Jiuxiang Dai

Polyimides (PIs) are advanced polymeric materials well known for their excellent thermal, electrical insulating, mechanical, chemical properties, and compatibility to various semiconducting materials. In this work, the new-type of PIs yielding high-k properties is synthesized and successfully applied to practical application for low-voltage operating all-printed electronics from unit to integrated devices.

Abstract

Polyimide-based dielectric films are widely used in various thin film devices including organic field-effect transistors (OFETs) owing to their promising thermal/chemical stability, mechanical flexibility, and insulating properties. On the other hand, considerable attention is paid to lowering the process temperature to allow coating on plastic substrates because high-temperature annealing (≈200 °C) is usually required to convert precursors to polyimide films with those excellent properties. In addition, polyimide-based dielectric films have low dielectric constants (k) (<4). Therefore, modifying the k properties of polyimide is a critical issue for applications as an insulating thin film for practical transistors. This paper reports a new type of polyimide-based gate dielectric comprising methacryloyl moiety (PI-MA) as a side chain for photo-pattern/processability and high-k properties. This study shows that the photocured PI-MA thin films show excellent insulating properties (leakage current densities < 10⁻⁸ A cm⁻² at 4 MV cm⁻¹) and high-k properties (≈8) even without a post-annealing process. Finally, the use of PI-MA in printed field-effect transistors results in high performance with low-voltage operation (within 5 V) and integrated logic-gate devices (NOT, NAND, and NOR gates).

Nature Materials, Published online: 08 January 2025; doi:10.1038/s41563-024-02067-9

Light chirality and electron spin interactions and the dependence of tunnelling photocurrent on the magnetic field are studied in indium selenide, exploiting its non-symmetric response to circularly polarized light to electrically detect chirality.

Nature, Published online: 08 January 2025; doi:10.1038/s41586-024-08295-y

Proximity ferroelectricity is reported in wurtzite heterostructures, which enables polarization reversal in wurtzites without the chemical or structural disorder that accompanies elemental substitution.

Nature, Published online: 08 January 2025; doi:10.1038/s41586-024-08373-1

A method to produce wireless microelectronic devices powered by light using standard nanofabrication techniques is described to convert any traditional 96-well or 384-well plate into an electrochemical reactor that can drive reactions in high throughput.

2D LaMnO₃ are prepared by a supercritical CO₂-guided passivation strategy, which successfully repair the oxygen defects in LaMnO₃. This provides new possibilities for device applications.

Abstract

The development of 2D magnetic materials and the modulation of intrinsic magnetism are essential for the exploration of new materials in the field of information storage. Despite its strong ferromagnetic properties, LaMnO₃ is hindered by a high number of oxygen defects, which result in a relatively short lifetime when employed in electronic memory devices. Here the successful transformation of bulk LaMnO₃ into a 2D structure using supercritical carbon dioxide.is reported. This technique enables the successful modulation of the magnetic properties of the material. Interestingly, it is found that the oxygen defect is repaired, which is in sharp contrast to conventional perovskites. These promising results demonstrate the potential of using the magnetic properties of LaMnO₃, which is of great importance in the context of expanding its application in electronic devices.

This study explores the temperature-dependent properties of TiO₂ thin films grown by atomic layer deposition using tetrakis dimethyl amino titanium and water. The films exhibit increased oxynitride incorporation as the process temperature increases from 150 to 350 °C, significantly influencing their optical and electrical properties. Findings highlight the role of secondary reaction pathways, providing insights to optimize TiO₂ films for optoelectronic applications through the choice of process conditions.

Abstract

This study investigates the presence of titanium oxynitride bonds in titanium dioxide (TiO₂) thin films grown by atomic layer deposition (ALD) using tetrakis dimethyl amino titanium (TDMAT) and water at temperatures between 150 and 350 °C and its effect on the films’ optical and electrical properties. Compositional analysis using X-ray photoelectron spectroscopy (XPS) reveals increased incorporation of oxynitride bonds as the process temperature increases. Furthermore, depth profile data demonstrates an increase in the abundance of this type of bonding from the surface to the bulk of the films. Ultraviolet-visible spectroscopy (UV-vis) measurements correlate increased visible light absorption for the films with elevated oxynitride incorporation. The optical constants (n, k) of the films show a pronounced dependence on the process temperature that is mirrored in the film conductivity. The detection of oxynitride bonding suggests a secondary reaction pathway in this well-established ALD process chemistry, that may impact film properties. These findings indicate that the choice of process chemistry and conditions can be used to optimize film properties for optoelectronic applications.

Nature Electronics, Published online: 06 January 2025; doi:10.1038/s41928-024-01306-w

Using a polymer stamp with a period arrangement of micro-posts on its surface and a high surface tension liquid, two-dimensional material films can be patterned and transferred on a large-scale with high yield.

Epitaxy is a key enabler of next-generation nano/microelectronics and solid-state quantum information systems. Demands on epitaxy of emerging materials including 2D materials and quantum materials are rapidly growing to realize various proposed applications. In the perspective, the current and foreseeable future of epitaxy research including integration of modeling and ultimate control of the epitaxy process are discussed.

Abstract

Epitaxy, a process to prepare crystalline materials in nanostructures and thin films, is the core technology for preparing high-quality materials as a key enabler of next-generation microelectronics and quantum information system. Progress in epitaxy has been expanding the choice of materials and their heterostructures beyond the combinations limited by materials compatibility. However, the improvement of material quality, physical implementation of materials with unique properties, and integration of incommensurate materials in an architecture have been the challenging issues. Emerging materials, including 2D materials and quantum materials, have opened opportunities to study epitaxy mechanisms and realize various functional devices. Acceleration of discovery and progress in epitaxy research should be accomplished by “understanding of epitaxy under various circumstances at multiple length scales” and “integration of experiments and models.” In the perspective, a basic summary of the status of epitaxially grown materials, the challenges in epitaxy research, and integration of modeling epitaxy and ultimate control of the epitaxy process with advanced characterization techniques are discussed.

Kinetically tailored CVD process is demonstrated for the synthesis of large-area thin films of 2D non-layered materials under a modulated vapor pressure of feedstock gas. The as-synthesized 2D non-layered MoN thin films exhibited excellent SERS properties and high stability.

Abstract

Non-layered 2D materials offer unique and more advantageous physicochemical properties than those of conventional 2D layered materials. However, the isotropic chemical bonding nature of non-layered materials hinders their lateral growth, making the synthesis of large-area continuous thin films challenging. Herein, a facile kinetically tailored chemical vapor deposition (KT-CVD) approach is introduced for the synthesis of 2D molybdenum nitride (MoN), a representative non-layered material. Large-scale thin films of MoN with lateral dimensions of up to 1.5 cm × 1.5 cm are obtained by modulating the vapor pressure of nitrogen feedstock and disrupting the thermodynamically favored growth kinetics of non-layered materials. The growth of stable crystalline phases of MoN (δ-MoN and γ-Mo₂N) is also realized using the proposed KT-CVD approach. The δ-MoN synthesized via KT-CVD demonstrates excellent surface-enhanced Raman scattering and robust thermal stability. This study provides an effective strategy for developing scalable and high-quality non-layered 2D materials, expanding the fabrication and application of devices based on non-layered materials.

Developing advanced technology to efficiently screen the Dirac materials in transition metal dichalcogenides (TMDCs) is highly critical for achieving advanced photoelectric properties. This work reports the establishment of a comprehensive database including 90 types of TMDCs and investigates their response behaviors under external strains regarding the presence of Dirac cones and electronic structure evolutions, supplying information from electronic perspectives.

Abstract

Discovering and utilizing the unique optoelectronic properties of transition metal dichalcogenides (TMDCs) is of great significance for developing next-generation electronic devices. In particular, research on Dirac state modulations of TMDCs under external strains is lacking. To fill this research gap, it has established a comprehensive database of 90 types of TMDCs and their response behaviors under external strains have been systematically investigated regarding the presence of Dirac cones and electronic structure evolutions. Among all the conditions, 27.3% of the TMDCs are Dirac materials with three distinct types of Dirac cones, which are mainly attributed to the electron localizations induced by external strains. TMDCs based on tellurides with 1H phase favor the formation of Dirac cones under stresses, leading to metallic-like properties and ultra-fast charge transportation. Correlations among Dirac cones, energy, electronic properties, and lattice structures have been revealed, offering critical references for modulating the properties of well-known TMDCs. More importantly, it has confirmed that the phase transition points are not sufficient for the appearance of Dirac cones. This work provides critical guidance to facilitate the development of TMDCs-based superconducting and optoelectronic devices for broad applications.

npj 2D Materials and Applications, Published online: 07 January 2025; doi:10.1038/s41699-024-00520-6

Unconventional nonlinear Hall effects in twisted multilayer 2D materials

Nature Photonics, Published online: 07 January 2025; doi:10.1038/s41566-024-01598-6

Metasurfaces offer new possibilities for nonlinear optics, but efficiency is an issue. Researchers have now used DNA-mediated assembly to produce 3D nonlinear optical colloidal crystals whose effective nonlinear susceptibility rivals that of traditional dielectric nonlinear optical crystals.

Nature Reviews Chemistry, Published online: 08 January 2025; doi:10.1038/s41570-024-00671-6

Electrochemical methods to grow 2D metal chalcogenides are reviewed, emphasizing the effects of the precursor (or precursors), solvent and electrode designs. Emerging work using nano-band electrodes to promote in-plane 2D layer growth into ‘device-ready’ electrode structures is highlighted.

Driven by the pervasive and growing demands for miniaturization and energy efficiency in nanoelectronics, further reductions in the operating voltage of ferroelectric-based devices are dispensable in future information technologies. Here, the state-of-the-art strategies for reducing operating voltage in ferroelectric materials and devices, such as thickness scaling, defect engineering, chemical doping, surface and interfacial design, strain engineering, are reviewed.

Abstract

Ferroelectrics are considered to be promising candidates for highly energy-efficient electronic devices in future information technologies owing to their nonvolatile and low-energy operation of spontaneous electric polarization. Driven by the pervasive and growing demands for miniaturization and energy efficiency in nanoelectronics, further reductions in the operating voltage of ferroelectric-based devices are dispensable and thus have received immense attentions. Recent remarkable advances in atomic-scale synthesis, cutting-edge characterizations, and multiscale theoretical calculations of ferroelectrics have gained unprecedented insights into the manipulation of emergent functionalities in multiple length scales, which helps the discovery of nontrivial polar structures and designs of device architectures toward the promise of ultralow-power consumption. Here, state-of-the-art strategies for reducing operating voltage in ferroelectric materials and devices are reviewed. This article starts with a brief introduction and major achievements in ferroelectrics, and expounds on the techniques to probe the polarization-switching process. Moreover, this article focuses predominantly on recent advancements in achieving low operating voltages through various prevalent strategies such as thickness scaling, defect engineering, chemical doping, surface and interfacial design, strain engineering. Finally, perspectives with scientific and technical challenges are discussed, aiming to facilitate the energy-efficient applications of ferroelectric materials and devices in future information technologies.

Sputter-deposited large-area tellurium films with partial crystallinity are ineffective for detecting 532 nm light. To address this, Ar plasma treatment is introduced to improve the crystallinity of the tellurium films, which not only enhances their electrical characteristics but also significantly boosts their photoresponsivity.

Abstract

Promising 2D materials suitable for low-temperature processing are crucial for advancing beyond Moore's law. While p-type performance is as essential as n-type in CMOS technology, the development of high-performance p-type 2D materials has lagged behind their n-type counterparts. Here, high-performance p-type tellurium (Te) field-effect transistors (TeFETs) that undergo plasma treatment at low temperatures to enhance their electrical and optoelectrical properties are presented. Ar plasma-treated Te shows significantly improved crystallinity compared to untreated counterparts, confirmed by various characterization techniques. Plasma treatment shifts the Fermi level toward the valence band and induces subgap states near the valence band in the Te film. A valence band offset of 0.2 eV and 30.6% surface flattening are confirmed in plasma-treated TeFETs. The electrical performance of plasma-treated TeFETs exhibits a 20-fold increase in the Ion/Ioff ratio, from 1.2 × 104 to 2.7 × 104, and a 51% reduction in subthreshold swing, from 19.1 to 9.4 V per decade, compared to pristine devices. Stability and bias stress tests show resilience to degradation after plasma treatment. Notably, optoelectrical performance improves due to the trap-assisted photogating effect. These findings provide a promising pathway for improving p-type materials at low temperatures, facilitating their use in various next-generation electronic platforms.

Nature Synthesis, Published online: 03 January 2025; doi:10.1038/s44160-024-00704-4

A Li⁺-assisted liquid-phase reduction method is reported, which converts crystalline metal oxides into amorphous metal oxides. The electrostatic interaction between the naphthalene radical anions and Li⁺-inserted metal oxides is found to promote the amorphization process.

Two-dimensional (2D) nanomaterials, possessing unique physiochemical properties, revolutionize the field of biomedical engineering to address critical diagnostic and therapeutic challenges. This review unveils the periodic table of 2D immunomodulatory elements, assessing synthesis, properties, immunomodulatory mechanisms and biocompatibility. A comprehensive group-wise, element-by-element roadmap of nano-enabled immunomodulatory 2D materials is provided, discussing well-explored and emerging 2D elements, while noting those without current application in immunoengineering, drug delivery, cancer therapy and regenerative medicine.

Abstract

Periodic table of chemical elements serves as the foundation of material chemistry, impacting human health in many different ways. It contributes to the creation, growth, and manipulation of functional metallic, ceramic, metalloid, polymeric, and carbon-based materials on and near an atomic scale. Recent nanotechnology advancements have revolutionized the field of biomedical engineering to tackle longstanding clinical challenges. The use of nano-biomaterials has gained traction in medicine, specifically in the areas of nano-immunoengineering to treat inflammatory and infectious diseases. Two-dimensional (2D) nanomaterials have been found to possess high bioactive surface area and compatibility with human and mammalian cells at controlled doses. Furthermore, these biomaterials have intrinsic immunomodulatory properties, which is crucial for their application in immuno-nanomedicine. While significant progress has been made in understanding their bioactivity and biocompatibility, the exact immunomodulatory responses and mechanisms of these materials are still being explored. Current work outlines an innovative “immunomodulatory periodic table of elements” beyond the periodic table of life, medicine, and microbial genomics and comprehensively reviews the role of each element in designing immunoengineered 2D biomaterials in a group-wise manner. It recapitulates the most recent advances in immunomodulatory nanomaterials, paving the way for the development of new mono, hybrid, composite, and hetero-structured biomaterials.

A unipolar barrier photodetector uncooled long-wave infrared nBn photodetector is demonstrated. The exciting experimental results include a record high light on/off ratio of ≈10¹⁰ and competitive fast speed with τ _r = 699 ns and τ _d = 452 ns are demonstrated with a 637 nm laser. This finds offers an alternative way for highly sensitive free space communication.

Abstract

Unipolar barrier architecture is designed to enhance the photodetector's sensitivity by inducing highly asymmetrical barriers, a higher barrier for blocking majority carriers to depressing dark current, and a low minority carrier barrier without impeding the photocurrent flow through the channel. Depressed dark current without block photocurrent is highly desired for uncooled Long-wave infrared (LWIR) photodetection, which can enhance the sensitivity of the photodetector. Here, an excellent unipolar barrier photodetector based on multi-layer (ML) graphene (G) is developed, WSe₂, and PtSe₂ (G-WSe₂-PtSe₂) van der Waals (vdW) heterostructure, in which extremely low dark current of 1.61×10⁻¹³ A, a record high light on/off ≈10⁹ are demonstrated at 0 V. Notably, the device exhibits ultrafast response speed with rise time τ _r = 699 ns and decay time τ _d = 452 ns and high-power conversion efficiency (η) of 4.87%. The heterostructure demonstrates a broadband photoresponse from 365 nm to LWIR 10.6 µm at room temperature. Notably, the G-WSe₂-PtSe₂ nBn device demonstrates high photoresponsivity (R) of 1.8 AW⁻¹ with 10.6 µm laser at 1 V bias in ambient air. This unipolar barrier device architecture offers an alternative way for highly sensitive free space communication.

Largely-twisted van der Waals (vdW) homojunction of two thin Fe₃GeTe₂ flakes exhibits pseudotunnel-magnet resistance behaviors even without intentional introduction of tunnel barrier layers, due to lattice-mismatch driven vdW gaps.

Abstract

Twistronics, a novel engineering approach involving the alignment of van der Waals (vdW) integrated two-dimensional materials at specific angles, has recently attracted significant attention. Novel nontrivial phenomena have been demonstrated in twisted vdW junctions (the so-called magic angle), such as unconventional superconductivity, topological phases, and magnetism. However, there have been only few reports on integrated vdW layers with large twist angles θ _t, such as twisted interfacial Josephson junctions using high-temperature superconductors. Herein, vdW homojunctions of the thin-magnetic flakes, Fe₃GeTe₂ (FGT), with large θ _t ranging from 0° to 90°, without inserting any tunnel barriers are assembled. Nevertheless, these vdW homojunctions exhibit tunnel-magnetoresistance (TMR) like behavior (pseudo-TMR (PTMR) effect) with the ratios highly sensitive to the θ _t values, revealing that the vdW gap at the junction interface between the twisted FGT layers behaves like a tunnel barrier and the θ _t serves a control parameter for PTMR by drastically varying magnitudes of the lattice-mismatch and the subsequent appearance of antiferromagnetic (AFM) spin alignment. First-principles calculations considering vacuum gaps indicate strong dependence of TMR on the θ _t driven by the sixfold screw rotational symmetry of bulk FGT. The present homojunctions hold promise as a platform for novel AFM spin-dependent phenomena and spintronic applications.

A novel and efficient method is explored to synthesize 1D single-crystal sub-stoichiometric W_nO_3n-2 (n = 25) nanowire bundles. The approach utilizes selective low-energy He+ ion irradiation (27 eV) on Mo-Ni doped WO_x surface, achieving efficient catalyst-free self-organized growth of high aspect ratio nanowires at the temperature of 700 °C. The synergistic effects of multiple factors, including temperature, electric field, doping, and shielding, contribute to the successful growth of these structures.

Abstract

Tungsten oxides (WO_x) possess unique properties due to a synergy of multiple effects arising from their wide range of stoichiometric and sub-stoichiometric compositions, defect chemistry, and polymorphism. Synthesis and incorporation of 1D WO_x nano-assemblies is an attractive pathway to enable highly efficient next-generation photocatalysts, sensors, and optoelectronic devices offering tunability over electro-optical response in a wide range of the spectrum, from UV–vis to NIR. However, synthesis of the metal oxide nano-patterns represents a technological challenge, often requiring the presence of a catalyst. Herein, a simple and economical method of synthesizing a catalyst-free self-organized sub-stoichiometric W_nO_3n-2 (n = 25) single crystal nanowire bundles by selectively irradiating a Mo-Ni doped WO_x surface with low-energy He⁺ ions (27 eV) at 700 °C is reported. The synergetic effect of multiple factors including temperature, effective local electric field along the exposed area of the sample, and the micro-gap between the mask and the WO_x (Mo – Ni) film, suitable oxygen content, doping, as well as shielding the nanowire growth area from the direct He⁺ ion irradiation is suggested to drive the single-crystal wire growth. Adjustment is also observed in the effective refractive index and extinction coefficient values in the synthesized W_nO_3n-2 nanorods across the solar spectrum.

The electrical resistivity of conventional metals such as copper is known to increase in thin films as a result of electron-surface scattering, thus limiting the performance of metals in nanoscale electronics. Here, we find an unusual reduction of ...