(a) LPS Langmuir monolayer at the air/water interface enclosed by the movable barriers of a Langmuir trough (b) solid supported asymmetric PL/LPS bilayer (c) floating PL/LPS bilayer. The gold surface is coated with a monolayer of thiolated lipids (purple) which creates a ∼20 Å water cushion between the substrate and the asymmetric model membrane. Dashed lines represent the path of the beam in a NR experiment.