Phospholipid,a main component of cell membrane,has been explored as a model system of the cell membrane and temporary scaffold materials in recent studies.The properties of phospholipid layers are essentially interesting since it is involved in several biological processes.The penetration driven by the interaction(electrostatic or hydrogen bonds)with the polar groups of the lipid molecules alters the phase behavior(surface pressure-area,П-A,isotherm)of the monolayer.This is linked to changes of the packing and the cohesion of the molecules at the interface as it was revealed by AFM images.