Insights into the Growth Orientation and Phase Stability of Chemical-Vapor-Deposited Two-Dimensional Hybrid Halide Perovskite Films.

Chemical vapor deposition (CVD) offers a large-area, scalable, and conformal growth of perovskite thin films without the use of solvents. Low-dimensional organic-inorganic halide perovskites, with alternating layers of organic spacer groups and inorganic perovskite layers, are promising for enhancing the stability of optoelectronic devices. Moreover, their multiple quantum-well structures provide a powerful platform for tuning excitonic physics. In this work, we show that the CVD process is conducive to the growth of 2D hybrid halide perovskite films. Using butylammonium (BA) and phenylethylammonium (PEA) cations, the growth parameters of BA2PbI4 and PEA2PbI4 and mixed halide perovskite films were first optimized. These films are characterized by well-defined grain boundaries and display characteristic absorption and emission features of the 2D quantum wells. X-ray diffraction (XRD) and a noninteger dimensionality model of the absorption spectrum provide insights into the orientation of the crystalline planes. Unlike BA2PbI4, temperature-dependent photoluminescence measurements from PEA2PbI4 show a single excitonic peak throughout the temperature range from 20 to 350 K, highlighting the lack of defect states. These results further corroborate the temperature-dependent synchrotron-based XRD results. Furthermore, the nonlinear optical properties of the CVD-grown perovskite films are investigated, and a high third harmonic generation efficiency is observed.

Compressible sponge electrodes by oxidative molecular layer deposition (oMLD) of polyethylenedioxythiophene (PEDOT) onto open-cell polyurethane sponges.

The formation of compressible porous sponge electrodes is appealing to overcome diffusion limitations in porous electrodes for applications including electrochemical energy storage, electrochemical water desalination, and electrocatalysis. Previous work has employed wet chemical synthesis to deliver conductive materials into porous polymer sponge supports, but these approaches struggle to produce functional electrodes due to (1) poor electrical connectivity of the conductive network and (2) mechanical rigidity of the foam after coating. In this work we employ oxidative molecular layer deposition (oMLD) via sequential gas-phase exposures of 3,4 ethylenedioxythiophene (EDOT) and molybdenum pentachloride (MoCl5) oxidant to imbibe polyurethane (PU) sponges with electrically-conductive and redox-active poly(3,4 ethylenedioxythiophene) (PEDOT) coatings. We analyze the oMLD deposition on compressive PU sponges and modify the reaction conditions to obtain mechanically compressible and electrically conductive sponge electrodes. We specifically identify the importance MoCl5dose time to enhance the conductivity of the sponges and the importance of EDOT purge time to preserve the mechanical properties of the sponges. Controlling these variables produces an electrically conductive PEDOT network within the sponge support with reduced impact on the sponge's mechanical properties, offering advantages over wet-chemical synthesis approaches. The compressible, conductive sponges we generate have the potential to be used as compressible electrodes for water desalination, energy storage, and electrocatalysis.

Effects of film thickness on electrochemical properties of nanoscale polyethylenedioxythiophene (PEDOT) thin films grown by oxidative molecular layer deposition (oMLD).

Poly(3,4-ethylene dioxythiophene) (PEDOT) has a high theoretical charge storage capacity, making it of interest for electrochemical applications including energy storage and water desalination. Nanoscale thin films of PEDOT are particularly attractive for these applications to enable faster charging. Recent work has demonstrated that nanoscale thin films of PEDOT can be formed using sequential gas-phase exposures via oxidative molecular layer deposition, or oMLD, which provides advantages in conformality and uniformity on high aspect ratio substrates over other deposition techniques. But to date, the electrochemical properties of these oMLD PEDOT thin films have not been well-characterized. In this work, we examine the electrochemical properties of 5-100 nm thick PEDOT films formed using 20-175 oMLD deposition cycles. We find that film thickness of oMLD PEDOT films affects the orientation of ordered domains leading to a substantial change in charge storage capacity. Interestingly, we observe a minimum in charge storage capacity for an oMLD PEDOT film thickness of ∼30 nm (60 oMLD cycles at 150 °C), coinciding with the highest degree of face-on oriented PEDOT domains as measured using grazing incidence wide angle X-ray scattering (GIWAXS). Thinner and thicker oMLD PEDOT films exhibit higher fractions of oblique (off-angle) orientations and corresponding increases in charge capacity of up to 120 mA h g-1. Electrochemical measurements suggest that higher charge capacity in films with mixed domain orientation arise from the facile transport of ions from the liquid electrolyte into the PEDOT layer. Greater exposure of the electrolyte to PEDOT domain edges is posited to facilitate faster ion transport in these mixed domain films. These insights will inform future design of PEDOT coated high-aspect ratio structures for electrochemical energy storage and water treatment.

Laser-scribed conductive, photoactive transition metal oxide on soft elastomers for Janus on-skin electronics and soft actuators.

Laser-assisted fabrication of conductive materials on flexible substrates has attracted intense interests because of its simplicity, easy customization, and broad applications. However, it remains challenging to achieve laser scribing of conductive materials on tissue-like soft elastomers, which can serve as the basis to construct bioelectronics and soft actuators. Here, we report laser scribing of metallic conductive, photoactive transition metal oxide (molybdenum dioxide) on soft elastomers, coated with molybdenum chloride precursors, under ambient conditions. Laser-scribed molybdenum dioxide (LSM) exhibits high electrical conductivity, biocompatibility, chemical stability, and compatibility with magnetic resonance imaging. In addition, LSM can be made on various substrates (polyimide, glass, and hair), showing high generality. Furthermore, LSM-based Janus on-skin electronics are developed to record information from human skin, human breath, and environments. Taking advantage of its outstanding photothermal effect, LSM-based soft actuators are developed to build light-driven reconfigurable three-dimensional architectures, reshapable airflow sensors, and smart robotic worms with bioelectronic sensors.

Enhanced Mechanical and Durability Properties of Cement Mortar by Using Alumina Nanocoating on Carbon Nanofibers.

This study evaluated the effect of carbon nanofibers (CNFs) coated by aluminum oxide Al2O3 as a reinforcement on compressive strength, frost resistance, and drying shrinkage of cement mortars. Three weight ratios of 0.125%, 0.25%, and 0.5% of Al2O3/CNFs and bare CNF cement mortars were compared with reference cement mortar samples. The reactive porous and high surface area layer of alumina induced the hydration reaction and promoted the production of well-distributed hydration gel. Derivative thermal analysis-differential thermogravimetric (TGA-DTG) and X-ray powder diffraction (XRD) characterization showed that Al2O3/CNFs reinforcement led to greater hydration gel production than bare CNFs. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to study the coating and microstructure of the cement mortars evaluated in this paper. The results show that the optimum enhancement of the cement mortar properties was obtained at ratios of 0.125% for Al2O3/CNFs and 0.25% for CNFs. This enhancement was greater with Al2O3/CNFs-reinforced specimens in terms of high compressive strength, less compressive strength degradation after 150 cycles, and less drying shrinkage. The low use of the CNFs in Al2O3/CNFs samples indicates the coating is an economical and promising approach for improving the performance of cement mortars.

Wireless, battery-free push-pull microsystem for membrane-free neurochemical sampling in freely moving animals.

Extensive studies in both animals and humans have demonstrated that high molecular weight neurochemicals, such as neuropeptides and other polypeptide neurochemicals, play critical roles in various neurological disorders. Despite many attempts, existing methods are constrained by detecting neuropeptide release in small animal models during behavior tasks, which leaves the molecular mechanisms underlying many neurological and psychological disorders unresolved. Here, we report a wireless, programmable push-pull microsystem for membrane-free neurochemical sampling with cellular spatial resolution in freely moving animals. In vitro studies demonstrate the sampling of various neurochemicals with high recovery (>80%). Open-field tests reveal that the device implantation does not affect the natural behavior of mice. The probe successfully captures the pharmacologically evoked release of neuropeptide Y in freely moving mice. This wireless push-pull microsystem creates opportunities for neuroscientists to understand where, when, and how the release of neuropeptides modulates diverse behavioral outputs of the brain.

Bioinspired elastomer composites with programmed mechanical and electrical anisotropies.

Concepts that draw inspiration from soft biological tissues have enabled significant advances in creating artificial materials for a range of applications, such as dry adhesives, tissue engineering, biointegrated electronics, artificial muscles, and soft robots. Many biological tissues, represented by muscles, exhibit directionally dependent mechanical and electrical properties. However, equipping synthetic materials with tissue-like mechanical and electrical anisotropies remains challenging. Here, we present the bioinspired concepts, design principles, numerical modeling, and experimental demonstrations of soft elastomer composites with programmed mechanical and electrical anisotropies, as well as their integrations with active functionalities. Mechanically assembled, 3D structures of polyimide serve as skeletons to offer anisotropic, nonlinear mechanical properties, and crumpled conductive surfaces provide anisotropic electrical properties, which can be used to construct bioelectronic devices. Finite element analyses quantitatively capture the key aspects that govern mechanical anisotropies of elastomer composites, providing a powerful design tool. Incorporation of 3D skeletons of thermally responsive polycaprolactone into elastomer composites allows development of an active artificial material that can mimic adaptive mechanical behaviors of skeleton muscles at relaxation and contraction states. Furthermore, the fabrication process of anisotropic elastomer composites is compatible with dielectric elastomer actuators, indicating potential applications in humanoid artificial muscles and soft robots.

Paleoindian ochre mines in the submerged caves of the Yucatán Peninsula, Quintana Roo, Mexico.

Investigations in the now-submerged cave systems on the Yucatán Peninsula continue to yield evidence for human presence during the Pleistocene-Holocene transition. Skeletal remains are scattered throughout the caves of Quintana Roo, most representing individuals who died in situ. The reasons why they explored these underground environments have remained unclear. Here, we announce the discovery of the first subterranean ochre mine of Paleoindian age found in the Americas, offering compelling evidence for mining in three cave systems on the eastern Yucatán over a ~2000-year period between ~12 and 10 ka. The cave passages exhibit preserved evidence for ochre extraction pits, speleothem digging tools, shattered and piled flowstone debris, cairn navigational markers, and hearths yielding charcoal from highly resinous wood species. The sophistication and extent of the activities demonstrate a readiness to venture into the dark zones of the caves to prospect and collect what was evidently a highly valued mineral resource.

Construction of Polymeric Metal-Organic Nanocapsule Networks via Supramolecular Coordination-Driven Self-Assembly.

Polymeric metal-organic nanocapsule networks (polyMONCs), where metal-organic nanocapsules (MONCs) are connected by functional polymers, could possess the properties of traditional polymers and also retain the structures of MONCs. In this work, we constructed novel polyMONCs based on Mg-seamed pyrogallol[4]arene-containing MONCs through supramolecular coordination-driven self-assembly. The MONCs can be successfully polymerized using poly(ethylene glycol) as the linker, and the prepared polyMONCs can be further made into gels with self-healing properties and stimuli responsiveness. Advantageously, single crystals of MONCs cross-linked by ethylene glycol/diethylene glycol were obtained, giving us direct perspectives to mimic and investigate the self-assembly process of polyMONCs.

Hunter-Gatherers Harvested and Heated Microbial Biogenic Iron Oxides to Produce Rock Art Pigment.

Red mineral pigment use is recognized as a fundamental component of a series of traits associated with human evolutionary development, social interaction, and behavioral complexity. Iron-enriched mineral deposits have been collected and prepared as pigment for use in rock art, personal adornment, and mortuary practices for millennia, yet little is known about early developments in mineral processing techniques in North America. Microanalysis of rock art pigments from the North American Pacific Northwest reveals a sophisticated use of iron oxide produced by the biomineralizing bacterium Leptothrix ochracea; a keystone species of chemolithotroph recognized in recent advances in the development of thermostable, colorfast biomaterial pigments. Here we show evidence for human engagement with this bacterium, including nanostructural and magnetic properties evident of thermal enhancement, indicating that controlled use of pyrotechnology was a key feature of how biogenic iron oxides were prepared into paint. Our results demonstrate that hunter-gatherers in this area of study prepared pigments by harvesting aquatic microbial iron mats dominated by iron-oxidizing bacteria, which were subsequently heated in large open hearths at a controlled range of 750 °C to 850 °C. This technical gesture was performed to enhance color properties, and increase colorfastness and resistance to degradation. This skilled production of highly thermostable and long-lasting rock art paint represents a specialized technological innovation. Our results contribute to a growing body of knowledge on historical-ecological resource use practices in the Pacific Northwest during the Late Holocene.Figshare link to figures: https://figshare.com/s/9392a0081632c20e9484.

Spatial Restrictions in Chemotaxis Signaling Arrays: A Role for Chemoreceptor Flexible Hinges across Bacterial Diversity.

The chemotactic sensory system enables motile bacteria to move toward favorable environments. Throughout bacterial diversity, the chemoreceptors that mediate chemotaxis are clustered into densely packed arrays of signaling complexes. In these arrays, rod-shaped receptors are in close proximity, resulting in limited options for orientations. A recent geometric analysis of these limitations in Escherichia coli, using published dimensions and angles, revealed that in this species, straight chemoreceptors would not fit into the available space, but receptors bent at one or both of the recently-documented flexible hinges would fit, albeit over a narrow window of shallow bend angles. We have now expanded our geometric analysis to consider variations in receptor length, orientation and placement, and thus to species in which those parameters are known to be, or might be, different, as well as to the possibility of dynamic variation in those parameters. The results identified significant limitations on the allowed combinations of chemoreceptor dimensions, orientations and placement. For most combinations, these limitations excluded straight chemoreceptors, but allowed receptors bent at a flexible hinge. Thus, our analysis identifies across bacterial diversity a crucial role for chemoreceptor flexible hinges, in accommodating the limitations of molecular crowding in chemotaxis core signaling complexes and their arrays.

Comparison of two cleaning and sterilization protocols of diamond burr tips used in debridement for canine superficial chronic corneal epithelial defects.

OBJECTIVES: To serially evaluate morphologic and elemental composition changes to diamond burr tips (DBTs) comparing two sterilization protocols. ANIMALS STUDIED: A total of 300 fresh cadaver porcine globes. PROCEDURES: Six DBTs were randomly, equally assigned into Group 1 or 2, and then analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) at 0, 25, 50, and 100 cycles. Diamond burr debridement (DBD) was performed for 120 seconds on corneal stroma using the Algerbrush®. DBTs were cleaned, and then: Group 1 was sterilized by Germinator 500™; and Group 2 underwent ultrasonic cleaning and pre-vacuum autoclave. A cycle is defined as one DBD, cleaning and sterilization protocol. Data were quantified using custom MatLab program. RESULTS: Energy Dispersive Spectroscopy revealed minor buildup of sulfur on both groups. Group 1 displayed major buildup of carbon and calcium. All DBTs were stippled with inorganic particulate at baseline. Particulates were no longer present on Group 2 by 25 cycles, but remained on Group 1 at all time points. There was significantly more buildup on Group 1 at all time points (P = 0.0000, 0.0009, and 0.0003 for 25, 50, and 100 cycles, respectively). More damage to Group 2 at all time points (P = 0.003, 0.002, and 0.003 for 25, 50, and 100 cycles, respectively) was observed. CONCLUSIONS: No significant damage to Group 1 DBTs was noted after 100 cycles, however, particulate matter is not adequately removed using this sterilization technique. Ultrasonic cleaning is warranted between DBDs to achieve adequate particulate removal prior to sterilization; greater damage occurs with this technique which supports replacing DBTs regularly.

Transforming lignin into porous graphene via direct laser writing for solid-state supercapacitors.

Cost-effective valorization of lignin into carbon-based electrode materials remains a challenge. Here we reported a facile and ultrafast laser writing technique to convert lignin into porous graphene as active electrode material for solid-state supercapacitors (SCs). During laser writing, alkaline lignin experienced graphitization. By controlling laser parameters such as power the porous structure and graphitization degree can be well modulated. Graphene obtained at 80% of laser power setting (LIG-80) had higher graphene quality and more porous structure than that obtained at the lower power levels (i.e., 50%, 70%). TEM images revealed that LIG-80 had few-layer graphene structure with fringe-like patterns. LIG-80 proved to be an active electrode material for SCs with a specific capacitance as high as 25.44 mF cm-2 in a H2SO4/PVA gel electrolyte, which is comparable or even superior to SCs based on pristine LIG obtained from other carbon precursors. Taken together, our proposed technical route for lignin-based LIG and subsequent application in SCs would not only open a new avenue to lignin valorization, but also produce porous graphene from a renewable carbon precursor for energy storage applications.

Inhibition of regrowth of planktonic and biofilm bacteria after peracetic acid disinfection.

Peracetic acid (PAA) is a promising alternative to chlorine for disinfection; however, bacterial regrowth after PAA disinfection is poorly understood. This study compared the regrowth of bacteria (Gram-negative Pseudomonas aeruginosa PAO1 and Gram-positive Bacillus sp.) after disinfection with PAA or free chlorine. In the absence of organic matter, PAA and free chlorine prevented the regrowth of planktonic cells of P. aeruginosa PAO1 at C·t (= disinfectant concentration × contact time) doses of (28.5 ±â€¯9.8) mg PAA·min·L-1 and (22.5 ±â€¯10.6) mg Cl2·min·L-1, respectively, suggesting that they had comparable efficiencies in preventing the regrowth of planktonic bacteria. For comparison, the minimum C·t doses of PAA and free chlorine to prevent the regrowth of P. aeruginosa PAO1 biofilm cells in the absence of organic matter were (14,000 ±â€¯1,732) mg PAA·min·L-1 and (6,500 ±â€¯2,291) mg Cl2·min·L-1, respectively. PAA was less effective than free chlorine in killing bacteria within biofilms in the absence of organic matter most likely because PAA reacts with biofilm matrix constituents slower than free chlorine. In the presence of organic matter, although the bactericidal efficiencies of both disinfectants significantly decreased, PAA was less affected due to its slower reaction with organic matter and/or slower self-decomposition. For instance, in a dilute Lysogeny broth-Miller, the minimum concentrations of PAA and free chlorine to prevent the regrowth of planktonic P. aeruginosa PAO1 were 20 mg PAA·L-1 and 300 mg Cl2·L-1, respectively. While both disinfectants are strong oxidants disrupting cell membrane, environmental scanning electron microscopy (ESEM) revealed that PAA made holes in the center of the cells, whereas free chlorine desiccated the cells. Overall, this study shows that PAA is a powerful disinfectant to prevent bacterial regrowth even in the presence of organic matter.

Flexible Hinges in Bacterial Chemoreceptors.

Transmembrane bacterial chemoreceptors are extended, rod-shaped homodimers with ligand-binding sites at one end and interaction sites for signaling complex formation and histidine kinase control at the other. There are atomic-resolution structures of chemoreceptor fragments but not of intact, membrane-inserted receptors. Electron tomography of in vivo signaling complex arrays lack distinct densities for chemoreceptor rods away from the well-ordered base plate region, implying structural heterogeneity. We used negative staining, transmission electron microscopy, and image analysis to characterize the molecular shapes of intact homodimers of the Escherichia coli aspartate receptor Tar rendered functional by insertion into nanodisc-provided E. coli lipid bilayers. Single-particle analysis plus tomography of particles in a three-dimensional matrix revealed two bend loci in the chemoreceptor cytoplasmic domain, (i) a short, two-strand gap between the membrane-proximal, four-helix-bundle HAMP (histidine kinases, adenylyl cyclases, methyl-accepting chemoreceptors, and phosphatases) domain and the membrane-distal, four-helix coiled coil and (ii) aligned glycines in the extended, four-helix coiled coil, the position of a bend noted in the previous X-ray structure of a receptor fragment. Our images showed HAMP bends from 0° to ∼13° and glycine bends from 0° to ∼20°, suggesting that the loci are flexible hinges. Variable hinge bending explains indistinct densities for receptor rods outside the base plate region in subvolume averages of chemotaxis arrays. Bending at flexible hinges was not correlated with the chemoreceptor signaling state. However, our analyses showed that chemoreceptor bending avoided what would otherwise be steric clashes between neighboring receptors that would block the formation of core signaling complexes and chemoreceptor arrays.IMPORTANCE This work provides new information about the shape of transmembrane bacterial chemoreceptors, crucial components in the molecular machinery of bacterial chemotaxis. We found that intact, lipid-bilayer-inserted, and thus functional homodimers of the Escherichia coli chemoreceptor Tar exhibited bends at two flexible hinges along their ∼200-Å, rod-like, cytoplasmic domains. One hinge was at the short, two-strand gap between the membrane-proximal, four-helix-bundle HAMP (histidine kinases, adenylyl cyclases, methyl-accepting chemoreceptors, and phosphatases) domain and the membrane-distal, four-helix coiled coil. The other hinge was at aligned glycines in the extended, four-helix coiled coil, where a bend had been identified in the X-ray structure of a chemoreceptor fragment. Our analyses showed that flexible hinge bending avoided structural clashes in chemotaxis core complexes and their arrays.