Jiuxiang Dai

Carbon nitride thin films (CNTFs) of various thicknesses are deposited by thermal vapor condensation and transferred by water-assisted method. The visible-blind ultraviolet (UV) photodetector, fabricated by sensitizing graphene field effect transistors with CNTFs, shows 10³ A W⁻¹ responsivity to UV radiation at a switching and visible light rejection ratio of 157 and 48.2, respectively.

Abstract

Ultraviolet (UV) photodetectors often suffer from the lack of spectral selectivity due to strong interference from visible light. In this study, the exceptional electrical properties of graphene and the unique optical properties of carbon nitride thin films (CNTFs) are used to design visible-blind UV photodetectors. First, polycrystalline CNTFs with different thicknesses (12–94 nm) are produced by thermal vapor condensation. Compared to the bulk carbon nitride powder, these films have a considerable sp² nitrogen deficiency, which is thickness dependent. In addition to showing a wider bandgap than the bulk counterpart, their optical absorption profile (in the ultraviolet–visible range) is unique. Critically, the absorbance falls sharply above 400 nm, making the CNTFs suitable for ultraviolet photodetection. As a result, graphene field-effect transistors (GFETs) sensitized with CNTFs show 10³ A W⁻¹ responsivity to UV radiation, a stark contrast to the negligible value obtained in the visible spectrum. The effect of film thickness on the photoresponse is determined, with the thinner CNTF leading to much better device performance. The CNTF/GFET photodetectors are also characterized by their fast response and recovery times, 0.5 and 2.0 s, respectively. These findings pave a simple route for the development of sensitive, visible-blind UV photodetectors.

2D MoSe₂ is discovered with intrinsic low infrared emissivity and is further exfoliated into adequately aminated nanosheets with nice thermal camouflage performance. Experimental and density functional theory calculations together reveal mechanisms to affect infrared emissivity as electron–photon reflection and phonon–photon absorption. This work offers inspiration for two-dimensional materials selection and preparation toward desired infrared radiation properties in certain wavebands to satisfy numerous applications.

Abstract

Low infrared emissivity materials play a key role in thermal camouflage or retardation. Among these, fillers can be easily shaped into various flexible forms and normally provide an omnidirectional and polarization-insensitive emissivity. However, conventional fillers suffer from drawbacks of full-waveband ultrahigh reflectivity, unsatisfactory thermal camouflage performances, or poor chemical/thermal stabilities. Herein, 2D MoSe₂ is discovered as a new semiconductor with intrinsic low infrared emissivity after first-principle density functional theory calculation and experimental demonstration on eight types of two-dimensional materials (2DMs). Mechanisms of electron–photon reflection and phonon–photon absorption for the low infrared emissivity are proposed. A two-step microwave-assisted amination process is developed to exfoliate the nanosheets and obtain a desired low infrared emissivity. The as-obtained chitosan modified MoSe₂ (CS@MoSe₂) has an ultrahigh spectral reflectivity of 78%–86% in 8–14 µm, and its resin-based coating still exhibits a low infrared emissivity of 0.32 and shows a dramatic reduction in radiation temperature of 28 °C for a hot object at 70 °C. Besides, CS@MoSe₂ can endure a high temperature of 220 °C and is demonstrated with a long-term thermal camouflage efficiency in hot environments. This work will guide 2DMs selection and preparation toward desired infrared radiation properties to satisfy numerous applications.

This article comprehensively reviews the progress of chemical vapor deposition growth, characterization, and electrical properties of graphene depending on layer number and twist angle. The characterization methods for measuring the layer number and twist angle are summarized. Electrical properties and applications of graphene, particularly magic-angle twist bilayer graphene, are briefly introduced. Outlooks and challenges are presented.

Abstract

Numerous studies conducted on the layered graphene family—including the monolayer, bilayer, trilayer, few-layer, and multilayer—draw plenty of attention to stacking modes and twist angles, which are extensively explored for its controlled growth, properties, and applications. This review provides a comprehensive overview of current challenges and opportunities for the chemical vapor deposition (CVD) growth, characterization, and electrical properties of graphene depending on the layer number and twist angles. Various state-of-the-art innovations using the CVD method, which incorporates graphene synthesis through the control of metal substrates, layer numbers, and twist angles, are presented. The underlying growth mechanisms are discussed in terms of the interactions among graphene substrates/layers and its dynamic process. The characterization methods for determining the layer number and twist angle of graphene layers are summarized. Furthermore, the electrical properties and applications of graphene, particularly magic-angle twist bilayer graphene, are briefly introduced. Finally, outlooks and perspectives for the engineering of CVD graphene layers are discussed.

A technique capable of drawing at the nanoscale is introduced through controlling the macroscopic movement of the substrate. The structure of the surface nanopatterns is completely determined by the macroscopic moving track of the substrate and the size shrinking time from the macroscopic movement track to surface nanopatterns can be accurately manipulated and easily reach million times.

Abstract

Nanopatterns are important for applications in various nanodevice fields. Existing nanopatterning techniques mainly directly manufacture the nanopatterns through various lithographic methods, which usually are laborious, time-consuming, and need expensive equipment. Here, an extremely simple drawing at the nanoscale (DAN) concept to indirectly fabricate rational nanopatterns through controlling the macroscopic movement of the substrate , is demonstrated. The structure of the nanopatterns is completely determined by and can be shrunk by millions of times from the moving track of the substrate. Multiple surface nanopatterns of different materials with accurately tailorable relative positions can be simply stacked together by moving the substrate by macroscopic distances during different DAN processes. In combination with sophisticated lithographic methods, the DAN method is anticipated to enable substantial advances in nanofabrication.

Publication date: May 2022

Source: Materials Today, Volume 55

Author(s): Alexander A. Balandin, Fariborz Kargar, Tina T. Salguero, Roger K. Lake

2D TaSe₂-MoSe₂ metal–semiconductor heterostructures are successfully achieved usin an edge-induced epitaxial growth mode. The unique contact potential and strong current rectification behavior will facilitate the development high-performance transition metal dichalcogenide-based electronic devices.

Abstract

Van der Waals (vdWs) heterostructures based on 2D metals and semiconductors have attracted considerable attention due to their excellent properties and great application potential in next-generation electronic and optoelectronic devices. To obtain such vdWs heterostructures, the conventional approach with artificial exfoliation and stacking of 2D metals onto 2D semiconductors in the vertical direction is still far from satisfactory, because of the low yield and impurity-involved transfer process. Here, two-step vapor deposition growth of 2D TaSe₂-MoSe₂ metal–semiconductor heterostructures is reported. Raman maps confirm the precise spatial modulation of the as-grown 2D TaSe₂-MoSe₂ heterostructures. Structural analysis reveals that the upper 1T-TaSe₂ is formed heteroepitaxially on/around the presynthesized 2H-MoSe₂ monolayers with an epitaxial relationship of (10-10)_TaSe2//(10-10)_MoSe2 and [0001]_TaSe2//[0001]_MoSe2. Based on the detailed characterizations of morphology, structure, and composition, an edge-induced growth mechanism is proposed to illustrate the formation process of the 2D heterostructures, confirmed by first-principle calculations. In addition, Kelvin probe force microscope characterizations and electrical transport measurements confirm that the 2D metal–semiconductor heterostructures exhibit typical rectification characteristics with a contact potential height of ≈431 mV. The direct growth of high-quality 2D metal–semiconductor heterostructures marks an important step toward high-performance integrated optoelectronic devices.

Nature Nanotechnology, Published online: 02 May 2022; doi:10.1038/s41565-022-01115-2

Nature Electronics, Published online: 02 May 2022; doi:10.1038/s41928-022-00748-4

Nature Electronics, Published online: 02 May 2022; doi:10.1038/s41928-022-00755-5

Nanopatterning bridges the microstructure of 2D materials and integrated chip devices, essentially enabling and prompting their successful application in industry. A critical summary on the recent development of key nanopatterning technologies of 2D materials, with the aim of realizing large-scale device integration, is provided. This contribution offers a pioneering reference and guidelines to promote 2D materials from laboratory research to practical use.

Abstract

With the reduction of feature size and increase of integration density, traditional 3D semiconductors are unable to meet the future requirements of chip integration. The current semiconductor fabrication technologies are approaching their physical limits based on Moore's law. 2D materials such as graphene, transitional metal dichalcogenides, etc., are of great promise for future memory, logic, and photonic devices due to their unique and excellent properties. To prompt 2D materials and devices from the laboratory research stage to the industrial integrated circuit-level, it is necessary to develop advanced nanopatterning methods to obtain high-quality, wafer-scale, and patterned 2D products. Herein, the recent development of nanopatterning technologies, particularly toward realizing large-scale practical application of 2D materials is reviewed. Based on the technological progress, the unique requirement and advances of the 2D integration process for logic, memory, and optoelectronic devices are further summarized. Finally, the opportunities and challenges of nanopatterning technologies of 2D materials for future integrated chip devices are prospected.

Nature Materials, Published online: 03 May 2022; doi:10.1038/s41563-022-01228-y

CrSBr is a layered material possessing intralayer ferromagnetic and interlayer antiferromagnetic (AFM) ordering at low temperatures (T < 132 K). At higher temperatures or in the presence of modest magnetic fields, AFM correlations are suppressed, yielding a magnetic phase with a comparatively high sheet susceptibility (χ^2D). Magnetic force microscopy is sensitive to χ^2D and identifies local nanoscale magnetic ordering.

Abstract

2D materials can host long-range magnetic order in the presence of underlying magnetic anisotropy. The ability to realize the full potential of 2D magnets necessitates systematic investigation of the role of individual atomic layers and nanoscale inhomogeneity (i.e., strain) on the emergence of stable magnetic phases. Here, spatially dependent magnetism in few-layer CrSBr is revealed using magnetic force microscopy (MFM) and Monte Carlo-based simulations. Nanoscale visualization of the magnetic sheet susceptibility is extracted from MFM data and force–distance curves, revealing a characteristic onset of both intra- and interlayer magnetic correlations as a function of temperature and layer-thickness. These results demonstrate that the presence of a single uncompensated layer in odd-layer terraces significantly reduces the stability of the low-temperature antiferromagnetic (AFM) phase and gives rise to multiple coexisting magnetic ground states at temperatures close to the bulk Néel temperature (T _N). Furthermore, the AFM phase can be reliably suppressed using modest fields (≈16 mT) from the MFM probe, behaving as a nanoscale magnetic switch. This prototypical study of few-layer CrSBr demonstrates the critical role of layer parity on field-tunable 2D magnetism and validates MFM for use in nanomagnetometry of 2D materials (despite the ubiquitous absence of bulk zero-field magnetism in magnetized sheets).

2D MBenes, early transition metal borides, have recently gained tremendous attention due to their unique properties. This Perspective sheds light on the material–structure–property relationship of MBenes and elucidates the most prospective applications in various fields, thus opening a promising paradigm for designing new functional systems and high-performance devices with multipurpose functionalities.

Abstract

2D MBenes, early transition metal borides, are a very recent derivative of ternary or quaternary transition metal boride (MAB) phases and represent a new member in the flatland. Although holding great potential toward various applications, mainly theoretical knowledge about their potential properties is available. Theoretical calculations and preliminary experimental attempts demonstrate their rich chemistry, excellent reactivity, mechanical strength/stability, electrical conductivity, transition properties, and energy harvesting possibility. Compared to MXenes, MBenes’ structure appears to be more complex due to multiple crystallographic arrangements, polymorphism, and structural transformations. This makes their synthesis and subsequent delamination into single flakes challenging. Overcoming this bottleneck will enable a rational control over MBenes’ material–structure–property relationship. Innovations in MBenes’ postprocessing approaches will allow for the design of new functional systems and devices with multipurpose functionalities thus opening a promising paradigm for the conscious design of high-performance 2D materials.

A new MXene analogue, V-Mo-based 2D layered transition metal nitride solid solution (V_0.2Mo_0.8N_1.2), was synthesized via a catalytic molten-salt method. It exhibited excellent activity and stability for hydrogen evolution reaction, superior to most MXenes. Boosted electrocatalytic performance originates from an optimized electronic structure induced by V atom alloying.

Abstract

Electrocatalysts for high-rate hydrogen evolution reaction (HER) are crucial to clean fuel production. Nitrogen-rich 2D transition metal nitride, designated “nitridene”, has shown promising HER performance because of its unique physical/chemical properties. However, its synthesis is hindered by the sluggish growth kinetics. Here for the first time using a catalytic molten-salt method, we facilely synthesized a V−Mo bimetallic nitridene solid solution, V_0.2Mo_0.8N_1.2, with tunable electrocatalytic property. The molten-salt synthesis reduces the growth barrier of V_0.2Mo_0.8N_1.2 and facilitates V dissolution via a monomer assembly, as confirmed by synchrotron spectroscopy and ex situ electron microscopy. Furthermore, by merging computational simulations, we confirm that the V doping leads to an optimized electronic structure for fast protons coupling to produce hydrogen. These findings offer a quantitative engineering strategy for developing analogues of MXenes for clean energy conversions.

Nature Communications, Published online: 04 May 2022; doi:10.1038/s41467-022-29990-2

Nature Reviews Materials, Published online: 04 May 2022; doi:10.1038/s41578-022-00433-0

Abstract

Chemical vapor deposition (CVD) has emerged as a promising approach for the controlled growth of graphene films with appealing scalability, controllability, and uniformity. However, the synthesis of high-quality graphene films still suffers from low production capacity and high energy consumption in the conventional hot-wall CVD system. In contrast, owing to the different heating mode, cold-wall CVD (CW-CVD) system exhibits promising potential for the industrial-scale production, but the quality of as-received graphene remains inferior with limited domain size and high defect density. Herein, we demonstrated an efficient method for the batch synthesis of high-quality graphene films with millimeter-sized domains based on CW-CVD system. With reduced defect density and improved properties, the as-received graphene was proven to be promising candidate material for electronics and anti-corrosion application. This study provides a new insight into the quality improvement of graphene derived from CW-CVD system, and paves a new avenue for the industrial production of high-quality graphene films for potential commercial applications.

Nature Electronics, Published online: 28 April 2022; doi:10.1038/s41928-022-00759-1

Nature Electronics, Published online: 28 April 2022; doi:10.1038/s41928-022-00761-7