The application of ion beam analysis to calcium phosphate-based biomaterials

Ion beam technology may be applied in a straightforward fashion to the analysis and modification of biomaterials. For analytical purposes, characterization using megaelectron volt He²⁺ ions provides a standardless, nondestructive means for accurately quantifying the composition of material surfaces and the thickness of thin films. In this study, three complementary ion backscattering techniques were utilized to characterize hydroxyapatite (HA) films: Rutherford backscattering spectrometry (RBS) can determine composition and amounts of elements heavier than He; forward recoil elastic spectrometry (FRES) can determine hydrogen content; resonance-enhanced RBS can quantify small amounts of light elements, e.g. carbon, by choosing a particular incident beam energy resulting in excitation of the light element nucleus. At this resonance energy, the scattering cross section greatly increases, improving elemental sensitivity. Sol-gel chemistry was used to synthesize HA films by spin coating and annealing in a rapid thermal processor. Using these techniques, the chemical composition of unfired films was Ca_1.63O_5.4 H_1.8C_0.24P with a thickness of 3.01 x 10¹⁸ atoms/cm² and after firing at 800 °C as Ca_1.66O_4.0H_0.26C_0.09P with a thickness of 2.11 x 10¹⁸ atoms/cm². This compares favorably to stoichiometric HA, which has a composition of Ca_1.67O_4.33H_0.33P.