Calcium Phosphate Phase Identification Using XPS and Time-of-Flight Cluster SIMS.
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abstract
Reproducible time-of-flight 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 (15 mmol m(-)(2)). The phases studied were -tricalcium phosphate [-Ca(3)(PO(4))(2)], -tricalcium phosphate [-Ca(3)(PO(4))(2)], amorphous calcium phosphate [Ca(3)(PO(4))(2)xH(2)O], octacalcium phosphate [Ca(8)H(2)(PO(4))(6)H(2)O], brushite (CaHPO(4)2H(2)O), and hydroxyapatite [Ca(10)(PO(4))(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 1s orbitals and the relative O 1s loss intensity were examined. The PO(3)(-)/PO(2)(-) 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.