The surface structures of hexamethyldisiloxane (HMDSO) films prepared by rf plasma polymerization are investigated by Fourier transform infrared, solid-state Si-29 CP/MAS nuclear magnetic resonance and scanning electron microscope. The reactive species in HMDSO plasma and the mechanism of HMDSO plasma synthesis are studied by optic emission spectrum. The effect of continuous wave discharge and different pulse discharge parameters especially plasma "high power" time on chemical structure and physical morphology modifications of HMDSO polymer film is compared elaborately. The results show that HMDSO-continuous-wave polymer is an organic film without Si-O group. Its surface consists of several microscale islands with many clustered rods. While HMDSO-pulse-polyiner is a network of interconnected primary methylsiloxane units and minor hydroxyl, oxymethylene, hydrogen and carbonyl groups. The ratio of Si-O-Si to Si-(CH3)(n) and new functional groups of -OH, C=O and C-O are effectively "tailored" by changing plasma "high power" time. Moreover, HMDSO-pulse-polymer is a continuous, regular and compact film with a few asteroid protuberances. This deposited film becomes more regular after increasing plasma "high power" time and gradually presents perfect "straw-mat" morphology. It is indicated that pulse plasma polymerization is an effective way to tailor the surface structures of plasma polymer films through controlling plasma "high power" time. (c) 2005 Elsevier B.V. All rights reserved.