Properties Of Layered Materials Research Articles

Study on the mechanical properties of layered gradient structure PBT-based flame retardant composite materials

Abstract To enhance the flame retardancy of Polybutylene Terephthalate (PBT) based composite materials and overcome the decrease in mechanical properties due to the high content of nano-antimony trioxide (nano-Sb2O3), this study initially applies a composite modification method to treat the surface of nano-Sb2O3. Subsequently, composite materials with a gradient distribution of nano-Sb2O3 are prepared through lamination hot-pressing technology, and their mechanical and flame retardant properties are investigated. The results show that the modifiers CTAB and KH560 are successfully grafted onto the surface of nano-Sb2O3, altering its surface properties. Through lamination hot-pressing technology, a gradient distribution from the surface to the core is achieved. Compared to the homogeneous distribution P666, G828 exhibits a 6% increase in Limiting Oxygen Index (LOI), improving the flame retardancy of the composite material. As nano-Sb2O3 enriches on the composite material's surface, the amount of char residue increases. The tensile strength, bending strength, and impact strength of G828 composite material increase by 19.7%, 37.1%, and 103%, respectively, compared to the homogeneous composite material P666, proving the significant effect of G828's gradient distribution in enhancing the mechanical properties of the composite material.

Vanadium incorporation in 2D-layered MoSe2

Recent advances in experimental techniques have made it possible to manipulate the structural and electronic properties of two-dimensional layered materials (2DM) through interaction with foreign atoms. Using quantum mechanics calculations based on the density functional theory, we explored the dependency of the structural, energetic, electronic, and magnetic properties of the interaction between Vanadium (V) atoms and monolayer and bilayer MoSe2. Spin-polarized metallic behavior was observed for high V concentration, and a semiconductor/metal interface emerged due to V adsorption on top of BL MoSe2. Our research demonstrated that the functionalization of 2D materials makes an important contribution to the design of spintronic devices based on a 2D-layered materials platform.

Optoelectronic properties of novel layered materials under encapsulation: 2D Copper Iodide and Silver Iodide

Many novel freestanding two-dimensional materials can be stabilized when placed over a proper substrate or put under encapsulation. Among the different possibilities, graphene and h-BN are commonly used due to their availability and compatibility. In that scenario, it is important to understand how the possible interactions between the core and substrate/encapsulating layers as well as the lattice mismatch affect the optoelectronic properties of the core material. In this work, we use ab initio calculations to study the structural and optolectronic properties of the recently synthesized 2D CuI and AgI layers, which are stabilized under graphene encapsulation (Mustonen et al. (2022)). In addition, the possibility of h-BN encapsulation is also explored. We find that the optoelectronic properties of the core materials are greatly preserved under encapsulation—especially under h-BN. Their bandgaps suffer small variations that mainly originate from the internal strain that results from supercell relaxation. We also see a rehybridization of the electronic bands from the core material whenever they cross or lie close to bands from the encapsulating layers, as expected. This effect is particularly strong for graphene encapsulation. The optical absorption profiles show a combination of features coming from the spectra of the isolated layers with minor modifications introduced by these effects. In particular, a strong and broad absorption is seen in the UV range when using h-BN. Finally, we study a possible CuI-AgI heterobilayer, both isolated and under encapsulation. Interestingly, the structure presents a type-II band alignment that is well preserved under encapsulation, with potential applications in novel photovoltaic devices.

Chemically Reversible Translational Moiré Superlattice Formations in the Two-Dimensional Films of the Zinc Phthalate Complex.

The exciting electronic properties of two-dimensional layered materials introduced by twist angle and lattice mismatch between two consecutive layers are well-recognized. The major challenge lies in the control over the moiré periodicity. Herein, we report a chemically directed way to achieve the desired precision over moiré periodicity of the assembly of a complex of zinc ions and o-phthalic acid utilizing soft bonds. The reaction of o-phthalic acid with zinc ions in the aqueous medium at 80 °C for 1 h followed by preserving the reaction mixture at ambient temperature (35 °C) resulted in translational moiré superlattices with precise periods. Those lattices are further stacked angularly to give rotational super-moiré lattices. Further, the role of the π-zinc ion interaction in the origin of moiré fringes was examined with the reaction with 8-hydroxyquinoline-5-sulfonic acid (HQS) that also established the reversible nature of the superlattices. The present observations also suggest the formation of moiré superlattice through ion insertion in a chemical lattice.

In vitro comparison of the mechanical properties of single and triple layered clear aligner materials.

In vitro comparison of the mechanical properties of single and triple layered clear aligner materials.

Synergistic effect of bonding heterogeneity and phonon localization in introducing excellent thermoelectric properties in layered heteroanionic NdZnSbO material

Layered rare-earth metal oxides, harnessing the dual properties of oxides and two-dimensional layered materials, exhibit remarkable thermal stability and quantum confinement effects. Therefore, this work adopts the first-principles calculation combined with the Boltzmann transport theory to predict the thermoelectric properties of NdZnSbO compound. The coexistence of weak interlayer van der Waals interactions, robust intralayer ionic bonding, and partial covalent bonding leads to remarkable bonding heterogeneity, which engenders pronounced phonon scattering and imposes constraints on thermal transport along the out-of-plane direction. The weakened chemical bonds induced by the antibonding states, together with the rattling-like behavior of the Zn atom, culminate in the profound anharmonicity in the layered NdZnSbO compound. The weakening bond and heavy element contribute to the softness of phonon modes, which significantly diminishes the phonon group velocity. The redistribution-dominated four-phonon scattering process spans a large optical gap, which effectively reduces the lattice thermal conductivity. The NdZnSbO compound exhibits direct semiconductor characteristic with a bandgap of 0.73 eV by adopting the Heyd-Scuseria-Ernzerhof (HSE06) functional in combination with spin–orbit coupling (SOC) effect. The multi-valley feature of NdZnSbO compound augur favorably for band degeneracy, thus amplifying the power factor. Consequently, an optimal figure-of-merit (ZT) of 3.40 at 900 K is achieved for the n-type NdZnSbO compound. The present study delves deeply insights into the origins for the low thermal conductivity of NdZnSbO compound and proposes an optimization scheme to enhance overall thermoelectric performance.

Pressure-induced photo responsiveness enhancement and positive–negative switch in ZrSe2

ZrSe2, a member of the group-IVB transition metal dichalcogenides, shows favorable performance in optoelectronic applications. Here, the photoelectric properties of ZrSe2 under high pressure have been systematically investigated. At 13.5 GPa, the photocurrent of ZrSe2 increases three orders of magnitude greater than its initial value. Interestingly, above 23.5 GPa, ZrSe2 exhibits a negative photocurrent response, which can be attributed to the photothermal effect caused by pressure-induced metallization. This study demonstrates the critical role of pressure in regulating the optoelectronic properties of layered materials and the potential application of layered ZrSe2 in pressure-responsive optoelectronic devices.

Investigation of structural, dielectric and electrical properties of lead-free bismuth-based layered multifunctional material: CaBiGdNbVO9 for device fabrication

Investigation of structural, dielectric and electrical properties of lead-free bismuth-based layered multifunctional material: CaBiGdNbVO9 for device fabrication

Rational Construction of Two-Dimensional Conjugated Metal-Organic Frameworks (2D c-MOFs) for Electronics and Beyond.

ConspectusTwo-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as a novel class of multifunctional materials, attracting increasing attention due to their highly customizable chemistry yielding programmable and unprecedented structures and properties. In particular, over the past decade, the synergistic relationship between the conductivity and porosity of 2D c-MOFs has paved the way toward their widespread applications. Despite their promising potential, the majority of 2D c-MOFs have yet to achieve atomically precise crystal structures, hindering the full understanding and control over their electronic structure and intrinsic charge transport characteristics. When modulating the charge transport properties of two-dimensional layered framework materials, decoupling the charge transport processes within and in between layers is of paramount importance, yet it represents a significant challenge. Unfortunately, 2D c-MOFs systems developed so far have failed to address such a major research target, which can be achieved solely by manipulating charge transport properties in 2D c-MOFs. 2D c-MOFs offer a significant advantage over organic radical molecules and covalent organic frameworks: polymerization through oxidative coordination is a viable route to form "spin-concentrated assemblies". However, the role of these spin centers in charge transport processes is still poorly understood, and the intrinsic dynamics and properties of these spins have seldom been investigated. Consequently, overcoming these challenges is essential to unlock the full potential of 2D c-MOFs in electronics and other related fields, as a new type of quantum materials.In this Account, we summarize and discuss our group's efforts to achieve full control at the atomic level over the structure of 2D c-MOFs and their applications in electronics and spintronics, thereby providing distinct evidence on 2D c-MOFs as a promising platform for exploring novel quantum phenomena. First, we unravel the key role played by the rational design of the ligands to decrease the boundary defects, achieve atomically precise large single crystals, and investigate the intrinsic charge transport properties of 2D c-MOFs. The advantages and disadvantages of the current structural elucidation strategies will be discussed. Second, the fundamental challenge in 2D c-MOF charge transport studies is to decouple the in-plane and interlayer charge transport pathways and achieve precise tuning of the charge transport properties in 2D c-MOFs. To address this challenge, we propose a design concept for the second-generation conjugated ligands, termed "programmable conjugated ligands", to replace the current first-generation ligands which lack modifiability as they mainly consist of sp2 hybridization atoms. Our efforts also extend to controlling the spin dynamics properties of 2D c-MOFs as "spin concentrated assemblies" using a bottom-up strategy.We hope this Account provides enlightening fundamental insights and practical strategies to overcome the major challenges of 2D c-MOFs for electronics and spintronics. Through the rational design of structural modulation within the 2D plane and interlayer interactions, we are committed to making significant steps forward for boosting the functional complexity of this blooming family of materials, thereby opening clear perspectives toward their practical application in electronics with the ultimate goal of inspiring further development of 2D c-MOFs and unleashing their full potential as an emerging quantum material.

Investigation of the properties of layered perovskite materials with varying constituent elements as SOFC cathodes

Layered perovskite materials are gaining attention as electrode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). This study explores the incorporation of various elements into the lanthanide, alkaline earth, and transition metal sites within the layered perovskite crystal structure to create diverse compositions. Structural stability and O-ion conduction performance were evaluated through simulations employing a deep learning-assisted approach. Results indicate that at the simulation temperature of 1000 K, the Sm–Sr–Co composition displays structural instability, while the La–Sr–Fe and Sm/Gd–Ba–Fe compositions exhibit decreased O-ion conductivity attributed to phase transitions, rendering them unsuitable for SOFC cathodes. Conversely, the Pr–Ba–Co and La–Sr–Co compositions demonstrate structural stability along with the highest O-ion conductivity, suggesting further exploration of these materials. Additionally, compositions such as Sm/Gd–Ba–Co, Gd–Sr–Co, La–Ba–Fe, and Sm–Sr–Fe, which exhibit structural stability and reasonable O-ion conductivity, may also merit consideration as potential candidates.

Ultralow-Noise MoS2/Type II Superlattice Mixed-Dimensional van der Waals Barrier Long-Wave Infrared Detector.

Low-noise, high-performance long-wave infrared detectors play a crucial role in diverse applications, including in the industrial, security, and medical fields. However, the current performance of long-wave detectors is constrained by the noise associated with narrow bandgaps. Therefore, exploring novel heterostructures for long-wavelength infrared detection is advantageous for the development of compact and high-performance infrared sensing. In this investigation, we present a MoS2/type II superlattice mixed-dimensional van der Waals barrier long-wave infrared detector (Mixed-vdWH). Through the design of the valence band barrier, substantial suppression of device dark noise is achieved, resulting in 2 orders of magnitude reduction in dark current. The device exhibits outstanding performance, with D* reaching 4 × 1010 Jones. This integration approach synergizes the distinctive properties of two-dimensional layered materials (2DLM) with the well-established processing techniques of traditional three-dimensional semiconductor materials, offering a compelling avenue for the large-scale integration of 2DLM.

Thermoelectric Properties of Layered BaFZnP Material in Consideration of Fourth-Order Anharmonicity and Multiple Carrier Scattering Rates: First-Principles Calculations

Thermoelectric Properties of Layered BaFZnP Material in Consideration of Fourth-Order Anharmonicity and Multiple Carrier Scattering Rates: First-Principles Calculations

Tuning Properties of Layered Materials Based on Hexagonal Boron Nitride by Methylation: A Density Functional Theory Study.

In this work, the rational design of optoelectronic properties of two-dimensional materials based on hexagonal boron nitride (h-BN) by functionalization by methyl (CH3) groups is proposed. Using density functional theory, we examine the functionalization of single- or double-layer systems with either CH3 radicals alone or with both CH3 (cations) and chlorine (anions), i. e., under conditions of homolytic or heterolytic splitting of CH3Cl precursor molecules, respectively. Different degrees of methylation (coverages) are considered. The methylation of pure h-BN leads to a reduction of the band gap, while in h-BN/G heterostructures (with methylated graphene layer), methylation increases the band gap. As a consequence, h-BN/G heterostructures offer a high tunability of their optoelectronic properties. To guide possible experiments, vibrational properties and spectra of methylated h-BN and methylated h-BN/G are determined.

Effect of reduction rate on microstructure and properties of laminated steel/aluminium low density composites prepared by hot pressing

ABSTRACT A multi-layer composite material consisting of 316 L steel and Al6061 aluminium was prepared via hot pressing. The mechanical properties of this heterogeneous layered composite material were studied under various reduction rates. The results revealed that the overall performance of the material initially improved and then declined as the reduction rates increased. Notably, at a hot pressing temperature of 400°C, the material exhibited optimal performance at a reduction rate of 32%. Furthermore, finite element simulations of the material processing process were performed using ABAQUS software, and the stress-strain state was analysed. The findings indicated that the overall performance of the material is influenced by both the presence of intermetallic compounds (IMCs) at the interface and the shear stress at the interface. In comparison to the aluminium layer, the performance of the steel layer undergoes more pronounced changes at the same reduction rate.

Strong Exciton-Phonon Coupling as a Fingerprint of Magnetic Ordering in van der Waals Layered CrSBr.

The layered, air-stable van der Waals antiferromagnetic compound CrSBr exhibits pronounced coupling among its optical, electronic, and magnetic properties. As an example, exciton dynamics can be significantly influenced by lattice vibrations through exciton-phonon coupling. Using low-temperature photoluminescence spectroscopy, we demonstrate the effective coupling between excitons and phonons in nanometer-thick CrSBr. By careful analysis, we identify that the satellite peaks predominantly arise from the interaction between the exciton and an optical phonon with a frequency of 118 cm-1 (∼14.6 meV) due to the out-of-plane vibration of Br atoms. Power-dependent and temperature-dependent photoluminescence measurements support exciton-phonon coupling and indicate a coupling between magnetic and optical properties, suggesting the possibility of carrier localization in the material. The presence of strong coupling between the exciton and the lattice may have important implications for the design of light-matter interactions in magnetic semiconductors and provide insights into the exciton dynamics in CrSBr. This highlights the potential for exploiting exciton-phonon coupling to control the optical properties of layered antiferromagnetic materials.

Modification Strategies and Challenges of High‐Performance Lithium‐Rich Manganese‐Based Cathode Materials

Lithium‐rich manganese‐based (LRM) cathode materials have recently gained increasing attention for their remarkable reversible capacity of up to 378 mAh g−1. However, the development of these materials is hindered by several challenges, including oxygen deficiency, migration of transition metal ions, and structural changes from lamellar to spinel phases. As a result, these limitations result in a low initial Coulomb efficiency, capacity/voltage decay, and inadequate cycle life. To address these issues, the modification of layered lithium‐rich materials proves to be an effective approach. In this review, the structure and electrochemical properties of layered LRM materials are introduced and various systematic modification strategies are discussed. Herein, the current state and future prospects of several strategies such as doping, surface coating, and structure control are delved into. Furthermore, development ideas for achieving high‐capacity and long‐cycle‐layered LRM cathode materials are presented.

Polarization modulation scanning optical microscopy method

Since the discovery of monolayer graphene, the novel physical properties of two-dimensional (2D) materials, particularly those with fewer layers that often exhibit unique properties different from bulk materials, have received significant attention. Therefore, accurately determining the layer number or obtaining the microscopic surface morphology is crucial in the laboratory fabrication and during device manufacturing. However, traditional detection methods have numerous drawbacks. There is an urgent need for a convenient, accurate, and non-destructive scientific method to characterize the layer number and surface microstructure of 2D materials. By combining the experimental setup of laser scanning photocurrent spectroscopy, we develop a polarization-modulated scanning optical microscope based on the principle of reflectance difference spectroscopy. By monitoring the reflectivity of the samples, we can observe changes in the reflection signal strength of MoS<sub>2</sub> with different layer numbers. The intensity of the reflectance differential spectral signal reflects changes in the layer count within the sample. We can characterize the changes in the number of layers of 2D materials in a non-contact manner by using polarization-modulated scanning optical microscopy. Through the study of the reflectance differential spectra of two typical 2D layered materials, MoS<sub>2</sub> and ReSe<sub>2</sub>, we find that our polarization-modulated scanning optical microscope system is also more sensitive to the characteristics of the stacking anisotropy of the 2D materials than the conventional reflection microscope. This indicates that our research contributes to a better understanding of the layer number characteristics and anisotropic properties of layered 2D materials. Furthermore, our research also provides a non-contact optical method to characterize the number of layers and optical anisotropy of two-dimensional layered material.

Characteristics and performance of layered two-dimensional materials under doping engineering.

In recent years, doping engineering, which is widely studied in theoretical and experimental research, is an effective means to regulate the crystal structure and physical properties of two-dimensional materials and expand their application potential. Based on different types of element dopings, different 2D materials show different properties and applications. In this paper, the characteristics and performance of rich layered 2D materials under different types of doped elements are comprehensively reviewed. Firstly, 2D materials are classified according to their crystal structures. Secondly, conventional experimental methods of charge doping and heterogeneous atom substitution doping are summarized. Finally, on the basis of various theoretical research results, the properties of several typical 2D material representatives under charge doping and different kinds of atom substitution doping as well as the inspiration and expansion of doping systems for the development of related fields are discussed. Through this review, researchers can fully understand and grasp the regulation rules of different doping engineering on the properties of layered 2D materials with different crystal structures. It provides theoretical guidance for further improving and optimizing the physical properties of 2D materials, improving and enriching the relevant experimental research and device application development.

Local control of superconductivity in a NbSe2/CrSBr van der Waals heterostructure

Two-dimensional magnets and superconductors are emerging as tunable building-blocks for quantum computing and superconducting spintronic devices, and have been used to fabricate all two-dimensional versions of traditional devices, such as Josephson junctions. However, novel devices enabled by unique features of two-dimensional materials have not yet been demonstrated. Here, we present NbSe2/CrSBr van der Waals superconducting spin valves that exhibit infinite magnetoresistance and nonreciprocal charge transport. These responses arise from a unique metamagnetic transition in CrSBr, which controls the presence of localized stray fields suitably oriented to suppress the NbSe2 superconductivity in nanoscale regions and to break time reversal symmetry. Moreover, by integrating different CrSBr crystals in a lateral heterostructure, we demonstrate a superconductive spin valve characterized by multiple stable resistance states. Our results show how the unique physical properties of layered materials enable the realization of high-performance quantum devices based on novel working principles.

Engineering the Surface Chemistry of Graphite and Graphene by Covalently Anchored Triazole Derivative

Robust engineering the surface properties of layered materials is assigned as one of essential strategies for permanently improving their overall physicochemical behaviors towards high-end technology applications. In this regard, covalent functionalization of graphitic surfaces including graphene is performed upon electrografting of 4-(1H-1,2,4-triazol-1-ylmethyl) diazonium (4-TYD). The efficiency of this approach is determined by a state-of-the-art toolbox including cyclic voltammetry (CV), atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), Kelvin probe force microscopy (KPFM) and Raman spectroscopy. The degree of the covalent functionalization is dependent on the molecular concentration of 4-TYD, in which the full monolayer is obtained upon electrografting with a 1 mM 4-TYD containing solution. The electrografted layer could be removed by thermal annealing leaving the pristine graphitic surfaces behind. This finding provides an efficient approach for robustly anchoring bioactive compounds onto graphene and other 2D materials in a controlled manner towards high-end technology applications.