Probing Membrane Structures with a Round Beam
Lin Yang
National Synchrotron Light Source, Brookhaven National Laboratory
Lipids form layered thin films that provide model systems for studying cellular membrane-related biological processes. They also serve as an ideal platform for exploring self-assembled structures that are relevant to nanotechnology. These structures are often studied using the grazing incidence geometry, where the probing x-ray beam illuminates the sample at a shallow incident angle. I will discuss a handful of experimental issues that arise as a result of this scattering geometry and how these issues can be resolved by focusing the beam in the direction normal to the lipid film.
Vertically focused ERL beams recover the round shape after being projected onto the sample at grazing incident angles. Owing to the small horizontal beam size and divergence, no horizontal demagnification is necessary to achieve full beam illumination within a film size of 50-micron diameter. Such a bright beam is well suited for studying small 2D crystals with weak electron density contrast, such as 2D membrane protein crystals. The feasibility and potential problems will be discussed.
