Laser-mediated nanoparticle synthesis and self-assembling

Abstract

Elemental and compound nanoparticles (NPs) are increasingly attractive due to their peculiar physico-chemical properties. Any large scale application of NPs requires a strict control on their synthesis and self-assembling. Inherent to the synthesis stage is the control of size, shape, composition, structure of the single NP. When NPs self-assemble on a suitable substrate the morphology and nanostructure of the NP architecture are the key parameters driving the performance of the resulting artificial surface. Pulsed laser ablation allows to pursue the above goals under different conditions including nanosecond and ultra-short femtosecond laser pulses, as well as an ambient fluid, either a gas at high pressure, or a radiation transparent liquid, besides vacuum. In this chapter we offer an outline of the mechanisms underlying NP synthesis in the above environments and of the most popular models currently recognized in the literature to interpret observed experimental trends. Concerning plasma plume propagation through an ambient gas attention is focused on the prediction versus observation of the size of isolated NPs and on a critical discussion of the morphology—properties relationship of noble metal NP arrays, considering their optical properties in the frame of enhanced vibrational spectroscopies (SERS). Ablation in a liquid of a solid target leads to a chemically stable suspension of different nanostructures in a one-step, environment friendly, clean process. For noble metal NPs the effect of liquid layer thickness and laser spot diameter on the concentration, size distribution and mutual aggregation of the produced NPs is discussed in relation to a more general picture of the process. Irradiation under vacuum with ultra-short fs laser pulses is a clean physical method to synthesize NPs; indeed in the majority of materials, random stackings of NPs, whose size ranges between 10 and 100 nm constitute the deposited film. Selected experiments on NP synthesis upon fs ablation of mainly elemental targets are reviewed focusing mainly on the features of the expanding plasma and on established mechanisms of NP synthesis. Possible lines of future development in the field are envisaged.