An elastic printed circuit board (E-PCB) is a conductive framework used for the facile assembly of system-level stretchable electronics. E-PCBs require elastic conductors that have high conductivity, high stretchability, tough adhesion to various components, and imperceptible resistance changes even under large strain. We present a liquid metal particle network (LMP Net ) assembled by applying an acoustic field to a solid-state insulating liquid metal particle composite as the elastic conductor. The LMP Net conductor satisfies all the aforementioned requirements and enables the fabrication of a multilayered high-density E-PCB, in which numerous electronic components are intimately integrated to create highly stretchable skin electronics. Furthermore, we could generate the LMP Net in various polymer matrices, including hydrogels, self-healing elastomers, and photoresists, thus showing their potential for use in soft electronics.

Despite their potential, Li metal batteries have a poor cycle life due to being chemically unstable and having a fragile solid-electrolyte interphase (SEI). The SEI forms significant crack formations during cycling, resulting in Li dendrite growth. Such dendrites continuously consume electrolytes and deteriorate the cycle lifetime of Li-metal batteries. [2] Electrolyte engineering has been used widely to suppress Li dendrites by improving the formation of SEI. [3] In 2013, salt-type additives such as CsPF 6 , as proposed by Zhang et al. [4] can stabilize the Li-metal surface based on a self-healing electrostatic shield mechanism; the cation component creates a positive shielding layer near the dendrite's nucleation point and a repulsive interaction between the Li ions. The shielding cations push the Li ions to adjacent regions, inducing a smooth Li surface. However, these types of shielding cations are co-deposited with Li at a high current density, impairing the protective effect. [3a,5] Recently, ionic liquid (IL) has received great attention as a promising electrolyte additive for stabilizing Li-metal anodes due to a synergistic effect of the cation as a shielding agent [6] and the anion as an SEI-improving agent; [7] the cation enables uniform Li deposition, while anion builds a robust SEI. Recent advances in IL have revealed that a nonpolar alkyl chain to cations is a lithiophobic barrier that impedes Li ion transport toward the protruding tips. [6] Moreover, the IL cations modified with asymmetrically extended alkyl chains have been conceived as the most effective shielding agent for a uniform Li plating. [6a] Despite their potential to modulate Li deposits smoothly, research on the rational design of ILs for optimal control of Li plating has not been thoroughly developed and requires further improvement to achieve longlasting practical Li-metal batteries.Herein, we present a new design for IL additives and their self-assembly on Li protuberant tips for stable and high-performance Li-metal batteries. Uniquely, we introduce symmetric lithiophobic alkyl chains to pyrrolidium cations (Pyr + ). Pyrrolidium is a promising shielding moiety for Li-metal anodes because it can preferentially assemble near protuberances by the electric field and its reduction potential is lower than that of the Li ions (−3.04 V vs standard hydrogen electrode, SHE). [8] Modulating lithium metal deposition is vital for the realization of stable and energy-dense Li-metal batteries. Ionic liquid (IL) has been regarded as a promising electrolyte additive for a uniform Li deposition because its cation moiety forms a lithiophobic protective layer on Li protuberant tips. Despite recent advances in ILs forLi metal batteries, rational designs for IL additives are still in their infancy, and further improvement is required. Here, a new class of self-assembled protective layer based on the design of a new IL molecule enabling high-performance Li-metal batteries is reported. For the first time, symmetric design of lithiophobic side chain...

Novel functions emerge from novel structures. To develop efficient catalytic systems for challenging chemical transformations, chemists often seek inspirations from enzymatic catalysis. A large number of iron complexes supported by nitrogen‐rich multidentate ligands have thus been developed to mimic oxo‐transfer reactivity of dioxygen‐activating metalloenzymes. Such efforts have significantly advanced our understanding of the reaction mechanisms by trapping key intermediates and elucidating their geometric and electronic properties. Critical to the success of this biomimetic approach is the design and synthesis of elaborate ligand systems to balance the thermodynamic stability, structural adaptability, and chemical reactivity. In this Concept article, representative design strategies for biomimetic atom‐transfer chemistry are discussed from the perspectives of “ligand builders”. Emphasis is placed on how the primary coordination sphere is constructed, and how it can be elaborated further by rational design for desired functions.

Over the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m2) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications.

Atom-transfer chemistry represents an important class of reactions catalyzed by metalloenzymes. As a functional mimic of non-heme iron enzymes that deliver oxygen atoms to olefins, we have designed monoiron complexes supported by new N-donor chelates. These ligands take advantage of heme-like conformational rigidity of the π-conjugated molecular backbone, and synthetic flexibility of tethering non-heme donor groups for additional steric and electronic control. Iron complexes generated in situ can be used to carry out catalytic epoxidation of a wide range of olefin substrates by using mCPBA as a terminal oxidant. The fate of initial iron-peracid adduct and the involvement of iron-oxo species in this process were investigated further by mechanistic probes and isotope exchange studies. Our findings suggest that anilidopyridyl-derived [N,N]-bidentate motif could serve as a versatile structural platform to build non-heme ligands for catalytic oxidation chemistry.

The effective lowering of the Schottky barrier height in In0.52Al0.48As diodes under reverse bias conditions is investigated by fitting experimental reverse-bias I-T relationships to the thermionic-field emission theory. This lowering can be explained by thermionic-field emission without assuming a lack of Fermi level pinning. The electron effective mass deduced experimentally from the fitting procedure ranges from 0.072m0 to 0.087m0, which is comparable to the published data. The effective barrier height is largely dependent on the temperature range of the current. The amount of the lowering is dependent on the electron effective mass, but not on the zero-field Schottky barrier height.

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