Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

DFT investigation of geometrical, vibrational, elastic, electronic, optical, and thermoelectric properties of aluminum pnictogens compounds

The aim of this study is to investigate the geometrical, vibrational, elastic, electronic, optical, and thermoelectric characteristics of aluminum pnictides in monolayer square lattice and bilayer hexagonal phases (s- and h-AlX; X = N, P, As) using first principles. The s- and h-AlX materials are mechanically, energetically, and dynamically stable, through phonon dispersion and elastic properties investigations. It was observed that s-AlX materials exhibited both direct and indirect bandgaps, whereas h-AlX materials exhibited indirect bandgap behavior. The energy bandgap values for s- and h-AlX materials measured between 0.79 eV and 3.49 eV for the PBE functional, and between 1.49 eV and 4.74 eV for the HSE06 functional. The effective mass, mobility and relaxation time of electron carriers as well as hole carriers from the band structure of s- and h-AlX are examined to gain a better perception into these materials. The AlP monolayer square lattice phase has the highest mobility and relaxation time of 266129.60 cm2V-1s-1 and 740369.83 fs among entire s- and h-AlX materials. The optical characteristics of s- and h-AlX materials are examined in the existence of field polarizations. The thermoelectric properties of the AlX materials are assessed for temperature dependent. Our investigated results expose that AlP/AlP and AlAs/AlAs are the proficient thermoelectric materials at room temperature in the considered sequence. The present investigation shows that the s- and h-AlX materials are mostly active in the UV region of electromagnetic spectrum, and may find applications in UV-photodetectors and UV-protectant materials.

Advances of functional graphdiyne in separation and detection

Separation and detection technologies are essential tools for ensuring quality, safety and efficiency across various industries. Graphdiyne (GDY), a carbon material made up of alkyne bonds conjugated with benzene rings to form a planar all-carbon network, is increasingly utilized in the fields of separation and detection. GDY is becoming an ideal separation medium due to its adjustable pore sizes, unique alkyne-rich framework, and easy to be functionalized. On the other hand, GDY shows great potential in detection with the advantages of efficient photoelectric effect, high carrier mobility, and large surface areas to provide active sites. This review summarizes the progress of functional GDY in separation and detection from 2011 to 2024. Various synthesis methods were introduced on improving the properties of GDY in separation and detection. Efforts have increasingly focused on the development of functional GDY in separation functionalities such as magnetic and membranous separations. Moreover, the application of functional GDY in detection technologies are discussed such as electrochemical, spectroanalysis, and dual-mode approaches. Finally, the promising research directions and prospects of functional GDY are discussed to explore further applications in both separation and detection.

Unraveling the role of Ta in the phase transition of Pb(Ta1+xSe2)2 using temperature-dependent Raman spectroscopy

Phase engineering strategies in two-dimensional transition metal dichalcogenides (2D-TMDs) have garnered significant attention due to their potential applications in electronics, optoelectronics, and energy storage. Various methods, including direct synthesis, pressure control, and chemical doping, have been employed to manipulate structural transitions in 2D-TMDs. Metal intercalation emerges as an effective technique to modulate phase transition dynamics by inserting external atoms or ions between the layers of 2D-TMDs, altering their electronic structure and physical properties. Here, we investigate the significant structural phase transitions in Pb(Ta1+xSe2)2 single crystals induced by Ta intercalation using a combination of Raman spectroscopy and first-principles calculations. The results highlight the pivotal role of Ta atoms in driving these transitions and elucidate the interplay between intercalation, phase transitions, and resulting electronic and vibrational properties in 2D-TMDs. By focusing on Pb(Ta1+xSe2)2 as an ideal case study and investigating like metal intercalation, this study advances understanding in the field and paves the way for the development of novel applications for 2D-TMDs, offering insights into the potential of these materials for future technological advancements.

Comparison of structural, optical, and thermal properties in MoS2 based nanocomposites into cancer therapy

The objective of the present study is to evaluate the potential of novel molybdenum disulfide (MoS2)-based nanocomposites for photothermal therapy. For this purpose, MoS2-CuS (MoCS) and MoS2-AuNR (MoAu) nanocomposites were synthesized by physically mixing MoS2 suspensions with CuS and AuNRs, respectively. The structural and optical properties of these nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The photothermal performance of the nanocomposites was assessed under near-infrared (NIR) radiation at a power density of 1 W/cm2 for 10 min. The results demonstrated that both MoCS and MoAu nanocomposites exhibited enhanced photothermal heating compared to their individual components. Furthermore, the MoAu nanocomposite generated higher photothermal heat than the MoCS nanocomposite. These findings suggest that the MoCS and MoAu nanocomposites have strong potential as novel photothermal agents for cancer therapy.

What Is the Role of a Magnetic Mo Antisite Defect on Carrier Relaxation and Spin Dynamics in 2-D MoS2?

Antisite defects significantly influence the dynamic properties of monolayer MoS2, yet the carrier relaxation and spin dynamics in spin-polarized Mo antisite-defective MoS2 remain unclear. Understanding these processes is crucial for advancing optoelectronic, spintronic, and valleytronic devices. Here, we employ first-principles calculations and ab initio nonadiabatic molecular dynamics with spin-orbit coupling (SOC) to explore carrier relaxation and spin dynamics in MoS2 with a Mo antisite defect. This defect alters the material's magnetic properties, leading to distinct relaxation behaviors: electron relaxation is slower than hole relaxation, and charge carriers in different spin channels exhibit varied dynamics. These differences arise from variations in electron-phonon coupling, SOC strength, and phonon mode activation. Our findings provide key insights into charge and spin dynamics in MoS2 with magnetic defects and suggest strategies to enhance the performance of next-generation optoelectronic, spintronic, and valleytronic devices.

Neuromorphic Floating-Gate Memory Based on 2D Materials

In recent years, the rapid progression of artificial intelligence and the Internet of Things has led to a significant increase in the demand for advanced computing capabilities and more robust data storage solutions. In light of these challenges, neuromorphic computing, inspired by human brain's architecture and operation principle, has surfaced as a promising answer to the growing technological demands. This novel methodology emulates the biological synaptic mechanisms for information processing, enabling efficient data transmission and computation at the identical position. Two-dimensional (2D) materials, distinguished by their atomic thickness and tunable physical properties, exhibit substantial potential in emulating synaptic plasticity and find broad applications in neuromorphic computing. With respect to device architecture, memory devices based on floating-gate (FG) structures demonstrate robust data retention capabilities and have been widely used in the realm of flash memory. This review begins with a succinct introduction to 2D materials and FG transistors, followed by an in-depth discussion on remarkable research progress in the integration of 2D materials with FG transistors for applications in neuromorphic computing and memory. This paper offers a thorough review of the existing research landscape, encapsulating the notable progress in swiftly expanding field. In conclusion, it addresses the constraints encountered by FG transistors using 2D materials and delineates potential future trajectories for investigation and innovation within this area.

Enhanced piezoresponse in van der Waals 2D CuCrInP2S6 through nanoscale phase segregation

van der Waals metal chalcogen thiophosphates have drawn elevated interest for diverse applications, including energy harvesting, electronics and optoelectronics. Despite this progress, the role of nanoscale ion migration in complex intermediary thiophosphate compounds has not been well understood, resulting in their structure-property characteristics remaining elusive. Herein, we focus on copper-deficient CuCrInP2S6 as a prototypic layered thiophosphate compound to address this shortcoming. Piezo force microscopy reveals that this material exhibits unusual cage-like domain networks with an enhanced piezo response at the domain boundaries. The associated piezoelectric coefficient d33 is found to be among the highest across reported van der Waals multi-layered materials. These results are further complemented with Kelvin probe microscopy and second harmonic generation spectroscopy that disclose significantly elevated non-linear optical emission along these domain boundaries. Ab initio calculations performed in conjunction with nudge elastic theory provide a deeper insight into the diffusion processes responsible for these observed phenomena. These findings shed new light into intermediary thiophosphate based 2D compounds, highlighting future prospects towards their use in emergent piezoelectric based technological applications.

Recent progress in ultraviolet photodetectors based on low-dimensional materials

Ultraviolet (UV) photodetectors (PDs) are crucial for various advanced applications, yet conventional technologies suffer from limitations like low sensitivity, slow response, and high costs. Low-dimensional materials (LDMs) have emerged as a promising alternative due to their unique optoelectronic properties, including quantum confinement, tunable bandgaps, and high carrier mobility. While existing reviews on UV-PDs often focus narrowly on specific materials or structures, this review offers a comprehensive overview of LDM-based UV-PDs, covering 0D, 1D, and 2D materials and their heterostructures. We highlight recent advances that enhance UV-PD performance across the full UV spectrum, addressing challenges such as limited spectral range and high dark current. The review also explores diverse applications, from medicine to space science, demonstrating the growing impact of LDM-based UV-PDs. By focusing on the latest developments and addressing research gaps, this review provides essential insights into the future of UV photodetection.

The Unexploring Optoelectronic Features in Organic Trans-Dimensional Materials of Gridofluorenes at the Nanoscale

Organic grido-architectures offer not only state-of-the-art models for exploring the complex relationships of multicarrier coherence among excitons, charges, photons, electrons, and phonons but also organic high-dimensional nanomaterials for flexible electronics and organic intelligence. Herein, we initiate the fundamental progress and perspective on gridofluorene-based zero-, one-, two-, and three-dimensional nanomolecules and their optoelectronic features. From the future point of view, the sterically trans-dimensional and hierarchically cross-scale effects of these covalent frameworks and nanostructures are discussed on their photophysical, electrical, mechanical and thermal properties. Organic multiscale systems, with the feature of synergistically molecule-programmable integration of diverse functionalities, open a bright door to flexible electronics, intelligent molecules, devices, systems, and even organobots as well as artificially intelligent and robotic chemists (AiRCs).

Polarization-Sensitive and Self-Driven Photodetector Based on 2D PdSe2/InSe Asymmetric van der Waals Heterojunction with Vertical Transportation Channel

Polarized photodetectors are promising in civil and military fields. Limited response range and low integration level are critical challenges which can be solved by the introduction of a 2D asymmetric vertical heterojunction. Vertical structure design has the advantages of higher integration level and shorter channel length. In this work, a PdSe2/InSe vertical heterojunction is constructed with an asymmetric structure and a short vertical transportation channel for polarization-sensitive and self-driven photodetection. The device exhibits excellent photoresponse characteristics, including a wide spectral range spanning from 405 to 980 nm, a high responsivity of 296 mA/W, and a specific detectivity of 1.97 × 1011 Jones. It also demonstrates excellent photovoltaic performance with a notable open-circuit voltage reaching 480.6 mV and exhibits remarkable polarization sensitivity. Finally, the device is integrated into a polarized light imaging system successfully. This finding underscores the critical role of the PdSe2/InSe heterojunction in advancing compact, high-performance, broadband, and self-driven polarized photodetectors.

Janus group V1B-based pnictogen-halide monolayers: a new class of multifunctional quantum materials from first-principles predictions

This study employed density functional theory to discover a new family of 48 two-dimensional Janus monolayers with the formula MXY, where M stands for transition metals (Cr, Mo, or W), X represents a group V element (P, As, Sb, or Bi), and Y denotes a halide (F, Cl, Br, or I). The cohesive energy and phonon dispersion calculations show that most of these materials are energetically and dynamically stable. Subsequently, the thorough investigation into the electrical structure allows the classification of these monolayers as metals (CrPI and WPI) or semiconductors with narrow band gaps ranging from 0.69 to 2.15 eV. Meanwhile, the MoSbBr, MoSbI, and WBiCl monolayers are defined to be able to function as photocatalysts in the water splitting process, and the CrAsCl monolayer exhibits significant potential for valleytronic applications due to its intrinsic valence band splitting of about 90 meV. Finally, significant Rashba splitting was observed near the Γ point in the valence band of Janus MXY monolayers, where the growth in atomic weight (W > Mo > Cr and Bi > Sb > As > P) corresponds to a greater spin-orbit coupling effect on the Rashba parameter. Their Rashba values are comparable to those ofother well-known 2D materials, indicating great potential for spintronic applications. Our findings not only present a broad range of 2D materials, but also highlight their potential for next-generation electrical, photonic, and catalytic technologies.

Improved Metal-Semiconductor Interface in Monolayer (1L)-MoS2 via Thermally-Driven Ag Filaments as Atomic Scale Edge Contacts Triggered by Selective Annealing Process Using Long Wavelength (1064 nm) Pulsed Laser

Here, we explore the effectiveness of a pulsed laser annealing (PLA) process to trigger atomic scale edge contacts by Ag filaments in reducing the contact resistance of a MoS2 field-effect transistor (FET). Employing a long wavelength (1064 nm) pulsed laser, we anneal monolayer (1L)-MoS2 FETs with various metal electrodes, including Ag/Au, Ni/Au, and Cr/Au. A remarkable enhancement in FET performance could be achieved after the PLA treatment. Specifically, Ag/Au-contacted 1L-MoS2 FETs after the PLA treatment exhibit a peak field-effect mobility increase from 60 to 135 cm2 V-1 s-1 and an on-current improvement from 40.5 to 96.1 μA at a Vd of 1 V, accompanied by a significant decrease in contact resistance to 0.29 kΩ μm. PLA-treated 1L-MoS2 FETs showed a high on/off ratio of 107. TEM analysis provided insight into the mechanism of reduced contact resistance, revealing the thermally driven diffusion of Ag atoms into the 1L-MoS2 as Ag filaments to lateral contact with the edge of the 1L-MoS2, namely atomic scale edge contacts, as a key contributing factor. Furthermore, our investigation extends to the larger scale CVD-grown 1L-MoS2 films, where the PLA treatment demonstrates notable improvements in mobility, on-current, and on-off ratio.

Tuning of MoS2 Photoluminescence in Heterostructures with CrSBr

Monolayers of semiconducting transition metal dichalcogenides (TMDCs) are known for their unique excitonic photoluminescence (PL), which can be tuned by interfacing them with other materials. However, integrating TMDCs into van der Waals heterostructures often results in a significant quenching of the PL because of an increased rate of nonradiative recombination processes. We demonstrate a wide-range tuning of the PL intensity of monolayer MoS2 interfaced with another layered semiconductor, CrSBr. We discover that a thin CrSBr up to ≈20 nm in thickness enhances the PL of MoS2, while a thicker material causes PL quenching, which is associated with changes in the excitonic makeup driven by the charge redistribution in the CrSBr/MoS2 heterostructure. Transport measurements, Kelvin probe force microscopy, and first-principles calculations indicate that this charge redistribution most likely causes n- to p-type doping transition of MoS2 upon contact with CrSBr, facilitated by the type II band alignment and the tendency of CrSBr to act as an electron sink. Furthermore, we fabricate an efficient AC-regime photodetector with a responsivity of 105 A/W from a MoS2/CrSBr heterostructure.

Unveiling the Stable Semiconducting 1T'-HfCl2 Monolayer: A New 2D Material

Designing novel 2D materials is crucial for advancing next-generation optoelectronic technologies. This work introduces and analyzes the 1T'-HfCl2 monolayer, a novel low-symmetry variant within the 2D transition metal dichloride family. Phonon dispersion calculations reveal no imaginary frequencies, suggesting its dynamical stability. 1T'-HfCl2 exhibits semiconducting behavior with a direct band gap of 1.52 eV, promising for optoelectronics. Strong excitonic effects with a binding energy of 525 meV highlight significant electron-hole interactions typical of 2D systems. Furthermore, the monolayer achieves total reflection of linearly polarized light along the ŷ direction at photon energies above 2.5 eV, showcasing its potential as an optical polarizing filter. Raman spectra calculations also reveal distinct peaks between 96.72 and 270.38 cm-1. The tunable excitonic and optical properties of 1T'-HfCl2 highlight its potential in future functional devices, paving the way for its integration into semiconducting and optoelectronic applications.

2D Programmable Photodetectors Based on WSe2/h-BN/Graphene Heterojunctions

Programmable photovoltaic photodetectors based on 2D materials can modulate optical and electronic signals in parallel, making them particularly well-suited for optoelectronic hybrid dual-channel communication. This work presents a programmable non-volatile bipolar semi-floating gate photovoltaic photodetector (SFG-PD) constructed using tungsten diselenide (WSe2), hexagonal boron nitride (h-BN), and graphene (Gra). By controlling the voltage pulses applied to the control gate, the device generates opposing built-in electric field junctions (p+-p and n-p junctions), enabling reversible switching between positive and negative light responses with a rapid response time of up to 2.02 µs. Moreover, the application of this device is demonstrated in dual-channel optoelectronic hybrid communication, offering a practical solution for achieving high-speed, large-capacity, low-loss, and secure multi-channel communication.

Electrostatic control of transconductance oscillations in MoS2/WSe2heterostructure

The progression of quantum phenomena aligns closely with the miniaturization of nano-semiconductor transistors. This necessitates innovative quantum structures beyond traditional transistor types. Investigating electrostatically defined nanoscale devices within two-dimensional (2D) semiconductor heterostructures, particularly van der Waals heterostructures offers advantages like large-scale uniformity and flexibility. Here, we focus on the charge transport of a MoS2/WSe2encapsulated heterostructure controlled by a split-gate configuration, revealing a distinctive step-like current profile at a low temperature of 77 K. The observed distinguishable regimes in the current highlight the impact of quantum confinement induced by reduced lateral dimensions coupled with precise electrostatic confinement controlled by gate voltages. The temperature dependence of the device is also investigated to understand the role of thermal effects on the observed electrostatic-controlled transconductance oscillations phenomenon. This study contributes to a deeper understanding of electrostatic effects in 2D transition metal dichalcogenide heterostructures in narrow regimes. It holds promise for developing future integrated electronic devices based on 2D semiconducting nanomaterials with tailored confinement and enhanced functionalities.

Unveiling Anomalous Ultrafast Carrier Dynamics of Strong Spectral Overlapping in Few-Layer MoS2

Molybdenum disulfide (MoS2) nanosheets exhibit significant applications in photoelectric devices, and correctly revealing the photogenerated carrier dynamics in the material is crucial for understanding its photophysical response mechanism and optimizing the photoelectric response efficiency of the devices. Herein, we study the ultrafast photogenerated carrier dynamics in MoS2 nanosheets using femtosecond time-resolved transient absorption (TA) microscopy and find that the anomalous rebleaching phenomenon of the TA signals for A- and B-excitons takes place at high pump fluences. By performing a careful quantitative fitting of the time-resolved TA signals, we ascribe the anomalous rebleaching to a result of the superposition of photobleaching and photoinduced absorption induced by the bandgap renormalization effect. This work provides new perspectives for elucidating and comprehending the ultrafast carrier dynamics from the complex TA signals, especially when there is an overlap between positive and negative signals.

MXenes and MXene-based composites for biomedical applications

MXenes, a novel class of two-dimensional materials, have recently emerged as promising candidates for biomedical applications due to their specific structural features and exceptional physicochemical and biological properties. These materials, characterized by unique structural features and superior conductivity, have applications in tissue engineering, cancer detection and therapy, sensing, imaging, drug delivery, wound treatment, antimicrobial therapy, and medical implantation. Additionally, MXene-based composites, incorporating polymers, metals, carbon nanomaterials, and metal oxides, offer enhanced electroactive and mechanical properties, making them highly suitable for engineering electroactive organs such as the heart, skeletal muscle, and nerves. However, several challenges, including biocompatibility, functional stability, and scalable synthesis methods, remain critical for advancing their clinical use. This review comprehensively overviews MXenes and MXene-based composites, their synthesis, properties, and broad biomedical applications. Furthermore, it highlights the latest progress, ongoing challenges, and future perspectives, aiming to inspire innovative approaches to harnessing these versatile materials for next-generation medical solutions.

2D Materials-Based Field-Effect Transistor Biosensors for Healthcare

The need for accurate point-of-care (POC) tools, driven by increasing demands for precise medical diagnostics and monitoring, has accelerated the evolution of biosensor technology. Integrable 2D materials-based field-effect transistor (2D FET) biosensors offer label-free, rapid, and ultrasensitive detection, aligning perfectly with current biosensor trends. Given these advancements, this review focuses on the progress, challenges, and future prospects in the field of 2D FET biosensors. The distinctive physical properties of 2D materials and recent achievements in scalable synthesis are highlighted that significantly improve the manufacturing process and performance of FET biosensors. Additionally, the advancements of 2D FET biosensors are investigated in fatal disease diagnosis and screening, chronic disease management, and environmental hazards monitoring, as well as their integration in flexible electronics. Their promising capabilities shown in laboratory trials accelerate the development of prototype products, while the challenges are acknowledged, related to sensitivity, stability, and scalability that continue to impede the widespread adoption and commercialization of 2D FET biosensors. Finally, current strategies are discussed to overcome these challenges and envision future implications of 2D FET biosensors, such as their potential as smart and sustainable POC biosensors, thereby advancing human healthcare.

High-Entropy 1T-Phase Quantum Sheets of Transition-Metal Disulfides

Quantum sheets of transition-metal dichalcogenides (TMDs) are promising nanomaterials owing to the combination of both 2D nanosheets and quantum dots with distinctive properties. However, the quantum sheets usually possess semiconducting behavior associated with 2H phase, it remains challenging to produce 1T-phase quantum sheets due to the easy sliding of the basal plane susceptible to the small lateral sizes. Here, an efficient high-entropy strategy is developed to produce 1T-phase quantum sheets of transition-metal disulfides based on controllable introduction of multiple metal atoms with large size differences to retard the sliding of basal plane. The key is the topological conversion of in-plane ordered carbide laminates (i-MAX) compatible with multiple atoms to high-entropy transition-metal disulfides with high strains and 1T phase, which facilely triggers the fracture into 1T-phase quantum sheets with average size of 4.5 nm and thickness of 0.7 nm during the exfoliation process. Thus, the 1T-phase disulfide quantum sheets show high electrocatalytic activities for lithium polysulfides, achieving a good rate performance of 744 mAh g-1 at 5 C and a long cycle stability in lithium-sulfur batteries.

Homogeneous Integration of Polyoxometalates and Titania into Crumpled Layers

The crumpling and buckling in nanosheets are anticipated to provide new characteristics that could not be observed in ideal flat layers. However, the rigid lattice structure of inorganic metal oxides limits their assembly into well-defined crumpled layers. Here, this study demonstrates that at the sub-nm scale, polyoxometalates (POMs) clusters having well-defined structures can intercede during the nucleation process of titania and co-assemble with nuclei to form uniform, large-sized crumpled binary 2D layers with a thickness of 2 nm. The obtained crumpled layers are then used as a support material to immobilize Pd nanoclusters with an average size of 2 nm. Pd-immobilized crumpled layers are employed as heterogeneous catalysts for the partial hydrogenation of acetylene. This structurally and compositionally unique heterogeneous catalyst manifests exceptional selectivity to cis-alkene with almost 100% yield as compared to commercially available titania which only exhibits 10% diphenylacetylene conversion and 42% selectivity in the given period of time.

Cooling-induced Strains in 2D Materials and Their Modulation via Interface Engineering

2D materials exhibit unique properties for next-generation electronics and quantum devices. However, their sensitivity to temperature variations, particularly concerning cooling-induced strain, remains underexplored systematically. This study investigates the effects of cooling-induced strain on monolayer MoSe2 at cryogenic temperatures. It is emphasized that the mismatch in thermal expansion coefficients between the material and bulk substrate leads to significant external strain, which superimposes the internal strain of the material. By engineering the material-substrate 2D-bulk interface, the resulting strain conditions are characterized and reveal that substantial compressive strain induces new emission features linked to direct-to-indirect bandgap transition, as confirmed by photoluminescence and transient absorption spectroscopy studies. Finally, it is demonstrated that encapsulation with hexagonal boron nitride can mitigate the external strain by 2D-2D interfaces, achieving results similar to those of suspended samples. The findings address key challenges in quantifying and characterizing strain types across different 2D-bulk interfaces, distinguishing cooling-induced strain effects from other temperature-dependent phenomena, and designing strain-sensitive 2D material devices for extreme temperature conditions.

Resistively detected electron spin resonance andg-factor in few-layer exfoliated MoS2devices

MoS2has recently emerged as a promising material for enabling quantum devices and spintronic applications. In this context, an improved physical understanding of theg-factor of MoS2depending on device geometry is of great importance. Resistively detected electron spin resonance (RD-ESR) could be employed to determine theg-factor in micron-scale devices. However, its application and RD-ESR studies have been limited by Schottky or high-resistance contacts to MoS2. Here, we exploit naturallyn-doped few-layer MoS2devices with ohmic tin (Sn) contacts that allow the electrical study of spin phenomena. Resonant excitation of electron spins and resistive detection is a possible path to exploit the spin effects in MoS2devices. Using RD-ESR, we determine theg-factor of few-layer MoS2to be ∼1.92 and observe that theg-factor value is independent of the charge carrier density within the limits of our measurements.

Direct Observation of Unidirectional Exciton Polaritons in Layered van der Waals Semiconductors

Unidirectional excitation of highly confined guided modes is essential for nanoscale energy transport, photonic integrated devices, and quantum information processing. Among various feasible approaches, the mechanism based on optical spin-orbit coupling is investigated for unidirectional routing of surface plasmons and valley exciton-polaritons, without needing the use of complicated magneto-optical effects and parity symmetry breaking. So far, the direct near-field nanoimaging of such exotic polaritonic modes based on optical spin-orbit coupling has remained elusive. Here, the real-space nanoimaging of unidirectional polaritons in van der Waals semiconductors are reported. Specifically, photonic spins are coupled into the tip of a scattering-type scanning near-field optical microscopy for circular dipolar excitations of spin-orbit interactions, thus enabling the unidirectional waveguide exciton-polariton propagation with remarkable unidirectionality (ratio of spectrum amplitudes under opposite circularly polarized illumination) R = 0.291 for TM mode. Via switching to the opposite helicities, the reversed opposite directions are observed. The work offers a promising avenue for detecting and processing spin information for future communication technology at the nanoscale.

Self-Powered Broadband Photodetectors Based on WS2-Anchored MoS2 with Enhanced Responsivity and Detectivity

Self-powered broadband photodetectors utilizing 2D transition metal dichalcogenides (TMDs) are highly promising due to their remarkable light absorption capabilities and high sensitivity, making them suitable for applications such as military surveillance and wireless light detection systems. However, their performance is constrained by inadequate absorption, suboptimal charge carrier separation, and slow response times. In response to these limitations, the study fabricates a self-powered photodetector employing a heterostructure composed of WS2 nanoparticles anchored to CVD-synthesized MoS2, operating within the visible to near-infrared spectrum. The device demonstrates a responsivity of 283 mA W-1 and a detectivity 6.44 × 1012 Jones, alongside an external quantum efficiency of 61% under exposure of 580 nm. In comparison to pristine MoS2, the MoS2-WS2 photodetector exhibited approximately 12-fold and 11-fold enhancements in responsivity and detectivity, respectively, in addition to fast response time of ≈375 µs and 6 ms. Additionally, density functional theory (DFT) calculations are used to analyze the increase in dark current that is observed following WS₂ nanoparticle anchored on MoS₂. This investigation highlights the potential of 2D heterostructures in the development of high-performance broadband photodetectors, which offer improved responsivity, stability, and self-powered operation for advanced optoelectronic applications.

Interfacial Thermal Transport and Energy Dissipation in Multilayer PdSe2 Field Effect Transistors

The continuous miniaturization of 2D electronic circuits results in increased power density during device operation, leading to heat localization and placing higher demands on their performance thresholds. The risk to thermal breakdown and subsequent damage, due to the energy dissipation in the 2D semiconductor field-effect transistors (FETs) supported on the bulk substrates, represents a significant challenge in maintaining their optimal performance. Herein, this study investigates energy dissipation behavior in multilayer PdSe2 FETs for the first time. The high-field breakdown behavior is firstly studied in multilayer PdSe2 FETs on SiO2/Si substrates, where a maximum current density of ≈2.74 MA cm-2 is observed, which is comparable to that of multilayer black phosphorus FET and significantly higher-by about five times-than that of multilayer MoS2 FET. Additionally, the thermal boundary conductance (TBC) of PdSe2/SiO2 interface is measured at room temperature using Raman thermometry. The TBC is found to be ≈12-13 MW m-2 K-1, which is relatively low compared to the other known solid-solid interfaces, indicating that enhancing the performance of PdSe2 FETs can be possible by optimizing the TBC at the PdSe2/SiO2 interface. These findings provide valuable insights for design of high-quality and high-performance PdSe2 electronic and optoelectronic devices.

Ultrafast electron transfer at the ZnIn2S4/MoS2 S-scheme interface for photocatalytic hydrogen evolution

The performance of any photocatalyst relies on its solar harvesting and charge separation characteristics. Fabricating the S-scheme heterostructure is a proficient approach for designing next-generation photocatalysts with improved redox capabilities. Here, we integrated ZnIn2S4 (ZIS) and MoS2 nanosheets to develop a unique S-scheme heterostructure through an in situ hydrothermal technique. The designed ZIS/MoS2 heterostructure showcased a 2.8 times higher photocatalytic H2 evolution rate than pristine ZIS nanosheets. The steady-state optical measurements revealed enhanced visible light absorption and reduced charge recombination in the heterostructure. Transient absorption (TA) spectroscopy revealed the interfacial electron transfer from ZIS to MoS2. The X-ray photoelectron and electron/hole quenching TA spectroscopic measurements collectively confirmed the integration of both semiconductors in an S-scheme manner, facilitating enhanced H2 production in the case of the heterostructure. This study highlights the importance of in-depth spectroscopic investigations in advancing the photocatalytic performance of S-scheme heterostructure-based photocatalysts.

Recent advances in the fundamentals and in situ characterizations for mechanics in 2D materials

The growing need for integrating two-dimensional materials in electronic and functional devices requires the flexibility of the material. This necessitates the in situ characterization of their mechanical properties to understand their structure under stress loading in working devices. However, it is still challenging to directly characterize the mechanical behaviours of two-dimensional materials due to difficulties in handling these naturally fragile materials. In this review, we summarize the recent studies of mechanical properties in two-dimensional materials and their characterization using various microscopy techniques. This involves advances in fundamentals including the measurements of elastic properties, and the basic understanding of how structural parameters like defects and interfaces influence the deformation and failure process of two-dimensional materials. We also discuss the developed handling techniques for transferring two-dimensional materials to the characterization platforms, with the recent advances in in situ characterization studies based on atomic force microscopy and scanning/transmission electron microscopy. The above developments allowed the direct observation of unconventional mechanisms behind the deformation behaviour of two-dimensional materials, including plastic deformation, interlayer slip, phase transition and nanosized cracking. We then discuss the applications related to the mechanics of two-dimensional materials, including structural materials, electronic and optoelectronic properties, and further conclude with the opportunities and challenges in this field.

Bismuth oxychloride as avan der Waalsdielectric for 2D electronics

Two-dimensional (2D) semiconductors have received a lot of attention as the channel material for the next generation of transistors and electronic devices. On the other hand, insulating 2D gate dielectrics, as possible materials for gate dielectrics in transistors, have received little attention. We performed an experimental study on bismuth oxychloride, which is theoretically proposed to have good dielectric properties. High-quality bismuth oxychloride single crystals have been synthesized, and their high single crystallinity and spatial homogeneity have been thoroughly evidenced by x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and scanning TEM studies. We then mechanically exfoliated high-quality BiOCl crystals to fabricate metal-insulator-metal (MIM) capacitors and measured the dielectric properties at various frequencies and different thicknesses. We found that BiOCl exhibits an out-of-plane static dielectric constant up to 11.6, which is 3 times higher than 2D hexagonal boron nitride making it a suitable candidate for 2D dielectrics. We also carried out cross-section TEM studies to look into the MIM interface and provide some future directions for their integration with metal-dielectric interfaces and possibly with other 2D devices.

High Conductivity and Thermoelectric Power Factor in p-Type MoS2 Nanosheets

Transition metal dichalcogenides, particularly Nb-doped MoS2, present unique electronic and thermoelectric properties that make them promising candidates for a variety of applications, including photovoltaic cells and thermoelectric devices. Here, we investigate the influence of controlled substitutional doping on the electrical conductivity and thermoelectric performance of MoS2 as a function of crystal thickness. We report an exceptional bulk conductivity of up to 360 ± 30 S cm-1 and a peak power factor of 370 ± 80 μW m-1 K-2 at room temperature. Our findings reveal that the interplay between doping concentration and thickness can decouple the Seebeck coefficient from electrical conductivity, overcoming the typical trade-off observed in conventional materials. This research highlights the role of surface effects and depletion regions in p-type transition metal dichalcogenides, providing a pathway for developing efficient bipolar thermoelectric devices. The stability and tunability of p-type doping in MoS2 also suggest potential applications in microscale cooling, thermal sensors, and photovoltaic systems.

Commensurate, Incommensurate, and Reconstructed Structures of Multilayer Transition Metal Dichalcogenide and Their Applications

Multilayer transition metal dichalcogenides (ML-TMDs) with commensurate, incommensurate, and reconstructed structures, have emerged as a class of 2D materials with unique properties that differ significantly from their monolayer counterparts. While previous research has focused on monolayers, the discovery of various novel properties has sparked interest in multilayers with diverse structures engineered through stacking. These materials are characterized by interactions between layers and exhibit remarkable tunability in their structural, optical, and electronic behaviors depending on stacking order, twist angle, and interlayer coupling. This review provides an overview of ML-TMDs and explores their properties such as electronic band structure, optical responses, ferroelectricity, and anomalous Hall effect. Various synthetic methods employed to fabricate ML-TMDs, including mechanical stacking and chemical vapor deposition techniques, with an emphasis on achieving precise control of the twist angles and layer configurations, are discussed. This study further explores potential applications of ML-TMDs in nanoelectronics, optoelectronics, and quantum devices, where their unique properties can be harnessed for next-generation technologies. The critical role played by these materials in the development of future electronic and quantum devices is highlighted.

LoreX: A Low-Energy Region Explorer Boosts Efficient Crystal Structure Prediction

Machine learning has boosted the remarkable development of crystal structure prediction (CSP), greatly accelerating modern materials design. However, slow location of the low-energy regions on the potential energy surface (PES) is still a key bottleneck for the overall search efficiency. Here, we develop a low-energy region explorer (LoreX) to rapidly locate low-energy regions on the PES. This achievement stems from graph-deep-learning-based PES slicing, which classifies structures into different prototypes to divide and conquer the PES. The accuracy and efficiency of LoreX are validated on 27 typical compounds, showing that it correctly locates low-energy regions with only 100 selected samples. The powerful capability of LoreX is demonstrated in solving two challenging problems: discovering new boron allotropes and identifying the puzzling crystal structures of the ordered vacancy compound CuIn5Se8. This study establishes a new method for rapid PES exploration and offers a highly efficient and generally applicable approach to accelerating CSP.

Design of Self-Assembled Monolayer in Tungsten Diselenide Bilayer for Exciton Dissociation

Transition metal dichalcogenides (TMDs) have emerged as promising candidates for next-generation self-powered photodetectors due to their distinct optoelectronic properties, including strong light-matter interactions. However, their high exciton binding energies impede efficient exciton dissociation, hindering viable photodetector applications. This study, based on first-principles calculations, introduces a design approach featured by the asymmetrically enclosed structure of the TMD bilayer, i.e., two different self-assembled monolayers (SAMs) asymmetrically attached to each side of a tungsten diselenide bilayer by varying electron-donating and electron-withdrawing groups in SAMs. Compared to the electron-donating and electron-withdrawing tendencies, we demonstrate that the surface work function of the SAM is a crucial macroscopic parameter in fine-tuning the band offset without trap formation with a large degree of freedom. Optimizing the work function achieves trap-free exciton dissociation, establishing a type-II band alignment and a sufficient built-in electric field within the bilayer. This design approach offers not only a design strategy for two-dimensional (2D) self-powered photodetectors but also a guide to interface engineering of TMDs utilizing SAMs for integration into low-power applications.

Engineering Two-Dimensional Nanomaterials for Photothermal Therapy

Two-dimensional (2D) nanomaterials offer a transformative platform for photothermal therapy (PTT) due to their unique physicochemical properties and exceptional photothermal conversion efficiencies. This Minireview summarizes the photothermal mechanisms of common 2D nanomaterials and details their synthesis, surface modification, and optimization strategies. Recent advances leveraging 2D nanomaterials for enhanced PTT are highlighted, with particular emphasis on synergistic therapeutic modalities. Despite the significant potential of 2D nanomaterials in PTT, challenges persist, including scalable and reproducible manufacturing, precise targeted delivery, understanding of the underlying biological interactions, and comprehensive assessment of long-term biocompatibility and toxicity. Looking forward, emerging technologies such as machine learning are expected to play a crucial role in accelerating the design and optimization of 2D nanomaterials for PTT, enabling the prediction of optimal structures, properties, and therapeutic efficacy, and ultimately paving the way for personalized nanomedicine.

Progress and Perspectives in 2D Piezoelectric Materials for Piezotronics and Piezo-Phototronics

The emergence of two-dimensional (2D) materials has catalyzed significant advancements in the fields of piezotronics and piezo-phototronics, owing to their exceptional mechanical, electronic, and optical properties. This review provides a comprehensive examination of key 2D piezoelectric and piezo-phototronic materials, including transition metal dichalcogenides, hexagonal boron nitride (h-BN), and phosphorene, with an emphasis on their unique advantages and recent research progress. The underlying principles of piezotronics and piezo-phototronics in 2D materials is discussed, focusing on the fundamental mechanisms which enable these phenomena. Additionally, it is analyzed factors affecting piezoelectric and piezo-photoelectric properties, with a particular focus on the intrinsic piezoelectricity of 2D materials and the enhancement of out-of-plane polarization through various modulation techniques and materials engineering approaches. The potential applications of these materials are explored from piezoelectric nanogenerators to piezo-phototronic devices and healthcare. This review addresses future challenges and opportunities, highlighting the transformative impact of 2D materials on the development of next-generation electronic, optoelectronic, and biomedical devices.

Environmental implications of Si2BN nanoflakes in pharmaceutical pollutant detection and removal: insights from first-principle calculations

Pharmaceutical pollutants, such as carbamazepine (CBZ), are emerging contaminants that pose significant environmental and health risks due to their persistence in aquatic ecosystems and incomplete removal by conventional wastewater treatments. This study leverages density functional theory (DFT), a gold-standard computational quantum mechanical modeling method, to evaluate the efficacy of Si2BN nanoflakes-a novel two-dimensional material-for CBZ adsorption and detection. Our first-principles calculations reveal thermodynamically stable interactions between CBZ and Si2BN, with adsorption energies of - 0.83 eV (edge) and - 0.82 eV (surface). The material's responsive optical behavior is quantified through time-dependent DFT, showing a 138 nm blueshift in UV-Vis spectra upon adsorption, a hallmark of its sensing capability. Furthermore, DFT-calculated charge transfer (0.04-0.06 e) and Fermi-level shifts (- 4.52 to - 4.69 eV) underscore Si2BN's enhanced electronic properties, enabling selective pollutant detection. By bridging atomic-scale insights (bond distortions, orbital hybridization) with macroscale environmental applications, this work demonstrates how DFT-guided design unlocks Si2BN's dual functionality as a scalable adsorbent and optical sensor. These findings provide a quantum-mechanical foundation for advancing Si2BN nanoflakes as a scalable, stable, and effective material for addressing pharmaceutical pollutants in water, offering a sustainable alternative to conventional methods plagued by secondary contamination risks.

High-Speed and High-Responsivity Vertical van der Waals Heterostructure Waveguide Photodetector Operating in Telecom Band

Telecom-band waveguide photodetectors have revealed great potential for optical communication, computing, and light detection and ranging. Traditional silicon-based waveguide photodetectors based on bulk materials suffer from lattice and thermal expansion coefficient mismatch, resulting in the degradation of device performance. Recently, two-dimensional MoTe2 has become an attractive candidate for waveguide photodetectors due to the absence of dangling bonds and strong light-matter interaction. However, the large bandgap and low carrier mobility of MoTe2 pose an obstacle to achieving high responsivity and large bandwidth in the telecom band. Here, we demonstrate a high-speed and high-responsivity vertical graphene-MoTe2-graphene heterostructure photodetector. Benefiting from the strain-induced bandgap manipulation, the device exhibits a high responsivity of 20 mA W-1 in the telecom C-band (∼1550 nm) and a record-high responsivity of 567 mA W-1 in the telecom O-band (∼1310 nm). On the other hand, the vertical heterostructure minimizes the carrier transit path and promises a high 3 dB bandwidth of 4.81 GHz. Thanks to the comprehensive engineering of the band gap and carrier transition, the demonstrated device achieves a record-high responsivity-bandwidth product. This work demonstrates a high-responsivity and high-speed MoTe2 photodetector for telecom-band applications.

Theoretical Investigation of Stacked Two-Dimensional Transition-Metal Dichalcogenide Materials: The Role of Chemical Species and Number of Monolayers

We report a theoretical investigation, based on density functional theory calculations, of the role of chalcogen species and the number of monolayers in the physical-chemical properties of multilayer two-dimensional transition-metal dichalcogenides (TMDs, MQ2), where M belongs to groups 8 and 10 of the periodic table, Q = S, Se, or Te, and the multilayer is composed of 1 to 6 layers. From the analysis of structural energetic, and electronic properties, we found significant changes in lattice parameters and exfoliation energies as a function of the number of layers, particularly affected by the chalcogen Q species. The TMDs in group 8 exhibit similar lattice parameters for the same choice of chalcogens, making them suitable for constructing commensurate heterostructures, while the crystal phase and the lattice parameter of the TMDs in group 10 strongly depend on the choice of the transition-metal species. Furthermore, the decreasing trend of electronegativity from S to Te results in stronger exfoliation energies due to lower surface charges, thus governing the structural and electronic characteristics of few-layer TMDs. We find unexpected electronic characteristics, such as band gap increases driven by spin-orbit coupling for certain compositions, the emergence of polarization electric fields due to point inversion symmetry breaking, and semiconductor-to-metal transitions with minimal layer additions to the monolayer. The presence of sulfur improves the sensitivity of the surface properties, enabling precise tuning of band edge positions with the layer number.

Recent Developments of Advanced Broadband Photodetectors Based on 2D Materials

With the rapid development of high-speed imaging, aerospace, and telecommunications, high-performance photodetectors across a broadband spectrum are urgently demanded. Due to abundant surface configurations and exceptional electronic properties, two-dimensional (2D) materials are considered as ideal candidates for broadband photodetection applications. However, broadband photodetectors with both high responsivity and fast response time remain a challenging issue for all the researchers. This review paper is organized as follows. Introduction introduces the fundamental properties and broadband photodetection performances of transition metal dichalcogenides (TMDCs), perovskites, topological insulators, graphene, and black phosphorus (BP). This section provides an in-depth analysis of their unique optoelectronic properties and probes the intrinsic physical mechanism of broadband detection. In Two-Dimensional Material-Based Broadband Photodetectors, some innovative strategies are given to expand the detection wavelength range of 2D material-based photodetectors and enhance their overall performances. Among them, chemical doping, defect engineering, constructing heterostructures, and strain engineering methods are found to be more effective for improving their photodetection performances. The last section addresses the challenges and future prospects of 2D material-based broadband photodetectors. Furthermore, to meet the practical requirements for very large-scale integration (VLSI) applications, their work reliability, production cost and compatibility with planar technology should be paid much attention.

Twist angle dependent high degree of anisotropic emission and phonon scattering in WS2/NbOCl2 heterostructures

van der Waals (vdWs) heterostructures provide a superior platform to combine different low-dimensional materials together to tune their physical properties for different types of applications. Specifically, anisotropic heterostructures possess polarization-sensitive optical and electronic properties, which are highly needed in novel optoelectronic devices. However, the achieved degree of polarization (DOP) for the previously investigated heterostructure is relatively low and the induced polarization mechanism and key factors determining the DOP are still unclear. Here, we successfully fabricated an anisotropic TMDC/NbOCl2 heterostructure to break the rotation symmetry of WS2. Taking advantage of the strong anisotropy in NbOCl2, we achieved a high DOP of Raman scattering (0.813) and photoluminescence emission (0.801). Furthermore, we demonstrated that this anisotropy is also valid for bilayer WS2 with indirect exciton emissions. Twist angle is demonstrated to be an effective approach for further tuning the DOP. Density functional theory calculations reveal that increasing the coupling is twist angle dependent, leading to a twist angle-dependent DOP in the NbOCl2/TMDC heterostructure. Moreover, heterostructure formation also reduces intervalley scattering, leading to the observed valley polarization of WS2 at room temperature. Based on these findings, we proposed a conceptual framework to search for vdWs heterostructures with a high DOP. These findings are of critical importance in designing highly efficient anisotropic quantum emitters and optoelectronic devices using vdWs heterostructures.

Semiconductor-mediated radiosensitizers: progress, challenges and perspectives

Radiotherapy has become one indispensable treatment strategy for treating malignant tumors. However, the therapeutic effect of radiotherapy is limited due to the low sensitivity and large side effects of existing radiosensitizers. The rapid development of nanotechnology has created opportunities for various novel kinds of radiosensitizers with excellent radiosensitivity to sprout recently. In particular, due to the ease of modification and potential utilization capacity for a multifunctional radiotherapy platform, semiconductor radiosensitizers have attracted more and more attention. Recently, many novel semiconductor based radiosensitizers have been reported, which provides new ideas for the improvement of radiotherapy efficacy. To make further breakthroughs in semiconductor radiosensitizers, a systematic review is urgently needed and is herein provided. This review first elaborates on the principle of semiconductor induced radiosensitization, and then focuses on strategies such as doping and constructing heterojunctions to enhance the radiosensitivity of semiconductors. Next, it introduces in detail the principle and progress of different types of semiconductor radiosensitizers. Finally, challenges and perspectives of semiconductor radiosensitizers are proposed and discussed, offering guidance for future commercial applications of semiconductor radiosensitizers.

Carborane Nanomembranes

We report on the fabrication of a boron-based two-dimensional (2D) material via electron irradiation-induced cross-linking of carborane self-assembled monolayers (SAMs) on crystalline silver substrates. The SAMs of 1,2-dicarba-closo-dodecarborane-9,12-dithiol (O9,12) were prepared on flat crystalline silver substrates and irradiated with low-energy electrons, resulting in a 2D nanomembrane. The mechanical stability and compact character of the carborane nanomembrane were improved by using 12-(1',12'-dicarba-closo-dodecarboran-1'-yl)-1,12-dicarba-closo-dodecarborane-1-thiol (1-HS-bis-pCB), a longer, rod-like SAM precursor with two para-carborane units linked linearly together. The self-assembly, cross-linking process, and transfer of the resulting membranes onto holey substrates were characterized with different complementary surface-sensitive techniques including X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and low-energy electron diffraction (LEED) as well as scanning tunneling and electron microscopies (STM, SEM) to provide insight on the structural changes within the cross-linked SAMs. The presented methodology has potential for the development of boron-based 2D materials for applications in electronic and optical devices.

Synthesis, Crystal Structure, and Elementary Electrical Characterization of Quasi-One-Dimensional TiSe3

The solid-state synthesis at an applied pressure of 6 GPa, crystal structure, and elementary electronic properties of the previously unreported compound TiSe3 are described. The crystal structure, which is based on 1D chains of Ti-Se triangular prisms that are coupled to each other, with two-thirds of the Se involved in a Se-Se pair, is similar to that of TiS3. Unlike the trisulfide, the triselenide is only made under pressure at temperatures between 800 and 900 °C. The material is semiconducting and weakly diamagnetic.

Recent advances in endohedral metallofullerenes

Fullerenes are a collection of closed polycyclic polymers consisting exclusively of carbon atoms. Recent remarkable advancements in the fabrication of metal-fullerene nanocatalysts and polymeric fullerene layers have significantly expanded the potential applications of fullerenes in various domains, including electrocatalysis, transistors, energy storage devices, and superconductors. Notably, the interior of fullerenes provides an optimal environment for stabilizing a diverse range of metal ions or clusters through electron transfer, resulting in the formation of a novel class of hybrid molecules referred to as endohedral metallofullerenes (EMFs). The utilization of advanced synthetic methodologies and the progress achieved in separation techniques have played a pivotal role in expanding the diversity of the encapsulated metal constituents, consequently leading to distinctive structural, electronic, and physicochemical properties of novel EMFs that surpass conventional ones. Intriguing phenomena, including regioselective dimerization between EMFs, direct metal-metal bonding, and non-classical cage preferences, have been unveiled, offering valuable insights into the coordination interactions between metallic species and carbon. Of particular importance, the recent achievements in the comprehensive characterization of EMFs based on transition metals and actinide metals have generated a particular interest in the exploration of new metal clusters possessing long-desired bonding features within the realm of coordination chemistry. These clusters exhibit a remarkable affinity for coordinating with non-metal atoms such as carbon, nitrogen, oxygen, and sulfur, thus making them highly intriguing subjects of systematic investigations focusing on their electronic structures and physicochemical properties, ultimately leading to a deeper comprehension of their unparalleled bonding characteristics. Moreover, the versatility conferred by the encapsulated species endows EMFs with multifunctional properties, thereby unveiling potential applications in various fields including biomedicine, single-molecule magnets, and electronic devices.

Recent advances in nanoarchitectonics of two-dimensional nanomaterials for dental biosensing and drug delivery

Two-dimensional (2D) nanoarchitectonics involve the creation of functional material assemblies and structures at the nanoscopic level by combining and organizing nanoscale components through various strategies, such as chemical and physical reforming, atomic and molecular manipulation, and self-assembly. Significant advancements have been made in the field, with the goal of producing functional materials from these nanoscale components. 2D nanomaterials, in particular, have gained substantial attention due to their large surface areas which are ideal for numerous surface-active applications. In this review article, nanoarchitectonics of 2D nanomaterials based biomedical applications are discussed. We aim to provide a concise overview of how nanoarchitectonics using 2D nanomaterials can be applied to dental healthcare, with an emphasis on biosensing and drug delivery. By offering a deeper understanding of nanoarchitectonics with programmable structures and predictable properties, we hope to inspire new innovations in the dental bioapplications of 2D nanomaterials.

Uprising Unconventional Nanobiomaterials: Peptoid Nanosheets as a Multi-Modular Platform for Advanced Biological Studies

Peptoids are bio-inspired peptidomimetic polymers that can be designed to self-assemble into a variety of nanostructures. Among these different assemblies, peptoid nanosheets are the most studied. Peptoid nanosheets are 2D highly ordered nanostructures, able to free float in aqueous solutions while featuring versatile chemical displays that can be tuned to incorporate a plethora of functional units. In this review, the synthetic approach used to prepare sequence-defined oligomers and highlight their main characteristics is introduced. The ability of peptoids to fold into nanostructures is then reviewed with an extensive emphasis on peptoid nanosheets, and their physico-chemical characteristics, assembly mechanism, and stability. A particular focus is also placed on the variety of functionalization incorporated into the peptoid nanosheets to tune their properties toward specific applications, especially within the fields of biology and medicine. Finally, the comparison between peptoid nanosheets and other 2D nanomaterials is discussed to address the challenges in the current nanomaterials and underline the future development of peptoid nanosheets in the field of biology.

Magnetically confined surface and bulk excitons in a layered antiferromagnet

The discovery of two-dimensional van der Waals magnets has greatly expanded our ability to create and control nanoscale quantum phases. A unique capability emerges when a two-dimensional magnet is also a semiconductor that features tightly bound excitons with large oscillator strengths that fundamentally determine the optical response and are tunable with magnetic fields. Here we report a previously unidentified type of optical excitation-a magnetic surface exciton-enabled by the antiferromagnetic spin correlations that confine excitons to the surface of CrSBr. Magnetic surface excitons exhibit stronger Coulomb attraction, leading to a higher binding energy than excitons confined in bulk layers, and profoundly alter the optical response of few-layer crystals. Distinct magnetic confinement of surface and bulk excitons is established by layer- and temperature-dependent exciton reflection spectroscopy and corroborated by ab initio many-body perturbation theory calculations. By quenching interlayer excitonic interactions, the antiferromagnetic order of CrSBr strictly confines the bound electron-hole pairs within the same layer, regardless of the total number of layers. Our work unveils unique confined excitons in a layered antiferromagnet, highlighting magnetic interactions as a vital approach for nanoscale quantum confinement, from few layers to the bulk limit.

Prediction of two-dimensional narrow-gap Janus TiOXY (X, Y = Cl, Br, I; X ≠ Y) monolayers for electronic and optoelectronic applications

Two-dimensional (2D) transition metal oxyhalides have garnered significant interest due to their unique physical properties and promising potential applications. By using density functional theory and the non-equilibrium Green's function method, the anisotropic mechanical, electronic, optical, and transport properties of the Janus TiOXY (X, Y = Cl, Br, I; X ≠ Y) monolayers are systematically investigated. The proposed Janus TiOClBr, TiOBrI, and TiOClI monolayers exhibit favorable thermodynamic, dynamic, and mechanical stabilities, respectively. The Young's modulus of the Janus TiOClBr, TiOBrI, and TiOClI monolayers is 43.19-75.40 N m-1, 37.14-69.06 N m-1, and 40.11-66.26 N m-1, while their Poisson's ratios are 0.10-0.37, 0.12-0.38, and 0.11-0.34, respectively. The band gap of the semiconducting TiOClBr, TiOBrI, and TiOClI monolayer is 1.36 eV, 0.34 eV, and 0.46 eV, respectively. The Janus TiOClBr monolayer is found to be insensitive to the in-plane biaxial strain, while an indirect semiconductor-to-semimetal transition may be observed in the Janus TiOBrI and TiOClI monolayers under 4% and 4.9% compressive strain, respectively. The anisotropic optical properties as a function of photon energy of the Janus TiOClBr, TiOBrI, and TiOClI monolayers have been demonstrated. Remarkably, the constructed nanoelectronic devices based on the Janus TiOXY monolayers possess highly-anisotropic transport properties, such as the current-voltage curves, transmission spectra and local projected density of states (PDOS). The obtained results demonstrate that the 2D Janus TiOXY monolayers can be used as potential candidate platforms for novel nanoelectronic and optoelectronic applications.

Rational design of surface termination of Ti3C2T2 MXenes for lithium-ion battery anodes

Two-dimensional transition metal carbides, carbonitrides and nitrides (MXenes) have garnered increasing interest in the energy storage field due to their unique structural and electronic properties. However, the application performance is highly reliant on the surface termination, which is poorly understood from a chemical standpoint. In this work, the structural stability, chemical origin, electronic structure and lithium-ion (Li-ion) storage properties of 15 nonmetal terminated MXenes in the form of Ti3C2T2 (T = B, C, Si, N, P, As, O, S, Se, Te, F, Cl, Br, I and OH) were investigated using first-principles calculations. The results indicate that the partially occupied d-orbital and zero pseudogap lead to the high chemical activity of surface Ti, and that surface terminations can diminish its chemical activity. Furthermore, a large pseudogap of the d-orbital promotes the structural stability of Ti3C2T2. A useful descriptor, the antibonding state (Eσ*), was proposed to predict Li-ion adsorption energy. Combining the good electronic conductivity, high lithophilicity, low Li-ion diffusion barrier and high specific capacity, Ti3C2As2, Ti3C2S2 and Ti3C2Se2 are considered as promising anode candidates for Li-ion batteries. Additionally, S, Se and As doping can improve the Li-ion storage performance of oxygen terminated Ti3C2O2. This work offers insights into the chemical origin of the surface termination and paves the way for designing excellent Li-ion anode candidates based on MXenes.