A series of nanocrystalline diamond (NCD) films were deposited by a custom made microwave plasma enhanced chemical vapor deposition apparatus with linear antenna delivery at different substrate temperatures (520-600 degrees C) and pulsed plasma frequencies (2.7-14.3 kHz) in a hydrogen rich working gas mixture of H-2/CH4/CO2. Films were deposited onto naturally oxidized Si wafers pre-seeded with nanodiamond particles. Spectro-ellipsometry characterization of the NCD films was carried out considering various model structures (single and bi-layer models) and various NCD optical constant parameterizations (Tauc-Lorentz and effective medium approximation with different non-diamond component representations). It has been shown that substrate temperature can be lowered with a simultaneous increase in pulsed plasma frequency while still providing high quality NCD films with non-diamond component fraction in the bulk layer of about 5% (identically estimated by ellipsometry and Raman spectroscopy). Films' thickness and their surface roughness were found consistent with atomic force and secondary electron microscopies. Among various NCD structure models the most appropriate has been selected. (C) 2014 Elsevier B.V. All rights reserved.