X‐ray photoelectron spectroscopy applied to gold‐decorated mineral standards of biological interest

Reproducible high resolution spectra of nonconducting minerals of interest in biological calcification have been obtained by x‐ray photoelectron spectroscopy, utilizing a technique we call biased referencing, a combination of gold decoration and electron charge neutralization of the samples. Minerals examined were hydroxyapatite [Ca10(PO4)6(OH)2], fluorapatite [Ca10(PO4)6F2], calcium carbonate (CaCO3), octacalcium phosphate [Ca8H2(PO4)6 ⋅ 5H2O], monetite (CaHPO4), brushite (CaHPO4 ⋅ 2H2O), calcium pyrophosphate (Ca2P2O7), and an amorphous calcium phosphate synthesized at neutral pH (Ca/P=1.47). Samples were pressed into thin wafers onto which a small gold dot was affixed by vacuum deposition. Biased referencing provided calibration of sample core level ionizations (O 1s, Ca 2p, P 2p, F 1s, and C 1s) to the Fermi level of Au 4f7/2 set at a conductive value of 84.0 eV. Measured binding energies represent initial data for these gold‐decorated insulators and may be used to compare data similarly generated from mineralized biological tissues.