Examination of silver nanoparticle fabrication by pulsed-laser ablation of flakes in primary alcohols

This paper describes the formation and subsequent behavior of silver nanoparticles (NPs) observed by optical spectra, atomic force microscopy, and transmission electron microscopy in primary alcohols by nanosecond pulsed-laser irradiation (1064 and 532 nm, typically at 1 J/(cm(2) pulse)) of silver flakes. Effects of the carbon chain length of the solvents and the irradiation atmosphere of the solutions on the Ag NP formation were investigated. The effect of alcohol chain length in aerated solutions can be described as follows: (1) in short-chain alcohols such as methanol and ethanol, the NPs are extremely unstable and easily settled down to form precipitates by centrifugation treatment; (2) very stable NPs are formed with an appreciably smaller particle size distribution in alcohols with chain lengths from C-3 to C-5 than in alcohols with longer chain length than C-5; (3) the yield of NPs is dependent on the alcohol chain length. On the other hand, the yield of NPs is greater in Ar- and N-2-saturated solutions than in aerated solutions. Additionally, the yield is similar regardless of the chain length, with smaller size distributions than those in air-equilibrated solutions. Oxygen molecules dissolved in the solvents are responsible for these observations. The oxygen effect consists of two Parts: (1) the scavenging of electrons generated by the plasma formation and thermionic emission due to extremely high temperature under the ablation condition; (2) the formation of an oxide layer on the surface of particles that hampers further growth processes to form NPs. Furthermore, we observed the formation of string segments in evacuated ethanol due to coagulation and coalescence of bare metal particles, giving rise to the splitting of the plasmon band. Thus we demonstrated that the systematic change in the solvent and irradiation atmosphere can control the particle size and size distribution. The present findings may add a new aspect to better manipulate NP fabrication based upon the laser ablation method.