Jiuxiang Dai

This paper presents the wafer-scale synthesis of highly polycrystalline 2D molybdenum ditelluride (2H-MoTe₂), and its use as resistive switching layer in memristors. Most interestingly, the synthesized polycrystalline 2H-MoTe₂ film contains vertically aligned grain boundaries, providing confined diffusion paths for metal ions migration. This conductive filament confinement makes reliable resistive switching possible, applicable to artificial synaptic applications.

Abstract

2D materials have attracted attention in the field of neuromorphic computing applications, demonstrating the potential for their use in low-power synaptic devices at the atomic scale. However, synthetic 2D materials contain randomly distributed intrinsic defects and exhibit a stochasitc forming process, which results in variability of switching voltages, times, and stat resistances, as well as poor synaptic plasticity. Here, this work reports the wafer-scale synthesis of highly polycrystalline semiconducting 2H-phase molybdenum ditelluride (2H-MoTe₂) and its use for fabricating crossbar arrays of memristors. The 2H-MoTe₂ films contain small grains (≈30 nm) separated by vertically aligned grain boundaries (GBs). These aligned GBs provide confined diffusion paths for metal ions filtration (from the electrodes), resulting in reliable resistive switching (RS) due to conductive filament confinement. As a result, the polycrystalline 2H-MoTe₂ memristors shows improvement in the RS uniformity and stable multilevel resistance states, small cycle-to-cycle variation (<8.3%), high yield (>83.7%), and long retention times (>10⁴ s). Finally, 2H-MoTe₂ memristors show linear analog synaptic plasticity under more than 2500 repeatable pulses and a simulation-based learning accuracy of 96.05% for image classification, which is the first analog synapse behavior reported for 2D MoTe₂ based memristors.

Significant ferroelectricity in sub-6 nm thin films is boosted by atomic layer engineering on the HfO₂ seeding layer, triggering the morphotropic phase boundary effect correlated with the dramatic transition from antiferroelectric to ferroelectric phase in ZrO₂. Furthermore, clear images of surface grains taken by helium ion microscopy are employed to characterize the transformation of crystallographic structures for the first time.

Abstract

Atomic layer engineering is investigated to tailor the morphotropic phase boundary (MPB) between antiferroelectric, ferroelectric, and paraelectric phases. By increasing the HfO₂ seeding layer with only 2 monolayers, the overlying ZrO₂ layer experiences the dramatic phase transition across the MPB. Conspicuous ferroelectric properties including record-high remanent polarization (2P_r ≈ 60 µC cm⁻²), wake-up-free operation, and high compatibility with advanced semiconductor technology nodes, are achieved in the sub-6 nm thin film. The prominent antiferroelectric to ferroelectric phase transformation is ascribed to the in-plane tensile stress introduced into ZrO₂ by the HfO₂ seeding layer. Based on the high-resolution and high-contrast images of surface grains extracted precisely by helium ion microscopy, the evolution of the MPB between tetragonal, orthorhombic, and monoclinic phases with grain size is demonstrated for the first time. The result indicates that a decrease in the average grain size drives the crystallization from the tetragonal to polar orthorhombic phases.

N=8 armchair graphene nanoribbons (AGNRs) were successfully synthesized in solution utilizing a custom arylated polynaphthalene precursor. The resulting 8-AGNR exhibits a noteworthy near-infrared absorption profile which signifies an exceptionally low optical band gap of 0.52 eV and demonstrates a record high dc charge-carrier mobility of up to 270 cm² V⁻¹ s⁻¹.

Abstract

Structurally defined graphene nanoribbons (GNRs) have emerged as promising candidates for nanoelectronic devices. Low band gap (<1 eV) GNRs are particularly important when considering the Schottky barrier in device performance. Here, we demonstrate the first solution synthesis of 8-AGNRs through a carefully designed arylated polynaphthalene precursor. The efficiency of the oxidative cyclodehydrogenation of the tailor-made polymer precursor into 8-AGNRs was validated by FT-IR, Raman, and UV/Vis-near-infrared (NIR) absorption spectroscopy, and further supported by the synthesis of naphtho[1,2,3,4-ghi]perylene derivatives (1 and 2) as subunits of 8-AGNR, with a width of 0.86 nm as suggested by the X-ray single crystal analysis. Low-temperature scanning tunneling microscopy (STM) and solid-state NMR analyses provided further structural support for 8-AGNR. The resulting 8-AGNR exhibited a remarkable NIR absorption extending up to ∼2400 nm, corresponding to an optical band gap as low as ∼0.52 eV. Moreover, optical-pump TeraHertz-probe spectroscopy revealed charge-carrier mobility in the dc limit of ∼270 cm² V⁻¹ s⁻¹ for the 8-AGNR.

Abstract

In-situ integration of multiple materials with well-defined interfaces as heterostructures is of great interest due to their unique properties and potential for new device functionality. Because of its polymorphism and diverse bonding geometries, borophene is a promising candidate for two-dimensional heterostructures, but suitable synthesis conditions have limited its potential applications. Toward this end, we demonstrate the vertical borophene and graphene heterostructures which form by epitaxial growth of borophene onto multilayer graphene on Cu substrates via chemical vapor deposition, where hydrogen and NaBH₄ are respectively used as the carrier gas and the boron source. The lattice structure of the as-synthesized borophene well coincides with the predicted α′-boron sheet. The borophene-based photodetector shows an excellent broadband photoresponse from the ultraviolet (255 nm) to the infrared (940 nm) wavelengths, with enhanced responsivity compared to pristine borophene or graphene photodetectors. This work informs emerging efforts to integrate borophene into nanoelectronic applications for both fundamental investigations and technological applications.

npj 2D Materials and Applications, Published online: 27 September 2023; doi:10.1038/s41699-023-00433-w

Two-dimensional tellurium-based diodes for RF applications

The dynamic evolution process of sulfur vacancy lines under different heating temperatures is studied by low-voltage, in situ scanning transmission electron microscopy (STEM) observations. The anisotropic growth of vacancy lines exhibits both vacancy concentration dependence and temperature dependence, which gives fundamental insights into the similarity between defect structure growth at the atomic scale and 2D material growth at the micrometer scale.

Abstract

Understanding the growth behavior and morphology evolution of defects in 2D transition metal dichalcogenides is significant for the performance tuning of nanoelectronic devices. Here, the low-voltage aberration-corrected transmission electron microscopy with an in situ heating holder and a fast frame rate camera to investigate the sulfur vacancy lines in monolayer MoS₂ is applied. Vacancy concentration-dependent growth anisotropy is discovered, displaying first lengthening and then broadening of line defects as the vacancy densifies. With the temperature increase from 20 °C to 800 °C, the defect morphology evolves from a dense triangular network to an ultralong linear structure due to the temperature-sensitive vacancy migration process. Atomistic dynamics of line defect reconstruction on the millisecond time scale are also captured. Density functional theory calculations, Monte Carlo simulation, and configurational force analysis are implemented to understand the growth and reconstruction mechanisms at relevant time and length scales. Throughout the work, high-resolution imaging is closely combined with quantitative analysis of images involving thousands of atoms so that the atomic-level structure and the large-area statistical rules are obtained simultaneously. The work provides new ideas for balancing the accuracy and universality of discoveries in the TEM study and will be helpful to the controlled sculpture of nanomaterials.

Abstract

Metal-insulator-metal (MIM) cavity as a lithography-free structure to control light transmission and reflection has great potential in the field of optical sensing. However, the dense top metal layer of the MIM prohibits any external medium from entering the dielectric insulation layer, which limits the application of the cavity in the sensing field. Herein, we demonstrate a series of monolithic metal-organic frameworks (MOFs) based MIM cavities, which are treated by plasma etching to provide channels for chemical diffusion and to advance sensing. We modulate the bandwidth of the MIM filters by controlling the MOF thickness as insulator layers. Oxygen plasma-etching is applied to build channels on the top metal layer without altering their saturation and brightness for chemical sensing performance. The etching time regulates the number and size of channels on the top metal layer. Sensing behavior is demonstrated on the plasma-etched MOFs-based MIM cavity when external chemicals diffuse in the cavity. In addition, we generate patterned structure of the MOFs-based MIM cavity via plasma-mask method, which can transfer to different substrates and produce a controllable structure color change for chemical sensing. Our MIM cavity may promote the advancement and applications of structural color in security imaging, color display, information anticounterfeiting, and color printing.

Based on the existing piezoelectric theory, NiO with the centrosymmetric structure is not piezoelectric. However, herein, this study shows the observation of piezoelectric, rectifying and photovoltaic effects in (111)-oriented NiO films. These effects are attested to originate from the electric field produced by spontaneous polarization in the (111)-oriented NiO film. The polar structure piezoelectric and photovoltaic mechanism is thus presented.

Abstract

Based on the current piezoelectric theory, NiO with the centrosymmetric structure is not piezoelectric. However, herein, this study shows the first observation of piezoelectric generation, rectifyingand bulk photovoltaic behaviors in NiO films with [111] orientation and the change in NiO crystal structure in piezoelectric process. The piezoelectric generation, rectifying, and bulk photovoltaic performances are enhanced by increasing (111) orientation, and attenuated and eliminated by applying a persistent stress on the NiO film. The NiO [111] is polar direction, and thus a spontaneous electric field (E_S) is in the NiO film with [111] orientation. The existence of Es in (111) oriented NiO film is found to be the physical basis of the piezoelectric generators and photovoltaic and rectifying effects. Thus, NiO piezoelectric, rectifying, and bulk photovoltaic mechanism are presented at the atomic level. The mechanism may rewrite the current piezoelectric theory, and establish a unified theory of polar structure with wide implications. The polar-orientated films can be used to fabricate piezoelectric generators and other optoelectronic devices with high performances.

2D materials-based heterostructures, including 2D/0D, 2D/1D, 2D/2D, and 2D/3D, can produce the synergistic effect and heterointerface effect, and overcome the instinct restriction of individual 2D materials, thus can serve as potential electrocatalysts in the field of energy conversion, such as hydrogen evolution reaction, oxygen evolution reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, etc.

Abstract

2D materials, such as graphene, transition metal dichalcogenides, black phosphorus, layered double hydroxides, and MXene, have exhibited broad application prospects in electrochemical energy conversion due to their unique structures and electronic properties. Recently, the engineering of heterostructures based on 2D materials, including 2D/0D, 2D/1D, 2D/2D, and 2D/3D, has shown the potential to produce synergistic and heterointerface effects, overcoming the inherent restrictions of 2D materials and thus elevating the electrocatalytic performance to the next level. In this review, recent studies are systematically summarized on heterostructures based on 2D materials for advanced electrochemical energy conversion, including water splitting, CO₂ reduction reaction, N₂ reduction reaction, etc. Additionally, preparation methods are introduced and novel properties of various types of heterostructures based on 2D materials are discussed. Furthermore, the reaction principles and intrinsic mechanisms behind the excellent performance of these heterostructures are evaluated. Finally, insights are provided into the challenges and perspectives regarding the future engineering of heterostructures based on 2D materials for further advancements in electrochemical energy conversion.

A smart single-fluorophore polymer polyethyleneimine-grafted pyrene (PGP) incorporating four stimuli-triggers: amphiphilicity, supramolecular host–guest sites, pyrene fluorescence indicator, and reversible chelation sites, exhibits deformation and shape-dependent fluorescence in response to external stimuli. Besides, PGP driven by its reversible chelation capacity can be used as an advanced fluorescent ink with erasable and recoverable properties.

Abstract

A novel smart fluorescent polymer polyethyleneimine-grafted pyrene (PGP) is developed by incorporating four stimuli-triggers at molecular level. The triggers are amphiphilicity, supramolecular host–guest sites, pyrene fluorescence indicator, and reversible chelation sites. PGP exhibits smart deformation and shape-dependent fluorescence in response to external stimuli. It can deform into three typical shapes with a characteristic fluorescence color, namely, spherical core–shell micelles of cyan-green fluorescence, standard rectangular nanosheets of yellow fluorescence, and irregular branches of deep-blue fluorescence. A quasi-reversible deformation between the first two shapes can be dynamically manipulated. Moreover, driven by reversible coordination and the resulting intramolecular photoinduced electron transfer, PGP can be used as an aqueous fluorescence ink with erasable and recoverable properties. The fluorescent patterns printed by PGP ink on paper can be rapidly erased and recovered by simple spraying a sequence of Cu²⁺ and ethylene diamine tetraacetic acid aqueous solutions. This erase/recover transformation can be repeated multiple times on the same paper. The multiple stimulus responsiveness of PGP makes it have potential applications in nanorobots, sensing, information encryption, and anticounterfeiting.

Nature Electronics, Published online: 25 September 2023; doi:10.1038/s41928-023-01030-x

A machine-learning-based model can be used to perform atomistic simulations of phase changes along the germanium–antimony–tellurium composition line, up to a full-size memory device model that contains half a million atoms.

Nature Photonics, Published online: 21 September 2023; doi:10.1038/s41566-023-01291-0

Thanks to the unique properties of twisted double bilayer graphene heterostructures, an ultra-broadband photoconductivity spanning the spectral range of 2–100 μm with internal quantum efficiencies of approximately 40% at speeds of 100 kHz is reported.

Nature Materials, Published online: 21 September 2023; doi:10.1038/s41563-023-01656-4

The room-temperature self-healing behaviour of a nanotwinned diamond composite is quantitatively evaluated and found to stem from both the formation of nanoscale diamond osteoblasts and the atomic interaction transition from repulsion to attraction.

Solution-processed heterojunctions based on WSe₂ nanosheet networks are fabricated. The obtained heterojunctions display a high rectification ratio of up to ≈10⁴ at ±1 V in the dark and can be used as photodetectors in both photoconductor (1 V) and photodiode (0 and −1 V) modes under illumination.

Abstract

Solution-processed photodetectors incorporating liquid-phase-exfoliated transition metal dichalcogenide nanosheets are widely reported. However, previous studies mainly focus on the fabrication of photoconductors, rather than photodiodes which tend to be based on heterojunctions and are harder to fabricate. Especially, there are rare reports on introducing commonly used transport layers into heterojunctions based on nanosheet networks. In this study, a reliable solution-processing method is reported to fabricate heterojunction diodes with tungsten selenide (WSe₂) nanosheets as the optical absorbing material and PEDOT: PSS and ZnO as injection/transport-layer materials. By varying the transport layer combinations, the obtained heterojunctions show rectification ratios of up to ≈10⁴ at ±1 V in the dark, without relying on heavily doped silicon substrates. Upon illumination, the heterojunction can be operated in both photoconductor and photodiode modes and displays self-powered behaviors at zero bias.

This work reports directional single cell migration guided by a strain gradient, termed tensotaxis. A programmable uniaxial cell stretch device is developed to establish a continuous strain gradient field without generating a stiffness gradient. Focal adhesion analysis and motor-clutch model demonstrate that tensotaxis is driven by strain-introduced traction force and integrin fibronectin pairs' catch-release dynamics.

Abstract

Strain gradients widely exist in development and physiological activities. The directional movement of cells is essential for proper cell localization, and directional cell migration in responses to gradients of chemicals, rigidity, density, and topography of extracellular matrices have been well-established. However; it is unclear whether strain gradients imposed on cells are sufficient to drive directional cell migration. In this work, a programmable uniaxial cell stretch device is developed that creates controllable strain gradients without changing substrate stiffness or ligand distributions. It is demonstrated that over 60% of the single rat embryonic fibroblasts migrate toward the lower strain side in static and the 0.1 Hz cyclic stretch conditions at ≈4% per mm strain gradients. It is confirmed that such responses are distinct from durotaxis or haptotaxis. Focal adhesion analysis confirms higher rates of contact area and protrusion formation on the lower strain side of the cell. A 2D extended motor-clutch model is developed to demonstrate that the strain-introduced traction force determines integrin fibronectin pairs' catch-release dynamics, which drives such directional migration. Together, these results establish strain gradient as a novel cue to regulate directional cell migration and may provide new insights in development and tissue repairs.

High quality Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber is obtained by referencing the reflected color of first-layer precursor film. The thickness of first-layer precursor film is linked to its color according to the thin-film interference theory. This method provides a feasible and effective way to stabilize the quality of absorber and obtain high-efficient devices.

Abstract

Solution method provides a low-cost and environmentally friendly route for the fabrication of Cu₂ZnSn(S,Se)₄ (CZTSSe) thin-film solar cells. However, uncontrollable quality of the CZTSSe absorber layer will severely limit the device's performance. In this study, it is find that the thickness and the quality of the formed precursor is not stable because of the variation of the viscosity of the precursor solution. Combined by different characterization methods, the results disclose that such change is strongly related to the reflected color of the first coating layer during precursor growth. Further studies disclose that only by maintaining the appropriate reflected color can a well-crystallized CZTSSe film be prepared, thereby obtaining good solar cell efficiency. This semi-empirical pattern is confirmed by thin-film interference theory. Under the guidance of this method, CZTSSe absorbers with high quality are obtained easily, and the highly efficient CZTSSe solar cell can be fabricated easily. This study provides a feasible and effective strategy to obtain the optimal structure and composition of CZTSSe film toward the production of highly efficient kesterite solar cells, which can also be widely applied to the preparation of other films by solution-based method.

2D transition metal dichalcogenides (2D TMDs) have attracted increasing attention as promising electrode materials for supercapacitors (SCs). In this review, basic knowledge and information of 2D TMD-based SCs are introduced, recent advances in strategies focusing on doping, structure, composition, phase, configuration, electrolyte to improve their supercapacitor performance are summarized and future perspectives are proposed.

Abstract

Recently, the development of new materials and devices has become the main research focus in the field of energy. Supercapacitors (SCs) have attracted significant attention due to their high power density, fast charge/discharge rate, and excellent cycling stability. With a lamellar structure, 2D transition metal dichalcogenides (2D TMDs) emerge as electrode materials for SCs. Although many 2D TMDs with excellent energy storage capability have been reported, further optimization of electrode materials and devices is still needed for competitive electrochemical performance. Previous reviews have focused on the performance of 2D TMDs as electrode materials in SCs, especially on their modification. Herein, the effects of element doping, morphology, structure and phase, composite, hybrid configuration, and electrolyte are emphatically discussed on the overall performance of 2D TMDs-based SCs from the perspective of device optimization. Finally, the opportunities and challenges of 2D TMDs-based SCs in the field are highlighted, and personal perspectives on methods and ideas for high-performance energy storage devices are provided.

Nature Communications, Published online: 22 September 2023; doi:10.1038/s41467-023-41383-7

This paper reports the intralayer ferroelectric-to-antiferroelectric and ferroelectric-toparaelectric phase transitions in layered NbOCl2 and NbOI2 under a small pressure, respectively, along with the strong manipulations of nonlinear optics.

Author(s): Bidesh Biswas, Sourav Rudra, Rahul Singh Rawat, Nidhi Pandey, Shashidhara Acharya, Anjana Joseph, Ashalatha Indiradevi Kamalasanan Pillai, Manisha Bansal, Muireann de h-Óra, Debendra Prasad Panda, Arka Bikash Dey, Florian Bertram, Chandrabhas Narayana, Judith MacManus-Driscoll, Tuhin Maity, Magnus Garbrecht, and Bivas Saha

Traditionally, the Coulomb repulsion or Peierls instability causes the metal-insulator phase transitions in strongly correlated quantum materials. In comparison, magnetic stress is predicted to drive the metal-insulator transition in materials exhibiting strong spin-lattice coupling. However, this m…

[Phys. Rev. Lett. 131, 126302] Published Fri Sep 22, 2023

2D Cs₃Bi₂Br₉ nanoflakes are promising candidates for detecting X-ray but difficult to synthesize due to the existence of easy-oxidized Br⁻ vacancies in the crystal nucleus. Herein, an Ag⁺ assisted inversion temperature crystallization strategy is first proposed to prepare 2D Cs₃Bi₂Br₉ nanoflakes. Moreover, the fabricated device demonstrates ultrahigh sensitivity (1.9 CGy_air ⁻¹ cm⁻²) of detecting X-ray at very low driven voltage (0.5 V).

Abstract

2D perovskites have attracted wide attention for optoelectronic applications because of their unique layer structure and tunable outstanding optical/electrical properties. In addition, 2D Cs₃Bi₂Br₉ nanoflakes possess large effective atomic number, high resistivity, high density as well as excellent stability, rendering it a promising material for X-ray detection. Nevertheless, it is full of challenges to synthesize 2D Cs₃Bi₂Br₉ nanoflakes by conventional inversion temperature crystallization (ITC) strategy due to the existence of Br^- vacancies in the Cs₃Bi₂Br₉ crystal nucleus. Herein, an Ag⁺ assisted ITC (SAITC) strategy to grow 2D Cs₃Bi₂Br₉ nanoflakes is proposed. The synthesis mechanism revealed by both experiments and theoretical calculations can be mainly ascribed to the passivated Br⁻ vacancies and enhanced structure stability by adding Ag⁺ which can effectively prevent the oxidation of 2D Cs₃Bi₂Br₉ nanoflakes from growth of hybrid crystals. The synthesized high-crystallinity 2D Cs₃Bi₂Br₉ nanoflakes possess direct bandgap characteristic, and the mobility lifetime can reach 9.8 × 10⁻⁴ cm² V⁻¹. Excitingly, the fabricated device based on 2D Cs₃Bi₂Br₉ nanoflakes demonstrates ultrahigh sensitivity of detecting X-ray (1.9 CGy_air ⁻¹cm⁻²) at very low driven voltage (0.5 V) due to the photoconductive gain mechanism. The 2D Cs₃Bi₂Br₉ nanoflakes synthesized by SAITC method have great potential for developing highly sensitive optoelectronic devices.

The thermal oxidation behavior and mechanism of GaSe are directly uncovered at multi-scale using microscopic techniques. Various surface structures are obtained depending on the oxidation temperature, leading to the achievement of surface regulation. Importantly, the photoluminescence of GaSe is effectively enhanced due to the oxidation surface construction, indicating the oxidation surface engineering has great potential in design/development of Van der Waals chalcogenides with tunable properties.

Abstract

The investigation of the oxidation behavior of van der Waals chalcogenides holds significant importance in terms of preventing and controlling oxidation, utilizing surface oxidation structures to regulate properties, and advancing applications. Here, taking GaSe as a candidate, its thermal oxidation and surface structure evolution are intensively studied. Through systematic microscopic analyses, oxidized structures at multi-scale (from atomic scale to millimeters) are resolved, and various assembly heterogeneous surfaces including Ga₂Se₃/Ga₂O₃ and Ga₂O₃ multilayers are uncovered at different oxidation temperatures. The temperature-dependent oxidation behavior and surface structure evolution of the GaSe are revealed, and the oxidation mechanisms in the entire temperature range are also disclosed. Finally, the photoluminescence regulation of the GaSe is initially explored via thermal oxidation, demonstrating great potential for surface oxidation engineering. This study is not only of great importance for the deep understanding and utilization of GaSe oxidation, but also beneficial for materials/device design and development of relative systems.

Abstract

Due to unique and excellent properties, carbon nanotubes (CNTs) are expected to become the next-generation critical engineering mechanical and energy storage materials, which will play a key role as building blocks in aerospace, military equipment, communication sensing, and other cutting-edge fields. For practical application, the assembled macrostructures from individual CNTs are the common paradigms such as fibers or films. As the main representative, CNT films can not only retain the unique properties of their CNTs components, but also are more likely for mass-production than other macrostructures. Therefore, in this review, we focus on preparation of CNT films and discuss their emerging applications in the field of mechanical and electrochemical energy storage/conversion. Firstly, different preparation processes are systematically summarized. Then we introduce some typical strategies to improve their mechanical performances besides strengthening mechanism. Based on the progress of mass-production and performance optimization, we further discuss their potential utilization in mechanical and electrochemical energy storage/conversion devices. Finally, future perspectives for the development of CNT films in both production and application are proposed. We hope that this review will shed light on the preparation/assembly of CNT films and integrated application of excellent properties from individual to macroscopic dimensions. Moreover, the preparation and crossscale application paradigms of CNT films also offer a good model for other macroscopic ordered assemblies of one-dimensional nanomaterials.

Using initiated chemical vapor deposition (iCVD), organic and hybrid thin films can form directly on substrates of virtually any composition and geometry. Free-radical polymerization of adsorbed monomers is initiated by vapor phase radicals formed by thermal decomposition. The established fundamentals enable the rational optimization of iCVD polymers and copolymers for sensing, optoelectronics, electrochemical energy storage, and biotechnology.

Abstract

The initiated chemical vapor deposition (iCVD) technique is an all-dry method for designing organic and hybrid polymers. Unlike methods utilizing liquids or line-of-sight arrival, iCVD provides conformal surface modification over intricate geometries. Uniform, high-purity, and pinhole-free iCVD films can be grown with thicknesses ranging from >15 µm to <5 nm. The mild conditions permit damage-free growth directly onto flexible substrates, 2D materials, and liquids. Novel iCVD polymer morphologies include nanostructured surfaces, nanoporosity, and shaped particles. The well-established fundamentals of iCVD facilitate the systematic design and optimization of polymers and copolymers. The functional groups provide fine-tuning of surface energy, surface charge, and responsive behavior. Further reactions of the functional groups in the polymers can yield either surface modification, compositional gradients through the layer thickness, or complete chemical conversion of the bulk film. The iCVD polymers are integrated into multilayer device structures as desired for applications in sensing, electronics, optics, electrochemical energy storage, and biotechnology. For these devices, hybrids offer higher values of refractive index and dielectric constant. Multivinyl monomers typically produce ultrasmooth and pinhole-free and mechanically deformable layers and robust interfaces which are especially promising for electronic skins and wearable optoelectronics.

Giant mid-infrared second-harmonic generation performance (better than the visible region) is demonstrated in the newly discovered Weyl semiconductor −2D Te. Theoretical calculations reveal that it originated from the large Berry curvature dipole near the Weyl points of 2D Te. Therefore, even excited by continuous-wave laser, strong sum-frequency generation can be obtained in 2D Te.

Abstract

Due to its inversion-broken triple helix structure and the nature of Weyl semiconductor, 2D Tellurene (2D Te) is promising to possess a strong nonlinear optical response in the infrared region, which is rarely reported in 2D materials. Here, a giant nonlinear infrared response induced by large Berry curvature dipole (BCD) is demonstrated in the Weyl semiconductor 2D Te. Ultrahigh second-harmonic generation response is acquired from 2D Te with a large second-order nonlinear optical susceptibility (χ ⁽²⁾), which is up to 23.3 times higher than that of monolayer MoS₂ in the range of 700–1500 nm. Notably, distinct from other 2D nonlinear semiconductors, χ ⁽²⁾ of 2D Te increases extraordinarily with increasing wavelength and reaches up to 5.58 nm V⁻¹ at ≈2300 nm, which is the best infrared performance among the reported 2D nonlinear materials. Large χ ⁽²⁾ of 2D Te also enables the high-intensity sum-frequency generation with an ultralow continuous-wave (CW) pump power. Theoretical calculations reveal that the exceptional performance is attributed to the presence of large BCD located at the Weyl points of 2D Te. These results unravel a new linkage between Weyl semiconductor and strong optical nonlinear responses, rendering 2D Te a competitive candidate for highly efficient nonlinear 2D semiconductors in the infrared region.

Optoelectronic memristors (OMs) can emulate neurological functions within a bionic computing architecture, enabling energy-efficient in-memory computing. Identifying suitable techniques for integrating materials into integrated circuit platforms is imperative to advance the field. This review provides a comprehensive overview of the fundamental performance, mechanism, structures, applications, and integration roadmap of OMs aiming to establish a connection between materials and OM systems.

Abstract

Optoelectronic memristors (OMs) have emerged as a promising optoelectronic Neuromorphic computing paradigm, opening up new opportunities for neurosynaptic devices and optoelectronic systems. These OMs possess a range of desirable features including minimal crosstalk, high bandwidth, low power consumption, zero latency, and the ability to replicate crucial neurological functions such as vision and optical memory. By incorporating large-scale parallel synaptic structures, OMs are anticipated to greatly enhance high-performance and low-power in-memory computing, effectively overcoming the limitations of the von Neumann bottleneck. However, progress in this field necessitates a comprehensive understanding of suitable structures and techniques for integrating low-dimensional materials into optoelectronic integrated circuit platforms. This review aims to offer a comprehensive overview of the fundamental performance, mechanisms, design of structures, applications, and integration roadmap of optoelectronic synaptic memristors. By establishing connections between materials, multilayer optoelectronic memristor units, and monolithic optoelectronic integrated circuits, this review seeks to provide insights into emerging technologies and future prospects that are expected to drive innovation and widespread adoption in the near future.

Publication date: October 2023

Source: Materials Today, Volume 69

Author(s): Paul Albert L. Sino, Tzu-Chieh Lin, Sumayah Wani, Ling Lee, Chieh-Ting Chen, Ming-Jin Liu, Yao-Zen Kuo, Bushra Rehman, Kim Tuyen Le, Jyh-Ming Wu, Feng-Chuan Chuang, Yu-Lun Chueh