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<jats:title>Abstract</jats:title> <jats:p>Raman spectroscopy is widely used to assess the quality of 2D materials thin films. This report focuses on PtSe<jats:sub>2</jats:sub>, a noble transition metal dichalcogenide which has the remarkable property to transit from a semi-conductor to a semi-metal with increasing layer number. While polycrystalline PtSe<jats:sub>2</jats:sub> can be grown with various crystalline qualities, getting insight into the monocrystalline intrinsic properties remains challenging. We report on the study of exfoliated 1 to 10 layers PtSe<jats:sub>2</jats:sub> by Raman spectroscopy, featuring record linewidth. The clear Raman signatures allow layer-thickness identification and provides a reference metrics to assess crystal quality of grown films.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Control of the charge carrier concentration is essential for applications of graphene. Here, we demonstrate the doping of epitaxial graphene on SiC(0001) via charge transfer from an adsorbed layer of Cs atoms with sub-monolayer coverage. The electronic structure of the graphene is analyzed using X-ray and angle-resolved photoelectron spectroscopy (XPS, ARPES). In H-intercalated, quasi-freestanding monolayer graphene (QFMLG), the Dirac point can be tuned continuously from p-type to strong n-type doping. For strong n-type doping, analysis of the core level binding energies implies a deviation from a rigid band shift. This might be explained by an increased screening of the atomic core potential due to the higher number of charge carriers per C atom in the graphene layer. Furthermore, charge transfer into the SiC substrate leads to a change in band bending at the SiC/QFMLG interface, which saturates into a flat band scenario at higher Cs coverage. An analysis of the Fermi surfaces suggests an increasing electron-phonon-coupling in strongly doped QFMLG. In monolayer graphene (MLG), which is intrinsically n-type doped due to the presence of the buffer layer at the SiC interface, n-type doping can be enhanced by Cs evaporation in a similar fashion. In contrast to QFMLG, core level spectra and Dirac cone position in MLG apparently show a rigid band shift even for very high doping, emphasizing the importance of the substrate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of emergent quantum phases in twisted bilayer graphene prompted a flurry of activities in van-der-Waals (vdW) materials beyond graphene. Most current twisted experiments use a so-called tear-and-stack method using a polymer called PPC. However, despite the clear advantage of the current PPC tear-and-stack method, there are also technical limitations, mainly a limited number of vdW materials that can be studied using this PPC-based method. This technical bottleneck has been preventing further development of the exciting field beyond a few available vdW samples. To overcome this challenge and facilitate future expansion, we developed a new tear-and-stack method using a strongly adhesive polycaprolactone (PCL). With similar angular accuracy, our technology allows fabrication without a capping layer, facilitating surface analysis and ensuring inherently clean interfaces and low operating temperatures. More importantly, it can be applied to many other vdW materials that have remained inaccessible with the PPC-based method. We present our results on twist homostructures made with a wide choice of vdW materials – from two well-studied vdW materials (graphene and MoS2) to the first-ever demonstrations of other vdW materials (NbSe2, NiPS3, and Fe3GeTe2). Therefore, our new technique will help expand moiré physics beyond few selected vdW materials and open up more exciting developments.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We theoretically examined how the dielectric screening of two-dimensional layered materials affects the dipolar interaction between interlayer excitons in few-layer van der Waals structures. Our analysis indicates that the dipolar interaction is largely enhanced by two-dimensional dielectric screening at an inter-exciton separation of several nanometers or larger. The underlying mechanism can be attributed to the induced-charge densities in layered materials, which give rise to induced-dipole densities at large distances with directions parallel to that of the interlayer exciton. The interaction between quadrupolar excitons in trilayer structures are found to be enhanced even larger, with a magnitude one to two orders stronger than that without 2D dielectric screening. The strengths of these dipolar and quadrupolar interactions can be further tuned by engineering the dielectric environment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hydrogen-rich structures have recently gained attention as a candidate&amp;#xD;for room-temperature superconductors. Hydrogen has high phonon frequencies and&amp;#xD;can be an ideal component for superconductors if it also exhibits strong electronphonon&amp;#xD;coupling. In bulk materials, this has been achieved only under very high&amp;#xD;pressure. Two-dimensional (2D) hydrogen-decorated materials can also be expected&amp;#xD;to become superconductors. Recently, it was shown that a Janus MoSH monolayer&amp;#xD;can be synthesized [1], and a theoretical investigation of this MoSH monolayer claimed&amp;#xD;that Tc = 28.58K at atmospheric pressure [2]. In this work, we propose that tungsten&amp;#xD;sulfur hydride (WSH) is also a superconducting Janus monolayer. The Tc is carefully&amp;#xD;calculated with very high resolution via the Eliashberg spectral function and the&amp;#xD;electron self-energy. We find that WSH is a conventional BCS superconductor with&amp;#xD;Tc = 12.2K at ambient pressure. For practical applications, sensitive dependence&amp;#xD;on substrate is inferred. We also reported the electron self-energy of WSH, which&amp;#xD;can be compared directly with future measurements from angle-resolved photoelectron&amp;#xD;spectroscopy (ARPES).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigated the surface structure of a NbSe2 single crystal at room temperature, using angle-scanned X-ray photoelectron diffraction (XPD) combined with multiple scattering calculations. Different stacking sequences were tested (1T, 2Ha, 2Hc, and 3R), including possible stacking faults and a mixed 2H-3R stacking proposed earlier in the literature. We confirm the capability of XPD to distinguish different proposed structural models and, unambiguously, determine the true surface structure. Also, our findings provide reliable in-plane and interlayer distances. We observed expansions of the perpendicular distances between atomic planes within the monolayer and between monolayers of 3-5%. These results are important as accurate experimental input for the development of theoretical methods that involve a quantitative description of van der Waals systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ab initio driven density functional theory (DFT)-based high throughput simulations have been conducted to search for stable two-dimensional (2D) structures based on transition metal halides. Binary MeX2 and MeXY (Me – transition element, X and Y – Cr, Br, I, where X ≠ Y) 2D structures in two structural polymorphic modifications, which are 1T- phase and 1H-phase, have been studied. The main structural stability criteria, such as heat formation energy, elasticity constants, and phonon spectra and the following ab initio molecular dynamics (AIMD) simulations have been used to determine the stability of studied compounds. It has been shown that 35 MeX2 and 32 MeXY 2D structures comply with given stability criteria. Photocatalytic properties of these stable 2D MeX2 and 2D MeXY have been investigated. Based on the calculated band gap size Eg, work function Ф and electron affinity χ, it has been found that among all stable compounds 13 MeX2 and 16 MeXY 2D structures are promising photocatalysts for water splitting. However, only 7 compounds have solar-to-hydrogen (STH) efficiency overcome the 10% threshold, which is a critical parameter for solar hydrogen generation to be an economically viable resource. Among MeX2 2D structures 1T-CdI2 and 1H-VBr2 possess a STH efficiency of 11.58% and 17.23%. In the case of 2D MeXY, STH efficiencies are 22.79% (1T-ZnClI), 15.20% (1T-CdClI), 22.13% (1T-ZnBrI), 12.11% (1T-CdBrI) and 19.76% (1H-VClBr). Moreover, as a result of this work, a comprehensive publicly available database, containing detailed calculation parameters and fundamental properties of the discovered 2D transition metal halides, has been created.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In ferromagnet/superconductor bilayer systems, dipolar fields from the ferromagnet can create asymmetric energy barriers for the formation and dynamics of vortices through flux pinning. Conversely, the flux emanating from vortices can pin the domain walls of the ferromagnet, thereby creating asymmetric critical currents. Here, we report the observation of a superconducting diode effect in a NbSe<jats:sub>2</jats:sub>/CrGeTe<jats:sub>3</jats:sub> van der Waals heterostructure in which the magnetic domains of CrGeTe<jats:sub>3</jats:sub> control the Abrikosov vortex dynamics in NbSe<jats:sub>2</jats:sub>. In addition to extrinsic vortex pinning mechanisms at the edges of NbSe<jats:sub>2</jats:sub>, flux-pinning-induced bulk pinning of vortices can alter the critical current. This asymmetry can thus be explained by considering the combined effect of this bulk pinning mechanism along with the vortex tilting induced by the Lorentz force from the transport current in the NbSe<jats:sub>2</jats:sub>/CrGeTe<jats:sub>3</jats:sub> heterostructure. We also provide evidence of critical current modulation by flux pinning depending on the history of the field setting procedure. Our results suggest a method of controlling the efficiency of the superconducting diode effect in magnetically coupled van der Waals superconductors, where dipolar fields generated by the magnetic layer can be used to modulate the dynamics of the superconducting vortices in the superconductors.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hexagonal boron-nitride (h-BN) provides an ideal substrate for supporting graphene devices to achieve fascinating transport properties, such as Klein tunneling, electron optics and other novel quantum transport phenomena. However, depositing graphene on h-BN creates moiré superlattices, whose electronic properties can be significantly manipulated by controlling the lattice alignment between layers. In this work, the effects of these moiré structures on the transport properties of graphene are investigated using atomistic simulations. At large misalignment angles (leading to small moiré cells), the transport properties (most remarkably, Klein tunneling) of pristine graphene&amp;#xD;devices are conserved. On the other hand, in the nearly aligned cases, the moiré interaction induces stronger effects, significantly affecting electron transport in graphene. In particular, Klein tunneling is significantly degraded. In contrast, strong Fabry-Pérot interference (accordingly, strong quantum confinement) effects and non-linear I-V characteristics are observed. P-N interface smoothness engineering is also considered, suggesting as a potential way to improve these transport features in graphene/h-BN devices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This review delves into the intricacies of the interfaces formed between two-dimensional (2D) materials and metals, exploring a realm rich with fundamental insights and promising applications. Historically, our understanding of 2D materials emanated from studies employing dielectric substrates or suspended samples. However, integrating metals in the exfoliation and growth processes of 2D materials has opened up new avenues, unveiling various shades of interactions ranging from dispersive forces to covalent bonding.&amp;#xD;&amp;#xD;The resulting modifications in 2D materials, particularly transition metal dichalcogenides (TMDCs), offer more than a theoretical intrigue. They bear substantial implications for (opto)electronics, altering Schottky barrier heights and contact resistances in devices. We explore metal-mediated methods for TMDC exfoliation, elucidating the mechanisms and their impact on TMDC-metal interactions. Delving deeper, we scrutinize the fundamentals of these interactions, focusing primarily on MoS<jats:sub>2</jats:sub> and Au.&amp;#xD;&amp;#xD;Despite the recent surge of interest and extensive studies, critical gaps remain in our understanding of these intricate interfaces. We discuss controversies, such as the changes in Raman or photoemission signatures of MoS<jats:sub>2</jats:sub> on Au, and propose potential explanations. The interplay between charge redistribution, substrate-induced bond length variations, and interface charge transfer processes are examined. Finally, we address the intriguing prospect of TMDC phase transitions induced by strongly interacting substrates and their implications for contact design.</jats:p>