We investigated the aggregate morphologies of tetradecyl-dimethylamine oxide hemihydrochloride (C14DAO . 1/2HCl) on mica surface in the surfactant solutions by Atomic Force Microscopy (AFM). C14DAO . 1/2HCl forms a flat bilayer on mice. This morphology is different from spheres or cylinders which have been reported for other cationic surfactants with a single tetradecyl tail. The reason for this lower curvature of the C14DAO . 1/2HCl aggregate on mica is discussed in terms of the hydrogen bond between the headgroups.