Ultrasound-Assisted Fusion of Preformed Gold Nanoparticles

The influence of ultrasound waves (20 kHz) of high intensity (40 W.cm(-2)) on preformed citrate-protected gold nanoparticles (average diameter 25 +/- 7 nm) is demonstrated in pure water and in the presence of surfactants. Ultrasonic treatment for 20 min is sufficient to fuse gold nanoparticles at the contact in a dumbbell-like structure. Gold nanoparticles acquire a worm-like or ring-like structure after 60 min of sonication in water. Fused nanoparticles with spherical or oval shapes are formed after ultrasonic treatment in the presence of sodium dodecyl sulfate or dodecyl amine solutions. Dispersion of nanoparticles is found as an additional process during sonication, which is the weakest in pure water. The crystalline face centered cubic structure of ultrasonically treated gold nanoparticles is defected by ultrasound. The reported results could be of interest for ultrasonic melting of inorganic materials at the nanoscale to produce metal structures with different morphologies and properties.