Thermal Properties and Ultrafast Dynamics of Phase Change Materials

Phase Change Materials (PCMs) are materials which can be repeatedly switched between two or more phases; one amorphous and one or more crystalline.  With a growing interest in the applications of PCMs, especially for improved solid-state memory technology, it is becoming more important to gain a fundamental understanding of the dynamics of their switching in order to design materials with faster switching speeds. Our emphasis was on the kinetics of PCM samples as they are heated and the impact this heating has on their transmission.  The two methods used to measure the temperature dependence were a pump-probe test and FTIR spectroscopy.  The most significant result, found in both the pump-probe tests and the FTIR, was that transmission of the materials decreased as temperature increased.  Long-term effects from heating were also witnessed. One millisecond after being struck by the pump beam and one hour after being heated to 65° C in the FTIR, the transmission had not yet returned to its original value.  The future of this project focuses on altering the pump-probe measurement to ensure the witnessed effects are caused by thermal, not electrical, changes of the PCM.  This will be accomplished by measuring the temperature jump induced by the pump and comparing it to the FTIR measurements and by decreasing the rep-rate of the pump to find a change in the long-term effects on transmission.   With a better understanding of the kinetics of change in these materials, and the electric field-driven switching dynamics, we will be able to store our data reliably and compactly; vital characteristics of data storage in an increasingly mobile world.