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DOE OSTI · 1817199

Quantum-Well Bound States in Graphene Heterostructure Interfaces

Dai, Zhongwei·Gao, Zhaoli·Pershoguba, Sergey S.·Tiwale, Nikhil·Subramanian, Ashwanth·Zhang, Qicheng·Eads, Calley·Tenney, Samuel A.·Osgood, Richard M.·Nam, Chang-Yong·Zang, Jiadong·Johnson, A. T. Charlie·Sadowski, Jerzy T.
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Abstract

We present experimental evidence of electronic and optical interlayer resonances in graphene van der Waals heterostructure interfaces. Using the spectroscopic mode of a low-energy electron microscope (LEEM), we characterized these interlayer resonant states up to 10 eV above the vacuum level. Compared with nontwisted, AB-stacked bilayer graphene (AB BLG), an ≈ 0.2 Å increase was found in the interlayer spacing of 30° twisted bilayer graphene (30°-tBLG). In addition, we used Raman spectroscopy to probe the inelastic light-matter interactions. A unique type of Fano resonance was found around the D and G modes of the graphene lattice vibrations. This anomalous, robust Fano resonance is a direct result of quantum confinement and the interplay between discrete phonon states and the excitonic continuum.

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36 MATERIALS SCIENCERaman spectroscopyelectronic structuregrapheneheterostructureslow-energy electron microscopy

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Dai, Zhongwei, Gao, Zhaoli, Pershoguba, Sergey S., Tiwale, Nikhil, Subramanian, Ashwanth, Zhang, Qicheng, Eads, Calley, Tenney, Samuel A., Osgood, Richard M., Nam, Chang-Yong, Zang, Jiadong, Johnson, A. T. Charlie, Sadowski, Jerzy T.. 2021-08-20. Quantum-Well Bound States in Graphene Heterostructure Interfaces. https://doi.org/10.1103/physrevlett.127.086805

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DOE OSTI2026

Cyclic moisture reactivation of calcium sorbents for long duration thermochemical energy storage

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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