Spherical silver colloidal nanoparticles 10-30 nm in size prepared in gelatin stabilized ammonia-tartrate electroless deposition solution were exposed to irradiation of a pulsed laser radiation at 532 nm, 400 nm and 266 nm. The unfocused beams of the second (532 nm) and the forth (266 nm) harmonics of Nd: YAG laser operating at 10 Hz (pulse width 15 ns) as well as of a Ti:sapphire laser (its second harmonic output) at 400 nm were used.
The morphological changes of silver nanoparticles caused by the laser irradiation were investigated as a function of incident laser fluence. According to TEM evidence, after laser irradiation at 40 mJ/cm2 the size and shape of nanoparticles was the same as the initial colloids. However, the morphology of nanoparticles was changed by laser irradiation above 100 mJ/cm2. TEM investigation showed that the initial small silver particles irradiated at 250 mJ/cm2 with 3000 pulses (for 5 min) transformed to the right-angled crystals 1400-1500 nm in size probably via fusion of photo-thermally melted nanoparticles. Electron diffraction data evidence that these crystals are not compact, but made up of great many small silver particles. The relative amount of the right-angled particles was estimated to be approximately 20%. At laser fluences higher than 350 mJ/cm2 spherical particles 70-180 nm in size were formed instead of the right-angled particles. It should be emphasized that the fine 10-30 nm-sized particles were present in the solution in all above-mentioned cases.
The distinct changes in absorption spectra of silver colloids due to morphological changes of nanoparticles were also observed.
Thus, in this paper we show the possibility to change the morphology of silver nanoparticles under laser irradiation of different fluences. The conditions favoring the transformation of nanoparticles shapes and sizes have been determined.