Author Correction: Mechanically-tunable bandgap closing in 2D graphene phononic crystals
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Printable graphene inks with polypropylene carbonate for low-surface-tension solvents and mild-temperature post-processing
For dispersion stability, printable graphene inks commonly employ solvents with limited surface tensions or incorporate dispersant aids that require high-temperature post-processing, restricting printability and substrate compatibility. Here, printable graphene inks are introduced with low-surface-tension solvents and mild-temperature post-processing using polypropylene carbonate (PPC). Graphene is produced by liquid-phase exfoliation with PPC, and the exfoliated graphene/PPC is used to generate printable inks. As a dispersant aid, PPC improves graphene exfoliation, dispersion stability, and redispersability in solvents with low surface tensions (<30 mJ m–2), facilitating the formulation of desirable inks for efficient aerosol jet printing on diverse substrates. Moreover, the low decomposition temperature of PPC eases its thermal removal from printed graphene, allowing high electrical conductivity with a mild post-processing temperature of 220 °C. Consequently, the graphene inks enable the fabrication of fully-printed graphene micro-supercapacitors on heat-sensitive paper substrates, exhibiting high areal capacitances, cycling stability, and mechanical resilience against bending deformation.
Flash Joule heating for synthesis, upcycling and remediation
Electric heating methods are being developed and used to electrify industrial applications and lower their carbon emissions. Direct Joule resistive heating is an energy-efficient electric heating technique that has been widely tested at the bench scale and could replace some energy-intensive and carbon-intensive processes. In this Review, we discuss the use of flash Joule heating (FJH) in processes that are traditionally energy-intensive or carbon-intensive. FJH uses pulse current discharge to rapidly heat materials directly to a desired temperature; it has high-temperature capabilities (>3,000 °C), fast heating and cooling rates (>102 °C s−1), short duration (milliseconds to seconds) and high energy efficiency (~100%). Carbon materials and metastable inorganic materials can be synthesized using FJH from virgin materials and waste feedstocks. FJH is also applied in resource recovery (such as from e-waste) and waste upcycling. An emerging application is in environmental remediation, where FJH can be used to rapidly degrade perfluoroalkyl and polyfluoroalkyl substances and to remove or immobilize heavy metals in soil and solid wastes. Life-cycle and technoeconomic analyses suggest that FJH can reduce energy consumption and carbon emissions and be cost-efficient compared with existing methods. Bringing FJH to industrially relevant scales requires further equipment and engineering development.
Transparent, flexible graphene–ITO-based neural microelectrodes for simultaneous electrophysiology recording and calcium imaging of intracortical neural activity in freely moving mice
To understand the complex dynamics of neural activity in the brain across various temporal and spatial scales, it is crucial to record intracortical multimodal neural activity by combining electrophysiological recording and calcium imaging techniques. This poses significant constraints on the geometrical, mechanical, and optical properties of the electrodes. Here, transparent flexible graphene–ITO-based neural microelectrodes with small feature sizes are developed and validated for simultaneous electrophysiology recording and calcium imaging in the hippocampus of freely moving mice. A micro-etching technique and an oxygen plasma pre-treating method are introduced to facilitate large-area graphene transfer and establish stable low-impedance contacts between graphene and metals, leading to the batch production of high-quality microelectrodes with interconnect widths of 10 μm and recording sites diameters of 20 μm. These electrodes exhibit appropriate impedance and sufficient transparency in the field of view, enabling simultaneous recording of intracortical local field potentials and even action potentials along with calcium imaging in freely moving mice. Both types of electrophysiological signals are found to correlate with calcium activity. This proof-of-concept work demonstrates that transparent flexible graphene–ITO-based neural microelectrodes are promising tools for multimodal neuroscience research.
Unusual Li2O sublimation promotes single-crystal growth and sintering
Li2O is rarely used for cathode material synthesis due to its high melting point (1,438 °C). Here we discover that Li2O can sublimate at 800–1,000 °C under ambient pressure, opening new possibilities for cathode synthesis. We propose a mechanism that enables synthesis of single crystals—such as LiNi0.8Mn0.1Co0.1O2 (NMC811) or LiNi0.9Mn0.05Co0.05O2 (NMC90)—without direct contact with Li2O salts. We show that Li2O vapour successfully converts spent polycrystalline NMC811 into segregated single crystals without milling or post-treatment. The Li2O vapour, derived from Li2O solids, diffuses rapidly and reacts with precursors, mimicking a molten-salt environment, which facilitates single-crystal growth. The chemical lithiation process continuously drives Li2O sublimation, sintering the crystals. Single crystals derived from Li2O and fresh precursors or spent polycrystals exhibit outstanding cycling after 1,000 cycles in full cells. The demonstrated Li2O sublimation and its universal role in promoting single-crystal growth provides an effective approach for single-crystal synthesis, scale-up and recycling.
Inelastic resonant tunnelling through adjacent localised electronic states in van der Waals heterostructures
Van der Waals heterostructures offer unprecedented opportunities to design next stage functional electronic 2D devices. Most architectures of those devices incorporate large bandgap insulator – hBN as an encapsulating or tunnel barrier layers. Here, we use an architecture of gated vertical tunnelling transistors to study a generic phenomenon of electron resonant tunnelling through adjacent localised electronic states in hBN barriers. We demonstrate that in the case of two localised electronic states, the tunnelling can be of inelastic nature giving rise to explicitly strong resonant features. It allows accurate tunnelling spectroscopy of delicate features of emitting and collecting layer electronic density of states, such as second neutrality point bandgap of moiré monolayer and electric field induced bandgap of Bernal bilayer graphene. Our findings enrich the perception of interaction mechanisms among the localised electronic states in hBN barriers paving the way for future explorations into their applications.
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