Synthesis and characterization of calcium phosphate coatings by metalorganic chemical vapor deposition

Thin coatings of various calcium phosphates including tricalcium phosphate (TCP), calcium pyrophosphate, and hydroxyapatite were synthesized by plasma-enhanced metalorganic chemical vapor deposition (MOCVD). Structure, composition, and surface morphology of the coatings were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. All coatings were very dense and free of cracks. Xray diffraction showed that the as-grown coatings with the Ca/P ratio of 1.5+/-0.5 and 1.0+/-0.5 were crystalline alpha- TCP and pyrophosphate, respectively. However, hydroxyapatite coatings with the Ca/P ratio of similar to 1.67 were amorphous. The crystalline cl-TCP and pyrophosphate coatings exhibited strong growth texture. The textured orientations varied with different growth temperatures. In addition, the microstructure of the a-TCP coatings strongly depended on the growth temperatures.