Silicon stabilized tricalcium phosphate (Si-TCP) is formed, among other phases, as a result of sintering hydroxyapatite (HA) in the presence of silica (SiO2) at > 800 degrees C. Calcium phosphate films sintered at 1000 degrees C on quartz substrates are examined with and without additional SiO2 added to the starting precipitate. Data from transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) separate the undoped film morphology into a surface layer with a monoclinic crystal structure P2(1)/a characteristic of a or Si-tricalcium phosphate and grain size in the range 100-1000 nm and a substrate layer with a crystal structure which is predominantly apatitic P6(3)/m and grain size in the range 30-100 nm. The silicon content is greatest in the substrate layer. The addition of SiO2 to the film material during fabrication induces a more uniform grain size of 10-110 nm and a higher Si content. The structural and phase evolution of these films suggests the nucleation of alpha-TCP by the local formation of Si-TCP at a SiO2-hydroxyapatite interface. The results are consistent with X-ray diffraction studies and are explained by a model of nucleation and growth developed for bulk powders. (c) 2006 Springer Science + Business Media, Inc.