on the different scattering amplitudes, resulting in distinct interaction potentials, which are also expressed in refractive index.…”

Neutron Reflectometry for Studying Corrosion and Corrosion Inhibition

“…The reactors use a fission source (U 235 or Pu 239 ), while typical spallation targets are tungsten, mercury or uranium. Both methods produce high-energy protons that are moderated to give a more useful range of neutron wavelength [46]. NR often requires access to long wavelength neutrons obtained from a cold source/moderator (e.g., liquid hydrogen) [26].…”

“…The detection of neutrons is achieved by reaction with species such as 3 He, 6 Li or 10 B, producing charged products that can be detected. The neutron also has a spin ½ arising from its intrinsic magnetic moment, which enables it to interact with unpaired electrons and hence to probe magnetic structures [46]. Dedicated reflectometers at the various neutron sources have particular strengths and weaknesses dictated by their principal applications.…”

“…The object of the reflectometry experiment is to deduce the real space structure, expressed as the variation in scattering length density with positional coordinate, z, in real space, from the measured reflectivity profiles in Q space [46]. Similarly to diffraction, there is generally no unique inversion method from scattering to real space.…”