Jiuxiang Dai

Manganese-doped shells revolutionize InP quantum dots, enhancing their optical properties through improved core-shell interface engineering. This novel approach results in increased crystallinity, reduced defects, and stronger quantum confinement. The optimized quantum dots exhibit higher photoluminescence quantum yield in the green emission region, paving the way for high-performance, environmentally friendly optoelectronic materials.

Abstract

Indium phosphide (InP) quantum dots (QDs) offer a promising alternative to (Restriction of Hazardous Substances) restricted cadmium-based QDs, however, their performance is limited by surface defects and weak quantum confinement. This study introduces a novel approach to enhance the optical properties of InP QDs through manganese (Mn) doping into the zinc selenide and zinc sulfide shell. This aims to expand the bandgap of the shells and adjust its lattice constant to better match the InP core. A comprehensive investigation of the effect of Mn-doping concentration reveals that optimal properties are developed at a 10% feed ratio, resulting in improved crystallinity, reduced interfacial defects, and enhanced quantum confinement. X-ray diffraction and transmission electron microscopy confirm the structural improvements and spectroscopic analyses demonstrate remarkable enhancement of optical properties. Notably, the photoluminescence quantum yield reaches 83% in the green emission region (λ ≈535 nm), a significant improvement over undoped QDs. Time-resolved photoluminescence measurements indicate extended carrier lifetimes, supporting the effect of defect reduction. This strategy not only addresses the long-standing challenges of InP QDs but also opens new avenues for designing high-performance, environmentally friendly nanomaterials for various optoelectronic applications, including displays, lighting, and photovoltaics.

Experimentally, gate voltage and strain is introduced to achieve a tunable linear dichroism property in GeSe, witnessing a maximum enhancement of 44%. The explanation of the underlying mechanism is grounded in rigorous theoretical calculations. Moreover, two promising application avenues are showcased for GeSe-based flexible photoelectric sensors in the realm of wearable electronics.

Abstract

The direct detection of light polarization poses a crucial challenge in the field of optoelectronics and photonics. Herein, the tunable linear dichroism (LD) in GeSe-based polarized photodetectors is presented through electronic and structural asymmetry modulation, and demonstrate their application prospects in wearable electronics. An improvement in the dichroic ratio up to 34% is achieved under a gate voltage of 20 V, and the improvement reaches 44% by applying a tensile strain along the zigzag direction. Theoretical calculations reveal that the gate regulation of barrier height between GeSe and Au electrodes is responsible for the electrical-tunable LD, while the anisotropic optical absorption in response to strains leads to the strain-tunable LD. Moreover, flexible GeSe transistors are developed for wearable applications including motion sensors and glucose monitors. This study offers viable approaches for modulating the optical anisotropy of low-dimensional materials and emphasizes the versatility of van der Waals materials for practical applications in wearable electronic devices.

With the uniquely-designed one-pot method and space-confined process, the controlled growth of a series of 2D-3D perovskite lateral heterostructures is achieved. Based on the tunable dual-band optical response characteristics, a wavelength-tunable light communication system based on the lateral heterostructure is realized. This work provides a convenient and reliable approach for the direct growth of mixed-dimensional halide perovskite heterostructures, further demonstrating their potential in high-performance detecting and dual-band sensing fields.

Abstract

Lateral heterostructures based on halide perovskites exhibit great potential in the advancement of next-generation optoelectronic devices. Among them, mixed dimensional perovskite heterostructures, particularly 2D-3D ones, offer promising opportunities for semiconductor integration and device miniaturization by combining the advantages of 2D and 3D perovskites. However, the controllable and rapid growth of 2D-3D halide perovskite lateral heterostructures has not yet been achieved. This study presents an efficient strategy that integrates one-pot method and space-confined process to enable liquid-phase lateral growth of a series of 2D Ruddlesden-Popper (RP) perovskites on the sides of 3D perovskites. The photodetectors (PDs) based on (BA)₂MA_n-1Pb_nBr_3n+1-MAPbBr₃ (n = 1, 2, 3) lateral heterostructures demonstrate outstanding optoelectronic performance, featuring an on/off ratio of up to 1.4 × 10⁴, a high responsivity of 4.4 A W⁻¹ and a detectivity of 3.9 × 10¹³ Jones at 425 nm, 3 V bias. In addition, by combining the tunable dual-band photoresponse characteristic with the dual-beam irradiation modes, a wavelength-tunable light communication system based on the lateral heterostructure PDs is realized. This work provides a convenient and reliable approach for the direct growth of mixed-dimensional halide perovskite heterostructures, further demonstrating their potential in high-performance detecting and dual-band sensing fields.

Nature Communications, Published online: 02 November 2024; doi:10.1038/s41467-024-53907-w

A novel two-step method that facilitates the heterogeneous integration of high-quality BaTiO₃ (BTO) capacitors onto silicon substrates is presented, resulting in robust ferroelectric, electromechanical, and endurance characteristics. By employing a templated layer of BTO, larger-area heterogeneous integration of BTO on silicon is achieved. This advancement paves the way for incorporating epitaxial complex oxides with various functionalities onto different inorganic substrates.

Abstract

Integrating epitaxial BaTiO₃ (BTO) with Si is essential for leveraging its ferroelectric, piezoelectric, and nonlinear optical properties in microelectronics. Recently, heterogeneous integration approaches that involve growth of BTO on ideal substrates followed by transfer to a desired substrate show promise of achieving excellent device-quality films. However, beyond simple demonstrations of the existence of ferroelectricity, robust devices with high endurance are not yet demonstrated on Si using the latter approach. Here, using a novel two-step approach to synthesize epitaxial BTO using pulsed laser deposition on water-soluble Sr₃Al₂O₆ (on SrTiO₃ substrates), successful integration of high-quality BTO capacitors on Si is demonstrated, with remanent polarisation P_r = 7 µC cm⁻², coercive field E_c = 150 kV cm⁻¹, ferroelectric and electromechanical endurance of > 10⁶ cycles. The study further addresses the challenge of cracking and disintegration of thicker films by first transferring a large area (5 mm x 5 mm) of the templated layer of BTO (≈30 nm thick) on the desired substrate, followed by the growth of high-quality BTO on this substrate, as revealed by high-resolution X-ray diffraction (HRXRD) and high-resolution scanning transmission electron microscopy (HRSTEM) measurements. These templated Si substrates offer a versatile platform for integrating any epitaxial complex oxides with diverse functionalities onto any inorganic substrate.

In this work, the syntheses of two photo-sensitive and thermoresponsive hydrogel systems, a photo-stiffening and a photo-softening hydrogel, are reported. Their potential for fabricating soft materials with patterned mechanical properties is then demonstrated by fabricating an actuator whose higher-order bending properties can be switched on with light, and by encoding mechanical properties for digital information encryption and storage.

Abstract

Although different chemistries for the spatio-temporal localization of molecules and gradients of chemical signals within soft materials are now available, the achievement of spatio-temporal patterns of mechanical properties in such materials and their characterization remain considerable challenges. This study presents the syntheses of two novel photo-sensitive and thermoresponsive hydrogel systems, a photo-stiffening and a photo-softening hydrogel. Their potential for fabricating soft materials with patterned mechanical properties is then demonstrated by fabricating an actuator whose higher-order bending properties can be switched on with light, and by encoding mechanical properties for digital information encryption and storage. Microindentation and a custom-made data analysis software are essential for the characterization of all the materials. From a general perspective, this work opens a route to the fabrication of soft materials with patterned mechanical properties, addressing an important emerging challenge in soft materials science with applications in soft robotics and information encryption and storage.

A novel synthesis route of achieving 5-armchair graphene nanoribbons with high purity and long length via confined polymerization of non-halogen precursors inside single-walled carbon nanotubes is proposed, breaking the strong dependence on metal substrates and halogen-containing precursors in current on-surface synthesis of such graphene nanoribbons with a quasi-metallic gap promising in electronics and optoelectronics.

Abstract

Armchair graphene nanoribbons (AGNRs) known as semiconductors are holding promise for nanoelectronics applications and sparking increased research interest. Currently, synthesis of 5-AGNRs with a quasi-metallic gap has been achieved using perylene and its halogen-containing derivatives as precursors via on-surface synthesis on a metal substrate. However, challenges in controlling the polymerization and orientation between precursor molecules have led to side reactions and the formation of by-products, posing a significant issue in purity. Here a precision synthesis of confined 5-AGNRs using molecular-designed precursors without halogens is proposed to address these challenges. Perylene and its dimer quaterrylene are utilized for filling into single-walled carbon nanotubes (SWCNTs), following a precursor-driven transition into 5-AGNRs by heat-induced polymerization and cyclodehydrogenation. SWCNTs restrict the alignment of confined quaterrylene enabling their polymerization with a head-to-tail arrangement, which results in the formation of pure 5-AGNRs with three times higher yield than that of perylene, as the free rotation capability of perylene molecules inside SWCNTs lead to the formation of 5-AGNRs concomitant with by-products. This work provides a templated route for synthesizing desired GNRs based on molecular-designed precursors and confined polymerization, bringing advantages for their applications in electronics and optoelectronics.

A series of hollow TMDCs@C fibers are synthesized via a sacrificial template method and the confined growth strategy. The complex permittivity can be adjusted by tuning the content of CdS templates. Multidimensional interfacial design of the composites can enhance interfacial polarization and establish conductive networks simultaneously, thereby improving microwave absorption performance.

Abstract

Interface design has enormous potential for the enhancement of interfacial polarization and microwave absorption properties. However, the construction of interfaces is always limited in components of a single dimension. Developing systematic strategies to customize multidimensional interfaces and fully utilize advantages of low-dimensional materials remains challenging. Two-dimensional transition metal dichalcogenides (TMDCs) have garnered significant attention owing to their distinctive electrical conductivity and exceptional interfacial effects. In this study, a series of hollow TMDCs@C fibers are synthesized via sacrificial template of CdS and confined growth of TMDCs embedded in the fibers. The complex permittivity of the hollow TMDCs@C fibers can be adjusted by tuning the content of CdS templates. Importantly, the multidimensional interfaces of the fibers contribute to elevating the microwave absorption performance. Among the hollow TMDCs@C fibers, the minimum reflection loss (RL_min) of the hollow MoS₂@C fibers can reach −52.0 dB at the thickness of 2.5 mm, with a broad effective absorption bandwidth of 4.56 GHz at 2.0 mm. This work establishes an alternative approach for constructing multidimensional coupling interfaces and optimizing TMDCs as microwave absorption materials.

Here, results on the tailored growth of various 2D semiconductors’ monolayers of transition metal dichalcogenides are presented using chemical vapor deposition techniques. Basic electronic, photonic and optoelectronic properties of the grown quantum materials are studied by high-resolution microscopy and spectroscopy techniques and are analyzed for possible device applications.

Abstract

Here, results on the tailored growth of monolayers (MLs) of transition metal dichalcogenides (TMDs) are presented using chemical vapor deposition (CVD) techniques. To enable reproducible growth, the flow of chalcogen precursors is controlled by Knudsen cells providing an advantage in comparison to the commonly used open crucible techniques. It is demonstrated that TMD MLs can be grown by CVD on large scale with structural, and therefore electronic, photonic and optoelectronic properties similar to TMD MLs are obtained by exfoliating bulk crystals. It is shown that besides the growth of the “standard” TMD MLs also the growth of MLs that are not available by the exfoliation is possible including examples like lateral TMD₁–TMD₂ ML heterostructures and Janus TMDs. Moreover, the CVD technique enables the growth of TMD MLs on various 3D substrates on large scale and with high quality. The intrinsic properties of the grown MLs are analyzed by complementary microscopy and spectroscopy techniques down to the nanoscale with a particular focus on the influence of structural defects. Their functional properties are studied in devices including field-effect transistors, photodetectors, wave guides and excitonic diodes. Finally, an outlook of the developed methodology in both applied and fundamental research is given.

Nature Electronics, Published online: 23 October 2024; doi:10.1038/s41928-024-01244-7

Combining time-resolved optical spectroscopy and surface acoustic waves provide a powerful tool for investigating charge carrier dynamics in 2D materials. When interacting with the 2D semiconductor WSe₂, dynamic acoustic Poole–Frenkel activation of traps enhances the optical emission efficiency. The sub-nanosecond modulation of the optical signal serves as a sensitive local probe of defects and charge carrier trapping sites.

Abstract

The charge carrier dynamics are investigated by surface acoustic waves (SAWs) inside a WSe₂ monolayer on LiNbO₃ by scanning acousto-optoelectric spectroscopy. A strong enhancement of the PL emission intensity is observed almost over the entire area of the flake. This enhancement increases with increasing amplitude of the wave and is especially strong at or in the vicinity to defects. The latter is attributed to the SAW-driven Poole–Frenkel activation of trapped charge carriers bound to trapping sites at these defects. In addition, the PL intensity exhibit clear periodic modulations at the SAW's frequency f _SAW and at 2 f _SAW. These modulations are clear and unambiguous fingerprints of spatio-temporal carrier dynamics driven by the SAW. These occur on sub-nanosecond timescales which are found in good agreement with calculated exciton dissociation times. Mapping and analyzing both effects, this study shows that scanning acousto-electric spectroscopy provides a highly sensitive and local contact-free probe which uncovers distinct local features not resolved by conventional quasi-static photoluminescence techniques. The method is ideally suited to study carrier transport in 2D and other types of nanoscale materials and to reveal dynamic exciton modulation, and carrier localization and activation dynamics in the technologically important megahertz to gigahertz frequency range.

A robust plasma-assisted (RPA) synthesis strategy is introduced with a specially designed tube for a uniform plasma atmosphere. This enables broader growth parameter variations while preserving Janus MoSSe's morphology. Enhancements in photoluminescence (PL) are achieved through bis(trifluoromethane) sulfonimide (TFSI) treatment, resulting in a 70-fold PL intensity increase and a quantum yield (QY) of 31.2%.

Abstract

Janus transition metal dichalcogenides (TMDs) are a novel class of 2D materials with unique mirror asymmetry. Plasma-assisted synthesis at room temperature is favored for producing Janus TMDs due to its energy efficiency and prevention of alloying. However, current methods require stringent control over growth conditions, risking defects or unintended materials. A robust plasma-assisted (RPA) synthesis strategy is introduced, incorporating a built-in tube with a suitable inner diameter into the plasma-assisted system. This innovation creates a mild, uniform plasma atmosphere, allowing for broader variations in growth parameters without significantly affecting Janus MoSSe's morphology and characteristics. This approach simplifies the synthesis process and enhances the success rate of Janus TMD production. Additionally, methods are explored to enhance the photoluminescence (PL) of Janus MoSSe. Releasing MoSSe from the growth substrate and annealing it removes strain and unintentional doping, improving PL performance. MoSSe on hexagonal boron nitride (h-BN) flakes after annealing shows a 32-fold increase in PL intensity. Bis(trifluoromethane) sulfonimide (TFSI) treatment of MoSSe results in a remarkable 70-fold increase in PL intensity, a 2.5-fold extension in exciton lifetime, and quantum yield (QY) reaching up to ≈31.2%. These findings provide critical insights for optimizing the luminescence properties of 2D Janus materials, advancing Janus optoelectronics.

In this paper, it is observed that polarization retention and stability of ferroelectric Hf_0.5Zr_0.5O₂ (HZO) are significantly dependent on humidity. Elimination of absorbed water shows a significant effect in improving polarization stability and suppressing imprinting characteristics. This work provides a novel understanding of the relationship between surface electrochemistry and ferroelectricity in HfO₂-based ferroelectric materials.

Abstract

The discovery of nanoscale ferroelectricity in hafnia (HfO₂) has paved the way for next generation high-density, non-volatile devices. Although the surface conditions of nanoscale HfO₂ present one of the fundamental mechanism origins, the impact of external environment on HfO₂ ferroelectricity remains unknown. In this study, the deleterious effect of ambient moisture is examined on the stability of ferroelectricity using Hf_0.5Zr_0.5O₂ (HZO) films as a model system. It is found that the development of an intrinsic electric field due to the adsorption of atmospheric water molecules onto the film's surface significantly impairs the properties of domain retention and polarization stability. Nonetheless, vacuum heating efficiently counteracts the adverse effects of water adsorption, which restores the symmetric electrical characteristics and polarization stability. This work furnishes a novel perspective on previous extensive studies, demonstrating significant impact of surface water on HfO₂-based ferroelectrics, and establishes the design paradigm for the future evolution of HfO₂-based multifunctional electronic devices.

Nature Materials, Published online: 29 October 2024; doi:10.1038/s41563-024-02013-9

Out-of-plane magnetic field (B)-induced giant electric hysteretic responses to back-gate voltages in monolayer (ML) MoS₂ field-effect transistors (FETs) below 20 Kelvin are observed and attributed to asymmetric lattice expansion with increasing |B| in ML-MoS₂ FETs on rigid SiO₂/Si substrates, leading to mirror symmetry breaking in ML-MoS₂ and the emergence of a tunable out-of-plane ferroelectric-like polar order.

Abstract

In semiconducting monolayer transition metal dichalcogenides (ML-TMDs), broken inversion symmetry and strong spin-orbit coupling result in spin-valley lock-in effects so that the valley degeneracy may be lifted by external magnetic fields, potentially leading to real-space structural transformation. Here, magnetic field (B)-induced giant electric hysteretic responses to back-gate voltages are reported in ML-MoS₂ field-effect transistors (FETs) on SiO₂/Si at temperatures < 20 K. The observed hysteresis increases with |B| up to 12 T and is tunable by varying the temperature. Raman spectroscopic and scanning tunneling microscopic studies reveal significant lattice expansion with increasing |B| at 4.2 K, and this lattice expansion becomes asymmetric in ML-MoS₂ FETs on rigid SiO₂/Si substrates, leading to out-of-plane mirror symmetry breaking and the emergence of a tunable out-of-plane ferroelectric-like polar order. This broken symmetry-induced polarization in ML-MoS₂ shows typical ferroelectric butterfly hysteresis in piezo-response force microscopy, adding ML-MoS₂ to the single-layer material family that exhibits out-of-plane polar order-induced ferroelectricity, which is promising for such technological applications as cryo-temperature ultracompact non-volatile memories, memtransistors, and ultrasensitive magnetic field sensors. Moreover, the polar effect induced by asymmetric lattice expansion may be further generalized to other ML-TMDs and achieved by nanoscale strain engineering of the substrate without magnetic fields.

Publication date: Available online 29 October 2024

Source: Materials Today

Author(s): Bixuan Li, Lei Zheng, Yongji Gong, Peng Kang

Nature, Published online: 30 October 2024; doi:10.1038/s41586-024-08118-0

Nature, Published online: 30 October 2024; doi:10.1038/s41586-024-08116-2