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<jats:title>Abstract</jats:title> <jats:p>We report the epitaxial growth of PdTe2 ultrathin films on a topological insulator Bi2Se3. A prominent moiré pattern was observed in STM measurements. The moiré periodicity increases as film thickness decreases, indicating a lattice expansion of epitaxial PdTe2 thin films at lower thicknesses. In addition, our simulations based on a multilayer relaxation technique reveal uniaxial lattice strains at the edge of PdTe2 domains, and anisotropic strain distributions throughout the moiré supercell with a net change in lattice strain up to ~2.9%. Our DFT calculations show that this strain effect leads to a narrowing of the band gap at Γ point near the Fermi level. Under a strain of ~2.8%, the band gap at Γ closes completely. Further increasing the lattice strain makes the band gap reopen and the order of conduction band and valence bands inverted in energy. The experimental and theoretical results shed light on a method for constructing quantum grids of topological band structure under the modulation of moiré potentials.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Mirror twin grain boundary (MTB) defects, being a special type of high-symmetry one-dimensional (1D) defects in two-dimensional atomically thin transition metal dichalcogenides (TMDCs), have received considerable interests due to their unique structures and intriguing 1D properties. However, formation and distribution of MTBs in hybrid TMDC materials such as heterojunction remain scarcely studied. Herein, we investigate the spatial distribution, lattice registry and formation mechanism of MTBs in molecular beam epitaxy (MBE) grown monolayer WSe<jats:sub>2</jats:sub>-MoSe<jats:sub>2</jats:sub> lateral heterojunctions using atomic-resolution annular dark-field scanning transmission electron microscopy (ADF-STEM). MTBs manifest a much higher density in MoSe<jats:sub>2</jats:sub> than in WSe<jats:sub>2</jats:sub> domains with a few of them spanning coherently across the domain interface. Compositionally, a Mo-dominant rather than W-dominant configuration was observed in those MTBs located in WSe<jats:sub>2</jats:sub> domains and its origin can be attributed to the preferrable Mo substitution to W along the MTBs occurring at the later MoSe<jats:sub>2</jats:sub> growth period. This proposed mechanism is supported by <jats:italic>ab-initio</jats:italic> density functional theory calculations and substitution dynamics captured by <jats:italic>in-situ</jats:italic> ADF-STEM. The present study deepens our understanding of MTBs in heterostructured TMDCs, which may also serve as an excellent platform for the exploration of intriguing 1D physics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We propose that a device composed of two vertically stacked monolayer graphene Josephson&amp;#xD;junctions can be used for Cooper pair splitting. The hybridization of the Andreev bound states of&amp;#xD;the two Josephson junction can facilitate non-local transport in this normal-superconductor hybrid&amp;#xD;structure, which we study by calculating the non-local differential conductance. Assuming that one&amp;#xD;of the graphene layers is electron and the other is hole doped, we find that the non-local Andreev&amp;#xD;reflection can dominate the differential conductance of the system. Our setup does not require the&amp;#xD;precise control of junction length, doping, or superconducting phase difference, which could be an&amp;#xD;important advantage for experimental realization.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the search for novel 2D materials with potentially valuable properties, such as a tuneable band gap for optoelectronic or catalytic applications, solid solutions hold the potential to significantly expand the inventory of available 2D nanomaterials. In this study, we present for the first-time the synthesis of such 2D rhodium trihalide solid solutions: RhBr<jats:italic> <jats:sub>x</jats:sub> </jats:italic>Cl<jats:sub>3−<jats:italic>x</jats:italic> </jats:sub> and RhBr<jats:sub> <jats:italic>x</jats:italic> </jats:sub>I<jats:sub>3−<jats:italic>x</jats:italic> </jats:sub>. We use thermodynamic simulations and simultaneous thermal analysis to predict conditions for their rational synthesis and to investigate suitable chemical vapor transport (CVT) parameters for these solid solutions. The evolution of the lattice parameters is investigated by powder X-ray diffraction, showing an isostructural relationship of the synthesized compounds and only minor deviation from Vegard’s law. The optical band gap of these materials can be tuned in an energy range from 1.5 eV (RhCl<jats:sub>3</jats:sub>) to 1.2 eV (RhI<jats:sub>3</jats:sub>) by choosing the composition of the solid solution, while the samples also exhibit photoluminescence in similar energy ranges. Ultimately, the successful deposition of bulk as well as ultrathin 2D nanocrystals of RhBr<jats:italic> <jats:sub>x</jats:sub> </jats:italic>Cl<jats:sub>3−<jats:italic>x</jats:italic> </jats:sub> by CVT from 925 °C to 850 °C is shown, where the composition of the deposited crystals is precisely controlled by the choice of the starting composition and the initial amount of material. The high quality of the obtained nanocrystals is confirmed by atomic force microscopy, high resolution transmission electron microscopy and selected area electron diffraction. For RhBr<jats:sub> <jats:italic>x</jats:italic> </jats:sub>I<jats:sub>3−<jats:italic>x</jats:italic> </jats:sub>, the CVT from 900 °C to 825 °C is more difficult and has only been practically demonstrated for an exemplary case. According to the observed properties, these novel solid solutions and nanocrystals show a great potential for an application in optoelectronic devices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Nanomechanical spectroscopy (NMS) is a recently developed approach to determine optical absorption spectra of nanoscale materials via mechanical measurements. It is based on measuring changes in the resonance frequency of a membrane resonator vs. the photon energy of incoming light. This method is a direct measurement of absorption, which has practical advantages compared to common optical spectroscopy approaches. In the case of two-dimensional (2D) materials, NMS overcomes limitations inherent to conventional optical methods, such as the complications associated with measurements at high magnetic fields and low temperatures. In this work, we develop a protocol for NMS of 2D materials that yields two orders of magnitude improved sensitivity compared to previous approaches, while being simpler to use. To this end, we use electrical sample actuation, which simplifies the experiment and provides a reliable calibration for greater accuracy. Additionally, the use of low-stress silicon nitride membranes as our substrate reduces the noise-equivalent power to NEP = 890 fW/√Hz, comparable to commercial semiconductor photodetectors. We use our approach to spectroscopically characterize a two-dimensional transition metal dichalcogenide (WS<jats:sub>2</jats:sub>), a layered magnetic semiconductor (CrPS<jats:sub>4</jats:sub>), and a plasmonic supercrystal consisting of gold nanoparticles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Alkali metal halides have recently received great attention as additives in the chemical vapor deposition (CVD) process to promote the growth of transition metal dichalcogenides (TMDs). However, the multi-faceted role of these halide salts in modulating the properties and quality of the TMD monolayers remains mechanistically unclear. In this work, by introducing excessive gaseous NaCl into the CVD system, we demonstrate that preferential NaCl deposition along the monolayer edges causes large in situ strain that can invoke localized domains of high defect density and 2H to 1T phase transformation. HR-STEM, Raman mapping and molecular dynamic simulations revealed that higher NaCl concentrations can promote the coalescence of independent local strain domains, further increasing the 1T/2H phase ratio and defect density. Furthermore, excessive NaCl was also proven by DFT calculations to convert thermodynamic growth to kinetic growth, accounting for the unique cloud shape MoS2 crystals acquired. Compared with post-growth strain processing methods, this one-step approach for phase and defect engineering not only represents a deeper understanding of the role that NaCl plays in the CVD process, but also provides the convenient means to controllably synthesize conductive/defect-rich materials for further electrocatalysis and optoelectronic applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Novel ”quasi two dimensional” typically layered (semi) metals offer a unique opportunity to control the density and even the topology of the electronic matter. In intercalated MoT e2 type II Weyl semi - metal the tilt of the dispersion relation cones is so large that topologically of the Fermi surface is distinct from a more conventional type I. Superconductivity observed recently in this compound [Zhang et al, 2D Materials 9, 045027 (2022)] demonstrated two puzzling phenomena: the gate voltage has no impact on critical temperature, Tc, in wide range of density, while it is very sensitive to the inter - layer distance. The phonon theory of pairing in a layered Weyl material including the effects of Coulomb repulsion is constructed and explains the above two features in MoT e2. The first feature turns out to be a general one for any type II topological material, while the second reflects properties of the intercalated materials affecting the Coulomb screening.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two-dimensional (2D) materials are considered as promising candidates for constructing revolutionary electronic devices. However, the difficulties in control of the polarity, concentration, and spatial distribution of charge carriers in 2D materials make the construction of 2D p-n junctions rather challenging. Here, we report the successful construction of ultrafast-programmable 2D p-n homojunctions with semi-floating-gate (SFG) configuration based on vertically stacked molybdenum disulfide (MoS2)/hexagonal boron nitride (hBN)/multilayer graphene (MLG) van der Waals (vdWs) heterostructure. By partially electrostatically doping the MoS2 channel under different control-gate voltage pulses, three types of 2D homojunctions, including p-n, n+-n, and n-n, can be constructed. The 2D p-n homojunction can be ultrafastly programmed within 160 ns and exhibits a large rectification ratio of ~104. Based on a modified Schockley equation, an ideality factor of ~ 2.05 is extracted, indicating the recombination process dominated transport mechanism. The MoS2 2D p-n homojunction shows a maximum electrical power conversion efficiency up to 2.66% under a weak light power of 0.61 nW and a high photovoltage responsivity of 5.72×109 V/W. These results indicate that the ultrafast-programmable 2D p-n homojunction has great potential for high-performance photovoltaics and optoelectronics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic skyrmion, as a topologically protected whirl-like soliton, has been subjecting to growing interest in non-volatile spintronic memories and logic devices. More recently, much effort has been devoted to searching for skyrmion host materials in two-dimension (2D) systems, where intrinsic inversion symmetry breaking and large Dzyaloshinskii-Moriya interaction (DMI) are most desirable to realize the field-free skyrmion state. Among these, 2D magnetic Janus materials become important candidates for inducing sizable DMI and chiral spin textures. Herein, we demonstrate that layer-dependent DMI and field-free magnetic skyrmion can exist in multilayer MnSTe. Moreover, the strong interlayer exchange coupling existing Bethe-Slater-curve-like behaviors and arising from the Mn-Mn double exchange mechanism is illustrated in bilayer MnSTe. Concurrently, we uncover that the distributions of DMIs in multilayer MnSTe can be understood as the significant contribution of intermediate part DMI via using the three-site Fert-Lévy model. Our results unveil the great potential for designing skyrmion-based spintronic devices in multilayer 2D materials.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Two-dimensional (2D) MXenes have attracted significant attention in electromagnetic interference (EMI) shielding applications due to their unique properties, such as excellent metallic conductivity, high surface area, 2D geometry, tunable surface chemistry, and solution processability. In this study, we present a simple and versatile way for introducing multiple internal interfaces into the Ti<jats:sub>3</jats:sub>C<jats:sub>2</jats:sub>T<jats:italic> <jats:sub>x</jats:sub> </jats:italic> MXenes using insulating graphene oxide (GO) intercalants to enhance internal scattering, resulting in improved absorption loss and EMI shielding effectiveness (SE). Amine-functionalized MXene flakes exhibit a positive surface charge, while GO flakes have a negative charge at acidic pH levels. The functionalized MXene and GO flakes electrostatically self-assemble to form 2D/2D heterostack of MXene/GO nanosheets, and simultaneously generate multiple internal interfaces with significant impedance mismatch. The 2D/2D alternating heterostack of MXene/GO enhances the internal scattering of incident EM waves. Interestingly, despite their inferior electrical conductivity, the MXene/GO heterostack films exhibit higher EMI SE values than the randomly mixed hybrid films, and even outperform pristine MXene with larger electrical conductivity. This enhancement is attributed to enhanced absorption of electromagnetic waves resulting from strong internal scattering at the multiple internal interfaces in the heterostack film.</jats:p>