TY - JOUR
T1 - Hydroxyapatite and lead-substituted hydroxyapatite near-surface structures
T2 - Novel modelling of photoemission lines from X-ray photoelectron spectra
AU - López, Elvis O.
AU - Bernardo, Pablo L.
AU - Checca, Noemi R.
AU - Rossi, André L.
AU - Mello, Alexandre
AU - Ellis, Donald E.
AU - Rossi, Alexandre M.
AU - Terra, Joice
N1 - Funding Information:
The authors wish to thank the Synchrotron Light Brazilian National Laboratory (LNLS) in Campinas-Brazil for the XRD measurements; the X-ray Diffraction Multiuser Lab at CBPF; the Biomaterials Lab (LABIOMAT) at CBPF for the synthesis of hydroxyapatite and PbHA powder,the Multiuser Laboratory of Surfaces and Nanostructures of the CBPF for XPS measurements, the Brazilian government agencies CAPES, CNPq and FAPERJ for the scholarships grant awarded; and the High Performance Computing Center (COTEC) of the CBPF, where part of the electronic structure calculations was performed.
Publisher Copyright:
© 2021 Elsevier B.V.
PY - 2022/1/1
Y1 - 2022/1/1
N2 - X-ray photoelectron spectroscopy (XPS) is one of the main tools for hydroxyapatite (HA) surface characterization in developing materials for biomedical and heterogeneous catalysis. Despite the XPS technique's potential to correlate binding energies with existing photo-emitter sites on near-surfaces, few previous studies analyzed this aspect for HA and metal-substituted HA surfaces. In this work, we theoretically reconstructed the XPS spectra of stoichiometric HA and lead-substituted hydroxyapatite (PbCaHA, Ca10-xPbx(PO4)6(OH)2; x = 2, 10) using a first-principles linear combination of atomic orbitals embedded cluster approach and periodic supercell band structures within the framework of Density Functional Theory (DFT). We take into account photoemission lines contributions from Ca(1), Ca(2), Pb(1) and Pb(2) sites located on surface and near-surface depths (up to ∼15 Å) along the (0 0 1) and (1 0 0) surfaces. The calculated DFT spectra of HA and PbCaHA were compared with high-resolution XPS spectra previously characterized by synchrotron X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). A combined theoretical and experimental approach enables decoding of the complex structure of HA and PbCaHA in XPS spectra. It was found that XPS binding energies profiles depend significantly on photo-emitters from near-surface sites and surface crystallographic orientation. The main Ca 2p3/2 envelope peak in HA is predominantly from Ca(1) and Ca(2) sites (∼347.4 eV), while the weaker peak is due to the Ca(2) site only (∼345.0 eV). Variations on HA nanoparticle morphology could be a critical factor for changes in XPS binding energies' profile.
AB - X-ray photoelectron spectroscopy (XPS) is one of the main tools for hydroxyapatite (HA) surface characterization in developing materials for biomedical and heterogeneous catalysis. Despite the XPS technique's potential to correlate binding energies with existing photo-emitter sites on near-surfaces, few previous studies analyzed this aspect for HA and metal-substituted HA surfaces. In this work, we theoretically reconstructed the XPS spectra of stoichiometric HA and lead-substituted hydroxyapatite (PbCaHA, Ca10-xPbx(PO4)6(OH)2; x = 2, 10) using a first-principles linear combination of atomic orbitals embedded cluster approach and periodic supercell band structures within the framework of Density Functional Theory (DFT). We take into account photoemission lines contributions from Ca(1), Ca(2), Pb(1) and Pb(2) sites located on surface and near-surface depths (up to ∼15 Å) along the (0 0 1) and (1 0 0) surfaces. The calculated DFT spectra of HA and PbCaHA were compared with high-resolution XPS spectra previously characterized by synchrotron X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). A combined theoretical and experimental approach enables decoding of the complex structure of HA and PbCaHA in XPS spectra. It was found that XPS binding energies profiles depend significantly on photo-emitters from near-surface sites and surface crystallographic orientation. The main Ca 2p3/2 envelope peak in HA is predominantly from Ca(1) and Ca(2) sites (∼347.4 eV), while the weaker peak is due to the Ca(2) site only (∼345.0 eV). Variations on HA nanoparticle morphology could be a critical factor for changes in XPS binding energies' profile.
KW - Density functional theory (DFT)
KW - Hydroxyapatite
KW - Hydroxylpyromorphite
KW - Surface spectroscopy
KW - X-ray photoelectron spectroscopy (XPS)
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U2 - 10.1016/j.apsusc.2021.151310
DO - 10.1016/j.apsusc.2021.151310
M3 - Article
AN - SCOPUS:85115886639
SN - 0169-4332
VL - 571
JO - Applied Surface Science
JF - Applied Surface Science
M1 - 151310
ER -