Advances in Neutron Reflectometry at ISIS

The Goos-Hänchen effect is a spatial shift along an interface resulting from an interference effect that occurs for total internal reflection. This phenomenon was suggested by Sir Isaac Newton, but it was not until 1947 that the effect was experimentally observed by Goos and Hänchen. We provide the first direct, absolute, experimental determination of the Goos-Hänchen shift for a particle experiencing a potential well as required by quantum mechanics: namely, wave-particle duality. Here, the particle is a spin-polarized neutron reflecting from a film of magnetized material. We detect the effect through a subtle change in polarization of the neutron. Here, we demonstrate, through experiment and theory, that neutrons do exhibit the Goos-Hänchen effect and postulate that the associated time shift should also be observable.

Floating supported bilayers (FSBs) are new systems which have emerged over the past few years to produce supported membrane mimics, where the bilayers remain associated with the substrate, but are cushioned from the substrates constraining influence by a large hydration layer. In this paper we describe a new approach to fabricating FSBs using a chemically grafted phospholipid layer as the support for the floating membrane. The grafted lipid layer was produced using a Langmuir-Schaeffer transfer of acryloyl-functionalized lipid onto a pre-prepared substrate, with AIBN-induced cross-polymerization to permanently bind the lipids in place. A bilayer of DSPC was then deposited onto this grafted monolayer using a combination of Langmuir-Blodgett and Langmuir-Schaeffer transfer. The resulting system was characterized by neutron reflection under two water contrasts, and we show that the new system shows a hydrating layer of approximately 17.5 A in the gel phase, which is comparable to previously described FSB systems. We provide evidence that the grafted substrate is reusable after cleaning and suggest that this greatly simplifies the fabrication and characterization of FSBs compared to previous methods.