Characterization of biological thin films at the solid-liquid interface by x-ray reflectivity.

We demonstrate that 18 keV x-rays can be used to study organic thin films at the solid-liquid interface by x-ray reflectivity. We establish that this is a powerful technique for investigating biological systems in a previously inaccessible manner. Our measurements enabled the density distribution of single phospholipid bilayer membranes in bulk water to be measured with unprecedented precision. Previously, characterization of biomimetic structures normal to a "buried" interface was a domain of neutron reflectivity.