Mie scattering between incident light and nanoparticles (NPs) plays a vital role in improving the performance of optical and photonic devices, such as sensors, light-emitting diodes, and solar cells. While traditional far-field spectroscopy and electromagnetic simulations have been used to study Mie scattering, these methods lack real-space imaging capabilities, limiting their ability to capture single-particle scattering phenomena. Scanning probe microscopy-based nanoscopy techniques have become essential for studying Mie scattering at the nanoscale to address this limitation. This review explores the theoretical foundations of Mie scattering and the role of near-field microscopy in bridging the gap between theory and experiment through high-resolution imaging. By focusing on real-space imaging, we highlight the practical aspects of Mie scattering and its applications in fields such as biosensing, photocatalysis, and materials science. Nanoscopy techniques allow for direct visualization of scattering processes in nanostructures, offering more profound insights into how NPs interact with light at the nanoscale. Additionally, we discuss the potential of artificial intelligence (AI) to enhance near-field analysis, providing more accurate interpretations of Mie scattering phenomena. In conclusion, combining advanced nanoscopy and AI-driven analysis will significantly advance our understanding of Mie scattering and its diverse applications in various scientific and technological fields. The synergy between cutting-edge imaging methods and computational simulation not only enriches our theoretical understanding of scattering phenomena but also accelerates the development of next-generation photonic devices, paving the way for a wide range of practical applications across scientific and technological domains.

Twisted bilayer graphene (tBLG) with small twist angles has attracted significant attention because of its unique electronic properties arising from the formation of a moiré superlattice. In this study, we systematically characterized the twist-angle-dependent electronic and transport properties of tBLG grown via chemical vapor deposition. This characterization included parameters such as the charge-neutral point voltage, carrier concentration, resistance, and mobility, covering a wide range of twist angles from 0° to 30°. We experimentally demonstrated that these parameters exhibited twist-angle-dependent moiré period trends, with high twist angles exceeding 9°, revealing more practically useful features, including improved mobilities compared to those of single-layer graphene. In addition, we demonstrated that the doping states and work functions were weakly dependent on the twist angles, as confirmed by additional first-principles calculations. This study provides valuable insights into the transport properties of tBLG and its potential for practical applications in the emerging field of twistronics.

Abstract A method for patterning single‐layer graphene (SLG) and single‐layer oxidized graphene (SOG) within a continuous atomic layer to form lateral heterojunctions is presented. Raman spectroscopy is employed to investigate the evolution of defect‐related Raman peaks during excimer‐UV irradiation, facilitating the identification of structural changes and defect formation processes. Electrical transport measurements reveal that SOG‐patterned field‐effect transistors (FETs) exhibit varying characteristics depending on the degree of oxidation, thus offering the potential to tailor the electrical properties of graphene devices for specific requirements. Scanning Kelvin probe microscopy measurements reveal the surface potential and work function of the SOG regions compared with those of SLG. The effective functionality of the SOG pattern to operate as a resistor, allowing control of the electrical conductivity in the SOG‐patterned SLG channels, is demonstrated. This capability restricts the current flow while preserving the pristine electrical properties of the graphene channel. Moreover, the SOG pattern can serve as a potential barrier to constructing SLG‐SOG‐patterned integrated circuits, providing exciting opportunities for engineering advanced electronic components. This breakthrough in graphene devices simplifies the fabrication process of graphene‐based FETs and provides the foundation for developing atomically thin integrated circuits for a wide range of applications.

Although magnetic order is suppressed by a strong frustration, it appears in complex forms such as a cycloid or spin density wave in weakly frustrated systems. Herein, we report a weakly magnetically frustrated two-dimensional (2D) van der Waals material CrPSe3. Polycrystalline CrPSe3 was synthesized at an optimized temperature of 700 °C to avoid the formation of any secondary phases (e.g., Cr2Se3). The antiferromagnetic transition appeared at TN ≈ 127 K with a large Curie-Weiss temperature θCW ≈ -301 K via magnetic susceptibility measurements, indicating weak frustration in CrPSe3 with a frustration factor of f (|θCW|/TN) ≈ 2.4. Evidently, the formation of a long-range incommensurate antiferromagnetic order was revealed by neutron diffraction measurements at low temperatures (below 120 K). The monoclinic crystal structure of the C2/m symmetry is preserved over the studied temperature range down to 20 K, as confirmed by Raman spectroscopy measurements. Our findings on the incommensurate antiferromagnetic order in 2D magnetic materials, not previously observed in the MPX3 family, are expected to enrich the physics of magnetism at the 2D limit, thereby opening opportunities for their practical applications in spintronics and quantum devices.

High pressure or strain is an effective strategy for generating phase transformations in van der Waals (vdW) layered materials without introducing defects, but this approach remains difficult to perform consistently. We present a scalable and facile method for achieving phase transformation in vdW materials, wherein solid vdW materials are subject to internal thermal stress within a molten metal mantle as it undergoes cooling. This internal thermal stress is principally the product of differential thermal expansion between mantle and core and can be tuned by the mantle material and temperature conditions. We validated this approach by achieving phase transformation of red phosphorus to black phosphorus, and metallic 1T'- to semiconducting 2H-MoTe2 crystals. We further demonstrate quantum electronic phase transformation of suppressed charge density wave in TiSe2 by means of electron-phonon coupling using the same system.

One primary concern in diluted magnetic semiconductors (DMSs) is how to establish a long-range magnetic order with a low magnetic doping concentration to maintain the gate tunability of the host semiconductor, as well as to increase Curie temperature. Two-dimensional van der Waals semiconductors have been recently investigated to demonstrate the magnetic order in DMSs; however, a comprehensive understanding of the mechanism responsible for the gate-tunable long-range magnetic order in DMSs has not been achieved yet. Here, we introduce a monolayer tungsten diselenide (WSe2) semiconductor with V dopants to demonstrate the long-range magnetic order through itinerant spin-polarized holes. The V atoms are sparsely located in the host lattice by substituting W atoms, which is confirmed by scanning tunneling microscopy and high-resolution transmission electron microscopy. The V impurity states and the valence band edge states are overlapped, which is congruent with density functional theory calculations. The field-effect transistor characteristics reveal the itinerant holes within the hybridized band; this clearly resembles the Zener model. Our study gives an insight into the mechanism of the long-range magnetic order in V-doped WSe2, which can also be used for other magnetically doped semiconducting transition metal dichalcogenides.

We report the strong ferromagnetic order in van der Waals (vdW) layered SnS2 induced by cobalt substitution. The single-crystal Co-doped SnS2 grown by a self-flux method reveals a relatively high Curie temperature (TC) of ∼131 K with an in-plane magnetic easy axis and a large saturation magnetization of ∼0.65 emu g−1 for the 2 at. % Co concentration, which is two orders of magnitude larger than the previously reported value for transition-metal-doped SnS2. The average magnetic moment per Co atom, as high as 1.08 µB, is consistent with the calculated value based on density functional theory, i.e., 1 µB, indicating a negligible antiferromagnetic coupling between Co atoms. Magnetoresistance shows a change in sign from positive to negative, which further confirms the ferromagnetic order in Co-doped SnS2. Our s-p hybridized vdW layered SnS2 serves as a host semiconductor material to search for a suitable magnetic dopant with a high magnetic moment and room temperature TC for next-generation spintronics.

Discoveries of two-dimensional (2D) magnetism originated from confined atomic layers in van der Waals (vdW) crystals provide an interesting arena for elucidating its fundamentals and enrich magneto-electric and quantum properties. However, a material that exhibits intrinsic 2D magnetism of interstitial elec-trons occupying layered space, as a root system of magnetic vdW crystals, remains obscure. In this work, 2D ferromagnetic vdW electride, [RECl](2+) . 2e(-) (RE 1/4 Y and La) is reported with perfectly isolated ferromagnetic 2D blocks encompassing quasi-atomic electron layers. The ferromagnetism of the vdW electride with Curie temperature of 100 K originates from the spin-polarized quasi-atomic electrons with a substantial moment up to similar to 0.91 Bohr magneton, which behave as magnetic elements in paramagnetic lattice framework. Invariable ferromagnetism at the monolayer limit strongly supports the 2D ferro-magnetism of quasi-atomic electrons. These findings expand the variety of 2D magnetic crystals, providing a promising platform to study the emergent magnetism of low-dimensional electron phases. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

2D van der Waals magnetic semiconductors have emerged along with the possibilities of achieving an efficient gate tunability and a proximity effect with a high magnetic anisotropy compared with 3D counterparts. Little explored are multiple magnetic phases with a single crystallographic phase. Herein, the multiple magnetic phases in a Mn‐doped SnS 2 single crystal with different doping concentrations using a one‐step self‐flux method are reported. Two ferromagnetic phases with a canted spin direction exist regardless of the Mn‐doping concentration at up to 5 at%. Antiferromagnetism coexists with the ferromagnetic order and strengthens at high Mn‐doping concentrations. A magnetoresistance measurement conducted on a 2 at% Mn‐SnS 2 flake exhibits a positive‐to‐negative crossover with a value of as high as 50% and clear anisotropy, confirming the presence of ferromagnetic order in the material. By revealing multiple magnetic phases in Mn‐doped SnS 2 , the study broadens the scope of state‐of‐the‐art research on layered magnetic semiconductors.

Disruptive technologies are usually characterised by universal, versatile applications, which change many aspects of our life simultaneously, penetrating every corner of our existence. In order to become disruptive, a new technology needs to offer not incremental, but dramatic, orders of magnitude improvements. Moreover, the more universal the technology, the better chances it has for broad base success. Significant progress has been made in taking graphene and related materials from a state of raw potential to a point where they can revolutionize multiple industries. When it comes to electrochemical applications, Raman spectroscopy is an ideal non-destructive technique to study degradation in graphite anodes, as it is sensitive to doping, strain, defects, and interlayer coupling. I will discuss how in-situ Raman spectroscopy can unravel the signatures of Li-ion induced doping, intercalation staging and degradation upon cycling.

Graphene has been gradually studied as a high-frequency transmission line material owing to high carrier mobility with frequency independence up to a few THz. However, the graphene-based transmission lines have poor conductivity due to their low carrier concentration. Here, it is observed that the radio frequency (RF) transmission performance could be severely hampered by the defect-induced scattering, even though the carrier concentration is increased. As a possible solution, the deposition of the amorphous carbon on the graphene is studied in the high-frequency region up to 110 GHz. The DC resistance is reduced by as much as 60%, and the RF transmission property is also enhanced by 3 dB. Also, the amorphous carbon covered graphene shows stable performance under a harsh environment. These results prove that the carrier concentration control is an effective and a facile method to improve the transmission performance of graphene. It opens up the possibilities of using graphene as interconnects in the ultrahigh-frequency region.

Layers of transition metal dichalcogenides (TMDs) combine the enhanced effects of correlations associated with the two-dimensional limit with electrostatic control over their phase transitions by means of an electric field. Several semiconducting TMDs, such as MoS2, develop superconductivity (SC) at their surface when doped with an electrostatic field, but the mechanism is still debated. It is often assumed that Cooper pairs reside only in the two electron pockets at the K/K' points of the Brillouin Zone. However, experimental and theoretical results suggest that a multivalley Fermi surface (FS) is associated with the SC state, involving six electron pockets at Q/Q'. Here, we perform low-temperature transport measurements in ion-gated MoS2 flakes. We show that a fully multivalley FS is associated with the SC onset. The Q/Q' valleys fill for doping ≳ 2 × 1013 cm-2, and the SC transition does not appear until the Fermi level crosses both spin-orbit split sub-bands Q 1 and Q 2. The SC state is associated with the FS connectivity and promoted by a Lifshitz transition due to the simultaneous population of multiple electron pockets. This FS topology will serve as a guideline in the quest for new superconductors.

Optical harmonic generation occurs when high intensity light ($>10^{10}$W/m$^{2}$) interacts with a nonlinear material. Electrical control of the nonlinear optical response enables applications such as gate-tunable switches and frequency converters. Graphene displays exceptionally strong-light matter interaction and electrically and broadband tunable third order nonlinear susceptibility. Here we show that the third harmonic generation efficiency in graphene can be tuned by over two orders of magnitude by controlling the Fermi energy and the incident photon energy. This is due to logarithmic resonances in the imaginary part of the nonlinear conductivity arising from multi-photon transitions. Thanks to the linear dispersion of the massless Dirac fermions, ultrabroadband electrical tunability can be achieved, paving the way to electrically-tuneable broadband frequency converters for applications in optical communications and signal processing.

Nanoactuators are a key component for developing nanomachinery. Here, an electrically driven device yielding actuation stresses exceeding 1 MPa withintegrated optical readout is demonstrated. 10 nm thick Al2 O3 electrolyte films are sandwiched between graphene and Au electrodes. These allow reversible room-temperature solid-state redox reactions, producing Al metal and O2 gas in a memristive-type switching device. The resulting high-pressure oxygen micro-fuel reservoirs are encapsulated under the graphene, swelling to heights of up to 1 µm, which can be dynamically tracked by plasmonic rulers. Unlike standard memristors where the memristive redox reaction occurs in single or few conductive filaments, the mechanical deformation forces the creation of new filaments over the whole area of the inflated film. The resulting on-off resistance ratios reach 108 in some cycles. The synchronization of nanoactuation and memristive switching in these devices is compatible with large-scale fabrication and has potential for precise and electrically monitored actuation technology.

Quantum light emitters have been observed in atomically thin layers of transition metal dichalcogenides. However, they are found at random locations within the host material and usually in low densities, hindering experiments aiming to investigate this new class of emitters. Here, we create deterministic arrays of hundreds of quantum emitters in tungsten diselenide and tungsten disulphide monolayers, emitting across a range of wavelengths in the visible spectrum (610-680 nm and 740-820 nm), with a greater spectral stability than their randomly occurring counterparts. This is achieved by depositing monolayers onto silica substrates nanopatterned with arrays of 150-nm-diameter pillars ranging from 60 to 190nm in height. The nanopillars create localized deformations in the material resulting in the quantum confinement of excitons. Our method may enable the placement of emitters in photonic structures such as optical waveguides in a scalable way, where precise and accurate positioning is paramount.

Deterministic Single-Photon Sources in 2-D Semiconductors Two-dimensional semiconductors present a new potential solid-state host for single-photon sources. A notable characteristic of these systems compared with traditional single-photon sources, such as InGaAs quantum dots or color centers in diamond, is the ability to trap single-excitons at a surface. This asset could unlock the potential for developing highly effi cient photon extraction mechanisms and for coupling confi ned excitons to photonic structures and other quantum systems. Since 2015, single-photon emitt ing sites of unknow n origin have been reported to appear at random locations in monolayer fl akes of WSe2, WS2 and MoSe2. This year, we were able to deterministically engineer such sources at precise locations with a 96 percent yield, in unlimited numbers, in a scalable manner and with bett er optical properties than their randomly occurring counterparts.3 We accomplished this deterministic source by deforming the material locally at the nanoscale, using patt erned substrates. We fi rst exfoliated monolayer fl akes of WSe2 and WS2 from bulk crystals. Then, we transferred the fl akes onto silica substrates patt erned with square arrays of nanopillars, spaced 4 μm apart and ranging from 100 to 200 nm in height and with a 90-nm apex diameter. Atomicforce microscopy scans show that the fl akes tent over each nanopillar and att ach by Van der Waals forces to the fl at areas of the substrate in-between. Low-temperature photoluminescence (PL) measurements showed a brightening of PL and narrow spectral lines from the pillar locations. Photon-correlation measurements on these narrow lines confi rmed the single-photon nature of the emission, and high-resolution spectral measurements revealed a fi ne structure in the majority of dots. The parameters measured are very similar to those measured for the randomly appearing single-photon-emitt ing sites in the same materials, which suggests a common origin. Characterization of the quantum emission with increasing pillar height also yielded interesting results: the number of narrow lines per site decreases and the spectral wandering improves by an order of magnitude compared with the random emission sites. We believe that this work paves the way for a true singlephoton emitt er that can be easily scaled up and integrated with other photonic components. In addition, as a new platform for deterministic quantum light-matt er interaction between single-excitons and photons, it allows researchers to explore the potential for optical single-spin control toward quantum information applications. OPN

Saturable absorbers (SA) operating at terahertz (THz) frequencies can open new frontiers in the development of passively mode-locked THz micro-sources. Here we report the fabrication of THz SAs by transfer coating and inkjet printing single and few-layer graphene films prepared by liquid phase exfoliation of graphite. Open-aperture z -scan measurements with a 3.5 THz quantum cascade laser show a transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at THz frequencies. Fourier-transform infrared spectroscopy provides evidence of intraband-controlled absorption bleaching. These results pave the way to the integration of graphene-based SA with electrically pumped THz semiconductor micro-sources, with prospects for applications where excitation of specific transitions on short time scales is essential, such as time-of-flight tomography, coherent manipulation of quantum systems, time-resolved spectroscopy of gases, complex molecules and cold samples and ultra-high speed communications, providing unprecedented compactness and resolution.

Transition metal dichalcogenides (TMDs) are emerging as promising two-dimensional (2d) semiconductors for optoelectronic and flexible devices. However, a microscopic explanation of their photophysics -- of pivotal importance for the understanding and optimization of device operation -- is still lacking. Here we use femtosecond transient absorption spectroscopy, with pump pulse tunability and broadband probing, to monitor the relaxation dynamics of single-layer MoS2 over the entire visible range, upon photoexcitation of different excitonic transitions. We find that, irrespective of excitation photon energy, the transient absorption spectrum shows the simultaneous bleaching of all excitonic transitions and corresponding red-shifted photoinduced absorption bands. First-principle modeling of the ultrafast optical response reveals that a transient bandgap renormalization, caused by the presence of photo-excited carriers, is primarily responsible for the observed features. Our results demonstrate the strong impact of many-body effects in the transient optical response of TMDs even in the low-excitation-density regime.