Unidirectional Alignment Research Articles

Advancing High-Performance Piezoelectric Nanogenerators: Simple Electric Field Switching for Orientated and Aligned BaTiO3/PDMS Composite.

Barium titanate (BaTiO3) is renowned for its high dielectric constant and remarkable piezoelectric attributes, positioning it as a key element in the advancement of environmentally sustainable devices. Nevertheless, the effectiveness of piezoelectric nanogenerators (PENGs) that integrate BaTiO3 nanoparticles (NPs) and poly(dimethylsiloxane) (PDMS) poses a challenge, thereby restricting their utility in energy harvesting applications. This study presents a direct approach involving the cyclic manipulation of direct current (DC) power supply terminals to achieve unidirectional alignment of BaTiO3 NPs within a PDMS matrix, aiming to enhance the performance of the PENGs. Examination of the morphology and evaluation of diffraction planes, notably (111) and (200), in the aligned BaTiO3 PENGs exhibited well-oriented structures resulting from the repetitive switching between two electrodes, leading to improved piezoelectric properties. The BaTiO3 PENGs manifested notably higher output power (∼15 V and 1.91 μA) in contrast to devices containing randomly distributed polarized BaTiO3-PDMS composite films. The generated power was sufficient to directly operate six light-emitting diodes (LEDs) connected in series, with a collective nominal voltage of around 14 V, encompassing red, green, and blue LEDs. Nanoindentation verified the enhanced piezoelectric characteristics attributed to the alignment, sensitivity to bending, and energy-cohesive effects of clustered BaTiO3 one-dimensional (1D) pillars. These findings suggest a widely applicable technique for aligning and situating nanoparticles vertically within a polymer matrix, exploiting the intrinsic dielectric properties of the nanoparticles through a straightforward electric field switching mechanism.

Time-series domain adaptation via sparse associative structure alignment: Learning invariance and variance

Domain adaptation on time-series data, which is often encountered in the field of industry, like anomaly detection and sensor data forecasting, but received limited attention in academia, is an important but challenging task in real-world scenarios. Most of the existing methods for time-series data use the covariate shift assumption for non-time-series data to extract the domain-invariant representation, but this assumption is hard to meet in practice due to the complex dependence among variables and a small change of the time lags may lead to a huge change of future values. To address this challenge, we leverage the stableness of causal structures among different domains. To further avoid the strong assumptions in causal discovery like linear non-Gaussian assumption, we relax it to mine the stable sparse associative structures instead of discovering the causal structures directly. Besides the domain-invariant structures, we also find that some domain-specific information like the strengths of the structures is important for prediction. Based on the aforementioned intuition, we extend the sparse associative structure alignment model in the conference version to the Sparse Associative Structure Alignment model with domain-specific information enhancement (SASA2 in short), which aligns the invariant unweighted spare associative structures and considers the variant information for time-series unsupervised domain adaptation. Specifically, we first generate the segment set to exclude the obstacle of offsets. Second, we extract the unweighted sparse associative structures via sparse attention mechanisms. Third, we extract the domain-specific information via an autoregressive module. Finally, we employ a unidirectional alignment restriction to guide the transformation from the source to the target. Moreover, we further provide a generalization analysis to show the theoretical superiority of our method. Compared with existing methods, our method yields state-of-the-art performance, with a 5% relative improvement in three real-world datasets, covering different applications: air quality, in-hospital healthcare, and anomaly detection. Furthermore, visualization results of sparse associative structures illustrate what knowledge can be transferred, boosting the transparency and interpretability of our method.

Growth of centimeter-scale single-crystal graphene on polycrystalline copper foil for ultrahigh sensitive sweat sensors

The low-cost growth of wafer-scale single-crystal (SC) shows great potential in its practical application. Epitaxial growth of large-area SC graphene on pre-produced SC metal foil with a specific index surface has been reported, which requires a high cost and complexity of operational processes. Here, we demonstrate an easy and low-cost approach for the growth of wafer-scale SC graphene on polycrystalline copper foil, the growth kinetics and the lattice orientation for graphene growth controlled by induced surface steps. Despite graphene domains grown across the Cu grain boundary, the domains have a common crystal orientation at the macroscale induced by the surface steps. This work demonstrates the polycrystalline Cu foil can also grow graphene domains with unidirectional alignment and seamless stitching on the large area. The wearable 2D graphene array sensors have also been developed for the detection of interleukin-6 (IL-6) in sweat, which can locate and detect infection or disease in a non-invasive way. Our growth method and novel application put up a new way of production and utilization of SC two-dimensional (2D) materials.

Kilogram-scale production of strong and smart cellulosic fibers featuring unidirectional fibril alignment

ABSTRACT Multifunctional fibers with high mechanical strength enable advanced applications of smart textiles, robotics, and biomedicine. Herein, we reported a one-step degumming method to fabricate strong, stiff, and humidity-responsive smart cellulosic fibers from abundant natural grass. The facile process involves partially removing lignin and hemicellulose functioning as glue in grass, which leads to the separation of vessels, parenchymal cells, and cellulosic fibers, where cellulosic fibers are manufactured at kilogram scale. The resulting fibers show dense and unidirectional fibril structure at both micro- and nano-scales, which demonstrate high tensile strength of ∼0.9 GPa and Young's modulus of 72 GPa, being 13- and 14-times higher than original grass. Inspired by stretchable plant tendrils, we developed a humidity-responsive actuator by engineering cellulosic fibers into the spring-like structures, presenting superior response rate and lifting capability. These strong and smart cellulosic fibers can be manufactured at large scale with low cost, representing promising a fiber material derived from renewable and sustainable biomass.

Supramolecular assembled macroscopic soft scaffolds of thioindigo amphiphiles as cell-material interfaces

Biocompatible synthetic supramolecular systems have been proven success in fabricating regenerative biomedical materials with intrinsic functionality, tunability, and stimuli-responsiveness. However, it remains highly challenging to develop a supramolecular soft scaffold that allows transferring intrinsic microscopic aligned structural properties to cell attachments. Herein, we report a thioindigo bola-amphiphile (TIA) that is equipped with long alkyl-linker to connect the carboxylic acid end-group on the opposite side. Though photoresponsiveness of TIA is hindered in aqueous medium, it can be slightly improved by utilizing a co-solvent system or doping TIA with other amphiphiles. Electron microscopies and X-ray diffraction analysis suggest that a large aspect ratio of TIA nanostructures assembled into macroscopic soft scaffold with high degree of unidirectional alignment. The fabricated TIA macroscopic soft scaffold is further incubated with hMSCs, in revealing unidirectional aligned cell attachments. This work could provide an alternative strategy towards development of next-generation biocompatible soft functional materials.

Microstripe pattern substrate consisting of alternating planar and nanoprotrusive regions improved hiPSC-derived cardiomyocytes' unidirectional alignment and functional properties.

The alignment of each cell in human myocardium is considered critical for the efficient movement of cardiac tissue. We investigated 96-well microstripe-patterned plates to align human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs), which resemble fetal myocardium. The aligned CMs (ACMs) cultured on the microstripe-patterned plates exhibited pathology, motor function, gene expression, and drug response that more closely resembled those of adult cells than did unaligned CMs cultured on a flat plate (FCMs). We used these ACMs to evaluate drug side effects and efficacy, and to determine whether these were similar to adult-like responses. When CMs from patients with hypertrophic cardiomyopathy (HCMs) were seeded and cultured on the microstripe-patterned plates or layered on top of the ACMs, both sets of HCMs showed increased heart rate and synchronized contractions, indicating improved cardiac function. It is suggested that the ACMs could be used for drug screening as cells representative of adult-like CMs and be transplanted in the form of a cell sheet for regenerative treatment of heart failure.

Effect of polymer concentration on molecular alignment behavior during scanning wave photopolymerization

Molecularly aligned liquid-crystalline (LC) polymer films hold great promise for next-generation high-performance photonics, electronics, robotics, and medical devices. Photoalignment methods capable of achieving precise molecular alignment in a noncontact manner have been actively studied. Recently, we proposed the concept of using spatiotemporal photopolymerization to induce molecular diffusion and the resulting alignment, termed scanning wave photopolymerization (SWaP). The spatial gradient of the polymer concentration is the dominant factor in inducing the molecular diffusion and alignment of LCs. However, the effect of polymer concentration on molecular alignment behavior remains unclear. In this study, we performed SWaP at different exposure energies to modulate the polymer concentration during polymerization. We found that a certain polymer concentration was required to initiate the alignment. Furthermore, the phase diagram of the polymer/monomer mixtures and real-time observations during SWaP revealed that phase emergence and unidirectional molecular alignment occurred simultaneously when the polymer concentration exceeded 50%. Since SWaP achieves molecular alignment coincident with photopolymerization, it has the potential to revolutionize material fabrication by consolidating the multiple-step processes required to create functional materials in a single step.

Social bonding in groups of humans selectively increases inter-status information exchange and prefrontal neural synchronization.

Social groups in various social species are organized with hierarchical structures that shape group dynamics and the nature of within-group interactions. In-group social bonding, exemplified by grooming behaviors among animals and collective rituals and team-building activities in human societies, is recognized as a practical adaptive strategy to foster group harmony and stabilize hierarchical structures in both human and nonhuman animal groups. However, the neurocognitive mechanisms underlying the effects of social bonding on hierarchical groups remain largely unexplored. Here, we conducted simultaneous neural recordings on human participants engaged in-group communications within small hierarchical groups (n = 528, organized into 176 three-person groups) to investigate how social bonding influenced hierarchical interactions and neural synchronizations. We differentiated interpersonal interactions between individuals of different (inter-status) or same (intra-status) social status and observed distinct effects of social bonding on inter-status and intra-status interactions. Specifically, social bonding selectively increased frequent and rapid information exchange and prefrontal neural synchronization for inter-status dyads but not intra-status dyads. Furthermore, social bonding facilitated unidirectional neural alignment from group leader to followers, enabling group leaders to predictively align their prefrontal activity with that of followers. These findings provide insights into how social bonding influences hierarchical dynamics and neural synchronization while highlighting the role of social status in shaping the strength and nature of social bonding experiences in human groups.

Epitaxy of wafer-scale single-crystal MoS2 monolayer via buffer layer control

Monolayer molybdenum disulfide (MoS2), an emergent two-dimensional (2D) semiconductor, holds great promise for transcending the fundamental limits of silicon electronics and continue the downscaling of field-effect transistors. To realize its full potential and high-end applications, controlled synthesis of wafer-scale monolayer MoS2 single crystals on general commercial substrates is highly desired yet challenging. Here, we demonstrate the successful epitaxial growth of 2-inch single-crystal MoS2 monolayers on industry-compatible substrates of c-plane sapphire by engineering the formation of a specific interfacial reconstructed layer through the S/MoO3 precursor ratio control. The unidirectional alignment and seamless stitching of MoS2 domains across the entire wafer are demonstrated through cross-dimensional characterizations ranging from atomic- to centimeter-scale. The epitaxial monolayer MoS2 single crystal shows good wafer-scale uniformity and state-of-the-art quality, as evidenced from the ~100% phonon circular dichroism, exciton valley polarization of ~70%, room-temperature mobility of ~140 cm2v−1s−1, and on/off ratio of ~109. Our work provides a simple strategy to produce wafer-scale single-crystal 2D semiconductors on commercial insulator substrates, paving the way towards the further extension of Moore’s law and industrial applications of 2D electronic circuits.

A Study of Business English Translation Skills Based on Parallel Corpus

Abstract In this paper, the support vector machine is used as the overall classification of the paragraph alignment method. The paragraph length relationship is taken as an essential feature of the business English paragraph alignment model, the CRFs discriminative model is used as the word alignment task model, and the maximum likelihood estimation algorithm is used for model parameter training. Aiming at the real-time alignment needs at the sentence or paragraph level in Business English, the word alignment algorithm based on semantic similarity calculation is proposed, and the evaluation indexes of English-Chinese EC, Chinese-English CE unidirectional alignment and bi-directional fusion alignment, and semantic extension alignment are compared. Adding traditional business English translation techniques, comparing the effects of conventional translation techniques on business English sentence and paragraph translation versus parallel corpus-based translation techniques. The dynamic chunking accuracy of two-way fusion alignment and semantic expansion alignment is 94.57% and 94.32%, respectively, and the accuracy of semantic expansion alignment is 6.85% and 8.17% higher than that of EC one-way alignment. Meanwhile, the number of errors in business English translation works based on parallel corpora is reduced, which can help translators overcome the interference of Chinese chapter structures and improve the quality of their translation works.

Wafer scale growth of single crystal two-dimensional van der Waals materials.

Two-dimensional (2D) van der Waals (vdW) materials, including graphene, hexagonal boron nitride (hBN), and metal dichalcogenides (MCs), form the basis of modern electronics and optoelectronics due to their unique electronic structure, chemical activity, and mechanical strength. Despite many proof-of-concept demonstrations so far, to fully realize their large-scale practical applications, especially in devices, wafer-scale single crystal atomically thin highly uniform films are indispensable. In this minireview, we present an overview on the strategies and highlight recent significant advances toward the synthesis of wafer-scale single crystal graphene, hBN, and MC 2D thin films. Currently, there are five distinct routes to synthesize wafer-scale single crystal 2D vdW thin films: (i) nucleation-controlled growth by suppressing the nucleation density, (ii) unidirectional alignment of multiple epitaxial nuclei and their seamless coalescence, (iii) self-collimation of randomly oriented grains on a molten metal, (iv) surface diffusion and epitaxial self-planarization and (v) seed-mediated 2D vertical epitaxy. Finally, the challenges that need to be addressed in future studies have also been described.

Electric field-modulated evaporative thin film deposition of bio-particles for piezoelectric applications.

Bio-based functional materials can be used to replace or limit the use of synthetic materials sourced from unsustainable sources. However, the potential of such materials remains largely unexplored. In this study, we demonstrate the use of weak AC electric fields to deposit ultra-thin piezoelectric films from cellulose nanocrystals (CNC). This is the first time electric fields are used to realize <50 nm thick uniform bio-based piezoelectric films wherein the bioparticles exhibit unidirectional arrangement. Interestingly, we found that the use of weak AC electric fields of suitable frequencies completely mitigates the coffee ring effect (CRE), which results in defect-free uniform ultra-thin films. Additionally, the electric fields appear to help in realizing unidirectional alignment of particles in the films, which enhances their piezoelectric properties. The method was also tested for chitin nanocrystals (ChNC), which have a similar aspect ratio but bear opposite polarity surface charges, and the influence of the field on coffee ring formation and particle orientation in CNC thin film deposition was validated. The phenomena can be attributed to the constant spatio-temporal curvature of the evaporating liquid film, the transient state between the three-phase contact (TPC) line, the electric field-dependent contact angle, and the permanent and field-induced dipole moments. These factors lead to particle polarization and alignment. The films have an optimum electrical frequency of deposition at which they are continuous and uniformly thin, have unidirectional alignment of particles, and function as a single dipole.

Unidirectional alignment and orientation pinning mechanism of h-BN nucleation on Ir(111) via reactive probe atomic force microscopy

The epitaxial growth of wafer-scale single-crystalline two-dimensional materials requires precise control over the crystallographic orientation and morphology of clusters formed during the initial stages of nucleation. However, there is limited knowledge about the critical nucleus and its growth mechanism for h-BN on high-symmetry surfaces of transition metals. In this study, we provide atomic insights into h-BN nucleation on Ir(111) using scanning tunneling microscopy and noncontact atomic force microscopy, corraborated by density functional theory (DFT) calculations. The atomic-resolved structural characterization reveals that the smallest h-BN cluster, exhibiting a non-1:1 stoichiometric ratio of boron and nitrogen atoms, maintains a triangular shape with zigzag-type edges. Through force spectroscopy, individual B and N atoms within the cluster, as well as the N-termination edge, are clearly identified, indicating the atomic-scale elemental sensitivity of the chemical-reactive metallic tip. While DFT calculations suggest that the NtopBfcc configuration is thermodynamically favored for larger clusters, a predominant crystalline orientation is observed for nuclei of various sizes, unequivocally attributed to the NtopBhcp registry. This orientation pinning behavior presents opportunities for large-scale growth of binary and ternary materials by impeding rotational alignment of nuclei in the early stages of nucleation.

Izod impact resistance of 3D printed discontinuous fibrous composites with Bouligand structure

The Bouligand structure found in the dactyl club of mantis shrimps is known for its impact resistance. However, Bouligand-inspired reinforced composites with 3D shapes and impact resistance characteristics have not yet been demonstrated. Herein, direct ink writing was used to 3D print composites reinforced with glass microfibers assembled into Bouligand structures with controllable pitch angles. The energy absorption levels of the Bouligand composites under impact were found to surpass those of composites with unidirectional microfiber alignment. Additionally, the Bouligand composites with a pitch angle of 40° exhibited a maximum energy absorption of 2.4 kJ/m2, which was 140% higher than that of the unidirectional composites. Furthermore, the characterization of the topography of the fractured surface, supplemented with numerical simulations, revealed a combination of crack twisting and crack bridging mechanisms. Flexural tests conducted on the composites with a pitch angle of 40° revealed that these composites had the strongest properties, including a flexural strength of 36.9 MPa, a stiffness of 2.26 GPa, and energy absorption of 8 kJ/m2. These findings are promising for the microstructural design of engineered composites using direct ink writing for applications in aerospace, transportation, and defense.

Hierarchically Superstructured Anisotropic Carbon Particles by Multiscale Assembly Driven by Spinodal Decomposition.

Hierarchical superstructures have novel shape-dependent properties, but well-defined anisotropic carbon superstructures with controllable size, shape, and building block dimensionality have rarely been accomplished thus far. Here, a hierarchical assembly technique is presented that uses spinodal decomposition (SD) to synthesize anisotropic oblate particles of mesoporous carbon superstructure (o-MCS) with nanorod arrays by integrating block-copolymer (BCP) self-assembly and polymer-polymer interface behaviors in binary blends. The interaction of major and minor phases in binary polymer blends leads to the formation of an anisotropic oblate particle, and the BCP-rich phase enables ordered packing and unidirectional alignment of carbon nanorods. Consequently, this approach enables precise control over particles' size, shape, and over the dimensionality of their components. Exploiting this functional superstructure, o-MCS are used as an anode material in potassium-ion batteries, and achieve a notable specific capacity of 156mAhg-1 at a current density of 2Ag-1, and long-term stability for 3000 cycles. This work presents a significant advancement in the field of hierarchical superstructures, providing a promising strategy for the design and synthesis of anisotropic carbon materials with controlled properties, offering promising applications in energy storage and beyond.

Observation of aligned dipoles and angular chromism of exciplexes in organic molecular heterostructures

The dipole characteristics of Frenkel excitons and charge-transfer excitons between donor and acceptor molecules in organic heterostructures such as exciplexes are important in organic photonics and optoelectronics. For the bilayer of the organic donor 4,4′,4′′-tris[(3-methylphenyl)phenylamino]triphenylamine and acceptor 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine molecules, the exciplexes form aligned dipoles perpendicular to the Frenkel excitons, as observed in back focal plane photoluminescence images. The angular chromism of exciplexes observed in the 100 meV range indicates possible delocalization and angle-sensing photonic applications. The blue shift of the peak position and increase in the linewidth of photoluminescene spectra with increasing excitation power are caused by the repulsive aligned exciplex dipole moments with a long lifetime (4.65 μs). Electroluminescence spectra of the exciplex from organic light-emitting diodes using the bilayer are blue-shifted with increasing bias, suggesting unidirectional alignment of the exciplex dipole moments. The observation of exciplex dipole moment alignments across molecular interfaces can facilitate the controlled coupling of exciton species and increase efficiency of organic light-emitting diodes.

Lyotropic Boron Nitride Nanotube Liquid Crystals: Preparation, Characterization, and Wet-Spinning for Fabrication of Composite Fiber

Microfiber fabrication via wet-spinning of lyotropic liquid crystals (LCs) with anisotropic nanomaterials has gained increased attention due to the microfibers' excellent physical/chemical properties originating from the unidirectional alignment of anisotropic nanomaterials along the fiber axis with high packing density. For wet-spinning of the microfibers, however, preparing lyotropic LCs by achieving high colloidal stability of anisotropic nanomaterials, even at high concentrations, has been a critically unmet prerequisite, especially for recently emerging nanomaterials. Here, we propose a cationically charged polymeric stabilizer that can efficiently be adsorbed on the surface of boron nitride nanotubes (BNNTs), which provide steric hindrance in combination with Coulombic repulsion leading to high colloidal stability of BNNTs up to 22 wt %. The BNNT LCs prepared from the dispersions with various stabilizers were systematically compared using optical and rheological analysis to optimize the phase behavior and rheological properties for wet-spinning of the BNNT LCs. Systematic optical and mechanical characterizations of the BNNT microfibers with aligned BNNTs along the fiber axis revealed that properties of the microfibers, such as their tensile strength, packing density, and degree of BNNT alignment, were highly dependent on the quality of BNNT LCs directly related to the types of stabilizers.

Strong amplification of mid-infrared radiation absorption in nanotube-confined water

Energy absorption on a nanometer scale is vital for biochemical and climate systems. This paper reports that a two times amplification in absorption efficiency of mid-infrared (MIR) radiations can be achieved by water molecules confined in carbon nanotubes with a small radius compared to the bulk water absorption. This absorption enhancement is closely associated with the configurational change of water molecules into a unidirectional alignment under the nanotube confinement, which greatly augments the transition probability concerning the MIR absorption. In addition, the effect of confinement due to a (6,6) carbon nanotube is found to be very robust, equivalent to that of a 5 V/nm static electric field. These findings can be used to design energy-efficient nanodevices to modulate the microclimate variables by converting the redundant ambient MIR irradiation into the prompt heat conduction and are instructive for understanding the specific functioning of relevant biological channels.

Bridging Synthesis and Controllable Doping of Monolayer 4 in. Length Transition-Metal Dichalcogenides Single Crystals with High Electron Mobility.

Epitaxial growth and controllable doping of wafer-scale atomically thin semiconductor single crystals are two central tasks to tackle the scaling challenge of transistors. Despite considerable efforts are devoted, addressing such crucial issues simultaneously under 2D confinement is yet to be realized. Here, an ingenious strategy to synthesize record-breaking 4 in. length Fe-doped transition-metal dichalcogenides (TMDCs) single crystals on industry-compatible c-plane sapphire without special miscut angle is designed. Atomically thin transistors with high electron mobility (≈146 cm2 V-1 s-1 ) and remarkable on/off current ratio (≈109 ) are fabricated based on 4 in. length Fe-MoS2 single crystals, due to the ultralow contact resistance (≈489 Ω µm). In-depth characterizations and theoretical calculations reveal that the introduction of Fe significantly decreases the formation energy of parallel steps on sapphire surfaces and contributes to the edge-nucleation of unidirectional alignment TMDCs domains (>99%). This work represents a substantial leap in terms of bridging synthesis and doping of wafer-scale 2D semiconductor single crystals, which should promote the further device downscaling and extension of Moore's law.

Fatigue behavior of unidirectional fiber‐reinforced pultruded composites with high volume fiber fraction

AbstractPultrusion is a high‐volume manufacturing process for fiber‐reinforced polymer (FRP) composites ensuring high strength and quality products. However, research studies are very limited on the fatigue behavior of these products, especially with unidirectional fiber alignment. This study investigates the fatigue behavior of the unidirectional pultruded glass FRP (GFRP) composites with high fiber volume fraction ( ). Tension–tension fatigue loading was applied with different levels of applied stress, frequency, and gripping condition until failure. Results showed that the high composites have significantly low fatigue life cycle. Moreover, increasing the frequency showed better fatigue resistance, while the tabs geometry has insignificant effect on the fatigue behavior of the dog‐bone shaped specimens. Comparison with available literature showed that GFRP composites with high have lower fatigue performance than those with low . A fatigue capacity reduction factor is also proposed for unidirectional GFRP composites as a function of the .