Multiscale Modeling of Laser Ablation: Applications to Nanotechnology

Computational modeling has a potential of making an important contribution to the advancement of laser-driven methods in nanotechnology. In this paper we discuss two computational schemes developed for simulation of laser coupling to organic materials and metals and present a multiscale model for laser ablation and cluster deposition of nanostructured materials. In the multiscale model the initial stage of laser ablation is reproduced by the classical molecular dynamics (MD) method. For organic materials, the breathing sphere model is used to simulate the primary laser excitations and the vibrational relaxation of excited molecules. For metals, the two temperature model coupled to the atomistic MD model provides an adequate description of the laser energy absorption into the electronic system and fast electron heat conduction. A combined MD finite element method and the dynamic boundary condition are used to avoid reflection of the laser-induced pressure wave from the boundary of the MD computational cell. The direct simulation Monte Carlo method is used for simulation of the long term ablation plume expansion, and the MD method is used to simulate film growth by cluster deposition from the ablation plume. The proposed multiscale approach is applied to investigate the mechanisms of cluster formation in laser ablation and to analyze the distributions of clusters of different sizes in the ejected plume. MD simulations of cluster deposition are performed for different impact velocities and a strong dependence of the structure of the growing films on the parameters of the deposited clusters is revealed. A new technique for controlled implantation of functional organic molecules into sub-micron regions of a polymer substrate is investigated in molecular-level simulations and different regimes of molecular transfer are discussed. 1 Department of Materials Science & Engineering, University of Virginia; 116 Engineer’s Way, Charlottesville, Virginia 22904