Jiuxiang Dai

This review summarizes the recent advances in the strain engineering of twisted 2D materials, in particular twisted bilayer graphene, toward effectively modifying their Moiré superlattices and tuning electronic structures upon mechanical straining. Through highlighting the potential of diverse straining techniques in modulating various physical properties of twisted bilayer 2D materials, this review aims to provide prospective guidance for the emerging applications of “strain-twistronics” in future devices.

Abstract

The layer-by-layer stacked van der Waals structures (termed vdW hetero/homostructures) offer a new paradigm for materials design—their physical properties can be tuned by the vertical stacking sequence as well as by adding a mechanical twist, stretch, and hydrostatic pressure to the atomic structure. In particular, simple twisting and stacking of two layers of graphene can form a uniform and ordered Moiré superlattice, which can effectively modulate the electrons of graphene layers and lead to the discovery of unconventional superconductivity and strong correlations. However, the twist angle of twisted bilayer graphene (tBLG) is almost unchangeable once the interlayer stacking is determined, while applying mechanical elastic strain provides an alternative way to deeply regulate the electronic structure by controlling the lattice spacing and symmetry. In this review, diverse experimental advances are introduced in straining tBLG by in-plane and out-of-plane modes, followed by the characterizations and calculations toward quantitatively tuning the strain-engineered electronic structures. It is further discussed that the structural relaxation in strained Moiré superlattice and its influence on electronic structures. Finally, the conclusion entails prospects for opportunities of strained twisted 2D materials, discussions on existing challenges, and an outlook on the intriguing emerging field, namely “strain-twistronics”.

The nonlinear optical properties of 2D materials are of great significance to the design and analysis of applied materials and functional devices. In this article, a comprehensive review of measurement methods for nonlinear susceptibility is provided. Nonlinear susceptibility of different 2D materials are compared. Their applications in nonlinear photonic devices are discussed.

Abstract

2D materials are a subject of intense research in recent years owing to their exclusive photoelectric properties. With giant nonlinear susceptibility and perfect phase matching, 2D materials have marvelous nonlinear light-matter interactions. The nonlinear optical properties of 2D materials are of great significance to the design and analysis of applied materials and functional devices. Here, the fundamental of nonlinear optics (NLO) for 2D materials is introduced, and the methods for characterizing and measuring second-order and third-order nonlinear susceptibility of 2D materials are reviewed. Furthermore, the theoretical and experimental values of second-order susceptibility χ(2) and third-order susceptibility χ(3) are tabulated. Several applications and possible future research directions of second-harmonic generation (SHG) and third-harmonic generation (THG) for 2D materials are presented.

Amorphous Ga₂O₃ has high potential for flexible devices, but suffers from intrinsic high resistivity, thus, requiring traditional high-temperature doping methods. This study offers a novel approach to dope amorphous Ga₂O₃ films. Irradiating energetic ions on the SiO₂ substrate leads to nanoripple formation while leaving its topmost part rich in elemental Si (responsible for doping). Doped films show their worth with ultra-fast photodetection.

Abstract

Ga₂O₃ has emerged as a promising material for the wide-bandgap industry aiming at devices beyond the limits of conventional silicon. Amorphous Ga₂O₃ is widely being used for flexible electronics, but suffers from very high resistivity. Conventional methods of doping like ion implantation require high temperatures post-processing, thereby limiting their use. Herein, an unconventional method of doping Ga₂O₃ films with Si, thereby enhancing its electrical properties, is reported. Ion-beam sputtering (500 eV Ar⁺) is utilized to nanopattern SiO₂-coated Si substrate leaving the topmost part rich in elemental Si. This helps in enhancing the carrier conduction by increasing n-type doping of the subsequently coated 5 nm amorphous Ga₂O₃ films, corroborated by room-temperature resistivity measurement and valence band spectra, respectively, while the nanopatterns formed help in better light management. Finally, as proof of concept, metal-semiconductor-metal (MSM) photoconductor devices fabricated on doped, rippled films show superior properties with responsivity increasing from 6 to 433 mA W⁻¹ while having fast detection speeds of 861 µs/710 µs (rise/fall time) as opposed to non-rippled devices (377 ms/392 ms). The results demonstrate a facile, cost-effective, and large-area method to dope amorphous Ga₂O₃ films in a bottom-up approach which may be employed for increasing the electrical conductivity of other amorphous oxide semiconductors as well.

This review highlights the significance of thickness-controlled synthesis in non-Van der Waals self-intercalated Cr2X3 for exploring tunable magnetism in 2D materials. By manipulating the thickness and lattice size during synthesis, researchers have opened new possibilities for tailoring the magnetic properties of these materials. The review systematically discusses the interplay between synthesis methods, crystal structure variations, and resulting magnetism in Cr2X3 thin films. It provides a comprehensive summary of existing studies, shedding light on the importance of synthesis parameters in understanding the magnetic behavior of these materials.

Abstract

In the search for two-dimensional (2D) magnets operating under ambient conditions, quasi-2D non-van der Waals (vdW) materials have attracted considerable research interest over the last five years. In addition to their high Curie temperature (T_C), their superior air stability to that of vdW 2D magnets has made them potential candidates for future room-temperature spintronics applications. Furthermore, recent progress in the thickness-dependent crystal lattice and magnetic properties of non-vdW Cr₂X₃ (X = S, Se, or Te) has brought them to areas that are once set aside for 2D vdW magnets in fundamental research and applications. Despite covalent bonding between magnetic layers, various bottom-up synthesis methods produced thickness-controlled flakes of Cr₂X₃. Moreover, layer-dependent structural and magnetic properties are among the novel research directions in these materials. This review systematically summarizes recent studies on Cr₂X₃ crystal structure, their controllable synthesis, and their respective magnetic properties. A summary of some significant results on thickness-controlled synthesis in Cr₂X₃ and thickness-dependent magnetism in Cr₂Te₃ is presented. Additionally, experimental and theoretical reports are presented to explain interlayer magnetic interaction. The work reveals the interaction between synthesis, structure, and magnetism. Finally, future research directions of new Cr₂X₃-based materials, rich magnetism in Cr₂X₃, and their potential application are discussed.

Monodispersed and organic amine modified lanthanum hydroxide (OA-La(OH)₃) nanocrystals are synthesized via a nonaqueous wet-chemical method. The OA-La(OH)₃ nanocrystals further expose La adsorption sites and minimize mass transfer barrier by regulating the inner Helmholtz plane (IHP), thereby dramatically increasing its phosphate adsorption capacity, pH adaptability, and anti-interference performance.

Abstract

Advanced phosphate removal is critical for alleviating the serious and widespread aquatic eutrophication, strongly depending on the development of superior adsorption materials to overcome low chemical affinity and sluggish mass transfer at low phosphate concentrations. Herein, the first synthesis of monodispersed and organic amine modified lanthanum hydroxide nanocrystals (OA-La(OH)₃) for advanced phosphate removal by modulating inner Helmholtz plane (IHP), is reported. These OA-La(OH)₃ nanocrystals with positively charged surfaces and abundant exposed La sites exhibit specific affinity toward phosphate, delivering a maximum adsorption capacity of 168 mg P g⁻¹ and a wide pH adaptability from 3.0 to 11.0, as well as a robust anti-interference performance, far surpassing those of documented phosphate removal materials. The superior phosphate removal performance of OA-La(OH)₃ is attributed to its protonated organic amine in IHP, which enhances the electrostatic attraction around the adsorbent-solution interface. Impressively, OA-La(OH)₃ can treat ≈5 000 and ≈3 200 bed volumes of simulated and real phosphate-containing wastewater to below extremely strict standard (0.1 mg L⁻¹) in a fixed-bed adsorption mode, exhibiting great potential for advanced phosphate removal. This study offers a facile modification strategy to improve phosphate removal performance of nanoscale adsorbents, and sheds light on the structure-reactivity relationship of La-based materials.

Design of multilayer capacitor according to design rules for optimizing the breakdown field and energy storage capacity in the BZT/BST multilayer system, which presents an extremely large recoverable energy-storage density of 165.6 J cm⁻³ and high energy efficiency of 93% (left). Volume and surface-area recoverable energy-storage densities for some representative dielectric capacitors in bulk, thick-film, and thin-film structures (right).

Abstract

Future pulsed-power electronic systems based on dielectric capacitors require the use of environment-friendly materials with high energy-storage performance that can operate efficiently and reliably in harsh environments. Here, a study of multilayer structures, combining paraelectric-like Ba_0.6Sr_0.4TiO₃ (BST) with relaxor-ferroelectric BaZr_0.4Ti_0.6O₃ (BZT) layers on SrTiO₃-buffered Si substrates, with the goal to optimize the high energy-storage performance is presented. The energy-storage properties of various stackings are investigated and an extremely large maximum recoverable energy storage density of ≈165.6 J cm⁻³ (energy efficiency ≈ 93%) is achieved for unipolar charging–discharging of a 25-nm-BZT/20-nm-BST/910-nm-BZT/20-nm-BST/25-nm-BZT multilayer structure, due to the extremely large breakdown field of 7.5 MV cm⁻¹ and the lack of polarization saturation at high fields in this device. Strong indications are found that the breakdown field of the devices is determined by the outer layers of the multilayer stack and can be increased by improving the quality of these layers. Authors are also able to deduce design optimization rules for this material combination, which can be to a large extend justify by structural analysis. These rules are expected also to be useful for optimizing other multilayer systems and are therefore very relevant for further increasing the energy storage density of capacitors.

Nature Communications, Published online: 15 April 2024; doi:10.1038/s41467-024-47603-y

Nature Electronics, Published online: 15 April 2024; doi:10.1038/s41928-024-01152-w

Vertical graphene possesses unique structures that are appealing for energy applications. Defect and morphology structure can tailor reaction kinetics and mass/electron transportation in VG materials, which in turn, affects their electrochemical performance. Herein, recent advances of VG are summarized in terms of synthesis routine, regulation strategies, and applications in the energy field. Finally, the challenges and prospects of VG materials in energy field are discussed.

Abstract

Vertical graphene (VG) nanosheets have garnered significant attention in the field of electrochemical energy applications, such as supercapacitors, electro-catalysis, and metal-ion batteries. The distinctive structures of VG, including vertically oriented morphology, exposed, and extended edges, and separated few-layer graphene nanosheets, have endowed VG with superior electrode reaction kinetics and mass/electron transportation compared to other graphene-based nanostructures. Therefore, gaining insight into the structure-activity relationship of VG and VG-based materials is crucial for enhancing device performance and expanding their applications in the energy field. In this review, the authors first summarize the fabrication methods of VG structures, including solution-based, and vacuum-based techniques. The study then focuses on structural modulations through plasma-enhanced chemical vapor deposition (PECVD) to tailor defects and morphology, aiming to obtain desirable architectures. Additionally, a comprehensive overview of the applications of VG and VG-based hybrids d in the energy field is provided, considering the arrangement and optimization of their structures. Finally, the challenges and future prospects of VG-based energy-related applications are discussed.

A new approach for heterointegration of high-quality semiconductors on graphene, called anchor point nucleation (APN), is introduced. APN consists of controlled introduction of defects in the graphene layer, creating preferential nucleation sites for the epitaxial growth of defect-free semiconductor layers on graphene. APN approach enables the formation of semiconductor membranes, even for non-polar semiconductor materials, alleviating the limitations of Remote Epitaxy.

Abstract

The heterointegration of graphene with semiconductor materials and the development of graphene-based hybrid functional devices are heavily bound to the control of surface energy. Although remote epitaxy offers one of the most appealing techniques for implementing 3D/2D heterostructures, it is only suitable for polar materials and is hugely dependent on the graphene interface quality. Here, the growth of defect-free single-crystalline germanium (Ge) layers on a graphene-coated Ge substrate is demonstrated by introducing a new approach named anchor point nucleation (APN). This powerful approach based on graphene surface engineering enables the growth of semiconductors on any type of substrate covered by graphene. Through plasma treatment, defects such as dangling bonds and nanoholes, which act as preferential nucleation sites, are introduced in the graphene layer. These experimental data unravel the nature of those defects, their role in nucleation, and the mechanisms governing this technique. Additionally, high-resolution transmission microscopy combined with geometrical phase analysis established that the as-grown layers are perfectly single-crystalline, stress-free, and oriented by the substrate underneath the engineered graphene layer. These findings provide new insights into graphene engineering by plasma and open up a universal pathway for the heterointegration of high-quality 3D semiconductors on graphene for disruptive hybrid devices.

Fiber electronics have not yet used solution-processed 2D semiconducting flakes. This study introduces flexible and biocompatible fiber-based transistors utilizing 2D semiconducting flakes of WSe₂ and MoS₂ with high mobility >10 cm² V⁻¹ s⁻¹. The fiber transistors utilize a unique “knot” architecture, which can be scaled to reduce channel lengths and widths only limited by the fiber diameter.

Abstract

Wearable devices have generally been rigid due to their reliance on silicon-based technologies, while future wearables will utilize flexible components for example transistors within microprocessors to manage data. Two-dimensional (2D) semiconducting flakes have yet to be investigated in fiber transistors but can offer a route toward high-mobility, biocompatible, and flexible fiber-based devices. Here, the electrochemical exfoliation of semiconducting 2D flakes of tungsten diselenide (WSe₂) and molybdenum disulfide (MoS₂) is shown to achieve homogeneous coatings onto the surface of polyester fibers. The high aspect ratio (>100) of the flake yields aligned and conformal flake-to-flake junctions on polyester fibers enabling transistors with mobilities μ ≈1 cm² V⁻¹ s⁻¹ and a current on/off ratio, I _on/I _off ≈10²–10⁴. Furthermore, the cytotoxic effects of the MoS₂ and WSe₂ flakes with human keratinocyte cells are investigated and found to be biocompatible. As an additional step, a unique transistor ‘knot’ architecture is created by leveraging the fiber diameter to establish the length of the transistor channel, facilitating a route to scale down transistor channel dimensions (≈100 µm) and utilize it to make a MoS₂ fiber transistor with a human hair that achieves mobilities as high as μ ≈15 cm² V⁻¹ s⁻¹.

Microencapsulated mixtures of fluorescent dyes in organic phase change materials are used to generate composite-based thermoresponsive fluorescent pixels, which undergo multistep color and/or intensity emission changes upon temperature variation. Arrays of these pixels are exploited for high-security 3D information encryption and 4D data storage.

Abstract

Luminescent materials are emerging promising tools for digital data encoding due to their reduced cost, facile reading, robustness, and durability. For this, the use of fluorescent systems that combine multicolor emission with sensitivity to external stimuli will be highly desirable, as they can offer rewritable data encoding together with enhanced encryption security and storage density. Herein a novel strategy is pioneered to reach this goal, which exploits the temperature-responsive emission properties of the mixtures of regular fluorophores with simple organic phase change materials (PCMs) such as paraffins. By preparing a diversity of microcapsules of these mixtures comprising different dyes and PCMs, thermosensitive fluorescent pixels can be prepared in a low-cost, straightforward, and scalable manner that exhibits multicolor dynamic emission behavior. These features are capitalized to fabricate pixel arrays that perform two advanced digital encoding operations: high-security 3D information encryption, and 4D data storage.

Ferroelectric-driven dynamic modulation of lanthanide luminescence has been realized by coupling lanthanide dopant with an electrically responsive ferroelectric host. Such solution delivers an in situ and reversible amplification and modulation of lanthanide luminescence up to 2000 Hz. The proof-of-concept device can convert digital information signals into visible waveforms and visualize electrical logic and arithmetic operations.

Abstract

Modulation of light underpins a central part of modern optoelectronics. Conventional optical modulators based on refractive-index and absorption variation in the presence of an electric field serve as the workhorse for diverse photonic technologies. However, these approaches based on electro-refraction or electro-absorption effect impose limitations on frequency converting and signal amplification. Lanthanide-activated phosphors offer a promising platform for nonlinear frequency conversion with an abundant spectrum. Here, we propose a novel approach to achieve frequency conversion and digital modulation of light signal by coupling lanthanide luminescence with an electrically responsive ferroelectric host. The technological benefits of such paradigm-shifting solution are highlighted by demonstrating a quasi-continuous and enhancement of the lanthanide luminescence. The ability to locally manipulate light emission can convert digital information signals into visible waveforms, and visualize electrical logic and arithmetic operations. The proof-of-concept device exhibits perspectives for developing light-compatible logic functions. These results pave the way to design more controllable lanthanide photonics with desired opto-electronic coupling.

This article reviews recent breakthroughs in 2D transistor technology, including sub-nanometer gate length, ultra-low resistance contact, atomically thin dielectric, novel architecture form (2D fin field-effect transistor), and direct integration with Si complementary metal-oxide-semiconductor. The high-performance 2D InSe transistor approaches theoretical limit. The remaining challenges and exciting future prospects of 2D transistors for extending Moore's Law are also highlighted.

Abstract

Since Si-based Moore's law is physically limited, 2D semiconductors are proposed as successors to continue shrinking the transistor size for more Moore electronics. However, limited by experimental technology bottlenecks, the theoretical predicted superiorities of the 2D transistors over the state-of-the-art Si transistors have been lacking concrete evidence for a decade. In this review, recent exciting experimental breakthroughs for 2D transistors are presented, including gate length miniaturization to a sub-1 nm limit, electrode contact optimization to the resistance quantum limit, high-quality dielectric fabrication with an equivalent oxide thickness to sub-0.5 nm, novel architecture form (2D fin field-effect transistor), and back-end-of-line integration of directly grown 2D materials on Si complementary metal-oxide-semiconductor circuits. Remarkably, an ultrashort channel, Ohmic contact, ballistic transport, and ultrathin dielectric layer are simultaneously satisfied in the 2D InSe transistor, and device performances approaching the theoretical limit are observed. The measured key figures of merit of the ideal 2D InSe transistor are comparable to or even surpass those of the Si transistors. Finally, the challenges and outlook on more Moore electronics based on 2D transistors are highlighted.

Thermoelectric technology enables direct, pollution-free heat-to-electricity conversion. Silver-copper-based semiconductors (AgCuQ, Q = S, Se, Te) demonstrate compelling attributes, such as ultralow thermal conductivity, tunable electronic properties, and ductility. This review summarizes their fundamentalfeatures and recent achievements, including crystal structures, electronic bands, mechanical features, and strategies for performance enhancement, as well as addressing challenges and prospects.

Abstract

Thermoelectric technology, which enables a direct and pollution-free conversion of heat into electricity, provides a promising path to address the current global energy crisis. Among the broad range of thermoelectric materials, silver copper chalcogenides (AgCuQ, Q = S, Se, Te) have garnered significant attention in thermoelectric community in light of inherently ultralow lattice thermal conductivity, controllable electronic transport properties, excellent thermoelectric performance across various temperature ranges, and a degree of ductility. This review epitomizes the recent progress in AgCuQ-based thermoelectric materials, from the optimization of thermoelectric performance to the rational design of devices, encompassing the fundamental understanding of crystal structures, electronic band structures, mechanical properties, and quasi-liquid behaviors. The correlation between chemical composition, mechanical properties, and thermoelectric performance in this material system is also highlighted. Finally, several key issues and prospects are proposed for further optimizing AgCuQ-based thermoelectric materials.

An ultrathin, high-performance transistor layer suitable for multilayer stacking is developed for monolithic 3D integration, utilizing directly grown nanocrystalline graphene and dry-transferred MoS₂ film. This device structure retains the advantages of a dangling bond-free, ultrathin channel and low contact resistivity, making it a significant enabler for high-density 3D circuit technology.

Abstract

The potential of monolithic 3D integration technology is largely dependent on the enhancement of interconnect characteristics which can lead to thinner stacks, better heat dissipation, and reduced signal delays. Carbon materials such as graphene, characterized by sp2 hybridized carbons, are promising candidates for future interconnects due to their exceptional electrical, thermal conductivity and resistance to electromigration. However, a significant challenge lies in achieving low contact resistance between extremely thin semiconductor channels and graphitic materials. To address this issue, an innovative wafer-scale synthesis approach is proposed that enables low contact resistance between dry-transferred 2D semiconductors and the as-grown nanocrystalline graphitic interconnects. A hybrid graphitic interconnect with metal doping reduces the sheet resistance by 84% compared to an equivalent thickness metal film. Furthermore, the introduction of a buried graphitic contact results in a contact resistance that is 17 times lower than that of bulk metal contacts (>40 nm). Transistors with this optimal structure are used to successfully demonstrate a simple logic function. The thickness of active layer is maintained within sub-7 nm range, encompassing both channels and contacts. The ultrathin transistor and interconnect stack developed here, characterized by a readily etchable interlayer and low parasitic resistance, leads to heterogeneous integration of future 3D integrated circuits (ICs).

A comprehensive scheme combining an autoencoding regularized adversarial neural network and feature-adaptive variational active learning algorithm for screening low-contact electrodes for 2D semiconductor transistors in a limited data scenario is proposed. This scheme outperforms classical models and the state-of-the-art boosting techniques trained using limited datasets, as well as models trained using randomly selected data.

Abstract

Low-barrier and high-injection electrodes are crucial for high-performance (HP) 2D semiconductor devices. Conventional trial-and-error methodologies for electrode material screening are impractical because of their low efficiency and arbitrary specificity. Although machine learning has emerged as a promising alternative to tackle this problem, its practical application in semiconductor devices is hindered by its substantial data requirements. In this paper, a comprehensive scheme combining an autoencoding regularized adversarial neural network and a feature-adaptive variational active learning algorithm for screening low-contact electrode materials for 2D semiconductor transistors with limited data is proposed. The proposed scheme exhibits exceptional performance by training with only 15% of the total data points, where the mean square errors are 0.17 and 0.27 eV for the vertical and lateral Schottky barrier, respectively, and 2.88% for tunneling probability. Further, it exhibits an optimal predictive performance for 100 randomly sampled training datasets, reveals the underlying physical insight based on the identified features, and realizes continual improvement by employing detailed density-of-states descriptors. Finally, the empirical evaluations of the transport characteristics are conducted and verified by constructing MOSFET devices. These findings demonstrate the considerable potential of machine-learning techniques for screening high-efficiency electrode materials and constructing HP 2D semiconductor devices.

A novel facet-driven carbon nanotube network reorganization method is developed to prepare large-area flexible freestanding transparent and conductive carbon nanofilms with synergistic enhancement of multiple properties, such as mechanical strength, transmittance and conductivity, and the area up to A3 size and even meter-length. Based on the film, a new smart window is fabricated.

Abstract

Large-area flexible transparent conductive films (TCFs) are highly desired for future electronic devices. Nanocarbon TCFs are one of the most promising candidates, but some of their properties are mutually restricted. Here, a novel carbon nanotube network reorganization (CNNR) strategy, that is, the facet-driven CNNR (FD-CNNR) technique, is presented to overcome this intractable contradiction. The FD-CNNR technique introduces an interaction between single-walled carbon nanotube (SWNT) and Cu─-O. Based on the unique FD-CNNR mechanism, large-area flexible reorganized carbon nanofilms (RNC-TCFs) are designed and fabricated with A3-size and even meter-length, including reorganized SWNT (RSWNT) films and graphene and RSWNT (G-RSWNT) hybrid films. Synergistic improvement in strength, transmittance, and conductivity of flexible RNC-TCFs is achieved. The G-RSWNT TCF shows sheet resistance as low as 69 Ω sq⁻¹ at 86% transmittance, FOM value of 35, and Young's modulus of ≈45 MPa. The high strength enables RNC-TCFs to be freestanding on water and easily transferred to any target substrate without contamination. A4-size flexible smart window is fabricated, which manifests controllable dimming and fog removal. The FD-CNNR technique can be extended to large-area or even large-scale fabrication of TCFs and can provide new insights into the design of TCFs and other functional films.

A nondestructive crystallographic scanning technique for 2D materials is developed, leveraging sticky-note-like van der Waals assembling–disassembling. This method visualizes the detailed crystallography of each grain within polycrystalline graphene using a single-atom-thick single-crystalline graphene and Raman signals varying dependent on interlayer twist angles. It facilitates a deeper understanding of 2D material properties, promoting further material engineering and optimization breakthroughs.

Abstract

Crystallographic characteristics, including grain boundaries and crystallographic orientation of each grain, are crucial in defining the properties of two-dimensional materials (2DMs). To date, local microstructure analysis of 2DMs, which requires destructive and complex processes, is primarily used to identify unknown 2DM specimens, hindering the subsequent use of characterized samples. Here, a nondestructive large-area 2D crystallographic analytical method through sticky-note-like van der Waals (vdW) assembling–disassembling is presented. By the vdW assembling of veiled polycrystalline graphene (PCG) with a single-atom-thick single-crystalline graphene filter (SCG-filter), detailed crystallographic information of each grain in PCGs is visualized through a 2D Raman signal scan, which relies on the interlayer twist angle. The scanned PCGs are seamlessly separated from the SCG-filter using vdW disassembling, preserving their original condition. The remaining SCG-filter is then reused for additional crystallographic scans of other PCGs. It is believed that the methods can pave the way for advances in the crystallographic analysis of single-atom-thick materials, offering huge implications for the applications of 2DMs.

In this work, the vacancy engineering of 2D transition metal chalcogenides (TMCs) is reviewed from two aspects: introduction strategy and application in photocatalysis. Subsequently, the photocatalytic process of 2D TMCs with vacancy engineering is introduced. The synergies between vacancy engineering and TMCs modified by other strategies are discussed. Finally, expectations and suggestions for the development of transition metal chalcogenides are presented.

Abstract

Transition metal chalcogenides (TMCs) are widely used in photocatalytic fields such as hydrogen evolution, nitrogen fixation, and pollutant degradation due to their suitable bandgaps, tunable electronic and optical properties, and strong reducing ability. The unique 2D malleability structure provides a pre-designed platform for customizable structures. The introduction of vacancy engineering makes up for the shortcomings of photocorrosion and limited light response and provides the greatest support for TMCs in terms of kinetics and thermodynamics in photocatalysis. This work reviews the effect of vacancy engineering on photocatalytic performance based on 2D semiconductor TMCs. The characteristics of vacancy introduction strategies are summarized, and the development of photocatalysis of vacancy engineering TMCs materials in energy conversion, degradation, and biological applications is reviewed. The contribution of vacancies in the optical range and charge transfer kinetics is also discussed from the perspective of structure manipulation. Vacancy engineering not only controls and optimizes the structure of the TMCs, but also improves the optical properties, charge transfer, and surface properties. The synergies between TMCs vacancy engineering and atomic doping, other vacancies, and heterojunction composite techniques are discussed in detail, followed by a summary of current trends and potential for expansion.

Herein, a novel dual-interactive-mode HMI system that utilizes the synergistic effects of a TENG and synaptic transistor to enhance interaction and information processing is proposed. The TENG component incorporates a poly-methyl meth-acrylate (PMMA)-NiCo₂S₄/S membrane and an Al electrode, allowing for both contact and non-contact interactions.

Abstract

Imitating human neural networks via bio-inspired electronics advances human-machine interfaces (HMI), overcoming von Neumann limitations and enabling efficient, low-energy data processing in the big data era. However, single-contact mode HMIs have inherent limitations in terms of their capabilities and performances, such as constrained adaptability to dynamic environments, and reduced cognitive processing capabilities. Here, a dual-interactive-mode HMI system based on a triboelectric nanogenerator (TENG) and heterojunction synaptic transistor (HJST) is proposed for both contact and non-contact applications. The TENG incorporates a poly-methyl meth-acrylate (PMMA)-NiCo₂S₄/S film, in which the NiCo₂S₄/S composite traps and blocks electrons to optimize charge generation and storage. The heterojunction structure, mitigates the Debye screening effect, thereby improving transistor characteristics and reliability. The integrated TENG-HJST system exhibits synaptic functions, including excitatory/inhibitory postsynaptic current (EPSC/IPSC), paired-pulse facilitation/depression (PPF/PPD), and synaptic plasticity, enabling emulation of neural behavior and advanced information processing. Moreover, neural morphology manipulation is demonstrated in practical tasks, such as controlling international chess games. By integrating the TENG-HJST device with a robotic hand, conscious artificial responses are generated, enhancing event accuracy. This breakthrough in dual-interactive-mode interfacing holds promise for HMI systems and neural prostheses.