Characteristics of nanoparticles formed during pulsed laser ablation of SrBi₂Ta₂O₉

Particle formation was investigated during laser ablation of strontium bismuth tantalate (SBT) with a background of pure oxygen (O₂). For an O₂ pressure, P_O2, varying from 210 to 1300Pa, the mean particle size ranged from 9 to 22nm, and the particle concentration ranged from about 10¹² to 10⁸ cm^-3. For P_O2 = 210 Pa, the particle size ranged from 5 to 30 nm, and for P_O2 = 1300 Pa, the particle size ranged from 10 to 80 nm. Transmission electron microscopy measurement of particles sizeclassified at 10 and 20 nm showed that some particles were spherical and others were irregularly shaped. Electron diffraction of the particles showed that the spherical particles were partially crystallized whereas the irregularly shaped particles were amorphous. The formation of these two different morphologies is attributed to different particle cooling rates stemming from spatially nonuniform gas temperatures induced by laser ablation. Regardless of their shape, the particles were composed of strontium, bismuth, tantalum, and oxygen.