The structures of substrate/layer, layer/layer, and layer/air interfaces in optical multilayers made using plasma enhanced chemical vapor deposition (PECVD) have been probed for the first time using X-ray reflectivity and neutron reflectivity. From the point of view of optical applications the interfaces are extremely sharp, sharper than is often achievable with the self-assembly of block copolymers or deposition techniques in which the polymer layers contact while in a fluid state. The average interface width, a(1), between layers made from different precursors is about 40 Angstrom (16 Angstrom rms). The layer/layer interfaces are generally 2-3 times broader than the layer/air interfaces. Polymeric fluorocarbon films deposited on a Si substrate using PECVD with octafluorocyclobutane (OFCB) monomer show uniform scattering length density with depth except for a region of molecular thickness immediately adjacent to the substrate. Films made from deuterated benzene show uniform density throughout the film thickness. (C) 2004 Elsevier Ltd. All rights reserved.