Jiuxiang Dai

Journal of Applied Physics, Volume 133, Issue 12, March 2023.
In this paper, we proposed and numerically demonstrated a giant enhancement up to in both fo[math]rward and backward propagation of the second harmonic generation by combining the high-quality factor cavities of the bound states in the continuum and the excellent nonlinear optical crystal of lithium niobate. The enhancement factor is defined as the ratio of the second harmonic signal generated by the structure (lithium niobate membrane with Si grating) divided by the signal generated by the lithium niobate membrane alone. Furthermore, a minimum interaction time of 350 ps is achieved despite the etching less lithium niobate membrane with a conversion efficiency of 4.77 × 10−6. The origin of the enhancements is linked to the excitation of a Fano-like shape symmetry-protected mode that is revealed by finite-difference time-domain simulations. The proposed platform opens the way to a new generation of efficient integrated optical sources compatible with nano-photonic devices for classical and quantum applications.

Journal of Applied Physics, Volume 133, Issue 12, March 2023.
Hexagonal manganites exhibit three distinct domain patterns: stripe, loop, and vortex. Due to the high ferroelectric phase transition temperature and the lack of reliable visualization methods, it is still a mystery about the evolution and the formation of vortex networks. In this study, we managed to capture the coexistence of vortices, loops, and stripes by accurately controlling the annealing temperature right at Tc. We proposed a merging process between the V–AV pair and the stripe, which result in two different forms of vortex networks, namely, the normal vortex and the zigzag vortex. In addition, the connection between the density of stripes and the orientation of V–AV pairs is analyzed, which are both influenced by self-straining of the crystal. The mystery of evolution of the vortex network is unveiled by capturing the snapshot, and the experimental database provided calls for more analysis to understand the evolution of different domain topologies.

Journal of Applied Physics, Volume 133, Issue 12, March 2023.
The [math] (KNN)-based ceramics have been deemed one of the most promising lead-free piezoelectric materials replacing lead-containing ones. In our study, we have prepared both undoped and Mn-doped KNN nanofibers via the electrospinning method and investigated how the thermal annealing process affects their structural, crystallographic, and piezoelectric properties. X-ray diffraction measurements suggest that the crystallization occurs around [math] in these fibers, and with increasing annealing temperature, both undoped and Mn-doped nanofibers become granular with small grains forming along the fiber, accompanying the crystallization. Both exhibit increasing piezoelectric properties with annealing temperature based on the piezoresponse force microscopy measurements with Mn-doping, leading to a higher piezoelectric response.

Applied Physics Letters, Volume 122, Issue 13, March 2023.
We report results from a systematic analysis of thermal transport in 2D diamond superstructures in interlayer-bonded twisted bilayer graphene (IB-TBG) based on molecular-dynamics simulations. We find that the introduction of interlayer C–C bonds in these bilayer structures causes an abrupt drop in the thermal conductivity of pristine, non-interlayer-bonded bilayer graphene, while further increase in the interlayer C–C bond density (2D diamond fraction) leads to a monotonic increase in the thermal conductivity of the resulting superstructures with increasing 2D diamond fraction toward the high thermal conductivity of 2D diamond (diamane). We also find that a similar trend is exhibited in the thermal conductivity of interlayer-bonded graphene bilayers with randomly distributed individual interlayer C–C bonds (RD-IBGs) as a function of interlayer C–C bond density, but with the thermal conductivity of the IB-TBG 2D diamond superstructures consistently exceeding that of RD-IBGs at a given interlayer bond density. We analyze the simulation results employing effective medium and percolation theories and explain the predicted thermal conductivity dependence on interlayer bond density on the basis of lattice distortions induced in the bilayer structures as a result of interlayer bonding. Our findings demonstrate that the thermal conductivity of IB-TBG 2D diamond superstructures and RD-IBGs can be precisely tuned by controlling interlayer C–C bond density and have important implications for the thermal management applications of interlayer-bonded few-layer graphene derivatives.

Nanosecond laser annealing of amorphous ZrO₂ thin films is shown to produce the orthorhombic structure with ferroelectric properties: saturation polarization of 12.8 µC cm⁻², remnant polarization of 12.7 µC cm⁻² and coercive field of 1.2 MV cm⁻¹. Thus, the creation of ZrO₂-based memory devices by a simple industrial process is demonstrated.

Abstract

A new approach for the stabilization of the ferroelectric orthorhombic ZrO₂ films is demonstrated through nanosecond laser annealing (NLA) of as-deposited Si/SiO _x /W(14 nm)/ZrO₂(8 nm)/W(22 nm), grown by ion beam sputtering at low temperatures. The NLA process optimization is guided by COMSOL multiphysics simulations. The films annealed under the optimized conditions reveal the presence of the orthorhombic phase, as confirmed by X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of 12.8 µC cm⁻², remnant polarization of 12.7 µC cm⁻² and coercive field of 1.2 MV cm⁻¹. The films exhibit a wake-up effect that is attributed to the migration of point defects, such as oxygen vacancies, and/or a transition from nonferroelectric (monoclinic and tetragonal phase) to the ferroelectric orthorhombic phase. The capacitors demonstrate a stable polarization with an endurance of 6.0 × 10⁵ cycles, demonstrating the potential of the NLA process for the fabrication of ferroelectric memory devices with high polarization, low coercive field, and high cycling stability.

Author(s): Yi-Ming Wu, Zhengzhi Wu, and Hong Yao

We theoretically explore possible orders induced by weak repulsive interactions in twisted bilayer transition metal dichalcogenides (e.g., WSe2) in the presence of an out-of-plane electric field. Using renormalization group analysis, we show that superconductivity survives even with the conventional…

[Phys. Rev. Lett. 130, 126001] Published Thu Mar 23, 2023

This review outlines a unique category of van der Waals materials that support novel devices for high-performance detection. Based on the insight into the unique properties of the material systems and the underlying microscopic mechanisms, emerging trends in junction devices are discussed, a new morphology of photodetectors is proposed, and some potential innovative directions in the subject area are suggested.

Abstract

With the continuous advancement of nanofabrication techniques, development of novel materials, and discovery of useful manipulation mechanisms in high-performance applications, especially photodetectors, the morphology of junction devices and the way junction devices are used are fundamentally revolutionized. Simultaneously, new types of photodetectors that do not rely on any junction, providing a high signal-to-noise ratio and multidimensional modulation, have also emerged. This review outlines a unique category of material systems supporting novel junction devices for high-performance detection, namely, the van der Waals materials, and systematically discusses new trends in the development of various types of devices beyond junctions. This field is far from mature and there are numerous methods to measure and evaluate photodetectors. Therefore, it is also aimed to provide a solution from the perspective of applications in this review. Finally, based on the insight into the unique properties of the material systems and the underlying microscopic mechanisms, emerging trends in junction devices are discussed, a new morphology of photodetectors is proposed, and some potential innovative directions in the subject area are suggested.

To settle the shuttle effect and Li-dendrite growth issues of lithium–sulfur (Li–S) batteries simultaneously, the “two-in-one” host materials toward Li–S full cell, “two-birds-with-one-stone” modified separators, and tailored electrolyte additives for stabilizing sulfur/lithium electrodes are regarded as efficient strategies. Herein, a systematic and comprehensive review of recent studies, perspectives, and challenges confronted with Li–S batteries is presented.

Abstract

Lithium–sulfur (Li–S) batteries have become one of the most promising new-generation energy storage systems owing to their ultrahigh energy density (2600 Wh kg⁻¹), cost-effectiveness, and environmental friendliness. Nevertheless, their practical applications are seriously impeded by the shuttle effect of soluble lithium polysulfides (LiPSs), and the uncontrolled dendrite growth of metallic Li, which result in rapid capacity fading and battery safety problems. A systematic and comprehensive review of the cooperative combination effect and tackling the fundamental problems in terms of cathode and anode synchronously is still lacking. Herein, for the first time, the strategies for inhibiting shuttle behavior and dendrite-free Li–S batteries simultaneously are summarized and classified into three parts, including “two-in-one” S-cathode and Li-anode host materials toward Li–S full cell, “two birds with one stone” modified functional separators, and tailoring electrolyte for stabilizing sulfur and lithium electrodes. This review also emphasizes the fundamental Li–S chemistry mechanism and catalyst principles for improving electrochemical performance; advanced characterization technologies to monitor real-time LiPS evolution are also discussed in detail. The problems, perspectives, and challenges with respect to inhibiting the shuttle effect and dendrite growth issues as well as the practical application of Li–S batteries are also proposed.

Metal oxides play an increasingly important role in flexible electronics that aim to deliver emerging applications such as novel computing systems, integrating thin-film transistors and resistive memories (memristors) in crossbars arrays. Due to the low temperature processing in metal oxides, mechanical flexibility has been increasingly studied in related devices, and therefore it is covered in this review.

Abstract

Flexible electronics have seen extensive research over the past years due to their potential stretchability and adaptability to non-flat surfaces. They are key to realizing low-power sensors and circuits for wearable electronics and Internet of Things (IoT) applications. Semiconducting metal-oxides are a prime candidate for implementing flexible electronics as their conformal deposition methods lend themselves to the idiosyncrasies of non-rigid substrates. They are also a major component for the development of resistive memories (memristors) and as such their monolithic integration with thin film electronics has the potential to lead to novel all-metal-oxide devices combining memory and computing on a single node. This review focuses on exploring the recent advances across all these fronts starting from types of suitable substrates and their mechanical properties, different types of fabrication methods for thin film transistors and memristors applicable to flexible substrates (vacuum- or solution-based), applications and comparison with rigid substrates while additionally delving into matters associated with their monolithic integration.

npj 2D Materials and Applications, Published online: 27 March 2023; doi:10.1038/s41699-023-00390-4

Two-dimensional single crystal monoclinic gallium telluride on silicon substrate via transformation of epitaxial hexagonal phase

npj 2D Materials and Applications, Published online: 27 March 2023; doi:10.1038/s41699-023-00379-z

Large-area synthesis of high electrical performance MoS₂ by a commercially scalable atomic layer deposition process

A synthetic route to a large-area graphene/Eu/Si(001) heterostructure combining graphene with a submonolayer magnetic phase of Eu on silicon is proposed. Proximity coupling of graphene to the 2D magnet results in spin polarization of carriers in the graphene layer. The structure seeds a class of materials aiming at applications in graphene spintronics.

Abstract

Imprinting magnetism into graphene may lead to unconventional electron states and enable the design of spin logic devices with low power consumption. The ongoing active development of 2D magnets suggests their coupling with graphene to induce spin-dependent properties via proximity effects. In particular, the recent discovery of submonolayer 2D magnets on surfaces of industrial semiconductors provides an opportunity to magnetize graphene coupled with silicon. Here, synthesis and characterization of large-area graphene/Eu/Si(001) heterostructures combining graphene with a submonolayer magnetic superstructure of Eu on silicon are reported. Eu intercalation at the interface of the graphene/Si(001) system results in a Eu superstructure different from those formed on pristine Si in terms of symmetry. The resulting system graphene/Eu/Si(001) exhibits 2D magnetism with the transition temperature controlled by low magnetic fields. Negative magnetoresistance and the anomalous Hall effect in the graphene layer provide evidence for spin polarization of the carriers. Most importantly, the graphene/Eu/Si system seeds a class of graphene heterostructures based on submonolayer magnets aiming at applications in graphene spintronics.

Nature Reviews Chemistry, Published online: 27 March 2023; doi:10.1038/s41570-023-00489-8

A thermoelectric material is presented which adopts a tungsten bronze structure with high-entropy properties but without rare-earth metals. Through entropy engineering, the Seebeck coefficient is optimized and the thermal conductivity is minimized, thereby creating the most efficient thermoelectric material of its kind.

Nature, Published online: 27 March 2023; doi:10.1038/s41586-023-05973-1

Hybrid 2D/CMOS microchips for memristive applications

Nature Materials, Published online: 23 March 2023; doi:10.1038/s41563-023-01516-1

Subcentimetre-size black phosphorous and its alloy films have been achieved on conventional substrates through sustained feedstock release design, and exhibit high crystalline quality and composition-dependent bandgap tunability.

A novel high entropy sulfide (MoWReMnCr)S₂ is synthesized by facile thermal decomposition of a cocktail of five individual molecular precursors at a relatively low temperature of 500 °C for 1 h. The performance of the exfoliated 2D nanosheets derived from these high entropy layered materials are measured for electrocatalytic activity in the hydrogen evolution reaction (HER) and the results compared to the widely-studied electrocatalyst  2H-MoS₂.

Abstract

High-entropy (HE) metal chalcogenides are a class of materials that have great potential in applications such as thermoelectrics and electrocatalysis. Layered 2D transition-metal dichalcogenides (TMDCs) are a sub-class of high entropy metal chalcogenides that have received little attention to date as their preparation currently involves complicated, energy-intensive, or hazardous synthetic steps. To address this, a low-temperature (500 °C) and rapid (1 h) single source precursor approach is successfully adopted to synthesize the hexernary high-entropy metal disulfide (MoWReMnCr)S₂. (MoWReMnCr)S₂ powders are characterized by powder X-ray diffraction (pXRD) and Raman spectroscopy, which confirmed that the material is comprised predominantly of a hexagonal phase. The surface oxidation states and elemental compositions are studied by X-ray photoelectron spectroscopy (XPS) whilst the bulk morphology and elemental stoichiometry with spatial distribution is determined by scanning electron microscopy (SEM) with elemental mapping information acquired from energy-dispersive X-ray (EDX) spectroscopy. The bulk, layered material is subsequently exfoliated to ultra-thin, several-layer 2D nanosheets by liquid-phase exfoliation (LPE). The resulting few-layer HE (MoWReMnCr)S₂ nanosheets are found to contain a homogeneous elemental distribution of metals at the nanoscale by high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) with EDX mapping. Finally, (MoWReMnCr)S₂ is demonstrated as a hydrogen evolution electrocatalyst and compared to 2H-MoS₂ synthesized using the molecular precursor approach. (MoWReMnCr)S₂ with 20% w/w of high-conductivity carbon black displays a low overpotential of 229 mV in 0.5 M  H₂SO₄ to reach a current density of 10 mA cm⁻², which is much lower than the overpotential of 362 mV for MoS₂. From density functional theory calculations, it is hypothesised that the enhanced catalytic activity is due to activation of the basal plane upon incorporation of other elements into the 2H-MoS₂ structure, in particular, the first row TMs Cr and Mn.

Scanning tunneling microscopy is used to study the vicinity of defects in the Kondo lattice of samarium hexaboride (SmB6).

Scanning tunneling microscopy is used to study the vicinity of defects in the Kondo lattice of samarium hexaboride (SmB6).

Solid-state reactions formed vertical carpets of 2D metal carbides and nitrides on metal substrates.