Jiuxiang Dai

The tape exfoliation method is still the easiest and most convenient way to obtain large-area two-dimensional (2D) monolayers in experimental research. Recently, there are some important advances in tape exfoliation method for large 2D monolayer materials. This review mainly introduced three kinds of new tape exfoliation methods including modified Scotch tape exfoliation method, metal-assisted tape exfoliation method and gel-assisted tape exfoliation method. We highlight the operation process and exfoliated mechanism of each method. We point out several problems to be solved and give an outlook on the development direction of the new tape exfoliation method. We hope this review will help researchers, especially for beginners, quickly and easily obtain a variety of 2D monolayers for their own experiments.

An energy-efficient memristive device based on 2D HfSe₂ oxides is fabricated, which is able to implement functionally complete Boolean logic with operation current down to 100 pA. The low-power switching is realized by the formation and rupture of cone-shaped O-vacancy filaments in the ultrathin Hf−Se−O layer.

Abstract

Memristive logic device is a promising unit for beyond von Neumann computing systems and 2D materials are widely used because of their controllable interfacial properties. Most of these 2D memristive devices, however, are made from semiconducting chalcogenides which fail to gate the off-state current. To this end, a crossbar device using 2D HfSe₂ is fabricated, and then the top layers are oxidized into “high-k” dielectric HfSe _x O _y via oxygen plasma treatment, so that the cell resistance can be remarkably increased. This two-terminal Ti/HfSe _x O _y /HfSe₂/Au device exhibits excellent forming-free resistive switching performance with high switching speed (<50 ns), low operation voltage (<3 V), large switching window (10³), and good data retention. Most importantly, the operation current and the power consumption reach 100 pA and 0.1 fJ to 0.1 pJ, much lower than other HfO based memristors. A functionally complete low-power Boolean logic is experimentally demonstrated using the memristive device, allowing it in the application of energy-efficient in-memory computing.

Metal–oxide-based phototransistors conventionally have a limit of detection range and persistent photocurrent (PPC) phenomenon, which may hinder their potential applications in devices. To solve the aforementioned problems, the latest approaches for the absorption layer are reviewed according to surface treatment, structural engineering, and the absorption materials. Furthermore, perspectives on emerging applications and outlooks are introduced.

Abstract

Metal oxide thin-film transistors have been continuously researched and mass-produced in the display industry. However, their phototransistors are still in their infancy. In particular, utilizing metal oxide semiconductors as phototransistors is difficult because of the limited light absorption wavelength range and persistent photocurrent (PPC) phenomenon. Numerous studies have attempted to improve the detectable light wavelength range and the PPC phenomenon. Here, recent studies on metal oxide phototransistors are reviewed, which have improved the range of light wavelengths and the PPC phenomenon by introducing an absorption layer of oxide or non-oxide hybrid structure. The materials of the absorption layer applied to absorb long-wavelength light are classified into oxides, chalcogenides, organic materials, perovskites, and nanodots. Finally, next-generation convergence studies combined with other research fields are introduced and future research directions are detailed.

The developments in the construction of 2D silicene/silicon nanosheets for versatile biomedical applications, including top-down fabrication, multifunctionalization, surface engineering and their available biomedical applications in tumor theranostics and antibacteria, are highlighted. A multi variate analysis on the facing challenges and future developments of these silicene/silicon nanosheets is conducted and an outlook for further clinical translations is given.

Abstract

Silicon-composed nanomedicines are one of the most representative inorganic nanosystems in theranostic biomedicine. The emerging of new family members of silicon-composed nanosystems substantially contributes to their further clinical translation. 2D silicene/silicon nanosheets have recently been developed as an emerging topology of silicon-composed nanoparticles, which features unique planar nanostructure with large surface area, abundant surface chemistry, specific physiochemical property, and desirable biological effects. This progress report highlights and discusses the state-of-art developments of the elaborate construction of 2D silicene/silicon nanosheets for versatile biomedical applications, including top–down fabrication, multifunctionalization, surface engineering, and their available biomedical applications in tumor theranostics (e.g., bioimaging, photothermal ablation, chemotherapy, chemoreactive nanotherapy, radiotherapy, and synergistic nanotherapy) and antibacteria. Their large surface area originating from 2D nanostructure not only enables efficient loading and delivery of chemotherapeutic drugs, but also guarantees the multifunctionalization. Especially, 2D silicene/silicon nanosheets harness desirable photothermal-conversion performance for photonic hyperthermia and photoacoustic imaging in the near infrared biowindow, accompanied with the desirable biodegradability and biocompatibility, which is typically not possessed in other silicon-composed counterparts. The multivariate analysis on the facing challenges and future developments of these 2D silicene/silicon nanosheets have also been conducted and outlooked for further underpinning their clinical translations.

The graphene-like 2D III-nitride semiconductor materials have unique physical properties such as high stability, wide and tunable bandgap, and magnetism, etc. Those advantages prove them to be useful in optoelectronic, electronic, and spin-based devices and so on. The pro perties, growth methods, and applications of graphene-like 2D III-nitride materials are introduced and reviewed.

Abstract

2D III-nitride materials have been receiving considerable attention recently due to their excellent physicochemical properties, such as high stability, wide and tunable bandgap, and magnetism. Therefore, 2D III-nitride materials can be applied in various fields, such as electronic and photoelectric devices, spin-based devices, and gas detectors. Although the developments of 2D h-BN materials have been successful, the fabrication of other 2D III-nitride materials, such as 2D h-AlN, h-GaN, and h-InN, are still far from satisfactory, which limits the practical applications of these materials. In this review, recent advances in the properties, growth methods, and potential applications of 2D III-nitride materials are summarized. The properties of the 2D III-nitride materials are mainly obtained by first-principles calculations because of the difficulties in the growth and characterizations of these materials. The discussion on the growth of 2D III-nitride materials is focused on 2D h-BN and h-AlN, as the developments of 2D h-GaN and h-InN are yet to be realized. Therefore, applications have been realized mostly based on the 2D h-BN materials; however, many potential applications are cited for the entire range of 2D III-nitride materials. Finally, future research directions and prospects in this field are also discussed.

Comprehensive understanding into complete reconstruction of precatalysts is summarized, mainly including its fundamental understandings, advantages, and features of completely reconstructed catalysts, design principles/strategies, extensive electrocatalysis applications, and advanced characterizations. This review is expected to arouse attention on the complete reconstruction materials for multifunctional applications in energy storage and conversion.

Abstract

Reconstruction induced by external environment (such as applied voltage bias and test electrolytes) changes catalyst component and catalytic behaviors. Investigations of complete reconstruction in energy conversion recently receive intensive attention, which promote the targeted design of top-performance materials with maximum component utilization and good stability. However, the advantages of complete reconstruction, its design strategies, and extensive applications have not achieved the profound understandings and summaries it deserves. Here, this review systematically summarizes several important advances in complete reconstruction for the first time, which includes 1) fundamental understandings of complete reconstruction, the characteristics and advantages of completely reconstructed catalysts, and their design principles, 2) types of reconstruction-involved precatalysts for oxygen evolution reaction catalysis in wide pH solution, and origins of limited reconstruction degree as well as design strategies/principles toward complete reconstruction, 3) complete reconstruction for novel material synthesis and other electrocatalysis fields, and 4) advanced in situ/operando or multiangle/level characterization techniques to capture the dynamic reconstruction processes and real catalytic contributors. Finally, the existing major challenges and unexplored/unsolved issues on studying the reconstruction chemistry are summarized, and an outlook for the further development of complete reconstruction is briefly proposed. This review will arouse the attention on complete reconstruction materials and their applications in diverse fields.

Nature Materials, Published online: 10 May 2021; doi:10.1038/s41563-021-01001-7

Centimetre-scale growth of few-layer black phosphorous with high crystalline quality and homogeneity is realized by pulsed laser deposition.

Author(s): Y. Shimura, A. Wörl, M. Sundermann, S. Tsuda, D. T. Adroja, A. Bhattacharyya, A. M. Strydom, A. D. Hillier, F. L. Pratt, A. Gloskovskii, A. Severing, T. Onimaru, P. Gegenwart, and T. Takabatake

CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of TK∼480  K. We report a negative in-plane thermal expansion α/T below...

[Phys. Rev. Lett. 126, 217202] Published Thu May 27, 2021

A photovoltaic self-powered gas sensor based on MoS₂/GaSe heterojunction is fabricated via mechanical exfoliation and all-dry transfer method. Under visible light illumination, large numbers of free carriers (electrons and holes) are produced and separated in the heterojunction, thus the MoS₂/GaSe heterojunction can achieve self-powered gas sensing toward ppb-level NO₂ at room temperature.

Abstract

Traditional gas sensors are facing the challenge of low power consumption for future application in smart phones and wireless sensor platforms. To solve this problem, self-powered gas sensors are rapidly developed in recent years. However, all reported self-powered gas sensors are suffering from high limit of detection (LOD) toward NO₂ gas. In this work, a photovoltaic self-powered NO₂ gas sensor based on n-MoS₂/p-GaSe heterojunction is successfully prepared by mechanical exfoliation and all-dry transfer method. Under 405 nm visible light illumination, the fabricated photovoltaic self-powered gas sensors show a significant response toward ppb-level NO₂ with short response and recovery time and high selectivity at room temperature (25 °C). It is worth mentioning that the LOD toward NO₂ of this device is 20 ppb, which is the lowest of the reported self-powered room-temperature gas sensors so far. The discussed devices can be used as building blocks to fabricate more functional Internet of things devices.

Two-dimensional (2D) semiconductors beyond graphene represent the thinnest stable known nanomaterials. Rapid growth of their family and applications during the last decade of the twenty-first century have brou...

Nickel chalcogenide (S and Se) based nanostructures are considered as promising materials for energy conversion and storage devices due to their good electrochemical stability, eco-friendly nature, and low cost. The present review highlights the recent progress on fine-tuning of structural and morphological properties of nickel-(S and Se) to achieve maximum possible performance for solar cells, batteries, supercapacitors, and hydrogen production.

Abstract

Nickel chalcogenide (S and Se) based nanostructures intrigued scientists for some time as materials for energy conversion and storage systems. Interest in these materials is due to their good electrochemical stability, eco-friendly nature, and low cost. The present review compiles recent progress in the area of nickel-(S and Se)-based materials by providing a comprehensive summary of their structural and chemical features and performance. Improving properties of the materials, such as electrical conductivity and surface characteristics (surface area and morphology), through strategies like nano-structuring and hybridization, are systematically discussed. The interaction of the materials with electrolytes, other electro-active materials, and inactive components are analyzed to understand their effects on the performance of energy conversion and storage devices. Finally, outstanding challenges and possible solutions are briefly presented with some perspectives toward the future development of these materials for energy-oriented devices with high performance.

Structural evolution induced by Mn alloying is comprehensively investigated in thermoelectric materials, selecting SnTe as a case study. Comprehensive electron microscopy investigations indicate that, through rational structural manipulation, multiscale crystal imperfections are introduced as phonon scattering sources and in turn renders a high thermoelectric performance.

Abstract

Mn alloying in thermoelectrics is a long-standing strategy for enhancing their figure-of-merit through optimizing electronic transport properties by band convergence, valley perturbation, or spin-orbital coupling. By contrast, mechanisms by which Mn contributes to suppressing thermal transports, namely thermal conductivity, is still ambiguous. A few precedent studies indicate that Mn introduces a series of hierarchical defects from the nano- to meso-scale, leading to effective phonon scattering scoping a wide frequency spectrum. Due to insufficient insights at the atomic level, the theory remains as phenomenological and cannot be used to quantitatively predict the thermal conductivity of Mn-alloyed thermoelectrics. Herein, by choosing the SnTe as a case study, aberration-corrected transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) to characterize the lattice complexity of Sn_{1.02− x} Mn _x Te is employed. Mn as a “dynamic” dopant that plays an important role in SnTe with respect to different alloying levels or post treatments is revealed. The results indicate that Mn precipitates at x = 0.08 prior to reaching solubility (≈10 mol%), and then splits into Mn_Sn substitution and γ-MnTe hetero-phases via mechanical alloying. Understanding such unique crystallography evolution, combined with a modified Debye-Callaway model, is critical in explaining the decreased thermal conductivity of Sn_{1.02− x} Mn _x Te with rational phonon scattering pathways, which should be applicable for other thermoelectric systems.

By virtue of the lowered thickness of a diamond film from micrometer to nanometer, properties like the optical transparency and flexibility are enhanced, rendering ultrathin diamond films promising candidates for optical devices, transparent electrodes, soft electronics, et al. This review is focused on applications relying on ultrathin diamond films, their excellent properties, difficulties of synthesis, and strategies of enhanced nucleation.

Abstract

Diamond is a highly attractive material for ample applications in material science, engineering, chemistry, and biology because of its favorable properties. The advent of conductive diamond coatings and the steady demand for miniaturization in a plethora of economic and scientific fields resulted in the impetus for interdisciplinary research to develop intricate deposition techniques for thin (≤1000 nm) and ultra-thin (≤100 nm) diamond films on non-diamond substrates. By virtue of the lowered thickness, diamond coatings feature high optical transparency in UV–IR range. Combined with their semi-conductivity and mechanical robustness, they are promising candidates for solar cells, optical devices, transparent electrodes, and photochemical applications. In this review, the difficulty of (ultra-thin) diamond film development and production, introduction of important stepping stones for thin diamond synthesis, and summarization of the main nucleation procedures for diamond film synthesis are elucidated. Thereafter, applications of thin diamond coatings are highlighted with a focus on applications relying on ultrathin diamond coatings, and the excellent properties of the diamond exploited in said applications are discussed, thus guiding the reader and enabling the reader to quickly get acquainted with the research field of ultrathin diamond coatings.

In article number 2002119, Mika Pettersson, Zhipei Sun, and co-workers demonstrate an optical modification process that simultaneously creates topographical structures and alters the optical properties of MoS₂ monolayer. This local and controllable optical modification method shows great promise for applications in electronics, photonics, and mechanics.

Constructing heterostructures is an effective way to enhance the electrochemical performance of active materials due to the unique heterointerface structure and some unrevealed synergistic effects. An overview of the recent advancements in heterostructured materials in terms of enhanced mechanism, synthesis techniques, and electrochemical performance is provided. Future development trends for design of heterostructured electrodes are analyzed.

Abstract

With the ever-increasing adaption of large-scale energy storage systems and electric devices, the energy storage capability of batteries and supercapacitors has faced increased demand and challenges. The electrodes of these devices have experienced radical change with the introduction of nano-scale materials. As new generation materials, heterostructure materials have attracted increasing attention due to their unique interfaces, robust architectures, and synergistic effects, and thus, the ability to enhance the energy/power outputs as well as the lifespan of batteries. In this review, the recent progress in heterostructure from energy storage fields is summarized. Specifically, the fundamental natures of heterostructures, including charge redistribution, built-in electric field, and associated energy storage mechanisms, are summarized and discussed in detail. Furthermore, various synthesis routes for heterostructures in energy storage fields are roundly reviewed, and their advantages and drawbacks are analyzed. The superiorities and current achievements of heterostructure materials in lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), lithium-sulfur batteries (Li-S batteries), supercapacitors, and other energy storage devices are discussed. Finally, the authors conclude with the current challenges and perspectives of the heterostructure materials for the fields of energy storage.

Two Xene heterostructures based on two well-established configurations, silicene-on-Ag(111) and stanene-on-Ag(111), are presented. Various in situ and ex situ analysis, along with theoretical studies, confirm that one Xene layer can act as a suitable template for the other reciprocal Xene layer. This demonstration of the Xene heterostructure opens a door to a new atomic-scale materials engineering.

Abstract

The synthesis of new Xenes and their potential applications prototypes have achieved significant milestones so far. However, to date the realization of Xene heterostructures in analogy with the well known van der Waals heterostructures remains an unresolved issue. Here, a Xene heterostructure concept based on the epitaxial combination of silicene and stanene on Ag(111) is introduced, and how one Xene layer enables another Xene layer of a different nature to grow on top is demonstrated. Single-phase (4 × 4) silicene is synthesized using stanene as a template, and stanene is grown on top of silicene on the other way around. In both heterostructures, in situ and ex situ probes confirm layer-by-layer growth without intercalations and intermixing. Modeling via density functional theory shows that the atomic layers in the heterostructures are strongly interacting, and hexagonal symmetry conservation in each individual layer is sequence selective. The results provide a substantial step toward currently missing Xene heterostructures and may inspire new paths for atomic-scale materials engineering.

A “beam-bridge” like metal oxide precursor feeding strategy is designed to realize the synthesis of large-area uniform, millimeter-size monolayer MoSe₂ single crystals on a 6-centimeter-long soda-lime glass template via chemical vapor deposition. Several tenths of millimeter-scale, triangular-shaped monolayer MoSe₂ single crystals are obtained in one batch within 25 s’ growth, affording so far the fastest growth rate (≈50 µm s⁻¹).

Abstract

2D semiconducting transition metal dichalcogenides (TMDCs) have emerged as essential building blocks for engineering next-generation integrated electronics. To achieve this, the controllable synthesis of monolayer TMDCs with high crystal quality, low cost, and high yield is crucial, while it remains challenging. Herein, the direct synthesis of large-area uniform, millimeter-size monolayer MoSe₂ single crystals on a 6-centimeter-long soda-lime glass template, by using a designed “beam-bridge” assisted metal oxide precursor feeding strategy via chemical vapor deposition (CVD), is reported. Notably, several tenths of millimeter-scale, triangular-shaped monolayer MoSe₂ single crystals are obtained in one batch within 25 s’ growth, affording so far the fastest growth rate (≈50 µm s⁻¹). This ultrafast growth behavior is proposed to be mediated by the sufficient, homogeneous release of Mo-based precursor, the catalytic property of sodium atoms on soda-lime glass substrate, as well as the improved surface kinetics on the molten glass surface. Moreover, the thickness-controlled growth from monolayer to bilayers is also realized. This work provides brand new insights for the batch production of large single-crystal TMDCs, which should propel its practical applications in versatile fields.

We propose a design strategy to achieve van-der-Waals (vdW) deep-ultraviolet (DUV) nonlinear-optical (NLO) materials. Berborite Be₂BO₅H₃ with trigonal (BO₃)-(BeO₄H) layers and beryllium metaborate BeB₂O₄ with tetragonal (BO₄)-(BeO₄) layers are predicted as two promising vdW DUV NLO crystal candidates, exhibiting a good DUV NLO performance balance with ultrawide optical band gaps, strong NLO effects, and sufficiently large birefringence.

Abstract

Van-der-Waals (vdW) deep-ultraviolet (DUV) nonlinear-optical (NLO) materials hold great potential to extend DUV NLO applications to two dimensions, but they are rare in nature. In this study, we propose a design principle to realize vdW DUV NLO materials via structural evolution from the non-vdW (BO₃)-(BeO₃F) layers in KBe₂BO₃F₂ (KBBF) to the vdW (BO₃)-(BeO₄H) layers in berborite Be₂BO₅H₃ (BBH) and the vdW (BO₄)-(BeO₄) layers in beryllium metaborate BeB₂O₄ (BEBO). Based on first-principles calculations, the fundamental NLO properties of BBH and BEBO demonstrate that a balanced DUV NLO performance can be achieved in these two systems. Importantly, BBH, a layered material existing in nature, can achieve an available DUV phase-matched output with strong second harmonic generation (SHG) for 177.3/193.7 nm DUV lasers, which is almost identical to that of KBBF. Remarkably, BEBO shows an excellent DUV SHG capacity and an even shorter phase-matching wavelength than KBBF. Therefore, the newly discovered vdW BBH and BEBO, once verified by experiments, could provide an ideal platform to study DUV NLO effects in three dimensions and two dimensions.

Through encapsulation technique with atomic layer deposition-Al₂O₃, the film quality and device performance of chemical vapor deposition (CVD)-grown MoS₂ are significantly improved, yielding a mobility improvement by one order of magnitude, reaching up to 62.5 cm² Vs⁻¹, the corresponding phototransistors exhibit a responsivity of 10⁴ A W⁻¹ and a detectivity of 10¹² Jones.

Abstract

MoS₂ as a semiconducting 2D material has been a promising candidate for the next generation of optoelectronics due to its atomic thickness, mechanical flexibility, complementary metal-oxide-semiconductor compatibility, and large-scale manufacturing. However, the poor quality such as low mobility and numerous defects has much affected the corresponding device performances, which has limited their wide applications. Here, an effective strategy is proposed to significantly improve the quality of the chemical vapor deposition (CVD)-grown monolayer MoS₂ by the encapsulation technique with atomic layer deposition Al₂O₃. Benefiting from the passivation of defects and suppression of charge Coulomb scattering, the mobility can be improved by more than one order of magnitude, reaching up to 62.5 cm² Vs⁻¹. As a result, the photodetection performances in terms of response time, responsivity, and detectivity are also improved up to 20 ms, 1.1 × 10⁴ A W⁻¹, and 3.1 × 10¹² Jones, respectively. The developed encapsulation technique here for the improvement of film quality and device performance can further enable the practical application of large-scale 2D materials-based electronics and photodetectors.