Nanostructure of calcium phosphate films synthesized by pulsed laser deposition under 1 Torr: Effect of wavelength and laser energy

Abstract

In this study, we investigated aspects about the nanostructure of calcium phosphate films formed by pulsed laser deposition under a high-pressure gas (argon) environment (1 Torr) that are not addressed in the literature by using infrared and green laser sources. The plume generated from an ablated hydroxyapatite target was deposited directly over transmission electron microscopy (TEM) grids during 120 s to allow for the use of TEM techniques to investigate the morphology, composition and structure of deposited films from the micron to the nanoscale. The films were found to comprise five different calcium phosphate structures: (1) unstructured amorphous thin film formed by the deposition of ions and molecules over the substrate, (2) dense nanoparticles (<20 nm) formed over the substrate, (3) low Ca/P ratio spherical particles (<400 nm) formed on the way to the substrate, (4) rich Ca/P ratio ring-shaped particles (>400 nm) ejected from the target and (5) crystalline particles (~500 nm) removed from the target. Although all samples presented these five structures, the morphology, abundance and size population were all different. This work opens a window to elucidate the complex mechanism underlying calcium phosphate film deposition and growth by pulsed laser deposition.