Kind Of 2D Materials Research Articles

Hydrogen Bond Network Shaping Proton Penetration Behavior across Two-Dimensional Nanoporous Materials.

In this study, we investigate aqueous proton penetration behavior across four types of two-dimensional (2D) nanoporous materials with similar pore sizes using extensive ReaxFF molecular dynamics simulations. The results reveal significant differences in proton penetration energy barriers among the four kinds of 2D materials, despite their comparable pore sizes. Our analysis indicates that these variations in energy barriers stem from differences in the hydrogen bond (HB) network formed between the 2D nanoporous materials and the aqueous environment. The HB network can be classified into two categories: those formed between the surface of the 2D nanoporous materials and the aqueous environment, and those formed between the edge atoms of the nanopores and the water molecules inside the pores. A strong HB network formed between the surface of the 2D nanoporous materials and the aqueous environment induces an orientational preference of water molecules, resulting in an aggregated water layer with high density. This high-density water region traps protons, making it difficult for them to escape and penetrate the nanopores. On the other hand, a strong HB network formed between the edge atoms of the nanopores and the water molecules inside the pores impedes the rotation and migration of water molecules, further inhibiting proton penetration behavior. To facilitate the proton penetration process, in addition to a sufficiently large pore size, a weak HB network between the 2D nanoporous material and the aqueous environment is necessary.

Development of MXene-based flexible piezoresistive sensors

Abstract The flexibility and sensitivity of traditional sensors is hard to achieve unless wearable technology develops. Flexible piezoresistive sensor (FPS) is one of the solutions in the nondestructive health monitoring of living body. In the application of sensing devices for physiological or biochemical signals, fast feedback speed and accurate signal feedback are essential requirements for obtaining sensitive response signals. Additionally, the development of FPS has promoted the research of conductive materials that could be used in wearable devices. However, improving the performance of functional materials is an important way of effort for researchers. Recently, MXene as a new kind of 2D materials and their composites have made a tremendous impact in the field of sensors for wearable health sensors. Numerous conductive materials based 2D MXene could expedite their practical application in FPS by overcoming the present limitations of FPS such as poor responsivity, signal accuracy, and the narrower corresponding range. There has been plenty of breakthrough in the MXene-based FPS in the past several years. The main purpose of this paper is reviewing the recent development of MXene-based FPS and providing an outlook on the future development of it.

Two Dimensional Heterostructures for Optoelectronics: Current Status and Future Perspective.

Researchers have found various families of two-dimensional (2D) materials and associated heterostructures through detailed theoretical work and experimental efforts. Such primitive studies provide a framework to investigate novel physical/chemical characteristics and technological aspects from micro to nano and pico scale. Two-dimensional van der Waals (vdW) materials and their heterostructures can be obtained to enable high-frequency broadband through a sophisticated combination of stacking order, orientation, and interlayer interactions. These heterostructures have been the focus of much recent research due to their potential applications in optoelectronics. Growing the layers of one kind of 2D material over the other, controlling absorption spectra via external bias, and external doping proposes an additional degree of freedom to modulate the properties of such materials. This mini review focuses on current state-of-the-art material design, manufacturing techniques, and strategies to design novel heterostructures. In addition to a discussion of fabrication techniques, it includes a comprehensive analysis of the electrical and optical properties of vdW heterostructures (vdWHs), particularly emphasizing the energy-band alignment. In the following sections, we discuss specific optoelectronic devices, such as light-emitting diodes (LEDs), photovoltaics, acoustic cavities, and biomedical photodetectors. Furthermore, this also includes a discussion of four different 2D-based photodetector configurations according to their stacking order. Moreover, we discuss the challenges that remain to be addressed in order to realize the full potential of these materials for optoelectronics applications. Finally, as future perspectives, we present some key directions and express our subjective assessment of upcoming trends in the field.

Highly efficient visible-light-driven photocatalytic disinfection of flowing bioaerosol using mono/multilayer MXene based catalyst

In this study, two kinds of 2D materials (nanoscale mono/multi-layer MXene) were prepared, and a new visible-light-driven photocatalyst MXene@In2S3 was synthesized by one-step hydrothermal preparation. Due to the better conductivity and larger specific surface area of the monolayer MXene, monolayer MXene@In2S3 exhibited greater transient response photocurrent and smaller interfacial charge transfer resistance than those of multilayer MXene@In2S3 under visible light irradiation. All these indicated that the synergistic effect of type-II heterojunction and TiO2/Ti3C2Tx interface provided a shorter and more direct channel for electron transfer between In2S3, TiO2 and MXene. When bioaerosol was sterilized by dynamic continuous flow photocatalytic reactor carrying monolayer MXene@In2S3, it can reach 1.55 lg in 9.6 s (multilayer MXene@In2S3 was 1.19 lg). Biological particles of different particle sizes were effectively removed from the bioaerosol. The excellent photocatalytic disinfection performance was due to the oxidation substances (holes, ·O2– and ·OH) produced by the photocatalyst under visible light irradiation. Microbial cell membrane permeability was disrupted, causing irreversible physical damage that will ultimately lead to sustained inactivation within 16 h. Due to the unique physical and chemical properties of the two-dimensional material MXene, it has scope for further exploration in the field of disinfection and air purification.

Graphene Oxide for Nonlinear Integrated Photonics

AbstractIntegrated photonic devices operating via optical nonlinearities offer a powerful solution for all‐optical information processing, yielding processing speeds that are well beyond that of electronic processing as well as providing the added benefits of compact footprint, high stability, high scalability, and small power consumption. The increasing demand for high‐performance nonlinear integrated photonic devices has facilitated the hybrid integration of novel materials to address the limitations of existing integrated photonic platforms. Recently, graphene oxide (GO), with its large optical nonlinearity, high flexibility in altering its properties, and facile fabrication processes, has attracted significant attention, enabling many hybrid nonlinear integrated photonic devices with improved performance and novel capabilities. This paper reviews the applications of GO to nonlinear integrated photonics. First, an overview of GO's optical properties and the fabrication technologies needed for its on‐chip integration is provided. Next, the state‐of‐the‐art GO nonlinear integrated photonic devices are reviewed, followed by comparisons of the nonlinear optical performance of different integrated platforms incorporating GO as well as hybrid integrated devices including different kinds of 2D materials. Finally, the current challenges and future opportunities in this field are discussed.

Vertical WSe2/BP/MoS2 heterostructures with tunneling behaviors and photodetection

Van der Waals heterostructures show potential in electronic and optoelectronic devices. However, most heterostructures were formed based on the combination of two kinds two-dimensional (2D) materials. It is interesting to investigate the heterostructures of three kinds of 2D materials with unique band structure for photodetection and tunneling. In this work, vertical stacked WSe2/black phosphorus (BP)/MoS2 heterostructure has been made. By tuning the middle layer BP thickness from thin to thick, the device can be regarded as tunneling transistor and photodetector. Throughout thin BP (9 nm) sandwiched, tunneling transistor is realized in WSe2/BP/MoS2 heterojunction with a high ∼μA level tunneling current. Temperature dependent electrical characteristics proved tunneling mechanism. Throughout thicker BP (20–30 nm) flake sandwiched, high-performance photodetector can be achieved. The large bandgap of WSe2 and MoS2 can further reduce the dark current to ∼10 pA level at 3.0 V drain–source bias. Moreover, the unique band alignment facilitates the photo-electrons flow and blocked photo-holes in the BP channel. The photoresponsivity can reach 1.43 A/W at near infrared light with λ = 1342 nm. Our work suggests an effective scheme to design high performance electronic and optoelectronic devices assembled by 2D materials.

A study on surface plasmon resonance biosensor for the detection of CEA biomarker using 2D materials graphene, Mxene and MoS2

In this work, A surface plasmon resonance (SPR) biosensor is designed for the selective detection of carcinoembryonic antigen (CEA) present in the sensing medium (PBS solution) using three kinds of 2D materials i.e. graphene, molybdenum disulfide (MoS2) and mxene. Initially we introduce a basic design of Ti-Ag-Graphene based SPR biosensor for detection of CEA. After that, include the mxene and MoS2 layer between silver and graphene layer in basic Ti-Ag-Graphene structure separately for performance enhancement and also for comparative analysis. Over the graphene layer, bovine serum albumin (BSA) is deposited for the selective attachment of CEA biomarkers present in PBS solution in all structures. We find that the performance parameters are improved by the introduction of MoS2 and mxene as sandwiched between silver and graphene layers. The proposed design shows maximum sensitivity 144.72 deg./RIU and detection accuracy 2.24 for MoS2-Graphene based structure, which is better than other reported works. A comparative study shows that the MoS2-Graphene combination shows better performance as compared to Mxene-Graphene combination. This study may prove their importance to enhancement in sensitivity of SPR biosensors by using these 2D materials.

Artificial Neuron Networks Enabled Identification and Characterizations of 2D Materials and van der Waals Heterostructures.

Two-dimensional (2D) materials and their in-plane and out-of-plane (i.e., van der Waals, vdW) heterostructures are promising building blocks for next-generation electronic and optoelectronic devices. Since the performance of the devices is strongly dependent on the crystalline quality of the materials and the interface characteristics of the heterostructures, a fast and nondestructive method for distinguishing and characterizing various 2D building blocks is desirable to promote the device integrations. In this work, based on the color space information on 2D materials' optical microscopy images, an artificial neural network-based deep learning algorithm is developed and applied to identify eight kinds of 2D materials with accuracy well above 90% and a mean value of 96%. More importantly, this data-driven method enables two interesting functionalities: (1) resolving the interface distribution of chemical vapor deposition (CVD) grown in-plane and vdW heterostructures and (2) identifying defect concentrations of CVD-grown 2D semiconductors. The two functionalities can be utilized to quickly identify sample quality and optimize synthesis parameters in the future. Our work improves the characterization efficiency of atomically thin materials and is therefore valuable for their research and applications.

First‐Principles Study of the Electronic and Optical Properties of Bi2Se3/MoSe2 Heterojunction

MoSe2 and Bi2Se3 are two kinds of 2D materials that are gradually receiving more attention because of their unique electronic and optical properties. Herein, a Bi2Se3/MoSe2 van der Waals heterojunction (vdWH) is constructed and the electronic and optical properties of the heterojunction are calculated using first‐principles calculations. The effects of the external electric field and the interlayer distance on the electronic properties of the heterojunction are also studied. The calculated results show that the inherent Bi2Se3/MoSe2 vdWH has a type‐2 band alignment with a very small indirect bandgap (28 meV). It also has strong spin–orbit coupling effects, and the characteristics of Zeeman splitting and Rashba splitting are observed at the same time. Both applying an external electric field and changing the interlayer distance can effectively modulate the band structure of the heterojunction; these modulation methods can change the band alignment of the vdWH from type‐2 to type‐3 or even type‐1, and the bandgap type can be changed from indirect to direct. The infrared absorption of the heterojunction is much higher than that of Bi2Se3 and MoSe2. All the calculation results show that the Bi2Se3/MoSe2 vdWH has good application prospects in optoelectronic and spintronic devices.

Growth of two-dimensional material black phosphorus guided by gold substrates and its growth mechanism

<p indent=0mm>Two-dimensional (2D) materials are the frontier research direction of material sciences and condensed matter physics in recent years. Among different kinds of 2D materials, black phosphorus (BP) has received extensive attention due to its unique band gap and excellent optical and electrical anisotropy properties. Compared with graphene and transition metal dichalchogenides (TMDCs), BP stands out for its unique properties with widely tunable direct bandgaps ranging from <sc>0.3–1.7 eV,</sc> covering the wavelength from ~600 to <sc>4000 nm,</sc> which fill in the gap between graphene <sc>(0 eV)</sc> and TMDCs (~1.0–2.5 eV) and is considered the ideal material for optoelectronic applications, such as light detection and light modulation. For example, photodetectors are basic devices for optoelectronics, as they transform the information stored in light into electric signals. BP based photodetectors not only stand out for their wide detection range reaching far infrared (IR) region, but also for their high responsivity and high gain, demonstrating their excellent performance for mid-IR detection. In order to achieve above-mentioned applications, few or even monolayer BP flakes or continuous BP films are required. However, how to control the preparation of thin layer of BP is one of the biggest challenges in this field. In this paper, we carried out a systematic study on the growth of BP on different substrates and found that Au can guide and promote the growth of BP, thereby controlling its growth. Based on the above findings, the growth of BP nanosheets on the Au-Si substrate is achieved by using a Si substrate deposited with Au thin film on top, and by designing a strategy with gradient temperature and in confined space. We observed that the BP nanosheets grown by this system exhibited different shapes such as ribbons and flakes, and their thicknesses can be reduced to be about <sc>51 nm</sc> with a lateral size of around <sc>10 µm.</sc> In addition, by systematically tuning the growth parameters in the system, we found that the growth temperatures and the amount of red phosphorous loading are the key parameters for the growth of BP. With certain temperatures and precursor loadings, we achieve the growth of BP nanosheets, while by-products would be obtained on the substrate with other parameters. In our previous work, we found that the temperature gradients play a crucial role in the yield, purity, and crystal quality of bulk BP growth. Therefore, further optimization of temperature distribution is of great importance for the growth of BP nanosheets. In addition, we observed in this paper that Au would guide the nucleation and growth of BP. Therefore, it is important to regulate Au-P compounds during growth of BP, as on the one hand, it can control the by-products during the reaction and on the other hand, it can also improve the controllability of BP nucleation. Based on this, we believe that optimization of the temperature distribution and the growth regulation of Au-P compounds are important research directions, as to precisely control and reduce the thickness of BP nanosheets to grow few layer BP. The growth system proposed in this paper improves the chemical vapor transport (CVT) growth of traditional bulk BP from three aspects: Substrate design, confined space design, and temperature gradient control, which have paved the way for the future controllability growth of BP nanosheets and have deepened the understanding of BP growth mechanism.

Recent advances in anisotropic two-dimensional materials and device applications

Two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), black phosphorus (BP), MXene and borophene, have aroused extensive attention since the discovery of graphene in 2004. They have wide range of applications in many research fields, such as optoelectronic devices, energy storage, catalysis, owing to their striking physical and chemical properties. Among them, anisotropic 2D material is one kind of 2D materials that possess different properties along different directions caused by the intrinsic anisotropic atoms’ arrangement of the 2D materials, mainly including BP, borophene, low-symmetry TMDs (ReSe2 and ReS2) and group IV monochalcogenides (SnS, SnSe, GeS, and GeSe). Recently, a series of new devices has been fabricated based on these anisotropic 2D materials. In this review, we start from a brief introduction of the classifications, crystal structures, preparation techniques, stability, as well as the strategy to discriminate the anisotropic characteristics of 2D materials. Then, the recent advanced applications including electronic devices, optoelectronic devices, thermoelectric devices and nanomechanical devices based on the anisotropic 2D materials both in experiment and theory have been summarized. Finally, the current challenges and prospects in device designs, integration, mechanical analysis, and micro-/nano-fabrication techniques related to anisotropic 2D materials have been discussed. This review is aimed to give a generalized knowledge of anisotropic 2D materials and their current devices applications, and thus inspiring the exploration and development of other kinds of new anisotropic 2D materials and various novel device applications.

Sensitivity Enhancement of a Surface Plasmon Resonance Sensor with Platinum Diselenide.

The extraordinary optoelectronic properties of platinum diselenide (PtSe2), whose structure is similar to graphene and phosphorene, has attracted great attention in new rapidly developed two-dimensional (2D) materials beyond the other 2D material family members. We have investigated the surface plasmon resonance (SPR) sensors through PtSe2 with the transfer matrix method. The simulation results show that the anticipated PtSe2 biochemical sensors have the ability to detect analytic. It is evident that only the sensitivities of Ag or Au film biochemical sensors were observed at 118°/RIU (refractive index unit) and 130°/RIU, whereas the sensitivities of the PtSe2-based biochemical sensors reached as high as 162°/RIU (Ag film) and 165°/RIU (Au film). The diverse biosensor sensitivities with PtSe2 suggest that this kind of 2D material can adapt SPR sensor properties.

Structural, electronic, and electromechanical properties of MoSSe/blue phosphorene heterobilayer

Two-dimensional (2D) materials attract considerable interest due to their outstanding electronic and mechanical properties. Although extensive efforts have been made on seeking of new kinds of 2D materials, individual ones can hardly offer all required properties for practical applications in nanoelectronics and optoelectronics. To integrate the advantages of each individual component, in this work, we predict the structural and electromechanical properties of 2D van der Waals (vdW) heterobilayers constructed with single-layer Janus transition metal dichalcogenides and blue phosphorus (e.g., SMoSe/BlueP and SeMoS/BlueP) by means of density-functional theory (DFT) based calculations. The vdW interactions were carefully taken into account by employing the DFT-DF correction functional. It is found that the proposed vdW heterobilayers are dynamically stable with enhanced elastic moduli. The SeMoS/BlueP heterobilayer is shown as a type-I semiconductor with an indirect bandgap of 1.55 eV, and SMoSe/BlueP is also a type-I semiconductor with a slightly larger indirect bandgap of 1.76 eV. In addition, the piezoelectronic response of the heterobilayers was also carefully explored. In particular, the out-of-plane piezoelectric response of SeMoS/BlueP that is characterized by the piezoelectric coefficient e311(d311) gets enhanced compared to the Janus MoSSe monolayer. Our findings demonstrate a great potential for their applications in energy harvesting and sensors at the nanoscale.

Van der Waals Epitaxy of III-Nitride Semiconductors Based on 2D Materials for Flexible Applications.

III-nitride semiconductors have attracted considerable attention in recent years owing to their excellent physical properties and wide applications in solid-state lighting, flat-panel displays, and solar energy and power electronics. Generally, GaN-based devices are heteroepitaxially grown on c-plane sapphire, Si (111), or 6H-SiC substrates. However, it is very difficult to release the GaN-based films from such single-crystalline substrates and transfer them onto other foreign substrates. Consequently, it is difficult to meet the ever-increasing demand for wearable and foldable applications. On the other hand, sp2 -bonded two-dimensional (2D) materials, which exhibit hexagonal in-plane lattice arrangements and weakly bonded layers, can be transferred onto flexible substrates with ease. Hence, flexible III-nitride devices can be implemented through such 2D release layers. In this progress report, the recent advances in the different strategies for the growth of III-nitrides based on 2D materials are reviewed, with a focus on van der Waals epitaxy and transfer printing. Various attempts are presented and discussed herein, including the different kinds of 2D materials (graphene, hexagonal boron nitride, and transition metal dichalcogenides) used as release layers. Finally, current challenges and future perspectives regarding the development of flexible III-nitride devices are discussed.

Rolling up MoSe2 Nanomembranes as a Sensitive Tubular Photodetector.

Transition metal dichalcogenides, as a kind of 2D material, are suitable for near-infrared to visible photodetection owing to the bandgaps ranging from 1.0 to 2.0 eV. However, limited light absorption restricts photoresponsivity due to the ultrathin thickness of 2D materials. 3D tubular structures offer a solution to solve the problem because of the light trapping effect which can enhance optical absorption. In this work, thanks to mechanical flexibility of 2D materials, self-rolled-up technology is applied to build up a 3D tubular structure and a tubular photodetector is realized based on the rolled-up molybdenum diselenide microtube. The tubular device is shown to present one order higher photosensitivity compared with planar counterparts. Enhanced optical absorption arising from the multiple reflections inside the tube is the main reason for the increased photocurrent. This tubular device offers a new design for increasing the efficiency of transition metal dichalcogenide-based photodetection and could hold great potential in the field of 3D optoelectronics.

PMMA-BN composites incorporated with Au nanoparticle fabricated by laser ablation

As a class of layered materials, two dimensional (2D) materials have attracted great attention all around the world due to their inherent use for next generation nano technology devices. We can see 2D materials including carbon in our daily life and at many places, for instance, graphite, diamond and so on. New study is also being conducted to produce new functional materials by combining 2D material and polymer. Hexagonal boron nitride (h-BN) which is one kind of 2D material is dispersed in Poly methyl methacrylate (PMMA) or poly styrene (PS). The composite material of h-BN coated with polymer shows an improvement in the properties such as the higher thermal conductivity and higher mechanical strength. In this study, the composite material of PMMA, h-BN and gold nanoparticles has been synthesized. Boron nitride nano-structures were prepared by nanosecond laser ablation in acetone and was carried out at room temperature with laser ablation time of 120 min. The PMMA films were made by PMMA granules dissolved in acetone solvent and then mix with h-BN and gold colloid solution. The prepared composite films were characterized by scanning electron microscopy (SEM), and UV-vis spectroscopy. Such type of unique 2D nano-composite materials make their mark for the future exploitation in electronics and nanocomposite-related applications.

A review of graphene-based 3D van der Waals hybrids and their energy applications

Abstract Different kinds of 2D materials can be well hybridized by constructing van der Waals heterostructures of them. Among various kinds of 2D materials, graphene has caught the most attention attributed to its superior electronic and mechanical features. To fully maintain and demonstrate their intrinsic features, 3D nanostructured graphene materials are proposed and can be realized by the in-situ curving of graphene layers or the post-assembly of graphene nanosheets. Furthermore, by the integration of 3D graphene framework and other 2D materials, graphene-based 3D van der Waals hybrids can be obtained with superior performances and promising applications in various energy fields. In this review, recent advances on graphene-based 3D van der Waals hybrids for energy applications were summarized, highlighting the hybrids between graphene and transition-metal dichalcogenides, other transition metal compounds, metal-free 2D materials, and multiple 2D materials. We hope this review can inspire more innovative insights into this emerging topic in energy materials.

Wearable and Implantable Soft Bioelectronics Using Two-Dimensional Materials.

Soft bioelectronics intended for application to wearable and implantable biomedical devices have attracted great attention from material scientists, device engineers, and clinicians because of their extremely soft mechanical properties that match with a variety of human organs and tissues, including the brain, heart, skin, eye, muscles, and neurons, as well as their wide diversity in device designs and biomedical functions that can be finely tuned for each specific case of applications. These unique features of the soft bioelectronics have allowed minimal mechanical and biological damage to organs and tissues integrated with bioelectronic devices and reduced side effects including inflammation, skin irritation, and immune responses even after long-term biointegration. These favorable properties for biointegration have enabled long-term monitoring of key biomedical indicators with high signal-to-noise ratio, reliable diagnosis of the patient's health status, and in situ feedback therapy with high treatment efficacy optimized for the requirements of each specific disease model. These advantageous device functions and performances could be maximized by adopting novel high-quality soft nanomaterials, particularly ultrathin two-dimensional (2D) materials, for soft bioelectronics. Two-dimensional materials are emerging material candidates for the channels and electrodes in electronic devices (semiconductors and conductors, respectively). They can also be applied to various biosensors and therapeutic actuators in soft bioelectronics. The ultrathin vertically layered nanostructure, whose layer number can be controlled in the synthesis step, and the horizontally continuous planar molecular structure, which can be found over a large area, have conferred unique mechanical, electrical, and optical properties upon the 2D materials. The atomically thin nanostructure allows mechanical softness and flexibility and high optical transparency of the device, while the large-area continuous thin film structure allows efficient carrier transport within the 2D plane. In addition, the quantum confinement effect in the atomically thin 2D layers introduces interesting optoelectronic properties and superb photodetecting capabilities. When fabricated as soft bioelectronic devices, these interesting and useful material features of the 2D materials enable unconventional device functions in biological and optical sensing, as well as superb performance in electrical and biochemical therapeutic actuations. In this Account, we first summarize the distinctive characteristics of the 2D materials in terms of the mechanical, optical, chemical, electrical, and biomedical aspects and then present application examples of the 2D materials to soft bioelectronic devices based on each aforementioned unique material properties. Among various kinds of 2D materials, we particularly focus on graphene and MoS2. The advantageous material features of graphene and MoS2 include ultrathin thickness, facile functionalization, large surface-to-volume ratio, biocompatibility, superior photoabsorption, and high transparency, which allow the development of high-performance multifunctional soft bioelectronics, such as a wearable glucose patch, a highly sensitive humidity sensor, an ultrathin tactile sensor, a soft neural probe, a soft retinal prosthesis, a smart endoscope, and a cell culture platform. A brief comparison of their characteristics and performances is also provided. Finally, this Account concludes with a future outlook on next-generation soft bioelectronics based on 2D materials.

Transforming Monolayer Transition-Metal Dichalcogenide Nanosheets into One-Dimensional Nanoscrolls with High Photosensitivity.

One-dimensional (1D) nanoscrolls derived from two-dimensional (2D) nanosheets own unusual physical and chemical properties that arise from the spiraled 1D morphology and the atomic thin 2D building blocks. Unfortunately, preparation of large-sized nanoscrolls of transition-metal dichalcogenides (TMDCs) remains a big challenge, which greatly restricts the fabrication of single-scroll devices for their fundamental studies and further applications. In this work, we report a universal and facile method, by making use of the evaporation process of volatile organic solvent, to prepare TMDC (e.g., MoS2 and WS2) nanoscrolls with lengths of several tens to one hundred micrometers from their 2D precursors presynthesized by chemical vapor deposition on Si/SiO2. Both atomic force microscopy and electron microscopy characterizations confirmed the spirally rolledup structure in the resulting nanoscrolls. An interlayer spacing of as small as ∼0.65 nm was observed, suggesting the strong coupling between adjacent layers, which was further evidenced by the emergence of new breathing mode peaks in the ultralow frequency Raman spectrum. Importantly, compared with the photodetector fabricated from a monolayer MoS2 or WS2 nanosheet, the device based on an MoS2 or WS2 nanoscroll showed the much enhanced performance, respectively, with the photosensitivity greatly increased up to 2 orders of magnitude. Our work suggests that turning 2D TMDCs into 1D scrolls is promising in achieving high performances in various electronic/optoelectronic applications, and our general method can be extended to the preparation of large-sized nanoscrolls of other kinds of 2D materials that may bring about new properties and phenomena.

Few-Layered Black Phosphorus: From Fabrication and Customization to Biomedical Applications.

As a new kind of 2D material, black phosphorus has gained increased attention in the past three years. Although few-layered black phosphorus nanosheets (BPs) degrade quickly under ambient conditions to phosphate anions, which greatly hampers their optical and electronic applications, this property also makes BPs highly biocompatible and biodegradable, and is regarded as an advantage for various biomedical applications. This Concept summarizes the state-of-art progresses of BPs, from fabrication and surface modification to biomedical applications. It is expected that BPs with such fascinating properties will encourage more scientists to engage in expanding its biomedical applications by tackling the scientific challenges involved in their development.