Neutron/X-Ray Scattering in Thin Layers at Interfaces
To study features smaller than the wavelength of light, we use two experimental techniques that utilize the scattering of x-rays and neutrons: X-ray/neutron reflectivity and X-ray grazing incidence diffraction (GID). Parameters such as layer thickness, density, and interfacial roughness can be determined by characterizing the surface’s reflectivity-the intensity ratio of neutrons or X-rays scattered from the surface relative to the intensity of the incident beam. X-ray GID allows the characterization of thin crystalline layers at an interface and can provide in-plane (lateral) structural information. When supported by a smooth interface, these techniques allow structural determination in layers 5Å to 1mm thick. Systems we have studied with these techniques include:
- Neutron Scattering Measurements of Confined Complex Fluids-In this work, we use a novel apparatus, the Neutron Confinement Cell, to measure the molecular density and orientation of confined, ultra-thin complex fluids under static and dynamic flow conditions. Our studies focus on determining the structure of adsorbed polymer diblock films (polymer brush layers) at the solid-solution interface.
- Cholera Toxin’s Assault on Lipid Monolayers-The toxin’s effect on membrane structure is modeled using phospholipid monolayers at the air-water interface through X-ray reflectivity and GID, and correlated with changes in protein structure during activation as determined by neutron reflectivity.
- Characterization of Lipid Bilayers at the Solid-Liquid Interface-In these studies, we deposit model membranes in the form of lipid bilayers on ultra polished substrates. We then study the properties of lipid rafts and gel-phase domains.