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<jats:title>Abstract</jats:title> <jats:p>Optimization of the aqueous electrolyte concentration is a significant issue in the development of high-performance aqueous rechargeable magnesium ion batteries (MIBs). In this study, a novel magnesium ion-based hybrid electrolyte composed of 2 M magnesium sulfate (MgSO4)/ 2 M acetate (MgOAc) was designed, and its corresponding physiochemical properties were systemically investigated by simply tuning their molar ratios. Additionally, a δ-MnO2/reduced graphene oxide (rGO) composite cathode material was successfully synthesized and delivered a high specific capacity and excellent rate capability in the optimized hybrid electrolyte. The as-fabricated device based on the δ-MnO2/rGO composite cathode exhibited a high operating voltage of up to 2 V and delivered a maximum energy density of 29.8 Wh kg-1 at the power density of 823 W kg-1. More importantly, the device showed impressive discharge capacity and excellent cycling stability even at the low temperature of -20 C. In view of the outstanding electrochemical properties of the δ-MnO2/rGO composite cathode in an optimized hybrid electrolyte of MgSO4/MgOAc, it could be regarded as a novel prototype for low-cost aqueous MIBs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The substrate is one of the key components that determines the quality of the epitaxial layers. However, the implications of growing two-dimensional layers on three-dimensional bulk substrates have not yet been fully understood, and these implications need to be studied for different combinations of materials and substrates. Here, we present a study that addresses the influence of the sapphire substrate off-cut angle on the final growth of two-dimensional layers of hexagonal boron nitride (h-BN) by metal-organic vapor phase epitaxy (MOVPE). A two-step wafer-scale process was used in one epitaxial MOVPE procedure. The main process starts with a self-limiting continuous growth of a BN buffer followed by flow-modulated epitaxy in the second step, and is used to study substrates with different off-cuts angles, pre-growth nitridation steps, and post-growth annealing. An initial nitridation step at the growth temperature allowed for the growth of an AlN sublayer. This layer is shown to smooth out the underlying sapphire and establishes an “effective” sapphire/AlN substrate. This step is also responsible for enforcing a specific growth of the BN layer in a crystallographic orientation, which is shown to strongly deviate from the substrate for off-cut angles larger than 0.3°. A substrate with off-cut angle of 1° clearly yields the highest quality of h-BN layers as evidenced by the lowest amount of debris on the surface, most intense x-ray diffraction signal, minimal Raman phonon linewidth and thinnest amorphous BN (a-BN) at the interface with the effective substrate. Our study shows that the off-cut angles of sapphire substrates strongly influence the final epitaxial h-BN, clearly indicating the importance of optimal substrate preparation for the growth of two-dimensional BN layers. Post-growth annealing in N2 atmosphere at 800 °C improves the top surface morphology of the final stack, as well as suppresses further the presence of a-BN. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Detecting light at the single-photon level is one of the pillars of emergent photonic technologies. This is realized through state-of-the-art superconducting detectors that offer efficient, broadband and fast response. However, the use of low TC superconducting thin films limits their operation temperature below 4 K. Here, we demonstrate proof-of-concept nanodetectors based on exfoliated, two-dimensional cuprate superconductor Bi2Sr2CaCu2O8-δ that exhibit single-photon sensitivity at telecom wavelength at a record temperature of T = 20 K. These non-optimized devices exhibit a slow (~ ms) reset time and a low detection efficiency (~ 10^(-4)). We realize the elusive prospect of single-photon sensitivity on a high-TC nanodetector thanks to a novel approach, combining van der Waals fabrication techniques and a non-invasive nanopatterning based on light ion irradiation. This result paves the way for broader application of single-photon technologies, relaxing the cryogenic constraints for single-photon detection at telecom wavelength.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High-performance photodetectors in the near-infrared (NIR) regime are essential for many advanced applications, such as optical communication, intelligent driving, and imaging system. However, conventional photoconductive infrared detectors commonly suffer from slow response speed and narrow spectral response. Here, we demonstrate a high performance NIR photodetector based on plasmonic sub-stoichiometry molybdenum oxide (MoO3-x) nanostructures/Graphene heterostructure. Empowered by surface plasmon resonance induced near-field enhancement in MoO3-x and the subsequent hot-electron injection (HEI), a fast response time (rise time ~6.7 μs, decay time ~12.5 μs), high responsivity (3.3 A/W), low noise equivalent power (~4.9 pW/Hz1/2), as well as wide response range from visible light to NIR is obtained at room temperature. The weak carrier-phonon interaction in graphene prevents the relaxation of injected hot electrons and enables efficient electron extraction. The response speed is nearly 4 orders of magnitude improved compared with other graphene-based hybrid devices with similar device structures. Moreover, the interfacial HEI breaks the bandgap limits of molybdenum oxide and further extends the response spectrum of the device to conventional band (C-band) of optical communication. Our proposed device architecture offers new strategy for developing high-performance infrared photodetectors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Achieving efficient nitrogen reduction reaction (NRR) under mild conditions is desirable but still challenging due to the lack of high-performance catalysts. Herein, we report the feasibility of a new type of two-dimensional conjugated metal−organic frameworks (cMOFs) featuring dense single-metal-atom sites, namely TM3(HAT)2 monolayers (TM = transition metal from groups 4−10, HAT = 1,4,5,8,9,12-hexaazatriphenylene), as NRR catalysts. We construct an efficient four-step screening strategy and identify the W3(HAT)2 monolayer as a candidate with considerable stability, activity, and selectivity based on density functional theory (DFT) computations. The analysis of bonding, ICOHP, and Bader charge uncovers the NRR activity origin of the TM3(HAT)2 monolayers and elucidates the structure−performance correlations. Meanwhile, our results show that a simple descriptor φ based on the inherent nature of the TM atoms can be applied to accelerate the screening of candidates without explicit DFT calculations. This work highlights a feasible strategy to prescreen and design high-performance cMOF-based electrocatalysts. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>The family of antiferromagnetic layered metal hexathiohypo diphosphates, M2P2S6 represents a versatile class of materials, particularly interesting for fundamental studies on magnetic properties in low dimensional structures, and yet exhibiting great potential for a broad variety of applications including catalysis, energy storage and conversion, and spintronics. In this work, three representatives of this family of 2D materials (M = Fe, Ni, and Mn) are exfoliated in the liquid phase under inert conditions and the nanosheet’s properties are studied in detail for different sizes of all three compounds. Centrifugation-based size selection is performed for this purpose. The exfoliability and structural integrity of the nanosheets is studied by statistical AFM and TEM measurements. Further, we report size and thickness dependent optical properties and spectroscopic metrics for the average material dimensions in dispersion, as well as the nanomaterials’ magnetic response using a combination of cryo-Raman and SQUID measurements. Finally, the material stability is studied semi-quantitatively, using time and temperature dependent extinction and absorbance spectroscopy, enabling the determination of the materials’ half-life, portion of reacted substance and the macroscopic activation energy for the degradation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Proximity-induced fine features and spin-textures of the electronic bands in graphene-based van der Waals heterostructures can be explored from the point of tailoring a twist angle. Here we study spin-orbit coupling and exchange coupling engineering of graphene states in the proximity of 1T-TaS<jats:sub>2</jats:sub> not triggering the twist, but a charge density wave in 1T-TaS<jats:sub>2</jats:sub>—a realistic low-temperature phase. Using density functional theory and effective model we found that the emergence of the charge density wave in 1T-TaS<jats:sub>2</jats:sub> significantly enhances Rashba spin-orbit splitting in graphene and tilts the spin texture by a significant Rashba angle—in a very similar way as in the conventional twist-angle scenarios. Moreover, the partially filled Ta d-band in the charge density wave phase leads to the spontaneous emergence of the in-plane magnetic order that transgresses via proximity from 1T-TaS<jats:sub>2</jats:sub> to graphene, hence, simultaneously superimposing along the spin-orbit also the exchange coupling proximity effect. To describe this intricate proximity landscape we have developed an effective model Hamiltonian and provided a minimal set of parameters that excellently reproduces all the spectral features predicted by the first-principles calculations. Conceptually, the charge density wave provides a highly interesting knob to control the fine features of electronic states and to tailor the superimposed proximity effects—a sort of twistronics without twist.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Zn-air batteries are a promising source of renewable energy for portable electronic devices and automobiles because of low-cost and high energy density. The efficiency of Zn-air batteries significantly rely on the oxygen reduction reaction in air cathode, development of efficient electrochemical catalysts is kindly important. In the past decade, inspired by graphene, porous carbon nanosheets have been widely developed and studied in the field of energy conversion and storage due to their adjustable structure, good and long-distance conductivity, rich porosity and abundant active sites, as well as excellent performance. In this review, various rational preparation methods towards porous carbon nanosheet-based catalysts are summarized. Then, the catalytic active sites in porous carbon nanosheets are classified, and the relationship between performance and active sites are discussed. At the end of this review, the challenges and future prospects for rational development of two-dimensional porous carbon-based electrochemical oxygen reduction reaction catalysts as air cathode for Zn-air batteries are discussed. This review will give guideline for the development of novel porous carbon-based materials for energy conversion and storage.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hybrid organic/inorganic Van der Waals heterostructures have emerged recently with enormous potential applications in nanotechnology and industrial areas. In these heterostructures, the interfacial effects can modulate the final properties, creating further possibilities in the design and operation of innovative devices. With this perspective in mind, we report on an experimental investigation of a hybrid organic/inorganic heterostructure of coronene and a few-layers MoS2. We observe a local enhancement of MoS2 optical properties using both far-field and near-field Raman scattering and photoluminescence. Mainly located at the MoS2 edges and defects, the local enhancement is due to the assembling of coronene molecules in MoS2, as confirmed by atomic force microscopy. Quantum semi-empirical and fully atomistic molecular dynamics (MD) simulations were also used to gain further insights into these phenomena. Our results pave the way to engineer molecules in two-dimensional (2D) layered nanomaterials and control and modulate optical phenomena.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Excitons in thin layers of semiconducting transition metal dichalcogenides are highly subject to the strongly modified Coulomb electron-hole interaction in these materials. Therefore, they do not follow the model system of a two-dimensional hydrogen atom. We investigate experimentally and theoretically excitonic properties in both the monolayer (ML) and the bilayer (BL) of MoSe<jats:sub>2</jats:sub> encapsulated in hexagonal BN. The measured magnetic field evolutions of the reflectance contrast spectra of the MoSe<jats:sub>2</jats:sub> ML and BL allow us to determine <jats:italic>g</jats:italic>-factors of intralayer A and B excitons, as well as the <jats:italic>g</jats:italic>-factors of the interlayer exciton. We explain the dependence of <jats:italic>g</jats:italic>-factors on the number of layers and excitation state can be explained using first principles calculations. Furthermore, we demonstrate that the experimentally measured ladder of excitonic s states in the ML can be reproduced using the<jats:bold> k·p</jats:bold> approach with the Rytova-Keldysh potential that describes the electron-hole interaction. In contrast, the analogous calculation for the BL case require taking into account the out-of-plane dielectric response of the MoSe<jats:sub>2</jats:sub> BL. </jats:p>