Atomically Sharp Dual Grain Boundaries in 2D WS2 Bilayers

It is shown that tilt grain boundaries (GBs) in bilayer 2D crystals of the transition metal dichalcogenide WS₂ can be atomically sharp, where top and bottom layer GBs are located within sub‐nanometer distances of each other. This expands the current knowledge of GBs in 2D bilayer crystals, beyond the established large overlapping GB types typically formed in chemical vapor deposition growth, to now include atomically sharp dual bilayer GBs. By using atomic‐resolution annular dark‐field scanning transmission electron microscopy (ADF‐STEM) imaging, different atomic structures in the dual GBs are distinguished considering bilayers with a 3R (AB stacking)/2H (AA′ stacking) interface as well as bilayers with 2H/2H boundaries. An in situ heating holder is used in ADF‐STEM and the GBs are stable to at least 800 °C, with negligible thermally induced reconstructions observed. Normal dislocation cores are seen in one WS₂ layer, but the second WS₂ layer has different dislocation structures not seen in freestanding monolayers, which have metal‐rich clusters to accommodate the stacking mismatch of the 2H:3R interface. These results reveal the competition between maintaining van der Waals bilayer stacking uniformity and dislocation cores required to stitch tilted bilayer GBs together.     

Linking Grain Boundaries and Grain Growth in Ceramics

The macroscopic properties of most materials are strongly influenced by grain size. In ceramic materials the microstructure usually results from the sintering process. Understanding the basic mechanisms of grain growth on an atomic length scale in ceramics would be beneficial to tailor the microstructure for improved macroscopic performance of devices. A method is presented using grain growth experiments to select samples for closer examination of grain boundaries with transmission electron microscopy. The growth experiments are used to identify temperatures were changes at grain boundaries occur at high temperature. Subsequently samples of interest are investigated using transmission electron microscopy (TEM) methods. The correlation between TEM results and changes in grain growth behavior can be used to gain closer insight into the processes occurring during grain growth at an atomic length scale. Strontium titanate is used as model system to demonstrate the combination of growth experiments with TEM results. Normal grain growth shows two distinct drops in growth rate in the temperature range between 1 300 and 1 425 °C, independent of the A‐site to B‐site stoichiometry of the perovskite. In previous studies a high preference for grain boundary planes oriented parallel to the 100 direction of one of the adjacent grains was found in the high temperature regime. This study shows that the preference does not exist in the low temperature regime possibly explaining the change in grain growth rate.     

Engineering Transport in Manganites by Tuning Local Nonstoichiometry in Grain Boundaries

Interface‐dominated materials such as nanocrystalline thin films have emerged as an enthralling class of materials able to engineer functional properties of transition metal oxides widely used in energy and information technologies. In particular, it has been proven that strain‐induced defects in grain boundaries of manganites deeply impact their functional properties by boosting their oxygen mass transport while abating their electronic and magnetic order. In this work, the origin of these dramatic changes is correlated for the first time with strong modifications of the anionic and cationic composition in the vicinity of strained grain boundary regions. We are also able to alter the grain boundary composition by tuning the overall cationic content in the films, which represents a new and powerful tool, beyond the classical space charge layer effect, for engineering electronic and mass transport properties of metal oxide thin films useful for a collection of relevant solid‐state devices.     

Grain Boundary Sliding at Serrated Grain Boundaries

A constitutive model is developed for grain boundary sliding (GBS) at serrated grain boundaries. Based on a previously developed GBS model, using the dynamics of grain boundary dislocation pile-up, the present model takes the average of the sliding rate over the characteristic dimensions of grain boundary serrations. Thus, a geometric factor is introduced to account for the effects of serration wave length and amplitude on the GBS rate, as compared to the GBS rate at planar boundaries. By considering the role of grain boundary shear stress in stress balancing, the proposed model removes the singularity at planar boundaries which exists in the diffusion-controlled GBS model at serrated grain boundaries. The modified model describes very well the transient creep of complex Ni-base superalloys with and without grain boundary serrations and should be suitable for other engineering alloys (with the exception of columnar grained and single crystal alloys).     

Supramolecular Chiral 2D Materials and Emerging Functions

Chiral materials are widely applied in various fields such as enantiomeric separation, asymmetric catalysis, and chiroptical effects, providing stereospecific conditions and environments. Supramolecular concepts to create the chiral materials can provide an insight for emerging chiro-optical properties due to their well-defined scaffolds and the precise functionalization of the surfaces or skeletons. Among the various supramolecular chiral structures, 2D chiral sheet structures are particularly interesting materials because of their extremely high surface area coupled with many unique chemical and physical properties, thereby offering potential for the next generation of functional materials for optically active systems and optoelectronic devices. Nevertheless, relatively limited examples for 2D chiral materials exhibiting specific functionality have been reported because incorporation of molecular chirality into 2D architectures is difficult at the present stage. Here, a brief overview of the recent advances is provided on the construction of chiral supramolecular 2D materials and their functions. The design principles toward 2D chirality and their potential applications are also discussed.     

Microwave-Frequency Vortex Dynamics in YBCO Grain Boundaries

We report measurements and modeling of microwave-frequency vortex dynamics in YBCO grain boundaries that are modeled as long Josephson junctions by numerically solving the sine-Gordon equation. YBCO bicrystal grain boundaries with misorientation angles from 2 to 24° have been studied experimentally using microwave resonator measurement techniques. Comparison between the measured and calculated microwave impedance and the harmonic generation of the 24° grain boundaries indicates that the 24° grain boundaries are weakly coupled long Josephson junctions. The corresponding results of lower angle grain boundaries are also presented. A transition from strong-coupled single-crystal-like behavior to weak-coupled Josephson-junction-like behavior has been observed in a 10° grain boundary between 55 and 75 K. The physics of Josephson-vortex dynamics and its impact on the microwave properties of superconducting thin films are discussed.     

Wearable Electronics Based on 2D Materials for Human Physiological Information Detection

Recently, advancement in materials production, device fabrication, and flexible circuit has led to the huge prosperity of wearable electronics for human healthcare monitoring and medical diagnosis. Particularly, with the emergence of 2D materials many merits including light weight, high stretchability, excellent biocompatibility, and high performance are used for those potential applications. Thus, it is urgent to review the wearable electronics based on 2D materials for the detection of various human signals. In this work, the typical graphene‐based materials, transition‐metal dichalcogenides, and transition metal carbides or carbonitrides used for the wearable electronics are discussed. To well understand the human physiological information, it is divided into two dominated categories, namely, the human physical and the human chemical signals. The monitoring of body temperature, electrograms, subtle signals, and limb motions is described for the physical signals while the detection of body fluid including sweat, breathing gas, and saliva is reviewed for the chemical signals. Recent progress and development toward those specific utilizations are highlighted in the Review with the representative examples. The future outlook of wearable healthcare techniques is briefly discussed for their commercialization.     

Ni36CrTiAl弹性合金晶界不连续析出相变动力学的研究

本文对高弹性合金NI_(36)CrTiAl的晶界不连续析出相变进行了动力学研究.动力学分析指出:在特定条件下,不连续析出相变的总体动力学不符合动力学定律(Avrami方程),而是符合与纤维组织发展相对应的线性动力学。     

Giant Thermal Expansion in 2D and 3D Cellular Materials

When temperature increases, the volume of an object changes. This property was quantified as the coefficient of thermal expansion only a few hundred years ago. Part of the reason is that the change of volume due to the variation of temperature is in general extremely small and imperceptible. Here, abnormal giant linear thermal expansions in different types of two‐ingredient microstructured hierarchical and self‐similar cellular materials are reported. The cellular materials can be 2D or 3D, and isotropic or anisotropic, with a positive or negative thermal expansion due to the convex or/and concave shape in their representative volume elements respectively. The magnitude of the thermal expansion coefficient can be several times larger than the highest value reported in the literature. This study suggests an innovative approach to develop temperature‐sensitive functional materials and devices.     

Memristors Based on 2D Materials as an Artificial Synapse for Neuromorphic Electronics

The memristor, a composite word of memory and resistor, has become one of the most important electronic components for brain-inspired neuromorphic computing in recent years. This device has the ability to control resistance with multiple states by memorizing the history of previous electrical inputs, enabling it to mimic a biological synapse in the neural network of the human brain. Among many candidates for memristive materials, including metal oxides, organic materials, and low-dimensional nanomaterials, 2D layered materials have been widely investigated owing to their outstanding physical properties and electrical tunability, low-power-switching capability, and hetero-integration compatibility. Hence, a large number of experimental demonstrations on 2D material-based memristors have been reported showing their unique memristive characteristics and novel synaptic functionalities, distinct from traditional bulk-material-based systems. Herein, an overview of the latest advances in the structures, mechanisms, and memristive characteristics of 2D material-based memristors is presented. Additionally, novel strategies to modulate and enhance the synaptic functionalities of 2D-memristor-based artificial synapses are summarized. Finally, as a foreseeing perspective, the potentials and challenges of these emerging materials for future neuromorphic electronics are also discussed.     

Segregation and Local Structure at Grain Boundaries in SiO2-Doped Tetragonal ZrO2 Polycrystalline Materials

SiO₂ doping in Y₂O₃ stabilized tetragonal ZrO₂ (TZP) materials introduced significant change in mechanical properties around 0.3 wt.% doping level [1]. In order to understand the influence of grain boundary structure and chemistry by doping, high purity undoped and SiO₂-doped 3Y-TZP samples were studied using high-resolution and analytical TEM. Typical grain boundary structures are different for the two types of samples, while amorphous film was not observed at most grain boundaries. A new EDS analysis method was introduced to detect the weak Si and Y signals which overlap with the predominent Zr peaks. It revealed that Si segregation to the grain boundary saturates at 12 at./nm² (or 1.5 monolayer of SiO₂) when the SiO₂ doping level reached and surpassed 0.3 wt.%. It is the segregated atoms which enhanced the grain boundary diffusivity and therefore altered the deformation mechanism.     

Formation Energy Profiles of Oxygen Vacancies at Grain Boundaries in Perovskite-Type Electroceramics

Oxygen vacancy formation energies play a major role in the electric field-assisted abnormal grain growth of technologically relevant polycrystalline perovskite phases. The underlying effect on the atomic scale is assumed to be a redistribution of cationic and anionic point defects between grain boundaries (GBs) and the bulk interior regions of the grains due to different defect formation energies in the structurally different regions, accompanied by the formation of space charge zones. Using atomistic calculations based on classical interatomic potentials, optimized structures of the symmetric tilt GBs Σ5(210)[001] and Σ5(310)[001], and of the asymmetric tilt GB (430)[001]||(100)[001] in the electroceramic perovskite materials SrTiO₃, BaTiO₃, and BaZrO₃, are derived and discussed. Profiles of oxygen vacancy formation energies across those GBs are presented and their dependence on composition and GB type is discussed.     

Electrical Contacts With 2D Materials: Current Developments and Future Prospects

Current electrical contact models are occasionally insufficient at the nanoscale owing to the wide variations in outcomes between 2D mono and multi-layered and bulk materials that result from their distinctive electrostatics and geometries. Contrarily, devices based on 2D semiconductors present a significant challenge due to the requirement for electrical contact with resistances close to the quantum limit. The next generation of low-power devices is already hindered by the lack of high-quality and low-contact-resistance contacts on 2D materials. The physics and materials science of electrical contact resistance in 2D materials-based nanoelectronics, interface configurations, charge injection mechanisms, and numerical modeling of electrical contacts, as well as the most pressing issues that need to be resolved in the field of research and development, will all be covered in this review.     

2D V‐V Binary Materials: Status and Challenges

2D phosphorene, arsenene, antimonene, and bismuthene, as a fast‐growing family of 2D monoelemental materials, have attracted enormous interest in the scientific community owing to their intriguing structures and extraordinary electronic properties. Tuning the monoelemental crystals into bielemental ones between group‐VA elements is able to preserve their advantages of unique structures, modulate their properties, and further expand their multifunctional applications. Herein, a review of the historical work is provided for both theoretical predictions and experimental advances of 2D V‐V binary materials. Their various intriguing electronic properties are discussed, including band structure, carrier mobility, Rashba effect, and topological state. An emphasis is also given to their progress in fabricated approaches and potential applications. Finally, a detailed presentation on the opportunities and challenges in the future development of 2D V‐V binary materials is given.     

Colloidal Nanosurfactants for 3D Conformal Printing of 2D van der Waals Materials

Printing techniques using nanomaterials have emerged as a versatile tool for fast prototyping and potentially large-scale manufacturing of functional devices. Surfactants play a significant role in many printing processes due to their ability to reduce interfacial tension between ink solvents and nanoparticles and thus improve ink colloidal stability. Here, a colloidal graphene quantum dot (GQD)-based nanosurfactant is reported to stabilize various types of 2D materials in aqueous inks. In particular, a graphene ink with superior colloidal stability is demonstrated by GQD nanosurfactants via the π–π stacking interaction, leading to the printing of multiple high-resolution patterns on various substrates using a single printing pass. It is found that nanosurfactants can significantly improve the mechanical stability of the printed graphene films compared with those of conventional molecular surfactant, as evidenced by 100 taping, 100 scratching, and 1000 bending cycles. Additionally, the printed composite film exhibits improved photoconductance using UV light with 400 nm wavelength, arising from excitation across the nanosurfactant bandgap. Taking advantage of the 3D conformal aerosol jet printing technique, a series of UV sensors of heterogeneous structures are directly printed on 2D flat and 3D spherical substrates, demonstrating the potential of manufacturing geometrically versatile devices based on nanosurfactant inks.     

2D Monoelemental Arsenene,Antimonene, and Bismuthene: Beyond Black Phosphorus

Two‐dimensional materials are responsible for changing research in materials science. After graphene and its counterparts, graphane, fluorographene, and others were introduced, waves of renewed interest in 2D binary compounds occurred, such as in metal oxides, transition‐metal dichalcogenides (most often represented by MoS₂), metal oxy/hydroxide borides, and MXenes, to name the most prominent. Recently, interest has turned to two‐dimensional monoelemental structures, such as monolayer black phosphorus and, very recently, to monolayer arsenic, antimony, and bismuth. Here, a short overview is provided of the area of exponentially increasing research in arsenene, antimonene, and bismuthene, which belong to the fifth main group of elements, the so‐called pnictogens. A short review of historical work is provided, the properties of bulk allotropes of As, Sb, and Bi discussed, and then theoretical and experimental research on mono‐ and few‐layered arsenene, antimonene, and bismuthene addressed, discussing their structures and properties.