Femtosecond-laser-induced bond breaking and structural modifications in silicon, TiO $$_2$$ 2 , and defective graphene: an ab initio molecular dynamics study

Abstract

By exciting or heating electrons, ultrashort laser pulses have a direct influence on bond strengths in two- and three-dimensional solids. Here, we present results of ab initio molecular dynamics simulations performed using our in-house Code for Highly-excIted Valence Electron Systems (CHIVES) for three systems, which each shows a distinctly different structural response to a femtosecond laser pulse. In solid silicon, we show that ultrafast laser-induced bond breaking leads to nonthermal melting, a process which occurs in three stages, involving subsequently superdiffusive, fractionally diffusive, and normally diffusive atomic motions. For TiO $$_2$$ , we find that the A $$_{1g}$$ phonon is coherently excited. At room temperature, we demonstrate that these oscillations are strongly coupled to other phonon modes. In graphene with a single Stone–Wales defect, we study the in-plane and out-of-plane laser-induced atomic motions and find bond breaking, which destroys the structure, when the electrons are heated to at least 31,000 K.