Calcium ions have been shown in a preliminary experiment to have a dramatic effect on the thickness and structure of free supported DPPC bilayer films. At low concentrations (5mM) the bilayer is severely disrupted, moving away from the SAM surface. As the ionic concentration is increased, the bilayer again becomes smooth, but is repelled by the SAM and surface charging. At still higher concentrations the bilayer moves back towards the surface due to charge screening. We wish to study the following effects: (i) get better resolution of the low concentration effects between 1 and 5mM, where the bilayer starts to disrupt. (ii) study the effect of moving to the fluid phase of DPPC, where the zwitterionic head group is more exposed to the solution (iii) decouple the effect of changing Ca2+ concentration on ionic strength