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

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2014-01, Vol.114 (1), p.1-9
• Main Authors: Zijlstra, Eeuwe, Zier, Tobias, Bauerhenne, Bernd, Krylow, Sergej, Geiger, Philipp, Garcia, Martin
• Format: Article
• Language: English
• Subjects: Bonding; Breaking; Diffusion; Diffusion welding; Dynamical systems; Graphene; Molecular dynamics; Titanium dioxide
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-013-8080-x

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.