Self-organized structures in thin films of phase-change material upon femtosecond laser excitation: From periodic ordering to ablation

Abstract

The paper describes a multistage process of surface nanostructuring which precedes the ablation of a Ge2Sb2Te5 thin film under femtosecond laser irradiation. Three forms of surface reconfiguration can be observed depending on the intensity and/or the number of laser pulses, all of them being of different origin. Low-energy irradiation leads to the formation of regular glassy nanospheres equal in size. We assume that the spheres result from the splitting of melted thin threads, as Plateau–Rayleigh instability foretells. In turn, melted threads are electromagnetic in nature: the interference between a surface plasmon-polariton wave and an incident light wave causes spatial temperature modulation and further melting at interference pattern maxima. Higher energies induce mass transfer processes and entail transformation of chains of nanospheres into alternating ridges and valleys. The last stage is achieved at critically high energy values and is simply the evaporation of the film from the substrate.