Reverse-directional explosive crystallization of microstructures in transparent film on absorbing substrate by a multipulse femtosecond radiation

The crystallization in a transparent precursor of a perovskite ferroelectric film deposited on an absorbing platinized silicon substrate initiated by multipulse femtosecond sharply focused laser beam of near-infrared spectral range is studied by transmission electron microscopy. Time dependences of the shapes of crystallized areas point to initiation of explosive crystallization with a seed on the opposite side of a heat source localized in a platinum interface layer. The radius of the crystalized semispheres varies from 150 to 900 nm, with maximal crystallization velocity up to 1.2 cm/s. Reverse direction of the spherical wave front propagation regarding to a heat source is explained in terms of the developed model based on thermal stress-induced modification of the activation energy.