Femtosecond laser processing of germanium: An ab initio molecular dynamics study

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 K) containing 64 germanium atoms with an ordered arrangement of 1.132 nm in each dimension, the femtosecond laser processing is simulated by applying a Nosé-Hoover thermostat to the electronic subsystem for ∼100 fs and continuing with a microcanonical ensemble simulation of ∼200 fs. The simulation results show solid, liquid and gas phases of germanium under adjusted intensities of the femtosecond laser irradiation. We find that the irradiated germanium is distinguishable from the usual germanium crystal by analysing their melting and dynamic properties.