Laser-assisted generation of elongated Au nanoparticles and analysis of their morphology under pulsed irradiation in water and CaCl2 solutions

Abstract

Abstract In this work we investigate the formation of elongated gold nanoparticles (NPs), which occurred by laser ablation of gold target in aqueous solutions containing CaCl2. In all our experiments Ytterbium fiber laser (wavelength at 1060-1070 nm, pulse width of 200 ns, pulse repetition rate of 20 kHz, pulse energy of 1 mJ) was used as a radiation source. In the present work first, laser-assisted formation of elongated Au nanoparticles by ablation of a solid Au (99, 99%) target in liquid was done using this laser source. Extinction spectra correlating with TEM images of the mentioned above nanoparticles show the appearance of absorption signal in red region and near IR-spectrum that corresponds to longitudinal plasmon resonance of electrons in elongated nanoparticles. Second, generated elongated Au nanoparticles were exposed to pulsed laser beam with different pulse energy and ablation time. The peculiarity of the experiments is the use of additives of bivalent cations. The experiments on irradiation of the gold target by laser ablation in liquid were carried out in water obtained by Milli-Q purification system with different concentration of calcium chloride (CaCl2). Extinction spectra show pronounced shift to red region in the absorption maximum with increasing concentration. Results of other experiments show that formation of elongated gold nanoparticles as chains is common process under laser ablation of the solid target in the presence of some divalent ions in water. The paper discusses the mechanisms of formation of elongated nanoparticles by laser ablation of solids depending on the concentration of divalent ions in the liquid and the time of laser exposure.