Laser Ablation of Nanoparticles: A Molecular Dynamics Study

Abstract

We study laser ablation of nanoparticles (NPs). The interaction of a high-intensity laser pulse with NPs brings the NP into a highly non-equilibrium state. Depending on the energy input from the laser, it will melt and may fragment and evaporate off atoms and clusters. We employ molecular dynamics simulation to study this interaction since thermodynamic properties can be extracted from output data of this simulation. The interatomic interaction is modeled by a Lennard-Jones (LJ) potential. The intensity of the laser is above the ablation threshold. The NP has been chosen to have a spherical shape with diameter 50 s in LJ units. The laser energy is given to the NP instantaneously at the beginning of the simulation and homogenously to all atoms; it corresponds to an energy input of 5.4 e per atom. The simulation is continued up to a time 200 t in LJ units. Temperature-density phase-space trajectories show that the nanoparticle density and temperature strongly decrease after the irradiation. The pressure in the sphere becomes strongly tensile after irradiation. The ablation proceeds by spallation of the irradiated cluster. We provide an analysis of the fragments produced by the ablation of the spherical NP. Our results are contrasted to the case of laser ablation of a thin-film target.

Influence of heating and cooling rates on thermodynamic properties of aluminum thin film from 300 to 1100 K

“…The increasing pressure (positive change) brought the atoms closed together and shrink the system, while the decreasing pressure indicate that the system is expanding. For higher negative pressure, it is known that it will tear the system into multiple void as in the case of ultrashort laser irradiation [1,2]. For the case of the highest heating rate, i.e., 80 K/ps, the system as shown in Figure 1 (a), composed mostly by high temperature atoms at t = 10 ps.…”

“…It consists of several types of treatment including heating and cooling which respected to period of time where it significantly changes the phase of a material. In a short time scale, heating could be done through laser irradiation [1,2] while for other significance of heating rate will gives benefit, e.g., in the context of fluorine containing slag [3].…”

Influence of thickness on heat treatment from 300 to 1100 K of aluminum thin film

“…In the context of thermal properties, it is interesting to observe the behavior of thin film corresponds to its thickness. In a way where heating could be done in a short time scale, it will gives information on the phase transition of the thin film, such as effected by ultrashort laser irradiation [2,3].…”

Structural change of aluminum thin film in the temperature range from 300 K to 1000 K

“…MD simulation could provide atomistic point of view of structural change since it follows the trajectory of the atoms within the simulation. In the general case where Lennard-Jones material is considered to shows the evolution of laser induced structural change of nanoparticle and thin film, Fahdiran and Urbassek [4,5] used MD simulation to show the small-angle scattering structural change due to heat absorbed from the laser. The results show that MD simulation could give insight into the material, especially the structure of the system.…”