Biomimetic-Mineralization-Assisted Self-Activation Creates a Delicate Porous Structure in Carbon Material for High-Rate Sodium Storage.

Porous carbons have shown their potential in sodium-ion batteries (SIBs), but the undesirable initial Coulombic efficiency (ICE) and rate capability hinder their practical application. Herein, learning from nature, we report an efficient method for fabricating a carbon framework (CK) with delicate porous structural regulation by biomimetic mineralization-assisted self-activation. The abundant pores and defects of the CK anode can improve the ICE and rate performance of SIBs in ether-based electrolytes, whereas they are confined in carbonate ester-based electrolytes. Notably, ether-based electrolytes enable CK anode to possess excellent ICE (82.9%) and high-rate capability (111.2 mAh g-1 at 50 A g-1). Even after 5500 cycles at a large current density of 10 A g-1, the capacity retention can still be maintained at 73.1%. More importantly, the full cell consisting of the CK anode and Na3V2(PO4)3 cathode delivers a high energy density of 204.4 Wh kg-1, with a power density of 2828.2 W kg-1. Such outstanding performance of the CK anode is attributed to (1) hierarchical pores, oxygen doping, and defects that pave the way for the transportation and storage of Na+, further enhancing ICE; (2) a high-proportion NaF-based solid-electrolyte-interphase (SEI) layer that facilitates Na+ storage kinetics in ether-based electrolytes; and (3) ether-based electrolytes that determine Na+ storage kinetics further to dominate the performance of SIBs. These results provide compelling evidence for the promising potential of our synthetic strategy in the development of carbon-based materials and ether-based electrolytes for electrochemical energy storage.

Heterostructures coupling ultrathin metal carbides and chalcogenides.

Non-layered transition metal carbides (TMCs) and layered transition metal dichalcogenides (TMDs) are two well-studied material families that have individually received considerable attention over the past century. In recent years, with the shift towards two-dimensional materials and heterostructures, a field has emerged that is focused on the structure and properties of TMC/TMD heterostructures, which through chemical conversion exhibit diverse types of heterostructure configuration that host coupled 2D-3D interfaces, giving rise to exotic properties. In this Review, we highlight experimental and computational efforts to understand the routes to fabricate TMC/TMD heterostructures. Furthermore, we showcase how controlling these heterostructures can lead to emergent electronic transport, optical properties and improved catalytic properties.

A substitutional quantum defect in WS2 discovered by high-throughput computational screening and fabricated by site-selective STM manipulation.

Point defects in two-dimensional materials are of key interest for quantum information science. However, the parameter space of possible defects is immense, making the identification of high-performance quantum defects very challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS2, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur (Co S 0 ) and fabricate it with scanning tunneling microscopy (STM). The Co S 0 electronic structure measured by STM agrees with first principles and showcases an attractive quantum defect. Our work shows how HT computational screening and nanoscale synthesis routes can be combined to design promising quantum defects.

Tuning the Fermi Level of Graphene by Two-Dimensional Metals for Raman Detection of Molecules.

Graphene-enhanced Raman scattering (GERS) offers great opportunities to achieve optical sensing with a high uniformity and superior molecular selectivity. The GERS mechanism relies on charge transfer between molecules and graphene, which is difficult to manipulate by varying the band alignment between graphene and the molecules. In this work, we synthesized a few atomic layers of metal termed two-dimensional (2D) metal to precisely and deterministically modify the graphene Fermi level. Using copper phthalocyanine (CuPc) as a representative molecule, we demonstrated that tuning the Fermi level can significantly improve the signal enhancement and molecular selectivity of GERS. Specifically, aligning the Fermi level of graphene closer to the highest occupied molecular orbital (HOMO) of CuPc results in a more pronounced Raman enhancement. Density functional theory (DFT) calculations of the charge density distribution reproduce the enhanced charge transfer between CuPc molecules and graphene with a modulated Fermi level. Extending our investigation to other molecules such as rhodamine 6G, rhodamine B, crystal violet, and F16CuPc, we showed that 2D metals enabled Fermi level tuning, thus improving GERS detection for molecules and contributing to an enhanced molecular selectivity. This underscores the potential of utilizing 2D metals for the precise control and optimization of GERS applications, which will benefit the development of highly sensitive, specific, and reliable sensors.

Effective plant virus enrichment using carbon nanotubes and microfluidics.

Plant virus detection and identification in crops is a pillar for disease management, import of crop material, production of clean stock plants and basic plant virology studies. In this report, we present a platform for the enrichment and isolation of known or unknown viruses. This platform is based on carbon nanotube arrays inside a microfluidic device that can be a solution for the identification of low titer viruses from plants. Using our microfluidic devices, we achieved enrichment of two economically important viruses, the orthotospovirus, tomato spotted wilt orthotospovirus (TSWV) and the potyvirus, zucchini yellow mosaic virus (ZYMV). The carbon nanotube arrays integrated in these microfluidic devices are capable of trapping viruses discriminated by their size; the virus rich arrays can be then analyzed by common downstream techniques including immunoassays, PCR, HTS and electron microscopy. This procedure offers a simple to operate and portable sample preparation device capable of trapping viruses from raw plant extracts while reducing the host contamination.

Light-driven C-H activation mediated by 2D transition metal dichalcogenides.

C-H bond activation enables the facile synthesis of new chemicals. While C-H activation in short-chain alkanes has been widely investigated, it remains largely unexplored for long-chain organic molecules. Here, we report light-driven C-H activation in complex organic materials mediated by 2D transition metal dichalcogenides (TMDCs) and the resultant solid-state synthesis of luminescent carbon dots in a spatially-resolved fashion. We unravel the efficient H adsorption and a lowered energy barrier of C-C coupling mediated by 2D TMDCs to promote C-H activation. Our results shed light on 2D materials for C-H activation in organic compounds for applications in organic chemistry, environmental remediation, and photonic materials.

Dual Activation for Tuning N, S Co-Doping in Porous Carbon Sheets Toward Superior Sodium Ion Storage.

Porous carbon has been widely focused to solve the problems of low coulombic efficiency (ICE) and low multiplication capacity of Sodium-ion batteries (SIBs) anodes. The superior energy storage properties of two-dimensional(2D) carbon nanosheets can be realized by modulating the structure, but be limited by the carbon sources, making it challenging to obtain 2D structures with large surface area. In this work, a new method for forming carbon materials with high N/S doping content based on combustion activation using the dual activation effect of K2 SO4 /KNO3 is proposed. The synthesized carbon material as an anode for SIBs has a high reversible capacity of 344.44 mAh g-1 at 0.05 A g-1 . Even at the current density of 5 Ag-1 , the capacity remained at 143.08 mAh g-1 . And the ICE of sodium-ion in ether electrolytes is ≈2.5 times higher than that in ester electrolytes. The sodium storage mechanism of ether/ester-based electrolytes is further explored through ex-situ characterizations. The disparity in electrochemical performance can be ascribed to the discrepancy in kinetics, wherein ether-based electrolytes exhibit a higher rate of Na+ storage and shedding compared to ester-based electrolytes. This work suggests an effective way to develop doubly doped carbon anode materials for SIBs.

Transition Metal Dichalcogenides: Making Atomic-Level Magnetism Tunable with Light at Room Temperature.

The capacity to manipulate magnetization in 2D dilute magnetic semiconductors (2D-DMSs) using light, specifically in magnetically doped transition metal dichalcogenide (TMD) monolayers (M-doped TX2 , where M = V, Fe, and Cr; T = W, Mo; X = S, Se, and Te), may lead to innovative applications in spintronics, spin-caloritronics, valleytronics, and quantum computation. This Perspective paper explores the mediation of magnetization by light under ambient conditions in 2D-TMD DMSs and heterostructures. By combining magneto-LC resonance (MLCR) experiments with density functional theory (DFT) calculations, we show that the magnetization can be enhanced using light in V-doped TMD monolayers (e.g., V-WS2 , V-WSe2 ). This phenomenon is attributed to excess holes in the conduction and valence bands, and carriers trapped in magnetic doping states, mediating the magnetization of the semiconducting layer. In 2D-TMD heterostructures (VSe2 /WS2 , VSe2 /MoS2 ), the significance of proximity, charge-transfer, and confinement effects in amplifying light-mediated magnetism is demonstrated. We attributed this to photon absorption at the TMD layer that generates electron-hole pairs mediating the magnetization of the heterostructure. These findings will encourage further research in the field of 2D magnetism and establish a novel design of 2D-TMDs and heterostructures with optically tunable magnetic functionalities, paving the way for next-generation magneto-optic nanodevices.

Engineering Vacancies for the Creation of Antisite Defects in Chemical Vapor Deposition Grown Monolayer MoS2 and WS2 via Proton Irradiation.

It is critical to understand the laws of quantum mechanics in transformative technologies for computation and quantum information science applications to enable the ongoing second quantum revolution calls. Recently, spin qubits based on point defects have gained great attention, since these qubits can be initiated, selectively controlled, and read out with high precision at ambient temperature. The major challenge in these systems is controllably generating multiqubit systems while properly coupling the defects. To address this issue, we began by tackling the engineering challenges these systems present and understanding the fundamentals of defects. In this regard, we controllably generate defects in MoS2 and WS2 monolayers and tune their physicochemical properties via proton irradiation. We quantitatively discovered that the proton energy could modulate the defects' density and nature; higher defect densities were seen with lower proton irradiation energies. Three distinct defect types were observed: vacancies, antisites, and adatoms. In particular, the creation and manipulation of antisite defects provides an alternative way to create and pattern spin qubits based on point defects. Our results demonstrate that altering the particle irradiation energy can regulate the formation of defects, which can be utilized to modify the properties of 2D materials and create reliable electronic devices.

Scalable Synthesis of a Porous Micro Si/Si-Ti Alloy Anode for Lithium-Ion Battery from Recovery of Titanium-Blast Furnace Slag.

The extensive utilization of Si-anode-based lithium-ion batteries faces obstacles due to their substantial volume expansion, limited intrinsic conductivity, and low initial Coulombic efficiency (ICE). In this study, we present a straightforward, cost-effective, yet scalable method for producing a porous micro Si/Si-Ti alloy anode. This method utilizes titanium-blast furnace slag (TBFS) as a raw material and combines aluminothermic reduction with acid etching. By adjusting the Al:TBFS ratio, the specific surface area of the material can be facilely tailored, ranging from 25.89 to 43.23 m2 g-1, enhancing the ICE from 78.2 to 85.5%. The incorporation of the Si-Ti alloy skeleton and porous structure contributes to the enhanced cyclic stability (capacity retention from 50.7 to 96.9%) and conductivity (Rct from 107.7 to 76.6 Ω). The Si/Si-Ti anode exhibits excellent electrochemical performance, including delivering a specific capacity of 1161 mAh g-1 at 200 mA g-1 after 200 cycles and 1112 mAh g-1 at 500 mA g-1 after 100 cycles, with an improved ICE of 81.2%. This study introduces a successful methodology for designing novel Si anodes from recycling waste materials, providing valuable insights for future advancements in this area.

Carbon Nanomaterial-Based Hydrogels as Scaffolds in Tissue Engineering: A Comprehensive Review.

Carbon-based nanomaterials (CBNs) are a category of nanomaterials with various systems based on combinations of sp2 and sp3 hybridized carbon bonds, morphologies, and functional groups. CBNs can exhibit distinguished properties such as high mechanical strength, chemical stability, high electrical conductivity, and biocompatibility. These desirable physicochemical properties have triggered their uses in many fields, including biomedical applications. In this review, we specifically focus on applying CBNs as scaffolds in tissue engineering, a therapeutic approach whereby CBNs can act for the regeneration or replacement of damaged tissue. Here, an overview of the structures and properties of different CBNs will first be provided. We will then discuss state-of-the-art advancements of CBNs and hydrogels as scaffolds for regenerating various types of human tissues. Finally, a perspective of future potentials and challenges in this field will be presented. Since this is a very rapidly growing field, we expect that this review will promote interdisciplinary efforts in developing effective tissue regeneration scaffolds for clinical applications.

Observation of Room-Temperature Exciton-Polariton Emission from Wide-Ranging 2D Semiconductors Coupled with a Broadband Mie Resonator.

Two-dimensional exciton-polaritons in monolayer transition metal dichalcogenides (TMDs) exhibit practical advantages in valley coherence, optical nonlinearities, and even bosonic condensation owing to their light-emission capability. To achieve robust exciton-polariton emission, strong photon-exciton couplings are required at the TMD monolayer, which is challenging due to its atomic thickness. High-quality (Q) factor optical cavities with narrowband resonances are an effective approach but typically limited to a specific excitonic state of a certain TMD material. Herein, we achieve on-demand exciton-polariton emission from a wide range of TMDs at room temperature by hybridizing excitons with broadband Mie resonances spanning the whole visible spectrum. By confining broadband light at the TMD monolayer, our one type of Mie resonator on different TMDs enables enhanced light-matter interactions with multiple excitonic states simultaneously. We demonstrate multi-Rabi splittings and robust polaritonic photoluminescence in monolayer WSe2, WS2, and MoS2. The hybrid system also shows the potential to approach the ultrastrong coupling regime.

Toward High-Performance p-Type Two-Dimensional Field Effect Transistors: Contact Engineering, Scaling, and Doping.

n-type field effect transistors (FETs) based on two-dimensional (2D) transition-metal dichalcogenides (TMDs) such as MoS2 and WS2 have come close to meeting the requirements set forth in the International Roadmap for Devices and Systems (IRDS). However, p-type 2D FETs are dramatically lagging behind in meeting performance standards. Here, we adopt a three-pronged approach that includes contact engineering, channel length (Lch) scaling, and monolayer doping to achieve high performance p-type FETs based on synthetic WSe2. Using electrical measurements backed by atomistic imaging and rigorous analysis, Pd was identified as the favorable contact metal for WSe2 owing to better epitaxy, larger grain size, and higher compressive strain, leading to a lower Schottky barrier height. While the ON-state performance of Pd-contacted WSe2 FETs was improved by ∼10× by aggressively scaling Lch from 1 µm down to ∼20 nm, ultrascaled FETs were found to be contact limited. To reduce the contact resistance, monolayer tungsten oxyselenide (WOxSey) obtained using self-limiting oxidation of bilayer WSe2 was used as a p-type dopant. This led to ∼5× improvement in the ON-state performance and ∼9× reduction in the contact resistance. We were able to achieve a median ON-state current as high as ∼10 µA/µm for ultrascaled and doped p-type WSe2 FETs with Pd contacts. We also show the applicability of our monolayer doping strategy to other 2D materials such as MoS2, MoTe2, and MoSe2.

Raman spectroscopy of a few layers of bismuth telluride nanoplatelets.

We can shape the electronic and phonon properties of Bi2Te3 crystals via the variation of the number of layers. Here, we report a Raman study with the aid of first-principles calculations on few-layered Bi2Te3 systems ranging from 5 to 24 nm layer thickness using 1.92, 2.41 and 2.54 eV excitation energies. We examine how the frequency position, intensity and lineshape of the main Raman modes (A11g, E2g, and A21g) behave by the variation of the layer thickness and excitation energy. We observed a frequency dispersion on the number of layers of the main modes, indicating changes in the inter- and intra-layers interaction. A resonant Raman condition is reached for all modes for samples with 11 and 18 nm thickness because of van Hove singularities at the electronic density of states. Also, the Breit-Wigner-Fano line shape of the A21g mode shows an increase of electron-phonon coupling for thick layers. These results suggest a relevant influence of numbers of layers on the Raman scattering mechanics in Bi2Te3 systems.

Effects of post-transfer annealing and substrate interactions on the photoluminescence of 2D/3D monolayer WS2/Ge heterostructures.

The ultraflat and dangling bond-free features of two-dimensional (2D) transition metal dichalcogenides (TMDs) endow them with great potential to be integrated with arbitrary three-dimensional (3D) substrates, forming mixed-dimensional 2D/3D heterostructures. As examples, 2D/3D heterostructures based on monolayer TMDs (e.g., WS2) and bulk germanium (Ge) have become emerging candidates for optoelectronic applications, such as ultrasensitive photodetectors that are capable of detecting broadband light from the mid-infrared (IR) to visible range. Currently, the study of WS2/Ge(100) heterostructures is in its infancy and it remains largely unexplored how sample preparation conditions and different substrates affect their photoluminescence (PL) and other optoelectronic properties. In this report, we investigated the PL quenching effect in monolayer WS2/Ge heterostructures prepared via a wet transfer process, and employed PL spectroscopy and atomic force microscopy (AFM) to demonstrate that post-transfer low-pressure annealing improves the interface quality and homogenizes the PL signal. We further studied and compared the temperature-dependent PL emissions of WS2/Ge with those of as-grown WS2 and WS2/graphene/Ge heterostructures. The results demonstrate that the integration of WS2 on Ge significantly quenches the PL intensity (from room temperature down to 80 K), and the PL quenching effect becomes even more prominent in WS2/graphene/Ge heterostructures, which is likely due to synergistic PL quenching effects induced by graphene and Ge. Density functional theory (DFT) and Heyd-Scuseria-Ernzerhof (HSE) hybrid functional calculations show that the interaction of WS2 and Ge is stronger than in adjacent layers of bulk WS2, thus changing the electronic band structure and making the direct band gap of monolayer WS2 less accessible. By understanding the impact of post-transfer annealing and substrate interactions on the optical properties of monolayer TMD/Ge heterostructures, this study contributes to the exploration of the processing-properties relationship and may guide the future design and fabrication of optoelectronic devices based on 2D/3D heterostructures of TMDs/Ge.

Charge Transfer Modulation in Vanadium-Doped WS2 /Bi2 O2 Se Heterostructures.

The field of photovoltaics is revolutionized in recent years by the development of two-dimensional (2D) type-II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)-doped WS2 is investigated, hereafter labeled V-WS2 , in combination with air-stable Bi2 O2 Se for use in high-performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS2 /Bi2 O2 Se, 0.4 at.% V-WS2 /Bi2 O2 Se, and 2 at.% V-WS2 /Bi2 O2 Se, respectively, indicating a superior charge transfer in V-WS2 /Bi2 O2 Se compared to pristine WS2 /Bi2 O2 Se. The exciton binding energies for WS2 /Bi2 O2 Se, 0.4 at.% V-WS2 /Bi2 O2 Se and 2 at.% V-WS2 /Bi2 O2 Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS2 . These findings confirm that by incorporating V-doped WS2 , charge transfer in WS2 /Bi2 O2 Se heterostructures can be tuned, providing a novel light-harvesting technique for the development of the next generation of photovoltaic devices based on V-doped transition metal dichalcogenides (TMDCs)/Bi2 O2 Se.

Bi-functional photocatalytic heterostructures combining titania thin films with carbon quantum dots (C-QDs/TiO2) for effective elimination of water pollutants.

In this study, carbon quantum dots (C-QDs), prepared via hydrothermal-microwave procedures, were successfully combined with nanostructured titania (TiO2). The photocatalytic oxidation/reduction activity of the C-QDs/TiO2 composite films was evaluated in the decomposition of organic-inorganic contaminants from aqueous solutions under UV illumination. Physicochemical characterizations were applied to investigate the crystal structure of the carbon quantum dots and the composites. It was found that the prepared C-QDs/TiO2 composites had great contribution to the photocatalytic reduction of hexavalent chromium (Cr+6) species and 4-Nitrophenol (PNP) as well as to the photocatalytic oxidation of methylene blue (MB) and Rhodamine B (RhB) dyes. The mechanism of the photocatalytic reaction was studied with trapping experiments, revealing that the electron (e-) radical species were powerfully supported for the photocatalytic reduction of Cr+6 and PNP and the holes (h+) are the main active species for the photocatalytic oxidation reactions.

Liquid Template Assisted Activation for "Egg Puff"-Like Hard Carbon toward High Sodium Storage Performance.

The slow solid diffusion dynamics of sodium ions and the side-reaction of sodium metal plating at low potential in the hard carbon anode of sodium ion batteries (SIBs) pose significant challenges to the safety manipulation of high-rate batteries. Herein, a simple yet powerful fabricating method is reported on for "egg puff"-like hard carbon with few N doping using rosin as a precursor via liquid salt template-assisted and potassium hydroxide dual activation. The as-synthesized hard carbon delivers promising electrochemical properties in the ether-based electrolyte especially at high rates, based on the absorption mechanism of fast charge transfer. The optimized hard carbon exhibits a high specific capacity of 367 mAh g-1 at 0.05 A g-1 and 92.9% initial coulombic efficiency (ICE), 183 mAh g-1 at 10 A g-1 , and ultra-long cycle stability of reversible discharge capacity of 151 mAh g-1 after 12,000 cycles at 5 A g-1 with the average coulombic efficiency of ≈99% and the decay of 0.0026% per cycle. These studies will undoubtedly provide an effective and practical strategy for advanced hard carbon anode of SIBs based on adsorption mechanism.

Recent Advances in 2D Material Theory, Synthesis, Properties, and Applications.

Two-dimensional (2D) material research is rapidly evolving to broaden the spectrum of emergent 2D systems. Here, we review recent advances in the theory, synthesis, characterization, device, and quantum physics of 2D materials and their heterostructures. First, we shed insight into modeling of defects and intercalants, focusing on their formation pathways and strategic functionalities. We also review machine learning for synthesis and sensing applications of 2D materials. In addition, we highlight important development in the synthesis, processing, and characterization of various 2D materials (e.g., MXnenes, magnetic compounds, epitaxial layers, low-symmetry crystals, etc.) and discuss oxidation and strain gradient engineering in 2D materials. Next, we discuss the optical and phonon properties of 2D materials controlled by material inhomogeneity and give examples of multidimensional imaging and biosensing equipped with machine learning analysis based on 2D platforms. We then provide updates on mix-dimensional heterostructures using 2D building blocks for next-generation logic/memory devices and the quantum anomalous Hall devices of high-quality magnetic topological insulators, followed by advances in small twist-angle homojunctions and their exciting quantum transport. Finally, we provide the perspectives and future work on several topics mentioned in this review.

Substrate-Induced Changes on the Optical Properties of Single-Layer WS2.

Among the most studied semiconducting transition metal dichalcogenides (TMDCs), WS2 showed several advantages in comparison to their counterparts, such as a higher quantum yield, which is an important feature for quantum emission and lasing purposes. We studied transferred monolayers of WS2 on a drilled Si3N4 substrate in order to have insights about on how such heterostructure behaves from the Raman and photoluminescence (PL) measurements point of view. Our experimental findings showed that the Si3N4 substrate influences the optical properties of single-layer WS2. Beyond that, seeking to shed light on the causes of the PL quenching observed experimentally, we developed density functional theory (DFT) based calculations to study the thermodynamic stability of the heterojunction through quantum molecular dynamics (QMD) simulations as well as the electronic alignment of the energy levels in both materials. Our analysis showed that along with strain, a charge transfer mechanism plays an important role for the PL decrease.