Ion-beam densification of hydroxyapatite thin films

The goal of this study is to demonstrate the feasibility of using ion irrad iation to densify a porous ceramic film. Ion irradiation is a room-temperat ure process, and thus may be preferable to the use of conventional high tem perature sintering, which is typically performed at temperatures in excess of 1000 degrees C. Thin films of the bio-ceramic hydroxyapatite (HA), Ca-10 (PO4)(6)(OH)(2), were deposited on silicon substrates using a sol-gel techn ique, The films processed in this study were 600 nm thick and had a density of 36% of fully dense HA, after drying at 620 degrees C for 3 min. The dri ed films were irradiated with 1 and 2 MeV Si++ ions with fluences ranging f rom 10(14) to 6x10(15) ions/cm(2). Samples irradiated with the largest flue nce reached densities of 83% of that of fully dense HA. Rutherford backscat tering spectrometry was used to verify the HA stoichiometry of the films an d to obtain the areal density. Scratch testing showed that implantation led to a substantial improvement in scratch resistance. Nano-indentation was a lso used to characterize the mechanical properties of the films. The hardne ss was increased by a factor of 15 by the irradiation. X-ray diffraction wa s used to characterize the crystalline phases present in the film. Ion irra diation caused some decrease in the already small degree of crystallinity o f the film. The advantage of ion-implantation over high temperature sinteri ng is shown as no secondary crystalline phases appear after densification. (C) 1998 Elsevier Science B.V. All rights reserved.