Laser nano- and micro-structuring of silicon using a laser-induced plasma for beam conditioning

A technique based on the interaction between a laser pulse and a laser-induced plasma is proposed as a very simple and potentially powerful method for surface nanostructuring. A laser pulse was focused onto a metallic target in order to generate a plasma, while a second laser pulse was directed to the plasma and crossed it perpendicularly to the first pulse and, subsequently, hit a silicon substrate. In this conditions, the second pulse interacts with the plasma which acted as an optical element whose properties could be modified by varying the energy density of the first pulse or the delay between the two pulses. Microscopic analysis carried out on the silicon surface revealed a wide variety of nanostructured patterns.

Tailored synthesis of nanostructures by laser irradiation of a precursor microdroplet stream in open-air

A method to synthesize multicomponent nanostructures in open-air is presented. A microdroplet precursor target is irradiated with a nanosecond laser pulse to induce plasma. At low droplet dispensing rates, the precursor and solvent are fully atomized without debris to produce nanoparticles and nanofilaments during plasma cooling. More complex structures like nanolayers or nanofoams can be synthetised at kilohertz droplet dispensing rates as additional droplets in the vicinity of the target droplet are subjected to the laser-induced plasma and its associated shockwave. Examples of both low- and fast-rate mechanisms are presented for Mn-Fe bi-metal oxide nanoparticles and zinc oxide nanoparticles, nanofilaments and nanofoams. Real-time diagnostics were carried out with time-resolved imaging, atomic emission spectroscopy, light scattering and shadowgraphy. In addition to overcoming some of the difficulties associated with pulsed-laser deposition (PLD), the use of a liquid precursor whose composition can be tailored on a droplet-to-droplet basis opens a number of possibilities.

Micro- and nanoparticle generation during nanosecond laser ablation: correlation between mass and optical emissions

The particulate emission during nanosecond ablation of gold targets was investigated at various fluences (10-100 Jcm(-2)) and vacuum levels (0.05-750 Torr). Atomic emission spectra were acquired during the ablation process and post-mortem characterization of particle spatial distribution was performed using scanning electron microscopy. The discussion of the results in the context of existing theoretical models permitted the identification of four distinct mass removal mechanisms. While the presence, shape and intensity of atomic emission lines is a telltale of the nanoparticle formation process, the fluctuations of the emission signal over a number of laser shots was linked to the production of microscopic debris.