Jiuxiang Dai

Local strain magnitude and in-plane distribution of CVD-grown MoS₂ largely determine its oxidative etching effects and dependently control over the unique morphologies of the resulted etching patterns.

Abstract

This study reveals a local strain-dependent etching behavior that enables the formation of distinguished etching patterns in differently strained chemical vapor deposited (CVD) 2D molybdenum disulfide (MoS₂) monolayers. It is demonstrated that when the local tensile strain of CVD 2D MoS₂ is as uniformly low as ɛ ≈ 0.33% or less, the oxidative etching pattern possesses conventional triangular etching pits (TEPs), while when the local tensile strain is as uniformly high as ɛ ≈ 0.55% or larger, the oxidative etching pattern consist of uniformly oriented hexagonal etching channels (HECs). More interestingly, when the CVD 2D MoS₂ monolayer has heterogenous strain distribution from ɛ ≈ 0.55% (center region) to ɛ ≈ 0.33% (perimeter region), the oxidative etching pattern comprise of non-uniformly hexagonal-mixed-parallel etching channels (HPECs). The further characterization and analysis reveal the formation mechanism of such strain-dependent etching patterns is built on the local strain-related fractures propagation under oxidative etching, as well as the anisotropy fractures-based oxidative etching kinetics. This study may enhance the understanding of the relationship between etching and growth features of 2D TMDs, and paves the way to etching-nanostructured (or defect) engineering of 2D TMDs and other 2D materials for potential applications in electrocatalysis and optoelectronics.

Several high-quality single-crystalline transition metal dichalcogenides are directly grown on an epitaxial h-BN/sapphire substrate via vdW epitaxy, indicating the h-BN is an ideal template for vdW epitaxy. The full width at half maximum of the X-ray diffraction rocking curve for the HfSe₂ layers on single-crystal h-BN is only 9.6 arcmin, indicating an extremely high degree of out-plane orientation and high crystallinity.

Abstract

Van der Waals (vdW) heterostructures comprising of transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN) are promising building blocks for novel 2D devices. The vdW epitaxy provides a straightforward integration method for fabricating high-quality TMDs/h-BN vertical heterostructures. In this work, the vdW epitaxy of high-quality single-crystal HfSe₂ on epitaxial h-BN/sapphire substrates by chemical vapor deposition is demonstrated. The epitaxial HfSe₂ layers exhibit a uniform and atomically sharp interface with the underlying h-BN template, and the epitaxial relationship between HfSe₂ and h-BN/sapphire is determined to HfSe₂ (0001)[12¯${\mathrm{\bar{2}}}$10]//h-BN (0001)[11¯${\mathrm{\bar{1}}}$00]//sapphire (0001)[11¯${\mathrm{\bar{1}}}$00]. Impressively, the full width at half maximum of the rocking curve for the epitaxial HfSe₂ layer on single-crystal h-BN is as narrow as 9.6 arcmin, indicating an extremely high degree of out-plane orientation and high crystallinity. Benefitting from the high crystalline quality of HfSe₂ epilayers and the weak interfacial scattering of HfSe₂/h-BN, the photodetector fabricated from the vdW epitaxial HfSe₂ on single-crystal h-BN shows the best performance with an on/off ratio of 1 × 10⁴ and a responsivity up to 43 mA W⁻¹. Furthermore, the vdW epitaxy of other TMDs such as HfS₂, ZrS₂, and ZrSe₂ is also experimentally demonstrated on single-crystal h-BN, suggesting the broad applicability of the h-BN template for the vdW epitaxy.

The heterogeneous integration of wide-bandgap semiconductors (WBGs) and 2D materials is emerging as a promising way to address various challenges faced by WBGs. This review covers recent advancements in fabrication techniques, mechanisms, devices, and novel functionalities of WBG/2D heterostructures. Furthermore, the directions and perspectives are outlined for realizing practical applications in the near future.

Abstract

Wide-bandgap semiconductors (WBGs) are crucial building blocks of many modern electronic devices. However, there is significant room for improving the crystal quality, available choice of materials/heterostructures, scalability, and cost-effectiveness of WBGs. In this regard, utilizing layered 2D materials in conjunction with WBG is emerging as a promising solution. This review presents recent advancements in the integration of WBGs and 2D materials, including fabrication techniques, mechanisms, devices, and novel functionalities. The properties of various WBGs and 2D materials, their integration techniques including epitaxial and nonepitaxial growth methods as well as transfer techniques, along with their advantages and challenges, are discussed. Additionally, devices and applications based on the WBG/2D heterostructures are introduced. Distinctive advantages of merging 2D materials with WBGs are described in detail, along with perspectives on strategies to overcome current challenges and unlock the unexplored potential of WBG/2D heterostructures.

A centimeter-scale and honeycomb-like Bi₂S₃ film is synthesized on an ultrathin flexible fluorophlogopite mica substrate. The Bi₂S₃ film consists of a well-stabilized arrangement of triangular unit structures forming an interconnected network structure. A flexible photodetector based on the honeycomb-like Bi₂S₃ film is constructed, displaying a high responsivity and fast response, and excellent stability after a continuous bending in the air.

Abstract

Films with honeycomb-like structures have became ideal network structures for the development of flexible photodetectors due to their superior mechanical stability and merits in large active surface area, high carrier transport efficiency and well light absorption capacity. In this work, a honeycomb-like Bi₂S₃ film with centimeter-scale (2 cm × 2 cm) is synthesized on an ultrathin flexible fluorophlogopite mica substrate, which consists of a well-stabilized arrangement of triangular unit structures forming an interconnected network structure. Based on the as-grown honeycomb-like Bi₂S₃ film, a flexible photodetector with a broadband response from ultraviolet to infrared is constructed, which displays the highest responsivity (R _λ) of 611.2 mA W⁻¹ and specific detectivity (D*) of 4.77 × 10¹⁰ Jones. And at 850 nm light illumination, there is nearly no deterioration in R _λ and D* of the Bi₂S₃ flexible photodetector after successive multiple bends, benefiting from the excellent structural stability of the triangular honeycomb network structure. Notably, the device maintains excellent detection performance after 1 week of prolonged bending in air without any encapsulation, and its photocurrent can still reach 90.39% of the initial photocurrent. In addition, the device also exhibits favorable durability, cycle stability, as well as high-definition imaging ability in bending state and after bending recovery.

Based on unique features of the photomodulated Ba₃MgSi₂O₈:Eu medium: photo-induced valence (PV) and photochromic (PC) phenomena, a robust, non-volatile, and multilevel photomemory is successfully designed. The dual-level storage channels are written and erased simultaneously by alternating 265 and 365 nm stimuli. The encrypted information can be decrypted by separately probing the Eu²⁺ and Eu³⁺ signals, thus ensuring information security.

Abstract

Non-volatile photomemory based on photomodulated luminescent materials offers unique advantages over voltage-driven memory, including low residual crosstalk and high storage speed. However, conventional materials have thus far been volatile and insecure for data storage because of low trap depth and single-level storage channels. Therefore, the development of a novel non-volatile multilevel storage medium for data encryption remains a challenge. Herein, a robust, non-volatile, multilevel optical storage medium is reported, based on a photomodulated Ba₃MgSi₂O₈:Eu³⁺, which combined the merits of light-induced valence (Eu³⁺ → Eu²⁺) and photochromic phenomena using optical stimulation effects, accompanied by larger luminescent and color contrasts (>90%). These two unique features provided dual-level storage channels in a single host, significantly improving the data storage security. Notably, dual-level optical signals could be written and erased simultaneously by alternating 265 and 365 nm light stimuli. Theoretical calculations indicated that robust color centers induced by intrinsic interstitial Mg and vacancy defects with suitable trap depths enable excellent reversibility and long-term storage capability. By relying on different luminescent readout mechanisms, the encrypted dual-level information can be accurately decrypted by separately probing the Eu²⁺ and Eu³⁺ signals, thus ensuring information security. This study proposes a novel approach for constructing multilevel information storage channels for information security.

Publication date: February 2025

Source: Progress in Materials Science, Volume 148

Author(s): Chang Liu, Shun Li, Yunpeng Zheng, Min Xu, Hongyang Su, Xiang Miao, Yiqian Liu, Zhifang Zhou, Junlei Qi, Bingbing Yang, Di Chen, Ce-Wen Nan, Yuan-Hua Lin

Nature Reviews Chemistry, Published online: 10 October 2024; doi:10.1038/s41570-024-00660-9

This review explores the innovative use of 2D materials in water filtration systems. It focuses on the nanoarchitectonics of these materials, showcasing their ability to remove contaminants efficiently. Various 2D material types, their properties, and applications in creating advanced filtration systems are discussed, highlighting their potential in addressing global water purification challenges.

Abstract

Water polluted by toxic chemicals due to waste from chemical/pharmaceuticals and harmful microbes such as E. Coli bacteria causes several fatal diseases; and therefore, water filtration is crucial for accessing clean and safe water necessary for good health. Conventional water filtration technologies include activated carbon filters, reverse osmosis, and ultrafiltration. However, they face several challenges, including high energy consumption, fouling, limited selectivity, inefficiencies in removing certain contaminants, dimensional control of pores, and structural/chemical changes at higher thermal conditions and upon prolonged usage of water filter. Recently, the advent of 2D materials such as graphene, BN, MoS₂, MXenes, and so on opens new avenues for advanced water filtration systems. This review delves into the nanoarchitectonics of 2D materials for water filtration applications. The current state of water filtration technologies is explored, the inherent challenges they face are outlines, and the unique properties and advantages of 2D materials are highlighted. Furthermore, the scope of this review is discussed, which encompasses the synthesis, characterization, and application of various 2D materials in water filtration, providing insights into future research directions and potential industrial applications.

2D materials are central to next-generation information technology. Exciting their bandgap with light has led to significant performance breakthroughs in 2D material sensors. This perspective covers the mechanisms, applications, and challenges of light-excited 2D material sensors, highlighting recent advancements and future directions.

Abstract

2D materials are highly regarded for their exceptional sensing application prospects, stemming from their distinctive atomic layer structure and exceptionally sensitive surfaces. Over the past decade, numerous high-performance 2D material sensors are extensively developed; however, challenges related to sensitivity, selectivity, and stability continue to impede their industrial advancement. The interaction between light and 2D materials has introduced unique properties, including absorption and emission characteristics, photoelectric effects, nonlinear optical effects, surface-enhanced Raman scattering, and light response enhancement. Consequently, exciting and adjusting the electronic structure and carrier concentration of 2D materials through light with specific wavelength ranges is an effective strategy for enhancing sensing performance. This strategy has yielded remarkable breakthroughs in applications such as photodetectors, semiconductor gas sensors, and fiber optic sensors. Moreover, it demonstrates extraordinary potential in emerging applications such as image sensors, flexible electronics, and biomedical sensors. However, the sensing mechanism, device structure design, and specific applications of 2D materials under light excitation remain unclear. This perspective endeavors to elucidate the intrinsic photophysical mechanisms between light-excited 2D materials and their target sensing analytes. Furthermore, it aims to explain the evolutionary pattern of sensing applications and provide novel insights and inspiration to advance this burgeoning field.

In this work, the discovery of a new family of layered crystalline LiMCl₆ (M = Ta/Nb) compounds is presented. The ionic conductivity and Li intercalation mechanism in LiTaCl6 is investigated in the context of an all-solid-state battery. These findings open the door to a wide range of substituted layered halides with competing ionic and electronic properties.

Abstract

A suitable solid electrolyte can turn the long-standing dream of a safe commercial all-solid-statebattery into reality in the same way as appropriate liquid electrolytes kickstarted the first commercial lithium-ion battery. Presently, halide-based electrolytes despite their reactivity with lithium metal are extensively studied as they offer better processability, malleability, oxidative stability, and safety over sulfide-based electrolytes. Particularly, LiMCl₆ (M = Ta/Nb) chloride-based amorphous electrolytes are generating widespread interest with their high conductivities, comparable to liquid electrolytes. In this context, with synchrotron X-ray and neutron powder diffraction techniques, well-crystallized triclinic layered LiMCl₆ (M = Ta/Nb) chlorides with an hcp AB-type stacking of chloride ions is reported. The hexagonally ordered NbCl₆ octahedra share edges with LiCl₆ octahedra forming a honeycomb pattern, whereas Li⁺ is intermixed with M⁵⁺ for M = Ta. Furthermore, it is found that crystalline LiTaCl₆ has an ionic conductivity of ≈10⁻⁵ mS cm⁻¹, six orders of magnitude lower than that reported for superionic amorphous LiTaCl₆. Nevertheless, crystalline LiTaCl₆ is utilized as an intercalation compound in an all-solid-state-battery, uncovering a solid-solution/two-phase/conversion pathway for lithium-insertion during the three distinct redox plateaus below 3 V versus Li⁺/Li°. Broadly, the findings give insights into the structure, ionic conduction, and intercalation in a new family of layered halides.

Here, the ability to exfoliate and process two representative van der Waals materials containing 1D motifs, namely MoI₃ and Ta₂Se₈I, at the scale of individual atomic chains is demonstrated. For MoI₃, it is observed that chains are the suspended and substrate-supported samples. For Ta₂Se₈I, processing capabilities with electron beams to achieve suspended individual atomic chains are shown.

Abstract

Experiments with graphene have demonstrated that 2D van der Waals materials can be stable, robust, and efficiently manipulated at the level of individual atomic planes. However, the stability and manipulation of 1D van der Waals materials and individual atomic chains remains elusive. Here, the ability to exfoliate and process two representative van der Waals materials containing 1D motifs, namely MoI₃ and Ta₂Se₈I, at the scale of individual atomic chains is demonstrated. High-resolution transmission electron microscopy and atomic force microscopy studies confirm the presence of stable individual atomic chains of MoI₃ at room temperature. It is further shown that 1D van der Waals materials with low exfoliation energy, such as Ta₂Se₈I, can be processed with electron beams to achieve suspended individual atomic chains. Ab initio calculations corroborate the findings regarding the cleavage energies and the thermodynamic stability of individual atomic chains in these 1D van der Waals materials. These results demonstrate that the top-down approach in material processing can be extended to the scale of individual chains.

Nature Photonics, Published online: 14 October 2024; doi:10.1038/s41566-024-01545-5

Nature Physics, Published online: 14 October 2024; doi:10.1038/s41567-024-02668-w

Nature Electronics, Published online: 15 October 2024; doi:10.1038/s41928-024-01256-3

Nature Electronics, Published online: 15 October 2024; doi:10.1038/s41928-024-01259-0

The manuscript introduces a multifunctional magnetic continuum robot designed for transluminal surgeries. It features noninteractive navigation through narrow lumina. A triple-individual Guider system enables independent control for versatile manipulation, including targeted delivery, precision coating, and obstacle clearing. This innovation provides a new technological roadmap for addressing the challenges of minimally invasive surgery.

Abstract

Soft continuum robots can navigate through narrow and tortuous lumina. However, its interactions with the lumina during steering pose a risk of luminal injuries, especially if it integrates multifunctional units, which increase both the robot's size and local stiffness. Therefore, a continuum robot comprising coaxially assembled Guider and Follower components is designed that utilize phase change materials for noninteractive navigation and versatile manipulation. Navigation occurs through alternating softening-hardening cycles: First, the Guider softens and advances under magnetic steering while the rigid Follower provides support. Then, the Guider solidifies to form a new backbone as the Follower softens to replicate its path. This process maintains structural integrity while enabling navigation along desired trajectories, thereby greatly reducing interactions with the lumen. To further accomplish complex tasks in large and open spaces, a continuum robot system with a triple-individual Guider is developed in which the multi-degree-of-freedom movement of the individuals is precisely and sequentially controlled through segmented stiffness regulation. This configuration achieves versatile manipulation, including targeted delivery, precision coating, grasping, and obstacle clearing in complex environments. Combining cooperative movement and diverse functionalities, this continuum robot design offers a new approach to dexterous navigation and intervention in minimally invasive surgical procedures.

An n-n type Bi₂O₂Se/SnSe₂ van der Waals tunneling heterojunction photodetector is presented, which introduces a novel strategy to overcome the limited detection capabilities of 2D devices under intense illumination. The photodetector demonstrated a responsivity of 1636.3 AW⁻¹, maintaining a tunable linear dynamic range (LDR) of ≈74.7 dB.

Abstract

2D materials are extensively employed in the fabrication of high-performance photodetectors owing to their exceptional physical properties. However, most 2D material photodetectors fail to sustain high gain under intense illumination due to the limited intrinsic trap states. Here, an n-n type Bi₂O₂Se/SnSe₂ van der Waals tunneling heterojunction photodetector with a detection range from visible to near-infrared (VIS-NIR) is presented. Under reverse bias, the heterojunction induces a significant electron barrier and hole potential well, ensuring low leakage current and ample hole defect states. Therefore, the photodetector demonstrated a responsivity of 1636.3 AW⁻¹ and a detectivity of 1.39  ×  10¹⁴ Jones under 660 nm illumination, maintaining a tunable linear dynamic range (LDR) of ≈74.7 dB. This performance is attributed to the hole potential well-suppressing the recombination of photogenerated carriers, thereby enhancing the device's gain. Furthermore, the tunneling of photogenerated electrons within the heterojunction's space charge region under bias enables rapid response (75.1 and 15.6 µs). In summary, the study introduces a novel strategy to overcome the limited detection capabilities of 2D devices under intense illumination, characterized by outstanding linearity for rapid detection and high-resolution imaging.

Mixed-dimensional magnetic van der Waals heterostructure is established to induce room temperature 2D ferromagnetism and corresponding photomagnetic effect. The spin-related charge transfer between Fe species and oxygen vacancy defects localized at the heterointerface is facilitated by illumination and contributes to spin-tunneling-enhanced photoconductivity performance. These findings offer valuable insights to manipulate photomagnetic process and optimize the optoelectronic properties of conventional semiconductors.

Abstract

All-optical magnetization reversal provides a low-power approach for investigating spin state manipulation in 2D magnets. However, the ambient observation of photomagnetic coupling presents significant challenges due to the low Curie temperatures exhibited by most 2D magnets. Herein, a mixed-dimensional heterostructure comprising a surface-oxidized Fe₃GeTe₂ nanosheet with enhanced magnetic properties and individual semiconducting ZnO nanorod is proposed to explore proximity photomagnetic modulation and spin-enhanced photodetection behaviors. The surface curvature of ZnO nanorod induces pronounced strains for Fe₃GeTe₂ nanosheet, leading to its anomalous Raman polarization and spin ordering at room temperature. Strain-activated itinerant spin electrons are immobilized on the O-2p orbitals of adjacent ZnO, thereby facilitating the optical demagnetization process in Fe₃GeTe₂ without aid of magnetic field. First-principles calculations together with in situ characterization experiments further confirm that the primary charge transfer channel involves coupling between Fe³⁺ and oxygen vacancy defects anchored at heterointerfaces. The rapid establishment of magnetization by illumination in ZnO nanorod contributes to spin-tunneling-enhanced photocurrent, device response dynamics, polarization detection and ultraviolet imaging capability. These findings offer valuable insights to optimize the optoelectronic properties of conventional semiconductors and advance complex dimensional spin-optoelectronic devices.

Fe³⁺,Er³⁺ co-doped double perovskite material has been successfully synthesized, showing remarkable characteristics including highly efficient NIR luminescence and multimode controllable luminescence. These findings highlight the immense potential in versatile photoelectric applications including optical anti-counterfeiting and NIR imaging, and provide valuable insights into the modification of luminescent properties by doping transition metal ions.

Abstract

Erbium ions are commonly used to extend the photoelectric properties of metal halide perovskites from visible to near-infrared range. However, achieving high-efficiency multimode luminescence in a single system is difficult due to the weak absorption associated with forbidden 4f-4f transitions. In this study, a unique strategy is proposed to adjust multimode luminescence and enhance the second near-infrared region (NIR-II) emission in Cs₂NaBiCl₆ by incorporating Fe³⁺ ions. The as-prepared material demonstrates reversible thermochromism, driven by strong electron-phonon coupling effect, and exhibits tunable luminescence that can be adjusted by altering excitation energy and temperature. Notably, benefitting from the charge transfer transition of Fe³⁺-Cl⁻ along with the influence of Fe³⁺ doping on the geometrical and electronic structures, the blue-excitable (450 nm) NIR-II emission around 1541 nm from Er³⁺ is realized for the first time, achieving an intensity 16.7 times higher and a maximum photoluminescence quantum yield (PLQY) of 22.5 %. This enhancement enables innovative applications such as two-dimensional information encryption by the multi-channel cooperative responses and improved NIR imaging. The study highlights the potential of Fe³⁺ doping in optimizing absorption and multimode luminescence in perovskites, opening avenues for advanced applications in blue-excitable NIR light emitting diodes (LEDs), thermometer, anti-counterfeiting, and NIR imaging.

Nature Communications, Published online: 13 October 2024; doi:10.1038/s41467-024-53125-4