Calcium phosphate phase identification using XPS and time-of-flight cluster SIMS

Reproducible time-of-night cluster static secondary ion mass spectra (ToF-SSIMS) were obtained for various standard calcium phosphate (CP) powders, which allowed for phase identification. X-ray diffraction was not able to detect signals from microscopic amounts of CP (similar to 15 mmol m(-2)). The phases studied were alpha-tricalcium phosphate [alpha-Ca-3(PO4)(2)], beta-tricalcium phosphate [beta-Ca-3-(PO4)(2)], amorphous calcium phosphate [Ca-3(PO4)(2). xH(2)O], octacalcium phosphate [Ca8H2(PO4)(6). H2O], brushite (CaHPO4. 2H(2)O), and hydroxyapatite [Ca-10(PO4)(6)(OH)(2)]. The SIMS spectra were obtained via bombardment with (CsI)Cs+ projectiles. X-ray photoelectron spectroscopy (XPS) core levels of the P 2p, Ca 2p, and O Is orbitals and the relative O Is loss intensity were examined. The PO3-/PO2- ratios from ToF-SSIMS spectra in conjunction with XPS of the CP powders showed much promise in differentiating between these phases at microscopic CP coverages on the metal oxide surface.