Browsing by Author "Zhou, Tao"

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    Optical Control of Adaptive Nanoscale Domain Networks
    (Wiley, 2024) Zajac, Marc; Zhou, Tao; Yang, Tiannan; Das, Sujit; Cao, Yue; Guzelturk, Burak; Stoica, Vladimir; Cherukara, Mathew J.; Freeland, John W.; Gopalan, Venkatraman; Ramesh, Ramamoorthy; Martin, Lane W.; Chen, Long-Qing; Holt, Martin V.; Hruszkewycz, Stephan O.; Wen, Haidan; Rice Advanced Materials Institute
    Adaptive networks can sense and adjust to dynamic environments to optimize their performance. Understanding their nanoscale responses to external stimuli is essential for applications in nanodevices and neuromorphic computing. However, it is challenging to image such responses on the nanoscale with crystallographic sensitivity. Here, the evolution of nanodomain networks in (PbTiO3)n/(SrTiO3)n superlattices (SLs) is directly visualized in real space as the system adapts to ultrafast repetitive optical excitations that emulate controlled neural inputs. The adaptive response allows the system to explore a wealth of metastable states that are previously inaccessible. Their reconfiguration and competition are quantitatively measured by scanning x-ray nanodiffraction as a function of the number of applied pulses, in which crystallographic characteristics are quantitatively assessed by assorted diffraction patterns using unsupervised machine-learning methods. The corresponding domain boundaries and their connectivity are drastically altered by light, holding promise for light-programable nanocircuits in analogy to neuroplasticity. Phase-field simulations elucidate that the reconfiguration of the domain networks is a result of the interplay between photocarriers and transient lattice temperature. The demonstrated optical control scheme and the uncovered nanoscopic insights open opportunities for the remote control of adaptive nanoscale domain networks.
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    Phase Transformation Driven by Oxygen Vacancy Redistribution as the Mechanism of Ferroelectric Hf0.5Zr0.5O2 Fatigue
    (Wiley, 2024) Zhang, Zimeng; Craig, Isaac; Zhou, Tao; Holt, Martin; Flores, Raul; Sheridan, Evan; Inzani, Katherine; Huang, Xiaoxi; Nag, Joyeeta; Prasad, Bhagwati; Griffin, Sinéad M.; Ramesh, Ramamoorthy
    As a promising candidate for nonvolatile memory devices, the hafnia-based ferroelectric system has recently been a hot research topic. Although significant progress has been made over the past decade, the endurance problem is still an obstacle to its final application. In perovskite-based ferroelectrics, such as the well-studied Pb[ZrxTi1−x]O3 (PZT) family, polarization fatigue has been discussed within the framework of the interaction of charged defects (such as oxygen vacancies) with the moving domains during the switching process, particularly at the electrode-ferroelectric interface. Armed with this background, a hypothesis is set out to test that a similar mechanism can be in play with the hafnia-based ferroelectrics. The conducting perovskite La-Sr-Mn-O is used as the contact electrode to create La0.67Sr0.33MnO3 / Hf0.5Zr0.5O2 (HZO)/ La0.67Sr0.33MnO3 capacitor structures deposited on SrTiO3-Si substrates. Nanoscale X-ray diffraction is performed on single capacitors, and a structural phase transition from polar o-phase toward non-polar m-phase is demonstrated during the bipolar switching process. The energy landscape of multiphase HZO has been calculated at varying oxygen vacancy concentrations. Based on both theoretical and experimental results, it is found that a polar to non-polar phase transformation caused by oxygen vacancy redistribution during electric cycling is a likely explanation for fatigue in HZO.