Electron diffraction from micro- and nanoparticles of hydroxyapatite

Hydroxyapatite (HAP) obtained from aqueous solutions under different conditions has been examined by high-resolution transmission electron microscopy (HRTEM) and electron diffraction, including selected-area electron diffraction (SAED) and microdiffraction. A Philips CM300 field-emission gun electron microscope with a Schottky W/ZrO field-emission tip and a spherical aberration constant of 0.65 mm was used at 300 kV. The HAP crystals had different sizes, ranging from a few nanometres to a few micrometres. Single-crystal diffraction patterns have been obtained from the largest microcrystals using the conventional SAED technique. Assemblies of nanoparticles gave only broad diffuse rings. Nevertheless, microdiffraction with electron microprobes 3.5-10 nm in diameter clearly indicated the crystalline character of the nanoparticles in these assemblies. Experimental HRTEM images, Fourier transforms and calculated images exhibited the fine structure of the HAP crystals.