Jiuxiang Dai

The multifunctional Nb₃Se₁₂I photodetector integrated broadband imaging and encrypted communications are realized based on the photothermoelectric effect and polarization sensitivity. The photothermoelectric and photoconductive effect synergistic detection mechanism enable high responsivity and rapid operation across a broad wavelength spectrum from deep-ultraviolet to terahertz. The encrypted method of polarization state compensation for photothermoelectric current converting image data into polarization states enhances information security. This work provides an effective strategy to advance anisotropic thermoelectric materials for high-capacity, secure communication applications.

Abstract

Securing high-capacity and safe communication holds great potential for ushering in the new era of digital society. In this study, a wide-band photodetector based on the quasi-1D niobium selenide compounds (Nb₃Se₁₂I), showing up photothermoelectric (PTE) dominated multiple synergistic effects with high responsivity across a wide wavelength range from deep-ultraviolet (254 nm) to terahertz (0.30 THz), providing an efficient strategy for high-capacity optical processing is introduced. Combined with the polarized-sensitive property of the Nb₃Se₁₂I photodetector, an encrypted imaging technology using polarization-resolved PTE current is developed. This technology is capable of transforming encrypted messages into polarization states, which can be restored through a specially designed decryption algorithm, greatly enhancing the concealment and security of the information transmission process. Overall, the Nb₃Se₁₂I-based detector manifests in terms of high responsivity (283.2 A W⁻¹ to 520 nm, 1632.4 A W⁻¹ to 980 nm, and 1868.1 A W⁻¹ for short-wave infrared light of 2200 nm), suitable response speed of 43 µs for 0.30 THz wave and polarization anisotropy ratio of 1.83. The versatile abilities of photodetector in the realm of ultrabroadband polarized detection and encryption imaging may advance the use of anisotropic thermoelectric materials in high-capacity and secure information communication applications.

Colossal strain tuning of ferroelectricity is demonstrated in biaxially compressive strained epitaxial KNbO₃ thin films, demonstrating a dramatic strain enhancement of ferroelectric polarization and the Curie temperature, eliminating all bulk phase transitions and stabilizing a single tetragonal phase from 5 K to 975 K.

Abstract

Strong coupling between polarization (P) and strain (ɛ) in ferroelectric complex oxides offers unique opportunities to dramatically tune their properties. Here colossal strain tuning of ferroelectricity in epitaxial KNbO₃ thin films grown by sub-oxide molecular beam epitaxy is demonstrated. While bulk KNbO₃ exhibits three ferroelectric transitions and a Curie temperature (T_c ) of ≈676 K, phase-field modeling predicts that a biaxial strain of as little as −0.6% pushes its T_c > 975 K, its decomposition temperature in air, and for −1.4% strain, to T_c > 1325 K, its melting point. Furthermore, a strain of −1.5% can stabilize a single phase throughout the entire temperature range of its stability. A combination of temperature-dependent second harmonic generation measurements, synchrotron-based X-ray reciprocal space mapping, ferroelectric measurements, and transmission electron microscopy reveal a single tetragonal phase from 10 K to 975 K, an enhancement of ≈46% in the tetragonal phase remanent polarization (P_r ), and a ≈200% enhancement in its optical second harmonic generation coefficients over bulk values. These properties in a lead-free system, but with properties comparable or superior to lead-based systems, make it an attractive candidate for applications ranging from high-temperature ferroelectric memory to cryogenic temperature quantum computing.

Author(s): Woncheol Lee, Antonios M. Alvertis, Zhenglu Li, Steven G. Louie, Marina R. Filip, Jeffrey B. Neaton, and Emmanouil Kioupakis

Atomically thin semiconductors, encompassing both 2D materials and quantum wells, exhibit a pronounced enhancement of excitonic effects due to geometric confinement. Consequently, these materials have become foundational platforms for the exploration and utilization of excitons. Recent ab initio stu…

[Phys. Rev. Lett. 133, 206901] Published Wed Nov 13, 2024

Nature Electronics, Published online: 14 November 2024; doi:10.1038/s41928-024-01299-6

Defects make better semiconductors

This article presents a retina-inspired X-ray optoelectronic synapse. The slow neutralization rate of V_O ²⁺ states in a-Ga₂O₃ is utilized to contribute to the non-volatile post-synaptic current. Real-time X-ray image sensing, memorizing, and contrast-enhancing functions are achieved on a 64 × 64 sensor array, effectively promoting the recognition efficiency of following artificial neutral network simulations.

Abstract

Machine vision techniques are widely applied for object identification in daily life and industrial production, where images are captured and processed by sensors, memories, and processing units sequentially. Neuromorphic optoelectronic synapses, as a preferable option to promote the efficiency of image recognition, are hotly pursued in non-ionizing radiation range, but rarely in ionizing radiation including X-rays. Here, the study proposes an X-ray optoelectronic synapse using amorphous Ga₂O₃ (a-Ga₂O₃) thin film. Boosted by the interfacial V_O ²⁺ defects and its slow neutralization rate, the enhanced electron tunneling process at metal/a-Ga₂O₃ interface produces remarkable X-ray-induced post-synaptic current, contributing to a sensitivity of 20.5, 64.3, 164.1 µC mGy⁻¹ cm⁻² for the 1st, 5th, and 10th excitation periods, respectively. Further, a 64 × 64 imaging sensor is constructed on a commercial amorphous Si (a-Si) thin film transistor (TFT) array. The image contrast can be apparently improved under a series of X-ray pulses due to an outstanding long-term plasticity of the single pixel, which is beneficial to the subsequent image recognition and classification based on artificial neural network. The merits of large-scale production ability and good compatibility with modern microelectronic techniques belonging to amorphous oxide semiconductors may promote the development of neuro-inspired X-ray imagers and corresponding machine vision systems.

Nature Electronics, Published online: 15 November 2024; doi:10.1038/s41928-024-01286-x

Ultrathin films of gallium oxide with a dielectric constant of around 30 can be formed on the surface of molybdenum disulfide using a liquid metal-based approach and used as the gate insulator in transistors.

We present a high-throughput approach for constructing macroscopic 3D superstructures with three-axis periodicity using single-crystalline 2D materials. We achieve rapid, bottom-up stacking to form 200-layer 3R-MoS₂ structures and incorporates oxide interlayers for quasi-phase matching in nonlinear optical crystals. This technique enables atomic layer precision in 3D crystal construction with tailored material properties.

Abstract

2D stacking presents a promising avenue for creating periodic superstructures that unveil novel physical phenomena. While extensive research has focused on lateral 2D material superstructures formed through composition modulation and twisted moiré structures, the exploration of vertical periodicity in 2D material superstructures remains limited. Although weak van der Waals interfaces enable layer-by-layer vertical stacking, traditional methods struggle to control in-plane crystal orientation over large areas, and the vertical dimension is constrained by unscalable, low-throughput processes, preventing the achievement of global order structures. In this study, a supercell multiplying approach is introduced that enables high-throughput construction of 3D superstructures on a macroscopic scale, utilizing artificially stacked single-crystalline 2D multilayers as foundational repeating units. By employing wafer-scale single-crystalline 2D materials and referencing the crystal orientation of substrates, the method ensures precise alignment of crystal orientation within and across each supercell, thereby achieving controllable periodicity along all three axes. A centimeter-scale 3R-MoS₂ crystal is successfully constructed, comprising over 200 monolayers of single-crystalline MoS₂, through a bottom-up stacking process. Additionally, the approach accommodates the integration of amorphous oxide, enabling the assembly of 3D non-linear optical crystals with quasi-phase matching. This method paves the way for the bottom-up construction of macroscopic artificial 3D crystals with atomic plane precision, enabling tailored optical, electrical, and thermal properties and advancing the development of novel artificial materials and high-performance applications.

Nature Communications, Published online: 20 November 2024; doi:10.1038/s41467-024-54360-5

Point defects in 2D semiconductors hold potential as single photon emitters (SPEs), but their controlled fabrication and microscopic understanding remain a challenge. Here, the authors report the synthesis of dilute Nb-doped monolayer WS2, showing that Nb impurities behave as SPEs with well-defined emission energies.

Advanced Materials, Volume 37, Issue 4, January 29, 2025.

This comprehensive study encompasses the coating of various carbon-based nanostructures on piston rings of a fired engine via modified electron cyclotron resonance–chemical vapor carbon deposition technique. Exceptional features of nanostructures from diamond-like carbon family along with precise experimental procedure and measurements provide considerable amount of enhancement in tribological characteristics of friction pairs which also yield reduction in fuel consumption, exhaust emissions, and improvement in engine power.

Electron cyclotron resonance-chemical vapor carbon deposition technique was altered via incorporation of nitrogen gas in the methane (CH₄)-based plasma, thermal annealing of the substrates, and Arduino-controlled sample rotating mechanism to bombard the contact surface of the piston ring samples. By placing the substrates very close to the plasma gun, various carbon-based structures including graphene oxide, nanodiamond, and reduced graphene oxide were successfully deposited. The formed structures were characterized via scanning electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray diffraction, and energy dispersive X-ray. Related tribological analyses such as surface hardness-roughness, coefficient of friction (COF), and wear rate were also carried out on the coated surfaces. The morphology and chemical composition of the worn surfaces were observed via SEM and EDX. The coated samples were installed in a small spark-ignition engine to determine the effect of coating on brake power (P _e), specific energy consumption (β), carbon monoxide (CO), and unburned hydrocarbon (UHC) emissions. Very promising results of 14% increase in surface hardness, 11% reduction in β, 15% enhancement in P _e, 50% decrease in COF, 12.5% and 9% improvements in CO, and UHC emissions were obtained.

Publication date: December 2024

Source: Materials Today, Volume 81

Author(s): Chao Zhao, Liang Shan, Rong Sun, Xiao Wang, Feng Ding

Nature Synthesis, Published online: 15 November 2024; doi:10.1038/s44160-024-00679-2

Phase-switchable preparation of two-dimensional WS2 is achieved through an electrochemical Li+ intercalation-based exfoliation strategy. A low discharge current density with high cutoff voltage produces pure semiconducting 2H phase WS2 bilayers, while a higher discharge current density with a lower cutoff voltage favours semimetallic 1T′ phase WS2 monolayers.

The growth and shape evolution of indium nanoplate by in situ liquid cell transmission electron microscopy is observed. The growth mechanism and the important role of multiple twins are also provided.

Abstract

Understanding the growth mechanisms of nanomaterials is crucial for effectively controlling their morphology which may affect their properties. Here, the growth process of indium nanoplates is studied using in situ liquid cell transmission electron microscopy. Quantitative analysis shows that the growth of indium nanoplate is limited by surface reaction. Besides, the growth process has two stages, which is different from that of other metal nanoplates reported previously. At the first stage, indium particles transform gradually from face-centered cubic to body-centered tetragonal (bct) structure as the seeds grow. At the second stage, the seeds grow faster than at the first stage and form indium triangular nanoplates. Indium triangular nanoplates have a bct structure with {011}-twin, which is found to form through kinetic reactions. In addition, the shape evolution of truncated triangle nanoplate with multiple twin planes is studied. The growth rate of truncated edge changes with the varied number of re-entrant grooves. The present work provides valuable insights into the growth mechanism of metal nanoplates with low-symmetric structure and the role of twin planes in the shape evolution of plate-like metal nanomaterials.

Nature Physics, Published online: 12 November 2024; doi:10.1038/s41567-024-02709-4

Complex oxides have competing phases with different spin, electronic and orbital order. Now it has been shown that growing thin films on different facets of a low-symmetry substrate can be used to control the phase of the ground state.