Nanoparticles and nanostructures formed by laser: What can we learn from the modeling?

Abstract

The processes involved in nanoparticle and nanostructure formation by laser are analyzed. Relative contributions of several mechanisms involved are compared. First, we consider the formation of "primary" particles and discuss the difference between femtosecond and nanosecond regimes. Then, "secondary" particle/aggregate formation is discussed. In particular, attention is focused on (i) direct cluster ejection from a target under rapid laser interaction; (ii) condensation/evaporation; (iii) fragmentation/aggregation processes during cluster diffusion; (iv) diffusion, aggregation, and/or coalescence. In addition, routes of control over particle size distribution are proposed. Possibility of formation of colloidal nanoparticles with very narrow size distribution is proven numerically. The role of such parameters as ablation yield, laser wavelength and laser fluence, and surface tension are examined. Finally, controlled nanoparticle selfassembly is discussed as a potential technique for future development of nanomaterials.

Evidence of diffusive fractal aggregation of TiO2 nanoparticles by femtosecond laser ablation at ambient conditions

“…9,10 When the laser pulse duration is reduced to less than a picosecond, PLD enters in the femtosecond regime (fs-PLD), and a different physical mechanism for ablation sets in. 11 In this case, since the pulse duration is shorter than the electron-phonon relaxation time, which is of the order of few picoseconds, the ablation mechanism is not due to thermal melting as in the ns case. Fractal nanostructures in the fs-PLD regime have been reported in different conditions.…”

“…Fractal nanostructures in the fs-PLD regime have been reported in different conditions. 6,7,11,12 Various formation mechanisms have been conjectured for fractal nanostructures in PLD experiments: they could form in flight during the plume expansion 13 or by nanoparticle diffusion and aggregation on the surface 7 or in both ways. In the literature it was suggested that diffusion of the ablated material after landing should play an important role in the fractal formation.…”

Composition of silicon fibrous nanostructures synthesized using ultrafast laser pulses under ambient conditions

“…The required conditions for web-like fibrous nanostructure generation is provided by parameters which includes laser power, pulse repetition rate and laser interaction time with material. The basic nanoparticles formation mechanisms with irradiation of ultrafast laser pulses discussed are particles that are directly ejected from by expulsion of molten material from the irradiated area and/or particles formed by nucleation in the vapour of laser generated plasma [25,26]. In the present experiment, the irradiation of silicon surface with MHz repetition rate femtosecond laser pulses maintains a supersaturated vapour system against the atmospheric pressure.…”

15. The problem of the Aryans and the Soma: Textual-linguistic and archaeological evidence

“…Cemeteries at several sites of the same Petrovska complex (Sintashta I, Uly ubai, Berlik and Satan) have produced the earliest known examples of light-wheeled horse-drawn chariots (Kuz'mina 1994). The Tazabag"yab culture, partly continuing the traditions of the earlier local Neolithic Kel'teminar culture, was characterised by limited irrigation agriculture and pastoral nomadism (sheep, cattle and horse); the necropolis of Kokcha 3 has warrior tombs (Itina 1961(Itina , 1977Francfort 1989,1: 424ff. The chariot has a rectangular body measuring 120*60-70 cm, an axle 140 cm wide and two wheels 90-120 cm in diametre, probably with 10-12 spokes.…”