EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Phase switching in chalcogenide alloys (containing Ge, Te and Sb) is a commercially used technique for optical and electronic data storage in phase change memory (PCM) devices. The unique behavior of those materials exploited in PCM applications is an ability of being quickly molten by an optical laser pulse, quenched into a glassy (amorphous) state and subsequently switched back to a crystalline phase by rapid laser annealing above the crystallization temperature [1]. A particular feature of this technique is a possibility of reaching a number of intermediary, mixed amorphous/crystalline states allowing storage of multiple bits in a single cell. In this work, we demonstrate that similar, reversible laser-induced phase switching can be achieved in metallic Pd$_{95}$Si$_5$ thin films. The investigated alloy is a marginal glass-former which can be vitrified only when quenched from the liquid extremely rapidly and which crystallizes easily on annealing of a glass. The evolution of the atomic structure during switching was monitored by micro-beam X-ray diffraction (XRD). We found that partial amorphization of the initially fully crystalline film can be achieved by irradiation with a single, high-energy fs laser pulse which induces melting followed by an ultrafast ($10^{12}$ K/s) quenching by dissipation of heat into the film substrate. Progressive, step-wise recrystallization is driven by repetitive irradiation with a series of low-energy fs laser pulses. By a quantitative analysis of the XRD pattern acquired at different stages of transformation, we trace the structural pathway of the system on its way between the amorphous and the crystalline state. Finally, we show the reversible character of phase switching important for potential applications for fast-crystallizing metallic systems in PCM devices.