A direct comparison of sizes characterized by TEM and APM for Fe2O3 nanoparticles prepared by laser ablation

In order to clarify the relationship between nanoparticle size data obtaine d by atomic force microscopy (AFM) and that obtained by transmission electr on microscopy (TEM), we compared images of the same Fe2O3 nanoparticles obt ained by laser ablation under 133 to 800 Pa of Ar. First, Fe2O3 nanoparticl es deposited on NaCl single crystals by laser ablation were characterized b y AFM. The same area of the samples was then analyzed by TEM after the depo sition of carbon films and the removal of the NaCl substrate. Fe2O3 was dep osited under 133 to 800 Pa of Ar. Under these conditions, aggregates of nan oparticles started to form and the size of the aggregates as found by TEM i ncreased with the pressure. The particle size obtained by AFM images corres ponded not to nanoparticles constituting aggregates but to aggregates thems elves. This indicates that when AFM is used to characterize the sizes of th e nanoparticles, we must be aware of the possibility of aggregated nanopart icles. Our results indicate that AFM can be used to characterize nanopartic le sizes accurately only when the tip curvature radius is much less than th e nanoparticle sizes and when the nanoparticles are well isolated compared to the curvature radius of the tip.