Pressure dependence of the morphology and size of cobalt (II,III) oxide nanoparticles prepared by pulsed-laser ablation
The effect of ambient Ar pressure on the mean diameters and aggregate state of cobalt (II,III) oxide nanoparticles prepared by pulsed-laser ablation is investigated. TEM images show that the mean diameters of the primary nanoparticles are in the range 1.2-3.2 nm when the ambient pressure is varied from 13.3 Pa to 13.3 kPa. With the increase of Ar pressure, the mean diameters of the primary nanoparticles increase and show a maximum at a pressure of 100 Pa. A further increase of ambient pressure results in a decrease in mean diameter of the primary nanoparticles. In the pressure range from 267 Pa to 2.67 kPa, the mean diameters of the prepared nanoparticles are almost constant, and aggregated nanoparticles are observed. Above 2.67 kPa, aggregated Co3O4 particles dominate the ablated product and the mean diameter of the primary nanoparticles decreases with increasing ambient pressure. A dynamic process is suggested to explain the experimental results.