Phase transformations induced in Ge1Sb2Te4 films by single femtosecond pulses

We have investigated the phase transformations induced in a Ge1Sb2Te4 system by a femtosecond laser exposure. The system has a multilayer structure of 10 nm ZnS–SiO2/(10–100 nm) Ge1Sb2Te4/80 nm ZnS–SiO2/0.6 mm polycarbonate substrate. The morphology and contrast of marks written in both amorphous and crystalline backgrounds by single fs pulses were characterized using an optical microscope. X-ray diffraction was applied to identify the crystal structures formed by single 108 fs shots. The characteristics and the conditions of crystalline → amorphous or amorphous → crystalline transitions in the multilayer structures with different Ge1Sb2Te4 layer thickness triggered by single shots were investigated. The pulse energy window for the crystallization or amorphization in the Ge1Sb2Te4 systems was established. The mechanism of phase changes triggered by femtosecond laser pulses is discussed.