Characteristics of Calcium Phosphate Films Prepared by Pulsed Laser Deposition under Various Water Vapor Pressures

Abstract

Calcium phosphate films were prepared by using a pulsed laser deposition (PLD) technique with a KrF excimer laser (248 nm, 2 J/cm²) under a wide range of H2O pressures at a substrate temperature of 600℃. Sintered hydroxyapatite (HA) was used as the target. The background H2O pressure during deposition critically affected the density and the composition of the deposited films. With increasing H2O pressure, the growth rate increased, and the mass deposited was almost constant. Consequently, the density gradually decreased with H2O pressure, resulting in a porous microstructure under 0.37 Torr. The Ca/P ratio of the film decreased with H2O pressure, and the crystal structure of the deposited film changed in accordance with the Ca/P ratio. The observed peaks were from hydroxyapatite (Ca/P = 1.67) for H2O pressures above 0.13 Torr, and the peaks from high Ca/P phases, such as tetracalcium phosphate [Ca4O(PO4)2, Ca/P = 2] and CaO (Ca/P = ∞), were observed for the film deposited at 0.02 Torr. A high-density hydroxyapatite film with a high degree of crystallinity was obtained under a H2O pressure of 0.25 Torr.