Department of Engineering and System Science, National Tsing-Hua University,
Hsinchu, Taiwan 300
| The silver nanoparticles were synthesized by mixing 10 ml 0.5 mM AgNO3, 10 ml 0.5 mM trisodium citrate, and 0.6 ml 10 mM NaBH4 at room temperature. Right after mixing, the solution turned gold-yellow color indicating that silver nanoparticles were formed. It was discovered accidentally that the produced silver nanoparticles change color from gold to red-brown by laser irradiation during dynamic light scattering measurement (with Argon laser, wavelength 488 nm). The UV-vis absorption spectra of the laser irradiated solutions containing the silver nanoparticles exhibit two absorption peaks centered at 400 nm and about 550 nm wavelength. The intensity of the 550 nm peak increases with increasing laser exposure time while the intensity of the 400 nm peak decreases with increasing exposure time. This indicates the shape transformation from globular particle into short rod-like particle due to the laser irradiation. The small-angle X-ray scattering from the laser irradiated samples also confirm the formation of rod-like particles. The analysis shows that these as-produced silver particles have a mean radius of about 6.6 nm and the laser induced rod-like particles have a length of about 28 nm and a radius of the cross section about 8 nm (an aspect ratio of 1.75). It is likely that laser irradiation can cause closely adjacent globular silver nanoparticles to fuse together to form a rod-like particle. |
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