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Lithium metal anodes offer high theoretical capacities (3,860 milliampere-hours per gram) 1 , but rechargeable batteries built with such anodes suffer from dendrite growth and low Coulombic efficiency (the ratio of charge output to charge input), preventing their commercial adoption 2 , 3 . The formation of inactive (‘dead’) lithium— which consists of both (electro)chemically formed Li + compounds in the solid electrolyte interphase and electrically isolated unreacted metallic Li 0 (refs 4 , 5 )—causes capacity loss and safety hazards. Quantitatively distinguishing between Li + in components of the solid electrolyte interphase and unreacted metallic Li 0 has not been possible, owing to the lack of effective diagnostic tools. Optical microscopy 6 , in situ environmental transmission electron microscopy 7 , 8 , X-ray microtomography 9 and magnetic resonance imaging 10 provide a morphological perspective with little chemical information. Nuclear magnetic resonance 11 , X-ray photoelectron spectroscopy 12 and cryogenic transmission electron microscopy 13 , 14 can distinguish between Li + in the solid electrolyte interphase and metallic Li 0 , but their detection ranges are limited to surfaces or local regions. Here we establish the analytical method of titration gas chromatography to quantify the contribution of unreacted metallic Li 0 to the total amount of inactive lithium. We identify the unreacted metallic Li 0 , not the (electro)chemically formed Li + in the solid electrolyte interphase, as the dominant source of inactive lithium and capacity loss. By coupling the unreacted metallic Li 0 content to observations of its local microstructure and nanostructure by cryogenic electron microscopy (both scanning and transmission), we also establish the formation mechanism of inactive lithium in different types of electrolytes and determine the underlying cause of low Coulombic efficiency in plating and stripping (the charge and discharge processes, respectively, in a full cell) of lithium metal anodes. We propose strategies for making lithium plating and stripping more efficient so that lithium metal anodes can be used for next-generation high-energy batteries. Titration gas chromatography is developed as an analytical method of distinguishing between lithium metal and lithium compounds within a cycled battery and assessing the amount of unreacted metallic lithium available.

Friction as a fundamental physical phenomenon dominates nature and human civilization, among which the achievement of molecular rolling lubrication is desired to bring another breakthrough, like the macroscale design of wheel. Herein, an edge self-curling nanodeformation phenomenon of graphite nanosheets (GNSs) at cryogenic temperature is found, which is then used to promote the formation of graphite nanorollers in friction process towards molecular rolling lubrication. The observation of parallel nanorollers at the friction interface give the experimental evidence for the occurrence of molecular rolling lubrication, and the graphite exhibits abnormal lubrication performance in vacuum with ultra-low friction and wear at macroscale. The molecular rolling lubrication mechanism is elucidated from the electronic interaction perspective. Experiments and theoretical simulations indicate that the driving force of the self-curling is the uneven atomic shrinkage induced stress, and then the shear force promotes the intact nanoroller formation, while the constraint of atomic vibration decreases the dissipation of driving stress and favors the nanoroller formation therein. It will open up a new pathway for controlling friction at microscale and nanostructural manipulation. Molecular rolling lubrication can control friction phenomenon like a wheel. Here, the authors find the self-curled deformation effect of graphite nanosheets at cryogenic temperature, which promotes the in-situ formation of parallel nano-rollers, and acquire molecular rolling lubrication.

The emergence of two-dimensional crystals has revolutionized modern solid-state physics. From a fundamental point of view, the enhancement of charge carrier correlations has sparked much research activity in the transport and quantum optics communities. One of the most intriguing effects, in this regard, is the bosonic condensation and spontaneous coherence of many-particle complexes. Here we find compelling evidence of bosonic condensation of exciton–polaritons emerging from an atomically thin crystal of MoSe 2 embedded in a dielectric microcavity under optical pumping at cryogenic temperatures. The formation of the condensate manifests itself in a sudden increase of luminescence intensity in a threshold-like manner, and a notable spin-polarizability in an externally applied magnetic field. Spatial coherence is mapped out via highly resolved real-space interferometry, revealing a spatially extended condensate. Our device represents a decisive step towards the implementation of coherent light-sources based on atomically thin crystals, as well as non-linear, valleytronic coherent devices. A coherent condensate of exciton–polaritons, extending spatially up to 4 µm and spin-polarizable with an external magnetic field, is observed at cryogenic temperatures in a MoSe 2 monolayer embedded in a vertical microcavity.

Efficient cytosolic delivery of RNA molecules remains a formidable barrier for RNA therapeutic strategies. Lipid nanoparticles (LNPs) serve as state-of-the-art carriers that can deliver RNA molecules intracellularly, as exemplified by the recent implementation of several vaccines against SARS-CoV-2. Using a bottom-up rational design approach, we assemble LNPs that contain programmable lipid phases encapsulating small interfering RNA (siRNA). A combination of cryogenic transmission electron microscopy, cryogenic electron tomography and small-angle X-ray scattering reveals that we can form inverse hexagonal structures, which are present in a liquid crystalline nature within the LNP core. Comparison with lamellar LNPs reveals that the presence of inverse hexagonal phases enhances the intracellular silencing efficiency over lamellar structures. We then demonstrate that lamellar LNPs exhibit an in situ transition from a lamellar to inverse hexagonal phase upon interaction with anionic membranes, whereas LNPs containing pre-programmed liquid crystalline hexagonal phases bypass this transition for a more efficient one-step delivery mechanism, explaining the increased silencing effect. This rational design of LNPs with defined lipid structures aids in the understanding of the nano-bio interface and adds substantial value for LNP design, optimization and use. The authors display the bottom-up design, assembly, and in-depth characterization of defined lipid-RNA structures in the core of lipid nanoparticles. The inverted structures are thermostable and provide better transfection over lamellar structures.

High-entropy alloys (HEAs) are multi-component alloys with a novel designed concept. These HEAs exhibit unique composition design and structural characteristics leading to excellent properties, which have attracted considerable attention in various fields. The extensively investigated HEAs exhibit excellent strength–ductility combination and excellent damage resistance at cryogenic temperature. Therefore, HEAs have potential applications in cryogenic temperature structural materials. It is important to study their deformation behavior and microstructural evolution at cryogenic temperature to provide the understanding needed for further alloy development. In this paper, the effects of different phase structure, grain size and stacking fault energy (SFE) on cryogenic temperature deformation behavior are reviewed. The research and development of tensile, compressive and fracture toughness of HEAs at cryogenic temperature are briefly reviewed. We discuss how individual deformation mechanisms can compete or operate synergistically with each other during cryogenic temperature plastic deformation, including dislocation slip, strain-induced twin formation and strain-induced phase transformation. In addition, the future trends and some problems faced by HEAs at cryogenic temperature are discussed, and prospects of HEAs are put forward.

Laser plasma-based particle accelerators attract great interest in fields where conventional accelerators reach limits based on size, cost or beam parameters. Despite the fact that particle in cell simulations have predicted several advantageous ion acceleration schemes, laser accelerators have not yet reached their full potential in producing simultaneous high-radiation doses at high particle energies. The most stringent limitation is the lack of a suitable high-repetition rate target that also provides a high degree of control of the plasma conditions required to access these advanced regimes. Here, we demonstrate that the interaction of petawatt-class laser pulses with a pre-formed micrometer-sized cryogenic hydrogen jet plasma overcomes these limitations enabling tailored density scans from the solid to the underdense regime. Our proof-of-concept experiment demonstrates that the near-critical plasma density profile produces proton energies of up to 80 MeV. Based on hydrodynamic and three-dimensional particle in cell simulations, transition between different acceleration schemes are shown, suggesting enhanced proton acceleration at the relativistic transparency front for the optimal case. Laser-produced plasma can be used for particle acceleration in different schemes. Here the authors demonstrate proton acceleration from the intense ultrashort laser pulse interaction with micron-sized cryogenic hydrogen jet.

A robust cryogenic infrastructure in form of a wired, thermally optimized dilution refrigerator is essential for solid-state based quantum processors. Here, we engineer a cryogenic setup, which minimizes passive and active heat loads, while guaranteeing rapid qubit control and readout. We review design criteria for qubit drive lines, flux lines, and output lines used in typical experiments with superconducting circuits and describe each type of line in detail. The passive heat load of stainless steel and NbTi coaxial cables and the active load due to signal dissipation are measured, validating our robust and extensible concept for thermal anchoring of attenuators, cables, and other microwave components. Our results are important for managing the heat budget of future large-scale quantum computers based on superconducting circuits.

Service performance is important in the subsequent local feature forming of the large thin-wall component manufactured by cryogenic forming. Therefore, the elevated temperature should be controlled. The strain distribution of 2219 cryogenic pre-stretched specimens at different elevated temperatures was analyzed at different gauge lengths. The mechanical properties were also studied through elevated temperature uniaxial tensile tests assisted by the DIC system. The deformation inhomogeneity of the material decreases with the increase in temperature. With the increase in temperature, the elongation of specimens first increases and then slightly decreases.

For high precision storage ring experiments as the future P̅ANDA experiment, very sophisticated internal targets have to be used. For this purpose, a state-of-the-art cluster-jet target was developed at the University Münster. Basically, hydrogen is cooled to cryogenic temperatures and pressed through a specially shaped Laval nozzle to form a cluster-jet expanding into vacuum. Due to the stability and large mass of the clusters, a practically undisturbed flight path in vacuum of above 5 m is possible, leading to manifold possible applications, including the interaction with a storage ring beam at a distance of 2.25 m as desired for the P̅ANDA experiment. With a first prototype target, the “proof-of-principle” was delivered, and after first improvements the world record in target thickness in such large distance to the nozzle was measured. Based on this work, the final P̅ANDA cluster-jet target was developed and built up, and is presented in this article.

Stainless steel was widely used in thin-walled components of aerospace applications due to its low cost and easy processing. However, the high mass density of steel constrained its application. Recently developed cryogenic forming can achieve the high strength and lightweight requirements, as well as the strength improvement of stainless steel. A curved part of 304 stainless steel was formed under cryogenic conditions. The strain distribution of the curved part was studied through numerical simulation. The hardness distribution was investigated to reveal the strengthening effect. The strengthening mechanism was revealed by electron back-scattering diffraction. The results show that the strain distribution of the curved part is more uniform after cryogenic forming. The hardness was more excellent because the martensitic transformation was promoted under cryogenic deformation.