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With rapid advancements in aerospace technology, research interest in the near-space atmospheric environment has surged. Active space release experiments, known for their high controllability and observational advantages, offer a well-established approach to investigating space physics, particularly in the ionosphere. Extending this technique to near-space is essential for deepening our understanding of its environmental properties and underlying physics. However, significant differences in pressure, chemical reactivity, and constituent distribution between near-space and the ionosphere introduce substantial complexity to active release experiments in this region. This study systematically evaluates the influence of the near-space environment on alkali metal releases. A kinetic model for such releases in near-space is developed, and the feasibility of their implementation is assessed. Numerical simulations demonstrate that releasing 10 kg of alkali metals at an altitude of 100 km can generate an artificial electron cloud that persists for over 30 min. The spatial scale and persistence time of the artificial electron cloud decrease markedly with decreasing release altitude. In the vicinity of an altitude of 70 km, intense recombination reactions rapidly deplete released material within seconds, preventing the formation of a stable electron cloud. This indicates a lower altitude limit for effective application of this technique. Single-point releases yield electron clouds with insufficient spatial extent and duration, employing multipoint release can effectively address this limitation. Ray-tracing simulations further indicate that electron clouds substantially alter radio wave propagation paths, creating a radio shadow region that impedes wave penetration. Crucially, these clouds also establish a new propagation path, forming an \"air bridge\" in near-space with the potential to enable autonomous, reliable long-distance (> 300 km) wireless communication. This work provides a new perspective and approach for near-space research, promising applications in technologies such as artificial communication channels and electromagnetic shielding. Graphical abstract

Microplastics (MPs) are widespread environmental pollutants. This study primarily examines the changes in electro distribution of aged MPs in aquatic environments and their subsequent impact on the environment. Under the action of natural and artificial aging, the electron cloud arrangement of MPs will change, thus affecting the relevant properties of MPs. Among them, the free radicals formed by advanced oxidation technology will be enriched on the surface of MPs carrying benzene rings, and react with other pollutants (organic pollutants, heavy metals, etc.) adsorbed by MPs to form environmental persistent free radicals (EPFRs). The electron cloud density of MPs carrying EPFRs increases, and the reactivity will also increase. Additionally, the oxygen-containing functional groups on the surface of aged MPs enhance their selective adsorption, altering their environmental impact. MPs can serve as a source of free radicals in the environment, enhance the oxidation capacity of other substances in the environment, and even affect the expression of antibiotic resistance genes. In addition, MPs have a high mobility, which will have a greater negative impact in the environment. Additionally, the high mobility of MPs amplifies their negative environmental impact. This study examines the changes in electron distribution of aged MPs and highlights their effects on aquatic ecosystems, providing insights into pollution control, toxicity, and degradation mechanisms. Graphical abstract

Electron clouds forming inside the beam vacuum chamber due to photoemission and secondary emission may limit the accelerator performance. Specifically, the electron clouds can blow up the vertical emittance of a positron beam, through a head-tail-type single-bunch instability, if the central electron density exceeds a certain threshold value, that can be estimated analytically. Using the codes PyECLOUD and VSim, we carried out detailed simulations of the electron-cloud build up for the main arcs and the damping ring of the FCC-ee collider, in order to identify the effective photoemission rate and secondary emission yield required for achieving and maintaining the design emittance. To this end, we present the simulated electron density at the centre of the beam pipe for various bunch spacings, secondary emission yields, and photoemission parameters, in the damping ring and in the arcs of the collider positron ring. To gain further insight into the underlying dynamics, the obtained spatial and energy distributions of the cloud electrons are illustrated as a function of time. In addition, we compare results obtained for two different secondary emission models (“Furman–Pivi” and “ECLOUD”), thereby indicating the uncertainty inherent in this type of study, without any prototype vacuum chambers yet available. We also point out a few situations where the two secondary-emission models yield similar density values. Finally, based on our simulation results for two different design variants, we conclude that the new parameter baseline of the FCC-ee will facilitate electron-cloud mitigation.

For improving the vacuum and mitigating the electron clouds in ultra-high vacuum chamber systems of high-energy accelerators, the deposition of Ti-V-Hf-Zr getter film on a laser-treated aluminum alloy substrate was proposed and exploited for the first time in this study. The laser-treated aluminum surface exhibits a low secondary electron yield (SEY), which is even lower than 1 for some selected laser parameters. Non-evaporable getter (NEG) Ti-V-Hf-Zr film coatings were prepared using the direct current (DC) sputtering method. The surface morphology, surface roughness and composition of Ti-V-Hf-Zr getter films were characterized and analyzed. The maximum SEY of unactivated Ti-V-Hf-Zr getter film on laser-treated aluminum alloy substrates ranged from 1.10 to 1.48. The X-ray photoelectron spectroscopy (XPS) spectra demonstrate that the Ti-V-Hf-Zr coated laser-treated aluminum alloy could be partially activated after being heated at 100 and 150 °C, respectively, for 1 h in a vacuum and also used as a pump. The results were demonstrated initially and the potential application should be considered in future particle accelerators.

The electron’s spin is essential to the stability of matter, and control over the spin opens up avenues for manipulating the properties of molecules and materials. The Pauli exclusion principle requires that two electrons in a single spatial eigenstate have opposite spins, and this fact dictates basic features of atomic states and chemical bond formation. The energy associated with interacting electron clouds changes with their relative spin orientation, and by manipulating the spin directions, one can guide chemical transformations. However, controlling the relative spin orientation of electrons located on two reactants (atoms, molecules or surfaces) has proved challenging. Recent developments based on the chiral-induced spin selectivity (CISS) effect show that the spin orientation is linked to molecular symmetry and can be controlled in ways not previously imagined. For example, the combination of chiral molecules and electron spin opens up a new approach to (enantio)selective chemistry. This Review describes the theoretical concepts underlying the CISS effect and illustrates its importance by discussing some of its manifestations in chemistry, biology and physics. Specifically, we discuss how the CISS effect allows for efficient long-range electron transfer in chiral molecules and how it affects biorecognition processes. Several applications of the effect are presented, and the importance of controlling relative spin orientations in multi-electron processes, such as electrochemical water splitting, is emphasized. We describe the enantiospecific interaction between ferromagnetic substrates and chiral molecules and how it enables the separation of enantiomers with ferromagnets. Lastly, we discuss the relevance of CISS effects to biological electron transfer, enantioselectivity and CISS-based spintronics applications. Chiral molecules can filter electrons according to their spin. This chiral-induced spin selectivity (CISS) effect can have important applications, such as in spintronics and in enantioseparation. This Review describes the CISS effect, its mechanism and its fascinating applications.

Under high-level ab initio calculations, the geometrical structures and nonlinear optical properties of M@P 4 (M=Li, Na, K and Li 3 O) and M@C 3 H 6 (M=Li and Li 3 O) were investigated; all were found to exhibit considerable first hyperpolarizabilities (18110, 1440, 22490, 50487, 2757 and 31776 au, respectively). The computational results revealed that when doping the (super)alkali atom M into the tetrahedral P 4 molecule, the original dual spherical aromaticity of the P 4 moiety is broken and new σ electron cloud is formed on the face of P 4 part interacting with the M atom. It was found that interaction of the (super)alkali atom with the σ electron cloud is a novel mode to produce diffuse excess electrons effectively to achieve a considerable β 0 value. Further, beyond the alkali atom, employing the superalkali unit can be a more effective approach to significantly enhance the first hyperpolarizability of the systems, due to the much lower vertical ionization potential. These results were further supported by the case of the (super)alkali atom interacting with the cyclopropane C 3 H 6 molecule with its typical σ aromatic electron cloud. Moreover, the β 0 values of the M@P 4 series are nonmonotonic dependent on alkali atomic number, namely, 1440 au (M = Na) < 18110 au (Li) < 22490 au (K), inferring that the distance between the alkali atom and the interacting surface with the σ electron cloud in P 4 is a crucial geometrical factor in determining their first hyperpolarizabilities. These intriguing findings will be advantageous for promoting the design of novel high-performance nonlinear optical materials. Figure A new mode through a (super)alkali atom interacting with the σ electron cloud is proposed to introduce diffuse excess electrons, which leads to large first hyperpolarizability ( β 0 ) in the sampled M@P 4 and M@C 3 H 6 (M=Li, Na, K and Li 3 O) series. Doping the superalkali atom could be an effective approach to enhancing the β 0 value of these systems because of the much lower vertical ionization potential

Photoexcitation in solids brings about transitions of electrons/holes between different electronic bands. If the solid lacks an inversion symmetry, these electronic transitions support spontaneous photocurrent due to the geometric phase of the constituting electronic bands: the Berry connection. This photocurrent, termed shift current, is expected to emerge on the timescale of primary photoexcitation process. We observe ultrafast evolution of the shift current in a prototypical ferroelectric semiconductor antimony sulfur iodide (SbSI) by detecting emitted terahertz electromagnetic waves. By sweeping the excitation photon energy across the bandgap, ultrafast electron dynamics as a source of terahertz emission abruptly changes its nature, reflecting a contribution of Berry connection on interband optical transition. The shift excitation carries a net charge flow and is followed by a swing over of the electron cloud on a subpicosecond timescale. Understanding these substantive characters of the shift current with the help of first-principles calculation will pave the way for its application to ultrafast sensors and solar cells.

When mobile impurities are introduced and coupled to a Fermi sea, new quasiparticles known as Fermi polarons are formed. There are two interesting, yet drastically different regimes of the Fermi polaron problem: (i) the attractive polaron (AP) branch connected to pairing phenomena spanning the crossover from BCS superfluidity to the Bose-Einstein condensation of molecules and (ii) the repulsive branch (RP), which underlies the physics responsible for Stoner’s itinerant ferromagnetism. Here, we study Fermi polarons in two-dimensional systems, where many questions and debates regarding their nature persist. The model system we investigate is a dopedMoSe2monolayer. We find the observed AP-RP energy splitting and the quantum dynamics of attractive polarons agree with the predictions of polaron theory. As the doping density increases, the quantum dephasing of the attractive polarons remains constant, indicative of stable quasiparticles, while the repulsive polaron dephasing rate increases nearly quadratically. The dynamics of Fermi polarons are of critical importance for understanding the pairing and magnetic instabilities that lead to the formation of rich quantum phases found in a wide range of physical systems including nuclei, cold atomic gases, and solids.

Molecular passivation is a prominent approach for improving the performance and operation stability of halide perovskite solar cells (HPSCs). Herein, we reveal discernible effects of diammonium molecules with either an aryl or alkyl core onto Methylammonium-free perovskites. Piperazine dihydriodide (PZDI), characterized by an alkyl core-electron cloud-rich-NH terminal, proves effective in mitigating surface and bulk defects and modifying surface chemistry or interfacial energy band, ultimately leading to improved carrier extraction. Benefiting from superior PZDI passivation, the device achieves an impressive efficiency of 23.17% (area ~1 cm 2 ) (low open circuit voltage deficit ~0.327 V) along with superior operational stability. We achieve a certified efficiency of ~21.47% (area ~1.024 cm 2 ) for inverted HPSC. PZDI strengthens adhesion to the perovskite via -NH 2 I and Mulliken charge distribution. Device analysis corroborates that stronger bonding interaction attenuates the defect densities and suppresses ion migration. This work underscores the crucial role of bifunctional molecules with stronger surface adsorption in defect mitigation, setting the stage for the design of charge-regulated molecular passivation to enhance the performance and stability of HPSC. Molecular passivation is promising for improving the performance and operation stability of perovskite solar cells. Here, authors employ piperazine dihydriodide to strengthen adhesion to MA-free perovskite via −NH 2 I and Mulliken charge distribution, realizing charge-regulated molecular passivation.

Low dimensional carbon-based materials can show intrinsic magnetism associated to p-electrons in open-shell π -conjugated systems. Chemical design provides atomically precise control of the π -electron cloud, which makes them promising for nanoscale magnetic devices. However, direct verification of their spatially resolved spin-moment remains elusive. Here, we report the spin-polarization of chiral graphene nanoribbons (one-dimensional strips of graphene with alternating zig-zag and arm-chair boundaries), obtained by means of spin-polarized scanning tunnelling microscopy. We extract the energy-dependent spin-moment distribution of spatially extended edge states with π -orbital character, thus beyond localized magnetic moments at radical or defective carbon sites. Guided by mean-field Hubbard calculations, we demonstrate that electron correlations are responsible for the spin-splitting of the electronic structure. Our versatile platform utilizes a ferromagnetic substrate that stabilizes the organic magnetic moments against thermal and quantum fluctuations, while being fully compatible with on-surface synthesis of the rapidly growing class of nanographenes. Zig-Zag graphene nanoribbons have edge states that are predicted to be spin-polarized, however, measurement of these spin-polarized states has proved elusive. Here, Brede et al overcome this challenge by growing graphene nanoribbons on ferromagnetic GdAu2, allowing for the direct observation of the spin-polarized edge states.