Jing Zhang

A series of Er³⁺-doped BaF₂ crystals is studied to identify the most efficient converters from Vis to NIR wavelengths. The sample containing 5 mol.% of Er³⁺ exhibits a remarkable PLQY of 153% for the NIR emission of Er³⁺ ions under 405 nm excitation due to the down-conversion within the studied material. The short-circuit current of a Ge-photodiode is calculated and then experimentally validated.

Abstract

Down-conversion (DC) is a phenomenon that can enable the observation of photoluminescent quantum yield (PLQY) values exceeding 100%. A comprehensive study of the DC properties of BaF₂–based single crystals with different Er³⁺ doping levels (1–25 mol.%) is presented. The samples exhibit a PLQY of 110% in the 1550–1650 nm under 405 nm excitation. This remarkable PLQY is attributed to a cross-relaxation process within the energy levels of Er³⁺. Furthermore, when considering all emitted photons in the 1000–1650 nm range, the PLQY reaches 153% for a sample doped with 5 mol.% of Er³⁺. By integrating the emission of this single crystal with a Ge diode, serving as an example of a photovoltaic device sensitive to short-wave infrared light, a significant enhancement in short-circuit current is demonstrated. In a broader context, the presented material holds promise for improving the spectral response of low-bandgap photovoltaic devices.

A new class of Yb³⁺/Er³⁺-doped Cs₂ZrF₆ UCNCs that exhibit thermal enhancement of upconversion is reported for the first time. Further incorporation of Na⁺ ions enables the fabrication of Cs₂ZrF₆:Yb/Er UCNCs with slightly reduced size but highly improved crystallinity and consequently largely enhanced UC emission intensity, making them promising candidates as supersensitive nanothermometer for ratiometric temperature sensing.

Abstract

Alkaline zirconium fluorides (A_xZr_yF_x+y, A = Li, Na, and K), featuring unique crystallographic structures, have recently emerged as a class of attractive hosts for fabricating lanthanide (Ln³⁺)-doped upconversion nanocrystals (UCNCs) that exhibited distinct morphology, upconversion luminescence (UCL) performance, and physicochemical property. In this paper, for the first time the controlled preparation of Yb³⁺/Er³⁺-doped UCNCs is reported based on the trigonal Cs₂ZrF₆ host, leading to tunable morphology and size of the resulting UCNCs by varying the reaction temperature and time. By further incorporating Na⁺ ions into the Cs₂ZrF₆ crystal lattice, sub-10 nm Yb³⁺/Er³⁺/Na⁺ tridoped UCNCs with highly improved crystallinity and thus greatly enhanced UCL intensity are obtained. Moreover, these resulting UCNCs display abnormal thermal enhancement of UCL over a temperature range from 333 to 493 K, enabling the fabrication of supersensitive luminescent nanothermometers for temperature sensing. Based on the luminescence intensity ratio of two nonthermally coupled levels (i.e., ⁴F_9/2 and ²H_11/2) of Er³⁺, the as-prepared Cs₂ZrF₆:Yb/Er/Na UCNCs exhibit an extremely large absolute sensitivity of 177.3% K⁻¹ and a considerably high relative sensitivity of 1.52% K⁻¹ at 333 K. These results unambiguously demonstrate that Cs₂ZrF₆ is a suitable host material for preparing small-sized Ln³⁺-doped UCNCs as nanothermometer for high-performance ratiometric temperature sensing.

Four classes of tessellations composed of chains of non-hexagonal rings separated by nanoribbons of hexagonal rings are established to construct highly stable 2D crystals. Based on the interaction between polygonal rings, a modified Read–Shockley model is further proposed to describe the stability of such 2D crystals, and peculiar topological electronic structures are found.

Abstract

Reticular chemistry has been a cornerstone in the design of novel 2D materials. Despite numerous possibilities for topological arrangements, only a few with high symmetry can form stable networks. Here, starting from 2D carbons, four types of highly stable tessellations are discovered, which consist of chains of non-hexagonal rings separated by hexagonal ribbons. A modified Read–Shockley model is established to perfectly describe the stability of these highly stable frameworks, which is based on the interaction between non-hexagonal rings. Moreover, these four types of tessellations and the modified Read–Shockley model are found to be of general validity in designing highly stable 2D materials, which is verified by the calculations on polymorphs of boron nitride and molybdenum disulfide. Besides, among the studied 2D carbon allotropes, two semi-metallic structures with highly anisotropic Dirac cones and one semimetal with a Dirac nodal line at the Fermi level are discovered, as protected by their D _2h symmetry. Spin-orbital coupling is further found to open small bandgaps for these three Dirac structures, making them nontrivial topological insulators. The in-depth understanding of the stability of 2D crystals in this study provides a new way for rational design of 2D crystals that may show peculiar electronic structures.

Nature Nanotechnology, Published online: 18 March 2024; doi:10.1038/s41565-024-01647-9

Author Correction: 3D nanofabricated soft microrobots with super-compliant picoforce springs as onboard sensors and actuators

Nature Materials, Published online: 18 March 2024; doi:10.1038/s41563-024-01844-w

Single-crystal black phosphorus nanoribbons have been grown through chemical vapour transport, using black phosphorus nanoparticles as seeds. The nanoribbons orient exclusively along the zigzag direction and have good semiconductor properties that render them suitable for use as channel material in field-effect transistors.

npj 2D Materials and Applications, Published online: 18 March 2024; doi:10.1038/s41699-024-00460-1

Hard ferromagnetism in van der Waals Fe₃GaTe₂ nanoflake down to monolayer

This work reports the direct synthesis of novel 1D-defect-induced Co₄Te₇ superlattices on lattice-matched SrTiO₃(001) substrates, derived from 1T-CoTe₂ with spontaneously-evolved Te line defects in the upper Te layer. The detailed atomic structure of monolayer Co₄Te₇ and its distinctive electronic states related to flat bands are unveiled by scanning tunneling microscopy/spectroscopy (STM/STS).

Abstract

1D structures/patterns (e.g., line defect arrays, 1D Moiré patterns) embedded in 2D materials provide fascinating platforms for exploring versatile intriguing phenomena, for example, 1D Luttinger liquids and charge density waves (CDWs). Despite persistent efforts, incorporating periodic 1D patterns into 2D materials remains an ongoing pursuit. Herein, the direct preparation of monolayer 1D-defect-induced Co₄Te₇ superlattices (with periodic Te defect lines in the upper Te layer in 1T-CoTe₂) is reported, on lattice-matched SrTiO₃(001) (STO(001)) substrates via molecular beam epitaxy (MBE). Utilizing on-site scanning tunneling microscopy/spectroscopy (STM/STS) combined with density functional theory (DFT) calculations, the detailed atomic structure of monolayer Co₄Te₇ is identified, and its formation mechanisms from the synergistic effects of the Co/Te precursor ratio and adlayer-substrate interfacial coupling are uncovered. The potential flat-band feature of the monolayer Co₄Te₇ is also unveiled. This work should hereby offer valuable insights into the engineering of periodic 1D-defect patterns in 2D materials, as well as the atomic-scale structure and electronic property characterizations, thus paving ways for their intriguing property investigations.

This study reveals the potentials and limitations of an amoeboid cell-driven system that moves microparticles as large as red blood cells and up to ≈240 microns in diameter while exerting forces in the sub-piconewton range on cargoes. The cell-generated forces increase in response to persistent drag on the cargo, highlighting the mechanoresponsive adaptation of this biohybrid system in complex environments.

Abstract

The integration of motile cells into biohybrid microrobots offers unique properties such as sensitive responses to external stimuli, resilience, and intrinsic energy supply. Here, biohybrid cell–cargo systems that are driven by amoeboid Dictyostelium discoideum cells are studied and how the cargo speed and the resulting viscous drag force scales with increasing radius of the spherical cargo particle are explored. Using a simplified geometrical model of the cell–cargo interaction, the findings toward larger cargo sizes, which are not accessible with the experimental setup, are extrapolated and a maximal cargo size is predicted beyond which active cell-driven movements will stall. The active forces exerted by the cells to move a cargo show mechanoresponsive adaptation and increase dramatically when challenged by an external pulling force, a mechanism that may become relevant when navigating cargo through complex heterogeneous environments.

Nature Synthesis, Published online: 14 March 2024; doi:10.1038/s44160-024-00504-w

Artificial intelligence is used to automate the synthesis of single molecules using the tip of a scanning probe microscope, as well as to extract chemical information from these reactions.

Nature Photonics, Published online: 14 March 2024; doi:10.1038/s41566-024-01390-6

Time-resolved lightwave-driven scanning tunnelling spectroscopy is developed to investigate how the spin–orbit-split energy levels of a selenium vacancy within a WSe2 monolayer shift under phonon displacement. Ultrafast snapshots of the electronic tunnelling spectra reveal transient energy shifts up to 40 meV.

A large-scale theory-driven approach predicts many new 2D materials

Lattice plainification using a grid-design strategy facilitates superior cooling capability in medium-temperature lead selenide thermoelectrics.

A two-photon absorbing Ir(III) complex is used as an antenna to sensitize Eu(III)-based emission from Eu_0.3La_0.7F₃ particles. The resulting Eu_0.3La_0.7F₃@Ir composite, in which the existence of Ir → Eu energy transfer is demonstrated, exhibits bright and color-tunable light emission under both UV–vis and near-infrared excitation. Its emission is analyzed on a particle-by-particle basis by photoluminescence lifetime imaging microscopy.

Abstract

The surface of Eu_0.3La_0.7F₃ submicron particles is functionalized with a blue-emitting Ir(III) complex (1) specifically designed to coordinate lanthanide(III) ions efficiently through a carboxylic unit. In this Eu_0.3La_0.7F₃@1 composite, the Ir(III) complexes are randomly coordinated to either superficial La(III) ions or Eu(III) ions (Ir-La_surface and Ir-Eu_surface pairs, respectively) and its color emission, a balance between blue (Ir-based) and red (Eu-based) light, can be tuned as a function of the excitation wavelength. Irradiation at the maximum of the excitation band in 1 promotes blue emission from Ir-La_surface pairs and red emission from Eu_surface ions sensitized by Ir → Eu_surface energy transfer (EnT). At λ_exc = 396 nm (maximum of the Eu(III) ⁵L₆ ← ⁷F₀ absorption band) the red emission from inner Eu(III) ions becomes dominant. Excitation of 1 can also be achieved by two photon-absorption (TPA) since this complex has a moderate cross-section of σ₂ = 9.4 ± 1.0 GM at 780 nm (σ₂ = 5.8 ± 0.6 GM at 800 nm). Phosphorescence lifetime imaging (PLIM) allows the emission of individual particles to be visualized and the Ir-, Eu_surface-, and Eu_core-based emissions can be distinguished due to the significant differences in their respective emission lifetimes.

A novel inorganic photochromic luminescent material, La₂MgSnO₆:Er,Fe, with reversible photochromic property induced by 275 and 365 nm is fabricated. By coupling different excitation bands of Er³⁺ to the photochromic responsive/non-responsive range of the material, an excitation wavelength-dependent dark-field selective dual-mode readout method, including static nondestructive readout in general and time-limited dynamic readout, is achieved.

Abstract

Inorganic photochromic luminescent materials hold immense promise as potential candidates for optical information storage applications. Unfortunately, static and single reading mode of photochromic luminescent materials in bright and dark environments pose a security threat to the stored information. Here, a novel material La₂MgSnO₆:Er³⁺,Fe³⁺ is developed, possessing both reversible photochromic and adjustable upconversion/downconversion photoluminescent (PL) properties. Upon exposure to 275 nm ultraviolet (UV) light, the sample changes in color from white to brown. And this transformation rapidly reverses when exposed to 365 nm UV light, resulting in a corresponding alteration in luminescence intensity. Notably, when combined with photochromic, the 980 nm excited upconversion PL maintains stable luminescence, while the 365 nm excited downconversion PL exhibits significant intensity changes. Inspired by this unique feature, a dark-field selective dual-mode reading is proposed that depends on the excitation wavelength, including static decrypt in long-time cases and dynamic reading in time-limited situations. These findings have the potential to revolutionize high-security data storage applications and drive advancements in the field.

Angle-resolved polarized Raman spectroscopy (ARPRS) of CrOCl under two typical and accurate configurations is systematically investigated for reliable crystal orientation. The phase-dependent ARPRS analysis emphasizes the importance of eliminating the analyzer angular deviation. 3D ARPRS reveals the high sensitivity of phase-dependent ARPRS in detecting LD-related effects. These results offer in-depth comprehension on precise controlling configurations for probing the photo-induced effects.

Abstract

Within angle-resolved polarized Raman spectroscopy (ARPRS) experiments, ensuring accurate configurations is crucial for obtaining reliable results, especially when dealing with anisotropic materials like CrOCl with anisotropic crystal structure and phonon properties. However, comprehensive understanding of phase-dependent ARPRS and the calibration of phase angle on anisotropic phonon modes from a crystallographic perspective are still lacking. Herein, detailed investigation on phase-dependent ARPRS and looked into the anisotropic photo-phonon interaction in CrOCl through in situ ARPRS is conducted. The Raman tensors and crystal orientation are acquired under two typical configurations. Phase-dependent ARPRS are thoroughly analyzed for the calibration of analyzer deviation. The anomalous anisotropic response in phase-dependent ARPRS is closely related to the intrinsic linear dichroism (LD) effect in CrOCl, which is further confirmed by angle-resolved polarization absorption. Moreover, the strong localized rules for various parallel energy bands of CrOCl have generated anomalous LD conversion effect near 470 nm, which expands the potential application of CrOCl in polarization-wavelength selected devices. This findings can offer in-depth comprehension on the anisotropic phonon physics of CrOCl and a feasible approach to utilize phase-dependent ARPRS for probing the undiscovered abundant photo-induced effects in low-symmetry 2D materials.

Drug Release

In article number 2306814, Wenqian Feng and co-workers report an innovative polymer-pattern-based platform, enabling the precise incorporation of multiple drugs and chemical reagents into individual microdroplets simultaneously, all programmable to be customized according to specific needs. This approach facilitates the engineering of high-throughput cell screening under conditional light, significantly reducing mechanical disruption while offering precise control over the timing, dosage, and integration of a wide range of drugs within cell microreservoirs, suitable for both suspension and adherent cultures.

Scanning microwave impedance microscopy (sMIM) is utilized to locally investigate α-phase indium selenide (α-In₂Se₃) on the material, metal oxide semiconductor (MOS) structure, and ferroelectric semiconductor transistor (FeSFET) device levels. The results shed light on understanding the electronic properties of van der Waals ferroelectrics encompassing semiconductivity and ferroelectricity toward device design and optimization.

Abstract

Van der Waals ferroelectric semiconductors, which encompass both ferroelectricity and semiconductivity, have garnered intensive research interests for developing novel non-volatile functional devices. Previous studies focus on ferroelectricity characterization and device demonstration, with little attention paid to the fundamental electronic properties of these materials and their functional structures, which are essential for both device design and optimization. In this study, scanning microwave impedance microscopy (sMIM) is utilized to investigate the ferroelectric semiconductor of α-phase indium selenide (α-In₂Se₃) and its synaptic field effect transistors. α-In₂Se₃ nanoflakes of varying thicknesses are visualized through capacitive signal detection, whose responses are consistent with finite element simulations manifesting dependence on both flake thickness and its semiconductor property. sMIM spectroscopy performed on α-In₂Se₃-based metal-oxide-semiconductor (MOS) structures reveals typical MOS capacitance-voltage characteristics, with additional hysteresis arising from the ferroelectric switching of α-In₂Se₃. The local conductance state changes of synaptic α-In₂Se₃ ferroelectric semiconductor transistors (FeSFET) in response to gate voltage stimuli are effectively detected by in situ sMIM, in good agreement with electrical device transport properties. This work deepens the understanding of ferroelectric semiconductor physics toward their practical device application.

In this work, some logic gate circuits are constructed using as-fabricated memristors. Furthermore, half-adder and full-adder are constructed to perform logical operations. Finally, an encryption unit is designed based on full adder for encryption and decryption of numeric, alphabetic strings and images.

Abstract

Benefiting from powerful logic-computing, higher packaging density, and extremely low electricity consumption, memristors are regarded as the most promising next-generation of electric devices and are capable of realizing brain-like neuromorphic computation. However, the design of emerging circuit devices based on memristors and their potential application in unconventional fields are very meaningful for achieving some tasks that traditional electronic devices cannot accomplish. Herein, a Cu/PEDOT:PSS-PP:PVDF/Ti structured memristor is fabricated by using the polyvinylidene difluoride (PVDF) dopped biomaterial papaya peel (PP) and organic poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) heterojunction as functional layer, which can be switched among resistive switching, self-rectification effect, and capacitive behavior by adjusting the voltage bias/scan rate. Through further fitting of the data and simulating interfacial group reactions, this work innovatively proposes a charge conduction mode of device driven by Fowler–Nordheim tunneling, complexation reactions, and PEDOT:PSS pore removal. Finally, the regular logic gate and adder circuits are constructed based on the fabricated memristor, while a fully adder-based encryption unit is designed to realize data encryption and image reconstruction. This work renders memristor compatible with logic circuits, widening a path toward data encryption and information security.

Nature Electronics, Published online: 12 March 2024; doi:10.1038/s41928-024-01133-z

This Review examines the development of electrical reservoir computing, considering the architectures, physical nodes, and input and output layers of the approach, as well as performance benchmarks and the competitiveness of different implementations.

A space-confined chemical vapor deposition method is used to create ultrathin germanium telluride (GeTe) nanosheets, and the GeTe resonant bonding epitaxy results in thickness-dependent photoelectric properties. The ultrathin GeTe-based field-effect transistor exhibits excellent p-type behavior with an on/off ratio of 10⁵ and broad photodetection from 450–980 nm with a responsivity of 10³ A W^–1.

Abstract

As p-type phase-change degenerate semiconductors, crystalline and amorphous germanium telluride (GeTe) exhibit metallic and semiconducting properties, respectively. However, the massive structural defects and strong interface scattering in amorphous GeTe films significantly reduce their performance. In this work, two-dimensional (2D) p-type GeTe nanosheets are synthesized via a specially designed space-confined chemical vapor deposition (CVD) method, with the thickness of the GeTe nanosheets reduced to 1.9 nm. The space-confined CVD method improves the crystallinity of ultrathin GeTe by lowering the partial pressure of the reactant gas, resulting in GeTe nanosheets with excellent p-type semiconductor properties, such as a satisfactory on/off ratio of 10⁵. Temperature-dependent electrical measurements demonstrate that variable-range hopping and optical-phonon-assisted hopping mechanisms dominate transport behavior at low and high temperatures, respectively. GeTe devices exhibit significantly high responsivity (6589 and 2.2 A W⁻¹ at 633 and 980 nm, respectively) and detectivity (1.67 × 10¹¹ and 1.3 × 10⁸ Jones at 633 and 980 nm, respectively), making them feasible for broadband photodetectors in the visible to near-infrared range. Furthermore, the fabricated GeTe/WS₂ diode exhibits a rectification ratio of 10³ at zero gate voltage. These satisfactory p-type semiconductor properties demonstrate that ultrathin GeTe exhibits enormous potential for applications in optoelectronic interconnection circuits.

A general overview of ion transport behavior in van der Waals (vdW) gaps of 2D materials is provided here. The 2D nanosheet synthesis, assembly methods of 2D lamellar membranes, ion transport mechanism, responsive regulation, and novel membrane applications are emphasized. This work will be an inspiring contribution to the development of multifunctional lamellar membranes based on 2D materials.

Abstract

2D materials, with advantages of atomic thickness and novel physical/chemical characteristics, have emerged as the vital building blocks for advanced lamellar membranes which possess promising potential in energy storage, ion separation, and catalysis. When 2D materials are stacked together, the van der Waals (vdW) force generated between adjacent layered nanosheets induces the construction of an ordered lamellar membrane. By regulating the interlayer spacing down to the nanometer or even sub-nanometer scale, rapid and selective ion transport can be achieved through such vdW gaps. The further improvement and application of qualified 2D materials-based lamellar membranes (2DLMs) can be fulfilled by the rational design of nanochannels and the intelligent micro-environment regulation under different stimuli. Focusing on the newly emerging advances of 2DLMs, in this review, the common top-down and bottom-up synthesis approaches of 2D nanosheets and the design strategy of functional 2DLMs are briefly introduced. Two essential ion transport mechanisms within vdW gaps are also involved. Subsequently, the responsive 2DLMs based on different types of external stimuli and their unique applications in nanofluid transport, membrane-based filters, and energy storage are presented. Based on the above analysis, the existing challenges and future developing prospects of 2DLMs are further proposed.

Cellular membranes feature a couple of unique properties to control various biological functions at this interface. Protein function can be modulated by specific lipids directly or by bulk membrane properties. Using this principle, a number of advanced membrane-based applications are conceivable where the membrane acts as a modulator of biological function.

Abstract

The sheet-like lipid bilayer is the fundamental structural component of all cell membranes. Its building blocks are phospholipids and cholesterol. Their amphiphilic structure spontaneously leads to the formation of a bilayer in aqueous environment. Lipids are not just structural elements. Individual lipid species, the lipid membrane structure, and lipid dynamics influence and regulate membrane protein function. An exciting field is emerging where the membrane-associated material properties of different bilayer systems are used in designing innovative solutions for widespread applications across various fields, such as the food industry, cosmetics, nano- and biomedicine, drug storage and delivery, biotechnology, nano- and biosensors, and computing. Here, the authors summarize what is known about how lipids determine the properties and functions of biological membranes and how this has been or can be translated into innovative applications. Based on recent progress in the understanding of membrane structure, dynamics, and physical properties, a perspective is provided on how membrane-controlled regulation of protein functions can extend current applications and even offer new applications.

2D materials can be effectively produced by liquid phase exfoliation (LPE) using different conditions. LPE generates 2D materials in aqueous solutions, represented by graphene, black phosphorus, transition metal dichalcogenides and hexagonal boron nitride, and possess a huge potential in the biomedical domain, spanning cancer therapy, drug delivery as well as antimicrobial and biosensing.

Abstract

2D materials (2DMs), such as graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP), have been proposed for different types of bioapplications, owing to their unique physicochemical, electrical, optical, and mechanical properties. Liquid phase exfoliation (LPE), as one of the most effective up-scalable and size-controllable methods, is becoming the standard process to produce high quantities of various 2DM types as it can benefit from the use of green and biocompatible conditions. The resulting exfoliated layered materials have garnered significant attention because of their biocompatibility and their potential use in biomedicine as new multimodal therapeutics, antimicrobials, and biosensors. This review focuses on the production of LPE-assisted 2DMs in aqueous solutions with or without the aid of surfactants, bioactive, or non-natural molecules, providing insights into the possibilities of applications of such materials in the biological and biomedical fields.

A set of porosity, coordination bonding between organic and inorganic building blocks, and the lack of inversion symmetry of optically transparent and label-free MOFs allows one to simultaneously create grayscale and multicolor images with 400 nm resolution, thereby revealing a new family of functional materials for direct laser writing method.

Abstract

Direct laser writing (DLW), being a universal tool for fast creating colorless/color images on different substrates, still suffers from simultaneous writing grayscale and color images inside the transparent media. Here, it is discovered that a unique set of porosity, coordination bonding between organic and inorganic building blocks, and the lack of inversion symmetry of the label-free metal-organic frameworks (MOFs), on the one hand, provides the possibility of laser writing the grayscale images through the amorphization/carbonization. On the other hand, the reduction of the laser writing power leads to controllable creation of color images via defect formation with sub-diffraction resolution inside the MOF crystals. The latter is due to the processes of self-absorption of generated optical harmonics by nonlinear MOFs within the visible spectral range. As a result, simultaneous grayscale and multicolor writing of QR codes and images are demonstrated with up to 400 nm resolution inside optically transparent MOF crystals, thereby discovering a new family of functional materials for DLW.

A highly reliable 2D MoS₂/GaPS₄ artificial synapse device displays high memory retention, even at 400 °C. Moreover, the device exhibits remarkable performances under electrical and optical stimulation, owing to the enhanced charge-trapping effect of the GaPS₄ layer.

Abstract

Artificial synaptic devices (ASDs) are attracting widespread attention as highly promising components for use in complex neuromorphic systems, playing crucial roles in addressing the challenges posed by the conventional von Neumann architecture. However, the instabilities of ASDs in high-temperature environments diminish the reliabilities of the device performances, significantly inhibiting their practical application. Herein, a highly reliable 2D MoS₂/GaPS₄ ASD that maintains its functionality even after exposure to 400 °C is proposed. Moreover, due to the enhanced charge-trapping effect of the GaPS₄ layer, the memory window expands from an initial 42 to 55 V, accompanied by a substantial on/off ratio of 10⁵, low off-leakage current of 10⁻¹¹ A, and high number of endurance cycles (10³). The device effectively simulates various biological synaptic functions via electric and light stimulation. Notably, the high electric and light paired-pulse facilitation indices suggest an exceptional synaptic performance. The findings introduce a novel approach to high-temperature neuromorphic applications via defect engineering.

Unlike the exclusive implementation of entropy engineering or vacancy engineering in SnTe-based materials, a strategy of entropy engineering involving vacancies is proposed in this work to leverage a promising cocktail effect. The approach results in the simultaneous attainment of high power factor and low lattice thermal conductivity, culminating in extraordinary thermoelectric performance at low-medium temperatures.

Abstract

The pursuit of high-power factor and low lattice thermal conductivity simultaneously in thermoelectric research is longstanding. Herein, great success has been achieved in SnTe-based materials by employing a proposed strategy of entropy engineering involving vacancies, thus leveraging the promising cocktail effect. Significant band convergence and flatness effects have given rise to exceptionally high density of state carrier effective mass and Seebeck coefficients. These effects have also led to the theoretical optimal carrier concentration closely aligning with the actual carrier concentration. Furthermore, the entropy engineering involving vacancies has induced pronounced lattice disorder and a wealth of nanostructures, facilitating multi-scale phonon scattering. Consequently, impressive thermoelectric performance is realized in AgSb₃Pb₂Ge₂Sn₆Te₁₅: room-temperature ZT of ≈0.4, peak ZT of ≈1.3 at 623 K, and average ZT of ≈1.0 (300–773 K). A thermoelectric module, comprising this p-type material and the homemade n-type PbTe, is assembled, demonstrating a competitive conversion efficiency of 9.3% at a temperature difference of 478 K. This work not only provides valuable insights into the modulation of electron/phonon transports but also establishes an effective paradigm of entropy engineering involving vacancies.

Herein, the photodetector based on the α-In₂Se₃/PdSe₂ homo-type ferroelectric van der Waals heterojunction is designed to achieve high-performance and broadband. The unilateral-depletion region of the homo-type heterojunction promotes the effective separation of photogenerated carriers and is further optimized by adjusting the ferroelectric polarization state of the α-In₂Se₃. This design has promising applications in next-generation optoelectronics.

Abstract

Two-dimensional (2D) materials have attracted extensive attention in the field of photodetection thanks to their unique physical properties. Among them, the PdSe₂ nanoflake shows great potential. However, the performance of the PdSe₂-based photodetector with a hetero-type heterojunction remains poor due to the severe tunneling-assisted interfacial recombination of photogenerated electron-hole pairs in the thin bilateral-depletion heterojunctions. In this work, a novel photodetector with a α-In₂Se₃/PdSe₂ homo-type heterojunction for both high-performance and broadband detection from visible to short-wave infrared is constructed. The high-performance of the photoresponsivity of 4.64 × 10³ A·W⁻¹, the external quantum efficiency of 1.08 × 10⁶%, and the specific detectivity of 1.55 × 10¹⁴ Jones at 532 nm is the result of the homo-type unilateral-depletion junction which can promote the effective separation of photogenerated electron-hole pairs compared to the hetero-type. Also, adjusting the α-In₂Se₃ ferroelectric polarization state further optimizes the unilateral depletion region. In addition, the photodetector can work in a self-powered mode. This study suggests that the PdSe₂-based homo-type device has great application potential in the field of 2D optoelectronics.

Atomically thin, p-type semiconducting SnSb₂Te₄ single crystals are grown via a chemical vapor deposition method. The SnSb₂Te₄-based photodetection devices show broadband detection through communication bands due to its bandgap of 0.42 eV and a fast response/recovery speed of tens of microseconds, exceeding most transition metal dichalcogenides, owing to its high room temperature mobility of 300 cm² V⁻¹s⁻¹.

Abstract

SnSb₂Te₄ (SST), a ternary van der Waals (vdW) material, has been widely investigated during last decades for potential applications in superconductivity, thermoelectricity, and optoelectronics. Recently, atomically thin SST has been predicted to show abnormal electronic band structure evolutions, high carrier mobility, and strong light–matter interaction. However, controllable synthesis of such SST crystals has been a huge challenge. Herein, atomically thin SST flakes are prepared via a chemical vapor deposition (CVD) method by using SbCl₃, SnCl₄·5H₂O, and Te as the precursors. Multiple structural characterizations reveal that the SST flakes are single crystals with high crystallinity. Due to the narrow bandgap of 0.42 eV, SST-based photodetectors have a broadband spectrum detection range from visible light through communication bands (480–1550 nm). More importantly, benefiting from a high room-temperature carrier mobility over 300 cm² V⁻¹ s⁻¹, the SST photodetectors demonstrate a response/recovery time of tens of tens of microseconds, which exceeds most typical transition metal dichalcogenide (TMDC) flakes. In addition, the photodetector maintains high performance after being exposed to the air for 2 months, suggesting good environmental stability. These excellent performances suggest that the SST flakes are promising for next-generation optoelectronics.