Femtosecond laser processing of germanium: anab initiomolecular dynamics study

Abstract

An ab initio molecular dynamics study of femtosecond laser processing of germanium is presented in this paper. The method based on the finite temperature density functional theory is adopted to probe the structural change, thermal motion of the atoms, dynamic property of the velocity autocorrelation, and the vibrational density of states. Starting from a cubic system at room temperature (300 ‫)ܭ‬ containing 64 germanium atoms with an ordered arrangement of 1.132 ݊݉ in each dimension, the femtosecond laser processing is simulated by imposing the Nose Hoover thermostat to the electronic subsystem lasting for ~100 ‫ݏ݂‬ and continuing with microcanonical ensemble simulation of ~200 ‫.ݏ݂‬ The simulation results show solid, liquid and gas phases of germanium under adjusted intensities of the femtosecond laser irradiation. We find the irradiated germanium distinguishes from the usual germanium crystal by analyzing their melting and dynamic properties.

Ab initio evidence for nonthermal characteristics in ultrafast laser melting

“…However, the RMSD rapidly increases unreasonably to 2.3Å in 400 fs, much larger than 0.6Å as observed in experiment 4 . More importantly, lattice temperature rapidly increases to T > 1400 K in 160 fs, which is a common feature of TTM reported also for Ge melting 26 , implying a thermal process. After all, the energy required to reach T e = 2.5 × 10 4 K is ∼ 4 times larger than the energy input from laser pulses (Table I), violating energy conservation law.…”

Study of mechanical properties and subsurface damage of quartz glass at high temperature based on MD simulation

“…MD simulation has been widely applied in the study of nanomachining process. It can simulate the nanoscale processing of many materials, like Cu [Zhang, 2011], Ge [Ji and Zhang, 2013], Si [Renke and Zhuji, 2006] and glasses [Liang et al, 2007;Pedone et al, 2008;Nath, 2013;Kilymis and Delaye, 2013]. They investigated the nanoscale processing, mechanical properties and surface modification though radiation of those materials, providing important support for ultra-precision machining.…”

Effects of Film Thickness on Femtosecond Laser Spallation and Ablation of Silver Film

“…Considerable attentions have been drawn in studying the ultrafast laser interaction with metal film. When the laser pulse duration is in the time scale shorter than picosecond, the nonequilibrium between the laser excited hot electron subsystem and the cold lattice subsystem is significant, which cannot be solved by using the classical heat transfer methods and models [7]. Therefore, the two-temperature model was proposed to describe the nonequilibrium state [8].…”

“…Therefore, the two-temperature model was proposed to describe the nonequilibrium state [8]. In this paper, a multiscale framework integrating the quantum mechanics (QM), molecular dynamics (MD) and two-temperature model (TTM), which was constructed in our previous work [7,9,10], is to be employed to fulfill the simulation of femtosecond laser irradiation on the silver film.…”