The advent of X-ray Free-electron Laser (FEL) such as the Linac Coherent Light Source (LCLS) has and will continue
to enable breakthroughs and discoveries in a wide range of scientific disciplines including physics, chemistry, structural biology, and material science. It has created high demand on user beamtime that is often left unfulfilled. We report here the fabrication, characterization and X-ray measurements of ultra-thin silicon single-crystal membranes for potentially beam-sharing the LCLS beam. Using a special fabrication process, samples of (111), (110), and (100) orientations were made with thicknesses ranging from 5 to 20 μm. Both high-resolution rocking curves and white-beam topographic data were first obtained using synchrotron X-rays, demonstrating near ideal diffraction qualities. Subsequent tests using the full LCLS FEL beam revealed lattice distortions from beam-induced membrane vibrations, which were then shown to be effectively reduced by ambient air or with smaller membrane dimensions. These findings are paving a way for a practical beam-sharing implementation at LCLS in the near future.