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DOE OSTI · 2888295

Analytical Model for Atomic Relaxation in Twisted Moiré Materials

Ezzi, Mohammed M. Al [National University of Singapore (Singapore)] (ORCID:000900018016726X)·Pallewela, Gayani N. [National University of Singapore (Singapore)] (ORCID:0000000299579029)·De Beule, Christophe [University of Pennsylvania, Philadelphia, PA (United States)] (ORCID:0000000262147150)·Mele, E. J. [University of Pennsylvania, Philadelphia, PA (United States)] (ORCID:0000000171405353)·Adam, Shaffique [National University of Singapore (Singapore); University of Pennsylvania, Philadelphia, PA (United States); Washington University in St. Louis, St. Louis, MO (United States)] (ORCID:0000000230959920)
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Abstract

By virtue of being atomically thin, the electronic properties of heterostructures built from two-dimensional materials are strongly influenced by atomic relaxation. The atomic layers behave as flexible membranes rather than rigid crystals. Here we develop an analytical theory of lattice relaxation in twisted moiré materials. We obtain analytical results for the lattice displacements and corresponding pseudo gauge fields, as a function of twist angle. We benchmark our results for twisted bilayer graphene and twisted WSe 2 bilayers using large-scale molecular dynamics simulations. Our single-parameter theory is valid in graphene bilayers for twist angles 𝜃 ≳ 0.7°, and in twisted WSe 2 for 𝜃 ≳ 1.6°. Furthermore, we also investigate how relaxation alters the electronic structure in twisted bilayer graphene, providing a simple extension to the continuum model to account for lattice relaxation.

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36 MATERIALS SCIENCEElectron RelaxationFlat BandsGrapheneTwistronicsVan der Waals Systems

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Ezzi, Mohammed M. Al [National University of Singapore (Singapore)] (ORCID:000900018016726X), Pallewela, Gayani N. [National University of Singapore (Singapore)] (ORCID:0000000299579029), De Beule, Christophe [University of Pennsylvania, Philadelphia, PA (United States)] (ORCID:0000000262147150), Mele, E. J. [University of Pennsylvania, Philadelphia, PA (United States)] (ORCID:0000000171405353), Adam, Shaffique [National University of Singapore (Singapore); University of Pennsylvania, Philadelphia, PA (United States); Washington University in St. Louis, St. Louis, MO (United States)] (ORCID:0000000230959920). 2024-12-23. Analytical Model for Atomic Relaxation in Twisted Moiré Materials. https://doi.org/10.1103/physrevlett.133.266201

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36 MATERIALS SCIENCE subjectElectron Relaxation subjectFlat Bands subjectGraphene subjectTwistronics subjectVan der Waals Systems subject

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The transition to a flexible and reliable energy infrastructure, using electro-thermal energy generation technologies such as geothermal, concentrated solar power, and nuclear, usually demands simultaneous advancement of thermal energy storage (TES) to support on-demand electricity generation and industrial applications while mitigating the inherent intermittency of renewable energy sources and power outages from direct energy generation. Among TES technologies, thermochemical energy storage (TCES) based on calcium looping emerges as a compelling high-power energy storage candidate due to its high reaction enthalpy, compatibility with elevated operating temperatures, and abundance of low-cost materials. However, the long-term durability of calcium-based sorbents for TCES is hindered by surface sintering and particle aggregation, leading to performance degradation over repeated thermal cycles. This study explores a moisture hydration-based strategy to regenerate a degraded calcium sorbent and mitigate performance degradation for long duration TCES. The addition of moisture transforms calcium oxide into calcium hydroxide and produces intercalation water layers, associated with a regenerated surface area and reduced calcium oxide crystallite size. Both these effects are beneficial in restoring the sorbents' reactivity for carbonization. Additionally, an optimized hydration-assisted reactivation protocol balances the recovered energy storage capacity with heating penalty required for moisture removal from hydrated samples, resulting in an enhanced energy storage capacity up to 176% compared to benchmark sorbents that undergo cycling without reactivation after 60 cycles. In conclusion, these results highlight the potential of hydration-assisted reactivation to enhance the long-term performance of TCES, providing an effective pathway to advancing electro-thermal storage technologies.

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