In this talk I will give examples of two different systems: phase-change materials (PCM) and self-assembled memristor at the interface of Al and LaNiO3, and demonstrate how our research on fundamental structure-property correlations enabled engineering novel electronic device functionalities in them.
System 1: Phase-change materials (PCMs) transform rapidly and reversibly between a stable crystalline phase and a meta-stable amorphous phase. This property has been exploited commercially for computer memory applications. Conventionally, crystal to amorphous phase transformation in PCMs occurs via a high power melt-quench pathway. We developed and implemented in situ transmission electron microscopy (TEM) experiments on GeTe and Ge2Sb2Te5PCM systems. This lead us to discovering a new pathway for amorphization: defect-templated pathway. This pathway is also accompanied by disorder-induced electronic transitions. Lessons learnt from these fundamental studies were put to test in real nanowire devices through defect-engineering . This strategy showed five orders of magnitude improvement in power consumption for memory operation. Physical mechanisms of defect engineered devices that enabled such energy efficiency will be discussed in detail.
System 2: We report a surprising and interesting memristive hysteresis at the Al-LaNiO3(metal-metal) interfaces. Using high resolution STEM and energy dispersive spectroscopy, we clearly show that Al, owing to its affinity for oxidation, forms a self-assembled interlayer of AlOx. Electron energy loss spectroscopy of devices in several resistance states allowed us to clearly understand that oxygen cycling and redox reactions between the AlOx and LaNiO3layer that give rise to the I-V hysteresis, and propose guidelines on how to make such self-assembled interfacial memristors.
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2 Nukala, et al., Nat. Comm. 7, 10482 (2016)
3 Nukala, Tian et al., Phys. Chem. Chem. Phys.,19, 16960 (2017)