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Solar-blind deep ultraviolet (DUV) photodetectors with high responsivity (R) and fast response speed are crucial for practical applications in astrophysical analysis, environmental pollution monitoring, and communication. Recently, 2D tellurium has emerged as a potential optoelectronic material because of its excellent photoelectric properties. In this study, solar-blind DUV photodetectors are demonstrated based on solution-synthesized and air-stable quasi-2D Te nanosheets (Te NSs). An R of 6.5 × 104 A/W at 261 nm and an external quantum efficiency (EQE) of higher than 2.26 × 106% were obtained, which are highest among most other 2D material-based solar-blind DUV photodetectors. Moreover, the photoelectric performance of the quasi-2D Te-based photodetector exhibited good stability even after ambient exposure for 90 days without any encapsulation. These results indicate that quasi-2D Te NSs provide a viable approach for developing solar-blind DUV photodetectors with ultrahigh R and EQE.

Due to their excellent and tailorable optoelectronic performance, low cost, facile fabrication, and compatibility with flexible substrates, solution-processed inorganic and hybrid photo-active materials have attracted extensive interest for next-generation photodetector applications. This review gives a comprehensive compilation of solution-processed photodetectors. The basic structures of the device and important parameters of photodetectors will be firstly summarized. Then the development of various solution processing technologies containing solution synthesis and liquid phase film-forming processes for the preparation of semiconductor films is described. From the materials science point of view, we give a comprehensive overview about the current status of solution processed semiconductor materials including inorganic and hybrid photo-active materials for the application of photodetectors. Moreover, challenges and future trends in the field of solution-processed photodetectors are proposed.

The functional deficiency between physically separated electronic components makes the up-to-date artificial photo memory devices undergo an intricate preparation and assembly process for the discrete elements, modules and final product. In this research, a multi-functional composite, which consists of conductive nanoparticles with a photothermal conversion effect and a polymeric matrix with memory characteristics, is proposed to realize the sensing and successive memory of optical information in the same material instead of device integration. Nanoparticles in the composite can convert light into heat, and heat can change the irreversible viscous flow of the polymers, which results in changing the distribution distance of conductive nanoparticles in the matrix, as well as the resistance of the composite. Therefore, the composite itself can realize light perception and memory. The composite can mimic multiple basic neuro behaviors. This new way of thinking about the polymer physical properties may open doors for polymers in the electronics area, which may be applied in future flexible and wearable electronics or even artificial intelligence with sensory demands.

Two-dimensional (2D) ferromagnetism is critical for both scientific investigation and technological development owing to its low-dimensionality that brings in quantization of electronic states as well as free axes for device modulation. However, the scarcity of high-temperature 2D ferromagnets has been the obstacle of many research studies, such as the quantum anomalous Hall effect (QAHE) and thin-film spintronics. Indeed, in the case of the isotropic Heisenberg model with finite-range exchange interactions as an example, low-dimensionality is shown to be contraindicated with ferromagnetism. However, the advantages of low-dimensionality for micro-scale patterning could enhance the Curie temperature (TC) of 2D ferromagnets beyond the TC of bulk materials, opening the door for designing high-temperature ferromagnets in the 2D limit. In this paper, we review the recent advances in the field of 2D ferromagnets, including their material systems, physical properties, and potential device applications.

Monitoring harmful and toxic chemicals, gases, microorganisms, and radiation has been a challenge to the scientific community for the betterment of human health and environment. Two-dimensional (2D)-material-based sensors are highly efficient and compatible with modern fabrication technology, which yield data that can be proficiently used for health and environmental monitoring. Graphene and its oxides, black phosphorus (BP), transition metal dichalcogenides (TMDCs), metal oxides, and other 2D nanomaterials have demonstrated properties that have been alluring for the manufacture of highly sensitive sensors due to their unique material properties arising from their inherent structures. This review summarizes the properties of 2D nanomaterials that can provide a platform to develop high-performance sensors. In this review, we have also discussed the advances made in the field of infrared photodetectors and electrochemical sensors and how the structural properties of 2D nanomaterials affect sensitivity and performance. Further, this review highlights 2D-nanomaterial-based electrochemical sensors that can be used to check for contaminations from heavy metals, organic/inorganic compounds, poisonous gases, pesticides, bacteria, antibiotics, etc., in water or air, which are severe risks to human wellbeing as well as the environment. Moreover, the limitations, future prospects, and challenges for the development of sensors based on 2D materials are also discussed for future advancements.

As a “hot” member of two-dimensional (2D) materials, black phosphorus (BP) has received growing interest in a variety of fields in physics, chemistry, materials, and biomedicine since 2014. Owing to the exclusive 2D layered structure, some fantastic properties such as tunable band structure, high charge mobility, and in-plane anisotropy provide BP with great potential for application in electronic/optoelectronic devices, energy source conversion and storage, etc. However, with in-depth investigations, the performance deficiencies of BP-based devices are exposed, originating from the poor chemical stability of BP. To address the above issues, a variety of BP/carbon hybrid composites have been constructed as an emerging type of multifunctional materials by the integration of the unique properties of carbon materials with the merits of BP into a single hybrid heterostructure, showing improved performance for applications. In this review, the enhanced stability of BP is presented based on the fundamental chemistry of BP degradation, which originates from the formation of P–C/P–O–C bonds or van der Waals interactions in BP/carbon hybrid composites. Recent research studies focusing on the utilization of BP/carbon hybrid composites for electrochemical energy storage, photocatalytic hydrogen production and optoelectronic devices are summarized, in which approaches toward the assembly of BP/carbon hybrid composites are introduced. Finally, the extant challenges and potential applications of BP/carbon hybrid materials are also proposed.

The previous decades have witnessed increasing prevalence of research on chemiresistive gas sensors due to their high response, simple configuration and low cost. Chemiresistive gas sensors based on low-dimensional (0D, 1D and 2D) nanomaterials are remarkable because their high specific areas, abundant active sites and quantum effects in a certain dimension endow them with extraordinary gas sensing performance. Additionally, it has been gradually demonstrated that fabricating nanocomposites from various low-dimensional nanomaterials can further improve their sensing performance. The nanocomposites are generally in the form of 0D nanostructure-functionalized 1D or 2D nanomaterials. This review aims to elaborate the functionalization of 0D nanomaterials, including metal oxide semiconductors (MOSs), noble metals (NMs), metal chalcogenides (MCs), metal organics, conductive polymers (CPs) and others, on various 1D or 2D backbone nanomaterials. The content includes methods for depositing 0D nanomaterials on 1D or 2D backbones as well as the gas sensing performance and underlying mechanisms of 0D–1D and 0D–2D nanocomposites.

As promising non-volatile memory devices, memristors have received extensive attention since they can effectively mimic synapses and enable the fabrication of neuromorphic systems. In recent years, 2D materials have been widely used in memristors because of their unique advantages, which not only improve the performance of memristors, but also promote the applicability of memristors in flexible electronics, low-power high-temperature devices, neuromorphic computing, etc. In this review, we summarize the applications of 2D materials in fabricating memristors and their physical switching mechanisms. The challenges involved are discussed and the corresponding strategies are reviewed.

Based on the extensive investigation on graphene and graphene derivatives asymmetrically functionalized with a variety of molecular groups and the concept of Janus materials with asymmetric facial properties, Janus two-dimensional (2D) materials as derivatives of the 2D material family, including Janus graphene, Janus transition metal chalcogenides, etc., have attracted much attention in recent years. Janus 2D materials have been demonstrated experimentally and theoretically to possess unique properties such as an out-of-plane piezoelectric polarization and strong Rashba effect due to their out-of-plane asymmetry. Here, the recent progress of emerging Janus 2D materials, including Janus graphene, prediction and fabrication of various different Janus 2D materials and Janus 2D van der Waals heterostructures, is presented. The investigations on the unique properties and potential device applications of Janus 2D materials are summarized. Finally, the conclusion and prospects for the future explorations on Janus 2D materials are also provided.

The use of a wide range of methods for incorporating nitrogen atoms on robust catalysts has given rise to fundamental advances in the field of energy conversion and storage. Recently, nitrogen incorporation has proven to be able to fine-tune the electron densities of exposed active sites to create high-performance electrocatalysts. The preservation of a strong interface between the local atomic coordination of nitrogen atoms on bare carbon, single metal atoms, transition metal oxides, metal chalcogenides, and MXenes during synthesis plays an important role in producing an efficient electrocatalysts. In addition, the ability of nitrogen atoms to bind with carbon or metal atoms can be influenced by processing conditions. In this regard, this review is the first comprehensive overview of the range of synthetic strategies to form nitrogen incorporated catalysts and assess their chemical, structural, physical electronic property modification and their influence on electrocatalytic ORR, OER, and HER performance. This review will describe how specific strategies have been utilized to realise effective electrocatalytic systems, including the energy conversion of nitrogen incorporated catalysts, structural coordination, and material optimization. Finally, the main challenges to be considered in future investigations in order to initiate new research efforts in this promising research area are discussed.

Two-dimensional (2D) indium selenide (InSe) has been widely studied for application in transistors and photodetectors, which benefit from its excellent optoelectronic properties. Among the three specific polytypes (γ-, ϵ- and β-phase) of InSe, only the crystal lattice of InSe in β-phase (β-InSe) belongs to a non-symmetry point group of $D_{6h}^4$, which indicates stronger anisotropic transport behavior and potential in the polarized photodetection of β-InSe-based optoelectronic devices. Therefore, we prepare the stable p-type 2D-layered β-InSe via temperature gradient method. The anisotropic Raman, transport and photoresponse properties of β-InSe have been experimentally and theoretically proven, showing that the β-InSe-based device has a ratio of 3.76 for the maximum to minimum dark current at two orthogonal orientations and a high photocurrent anisotropic ratio of 0.70 at 1 V bias voltage, respectively. The appealing anisotropic properties demonstrated in this work clearly identify β-InSe as a competitive candidate for filter-free polarization-sensitive photodetectors.

The flexible electronics technology revolution is driven ever forward by a strong demand for portable, wearable and lightweight electronic products in the market. Flexible lithium-ion batteries (LIBs) have attracted considerable attention because of their excellent electrochemical and mechanical properties. Due to the particular folded structure, high electrical conductivity and excellent flexibility, several emerging two-dimensional (2D) noncarbon nanomaterials such as phosphorene, borophene, MoS2, Ti3C2Tx and V2O5 have been widely applied to flexible LIBs with bright prospects. This review examines the existing literature and recent advances of flexible LIBs based on 2D materials, covering the classifications, synthetic methods and merits of emerging 2D noncarbon nanomaterials. Theoretical research and practical applications of emerging 2D noncarbon nanomaterials as electrode materials for flexible LIBs are reviewed as well. In addition, challenges faced by emerging 2D noncarbon nanomaterials are summarized and prospects of these 2D nanomaterials are given in order to broaden their potential in flexible LIBs.

Over the past decade, two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous research interest for future electronics owing to their atomically thin thickness, compelling properties and various potential applications. However, interface engineering including contact optimization and channel modulations for 2D TMDCs represents fundamental challenges in ultimate performance of ultrathin electronics. This article provides a comprehensive overview of the basic understanding of contacts and channel engineering of 2D TMDCs and emerging electronics benefiting from these varying approaches. In particular, we elucidate multifarious contact engineering approaches such as edge contact, phase engineering and metal transfer to suppress the Fermi level pinning effect at the metal/TMDC interface, various channel treatment avenues such as van der Waals heterostructures, surface charge transfer doping to modulate the device properties, and as well the novel electronics constructed by interface engineering such as diodes, circuits and memories. Finally, we conclude this review by addressing the current challenges facing 2D TMDCs towards next-generation electronics and offering our insights into future directions of this field.

Nanoengineered Heterostructures In article number 2100503, Zhinan Guo, Han Zhang, Paras N. Prasad, and co‐workers report a nanoengineered heterostructure for the first time demonstration of an nanointerface using an inserted graphene layer between black phosphorus (BP) and InSe which inhibits interlayer recombination and greatly improved photodetection performances. [Image: see text]

The electrochemical nitrogen reduction reaction (eNRR) provides a sustainable way to generate ammonia (NH3) but its Faradaic efficiency (FE) is relatively low and could be further improved, especially on the highly active molybdenum carbide (Mo2C) electrocatalyst. Our theoretical calculations suggest that unlike substitute doping model, interstitial Fe doping into Mo2C is highly eNRR-selective due to decreasing hydrogen evolution activity and unique surface-hydrogenation mechanism on negatively charged Mo sites around Fe atoms. Inspired by this prediction, we successfully developed a novel interstitial Fe doped Mo2C electrocatalyst by the pyrolysis of Fe-doped Mo/Zn bimetallic imidazolate frameworks (Fe-Mo/Zn BIFs) as a precursor where Fe atoms substitute Zn sites to obtain the spatial confinement effect. When evaluated in eNRR catalysis, Fe/Mo2C catalyst therefore exhibits a much higher FE of 20.1% at −0.45 V vs. RHE (reversible hydrogen electrode), which is almost double that of pristine Mo2C and substitute type. Moreover, the Fe/Mo2C catalyst also exhibits high ammonia yield rate with excellent durability over the six continuous cycles.

Great success in 2D van der Waals (vdW) heterostructures based photodetectors is obtained owing to the unique electronic and optoelectronic properties of 2D materials. Performance of photodetectors based 2D vdW heterojunctions at atomic scale is more sensitive to the nanointerface of the heterojunction than conventional bulk heterojunction. Here, a nanoengineered heterostructure for the first‐time demonstration of a nanointerface using an inserted graphene layer between black phosphorus (BP) and InSe which inhibits interlayer recombination and greatly improves photodetection performances is presented. In addition, a transition of the transport characteristics of the device is induced by graphene, from diffusion motion of minority carriers to drift motion of majority carriers. These two reasons together with an internal photoemission effect make the BP/G/InSe‐based photodetector have ultrahigh specific detectivity at room temperature. The results demonstrate that high‐performance vdW heterostructure photodetectors can be achieved through simple structural manipulation of the heterojunction interface on nanoscale., A nanoscale interface engineering in which few‐layer graphene (G) is inserted into the interlayer of black phosphorus (BP)/InSe, forming a 2D BP/G/InSe van der Waals heterojunction, is introduced. Effective electron transfer from BP to InSe is facilitated by the insertion of G, which induces a better photoresponse performance of the BP/G/InSe device.

Low-symmetry layered materials such as black phosphorus (BP) have been revived recently due to their high intrinsic mobility and in-plane anisotropic properties, which can be used in anisotropic electronic and optoelectronic devices. Since the anisotropic properties have a close relationship with their anisotropic structural characters, especially for materials with low-symmetry, exploring new low-symmetry layered materials and investigating their anisotropic properties have inspired numerous research efforts. In this paper, we review the recent experimental progresses on low-symmetry layered materials and their corresponding anisotropic electrical transport, magneto-transport, optoelectronic, thermoelectric, ferroelectric, and piezoelectric properties. The boom of new low-symmetry layered materials with high anisotropy could open up considerable possibilities for next-generation anisotropic multifunctional electronic devices.

The growth and wetting of water on two-dimensional(2D) materials are important to understand the development of 2D material based electronic, optoelectronic, and nanomechanical devices. Here, we visualize the liquefaction processes of water on the surface of graphene, MoS2 and black phosphorus (BP) via optical microscopy. We show that the shape of the water droplets forming on the surface of BP, which is anisotropic, is elliptical. In contrast, droplets are rounded when they form on the surface of graphene or MoS2, which do not possess orthometric anisotropy. Molecular simulations show that the anisotropic liquefaction process of water on the surface of BP is attributed to the different binding energies of H2O molecules on BP along the armchair and zigzag directions. The results not only reveal the anisotropic nature of water liquefaction on the BP surface but also provide a way for fast and nondestructive determination of the crystalline orientation of BP., Structural anisotropy of surfaces determines properties relevant for applications. Here the authors observe a relationship between the shape of water droplets forming on graphene, MoS2and black phosphorous and the surface structure, proposing a method to determine lattice orientation by optical microscopy.

Density functional theory calculations of the layer (L)-dependent electronic band structure, work function and optical properties of &beta, InSe have been reported. Owing to the quantum size effects (QSEs) in &beta, InSe, the band structures exhibit direct-to-indirect transitions from bulk &beta, InSe to few-layer &beta, InSe. The work functions decrease monotonically from 5.22 eV (1 L) to 5.0 eV (6 L) and then remain constant at 4.99 eV for 7 L and 8 L and drop down to 4.77 eV (bulk &beta, InSe). For optical properties, the imaginary part of the dielectric function has a strong dependence on the thickness variation. Layer control in two-dimensional layered materials provides an effective strategy to modulate the layer-dependent properties which have potential applications in the next-generation high performance electronic and optoelectronic devices.

Transition metal dichalcogenides (TMDCs), such as MoS2 and WS2, have attracted much attention in biosensing and bioimaging due to its excellent stability, biocompatibility, high specific surface area, and wide varieties. In this review, we overviewed the application of TMDCs in biosensing and bioimaging. Firstly, the synthesis methods and surface functionalization methods of TMDCs were summarized. Secondly, according to the working mechanism, we classified and gave a detailed account of the latest research progress of TMDC-based biosensing for the detection of the enzyme, DNA, and other biological molecules. Then, we outlined the recent progress of applying TMDCs in bio-imaging, including fluorescence, X-ray computed tomographic, magnetic response imaging, photographic and multimodal imaging, respectively. Finally, we discussed the future challenges and development direction of the application of TMDCs in medical diagnosis. Also, we put forward our view on the opportunity of TMDCs in the big data of modern medical diagnosis.

Efficiently tuning the output intensity of an optical device is of vital importance for the establishment of optical interconnects and networks. Thermo-optical modulation is an easily implemented and convenient approach and has been widely employed in photonic devices. In this paper, we proposed a novel thermo-optical modulator based on a microfiber knot resonator (MKR) and graphene heater. Upon applying voltage to graphene, the resonant property of the MKR could be thermally tuned with a maximum phase shift of 2.1π. Intensity modulation shows a fast optical response time thanks to the high thermal conductivity of graphene and the thin microfiber diameter of the MKR.

From the group-IIIA (borophene), to the group-IVA (silicene, germanene and stanine), as well as the group-VA (phosphorene, arsenene, antimonene and bismuthene) and even the group-VIA (selenene and tellurene nanosheets), these two-dimensional (2D) monoelemental materials are highly similar to graphene in lattice structure, and they can also be collectively referred to as Xenes. However, the unique specific atomic arrangement of these materials gives rise to a vast diversity of properties, and these single element 2D materials as graphene analogues are the most chemically tractable materials for synthetic exploration, thus attracting widespread attention and research. Intrinsic defects, as an defects inevitably introduced in the of experimental preparation, and extrinsic defects, as an artificially introduced and controllable way, both of them can effectively improve the environmental stability of single element materials and regulate the properties of Xenes. Herein, a review of the historical work about the properties and application of defective 2D monoelemental materials is presented. Based on the structure and properties of original single element 2D materials, the change of electronic and optoelectronic properties of these materials from different main groups under the action of different defects are classified and compared. In addition, the existing methods of realizing defects of 2D Xenes-based materials are summarized, and the application of the defects engineering in the field of optoelectronic devices, energy storage and conversion, catalysts as well are also comprehensively searched and reviewed. Finally, this review provides the prospect and challenge for the preparation and application of defective 2D monoelemental materials on the basis of the current research and development.

2D crystals are emerging new materials in multidisciplinary fields including condensed state physics, electronics, energy, environmental engineering, and biomedicine. To employ 2D crystals for practical applications, these nanoscale crystals need to be processed into macroscale materials, such as suspensions, fibers, films, and 3D macrostructures. Among these macromaterials, fibers are flexible, knittable, and easy to use, which can fully reflect the advantages of the structure and properties of 2D crystals. Therefore, the fabrication and application of 2D crystal-based fibers is of great importance for expanding the impact of 2D crystals. In this Review, 2D crystals that are successfully prepared are overviewed based on their composition of elements. Subsequently, methods for preparing 2D crystals, 2D crystals dispersions, and 2D crystal-based fibers are systematically introduced. Then, the applications of 2D crystal-based fibers, such as flexible electronic devices, high-efficiency catalysis, and adsorption, are also discussed. Finally, the status-of-quo, perspectives, and future challenges of 2D crystal-based fibers are summarized. This Review provides directions and guidelines for developing new 2D crystal-based fibers and exploring their potentials in the fields of smart wearable devices.