E-beam-enhanced solid-state mechanical amorphization of alpha-quartz: Reducing deformation barrier via localized excess electrons as mobile anions

Under hydrostatic pressure, alpha-quartz undergoes solid-state mechanical amorphization wherein the interpenetration of SiO4 tetrahedra occurs and the material loses crystallinity. This phase transformation requires a high hydrostatic pressure of 14 GPa because the repulsive forces resulting from the ionic nature of the Si-O bonds prevent the severe distortion of the atomic configuration. Herein, we experimentally and computationally demonstrate that e-beam irradiation changes the nature of the interatomic bonds in alpha-quartz and enhances the solid-state mechanical amorphization at nanoscale. Specifically, during in situ uniaxial compression, a larger permanent deformation occurs in alpha-quartz micropillars compressed during e-beam irradiation than in those without e-beam irradiation. Microstructural analysis reveals that the large permanent deformation under e-beam irradiation originates from the enhanced mechanical amorphization of alpha-quartz and the subsequent viscoplastic deformation of the amorphized region. Further, atomic-scale simulations suggest that the delocalized excess electrons introduced by e-beam irradiation move to highly distorted atomic configurations and alleviate the repulsive force, thus reducing the barrier to the solid-state mechanical amorphization. These findings deepen our understanding of electron-matter interactions and can be extended to new glass forming and processing technologies at nano- and microscale.Comment: 24 pages, 6 figure

Intertwined CNT Assemblies as an All-Around Current Collector for Volume-Efficient Lithium-Ion Hybrid Capacitors

The increasing demands for conversionsystems for cleanenergy,wearable devices powered by energy storage systems, and electric vehicleshave greatly promoted the development of innovative current collectorsto replace conventional metal-based foils, including those in multidimensionalforms. In this study, carbon nanotubes (CNTs) with desirable featuresand ease of processing are used in the preparation of floating catalyst-chemicalvapor deposition-derived CNT sheets for potential use as all-aroundcurrent collectors in two representative energy storage devices: batteriesand electrochemical capacitors. Due to their short and multidirectionalelectron pathways and multimodal porous structures, CNT-based currentcollectors enhance ion transport kinetics and provide many ion adsorptionand desorption sites, which are crucial for improving the performanceof batteries and electrochemical capacitors, respectively. By assemblingactivated carbon-CNT cathodes and prelithiated graphite-CNTanodes, high-performance lithium-ion hybrid capacitors (LIHCs) aresuccessfully demonstrated. Briefly, CNT-based LIHCs exhibit 170% largervolumetric capacities, 24% faster rate capabilities, and 21% enhancedcycling stabilities relative to LIHCs based on conventional metalliccurrent collectors. Therefore, CNT-based current collectors are themost promising candidates for replacing currently used metallic materialsand provide a valuable opportunity to possibly redefine the rolesof current collectors.N

Athermal glass work at the nanoscale: Engineered electron-beam-induced viscoplasticity for mechanical shaping of brittle amorphous silica

© 2022 Acta Materialia Inc.Amorphous silica deforms viscoplastically at elevated temperatures, which is common for brittle glasses. The key mechanism of viscoplastic deformation involves interatomic bond switching, which is thermally activated. Here, we precisely control the mechanical shaping of brittle amorphous silica at the nanoscale via engineered electron–matter interactions without heating. We observe a ductile plastic deformation of amorphous silica under a focused scanning electron beam with low acceleration voltages (few to tens of kilovolts) during in-situ compression studies, with unique dependence on the acceleration voltage and beam current. By simulating the electron–matter interaction, we show that the deformation of amorphous silica depends strongly on the volume where inelastic scattering occurs. The electron–matter interaction via e-beam irradiation alters the Si–O interatomic bonds, enabling the high-temperature deformation behavior of amorphous silica to occur athermally. Finally, by systematically controlling the electron–matter interaction volume, it is possible to mechanically shape the brittle amorphous silica on a small scale at room temperature to a level comparable to glass shaping at high temperatures. The findings can be extended to develop new fabrication processes for nano- and microscale brittle glasses.N