Multipurpose x-ray reflectometer optimized for the characterization of organic surface films on aqueous subphases

A reflectometer based on a conventional sealed x-ray source for the study o f molecular organic surface films (such as Langmuir monolayers) has been de vised, which outperforms similar instruments using rotating anode generator s and approaches even most advanced experimental stations attached to third generation synchrotron sources. Reflectivities of similar to 5x10(-9) are thus becoming available while the measurement of a full reflectivity curve takes approximately 4 h to complete. The instrument is operated under full digital control, permitting the automated recording of measurement programs . In an example of its performance we demonstrate that dipalmitoylphosphati dylglycerol monolayers on electrolytic subphases may be characterized to a level of detail which until recently was not even available at synchrotron sources. While conventional box models of lipid monolayers are inadequate f or modeling experimental data at the high momentum transfer that has become accessible with the new instrument, a recently developed modeling techniqu e based on volume-restricted distribution functions [Schalke , Biochim. Bio phys. Acta 1464, 113 (2000)] enables studies of ion binding to the phosphol ipid in submolecular detail. (C) 2001 American Institute of Physics.