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<jats:title>Abstract</jats:title> <jats:p>We present a computational search for spin spiral ground states in two-dimensional transition metal halides that are experimentally known as van der Waals bonded bulk materials. Such spin spirals break the rotational symmetry of the lattice and lead to polar ground states where the axis of polarization is strongly coupled to the magnetic order (type II multiferroics). We apply the generalized Bloch theorem in conjunction with non-collinear density functional theory calculations to find the spiralling vector that minimizes the energy and then include spin–orbit coupling to calculate the preferred orientation of the spin plane with respect to the spiral vector. We find a wide variety of magnetic orders ranging from ferromagnetic, stripy anti-ferromagnetic, 120<jats:sup>∘</jats:sup> non-collinear structures and incommensurate spin spirals. The latter two introduce polar axes and are found in the majority of materials considered here. The spontaneous polarization is calculated for the incommensurate spin spirals by performing full supercell relaxation including spinorbit coupling and the induced polarization is shown to be strongly dependent on the orientation of the spiral planes. We also test the effect of Hubbard corrections on the results and find that for most materials LDA + U results agree qualitatively with LDA. An exception is the Mn halides, which are found to exhibit incommensurate spin spiral ground states if Hubbard corrections are included whereas bare LDA yields a 120<jats:sup>∘</jats:sup> non-collinear ground state.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The development of multifunctional electromagnetic wave (EMW) absorbing materials become the inevitable course for the rapid progress of military weapons and 5 G smart communication technology. The construction of engineered multi-relaxation interfaces provides an effective means for materials to enhance EMW attenuation. Herein, MXene derived Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/TiO<jats:sub>2</jats:sub> heterogeneous interface is tailored through the <jats:italic>in-situ</jats:italic> anneal, where the multi-relaxation nano-interfaces are achieved. When the annealed temperature reaches 450 °C, the maximum reflection loss of Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/TiO<jats:sub>2</jats:sub> is −30.4 dB at 5.67 GHz due to the enhanced interfacial polarization and optimized impedance matching. More importantly, an effective reduction in the radar cross section up to −53 dBm<jats:sup>2</jats:sup> was achieved by using the Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/TiO<jats:sub>2</jats:sub> as the octagonal patch through effective shape design. Therefore, we believe that Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/TiO<jats:sub>2</jats:sub> with optimized shape has a broad application prospect in the field of radar stealth and practical electromagnetic protection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The rose-inspired photocatalyst, 1T-MoS<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/TiO<jats:sub>2</jats:sub>, demonstrated exceptional activity in the simultaneous removal of hexavalent chromium (Cr(VI)) and methylene blue (MB), achieving high efficiencies of 97.7% and 97.2% respectively. Furthermore, it exhibited effective degradation of another dye, Rhodamine B (Rh.B). Scanning electron microscopy figures showed its unique nanoflower morphology. The introduction of titanium carbide nanosheets (Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic>) and the formation of Schottky junctions can effectively prolong the carrier lifetime. The degradation path of MB was deduced by liquid chromatography–mass spectrometry, which confirmed the process of photocatalytic decomposition of organic pollutants. Compared to physical purification methods, it offers the advantage of not only removing pollutants but also degrading them. Furthermore, by utilizing MB as a sacrificial agent, the reduction can take place in a mild neutral environment, resulting in minimized secondary pollution. Through its distinctive three-dimensional structure and the Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic> cocatalyst, the 1T-MoS<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic>/TiO<jats:sub>2</jats:sub> photocatalyst demonstrates remarkable catalytic activity, and effective purification of wastewater containing Cr(VI) and organic dyes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work reports on the hardware implementation of analog dot-product operation on arrays of two-dimensional (2D) hexagonal boron nitride (h-BN) memristors. This extends beyond previous work that studied isolated device characteristics towards the application of analog neural network accelerators based on 2D memristor arrays. The wafer-level fabrication of the memristor arrays is enabled by large-area transfer of CVD-grown few-layer (8 layers) h-BN films. Individual devices achieve an on/off ratio of &gt;10, low voltage operation (∼0.5 <jats:italic>V</jats:italic> <jats:sub>set</jats:sub>/<jats:italic>V</jats:italic> <jats:sub>reset</jats:sub>), good endurance (&gt;6000 programming steps), and good retention (&gt;10<jats:sup>4</jats:sup> s). The dot-product operation shows excellent linearity and repeatability, with low read energy consumption (∼200 aJ to 20 fJ per operation), with minimal error and deviation over various measurement cycles. Moreover, we present the implementation of a stochastic logistic regression algorithm in 2D h-BN memristor hardware for the classification of noisy images. The promising resistive switching characteristics, performance of dot-product computation, and successful demonstration of logistic regression in h-BN memristors signify an important step towards the integration of 2D materials for next-generation neuromorphic computing systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Graphene absorption from the visible to infrared spectrum has great potential and broad applications in miniature of modern optoelectronic biosensors and photodetectors. However, graphene has zero bandgap energy, which limits its absorption to 2.3% in the visible and infrared spectrums. Here, we propose a metastructure to optimize graphene absorption in the visible to near-infrared frequency regions. The metastructure, comprising an array of aluminum square blocks (Al-SBs) on a graphene layer, a silica spacer, and an Al reflector, is investigated for absorption enhancement. This work deciphers the effect of the periodicity of decorated Al-SBs on the evolution of dual-band absorption in single-layer graphene under normal incidence. The electromagnetic signatures of two excited modes indicate that surface plasmons and magnetic dipole plasmons are mediators of absorption. The investigation into the impact of geometrical parameters illustrates that the coexisting phenomena of a relative broad peak and a relative sharp peak have been achieved simultaneously with high efficiency. The dynamic manipulation of surface plasmons and magnetic dipole plasmons presents great potential for a diverse range of applications, such as sensing and imaging. By controlling the periodicity of Al-SBs, it is possible to achieve active control of surface plasmon resonance, and a detection range of 300 nm is observed. Dynamic control of the magnetic dipole plasmon is successfully achieved by modifying the electrical environment of the graphene layer, which is realized by altering the underlying spacer material. Collectively, the findings of this study demonstrate the significant potential of the suggested metastructure for its prospective applications in optoelectronic devices, including biosensors, photovoltaics, and photodetectors that rely on the dynamic control of surface and magnetic plasmon resonances.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Integration of graphene and hexagonal boron nitride (hBN) in lateral heterostructures has provided a route to broadly engineer the material properties by quantum confinement of electrons or introduction of novel electronic and magnetic states at the interface. In this work we demonstrate lateral heteroepitaxial growth of graphene nanoribbons (GNRs) passivated by hBN using high-temperature molecular beam epitaxy (HT-MBE) to grow graphene in oriented hBN trenches formed <jats:italic>ex-situ</jats:italic> by catalytic nanoparticle etching. High-resolution atomic force microscopy (AFM) reveals that GNRs grow epitaxially from the etched hBN edges, and merge to form a GNR network passivated by hBN. Using conductive AFM we probe the nanoscale electrical properties of the nanoribbons and observe quasiparticle interference patterns caused by intervalley scattering at the graphene/hBN interface, which carries implications for the potential transport characteristics of hBN passivated GNR devices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The energy landscape of optical excitations in mono- and few-layer transition metal dichalcogenides (TMDs) is dominated by optically bright and dark excitons. These excitons can be fully localized within a single TMD layer, or the electron- and the hole-component of the exciton can be charge-separated over multiple TMD layers. Such intra- or interlayer excitons have been characterized in detail using all-optical spectroscopies, and, more recently, photoemission spectroscopy. In addition, there are so-called hybrid excitons whose electron- and/or hole-component are delocalized over two or more TMD layers, and therefore provide a promising pathway to mediate charge-transfer processes across the TMD interface. Hence, an in-situ characterization of their energy landscape and dynamics is of vital interest. In this work, using femtosecond momentum microscopy combined with many-particle modeling, we quantitatively compare the dynamics of momentum-indirect intralayer excitons in monolayer WSe<jats:sub>2</jats:sub> with the dynamics of momentum-indirect hybrid excitons in heterobilayer WSe<jats:sub>2</jats:sub>/MoS<jats:sub>2</jats:sub>, and draw three key conclusions: First, we find that the energy of hybrid excitons is reduced when compared to excitons with pure intralayer character. Second, we show that the momentum-indirect intralayer and hybrid excitons are formed via exciton-phonon scattering from optically excited bright excitons. And third, we demonstrate that the efficiency for phonon absorption and emission processes in the mono- and the heterobilayer is strongly dependent on the energy alignment of the intralayer and hybrid excitons with respect to the optically excited bright exciton. Overall, our work provides microscopic insights into exciton dynamics in TMD mono- and bilayers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Here we perform angle and time-resolved photoelectron spectroscopy on the commensurate Charge Density Wave (CDW) phase of 1T-TaS2. Data with different probe pulse polarization are employed to map the dispersion of electronic states below and above the chemical potential. Upon photoexcitation, the fluctuations of CDW order erase the band dispersion and squeeze the electronic states near to the chemical potential. This transient phase sets within half a period of the coherent lattice motion and is favored by strong electronic correlations. The experimental results are compared to Density-Functional Theory (DFT) calculations with a self-consistent evaluation of the Coulomb repulsion. Our simulations indicate that the screening of Coulomb repulsion depends on the stacking order of the TaS2 layers. The entanglement of such degrees of freedom suggest that both the structural order and electronic repulsion are locally modified by the photoinduced CDW fluctuations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In a two-dimensional noncentrosymmetric transition metal dichalcogenide Ising superconductor in the fluctuating regime under the action of a uniform external electromagnetic field, a second-harmonic generation effect takes place.&amp;#xD;There emerge two contributions to this effect, one conventional, which is due to the electron gas in its normal state, and the other one is of the Aslamazov-Larkin nature. &amp;#xD;Namely, it originates from the presence of fluctuating Cooper pairs in the system when the temperature approaches the temperature of the superconducting transition in the sample from above. &amp;#xD;Employing a usual approach to Ising superconductors, we lift the valley degeneracy by application of a weak out-of-plane external magnetic field, which produces a Zeeman effect. &amp;#xD;In calculations, we use the Boltzmann equations approach for the electron gas in the normal state and the time-dependent Ginzburg-Landau equations for the fluctuating Cooper pairs and show the emergence of second harmonic generation current characterized by temperature-dependent broadening and redshift.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Nowadays, the production of pure water from saltwater and wastewater is one of the most challenging issues. Polymeric materials represent, at the moment, the best solution for membranes technology but new materials with improved functionalities are desirable to overcome the typical limitations of polymers. In this work, graphene membranes with superior filtration properties are fabricated by stacking up to three graphene layers on a porous support and exploiting the intrinsic nanopores of graphene to filter diclofenac (drug), and methylene blue (dye). The rejection improves increasing the number of the stacked graphene layers, with the best results obtained with three graphene layers. Mass diffusion properties depend on the size of the probe molecule, consistently with the existence of intrinsic nanometer-sized pores within graphene. From the results of an in depth TEM analysis and molecular dynamics simulations it is inferred that graphene staking results in a decrease of effective membrane pore sizes to about 13 Å diameter which corresponds to 97% rejection for diclofenac, and methylene blue after one hour filtration.</jats:p>