Zincophile Zn2+ Conductor Regulation by Ultrathin Nano MoO3 Coating for Dendrite-Free Zn Anode.

Aqueous battery with nonflammable and instinctive safe properties has received great attention. However, issues related to Zn anode such as side reactions and rampant dendrite growth hinder the long-term circulation of AZMBs. Herein, an ultrathin(35 nm) MoO3 coating is deposited on the Zn anode by means of vacuum vapor deposition for the first time. Due to the peculiar layer structure of MoO3, insertion of Zn2+ in ZnxMoO3 acts as Zn2+ ion conductor, which regulates Zn2+ deposition in an ordered manner. Additionally, the MoO3 coating can also inhibit the hydrogen evolution and corrosion reactions at the interface. Therefore, both Zn//MoO3@Cu asymmetric battery and Zn symmetric battery cells manage to deliver satisfactory electrochemical performances. The symmetric cell assembled with MoO3@Zn shows a significant long cycle life of more than 1600 h at a current density of 2 mA cm-2. Meanwhile, the MoO3@Zn//Cu asymmetric cell exhibits an ultrahigh Zn deposition/stripping efficiency of 99.82% after a stable cycling of 650 h at 2 mA cm-2. This study proposes a concept of "zincophile Zn2+ conductor regulation" to dictate Zn electrodeposition and broadens novel design of vacuum evaporation for nano MoO3 modified Zn anodes.

Highly Sensitive Perovskite Photoplethysmography Sensor for Blood Glucose Sensing Using Machine Learning Techniques.

Accurate non-invasive monitoring of blood glucose (BG) is a challenging issue in the therapy of diabetes. Here near-infrared (NIR) photoplethysmography (PPG) sensor based on a vapor-deposited mixed tin-lead hybrid perovskite photodetector is developed. The device shows a high detectivity of 5.32 × 1012 Jones and a large linear dynamic range (LDR) of 204 dB under NIR light, guaranteeing accurate extraction of eleven features from the PPG signal. By a combination of machine learning, accurate prediction of blood glucose level with mean absolute relative difference (MARD) as small as 2.48% is realized. The self-powered PPG sensor also works for real-time outdoor healthcare monitors using sunlight as a light source. The potential for early diabetes diagnoses by the perovskite PPG sensor is demonstrated.

Precise surface engineering: Leveraging chemical vapor deposition for enhanced biocompatibility and durability in biomedical implants.

Biomedical implants have revolutionized modern medicine, providing diverse treatment options for various medical conditions. Ensuring the long-term success of certain materials used in various applications requires careful consideration of their ability to interact with biological systems and withstand harsh biological conditions. Optimizing surface properties is crucial for successfully integrating biomedical implants into the human body, ensuring biocompatibility, durability, and functionality. Chemical Vapor Deposition (CVD) has become a crucial technology in surface engineering, offering a precise technique for applying thin films with customized properties. This article provides a comprehensive study of surface engineering for biomedical implants, specifically emphasizing the CVD coating technique. By carefully manipulating chemical reactions in the vapor phase, CVD allows for the creation of coatings that enhance wear resistance, minimize friction, and improve biocompatibility. This review also explores the underlying principles of CVD, the various process parameters involved, and the subsequent enhancements in implant performance. Using case studies and experimental findings, it showcases the ability of CVD to greatly enhance the durability and effectiveness of biomedical implants.

Impact of the Interruption Duration on Photoluminescence Properties of MOCVD-Grown GaAsP/InAlGaAs Quantum Well Structures.

The growth interruption technology is introduced to the growth of GaAsP/InAlGaAs quantum well (QW) structure using metal-organic chemical vapor deposition (MOCVD). The effect of growth interruption time (GIT) on the crystalline quality and optical properties are investigated. The two distinctive emission peaks are the transition recombination between the electron level of conduction band and the light and heavy hole level of valence band in the photoluminescence (PL) at room temperature. The PL peaks present a redshift and merge together with the increasing GIT, which is attributed to the QW energy level shift caused by the increase in arsenic concentrations in GaAsP QW, the diversified thickness of QW and the variations of indium components in the InAlGaAs barrier layer. The Gaussian deconvolution parameters in temperature-dependent PL (TDPL) show that the GaAsP/InAlGaAs QW with a GIT of 6 s has a 565.74 meV activation energy, enhancing the carrier confinement in QW and the PL intensity, while the 6 s-GIT GaAsP QW has the increasing interface roughness and the non-radiative centers at the InGaAsP intermediate layer, leading to a spectral broadening. The QW with 10 s-GIT exhibits a small full width at half maximum (FWHM) with the various temperature, indicating reduced interface roughness and excellent crystal quality. An increase in GIT may be suitable for optimizing the optical properties of GaAsP/InAlGaAs QW.

Heterogeneous Morphologies and Hardness of Co-Sputtered Thin Films of Concentrated Cu-Mo-W Alloys.

Heterogeneous microstructures in Cu-Mo-W alloy thin films formed by magnetron co-sputtering immiscible elements with concentrated compositions are characterized using scanning transmission electron microscopy (STEM) and nanoindentation. In this work, we modified the phase separated structure of a Cu-Mo immiscible system by adding W, which impedes surface diffusion during film growth. The heterogeneous microstructures in the Cu-Mo-W ternary system exhibited bicontinuous matrices and agglomerates composed of Mo(W)-rich phase. This is unique, as these are the slower-diffusing species, contrasting past reports of binary Cu-Mo thin films that exhibited Cu-rich agglomerates. The bicontinuous matrices comprised of Cu-rich and Mo(W)-rich phases exhibited bilayer thicknesses of less than 5 nm. The hardness of these thin films measured using nanoindentation is reported and compared to similar multilayers and nanocomposites in binary systems.

PRISM: three-dimensional sub-diffractive phase-resolved imaging spectroscopic method.

We demonstrate a genuine method for three-dimensional pictorial reconstructions of two-dimensional, three-dimensional, and hybrid specimens based on confocal Raman data collected in a back-scattering geometry of a 532-nm setup. The protocol, or the titular PRISM (Phase-Resolved Imaging Spectroscopic Method), allows for sub-diffractive and material-resolved imaging of the object's constituent material phases. The spacial component comes through either the signal distal attenuation ratio (direct mode) or subtle light-matter interactions, including interference enhancement and light absorption (indirect mode). The phase component is brought about by scrutinizing only selected Raman-active modes. We illustrate the PRISM approach in common real-life examples, including photolithographically structured amorphous Al2O3, reactive-ion-etched homoepitaxial SiC, and Chemical Vapor Deposition graphene transferred from copper foil onto a Si substrate and AlGaN microcolumns. The method is implementable in widespread Raman apparatus and offers a leap in the quality of materials imaging. The lateral resolution of PRISM is stage-limited by step motors to 100 nm. At the same time, the vertical accuracy is estimated at a nanometer scale due to the sensitivity of one of the applied phenomena (interference enhancement) to the physical property of the material (layer thickness).

Chemically Tailored Growth of 2D Semiconductors via Hybrid Metal-Organic Chemical Vapor Deposition.

Two-dimensional (2D) semiconducting transition-metal dichalcogenides (TMDCs) are an exciting platform for excitonic physics and next-generation electronics, creating a strong demand to understand their growth, doping, and heterostructures. Despite significant progress in solid-source (SS-) and metal-organic chemical vapor deposition (MOCVD), further optimization is necessary to grow highly crystalline 2D TMDCs with controlled doping. Here, we report a hybrid MOCVD growth method that combines liquid-phase metal precursor deposition and vapor-phase organo-chalcogen delivery to leverage the advantages of both MOCVD and SS-CVD. Using our hybrid approach, we demonstrate WS2 growth with tunable morphologies─from separated single-crystal domains to continuous monolayer films─on a variety of substrates, including sapphire, SiO2, and Au. These WS2 films exhibit narrow neutral exciton photoluminescence line widths down to 27-28 meV and room-temperature mobility up to 34-36 cm2 V-1 s-1. Through simple modifications to the liquid precursor composition, we demonstrate the growth of V-doped WS2, MoxW1-xS2 alloys, and in-plane WS2-MoS2 heterostructures. This work presents an efficient approach for addressing a variety of TMDC synthesis needs on a laboratory scale.

Robust Growth of 2D Transition Metal Dichalcogenide Vertical Heterostructures via Ammonium-Assisted CVD Strategy.

Two dimension (2D) transition metal dichalcogenides (TMD) heterostructures have opened unparalleled prospects for next-generation electronic and optoelectronic applications due to their atomic-scale thickness and distinct physical properties. The chemical vapor deposition (CVD) method is the most feasible approach to prepare 2D TMD heterostructures. However, the synthesis of 2D vertical heterostructures faces competition between in-plane and out-of-plane growth, which makes it difficult to precisely control the growth of vertical heterostructures. Here, a universal and controllable strategy is reported to grow various 2D TMD vertical heterostructures through an ammonium-assisted CVD process. The ammonium-assisted strategy shows excellent controllability and operational simplicity to prevent interlayer diffusion/alloying and thermal decomposition of the existed TMD templates. Ab initio simulations demonstrate that the reaction between NH4Cl and MoS2 leads to the formation of MoS3 clusters, promoting the nucleation and growth of 2D MoS2 on existed 2D WS2 layer, thereby leading to the growth of vertical heterostructure. The resulting 2D WSe2/WS2 vertical heterostructure photodetectors demonstrate an outstanding optoelectronic performance, which are comparable to the performances of photodetectors fabricated from mechanically exfoliated and stacked vertical heterostructures. The ammonium-assisted strategy for robust growth of high-quality vertical van der Waals heterostructures will facilitate fundamental physics investigations and device applications in electronics and optoelectronics.

Enhanced Responsivity and Photostability of Cs3Bi2I9-Based Self-Powered Photodetector via Chemical Vapor Deposition Engineering.

Lead-based halide perovskites have gained significant prominence in recent years in optoelectronics and photovoltaics, owing to their exceptional optoelectronic properties. Nonetheless, the toxicity of lead (Pb) and the stability concern pose obstacles to their potential for future large-scale market development. Herein, stable lead-free Cs3Bi2I9 (CBI) films are presented with smooth and compact morphologies synthesized via chemical vapor deposition (CVD), demonstrating their application as an UV photodetector in a self-powered way. The self-powered photodetectors (SPDs) exhibit remarkable characteristics, including a responsivity of 1.57 A W-1 and an impressive specific detectivity of 3.38 × 1013 Jones under the illumination of 365 nm at zero bias. Furthermore, the SPDs exhibit a nominal decline (≈2.2%) in the photocurrent under constant illumination over 500 h, highlighting its impressive long-term operational stability. Finally, the real-time UV-detection capability of the device is demonstrated by measuring the photocurrent under various conditions, including room light and sunlight at different times. These findings offer a new platform for synthesizing stable and high-quality perovskite films, and SPDs for advancing the development of wearable and portable electronics.

Decoupled High-Mobility Graphene on Cu(111)/Sapphire via Chemical Vapor Deposition.

The growth of high-quality graphene on flat and rigid templates, such as metal thin films on insulating wafers, is regarded as a key enabler for technologies based on 2D materials. In this work, the growth of decoupled graphene is introduced via non-reducing low-pressure chemical vapor deposition (LPCVD) on crystalline Cu(111) films deposited on sapphire. The resulting film is atomically flat, with no detectable cracks or ripples, and lies atop of a thin Cu2O layer, as confirmed by microscopy, diffraction, and spectroscopy analyses. Post-growth treatment of the partially decoupled graphene enables full and uniform oxidation of the interface, greatly simplifying subsequent transfer processes, particularly dry-pick up - a task that proves challenging when dealing with graphene directly synthesized on metallic Cu(111). Electrical transport measurements reveal high carrier mobility at room temperature, exceeding 104 cm2 V-1 s-1 on SiO2/Si and 105 cm2 V-1 s-1 upon encapsulation in hexagonal boron nitride (hBN). The demonstrated growth approach yields exceptional material quality, in line with micro-mechanically exfoliated graphene flakes, and thus paves the way toward large-scale production of pristine graphene suitable for high-performance next-generation applications.

Long-Lasting, Transparent Antibacterial Shield: A Durable, Broad-Spectrum Anti-Bacterial, Non-Cytotoxic, Transparent Nanocoating for Extended Wear Contact Lenses.

The increasing incidence of serious bacterial keratitis, a sight-threatening condition often exacerbated by inadequate contact lens (CLs) care, highlights the need for innovative protective technology. This study introduces a long-lasting antibacterial, non-cytotoxic, transparent nanocoating for CLs via a solvent-free polymer deposition method, aiming to prevent bacterial keratitis. The nanocoating comprises stacked polymer films, with poly(dimethylaminomethyl styrene-co-ethylene glycol dimethacrylate) (pDE) as a biocompatible, antibacterial layer atop poly(2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane) (pV4D4) as an adhesion-promoting layer. The pD6E1-grafted (g)-pV4D4 film shows non-cytotoxicity toward two human cell lines and antibacterial activity of >99% against four bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), an antibiotic-resistant bacteria and Pseudomonas aeruginosa, which causes ocular diseases. Additionally, the film demonstrates long-lasting antibacterial activity greater than 96% against MRSA for 9 weeks in phosphate-buffered saline. To the best knowledge, this duration represents the longest reported long-term stability with less than 5% decay of antibacterial performance among contact-killing antibacterial coatings. The film exhibits exceptional mechanical durability, retaining its antibacterial activity even after 15 washing cycles. The pD6E1-g-pV4D4-coated CL maintains full optical transmittance compared to that of pristine CL. It is expected that the unprecedentedly prolonged antibacterial performance of the coating will significantly alleviate the risk of infection for long-term CL users.

Low defect density in MoS2 monolayers grown on Au(111) by metal-organic chemical vapor deposition.

Monolayers of transition metal dichalcogenides (TMDs) possess high potential for applications in novel electronic and optoelectronic devices and therefore the development of methods for their scalable growth is of high importance. Among different suggested approaches, metal-organic chemical vapor deposition (MOCVD) is the most promising one for technological applications because of its lower growth temperature compared to the most other methods, e.g., conventional chemical vapor or atomic layer deposition (CVD, ALD). Here we demonstrate for the first time the epitaxial growth of MoS2 monolayers on Au(111) by MOCVD at 450 °C. We confirm the high quality of the grown TMD monolayers down to the atomic scale using several complementary methods. These include Raman spectroscopy, non-contact atomic force microscopy (nc-AFM), X-ray photoelectron spectroscopy and scanning tunneling microscopy (STM). The topographic corrugation of the MoS2 monolayer on Au(111), revealed in a moiré structure, was measured as ≈20 pm by nc-AFM. The estimated defect density calculated from STM images of the as-grown MoS2 monolayers is in the order of 1012 vacancies/cm2. The defects are mainly caused by single sulfur vacancies. Our approach is a step forward towards the technologically relevant growth of high-quality, large-area TMD monolayers.

Conveyor CVD to high-quality and productivity of large-area graphene and its potentiality.

The mass production of high-quality graphene is required for industrial application as a future electronic material. However, the chemical vapor deposition (CVD) systems previously studied for graphene production face bottlenecks in terms of quality, speed, and reproducibility. Herein, we report a novel conveyor CVD system that enables rapid graphene synthesis using liquid precursors. Pristine and nitrogen-doped graphene samples of a size comparable to a smartphone (15 cm × 5 cm) are successfully synthesized at temperatures of 900, 950, and 1000 °C using butane and pyridine, respectively. Raman spectroscopy allows optimization of the rapid-synthesis conditions to achieve uniformity and high quality. By conducting compositional analysis via X-ray photoelectron spectroscopy as well as electrical characterization, it is confirmed that graphene synthesis and nitrogen doping degree can be adjusted by varying the synthesis conditions. Testing the corresponding graphene samples as gas-sensor channels for NH3 and NO2 and evaluating their response characteristics show that the gas sensors exhibit polar characteristics in terms of gas adsorption and desorption depending on the type of gas, with contrasting characteristics depending on the presence or absence of nitrogen doping; nitrogen-doped graphene exhibits superior gas-sensing sensitivity and response speed compared with pristine graphene.

Giant Second Harmonic Generation in Supertwisted WS2 Spirals Grown in Step-Edge Particle-Induced Non-Euclidean Surfaces.

In moiré crystals resulting from the stacking of twisted two-dimensional (2D) layered materials, a subtle adjustment in the twist angle surprisingly gives rise to a wide range of correlated optical and electrical properties. Herein, we report the synthesis of supertwisted WS2 spirals and the observation of giant second harmonic generation (SHG) in these spirals. Supertwisted WS2 spirals featuring different twist angles are synthesized on a Euclidean or step-edge particle-induced non-Euclidean surface using carefully designed water-assisted chemical vapor deposition. We observed an oscillatory dependence of SHG intensity on layer number, attributed to atomically phase-matched nonlinear dipoles within layers of supertwisted spiral crystals where inversion symmetry is restored. Through an investigation into the twist angle evolution of SHG intensity, we discovered that the stacking model between layers plays a crucial role in determining the nonlinearity, and the SHG signals in supertwisted spirals exhibit enhancements by a factor of 2 to 136 when compared with the SHG of the single-layer structure. These findings provide helpful perspectives on the rational growth of 2D twisted structures and the implementation of twist angle adjustable endowing them great potential for exploring strong coupling correlation physics and applications in the field of twistronics.

WS2 with Controllable Layer Number Grown Directly on W Film.

As a layered material with single/multi-atom thickness, two-dimensional transition metal sulfide WS2 has attracted extensive attention in the field of science for its excellent physical, chemical, optical, and electrical properties. The photoelectric properties of WS2 are even more promising than graphene. However, there are many existing preparation methods for WS2, but few reports on its direct growth on tungsten films. Therefore, this paper studies its preparation method and proposes an innovative two-dimensional material preparation method to grow large-sized WS2 with higher quality on metal film. In this experiment, it was found that the reaction temperature could regulate the growth direction of WS2. When the temperature was below 950 °C, the film showed horizontal growth, while when the temperature was above 1000 °C, the film showed vertical growth. At the same time, through Raman and band gap measurements, it is found that the different thicknesses of precursor film will lead to a difference in the number of layers of WS2. The number of layers of WS2 can be controlled by adjusting the thickness of the precursor.

Advances in LDI-MS Analysis: The Role of Chemical Vapor Deposition-Synthesized Silver Nanoparticles in Enhancing Detection of Low-Molecular-Weight Biomolecules.

In this investigation, we detail the synthesis of silver nanoparticles (AgNPs) via a precise chemical vacuum deposition (CVD) methodology, aimed at augmenting the analytical performance of laser desorption/ionization mass spectrometry (LDI-MS) for the detection of low-molecular-weight analytes. Employing a precursor supply rate of 0.0014 mg/s facilitated the formation of uniformly dispersed AgNPs, characterized by SEM and AFM to have an average diameter of 33.5 ± 1.5 nm and a surface roughness (Ra) of 11.8 nm, indicative of their homogeneous coverage and spherical morphology. XPS and SEM-EDX analyses confirmed the metallic silver composition of the nanoparticles with Ag peak splitting, reflecting the successful synthesis of metallic Ag. Comparative analytical evaluation with traditional MALDI matrices revealed that AgNPs significantly reduce signal suppression, thereby enhancing the sensitivity and specificity of LDI-MS for low-molecular-weight compounds such as triglycerides, saccharides, amino acids, and carboxylic acids. Notably, the application of AgNPs demonstrated a superior linear response for triglyceride signals with regression coefficients surpassing 0.99, markedly outperforming conventional matrices. The study further extends into quantitative analysis through nanoparticle-based laser desorption/ionization (NALDI), where AgNPs exhibited enhanced ionization efficiency, characterized by substantially lower limits of detection (LOD) and quantification (LOQ) for tested standards. Particular attention was paid to lipids with a detailed examination of their fragmentation pathways. These results highlight the significant potential of AgNPs synthesized via CVD to transform the analytical detection and quantification of low-molecular-weight compounds using NALDI. This approach offers a promising avenue for expanding the scope of analytical applications in mass spectrometry and introducing innovative methodologies for enhanced precision and sensitivity.

Epitaxial growth of quasi-2D van der Waals ferromagnets on crystalline substrates.

Intrinsic magnetism in van der Waals materials has instigated interest in exploring magnetism in the 2D limit for potential applications in spintronics and also in understanding novel control of 2D magnetism via variation of layer thickness, gate tunability and magnetoelectric effects. The chromium telluride (CrxTey) family is an interesting subsection of ferromagnetic materials with highTCvalues, also presenting diverse stoichiometry arising from self-intercalation of Cr. Apart from the layered CrTe2system, the other non-layered CrxTeycompounds also offer exceptional magnetic properties, and a novel growth technique to grow thin films of these non-layered compounds offers exciting possibilities for ultra-thin spin-based electronics and magnetic sensors. In this work, we discuss the role of crystalline substrates in chemical vapor deposition growth of non-layered 2D ferromagnets, where the crystal symmetry of the substrate as well as the misfit and strain are the key players governing the growth mechanism of ultra-thin Cr5Te8, a non-layered ferromagnet. The magnetic studies of the as-grown Cr5Te8reveal the signatures of co-existing soft and hard ferromagnetic phases, which makes this system an intriguing system to search for emergent topological phases, such as magnetic skyrmions.

Spectroscopic Analysis on Different Stacking Configurations of Multilayered MoSe2.

Transition metal dichalcogenides (TMDs) are drawing significant attention due to their intriguing photoelectric properties, and these interesting properties are closely related to the number of layers. Obtaining layer-controlled and high-quality TMD is still a challenge. In this context, we use the salt-assisted chemical vapor deposition to grow multilayered MoSe2 flake and characterize it by Raman spectroscopy, second harmonic generation, and photon luminescence. Spectroscopic analysis is an effective way to characterize the stacking order and optoelectronic properties of two-dimensional materials. Notably, the corresponding mapping reflects the film quality and homogeneity. We found that the grown continuous monolayer, bilayer, and trilayer of MoSe2 sheets with different stacking orders exhibit distinctive features. For bilayer MoSe2, the most stable stacking configurations are the AA' and AB order. And the uniformity of the spectroscopy maps demonstrates the high quality of the stacked MoSe2 sheets.

Active Learning for Rapid Targeted Synthesis of Compositionally Complex Alloys.

The next generation of advanced materials is tending toward increasingly complex compositions. Synthesizing precise composition is time-consuming and becomes exponentially demanding with increasing compositional complexity. An experienced human operator does significantly better than a novice but still struggles to consistently achieve precision when synthesis parameters are coupled. The time to optimize synthesis becomes a barrier to exploring scientifically and technologically exciting compositionally complex materials. This investigation demonstrates an active learning (AL) approach for optimizing physical vapor deposition synthesis of thin-film alloys with up to five principal elements. We compared AL-based on Gaussian process (GP) and random forest (RF) models. The best performing models were able to discover synthesis parameters for a target quinary alloy in 14 iterations. We also demonstrate the capability of these models to be used in transfer learning tasks. RF and GP models trained on lower dimensional systems (i.e., ternary, quarternary) show an immediate improvement in prediction accuracy compared to models trained only on quinary samples. Furthermore, samples that only share a few elements in common with the target composition can be used for model pre-training. We believe that such AL approaches can be widely adapted to significantly accelerate the exploration of compositionally complex materials.

Controlled Synthesis of 2D Ferromagnetic/Antiferromagnetic Cr7Te8/MnTe Vertical Heterostructures for High-Tunable Coercivity.

Two-dimensional ferromagnetic/antiferromagnetic (2D-FM/AFM) heterostructures are of great significance to realize the application of spintronic devices such as miniaturization, low power consumption, and high-density information storage. However, traditional mechanical stacking can easily damage the crystal quality or cause chemical contamination residues for 2D materials, which can result in weak interface coupling and difficulty in device regulation. Chemical vapor deposition (CVD) is an effective way to achieve a high-quality heterostructure interface. Herein, high-quality interface 2D-FM/AFM Cr7Te8/MnTe vertical heterostructures were successfully synthesized via a one-pot CVD method. Moreover, the atomic-scale structural scanning transmission electron microscope (STEM) characterization shows that the interface of the vertical heterostructure is clear and flat without an excess interface layer. Compared to the parent Cr7Te8, the coercivity (HC) of the high-quality interface Cr7Te8/MnTe heterostructure is significantly reduced as the thickness of MnTe increases, with a maximum decrease of 74.5% when the thickness of the MnTe nanosheet is around 30 nm. Additionally, the HC of the Cr7Te8/MnTe heterostructure can also be regulated by applying a gate voltage, and the HC increases or decreases with increasing positive or negative gate voltages. Thus, the effective regulation of HC is essential to improving the performance of advanced spintronic devices (e.g., MRAM and magnetic sensors). Our work will provide ideas for spin controlling and device application of 2D-FM/AFM heterostructures.