Anisotropy Ratio Research Articles

Laminated bamboo materials for plated building structures

Current bamboo composite materials have typical unidirectional properties. Along the bamboo fiber the strength is high while transverse to the fiber the strength is ultra-low. Such bamboo composite can be applied to construct beams and columns. To construct plated building structures, the anisotropy will greatly weaken the load carrying capacity. A novel cross-laminated bamboo (CLB) composite material was firstly designed, manufactured and tested in this research. Seven kinds of CLB specimens with fiber orientation changing from 0° to 90° at an interval of 15° were prepared for tension, compression and bending experiments to investigate the anisotropic mechanical behaviors of the CLB. Experimental results show that the laminated structure greatly attenuates the anisotropy of the bamboo composite. The anisotropic ratios of the tensile strength, the compressive strength and the flexural strength are 3.33, 1.38 and 2.10 respectively. In addition, CLB also has good strength and stiffness, and might be an excellent bamboo for plated building structures.

Anisotropy of soil water diffusivity of hillslope soil under spruce forest derived by X-ray CT and lab experiments

The idea of the study is to indicate direction-dependent differences in hydraulic conductivity, K(Se), and soil water diffusivity, D(θ), as function of the volume fraction related to the fractional capillary potential for each of the characteristic pore size classes by extended anisotropy factors. The study is exemplary focused on a BwC horizon of a Dystric Cambisol under spruce forest formed on the weathered and fractured granite bedrock in the mountainous hillslopes Uhlirska catchment (Czech Republic). Thus, undisturbed soil samples were taken in vertical (0°, y = x-axis) and horizontal (90°, z-axis) direction. The D(θ) values and especially the D(θ)-weighted anisotropy ratios showed that anisotropy increases with the volume fraction of macropores, MaP (d > 0.03 mm), with r2 between 0.89 and 0.92. The X-ray computer tomography (CT) based anisotropy ratio (ACT) is larger for the horizontal sampled soil core with 0.31 than for the vertical with 0.09. This underlines the existence of a predominantly horizontally oriented pore network and the fact that weathered bedrock strata can initiate lateral preferential flow. The study results suggest that combining the hydraulic conductivity as intensity and the capacity parameter by means of diffusivity results in an extended anisotropy ratio which unveils the role of the soil hydraulic characteristics in generation of small-scale lateral preferential flow. In future, the small-scale direction-dependent differences in the soil hydraulic capacity and intensity parameter will be used for model-based upscaling for better understanding of preferential flow at the catchment scale.

Visualization of Human Skeletal Muscle Mechanical Anisotropy by Using Dual-Direction Shear Wave Imaging.

Ultrasound (US) shear wave elasticity imaging (SWEI) is a mature technique for diagnosing the elasticity of isotropic tissues. However, the elasticity of anisotropic tissues, such as muscle and tendon, cannot be diagnosed correctly using SWEI because the shear wave velocity (SWV) varies with tissue fiber orientations. Recently, SWEI has been studied for measuring the anisotropic properties of muscles by rotating the transducer; however, this is difficult for clinical practice. In this study, a novel dual-direction shear wave imaging (DDSWI) technique was proposed for visualizing the mechanical anisotropy of muscles without rotation. Longitudinal and transverse shear waves were created by a specially designed external vibrator and supersonic pushing beam, respectively; the SWVs were then tracked using ultrafast US imaging. Subsequently, the SWV maps of two directions were obtained at the same scanning cross section, and the mechanical anisotropy was represented as the ratio between them at each pixel. The performance of DDSWI was verified using a standard phantom, and human experiments were performed on the gastrocnemius and biceps brachii. Experimental results of phantom revealed DDSWI exhibited a high precision of <0.81% and a low bias of <3.88% in SWV measurements. The distribution of anisotropic properties in muscle was visualized with the anisotropic ratios of 1.54 and 2.27 for the gastrocnemius and biceps brachii, respectively. The results highlight the potential of this novel anisotropic imaging in clinical applications because the conditions of musculoskeletal fiber orientation can be easily and accurately evaluated in real time by DDSWI.

Utility of Diffusion and Magnetization Transfer MRI in Cervical Spondylotic Myelopathy: A Pilot Study.

Diffusion tensor imaging (DTI) and magnetization transfer (MT) magnetic resonance imaging (MRI) can help detect spinal cord pathology, and tract-specific analysis of their parameters, such as fractional anisotropy (FA), mean diffusivity, axial diffusivity (AD), radial diffusivity (RD) and MT ratio (MTR), can give microstructural information. We performed the tract-based acquisition of MR parameters of three major motor tracts: the lateral corticospinal (CS), rubrospinal (RuS) tract, and lateral reticulospinal (RS) tract as well as two major sensory tracts, i.e., the fasciculus cuneatus (FC) and spinal lemniscus, to detect pathologic change and find correlations with clinical items. MR parameters were extracted for each tract at three levels: the most compressed lesion level and above and below the lesion. We compared the MR parameters of eight cervical spondylotic myelopathy patients and 12 normal controls and analyzed the correlation between clinical evaluation items and MR parameters in patients. RuS and lateral RS showed worse DTI parameters at the lesion level in patients compared to the controls. Worse DTI parameters in those tracts were correlated with weaker power grasp at the lesion level. FC and lateral CS showed a correlation between higher RD and lower FA and MTR with a weaker lateral pinch below the lesion level.

Perpendicularly Reversed Polarization Sensitivity of Double‐faced Photodetection based on Sb2Se3 Microbelt

AbstractLow‐dimensional polarization‐sensitive photodetectors have captured ever‐increasing attention due to their unique applications in navigation, optical switching, and communication. However, to date, the study of dimensionality‐dependent polarization‐sensitive photodetectors has not received much attention. Herein, a double‐faced polarization‐sensitive photodetector based on an individual high‐quality Sb2Se3 microbelt is proposed, where both the wide and narrow side facets serve as irradiation targets. Polarization‐sensitive measurements reveal the anisotropy in the photocurrents recorded parallel and perpendicular to the long axis of the Sb2Se3 microbelt. Strikingly, the single Sb2Se3 microbelt photodetector reveals the obvious perpendicular reversal with a 90° angle on polarization sensitivity from the wide surface to the narrow surface. With decreasing inclination angle, the anisotropic ratio varies from 1.18 to 0.87 gradually. Interestingly, the photodetector can lose its polarization sensitivity at a particular inclination angle. Angle‐resolved polarized Raman spectroscopy confirms the asymmetry and anisotropic character of the Sb2Se3 microbelt. The polarization sensitivity of the Sb2Se3 microbelt photodetectors originates from the optical anisotropy induced by the crystal structure anisotropy, rather than one‐dimensional geometry morphological anisotropy. The use of an anisotropic Sb2Se3 microbelt in double‐faced polarization‐sensitive photodetection may contribute to new functionality in innovative optoelectronic applications.

A Predicting Model for the Effective Thermal Conductivity of Anisotropic Open-Cell Foam

The structural anisotropy of open-cell foam leads to the anisotropy of effective thermal conductivity (ETC). To quantitatively analyze the effect of structural anisotropy on the anisotropy of ETC, a new predicting model for the ETC of anisotropic open-cell foam was proposed based on an anisotropy tetrakaidecahedron cell (ATC). Feret diameters in three orthogonal directions obtained by morphological analysis of real foam structures were used to characterize the anisotropy of ATC. To validate our proposed anisotropic model, the ETCs of real foam structures in three orthogonal directions predicted by it were compared with the numerical results, for which the structures of numerical models are reconstructed by X-ray computed tomography (X-CT). Using the present anisotropic model, the influences of the thermal conductivity ratio (TCR) and porosity of the foams on the anisotropic ratios of ETCs are also investigated. Results show that there is good consistency between the ETCs obtained by the anisotropic model and the numerical method. The maximum relative errors between them are 2.84% and 13.57% when TCRs are 10 and 100, respectively. The present anisotropic model can not only predict the ETCs in different orthogonal directions but also quantitatively predict the anisotropy of ETC. The anisotropies of the ETCs decrease with porosity because the proportion of the foam skeleton decreases. However, the anisotropies of ETCs increase with TCR, and there exist asymptotic values in anisotropic ratios of ETCs as TCR approaches infinity and they are equal to the relative Feret diameters in different orthogonal directions.

Indentation of Anisotropic Tissue Using a Three-Dimensional Mechanical Bidomain Model

Computation-based mathematical models of tissue indentation are capable of predicting the distribution of forces and mechanical properties of soft tissues. This paper presents a three-dimensional mathematical model of anisotropic tissue indentation developed using the mechanical bidomain model. The mechanical bidomain model hypothesizes that the relative displacement between intra- and extracellular spaces triggers a force on the mechanosensitive proteins in the membrane: integrins. Some soft tissues, such as cardiac muscle, are anisotropic, a property which arises from the fibrous structure of the tissue. The degree of anisotropy in intra- and extracellular spaces can be different. Tissue indentation for different anisotropy ratios that indicate isotropy, equal anisotropy and unequal anisotropy, were tested using the model. Results of the tissue indentation analysis compared the spatial distribution of the magnitude of bidomain displacement for different anisotropy conditions between monodomain and bidomain models. The proposed mathematical model predicted unexpected spatial patterns of cardiac mechanotransduction for unequal anisotropy ratios of mechanical modulus.

CO2 Sequestration and Enhanced Oil Recovery via the Water Alternating Gas Scheme in a Mixed Transgressive Sandstone-Carbonate Reservoir: Case Study of a Large Middle East Oilfield

The knowledge on CO2 sequestration and CO2 enhanced oil recovery (CO2-EOR) in mature mixed and interbedded hydrocarbon reservoirs are limited. In this vein, the feasibility of CO2-water alternating gas (CO2-WAG) for coupling CO2 sequestration and CO2-EOR in a mature mixed sandstone-carbonate reservoir was investigated using the S1A reservoir. First, core sample analysis and scanning electron microscopy (SEM) were conducted to evaluate the reservoir characterization. Next, a geological model with dual porosity and permeability was developed and transferred to a reservoir simulation model, and 21-year field production data were utilized for history matching and constraining of the reservoir model. Then, continuous CO2 and CO2-WAG injection methods were simulated using newly developed and history-matched geo-models and compared to assess their CO2-EOR and CO2 storage mechanisms and determine their potential in a mixed sandstone-carbonate reservoir. The effect of the anisotropic permeability ratio and hysteresis on CO2 storage mechanisms was addressed in this work. The results indicate that the CO2-WAG scheme can yield a +3% oil recovery factor than the continuous CO2 injection method, and CO2-WAG injection can utilize up to 14 and 12% of the total CO2 injected for residual and solubility trappings, respectively, while a minimal 2.9 and 0.03% was utilized from continuous CO2 injection for residual and solubility trappings, respectively. The WAG ratio of 2:1 could yield a higher recovery factor and greater CO2 utilization for solubility and residual trappings in a mixed reservoir. In mixed and interbedded reservoirs, geological anisotropy can also strongly influence reservoir performance during the CO2-EOR process, in which higher values of the anisotropy ratio (Kv/Kh) in CO2-WAG can yield greater oil recovery and more CO2 storage; also, hysteresis has great impact on residual trapping. This study provides valuable insights into the potential of CO2-WAG for CO2 sequestration and CO2-EOR in mature mixed and interbedded reservoirs.

Strong Anisotropy of Multilayer γ‐InSe‐Enabled Polarization Division Multiplexing Photodetection

Polarized light detection is consequential for optical communication and polarized light imaging. InSe is considered a promising candidate for narrow‐bandgap photodetector. However, monolayer γ‐InSe is an indirect bandgap semiconductor and is ignored for a long time for polarized light detection. In this work, by virtue of the indirect–direct conversation and the surface‐bound excitons, the intrinsic anisotropy of multilayer γ‐InSe is revealed by the photoluminescence (PL) measurement under polarized light. Due to the anisotropy of surface‐bound exaction and in‐plane exciton, there are significant differences in the photocurrent under irradiation of laser with different polarization angles. The γ‐InSe‐based photodetector exhibits considerable polarization‐dependent photocurrent with an outstanding anisotropic ratio of 2.7. Moreover, the multilayer γ‐InSe photodetector shows high responsivity of 7.47 A W−1 and specific detectivity of 4.56 × 1013 Jones under 785 nm laser. Based on the InSe polarization photodetector, a polarization division multiplexing that can simultaneously process four information tracks and enhance the communication speed by 24 is explored. The multilayer InSe polarization photodetector proposed in this work broadens a new path for polarized light detection, and brings a potential solution to the field of optical communications.

Bearing capacity of conical footing on anisotropic and heterogeneous clays using FEA and ANN

The paper presents axisymmetric FEA solutions for the bearing capacity of conical footings embedded in anisotropic and inhomogeneous clays using NGI-ADP model. The bearing capacity factor of conical footings is defined to be a function of three dimensionless parameters: (i) the cone apex angle, (ii) the increasing strength gradient ratio, and (iii) the anisotropic shear strength ratio. A series of parametric studies is carried out to portray the influence of all input parameters on the bearing capacity factors. Based on the FEA results of 216 investigated cases, the artificial neural network (ANN) is adopted to capture the relationship between input parameters and output bearing capacity factors. The complex relationship between input parameters and output bearing capacity is studied through the use of design charts and failure patterns. A new accurate equation with a high value of R2 is proposed and the sensitivity of each input parameter on the output results is scored by adopting the results from the ANN model. This study has provided some practical insights into the performance of conical footings embedded in anisotropic and inhomogeneous clays.

High Photocurrent Anisotropy in Domain‐Engineered Ferroelectrics for Visible‐Light Polarization Detection

AbstractVisible‐light polarization detection is a critical challenge for next‐generation light communication and imaging technologies. While low‐dimensional nanomaterials exhibit polarization‐dependent photocurrents originating from their anisotropic absorption, ferroelectric photovoltaics provide a photocurrent derived from spatial inversion symmetry breaking. Here, it is reported that domain‐engineered ferroelectrics are promising materials for visible‐light polarization detection. Polarization angle‐resolved photocurrent measurements demonstrate that the introduction of domain walls in ferroelectric BiFe0.95Mn0.05O3 films increases the photocurrent anisotropy ratio up to 7.9 under visible light with hν = 2.4 eV (λ = 515 nm), which is much higher than that of typical nanomaterials (≈2–3). Simulations of polarization‐dependent photocurrents show that the domain walls provide an additional degree of freedom for designing ferroelectrics with quite high photocurrent anisotropy. This study opens up the possibility of developing ferrophotovoltaic‐based visible‐light polarization detectors with simple device structures.

Gate‐Tunable Photovoltaic Behavior and Polarized Image Sensor Based on All‐2D TaIrTe4/MoS2 Van Der Waals Schottky Diode

Abstract2D Weyl semimetal shows potential applications in photodetection, polarization‐sensitive imaging, and Schottky barrier diodes, due to its unique band structure and topological nature. However, its inherently large dark current hinders further improvements of the Weyl semimetal‐based photodetector's performance. Herein, a Td‐TaIrTe4/n‐type MoS2 van der Waals (vdWs) heterojunction photodetector is reported. Owing to the effective lateral build‐in electric field of 145.3 meV, the Schottky diode shows a high rectification ratio of 6 × 103. Benefiting from the photovoltaic effect, a maximum responsivity (R) of 750 mA W−1 and an Ion/Ioff ratio of 104 under 635 nm illumination are achieved. What's more, the photovoltaic R can be enhanced to 890 mA W−1 at the Vg of 40 V. Because of the highly anisotropic crystalline structure of TaIrTe4 component, a high self‐powered photocurrent anisotropic ratio up to 4.19 is realized under 635 nm light at Vg = 40 V. Under self‐powered mode, a high‐resolution letter of “T” within 150 × 120 pixels can be displayed when the polarization direction is parallel to the armchair direction, while it becomes weak along the zigzag direction. This work provides a valuable route to fabricate anisotropic Weyl semimetal/semiconductor vdWs junction for highly integrated optoelectronics.

Solute Transport in a Doublet‐Type Flow Configuration Through a Weakly Heterogeneous Porous Formation

AbstractSteady flow generated by an injecting and a pumping well (doublet) takes place in a porous formation where the spatially variable hydraulic conductivity K is modeled as a stationary, lognormal, random field with anisotropic two‐point autocorrelation. The latter is characterized by a vertical integral scale, that is, Iv, smaller than the horizontal one, that is, I. A solute, either passive or reactive, is injected in the medium, and we aim at computing the breakthrough curve (BTC) and its moments not only at the recovery (pumping) well, but also at any location between the two wells. The strong coupling between K and the nonuniformity of the flow renders the problem very difficult. Nevertheless, a simple (analytical) solution is obtained by adopting a few assumptions: (a) wells are replaced by lines of singularity, (b) a perturbation solution which regards the variance of the log‐conductivity Y = ln K as a perturbation parameter is employed, (c) the study is limited to strongly anisotropic heterogeneous formations (for which the anisotropy ratio λ = Iv/I is much smaller than one), and (d) the impact of pore‐scale dispersion is neglected. Central for the computation of the BTC is the statistics of the travel time of a fluid particle released at the injecting well and reaching a control plane located at any position x1 along the distance connecting the two wells. It is shown that the spatial variability of Y acts de facto like a dispersion mechanism: it enhances spreading, especially in the early arrivals. Useful closed form expressions for moments of the travel time along the central trajectory are also obtained. Finally, the theoretical framework presented in this study is applied to two transport experiments in order to compute the second‐order (temporal) moment as function of x1, and therefore to quantify dispersion occurring in the zone delimited by the two wells.

Polarization-Resolved p-Se/n-WS2 Heterojunctions toward Application in Microcomputer System as Multivalued Signal Trigger.

Polarization-sensitive photodetectors based on van der Waals heterojunctions (vdWH) have excellent polarization-resolved optoelectronic properties that can enable the applications in polarized light identification and imaging. With the development of optical microcomputer control systems (OMCS), it is crucial and energy efficient to adopt the self-powered and polarization-resolved signal-generators to optimize the circuit design of OMCS. In this work, the selenium (Se) flakes with in-plane anisotropy and p-type character are grown and incorporated with n-type tungsten disulfide (WS2 ) to construct the type-II vdWH for polarization-sensitive and self-powered photodetectors. Under 405nm monochrome laser with 1.33mW cm-2 power density, the photovoltaic device exhibits superior photodetection performance with the photoelectric conversion efficiency (PCE) of 3.6%, the responsivity (R) of 196mA W-1 and the external quantum efficiency (EQE) of about 60%. The strong in-plane anisotropy of Se crystal structure gives rise to the capability of polarized light detection with anisotropic photocurrent ratio of ≈2.2 under the 405nm laser (13.71mW cm-2 ). Benefiting from the well polarization-sensitive and photovoltaic properties, the p-Se/n-WS2 vdWH is successfully applied in the OMCS as multivalued signal trigger. This work develops the new anisotropic vdWH and demonstrates its feasibility for applications in logic circuits and control systems.

Strain-Dependent Diffusivity of Small and Large Molecules in Meniscus.

Due to lack of full vascularization, the meniscus relies on diffusion through the extracellular matrix to deliver small (e.g., nutrients) and large (e.g., proteins) to resident cells. Under normal physiological conditions, the meniscus undergoes up to 20% compressive strains. While previous studies characterized solute diffusivity in the uncompressed meniscus, to date, little is known about the diffusive transport under physiological strain levels. This information is crucial to fully understand the pathophysiology of the meniscus. The objective of this study was to investigate strain-dependent diffusive properties of the meniscus fibrocartilage. Tissue samples were harvested from the central portion of porcine medial menisci and tested via fluorescence recovery after photobleaching to measure diffusivity of fluorescein (332 Da) and 40 K Da dextran (D40K) under 0%, 10%, and 20% compressive strain. Specifically, average diffusion coefficient and anisotropic ratio, defined as the ratio of the diffusion coefficient in the direction of the tissue collagen fibers to that orthogonal, were determined. For all the experimental conditions investigated, fluorescein diffusivity was statistically faster than that of D40K. Also, for both molecules, diffusion coefficients significantly decreased, up to ∼45%, as the strain increased. In contrast, the anisotropic ratios of both molecules were similar and not affected by the strain applied to the tissue. This suggests that compressive strains used in this study did not alter the diffusive pathways in the meniscus. Our findings provide new knowledge on the transport properties of the meniscus fibrocartilage that can be leveraged to further understand tissue pathophysiology and approaches to tissue restoration.

Tuning structural and mechanical anisotropy of PVA hydrogels

Hydrogel materials are widely applicable due to their high water content, biocompatibility, and broad tunability. While the overall mechanical performance of hydrogels can be tuned by methods such as altering the recipe, introducing a secondary network, and adding a post-treatment step, anisotropic mechanical properties with specific anisotropic ratios are not readily achievable. Moreover, the relation between anisotropic structures and the resulting difference in mechanical performance along various directions is not yet clearly understood. In this paper, we fabricated poly (vinyl alcohol) hydrogels with tunable anisotropic ratios of Young's moduli by a bidirectional ice-templating method. Then we characterized the morphologies and mechanical properties in different directions to study the correlation between structure and property anisotropy. An analytical model based on Eshelby's equivalence principle and Mori-Tanaka's mean-field theory was established to predict the anisotropic ratios of the effective moduli for the porous hydrogels, which agrees well with the experimental results. This model reveals the key parameters that govern the degree of anisotropy and has the potential of providing guidance for designing micro-structured hydrogels with specified mechanical properties.

Ultralow and anisotropic thermal conductivity in graphene phononic metamaterials

Phononic metamaterials based on the idea of phonon coherent resonance attract increasing research attention because of their unique properties. In this paper, we have studied the heat transport in graphene phononic metamaterials (GPMs, pillared graphene nanoribbons) using molecular dynamics simulations. The results show that, GPMs have lower thermal conductivities in the different in-plane directions and stronger anisotropy in thermal conductance, compared with graphene nanoribbons (GNRs). As the temperature decreases or the height and width of pillar increases, the GPM thermal conductivity in both directions decreases and the anisotropic ratio increases. The pillar-driven suppression of thermal conductivity along the periodic direction is attributed to the phonon localization and the local resonance leading to the flat bands and band gaps, while the reduction in thermal conductivity along the aperiodic direction is due to the phonon boundary scattering. The thermal anisotropy results from the anisotropic phonon relaxation times and the anisotropic contributions of low-frequency-phonons. Our findings reveal the phonon transport mechanisms of GPMs in different directions, and shed some light on the GPM potential for thermoelectric and directional heat management applications.

Electric-Field Control of Magnetoresistance Behavior in a Conetic Alloy Thin Film/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 Multiferroic Heterostructure

In this work, we investigate the influence of electric fields (E-fields) on the room-temperature magnetotransport behavior of an artificial multiferroic heterostructure, a Conetic alloy (Ni77Fe14Cu5Mo4) thin film/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (011). When the external magnetic field is parallel to the applied current, the switching field increases from 0.8 to 3.3 Oe at 0 and 8 kV/cm, respectively, and the corresponding magnetoresistance (MR) ratio at 20 Oe respectively decreases from 0.14% to 0.03% at 0 and 8 kV/cm. However, when the external magnetic field is perpendicular to the current, the switching field decreases from 10.1 to 1.7 Oe at 0 and 8 kV/cm, and the MR ratio in such a case decreases from −0.001% to −0.10%, respectively. Consequently, under the parallel and perpendicular modes, the tunabilities of the switching field are approximately +313% and −83%, and the MR ratio tunabilities under E-fields are approximately −79% and +9,900%, respectively. Such a large and anisotropic tunability of both the switching field and MR ratio is attributed to the ultrasoft magnetic property of the Conetic alloy thin film and anisotropic in-plane strain-mediated magnetoelectric coupling. However, the anisotropic MR ratio is approximately 0.15% and does not vary with the applied E-fields owing to the intrinsic property of Conetic thin films using transfer and circle transfer curve measurements, rather than the magnetization rotation caused by E-field-induced magnetoelastic anisotropy. This work demonstrates that multiferroic heterostructures with electrically tunable MR show considerable potential in designing energy-efficient electronic and spintronic devices.

Self-Assembly of 2D Hybrid Double Perovskites on 3D Cs2 AgBiBr6 Crystals towards Ultrasensitive Detection of Weak Polarized Light.

We report the self-assembly of 2D double perovskite (BLA)2 CsAgBiBr7 (BLA=benzylammonium) on 3D Cs2 AgBiBr6 crystals, providing the first demonstration of polarization-sensitive photodetection using lead-free double perovskite heterocrystals (HCs). The (BLA)2 CsAgBiBr7 /Cs2 AgBiBr6 HC successfully combines the anisotropy of 2D double perovskites with the well-defined interface provided by heterogeneous integration. Driven by the built-in electric field in junction, photodetectors of HCs exhibit unique polarization dependence of zero-bias photocurrent with a large anisotropy ratio up to 9, which is 6 times amplified as compared to the pristine 2D (BLA)2 CsAgBiBr7 . More importantly, the present devices can remain polarization-sensitive with incident light intensity down to the nW cm-2 level. Our study on lead-free hybrid perovskite HCs marks a step toward establishing robust material foundations for fundamental scientific investigations and the development of optoelectronic devices.

Self‐Assembly of 2D Hybrid Double Perovskites on 3D Cs2AgBiBr6 Crystals towards Ultrasensitive Detection of Weak Polarized Light

AbstractWe report the self‐assembly of 2D double perovskite (BLA)2CsAgBiBr7 (BLA=benzylammonium) on 3D Cs2AgBiBr6 crystals, providing the first demonstration of polarization‐sensitive photodetection using lead‐free double perovskite heterocrystals (HCs). The (BLA)2CsAgBiBr7/Cs2AgBiBr6 HC successfully combines the anisotropy of 2D double perovskites with the well‐defined interface provided by heterogeneous integration. Driven by the built‐in electric field in junction, photodetectors of HCs exhibit unique polarization dependence of zero‐bias photocurrent with a large anisotropy ratio up to 9, which is 6 times amplified as compared to the pristine 2D (BLA)2CsAgBiBr7. More importantly, the present devices can remain polarization‐sensitive with incident light intensity down to the nW cm−2 level. Our study on lead‐free hybrid perovskite HCs marks a step toward establishing robust material foundations for fundamental scientific investigations and the development of optoelectronic devices.