Elsevier

Surface and Coatings Technology

Volume 279, 15 October 2015, Pages 16-24
Surface and Coatings Technology

Nanoscale analysis of calcium phosphate films obtained by RF magnetron sputtering during the initial stages of deposition

https://doi.org/10.1016/j.surfcoat.2015.08.021Get rights and content
Under an Elsevier user license
open access

Highlights

  • Nanostructure of calcium phosphate films deposited by magnetron sputtering

  • Calcium phosphate nanospheres identified within the early stages of deposition

  • Presence of nanocrystalline regions after sputtering for 60 s

  • Hydroxyapatite nanocrystals observed in association with nanospheres

Abstract

In the present work, we investigated the nanostructure of calcium phosphate films formed during the initial stages of deposition (between 30 and 240 s; deposition rate of 3.7 nm/min) by radio-frequency magnetron sputtering. The sputtering deposition parameters and the plasma energy were previously adjusted to produce nearly stoichiometric nanocrystalline hydroxyapatite films after 180 min. Grazing-incidence X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the films formed in the initial stages were composed of an amorphous calcium phosphate phase with a Ca/P ratio Ca/P = 1.60 ± 0.12, which is close to that of hydroxyapatite. Using high-resolution transmission electron microscopy, we demonstrated that the films were not a unique amorphous phase. An additional phase composed of dense calcium phosphate nanospheres was found in all periods and investigated. The nanospheres grew in size as the deposition time increased, and small nanospheres were always observed. This observation suggests the continuous formation of nanospheres at the surface of the film. Nanocrystalline regions were revealed by electron diffraction and high-resolution electron microscopy after a deposition of 60 s with a corresponding film thickness of 3.7 nm. Electron energy-loss spectroscopy analysis comparing individual nanospheres to the amorphous calcium phosphate layer showed differences in the oxygen K edge, suggesting a difference in the chemical bonding of the oxygen species. Nanospheres were observed in association with isolated crystals, suggesting that the nanospheres may participate in the crystallization of hydroxyapatite according to a heterogeneous nucleation process.

Keywords

Amorphous calcium phosphate
RF magnetron sputtering
Transmission electron microscopy
Hydroxyapatite

Cited by (0)