Jiuxiang Dai

Owing to its large bandwidth, we identify layered semiconducting antiferromagnet CrPS₄ as an ideal candidate to realize field-effect transistors based on 2D magnetic materials. Low-temperature measurements exhibit a gate-tunable magnetoconductance exceeding 5000%, as well as the ability to continuously tune electrostatically the boundaries between different states in the magnetic phase diagram of the material.

Abstract

Using field-effect transistors (FETs) to explore atomically thin magnetic semiconductors with transport measurements is difficult, because the very narrow bands of most 2D magnetic semiconductors cause carrier localization, preventing transistor operation. Here, it is shown that exfoliated layers of CrPS₄—a 2D layered antiferromagnetic semiconductor whose bandwidth approaches 1 eV—allow the realization of FETs that operate properly down to cryogenic temperature. Using these devices, conductance measurements as a function of temperature and magnetic field are performed to determine the full magnetic phase diagram, which includes a spin-flop and a spin-flip phase. The magnetoconductance, which depends strongly on gate voltage, is determined. reaching values as high as 5000% near the threshold for electron conduction. The gate voltage also allows the magnetic states to be tuned, despite the relatively large thickness of the CrPS₄ multilayers employed in the study. The results show the need to employ 2D magnetic semiconductors with sufficiently large bandwidth to realize properly functioning transistors, and identify a candidate material to realize a fully gate-tunable half-metallic conductor.

Ultralong deep potassium storage enabled by a BiOCl/MXene van der Waals heterostructure is attained for conversion/alloying-type anodes, delivering 225 mAh g⁻¹ after 10 month cycling at 100 mA g⁻¹. The stabilized conversion and alloying/de-alloying reactions can be attributed to the improved dispersion of potassium ions during the initial optimized intercalation and facilitated ion diffusion kinetics.

Abstract

Conversion/alloying-type anodes are drawing attention due to their high theoretical capacities, but inferior reversibility, especially under low current densities, has hampered potential applications. Conventional strategies mainly focus on conversion/alloying processes, whereas the intercalation process is rarely analyzed. Herein, the intercalation process is correlated with conversion/alloying processes by ion dispersion states. BiOCl/Ti₃C₂T _x MXene van der Waals heterostructure is selected as a proof-of-concept system. Multifunctional MXenes not only contribute to atomic dispersion and boosted ion diffusion at the first cycle by constructing a novel heterostructure but serve as supporting frameworks to sustain long-term structural stability. Consequently, a cell with BiOCl/MXene anode delivers an ultralong cycle-life of running over ten months, maintaining a high capacity of 225 mAh g⁻¹ over 1300 cycles at 100 mA g⁻¹ and a retention of 81.3%. These findings verify that enhanced initial intercalation can facilitate higher reversibility and shed light on developing high-performance conversion/alloying-type anodes.

Laser-Induced Carbonization

Laser-induced carbonization is a viable method for creating anticounterfeiting tags on flexible printed circuit boards. In article number 2211762, Sunkook Kim, Hogun Park, and co-workers illustrate that using a laser, a pattern can be configured in any desired shape, such as a fingerprint. The laser beam is used to create random size carbonized spots that are distributed according to the pattern inputted into the laser. The pattern's outer circles can be extracted and digitized for authentication purposes.

In this work, a strain engineering technique is developed to controllably introduce an inhomogeneous strain in monolayer 1T-NbSe₂, a correlated insulator with charge density wave, and verify the existence of the multiple electronic-phase coexisting signature at the nanoscale with the combination of scanning tunneling microscopy/spectroscopy measurements and first-principles calculations.

Abstract

Monolayer transition metal dichalcogenides (TMDs) can host exotic phenomena such as correlated insulating and charge-density-wave (CDW) phases. Such properties are strongly dependent on the precise atomic arrangements. Strain, as an effective tuning parameter in atomic arrangements, has been widely used for tailoring material's structures and related properties, yet to date, a convincing demonstration of strain-induced dedicate phase transition at nanometer scale in monolayer TMDs has been lacking. Here, a strain engineering technique is developed to controllably introduce out-of-plane atomic deformations in monolayer CDW material 1T-NbSe₂. The scanning tunneling microscopy and spectroscopy (STM and STS) measurements, accompanied by first-principles calculations, demonstrate that the CDW phase of 1T-NbSe₂ can survive under both tensile and compressive strains even up to 5%. Moreover, significant strain-induced phase transitions are observed, i.e., tensile (compressive) strains can drive 1T-NbSe₂ from an intrinsic-correlated insulator into a band insulator (metal). Furthermore, experimental evidence of the multiple electronic phase coexistence at the nanoscale is provided. The results shed new lights on the strain engineering of correlated insulator and useful for design and development of strain-related nanodevices.

The degree of 1T-phase in monolayer molybdenum disulfide can be enhanced via Pd sulfidation, resulting in a considerably greater proportion of 1T fraction (≈86%) without using alkali-metal-based approaches. The maximized surface atom activation and metal utilization efficiency in Pd _x S _y /1T-MoS₂ lead to unprecedentedly high mass activity (−3444 A mg_Pd ⁻¹) and turnover frequency (1892 s⁻¹).

Abstract

For single-atom-layer hydrogen evolution reaction catalysts, enrichment of the 1T-phase in monolayer molybdenum disulfide is important to achieve ideal metal utilization efficiency and exposure of active surface atoms. Herein, it is discovered that the 1T-phase degree in monolayer MoS₂ can be enhanced through sulfidation of the Pd species deposited on MoS₂ (Pd _x S _y /1T-MoS₂). Raman and X-ray photoelectron spectroscopy reveal that the sulfidation-assisted phase transition results in considerably greater proportions of 1T-phase fraction (up to 86%) without using alkali-metal-based approaches. Observations of S-atom displacement/translation at the atomic level contribute to the understanding of the phase transformation of MoS₂. The maximized surface atom activation and metal utilization efficiency in Pd _x S _y /1T-MoS₂ lead to unprecedentedly high mass activity (−3444 A mg_Pd ⁻¹) and turnover frequency (1892 s⁻¹), three orders of magnitude higher than those of commercial Pt/C 10 wt% (3.6 A mg_Pt ⁻¹ and 3.6 s⁻¹). The sulfidation-assisted 1T-phase enrichment has major implications for the designs of efficient electrocatalysts through MoS₂ phase engineering.

Nature Communications, Published online: 24 April 2023; doi:10.1038/s41467-023-37887-x

The integration of high-κ dielectric layers with 2D semiconductors is essential for electronic applications, but remains challenging. Here the authors report a dry transfer method of wafer-scale Al2O3 and HfO2 thin films for the realization of top-gated monolayer MoS2 transistors and logic gates.

Light: Science & Applications, Published online: 25 April 2023; doi:10.1038/s41377-023-01092-8

Upconversion of light from its fundamental wavelength (FW) to its second harmonic (SH) is enhanced 32× in micron-scale lithium niobate (LiNbO3) spheres through near-field interactions with gold (Au) nanoparticles.

In this work, the twisted 3R-stacked MoSe₂ spirals with specific SD arms are successfully synthesized on SiO₂/Si substrates for the first time, via designing a water-assisted APCVT approach. Significantly, the broad available band response and up to three orders of magnitude enhancement of the SHG effects are demonstrated in twisted 3R stacked MoSe₂ spirals.

Abstract

Enhanced second-harmonic generation (SHG) responses are reported in monolayer transition metal dichalcogenides (e.g., MX₂, M: Mo, W; X: S, Se) due to the broken symmetries. The 3R-like stacked MX₂ spiral structures possessing the similar broken inversion symmetry should present dramatically enhanced SHG responses, thus providing great flexibility in designing miniaturized on-chip nonlinear optical devices. To achieve this, the first direct synthesis of twisted 3R-stacked chiral molybdenum diselenide (MoSe₂) spiral structures with specific screw dislocations (SD) arms is reported, via designing a water-assisted chemical vapor transport (CVT) approach. The study also clarifies the formation mechanism of the MoSe₂ spiral structures, by precisely regulating the precursor supply accompanying with multiscale characterizations. Significantly, an up to three orders of magnitude enhancement of the SHG responses in twisted 3R stacked MoSe₂ spirals is demonstrated, which is proposed to arise from the synergistic effects of broken inversion symmetry, strong light–matter interaction, and band nesting effects. Briefly, the work provides an efficient synthetic route for achieving the 3R-stacked TMDCs spirals, which can serve as perfect platforms for promoting their applications in on-chip nonlinear optical devices.

Ultrathin, free-standing, and surfactant-free bismuth nanosheets were synthesized by the controllable reduction-melting-crystallization method. Increasing the high-index facets of bismuth nanosheets can modify their surface electronic structures to strengthen the adsorption of CO₂, lower the reaction energy barriers, and promote CO₂ reduction reaction selectivity and activity for formate in wide pH environments, realizing high-energy-efficiency CO₂-to-HCOOH conversion in a flow cell system.

Abstract

Two-dimensional low-melting-point (LMP) metal nanocrystals are attracting increasing attention with broad and irreplaceable applications due to their unique surface and topological structures. However, the chemical synthesis, especially the fine control over the nucleation (reduction) and growth (crystallization), of such LMP metal nanocrystals remains elusive as limited by the challenges of low standard redox potential, low melting point, poor crystalline symmetry, etc. Here, a controllable reduction-melting-crystallization (RMC) protocol to synthesize free-standing and surfactant-free bismuth nanocrystals with tunable dimensions, morphologies, and surface structures is presented. Especially, ultrathin bismuth nanosheets with flat or jagged surfaces/edges can be prepared with high selectivity. The jagged bismuth nanosheets, with abundant surface steps and defects, exhibit boosted electrocatalytic CO₂ reduction performances in acidic, neutral, and alkaline aqueous solutions, achieving the maximum selectivity of near unity at the current density of 210 mA cm^–2 for formate evolution under ambient conditions. This work creates the RMC pathway for the synthesis of free-standing two-dimensional LMP metal nanomaterials and may find broader applicability in more interdisciplinary applications.

This review provides a critical summary on the recent development of substrate engineering strategies, in specific, surface-stepping approaches, chemical-functionalization methods, substrate seeding strategies and so on, with the aim of the growth of large-scale 2D transition metal dichalcogenides (TMDs). The contribution might guide the deep understanding on the controlled growth of high-quality 2D TMDs toward their industrial-scale practical applications.

Abstract

The large-scale production of 2D transition metal dichalcogenides (TMDs) is essential to realize their industrial applications. Chemical vapor deposition (CVD) has been considered as a promising method for the controlled growth of high-quality and large-scale 2D TMDs. During a CVD process, the substrate plays a crucial role in anchoring the source materials, promoting the nucleation and stimulating the epitaxial growth. It thus significantly affects the thickness, microstructure, and crystal quality of the products, which are particularly important for obtaining 2D TMDs with expected morphology and size. Here, an insightful review is provided by focusing on the recent development associated with the substrate engineering strategies for CVD preparation of large-scale 2D TMDs. First, the interaction between 2D TMDs and substrates, a key factor for the growth of high-quality materials, is systematically discussed by combining the latest theoretical calculations. Based on this, the effect of various substrate engineering approaches on the growth of large-area 2D TMDs is summarized in detail. Finally, the opportunities and challenges of substrate engineering for the future development of 2D TMDs are discussed. This review might provide deep insight into the controllable growth of high-quality 2D TMDs toward their industrial-scale practical applications.

Antimonene spirals are epitaxially grown on a germanium substrate. Owing to the presence of a helical dislocation, the as-grown spiral is anisotropically strained. The strain in the spiral can be changed by scanning tunneling microscopy tip manipulation, resulting in modulations of the electronic density of states and the work function.

Abstract

Van der Waals (vdW) layered materials exhibit fruitful novel physical properties. The energy band of such materials depends strongly on their structures, and a tremendous variation in their physical properties can be deduced from a tiny change in inter-layer spacing, twist angle, or in-plane strain. In this work, a kind of vdW layered material of spiral antimonene is constructed, and the strain effects in the material are studied. The spiral antimonene is grown on a germanium (Ge) substrate and is induced by a helical dislocation penetrating through few atomic-layers of antimonene (β-phase). The as-grown spiral is intrinsically strained, and the lattice distortion is found to be pinned around the dislocation. Both spontaneous inter-layer twist and in-plane anisotropic strain are observed in scanning tunneling microscope (STM) measurements. The strain in the spiral antimonene can be significantly modified by STM tip interaction, leading to a variation in the surface electronic density of states (DOS) and a large modification in the work function of up to a few hundreds of millielectron-volts (meV). Those strain effects are expected to have potential applications in building up novel piezoelectric devices.

T_d-MoTe₂ is type-II Weyl semimetal, which have great potential in THz detection via peculiar topology band structure and exotic transport. T_d-MoTe₂/mica structure grown by MBE is first reported as a photodetector from THz to SMM regime. T_d-MoTe₂/mica detectors show flexible and high-resolution terahertz imaging, which is suitable for smart wearable devices, contributing to the application of terahertz technology in daily life.

Abstract

Flexible photodetectors with ultra-broadband sensitivities, fast response, and high responsivity are crucial for wearable applications. Recently, van der Waals (vdW) Weyl semimetals have gained much attention due to their unique electronic band structure, making them an ideal material platform for developing broadband photodetectors from ultraviolet (UV) to the terahertz (THz) regime. However, large-area synthesis of vdW semimetals on a flexible substrate is still a challenge, limiting their application in flexible devices. In this study, centimeter-scale type-II vdW Weyl semimetal, T_d-MoTe₂ films, are grown on a flexible mica substrate by molecular beam epitaxy. A self-powered and flexible photodetector without an antenna demonstrated an outstanding ability to detect electromagnetic radiation from UV to sub-millimeter (SMM) wave at room temperature, with a fast response time of ≈20 µs, a responsivity of 0.53 mA W⁻¹ (at 2.52 THz), and a noise-equivalent power (NEP) of 2.65 nW Hz^−0.5 (at 2.52 THz). The flexible photodetectors are also used to image shielded items with high resolution at 2.52 THz. These results can pave the way for developing flexible and wearable optoelectronic devices using direct-grown large-area vdW semimetals.

The M3D integration of high-performance aligned carbon nanotube (A-CNT) transistors and ICs is demonstrated, featuring a low-κ (~3) interlayer dielectric layer with low parasitic effects and excellent planarization. A high-quality A-CNT film with a carrier mobility of 650 cm² V⁻¹ s⁻¹ is prepared at top layer enabling the upper CNT FETs to exhibit high on-state current (1 mA μm⁻¹) and peak transconductance (0.98 mS μm⁻¹). Five-stage ring oscillators utilizing the M3D architecture show a gate propagation delay of 17 ps and an active region of approximately 100 μm², representing the fastest and most compact M3D ICs to date.

Abstract

Carbon nanotube field-effect transistors (CNT FETs) have been demonstrated to exhibit high performance only through low-temperature fabrication process and require a low thermal budget to construct monolithic three-dimensional (M3D) integrated circuits (ICs), which have been considered a promising technology to meet the demands of high-bandwidth computing and fully functional integration. However, the lack of high-quality CNT materials at the upper layer and a low-parasitic interlayer dielectric (ILD) makes the reported M3D CNT FETs and ICs unable to provide the predicted high performance. In this work, we demonstrate a multilayer stackable process for M3D integration of high-performance aligned carbon nanotube (A-CNT) transistors and ICs. A low-κ (~3) interlayer SiO₂ layer is prepared from spin-on-glass (SOG) through processes with a highest temperature of 220°C, presenting low parasitic capacitance between two transistor layers and excellent planarization to offer an ideal surface for the A-CNT and device fabrication process. A high-quality A-CNT film with a carrier mobility of 650 cm² V^–1 s^–1 is prepared on the ILD layer through a clean transfer process, enabling the upper CNT FETs fabricated with a low-temperature process to exhibit high on-state current (1 mA μm^–1) and peak transconductance (0.98 mS μm^–1). The bottom A-CNT FETs maintain pristine high performance after undergoing the ILD growth and upper FET fabrication. As a result, 5-stage ring oscillators utilizing the M3D architecture show a gate propagation delay of 17 ps and an active region of approximately 100 μm², representing the fastest and the most compact M3D ICs to date.

A polar tungsten bronze, Pb_1.91K_3.22□_0.85Li_2.96Nb₁₀O₃₀, reveals extremely large second-harmonic generation efficiency of ≈71.5 times that of KH₂PO₄ attributed to the constructive effect of moments arising from the well-aligned distorted NbO₆ octahedra, structural distortions at the quadrangular sites with vacancies, and strong interactions of the backbone with highly polarizable cations.

Abstract

A polar tetragonal tungsten bronze, Pb_1.91K_3.22□_0.85Li_2.96Nb₁₀O₃₀ (□: vacancies), has been successfully synthesized by a high temperature solid-state reaction. Single crystal and powder X-ray diffraction indicate that the structure of Pb_1.91K_3.22□_0.85Li_2.96Nb₁₀O₃₀ crystallizing in the noncentrosymmetric (NCS) space group, P4bm, consists of 3D framework with highly distorted NbO₆, LiO₉, PbO₁₂, and (Pb/K)O₁₅ polyhedra. While NCS Pb_1.91K_3.22□_0.85Li_2.96Nb₁₀O₃₀ undergoes a reversible phase transition between polar (P4bm) and nonpolar (P4/mbm) structure at around 460 °C, the material decomposes to centrosymmetric Pb_1.45K_3.56Li_3.54Nb₁₀O₃₀ (P4/mbm) once heated to 1200 °C. Powder second-harmonic generation (SHG) measurements with 1064 nm radiation indicate that Pb_1.91K_3.22□_0.85Li_2.96Nb₁₀O₃₀ exhibits a giant phase-matchable SHG intensity of ≈71.5 times that of KH₂PO₄, which is the strongest intensity in the visible range among all nonlinear optical materials reported to date. The observed colossal SHG should be attributable to the synergistic effect of dipole moments from the well-aligned NbO₆ octahedra, the constituting distortive channels with vacancies, and highly polarizable cations.

Colossal topological Hall effect (THE) is observed in noncoplanar ferromagnet Cr₅Te₆ thin films. The theoretical calculations further corroborate the existence of the THE, which is attributed to the noncoplanar spin textures induced by the interaction of the in-plane ferromagnetism and antiferromagnetism infrastructures. This work paves the way to the robust chiral spin textures in large-area ferromagnetic films for chiral spintronics.

Abstract

The topological Hall effect (THE) is critical to the exploration of the spin chirality generated by the real-space Berry curvature, which has attracted worldwide attention for its prospective applications in spintronic devices. However, the prominent THE remains elusive at room temperature, which severely restricts the practical integration of chiral spin textures. Here, a colossal intrinsic THE is showed up to ≈1.6 µΩ cm in large-area ferromagnet Cr₅Te₆ thin films epitaxially grown by pulsed laser deposition. Such a THE can be maintained until 270 K, which is attributed to the field-stimulated noncoplanar spin textures induced by the interaction of the in-plane ferromagnet and antiferromagnet infrastructures. The first-principles calculations further verify the considerable Dzyaloshinskii-Moriya interaction in Cr₅Te₆. This work not only paves the way for robust chiral spin textures near room temperature in large-area low-dimensional ferromagnetic films for practical applications, but also facilitates the development of high-density and dissipationless spintronic devices.

A unique strain-mediated lattice rotation strategy is introduced via nanocompositing to upsurge the optimized limits in the composition-to-structural pathway on rationally engineering the efficient thermoelectric material. The obtained ultra-high ZT_max (=1.13 at T = 773 K) successfully demonstrates the effectiveness of doping-induced structural variation and lattice rotation strategy, unlocking new prospects to develop atomistic lattice engineering in thermoelectric materials.

Abstract

A unique strain-mediated lattice rotation strategy is introduced via nanocompositing to upsurge the optimized limits in the composition-to-structural pathway on rationally engineering the efficient thermoelectric material. In this study, a special lattice rotation via strain engineering is realized to optimize the desired electronic and chemical environment for enhancing thermoelectric properties in n-type Bi₂S₂Se. This approach results in a unique transport phenomenon to assist high-energy electrons in transferring through the optimized transport channels, and appropriate structure disparity to significantly localize phonons. As a result, Sb over Cl doping in Bi₂S₂Se gently reduces E _g and introduces defect states in bandgap with shifting down the Fermi level, thus causing increase in carrier concentration, which contributes to a higher power factor of ≈7.18 µW cm⁻¹ K⁻² (at T = 773 K). Besides, a lower thermal conductivity of ≈0.49 W m⁻¹ K⁻¹ is driven through lattice strain and defect engineering. Consequently, an ultra-high ZT _max = 1.13 (at T = 773 K) and a high ZT _ave = 0.54 (323 K-773 K) are realized. This study not only leads to an extraordinary thermoelectric performance but also reveals a unique paradigm for electron transportation and phonon localization via lattice strain engineering.

The metallic nanoparticles’ formation and growth mechanisms on carbon substrates are revealed via in situ transmission electron microscopy (TEM). Nanoparticles with thermodynamically stable phase formed on both carbon substrates are independent of their size. Nanoparticles on reduced graphene oxide formed at higher temperatures, demonstrate a high degree of stabilization considering less catalytic graphitization, stronger interaction compared to amorphous carbon.

Abstract

Understanding the thermal decomposition of metal salt precursors on carbon structures is essential for the controlled synthesis of metal-decorated carbon nanomaterials. Here, the thermolysis of a Ni precursor salt, NiCl₂·6H₂O, on amorphous carbon (a-C) and graphene oxide (GO) substrates is explored using in situ transmission electron microscopy. Thermal decomposition of NiCl₂·6H₂O on GO occurs at higher temperatures and slower kinetics than on a-C substrate. This is correlated to a higher activation barrier for Cl₂ removal calculated by the density functional theory, strong Ni-GO interaction, high-density oxygen functional groups, defects, and weak van der Waals using GO substrate. The thermolysis of NiCl₂·6H₂O proceeds via multistep decomposition stages into the formation of Ni nanoparticles with significant differences in their size and distribution depending on the substrate. Using GO substrates leads to nanoparticles with 500% smaller average sizes and higher thermal stability than a-C substrate. Ni nanoparticles showcase the fcc crystal structure, and no size effect on the stability of the crystal structure is observed. These findings demonstrate the significant role of carbon substrate on nanoparticle formation and growth during the thermolysis of carbon–metal heterostructures. This opens new venues to engineer stable, supported catalysts and new carbon-based sensors and filtering devices.

The discovery of high-temperature antiferromagnetism in NiSi with T _N ⩾ 700 K is reported. The antiferromagnetism is accompanied by a small uncompensated ferromagnetic component, which can be independently tuned by a small magnetic field, resulting in a one-step magnetic switching transition. Thus, a new venue for spintronics research is envisaged in this technologically important material.

Abstract

Envisaging antiferromagnetic spintronics pivots on two key criteria of high transition temperature and tuning of underlying magnetic order using straightforward application of magnetic field or electric current. Here, it is shown that NiSi metal can provide suitable new platform in this quest. First, the study unveils high-temperature antiferromagnetism in single-crystal NiSi with Néel temperature, T _N ⩾ 700 K. Antiferromagnetic order in NiSi is accompanied by non-centrosymmetric magnetic character with small ferromagnetic component in the a–c plane. Second, it is found that NiSi manifests distinct magnetic and electronic hysteresis responses to field applications due to the disparity in two moment directions. While magnetic hysteresis is characterized by one-step switching between ferromagnetic states of uncompensated moment, electronic behavior is ascribed to metamagnetic switching phenomena between non-collinear spin configurations. Importantly, the switching behaviors persist to high temperature. The properties underscore the importance of NiSi in the pursuit of antiferromagnetic spintronics.

Mechanically driven reversible polarization switching is realized in ferroelectric BiFeO₃ thin films. The reversible mechanical switching arises from the interplay among the flexoelectric effect, the piezoelectric effect, and the internal upward built-in field in BiFeO₃ films. This study gains a deeper insight into the mechanism and control of mechanically driven ferroelectric switching, and provides guidance for exploring potential ferroelectric-based electro-mechanical microelectronics.

Abstract

Mechanically driven polarization switching via scanning probe microscopy provides a valuable voltage-free strategy for designing ferroelectric nanodomain structures. However, it is still challenging to realize reversible polarization switching with mechanical forces. Here, the mechanically driven reversible polarization switching observed in imprinted ferroelectric BiFeO₃ thin films is reported, i.e., up-to-down switching by a sharp scanning tip and down-to-up switching by a blunt tip. Free energy calculations, phase-field simulations, and piezoresponse force microscopy reveal that reversible mechanical switching arises from the interplay among the flexoelectric effect, the piezoelectric effect, and the internal upward built-in field in BiFeO₃ films. This study gains a deeper insight into the mechanism and control of mechanically driven polarization switching, and provides guidance for exploring potential ferroelectric-based electro-mechanical microelectronics.

Light: Science & Applications, Published online: 21 April 2023; doi:10.1038/s41377-023-01139-w

The first family of far-infrared transparent conductive materials was developed by increasing the optical dielectric constant.

Here, ‘Sandwich-like’ porous metal-organic frameworks / 2D conductive heterostructures for realizing ultra-stable and selective surface reactivity of conductive 2D materials as proven by chemical sensing case study and multiscale simulations are described for the first time.

Abstract

2D transition metal dichalcogenides (TMDs) have significant research interests in various novel applications due to their intriguing physicochemical properties. Notably, one of the 2D TMDs, SnS₂, has superior chemiresistive sensing properties, including a planar crystal structure, a large surface-to-volume ratio, and a low electronic noise. However, the long-term stability of SnS₂ in humid conditions remains a critical shortcoming towards a significant degradation of sensitivity. Herein, it is demonstrated that the subsequent self-assembly of zeolite imidazolate framework (ZIF-8) can be achieved in situ growing on SnS₂ nanoflakes as the homogeneous porous materials. ZIF-8 layer on SnS₂ allows the selective diffusion of target gas species, while effectively preventing the SnS₂ from severe oxidative degradation. Molecular modeling such as molecular dynamic simulation and DFT calculation, further supports the mechanism of sensing stability and selectivity. From the results, the in situ grown ZIF-8 porous membrane on 2D materials corroborates the generalizable strategy for durable and reliable high-performance electronic applications of 2D materials.

Targeted modified anions can induce ferroelectricity and result in an enhanced ferroelectric ordering indirectly. The facile optimization strategy takes full advantage of structural flexibility of hybrid materials and provides a totally novel and expansive platform for construction of ferroelectrics and optimization of ferroelectricity in corresponding fields.

Abstract

Construction of ferroelectric and optimization of macroscopic polarization has attracted tremendous attention for next generation light weight and flexible devices, which brings fundamental vitality for molecular ferroelectrics. However, effective molecular tailoring toward cations makes ferroelectric synthesis and modification relatively elaborate. Here, the study proposes a facile method to realize triggering and optimization of ferroelectricity. The experimental and theoretical investigation reveals that orientation and alignment of polar cations, dominated factors in molecular ferroelectrics, can be controlled by easily processed anionic modification. In one respect, ferroelectricity is induced by strengthened intermolecular interaction. Moreover, ≈50% of microscopic polarization enhancement (from 8.07 to 11.68 µC cm⁻²) and doubling of equivalent polarization direction (from 4 to 8) are realized in resultant ferroelectric FEtQ2ZnBrI₃ (FEQZBI, FEtQ = N-fluoroethyl-quinuclidine). The work offers a totally novel platform for control of ferroelectricity in organic–inorganic hybrid ferroelectrics and a deep insight of structure–property correlations.

The features of this review include 1) synthetic strategies, including doping heteroatoms, matrix-assisted method, and self-protection method; 2) performance regulations, such as multicolor phosphorescence, lifetime regulation, the conversion from phosphorescence to delayed fluorescence, and room temperature phosphorescence (RTP) carbon dots (CDs) in water; 3) applications of RTP CDs in anti-counterfeiting, information encryption, sensing, white light emitting diodes, and biomedicine.

Abstract

Room temperature phosphorescence (RTP) materials have drawn considerable attention by virtue of their outstanding features. Compared with organometallic complexes and pure organic compounds, carbon dots (CDs) have emerged as a new type of RTP materials, which show great advantages, such as moderate reaction condition, low toxicity, low cost, and tunable optical properties. In this review, the important progress made in RTP CDs is summarized, with an emphasis on the latest developments. The synthetic strategies of RTP CDs will be comprehensively summarized, followed by detailed introduction of their performance regulation and potential applications in anti-counterfeiting, information encryption, sensing, light-emitting diodes, and biomedicine. Finally, the remaining major challenges for RTP CDs are discussed and new opportunities in the future are proposed.

The monolayer WS₂ crystal field can effectively split the electronic bands of the Ce dopant’ f orbital. The electrons in the split electronic bands can bind the holes in the valence band maximum of the Ce-WS₂, forming optical bright excitons. These excitons collide with the free A excitons when increasing the pump fluences, reducing the A exciton's lifetime.

Abstract

Substitutional lanthanide doping of 2D transition metal dichalcogenides (TMDs) is expected to be a promising strategy to engineer optical, electronic, and optoelectronic properties of TMDs. Understanding the interactions between lanthanide dopants and 2D TMDs host is one of the key problems to be resolved for their profound research studies. Herein, the interactions between Ce dopants and monolayer WS₂ in a physical vapor deposition grown Ce-doped WS₂ monolayer are studied by combining scanning tunneling microscopy with optical characterizations with high spatial and temporal resolution. It is found that the highly anisotropic crystal field can effectively split the energy levels of the Ce dopants’ f orbital. The electrons in the split energy levels can bind the holes in the valence band maximum of the Ce-doped WS₂, forming optical bright excitons. These excitons collide with the free A excitons when increasing the pump fluences, reducing the A exciton's lifetime. This study may be beneficial for the design and fabrication of optical, electronic, and optoelectronic devices based on lanthanide-doped TMDs.