Jiuxiang Dai

A 2D monolayer MoS₂ when combined with a bulk p-type silicon forms a van der Waals p–n junction. The atomic thickness in 2D materials makes them very much sensitive to the surrounding environment. This sensitivity is utilized here to produce a three-order enhancement in photoresponse by modulating the surrounding dielectric environment of the van der Waals p–n junction.

Abstract

The reduced dielectric screening in the out of plane direction, makes 2D materials sensitive to the surrounding environment, offering a unique platform with greatly tunable optoelectronic properties. Large exciton binding energy in 2D materials limits their photogeneration efficiency. The strong electric field generated at a p–n junction will help in separating these strongly bound electron hole pairs. Here, the present study demonstrates how engineering the surrounding dielectric environment would facilitate a mixed dimensional van der Waals p–n junction to improve the photoresponse to a great extent. A 3D silicon-2D monolayer MoS₂ heterostructure is fabricated as a model system. Nearly three orders of magnitude enhancement in photoresponse is observed by modulating the surrounding dielectric environment. This huge enhancement is attributed to the easy separation of photogenerated carriers due to the screening of Coulomb interaction. The dielectric also screens the impurity potential, reducing the charge carrier scattering. In addition, there is a change in the overall bandgap of the heterostructure producing a lower energy barrier for the charge carriers. The findings lay a general pathway for improving the efficiency of 2D material based photodetectors through dielectric engineering.

Due to the availability of abundant exposed edge sites in vertically aligned layered materials, unique physicochemical properties can be achieved which are favorable for various device applications. This article reviews recent developments in the properties, preparation, and applications and discusses the future perspectives of these emerging vertically aligned layered materials.

Abstract

2D materials exhibit strong physical orientation-dependent properties due to their intrinsic anisotropic crystallinity. Herein, the authors review the recent developments on the properties, preparation, and applications of emerging vertically aligned 2D materials. This report initially discusses the various properties of vertically aligned materials such as electronic, optical, magnetic, thermal, mechanical, and super wetting. The tuning of these properties is also highlighted based on strategies such as scale, doping, defect, vacancy, intercalation, and phase engineering. Then, this review provides a succinct and critical survey of the recent progress in designing, preparation techniques, and the manufacturing conditions of vertically aligned materials. After investigating the properties, tunability of properties, and preparation methods for vertically aligned 2D materials, their performances in numerous applications are comprehensively summarized. The presence of predominantly exposed edge sites significantly alters their properties and chemical reactivity owing to their enriched dangling bonds and offers several advantages for a wide range of applications including chemical and gas sensors, field emission, energy storage, catalysis, and optoelectronic devices. Finally, some developmental challenges, a few outlooks, future possibilities, and directions are summarized to inspire readers toward exploring vertically aligned 2D materials with new advances and functionalities.

A novel highly sensitive WS₂/Bi₂O₂Se van der Waals (vdWs) heterostructure with straddling band configuration is assembled on fluorophlogopite substrate. Owing to the effective separation of photogenerated electron–hole pairs and the quantum tunneling effect, WS₂/Bi₂O₂Se heterostructures exhibit excellent responsivity under 532 nm illumination. Furthermore, the heterostructure achieves a broadband photodetection capability from 532 to 1450 nm.

Abstract

2D bismuth oxyselenide (Bi₂O₂Se) nanosheets have received increasing attention in the field of electronics and optoelectronics due to their high-mobility, moderate energy bandgap, and air-stability. However, due to the intrinsic high mobility, the photodetectors based on 2D Bi₂O₂Se have an inevitable high dark current, leading to high power consumption and limiting its potential application in photodetection. Herein, a novel highly sensitive WS₂/Bi₂O₂Se van der Walls (vdWs) heterostructure with straddling band configuration is assembled on fluorophlogopite substrate. Owing to the effective separation of photogenerated electron–hole pairs and the quantum tunneling effect, the responsivity and external quantum efficiency of the WS₂/Bi₂O₂Se heterostructure are 628 mA W⁻¹ and 147.6% under 532 nm illumination, respectively. The I _photo/I _dark ratio with more than two orders of magnitude can be obtained, and the rise time is ≈33 ms, while the fall time is 38 ms. Furthermore, the heterostructure achieves a broadband photodetection capability from visible to near infrared (532–1450 nm). The results suggest that the WS₂/Bi₂O₂Se vdWs heterostructure possesses a promising potential application prospect in high performance and broadband photodetectors.

A bottom-up technique has been used to prepare 2-dimensional molecularly-thin nitrogen-doped film material, fullerphene nanosheet. The N-doped hierarchically micro-/mesoporous structure allows repetitive adsorption/desorption of small molecule carboxylic acids leading to highly selective sensing of formic acid over acetic acid. Fullerene-based fullerphene nanosheet is an excellent functional material for sensing and other advanced applications.

Abstract

Ultrathin 2D nanoporous materials offer enhanced sensitivity and high spatial resolution in sensing applications making them important for the selective discrimination of guest molecules. Here bottom-up fabrication is reported of a novel molecularly-thin nitrogen-doped 2D fullerphene. Thermal annealing at 700 °C of a bottom-up assembled fullerene C₆₀-ethylenediamine (EDA) thin film results in formation of a nitrogen-doped ultrathin carbon film, fullerphene, which exhibits a hierarchically micro/mesoporous structure at its surfaces. N-doping of fullerphene is dominated by pyrrolic and quaternary nitrogen atoms, which allow selective and repetitive adsorption and desorption of low-molecular-weight carboxylic acid vapors through noncovalent interactions. The large surface area (655.2 m² g^–1) and pore volume (0.659 cc g^–1) offered by the hierarchical micro/mesoporous architecture leads to superior sensitivity of fullerphene to formic acid over acetic acid in the vapor phase demonstrating that novel 2D fullerphene provides an attractive platform for the discrimination of carboxylic acids at the single-carbon-atom level.

A high-quality saturable absorber (SA) based on GeAs₂ nanosheets is introduced. The saturation intensity and the modulation depth are measured to be 1.23 GW cm⁻² and 5.2%, respectively. By incorporating this GeAs₂ SA into fiber lasers, a high stable ultrafast fiber laser with a pulse duration of 371 fs and a single-frequency fiber laser with a linewidth of ≈678 Hz are demonstrated, respectively.

Abstract

As a new IV–V group semiconductor, germanium-diarsenide (GeAs₂) compounds have attracted considerable attention due to their outstanding optical and electrical properties, thickness-dependent bandgap, in-plane anisotropy, and excellent optical absorption. However, the potential of GeAs₂ in the field of ultrafast and ultranarrow fiber laser has not been studied. In this article, a high-quality GeAs₂ nanosheets saturable absorber (SA) is successfully prepared by liquid-phase exfoliation. The nonlinear optical characteristics of GeAs₂ nanosheets have been investigated based on a balanced twin-detector measurement system. The modulation depth, nonsaturable loss, and saturation intensity are measured to be 5.2%, 24%, and 1.23 GW cm⁻², respectively. GeAs₂ has been successfully applied as an SA in an ultrafast and single-frequency fiber laser. A stable mode-locked laser pulses operation with a duration as short as 371 fs and a repetition rate of 8.19 MHz at a wavelength of 1560 nm is achieved. Moreover, ultranarrow fiber lasers with a high signal-to-noise ratio of 80 dB and a linewidth of ≈678 Hz are obtained. The findings validate that 2D GeAs₂ can be used as an SA and has promising applications in ultrafast and ultranarrow photonics.

A strain-tailoring strategy is proposed in AlN epitaxy on a high temperature annealed AlN template and thus the first 4-inch crack-free high power UVC-LED wafer is demonstrated. Such a success pushes UVC-LEDs into the same 4-inch area as commercially mature blue LEDs, enabling the possibility of large-scale epitaxy and chip manufacturing at a significantly reduced cost.

Abstract

Ultraviolet-C light-emitting diodes (UVC-LEDs) have great application in pathogen inactivation under various kinds of situations, especially in the fight against COVID-19. Unfortunately, its epitaxial wafers are so far limited to a size of 2 inches, which greatly increases the cost of massive production. In this work, a 4-inch crack-free high-power UVC-LED wafer is reported. This achievement relies on a proposed strain-tailored strategy, where a 3D to 2D (3D-2D) transition layer is introduced during the homo-epitaxy of AlN on the high temperature annealed (HTA)-AlN template, which successfully drives the original compressive strain into a tensile one and thus solves the challenge of realizing a high-quality Al_0.6Ga_0.4N layer with a flat surface. This smooth Al_0.6Ga_0.4N layer is nearly pseudomorphically grown on the strain-tailored HTA-AlN template, leading to 4-inch UVC-LED wafers with outstanding performances. The strategy succeeds in compromising the bottlenecked contradictory in producing a large-sized UVC-LED wafer on pronounced crystalline AlN template: The compressive strain in HTA-AlN allows for a crack-free 4-inch wafer, but at the same time leads to a deterioration of the AlGaN morphology and crystal quality. The launch of 4-inch wafers makes the chip fabrication process of UVC-LEDs match the mature blue one, and will definitely speed up the universal application of UVC-LED in daily life.

Twist angle induces various Moiré-related properties in 2D materials, but most studies only focus on bilayer systems. Here, via a folding strategy, multilayer MoS₂ Moiré superlattices are fabricated whose interlayer coupling, indirect bandgap, and degree of circular polarization (DOCP) are tunable by twist angle. The highest DOCP for folded bilayer MoS₂ can reach 86% above liquid nitrogen temperature.

Abstract

Twist angle provides a new degree of freedom for 2D material modifications. In principle, the intrinsic properties of twisted multilayers can be regulated by twist angle between each adjacent layer and thus have greater tunability than widely studied bilayer structures. Considering its complexity, it is important to first investigate the simplest twisted multilayers with only one interface twisted. In this work, multilayer Moiré superlattices with only one twisted interface via paraffin-assisted folding of non-twisted stacked (highly symmetrically stacked) multilayer MoS₂ are successfully fabricated, and their twist-angle dependent optical properties are systematically studied. Compared to non-twisted stacked multilayer MoS₂, the one-interface-twisted multilayers show a 2–3.5 times higher PL intensity, and their interlayer coupling, indirect bandgap, and degree of circular polarization (DOCP) are tunable by twist angle. Notably, the DOCP for the one-interface-twisted four-layer (folded bilayer) can reach 86%, which is the highest value ever reported for transition metal dichalcogenide homostructures above liquid nitrogen temperature. This work provides a solid base for understanding twist-angle dependent properties of twisted multilayer 2D-materials.

The authors provide insight into important research goals to enhance the world of MXene synthesis and understanding. Through these discussions, recent attempts into nitride MXene synthesis, and current stopgaps in this field are discussed. Finally, the authors review works pertaining to in situ/operando study of MXenes and what advancements still need to be made on this front.

Abstract

As nanomaterials are becoming a key component in various electronics, 2D nanomaterials are emerging and attracting tremendous attention in the scientific community due to their unique physical, chemical, and structural properties. In recent years, a new family of 2D carbides and nitrides, known as MXenes, has become the center of attention for many electrochemical energy storage and conversion systems. While nitride MXenes have some publications centered around them, the overwhelming majority revolve around carbide and their direct application to systems without understanding the underlying mechanism behind their performance. The lack of publications in both of these fields, nitrides and mechanistic understanding, causes a major stopgap in MXene research and needs to be remedied in order to truly utilize their potential for future electronics and energy conversion systems. In this work, the limited works on nitride MXenes and the applications of in situ/operando characterization techniques in understanding the underlying mechanisms of energy storage and conversion in MXenes are reviewed, major progress and remaining challenges in both fields are identified, recommendations on how to circumvent the challenges and limitations are provided, and finally, new research directions that must be performed to advance the field of 2D carbide and nitride MXenes are proposed.

Recent nanostructure and catalytic center design of emerging 2D materials for electrocatalytic applications are summarized in this review. The synthetic pathways and state-of-the-art strategies for designing these multifaceted 2D electrocatalysts are systematically discussed, especially promoting catalytic activities and exploring the corresponding structure–function relationships. Furthermore, the electrocatalytic applications, current challenges, and future directions in different fields are also summarized.

Abstract

Currently, the development of advanced 2D nanomaterials has become an interdisciplinary subject with extensive studies due to their extraordinary physicochemical performances. Beyond graphene, the emerging 2D-material-derived electrocatalysts (2D-ECs) have aroused great attention as one of the best candidates for heterogeneous electrocatalysis. The tunable physicochemical compositions and characteristics of 2D-ECs enable rational structural engineering at the molecular/atomic levels to meet the requirements of different catalytic applications. Due to the lack of instructive and comprehensive reviews, here, the most recent advances in the nanostructure and catalytic center design and the corresponding structure–function relationships of emerging 2D-ECs are systematically summarized. First, the synthetic pathways and state-of-the-art strategies in the multifaceted structural engineering and catalytic center design of 2D-ECs to promote their electrocatalytic activities, such as size and thickness, phase and strain engineering, heterojunctions, heteroatom doping, and defect engineering, are emphasized. Then, the representative applications of 2D-ECs in electrocatalytic fields are depicted and summarized in detail. Finally, the current breakthroughs and primary challenges are highlighted and future directions to guide the perspectives for developing 2D-ECs as highly efficient electrocatalytic nanoplatforms are clarified. This review provides a comprehensive understanding to engineer 2D-ECs and may inspire many novel attempts and new catalytic applications across broad fields.

Inserting an atomic hexagonal boron nitride layer at the interface of metal and WS₂ to form a metal–insulator–semiconductor (MIS) contact is a practical method to improve mobility and contact resistance of four-layer WS₂ transistors. This study provides an opportunity to understand the impact of the metal work-function and the mechanism of the Schottky barrier reduction of the MIS-structured WS₂ transistors.

Abstract

Transition metal dichalcogenides (TMDs) are of great interest owing to their unique properties. However, TMD materials face two major challenges that limit their practical applications: contact resistance and surface contamination. Herein, a strategy to overcome these problems by inserting a monolayer of hexagonal boron nitride (h-BN) at the chromium (Cr) and tungsten disulfide (WS₂) interface is introduced. Electrical behaviors of direct metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) contacts with mono- and bilayer h-BN in a four-layer WS₂ field-effect transistor (FET) are evaluated under vacuum from 77 to 300 K. The performance of the MIS contacts differs based on the metal work function when using Cr and indium (In). The contact resistance is significantly reduced by approximately ten times with MIS contacts compared with that for MS contacts. An electron mobility up to ≈115 cm² V^-1 s^-1 at 300 K is achieved with the insertion of monolayer h-BN, which is approximately ten times higher than that with MS contacts. The mobility and contact resistance enhancement are attributed to Schottky barrier reduction when h-BN is introduced between Cr and WS₂. The dependence of the tunneling mechanisms on the h-BN thickness is investigated by extracting the tunneling barrier parameters.

Good-quality centimeter-scale antiferromagnetic semiconductor FeOCl single crystals are controllably synthesized by developing a temperature-oscillation chemical vapor transport method. The semiconducting characteristics, strong in-plane anisotropies, and spin−phonon coupling effect of the 2D FeOCl are explored in detail. This study provides a high-quality low-symmetry van der Waals magnetic candidate for miniaturized spintronic devices.

Abstract

2D van der Waals (vdW) transition-metal oxyhalides with low symmetry, novel magnetism, and good stability provide a versatile platform for conducting fundamental research and developing spintronics. Antiferromagnetic FeOCl has attracted significant interest owing to its unique semiconductor properties and relatively high Néel temperature. Herein, good-quality centimeter-scale FeOCl single crystals are controllably synthesized using the universal temperature-oscillation chemical vapor transport (TO-CVT) method. The crystal structure, bandgap, and anisotropic behavior of the 2D FeOCl are explored in detail. The absorption spectrum and electrical measurements reveal that 2D FeOCl is a semiconductor with an optical bandgap of ≈2.1 eV and a resistivity of ≈10⁻¹ Ω m at 295 K, and the bandgap increases with decreasing thickness. Strong in-plane optical and electrical anisotropies are observed in 2D FeOCl flakes, and the maximum resistance anisotropic ratio reaches 2.66 at 295 K. Additionally, the lattice vibration modes are studied through temperature-dependent Raman spectra and first-principles density functional calculations. A significant decrease in the Raman frequencies below the Néel temperature is observed, which results from the strong spin−phonon coupling effect in 2D FeOCl. This study provides a high-quality low-symmetry vdW magnetic candidate for miniaturized spintronics.

A heterojunction post-annealing treatment is utilized to suppress the nonradiative recombination for a highly competitive power conversion efficiency of 8.64% and a record open-circuit voltage (V _OC) of 520 mV in Sb₂Se₃ thin-film solar cells. The V _OC deficit of the device is lower than that of any other reported efficient antimony chalcogenide solar cells.

Abstract

Despite the fact that antimony triselenide (Sb₂Se₃) thin-film solar cells have undergone rapid development in recent years, the large open-circuit voltage (V _OC) deficit still remains as the biggest bottleneck, as even the world-record device suffers from a large V _OC deficit of 0.59 V. Here, an effective interface engineering approach is reported where the Sb₂Se₃/CdS heterojunction (HTJ) is subjected to a post-annealing treatment using a rapid thermal process. It is found that nonradiative recombination near the Sb₂Se₃/CdS HTJ, including interface recombination and space charge region recombination, is greatly suppressed after the HTJ annealing treatment. Ultimately, a substrate Sb₂Se₃/CdS thin-film solar cell with a competitive power conversion efficiency of 8.64% and a record V _OC of 0.52 V is successfully fabricated. The device exhibits a much mitigated V _OC deficit of 0.49 V, which is lower than that of any other reported efficient antimony chalcogenide solar cell.

Interfacial Atomic Configurations

In article number 2106814, Kaihui Liu, Xin-Zheng Li, Xinqiang Wang, and co-workers profile a novel perspective of the lattice arrangement (polarity) manipulation of a quasi-van der Waals epitaxial hexagonal III-nitride film on graphene by interfacial atomic configuration engineering. Through using atomic O preirradiation and a specific supply sequence of Ga and N atoms to form the C–O–N–Ga(3) and C–O–Ga–N(3) configurations, N- and Ga-lattice polarity GaN films are achieved on transferred graphene, respectively.

A perspective of quantum materials and their prospects for applications over the next decade and beyond in the areas of quantum information science, spintronics, valleytronics, and twistronics and those involving topology is given. The material and processing challenges that may impede the potential applications will be discussed.

Abstract

A brief overview of quantum materials and their prospects for applications, in the near, mid, and far-term in the areas of quantum information science, spintronics, valleytronics, and twistronics and those involving topology are covered in this perspective. The material and processing challenges that will modulate the realism of the applications will be discussed as well.

Nature Nanotechnology, Published online: 03 February 2022; doi:10.1038/s41565-021-01060-6

Graphene has a centrosymmetric crystal symmetry, which prohibits second-order effects in transport experiments. Yet, giant second-order nonlinear transports can emerge in graphene moiré superlattices at zero magnetic field, originating from the skew scattering of chiral Bloch electrons in the superlattice and giving rise to both longitudinal and transverse nonlinear conductivities under time-reversal symmetry.

Nature, Published online: 02 February 2022; doi:10.1038/s41586-021-04296-3

The solution-phase irreversible synthesis of a two-dimensional polymer with excellent elastic modulus and yield strength is reported.

Nature Electronics, Published online: 31 January 2022; doi:10.1038/s41928-021-00711-9

Electric vehicles could help reduce greenhouse gas emissions and deliver a sustainable transport system. But the full life cycle of electric vehicles needs to be considered in order to avoid creating resource issues while trying to achieve the necessary climate goals.

A novel spatiotemporal photoexcitation which includes a cascaded process of hot-carrier expansion, negative contraction, and exciton diffusion is studied in 2D WS₂, determining an initial average diffusivity of nearly 10³ cm² s⁻¹ that is 10² times higher than the followed excitonic. This discovery has great potential for improving the efficiency and thermal management of transition metal dichalcogenides-based optoelectronic devices.

Abstract

The competition between different spatiotemporal carrier relaxation determines the carrier harvesting in optoelectronic semiconductors, which can be greatly optimized by utilizing the ultrafast spatial expansion of highly energetic carriers before their energy dissipation via carrier–phonon interactions. Here, the excited-state dynamics in layered tungsten disulfide (WS₂) are primarily imaged in the temporal, spatial, and spectral domains by transient absorption microscopy. Ultrafast hot carrier expansion is captured in the first 1.4 ps immediately after photoexcitation, with a mean diffusivity up to 980 cm² s⁻¹. This carrier diffusivity then rapidly weakens, reaching a conventional linear spread of 10.5 cm² s⁻¹ after 2 ps after the hot carriers cool down to the band edge and form bound excitons. The novel carrier diffusion can be well characterized by a cascaded transport model including 3D thermal transport and thermo-optical conversion, in which the carrier temperature gradient and lattice thermal transport govern the initial hot carrier expansion and long-term exciton diffusion rates, respectively. The ultrafast hot carrier expansion breaks the limit of slow exciton diffusion in 2D transition metal dichalcogenides, providing potential guidance for high-performance applications and thermal management of optoelectronic technology.

Nature Reviews Materials, Published online: 31 January 2022; doi:10.1038/s41578-021-00408-7

The ability to control interlayer excitons in van der Waals heterostructures provides a practical way to address the spin and valley degrees of freedom in solid-state devices. This Review surveys the recent progress in this field, with a focus on devices and engineering techniques.

A damage-free Au/h-BN/Au memristor fabricated using a metal transfer approach is demonstrated. Au electrodes are physically assembled onto layered h-BN with minimized damage and interfacial defects. The Au/h-BN/Au memristors demonstrate superior performance with the coexistence of nonpolar and threshold switching and can further implement logic functions. Cross-sectional STEM validates the feasibility of this nondestructive approach, the crucial role of sharp interface, and a direct observation of percolation path.

Abstract

2D materials with intriguing properties have been widely used in optoelectronics. However, electronic devices suffered from structural damage due to the ultrathin materials and uncontrolled defects at interfaces upon metallization, which hindered the development of reliable devices. Here, a damage-free Au/h-BN/Au memristor is reported using a clean, water-assisted metal transfer approach by physically assembling Au electrodes onto the layered h-BN which minimized the structural damage and undesired interfacial defects. The memristors demonstrate significantly improved performance with the coexistence of nonpolar and threshold switching as well as tunable current levels by controlling the compliance current, compared with devices with evaporated contacts. The devices integrated into an array show suppressed sneak path current and can work as both logic gates and latches to implement logic operations allowing in-memory computing. Cross-sectional scanning transmission electron microscopy analysis validates the feasibility of this nondestructive metal integration approach, the crucial role of high-quality atomically sharp interface in resistive switching, and a direct observation of percolation path. The underlying mechanism of boron vacancies-assisted transport is further supported experimentally by conductive atomic force microscopy free from process-induced damage, and theoretically by ab initio simulations.

Monolayer and bilayer lateral heterostructures based on ternary alloys of MoS_{2(1− x )}Se_{2 x} –WS_{2(1− x )}Se_{2 x} are successfully synthesized, the bandgap of both domains in the heterostructure is continuously tuned in the entire range of chalcogen compositions. Kelvin probe measurements reveal composition-dependent band alignments. Alloy-based lateral heterostructures greatly expand the available tools kit for 2D optoelectronic applications.

Abstract

2D heterostructures made of transition metal dichalcogenides (TMD) have emerged as potential building blocks for new-generation 2D electronics due to their interesting physical properties at the interfaces. The bandgap, work function, and optical constants are composition dependent, and the spectrum of applications can be expanded by producing alloy-based heterostructures. Herein, the successful synthesis of monolayer and bilayer lateral heterostructures, based on ternary alloys of MoS_{2(1− x )}Se_{2 x} –WS_{2(1− x )}Se_{2 x} , is reported by modifying the ratio of the source precursors; the bandgaps of both materials in the heterostructure are continuously tuned in the entire range of chalcogen compositions. Raman and photoluminescence (PL) spatial maps show good intradomain composition homogeneity. Kelvin probe measurements in different heterostructures reveal composition-dependent band alignments, which can further be affected by unintentional electronic doping during the growth. The fabrication of sequential multijunction lateral heterostructures with three layers of thickness, composed of quaternary and ternary alloys, is also reported. These results greatly expand the available tools kit for optoelectronic applications in the 2D realm.

The latest progress of additives-assisted chemical vapor deposition growth of 2D materials is reviewed, mainly summarized from the perspectives of promote effects, applications, and growth mechanisms, providing a guidance for 2D materials to move from labs toward industries.

Abstract

2D materials are increasingly becoming key components in modern electronics because of their prominent electronic and optoelectronic properties. The central and premise to the entire discipline of 2D materials lie in the high-quality and scaled preparations. The chemical vapor deposition (CVD) method offers compelling benefits in terms of scalability and controllability in shaping large-area and high-quality 2D materials. The past few years have witnessed development of numerous CVD growth strategies, with the use of additives attracting substantial attention in the production of scaled 2D crystals. This review provides an overview of different additives used in CVD growth of 2D materials, as well as a methodical demonstration of their vital roles. In addition, the intrinsic mechanisms of the production of scaled 2D crystals with additives are also discussed. Lastly, reliable guidance on the future design of optimal CVD synthesis routes is provided by analyzing the accessibility, pricing, by-products, controllability, universality, and commercialization of various additives.