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<jats:title>Abstract</jats:title> <jats:p>Chiral single photons are highly sought to enhance encoding capacities or enable propagation-dependent routing in nonreciprocal devices. Unfortunately, most semiconductor quantum emitters (QE) produce only linear polarized photons unless external magnets are applied. Magnetic proximity coupling utilizing 2D ferromagnets promises to make bulky external fields obsolete. Here we directly grow Fe-doped MoS2 (Fe:MoS2) via CVD that displays pronounced hard ferromagnetic properties even in monolayer form. This approach with monolayer ferromagnets enabled us to fully utilize the strain from the pillar stressor on the substrate to form QE in WSe2 deterministically. The Fe:MoS2/WSe2 heterostructures display strong hysteretic magneto-response and high-purity chiral single photons with a circular polarization degree of 92±1% without external magnetic fields. Furthermore, the chiral single photons are robust against uncontrolled external stray fields. This ability to manipulate quantum states and transform linear polarized photons into high-purity chiral photons on-chip enables nonreciprocal device integration in quantum photonics.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>How to enhance the spin polarization, the Curie temperature and the perpendicular magnetic anisotropy (PMA) is very crucial to the applications of 2D magnets in spintronic devices. In this work, based on the experimental FeCl2 flakes and the predicted in-plane magnetic anisotropy (IMA) and lower Curie temperature of FeCl2 monolayer, we use first-principles and Monte Carlo simulation to explore the strain and carrier-doping effects on the electronic and magnetic properties of Janus FeClF monolayer. The structure is stable within -10 % to 2 % biaxial strain. Janus FeClF monolayer can experience transitions from a half-semiconductor to a spin gapless semiconductor around the 6 % compressive strain, and from the IMA to the PMA at the 7 % compressive strain. The super-exchange Fe-F/Cl-Fe interaction induces the ferromagnetic coupling, and the Curie temperature can be considerably enhanced from 56 K to 281 K at the 10 % compressive strain. The half-metallicity can be achieved whether under electron doping or hole doping. The Fe-d orbitals and the spin-orbit coupling interaction between occupied and unoccupied intraorbital states are responsible for the electronic phase transition and the magnetic anisotropy, respectively. Remarkably, the compressive 10 % strain and the 0.02 e doping collectively increase the Curie temperature to near room temperature (286 K). The high spin polarization (exhibiting spin gapless semiconductor and half-metal), the PMA and the near-room-temperature ferromagnetism induced by strain and doping make Janus FeClF a promising candidate for 2D spintronic applications, which will stimulate experimental and theoretical broad studies on this class of Janus monolayers FeXY (X,Y=F, Cl, Br, and X≠Y).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetism in atomically thin two-dimensional (2D) materials is attractive for several applications such as memory devices, sensors, biomedical devices, etc. Here, we have synthesized 2D manganese telluride (MnTe) using a scalable synthesis method consisting of melting followed by liquid phase exfoliation (LPE). Both bulk and 2D MnTe samples were analyzed for their magnetic behavior at room temperature and low temperatures (10 K). A change from antiferromagnetic nature to paramagnetic behavior was observed in 2D MnTe flakes. Enhanced magnetic saturation values (up to 400% increase) were observed as compared to bulk MnTe in RT. Density functional theory (DFT) simulations explain the layer-dependent magnetic behavior of the 2D MnTe flakes, as well the antiferromagnetic to paramagnetic transition due to an unbalanced spin population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two-dimensional (2D) tin monoxide (SnO) has attracted much attention owing to its distinctive electronic and optical properties, which render itself suitable as a channel material in field effect transistors (FETs). However, upon contact with metals for such applications, the Fermi level pinning effect may occur, where states are induced in its band gap by the metal, hindering its intrinsic semiconducting properties. We propose the insertion of graphene at the contact interface to alleviate the metal-induced gap states. By using gold (Au) as the electrode material and monolayer SnO (mSnO) as the channel material, the geometry, bonding strength, charge transfer and tunnel barrier of charges, and electronic properties including the work function, band structure, density of states, and Schottky barriers are thoroughly investigated using first-principles calculations for the structures with and without graphene to reveal the contact behaviours and Fermi level depinning mechanism. It has been demonstrated that strong covalent bonding is formed between gold and mSnO, while the graphene interlayer forms weak van der Waals interactions with both materials, which minimises the perturbance to the band structure of mSnO. The effects of out-of-plane compression are also analysed to assess the performance of the contact under mechanical deformation, and a feasible fabrication route for the heterostructure with graphene is proposed. This work systematically explores the properties of the Au–mSnO contact for applications in FETs and provides thorough guidance for future exploitation of 2D materials in various electronic applications and for selection of buffer layers to improve the metal–semiconductor contact.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Oxidation-derived nanoparticles (CDs/TiOx) of Ti3C2 were prepared for the first time by simple oxidation of Ti3C2. CDs/TiOx was a two-dimensional hybrid of amorphous carbon and titanium oxides with a lateral dimension of about 50 nm. H2O2 was used as the oxygenator and the reduction product was H2O, which was environmentally friendly and inexpensive. Carboxyl, carbonyl, and hydroxyl groups are formed naturally during the oxidation derivative process. The decreased size increases the specific surface area and provides the possibility for the abundant presence of functional groups. The oxidation process converts MXene from reducing to oxidizing and achieves the ability of the derivatives to mimic peroxidase. Compared with natural horseradish peroxidase, the Michaelis constant for H2O2 was 10-fold lower. A cascade catalytic reaction system of glucose oxidase with CDs/TiOx was constructed, and the generated H2O2 could be further used to catalyze the oxidation of NADH to NAD+. With the assistance of NAD+-dependent dehydrogenase, NADH could be restored to 95% of the initial level. This assay system can detect glucose levels scientifically and accurately in the range of 0.02-10 mM and remains viable after 20 cycles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Manipulating the interlayer twist angle is a powerful tool to tailor the properties of layered two-dimensional crystals. The twist angle has a determinant impact on these systems’ atomistic structure and electronic properties. This includes the corrugation of individual layers, formation of stacking domains and other structural elements, and electronic structure changes due to the atomic reconstruction and superlattice effects. However, how these properties change with the twist angle, θ, is not yet well understood. Here, we monitor the change of twisted bilayer MoS2 characteristics as a function of θ. We identify distinct structural regimes, each with particular structural and electronic properties. We employ a hierarchical approach ranging from a reactive force field through the density-functional-based tight-binding approach and density-functional theory. To obtain a comprehensive overview, we analyzed a large number of twisted bilayers with twist angles in the range of θ = 0.2° . . . 59.6°. Some systems include up to half a million atoms, making structure optimization and electronic property calculation challenging. For 13° ≤ θ ≤ 47°, the structure is well-described by a moiré regime composed of two rigidly twisted monolayers. At small twist angles (θ ≤ 3° and 57° ≤ θ), a domain-soliton regime evolves, where the structure contains large triangular stacking domains, separated by a network of strain solitons and short-ranged high-energy nodes. The corrugation of the layers and the emerging superlattice of solitons and stacking domains affects the electronic structure. Emerging predominant characteristic features are Dirac cones at K and kagome bands. These features flatten for θ approaching 0° and 60°. Our results show at which range of θ the characteristic features of the reconstruction, namely extended stacking domains, the soliton network, and superlattice, emerge and give rise to exciting electronics. We expect our findings also to be relevant for other twisted bilayer systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two-dimensional (2D) materials possess remarkable strain tolerance and exhibit strain-tunable properties, making them highly promising for flexible device applications. Defects within these materials significantly impact their optoelectronic response to strain. In this study, we investigate the influence of strain on the electrical properties of monolayer MoS2, emphasizing the pivotal role played by intrinsic defects in shaping the material's electrical and optoelectronic response under strain. We observed an enhancement in photocurrent and persistent photoconductivity at specific strains, indicating the activation of defects at these strain values, thus enhancing the photoresponse. Moreover, our device exhibits diodic behaviour at specific strain values after prolonged measurements under a static field, suggesting a reduction in the migration energy of defects caused by the applied strain. This finding holds significant implications for memory, logic, and flexible devices. Additionally, we observe an increase in electron mobility under tensile strain, with our flexible field-effect transistor exhibiting higher mobility (~38 cm2/V.s) at 0.4% strain. Our study provides insight into the role of strain in the activation and migration of defects in monolayer MoS2 and opens up new avenues for the development of multifunctional ultra-thin flexible devices and memory applications..</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Phononic crystals (PnCs) are artificially patterned media exhibiting bands of allowed and forbidden zones for phonons – in analogy to the electronic band structure of crystalline solids arising from the periodic arrangement of atoms. Many emerging applications of PnCs from solid-state simulators to quantum memories could benefit from the on-demand tunability of the phononic band structure. Here, we demonstrate the fabrication of suspended graphene PnCs in which the phononic band structure is controlled by mechanical tension applied electrostatically. We show signatures of a mechanically tunable phononic band gap. The experimental data supported by simulation suggests a phononic band gap at 28–33 MHz in equilibrium, which upshifts by 9 MHz under a mechanical tension of 3.1 N/m. This is an essential step towards tunable phononics paving the way for more experiments on phononic systems based on 2D materials.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The magnetic topological insulator MnBi2Te4 has attracted a lot of research interests for its exotic properties due to the interplay between nontrivial topology and magnetism. Here, we report the photocurrent response of MnBi2Te4 flakes under the excitation wavelengths between 633nm and 4000nm measured by scanning photocurrent microscopy. We observe a significant polarization dependent photocurrent response at the interface between metal electrode and MnBi2Te4, while the photocurrent response remains polarization-independent at MnBi2Te4 layer steps. The polarization dependent photocurrent at the MnBi2Te4-metal electrode interface, which is attributed to the polarization dependent light absorption at the interface, preserves in the whole tested wavelength range. The responsivity of the device is 80 μA•W-1. This responsivity as well as photocurrent polarity is consistent with the results calculated based on a photo-thermoelectric generation mechanism, thus we infer that photo-thermoelectric effect dominates in the photocurrent generation at MnBi2Te4-metal interface. Our results reveal the photoelectric response mechanism of the emerging material MnBi2Te4 for its potential optoelectronic applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Employing the original, all-optical method, we quantify the magnetic susceptibility of a two-dimensional electron gas (2DEG) confined in the MoSe<jats:sub>2</jats:sub> monolayer in the range of low and moderate carrier densities. The impact of electron-electron interactions on the 2DEG magnetic susceptibility is found to be particularly strong in the limit of, studied in detail, low carrier densities. Following the existing models, we derive the value of <jats:italic>g</jats:italic> <jats:sub>0</jats:sub> = 2.5 ± 0.4 for the bare (in the absence of the interaction effects) <jats:italic>g</jats:italic>-factor of the ground state electronic band in the MoSe<jats:sub>2</jats:sub> monolayer. The derived value of this parameter is discussed in the context of estimations from other experimental approaches. Surprisingly, the conclusions drawn differ from theoretical ab-initio studies.</jats:p>