Jiuxiang Dai

In this work, planarization growth by hydride vapor phase epitaxy (HVPE) is studied as a method of enabling the direct use of spalled substrates without polishing. A 24%-efficient solar cell is achieved after in situ growth planarization of 3-µm-tall facets with equivalent open-circuit voltage compared to a device grown on a traditional planar substrate.

Abstract

A 24%-efficient single-junction GaAs solar cell grown directly on a faceted, spalled (100) GaAs substrate after in situ planarization growth by hydride vapor phase epitaxy (HVPE) is achieved. Controlled spalling, a promising low-cost substrate reuse technique, produces large facets in (100)-oriented GaAs substrates due to the orientation of the fracture planes used for lift-off. Planarization by HVPE offers a path toward direct use of these spalled substrates without costly polishing steps. Here, the growth rate anisotropy enabling planarization arising from diffusion and differences in the adsorption of growth species on {n11}B-type facets relative to (100) is determined. Consecutive planarization and device growth that results in a solar cell with a minimal performance difference relative to a control cell grown on an epitaxy-ready substrate are demonstrated. These results show that controlled spalling coupled with HVPE planarization is a viable pathway for lowering the cost of III-V photovoltaics.

In this work, using first-principles calculations, it proposes that the 2D d⁰-type ferromagnet Mg₄N₄ is a 2D Dirac half-metal candidate with a fourfold degenerate Dirac point at the S high-symmetry point, intrinsic magnetism, a high Curie temperature, 100% spin polarization, topology robust under the SOC and uniaxial and biaxial strains, and spin-polarized edge states.

Abstract

When spin-orbit coupling (SOC) is absent, all proposed half-metals with twofold degenerate nodal points at the K (or K′) point in 2D materials are classified as “Dirac half-metals” owing to the way graphene is utilized in the earliest studies. Actually, each band crossing point at the K or K′ point is described by a 2D Weyl Hamiltonian with definite chirality; hence, it should be a Weyl point. To the best of its knowledge, there have not yet been any reports of a genuine (i.e., fourfold degenerate) 2D Dirac point half-metal. In this work, using first-principles calculations, it proposes for the first time that the 2D d ⁰-type ferromagnet Mg₄N₄ is a genuine 2D Dirac half-metal candidate with a fourfold degenerate Dirac point at the S high-symmetry point, intrinsic magnetism, a high Curie temperature, 100% spin polarization, topology robust under the SOC and uniaxial and biaxial strains, and spin-polarized edge states. This work can serve as a starting point for future predictions of intrinsically magnetic materials with genuine 2D Dirac points, which will aid the frontier of topo-spintronics research in 2D systems.

Proceedings of the National Academy of Sciences, Volume 120, Issue 50, December 2023.

Nature Electronics, Published online: 04 December 2023; doi:10.1038/s41928-023-01087-8

Through layer-by-layer mechanical peeling, the channel region of a multilayer black phosphorus transistor can be reduced to a monolayer thickness without degrading its lattice and while retaining a multilayer contact region.

Nature Nanotechnology, Published online: 04 December 2023; doi:10.1038/s41565-023-01544-7

High-energy interlayer excitons in van der Waals semiconducting transition metal dichalcogenides lie far above the bandgap and emit in the ultraviolet range.

Author(s): Hao Hong, Chen Huang, Chenjun Ma, Jiajie Qi, Xuping Shi, Can Liu, Shiwei Wu, Zhipei Sun, Enge Wang, and Kaihui Liu

Optical phase matching involves establishing a proper phase relationship between the fundamental excitation and generated waves to enable efficient optical parametric processes. It is typically achieved through birefringence or periodic polarization. Here, we report that the interlayer twist angle i…

[Phys. Rev. Lett. 131, 233801] Published Mon Dec 04, 2023

High-quality InSb quantum dots(QDs) are synthesized using indium-carboxylate and tris(trimethylsilyl)antimony(TMS-Sb) precursors. To mitigate surface oxidation, InCl₃ is added as a co-precursor, inducing the presence of Cl^- ions that function as a protective layer on the QD surface. The QD is applied to photo-detector device, resulting in enhanced EQE values: 11.4% at λ=1370 nm and 6.3% at λ=1520 nm for the InSb core.

Abstract

III-V quantum dots (QDs) have emerged as significant alternatives to Cd- and Pb-based QDs, garnering notable attention over the past two decades. However, the understanding of III-V QDs, particularly in the short wave-infrared (SWIR) region, remains limited. InAs QDs are widely recognized as the most prominent SWIR QDs, but their absorption beyond 1400 nm presents various challenges. Consequently, InSb QDs with relatively narrower bandgaps have been investigated; however, research on their device applications is lacking. In this study, InSb QDs are synthesized with absorption ranging from 1000 to 1700 nm by introducing Cl⁻ ions to enhance QD surface stability during synthesis. Additionally, it coated InAs and ZnSe shells onto the InSb QDs to validate photoluminescence in the SWIR region and improve photostability. Subsequently, these QDs are employed in the fabrication of photodetector devices, resulting in photodetection above 1500 nm using Pb-free QDs. The photodetection device exhibited an external quantum efficiency (EQE) of 11.4% at 1370 nm and 6.3% at 1520 nm for InSb core QDs, and 4.6% at 1520 nm for InSb/InAs core/shell QDs, marking the successful implementation of such a device. In detail, the 1520 nm for InSb core device showed a dark current density(J_D) value of: 1.46 × 10⁻⁹ A/cm², responsivity(R): 0.078 A/W, and specific detectivity based on the shot noise(D_sh*): 3.6 × 10¹² Jones at 0 V.

The incorporation of Fe into CoO₂ slabs significantly improve the oxygen evolution reaction (OER) activity of layered Na_0.6CoO₂. The enhancement is mainly ascribed to the enriched active sites on the activated basal planes and the participation of oxidized oxygen as active sites independently, which breaks the scaling relationship limit in the OER process.

Abstract

With the CoO₂ slabs consisting of Co₄O₄ cubane structure, layered Na _x CoO₂ are considered promising candidates for oxygen evolution reaction (OER) in alkaline media given their earth-abundant and structural advantages. However, due to the strong adsorption of intermediates on the large basal planes, Na _x CoO₂ cannot meet the activity demands. Here, a novel one-pot synthesis strategy is proposed to realize the high solubility of iron in Na _x CoO₂ in an air atmosphere. The optimist Na_0.6Co_0.9Fe_0.1O₂ exhibits enhanced OER activity compared to their pristine and other reported Fe-doped Na _x CoO₂ counterparts. Such an enhancement is mainly ascribed to the abundant active sites on the activated basal planes and the participation of oxidized oxygen as active sites independently, which breaks the scaling relationship limit in the OER process. This work is expected to contribute to the understanding of the modification mechanism of Fe-doped cobalt-based oxides and the exploitation of layer-structured oxides for energy application.

Large-scale single-crystalline film of molecular ferroelectrics is achieved via a mild, simple, and substrate-independent chemical process. The ultrasmooth surface and enduring ferroelectricity of the film enable the successful construction and optical control of heterostructures, enabling ferroelectric films for large-scale flexible electronics.

Abstract

With outstanding advantages of chemical synthesis, structural diversity, and mechanical flexibility, molecular ferroelectrics have attracted increasing attention, demonstrating themselves as promising candidates for next-generation wearable electronics and flexible devices in the film form. However, it remains a challenge to grow high-quality thin films of molecular ferroelectrics. To address the above issue, a volume-confined method is utilized to achieve ultrasmooth single-crystal molecular ferroelectric thin films at the sub-centimeter scale, with the thickness controlled in the range of 100–1000 nm. More importantly, the preparation method is applicable to most molecular ferroelectrics and has no dependency on substrates, showing excellent reproducibility and universality. To demonstrate the application potential, two-dimensional (2D) transitional metal dichalcogenide semiconductor/molecular ferroelectric heterostructures are prepared and investigated by optical spectroscopic method, proving the possibility of integrating molecular ferroelectrics with 2D layered materials. These results may unlock the potential for preparing and developing high-performance devices based on molecular ferroelectric thin films.

In van der Waals (vdW) layered crystal In_4/3P₂S₆, defect-assisted extrinsic self-trapped exciton (STE) induces a strong sub-bandgap emission with 9.2% photoluminescence quantum yield (PLQY) due to the strong exciton-phonon coupling effect. Coupling the exciton with anisotropic lattice vibration, the STE emission also exhibits linear anisotropy and pressure tunability.

Abstract

Self-trapped exciton (STE) induced broad-band emission (BE) has sparked considerable interest due to its potential applications in white-light emitters and optoelectronics. This phenomenon is widely observed in organic–inorganic hybrid perovskites with soft lattice structures, and its physical origin is still under debate. Herein, strong sub-bandgap STE emission with a large Stokes shift and a photoluminescence quantum yield of up to 9.2% in van der Waals (vdW) layered In_4/3P₂S₆ is reported. Combining comprehensive optical characterizations and theoretical calculations, this concludes that defect-assisted extrinsic STE is responsible for the BE. The excitonic state can be further localized by hydrostatic pressure, resulting in a threefold PL intensity enhancement. In addition, angle-resolved polarized Raman demonstrates the anisotropic lattice dynamics in IPS, which may underpin the highly linear anisotropy of the STE emission. This work clarifies the defect, STE, and anisotropy coupling effect in vdW crystal, and provides innovative avenues to modulate the STE luminescence.

Transition metal dichalcogenides face challenges of applications in advancing semiconductors. This work demonstrates robust reproducibility in the growth of single-oriented MoS₂ on Fe₂O₃-decorated sapphire, achieving a remarkable 99% ratio. Simulations reveal a preferred 0° alignment on the Fe₂O₃-(0001) surface, ensuring single-oriented growth even on mirror-reflected surfaces. These findings highlight Fe₂O₃-decorated sapphires as effective substrates, enabling epitaxial control of TMD orientation.

Abstract

2D semiconducting transition metal dichalcogenides (TMDs) are emerging as promising candidates in the pursuit of advancing semiconductor technology. One major challenge for integrating 2D TMD materials into practical applications is developing an epitaxial technique with robust reproducibility for single-oriented growth and thus single-crystal growth. Here, the growth of single-orientated MoS₂ on c-plane sapphire with atomically thin Fe₂O₃ decoration layers under various growth conditions is demonstrated. The statistical data highlight robust reproducibility, achieving a single orientation ratio of up to 99%. Density functional theory calculations suggest that MoS₂ favors a 0° alignment ([112¯0]//[112¯0]$[ {11\bar{2}0} ]//\ [ {11\bar{2}0} ]$) on the Fe₂O₃ (0001) surface. This preference ensures single-oriented growth, even on mirror-reflected exposed surfaces which typically lead to antiparallel domains. Subsequent optical and electrical analyses confirm the uniformity and undoped nature of MoS₂ on Fe₂O₃-decorated sapphire, showing its quality is comparable to MoS₂ grown on bared sapphires. The results underscore the potential of Fe₂O₃-decorated sapphire as an effective substrate for the consistent and high-quality epitaxial growth of 2D TMDs, illuminating the pathway to epitaxial control of 2D TMD orientation through strategic modulation of crystalline atomic surfaces.

Planar Josephson junctions based on type-II Weyl semimetal MoTe₂ can function as superconducting diodes with the ratification efficiency up to 50.4% due to the asymmetric Josephson effect in perpendicular magnetic fields. The underlying physics is the Edelstein effect that induces a nontrivial phase shift in the current phase relation of the junctions.

Abstract

Superconducting diode effect (SDE) with nonreciprocal supercurrent transport has attracted intense attention recently, not only for its intriguing physics, but also for its great application potential in superconducting circuits. It is revealed in this work that planar Josephson junctions (JJs) based on type-II Weyl semimetal (WSM) MoTe₂ can exhibit a prominent SDE due to the emergence of asymmetric Josephson effect (AJE) in perpendicular magnetic fields. The AJE manifests itself in a very large asymmetry in the critical supercurrents with respect to the current direction. The sign of this asymmetry can also be effectively modulated by the external magnetic field. Considering the special noncentrosymmetric crystal symmetry of MoTe₂, this AJE is understood in terms of the Edelstein effect, which induces a nontrivial phase shift in the current phase relation of the junctions. Besides these, it is further demonstrated that the rectification of supercurrent in such MoTe₂ JJs with the rectification efficiency up to 50.4%, unveiling the great application potential of WSMs in superconducting electronics.

Magnetic liquid metal (MLM) is a mixture of magnetic particles with gallium-based liquid metals which utilizes an unconventional combination of fluidity, high thermal/electrical conductivity, biocompatibility, and magnetism. This work comprehensively reviews recent developments in the MLMs from the materials to methods of preparations, locomotion of MLMs, their applications, and future outlooks.

Abstract

Magnetic liquid metal (MLM) is a mixture of magnetic particles with gallium-based liquid metals which utilizes an unconventional combination of fluidity, high thermal/electrical conductivity, biocompatibility, and magnetism. Recently, from materials to applications, studies on MLMs have drastically increased. Single or multiple MLMs can be precisely positioned or can act as a carrier for handling other objects. MLMs are also used in biomedical applications such as cancer treatment by hyperthermia and precision delivery of cancer drugs on tumors, or antibacterial coating which kills bacteria. In electronics applications, MLMs are used for magnetic field-driven patterning of metallic lines, reconfigurable interconnects, electronic tattoos, and reconfigurable electromagnetic wave shielding. Phase change (solid/liquid) of MLMs adds another unique capability, morphing. A combination of innovations in the micro/nano robots and MLMs has huge potential to bring an unprecedented disruptive technology for a wide variety of applications including self-morphing shape-recovery robots, highly localized cancer treatment, and reconfigurable stealth/camouflage, among others. This article comprehensively reviews recent developments in MLMs from the materials to methods of preparation, locomotion of MLMs, their applications, and future outlooks.

Highly aligned 1D tellurium is epitaxially grown on 2D monolayer transition metal dichalcogenides (TMDs). A one-pot chemical vapor deposition (CVD) technique eliminates the normally required transfer steps, thereby producing mixed-dimensional heterostructures with an ultraclean interface and good contact. The mixed-dimensional p-n Te/MoSe₂ heterojunction photodetector presents self-driven behavior with high responsivity (328 mA W⁻¹), external quantum efficiency (79 %), and specific detectivity (8.2  ×  10⁹ Jones).

Abstract

Mixed-dimensional heterostructures provide additional freedom to construct diverse functional electronic and optoelectronic devices, gaining significant interest. Herein, highly-aligned pseudo-1D tellurium is epitaxially grown on 2D monolayer transition metal dichalcogenides (TMDs), including MoSe₂, MoS₂, and WS₂. A one-pot chemical vapor deposition (CVD) technique eliminates the normally required transfer steps, thereby producing mixed-dimensional heterostructures with an ultraclean interface. The controllable epitaxial growth of Te/TMD heterostructures are verified by Raman, scanning probe microscopy (SPM), and transmission electron microscopy (TEM) observation. The photoluminescence results indicate that the emission from TMDs is quenched in the heterostructure, confirming the efficient transfer of photogenerated carriers from TMDs to Te. Additionally, the mixed-dimensional p-n Te/MoSe₂ heterojunction photodetector presents self-driven behavior with high responsivity (328 mA W⁻¹), external quantum efficiency (79%), and specific detectivity (8.2 ×  10⁹ Jones). The modified facile synthesis strategy and proposed growth mechanism in this study shed light on synthesizing mixed-dimensional heterojunctions. This opens avenues for fabricating functional devices with reduced sizes and high densities, further enabling miniaturization and integration opportunities.

Nature Communications, Published online: 01 December 2023; doi:10.1038/s41467-023-43796-w

Intrinsic anomalous Hall effect has been observed in twisted graphene multilayers, but these structures are typically not energetically favorable. This study extends these observations to Bernal-stacked tetralayer graphene, which is the most stable configuration of four-layer graphene.

Abstract

Vapor catalysis was recently found to play a crucial role in superclean graphene growth via chemical vapor decomposition (CVD). However, knowledge of vapor-phase catalysis is scarce, and several fundamental issues, including vapor compositions and their impact on graphene growth, are ambiguous. Here, by combining density functional theory (DFT) calculations, an ideal gas model, and a designed experiment, we found that the vapor was mainly composed of Cu_i clusters with tens of atoms. The vapor pressure was estimated to be ∼ 10⁻¹²–10⁻¹¹ bar under normal low-pressure CVD system (LPCVD) conditions for graphene growth, and the exposed surface area of Cu_i clusters in the vapor was 22–269 times that of the Cu substrate surface, highlighting the importance of vapor catalysis. DFT calculations show Cu clusters, represented by Cu₁₇, have strong capabilities for adsorption, dehydrogenation, and decomposition of hydrocarbons. They exhibit an adsorption lifetime and reaction flux six orders of magnitude higher than those on the Cu surface, thus providing a sufficient supply of active C atoms for rapid graphene growth and improving the surface cleanliness of the synthesized graphene. Further experimental validation showed that increasing the amount of Cu vapor improved the as-synthesized graphene growth rate and surface cleanliness. This study provides a comprehensive understanding of vapor catalysis and the fundamental basis of vapor control for superclean graphene rapid growth.

Nature Communications, Published online: 02 December 2023; doi:10.1038/s41467-023-43414-9

The photonic applications of hyperbolic phonon polaritons (HPhPs) in anisotropic van der Waals materials are currently limited by their low tunability. Here, the authors report the static and ultrafast wavevector modulation of HPhPs in hexagonal boron nitride by tuning the plasma frequency of doped semiconductor substrates.

The oxygen-deficient TiO_2−x shows a large enhancement in NLO response using a model polaronic oxide, in which prominent polaronic states are located within the bandgap. The strong optical nonlinearity of the platonic TiO_2−x is exploited further for the development of all-optical switches for ultrashort pulse generation and all-optical data processing in the near-infrared (NIR) optical communication window.

Abstract

It has been well-established that light-matter interactions, as manifested by diverse linear and nonlinear optical (NLO) processes, are mediated by real and virtual particles, such as electrons, phonons, and excitons. Polarons, often regarded as electrons dressed by phonons, are known to contribute to exotic behaviors of solids, from superconductivity to photocatalysis, while their role in materials’ NLO response remains largely unexplored. Here, the NLO response mediated by polarons supported by a model ionic metal oxide, TiO₂, is examined. It is observed that the formation of polaronic states within the bandgap results in a dramatic enhancement of NLO absorption coefficient by over 130 times for photon energies in the sub-bandgap regions, characterized by a 100 fs scale ultrafast response that is typical for thermalized electrons in metals. The ultrafast polaronic NLO response is then exploited for the development of all-optical switches for ultrafast pulse generation in near-infrared (NIR) fiber lasers and modulation of optical signal in the telecommunication band based on evanescent interaction on a planar waveguide chip. These results suggest that the polarons supported by dielectric ionic oxides can fill the gaps left by dielectric and metallic materials and serve as a novel platform for nonlinear photonic applications.

Abstract

Nature provides a wealth of bio-inspiration for advanced material research. Assembling various nanomaterials into biomimetic microtextures with bioinspired functionalities has spurred increasing research interests and facilitated technological advances in various applications. In recent years, two-dimensional materials (2DMs) have emerged as important building block units in the biomimicry field due to their distinct chemical, physical, electrical, electrochemical, and catalytic properties. In this review article, various mechanically driven assembly approaches are summarized to fabricate various genealogies of biomimetic 2DM microtextures with bio-inspired multifunctionality. First, sequential deformation strategies are discussed to programmably construct higher dimensional 2DM microtextures, ranging from wrinkles/crumples (one-time deformation) to multiscale hierarchies (multiple deformations). Next, the current progress using higher dimensional 2DM microtextures to imitate different biological structures and/or induce bio-inspired multifunctionality is systematically summarized. Four showcases of bio-inspiration and biomimicry using different 2DM nanosheets are highlighted: (1) wrinkle patterns of an earthworm that spur the design of strain sensors with programmable working ranges and sensitivities, (2) wrinkle appearance of a Shar-Pei dog that motivates the fabrication of stretchable energy storage devices, (3) hierarchical scale textures of a desert lizard that inspire cation-induced gelation platforms for 2DM aerogels, and (4) wrinkle skin of an elephant that influences the development of 2DM protective skin for soft robots. Finally, challenges and future opportunities of adopting 2DM nanosheets to assemble biomimetic microstructures with synergistic functionalities are discussed.

Abstract

The remarkable optoelectronic features of halide perovskite promote their potential applications in semiconductor devices beyond solar cells, which require high-quality single crystals with controlled defect levels. Herein, we investigated the synthesis mechanism of chemical vapor deposited single-crystalline all-inorganic perovskite microplates (MPs), and reported a defect-modulated photocurrent which is closely related to the growth sequence of the MPs. The MP synthesis initiates from island-like nano-disks, and subsequently transits to a layer-by-layer fashion, resulting in a defect-rich area at the center of the MPs. At elevated temperatures, these central defects may be thermally activated and become highly mobile, leading to photoluminescence quenching and degression of local and overall optoelectronic attributes, as evidenced by the spatial resolved optical and electrical scanning probe microscopy. Overall, this work shines light on the formation, proliferation and dynamics of defects in perovskites, and offers guidance for preparation of high-quality perovskites micro-crystals for functional semiconductor devices with high temperature stability.

Abstract

Next generation power system needs dielectrics with increased dielectric energy density. However, the low energy density of dielectrics limits their development. Here, an asymmetric trilayered nanocomposite, with a transition layer (TL), an insulation layer (IL), and a polarization layer (PL), is designed based on poly(vinylidene fluoride)-polymethyl methacrylate (PVDF-PMMA) matrix using KNbO₃ (KN) and TiO₂ (TO) as the nanofillers. The morphology and defect control of the two-dimensional nano KN and nano TO fillers are realized via a hydrothermal method to increase the composite breakdown strength (E_b) and the composite energy density (U_e). The asymmetric trilayered structure leads to a gradient electric field distribution, and the KN and TO nanosheets block charges transfer along z direction. As a result, the development path of the electrical trees is greatly curved, and E_b is effectively improved. And the U_e value of the nanocomposites reaches 17.79 J·cm⁻³ at 523 MV·m⁻¹. On the basis, the composite U_e is further improved by defect control in TO nanosheets. The nanocomposite KN/TO/PVDF-PMMA containing TO with less oxygen vacancy concentration (calcined at oxygen atmosphere) acquires a high U_e of 21.61 J·cm⁻³ at 548 MV·m⁻¹. This study provides an idea for improving the energy storage performance by combining the design of the composite dielectric structure and the control of nanofillers’ defect and morphology.

Tunable magnetic bubbles and topological Hall effect (THE) are demonstrated in 2D magnet Fe₅GeTe₂. The density and size of bubbles can be modulated effectively by adjusting the magnetocrystalline anisotropy and dipolar interaction, respectively. Besides, the controlled topological transformation between skyrmion bubbles and trivial bubbles is achieved by varying the sample thickness, accompanied by the change of THE.

Abstract

Recent observations of nontrivial spin textures and topological Hall effect (THE) in 2D van der Waals (vdW) ferromagnets have stimulated high interest in both fundamental physics and prospective spintronic applications. However, effectively manipulating spin textures and their exhibiting THE, which is the prerequisite for topology-based 2D vdW devices, remains challenging. Here, the effective manipulation of the magnetic bubbles and THE is achieved in Fe₅GeTe₂ (FGT) crystals by utilizing Lorentz imaging and electrical transport measurements. The density and size of magnetic bubbles can be modulated effectively as the temperature and lamella thickness change, indicating the role of magnetocrystalline anisotropy and long-range magnetic dipolar interaction is demonstrated, respectively. More importantly, the spin configurations of bubbles along with THE signal vary with sample thickness, demonstrating a topological transition between skyrmion bubbles and trivial bubbles. The key point lies in the presence or absence of Bloch lines in the stripe domain at different thicknesses. This study presents the reliable manipulations of spin textures and THE in FGT, which may provide valuable insights into the design of 2D vdW devices in spintronics.

Compared to bilayer moiré superlattices with only one interface, the interference between moiré patterns at different interfaces in 2D multilayer structures allows the physical realization of more complicated lattice models. The concept is demonstrated by trilayer moiré superlattices of MoS₂, where the flat bands near the valence band edge can be mapped into the honeycomb lattice ionic Hubbard model with high tunability.

Abstract

Recent studies have revealed the potential of 2D moiré superlattices as a condensed matter quantum simulator. The realization of different lattice model Hamiltonians in moiré superlattices has become the focus of researches. Here, it shows that, compared to bilayer moiré superlattices where there is only one interface, the interference between moiré patterns at different interfaces in 2D multilayer structures allows the physical realization of more complicated lattice models. The concept is demonstrated by trilayer moiré superlattices (TMSLs) of MoS₂, where it finds that isolated flat moiré bands appear near the valence band edge, and they can be described by the honeycomb lattice ionic Hubbard model. More importantly, the hopping strength, the on-site Coulomb repulsion, and the staggered potential in the TMSLs are highly tunable through the control of the twist angle, the dielectric environment, and the perpendicular electric field. It is possible to achieve various transitions between distinct quantum phases in the TMSLs, spanning from weak to strong correlation regimes. Therefore, the proposed TMSLs can serve as a good platform to study the strong correlation physics in the honeycomb lattice ionic Hubbard model.

2D sub-nanoconfined annealed graphene oxide membranes are constructed for efficient synthesis of aspirin in directional flow. The reaction shows ≈100% conversion in an unprecedented short reaction time of <6.36 s at 23 °C. Density functional theory calculation indicates the synergistic effect of spatial confinement and surface electronic structure plays an important role in the efficient reaction.

Abstract

The aim of this work is to develop an environmentally friendly, safe, and simple route for realizing efficient preparation of aspirin. Here, inspired by enzyme synthesis in vivo, the aspirin synthesis has been realized by sub-nanoconfined esterification with directional flow and ≈100% conversion in an unprecedented reaction time of <6.36 s at 23 °C. Such flow esterification reaction is catalyzed by thermally transformed graphene oxide (GO) membranes with tailored physicochemical properties, which can be obtained simply through a mild annealing method. A possible mechanism is revealed by density functional theory calculation, indicating that the synergistic effect of spatial confinement and surface electronic structure can significantly improve the catalytic performance. By restricting reactants within 2D sub-nano space created by GO-based laminar flow-reactors, the present strategy provides a new route to achieve rapid flow synthesis of aspirin with nearly complete conversion.

Multicrystalline informatics, integrating experiment, theory, computation, and data science in multi-scale cyber and physical spaces, advances material science in multicrystalline materials. The formation of nanofacet structures associated with grain boundary bending is revealed as one of the universal origins of dislocation generation in multicrystalline silicon.

Abstract

A comprehensive analysis of optical and photoluminescence images obtained from practical multicrystalline silicon wafers is conducted, utilizing various machine learning models for dislocation cluster region extraction, grain segmentation, and crystal orientation prediction. As a result, a realistic 3D model that includes the generation point of dislocation clusters is built. Finite element stress analysis on the 3D model coupled with crystal growth simulation reveals inhomogeneous and complex stress distribution and that dislocation clusters are frequently formed along the slip plane with the highest shear stress among twelve equivalents, concentrated along bending grain boundaries (GBs). Multiscale analysis of the extracted GBs near the generation point of dislocation clusters combined with ab initio calculations has shown that the dislocation generation due to the concentration of shear stress is caused by the nanofacet formation associated with GB bending. This mechanism cannot be captured by the Haasen-Alexander-Sumino model. Thus, this research method reveals the existence of a dislocation generation mechanism unique to the multicrystalline structure. Multicrystalline informatics linking experimental, theoretical, computational, and data science on multicrystalline materials at multiple scales is expected to contribute to the advancement of materials science by unraveling complex phenomena in various multicrystalline materials.

A significant negative capacitance response is directly observed in the thin film of molecular ferroelectric trimethylchloromethyl ammonium trichlorocadmium. When compared to conventional inorganic ferroelectrics, molecular ferroelectrics, in which order–disorder transition of the molecular induces the occurrence of polarization, would have a smaller ferroelectric anisotropy parameter α and a larger domain wall formation energy.

Abstract

On the path of persisting Moore's Law, one of the biggest obstacles is the “Boltzmann tyranny,” which defines the lower limit of power consumption of individual transistors. Negative capacitance (NC) in ferroelectrics could provide a solution and has garnered significant attention in the fields of nanoelectronics, materials science, and solid-state physics. Molecular ferroelectrics, as an integral part of ferroelectrics, have developed rapidly in terms of both performance and functionality, with their inherent advantages such as easy fabrication, mechanical flexibility, low processing temperature, and structural tunability. However, studies on the NC in molecular ferroelectrics are limited. In this study, the focus is centered on the fabricated high-quality thin films of trimethylchloromethyl ammonium trichlorocadmium(II), and a pioneering investigation on their NC responses is conducted. The findings demonstrate that the NC exhibited by molecular ferroelectrics is comparable to that of conventional HfO₂-based ferroelectrics. This underscores the potential of molecular material systems for next-generation electronic devices.

Publication date: December 2023

Source: Materials Today, Volume 71

Author(s): Laurie Donaldson

Publication date: December 2023

Source: Materials Today, Volume 71

Author(s): Cordelia Sealy

Using a sacrificial material to generate pores in a ferroelectric polymer generates a large electrocaloric effect