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Abstract Lead (Pb) halide perovskite solar cells (PSCs) exhibit impressive power conversion efficiencies close to those of their silicon counterparts. However, they suffer from moisture instability and Pb safety concerns. Previous studies have endeavoured to address these issues independently, yielding minimal advancements. Here, a general nanoencapsulation platform using natural polyphenols is reported for Pb‐halide PSCs that simultaneously addresses both challenges. The polyphenol‐based encapsulant is solution‐processable, inexpensive (≈1.6 USD m−2), and requires only 5 min for the entire process, highlighting its potential scalability. The encapsulated devices with a power conversion efficiency of 20.7% retained up to 80% of their peak performance for 2000 h and up to 70% for 7000 h. Under simulated rainfall conditions, the encapsulant rich in catechol groups captures the Pb ions released from the degraded perovskites via coordination, keeping the Pb levels within the safe drinking water threshold of 15 ppb.

Abstract Crystallization of alloys from a molten state is a fundamental process underpinning metallurgy. Here the direct imaging of an intermetallic precipitation reaction at equilibrium in a liquid‐metal environment is demonstrated. It is shown that the outer layers of a solidified intermetallic are surprisingly unstable to the depths of several nanometers, fluctuating between a crystalline and a liquid state. This effect, referred to herein as crystal interface liquefaction, is observed at remarkably low temperatures and results in highly unstable crystal interfaces at temperatures exceeding 200 K below the bulk melting point of the solid. In general, any liquefaction process would occur at or close to the formal melting point of a solid, thus differentiating the observed liquefaction phenomenon from other processes such as surface pre‐melting or conventional bulk melting. Crystal interface liquefaction is observed in a variety of binary alloy systems and as such, the findings may impact the understanding of crystallization and solidification processes in metallic systems and alloys more generally.

This research designed and developed an ultrasonic reactor for a fast and on demand production of cold brew coffee, remarkably reducing the brewing time from 24 h to less than 3 min. The technology was engineered by utilizing resonance to induce ultrasonic waves around the walls of the brewing basket of an espresso machine. The sound transmission system comprised a transducer, a horn and a brewing basket. This arrangement transformed the coffee basket into an effective sonoreactor that injected sound waves at multiple points through its walls, thereby generating multiple regions for acoustic cavitation within the reactor. Furthermore, acoustic streaming induced greater mixing and enhanced mass transfer during brewing. The design was accomplished by modeling the transmission of sound, and acoustic cavitation. Brew characterization and chemical composition analysis was performed, considering factors such as pH, acidity, color, and the composition of caffeine, fatty acids, and volatiles. The efficiency of the extraction increased by decreasing the basket loading percentage (BLP). For instance, sonicating at 100 W doubled the extraction yield and caffeine concentration, from 15.05 % to 33.44 % at BLP = 33 %, and from 0.91 mg/mL to 1.84 mg/mL at BLP = 67 %, respectively. The total fatty acids increased from 1.16 mg/mL to 9.20 mg/mL, representing an eightfold increase, at BLP = 33 %. Finally, a sensory analysis was conducted to evaluate appearance, aroma, texture, flavor, and aftertaste, which demonstrated that coffee brewed for 1 and 3 min in the sonoreactor exhibited almost undistinguishable properties compared to a standard 24 h brewing without ultrasound.

Nano‐/microparticles of gallium (Ga), as a low‐melting‐point metal, are extensively used in the fields of soft electronics and sensors to provide thermal and electrical conductivity. However, a passivating oxide layer can be formed on the surface of Ga nano‐/microparticles during the synthesis process. This oxide layer is removed by a secondary sintering step, especially mechanical sintering, which is generally not a controllable process, and compromises the integrity of the system. Herein, thiol molecules, 1‐butanethiol, thiophenol, and 4‐mercaptopyridine, that can functionalize the surface of Ga via sonication to reduce the oxidation of Ga surface are used. The resulting particles exhibit electrical conductivity based on metal–molecule junctions without the requirement for a sintering step. In particular, 4‐mercaptopyridine functionalized, thiolated Ga particles exhibit higher electrical conductivity compared to the other three thiolated Ga systems as the organic material conjugation provides conductive pathways for the mix. Subsequently, using these particle systems, soft devices are developed that can be used for gas, exhalation, and flex sensing. This study provides insights into the possibility of creating combinations of organic molecules with liquid metal‐based nano‐/microparticles to generate electrically conductive mixes and the prospects of fabricating multifunctional sensors.

Wireless communications for ingestible and implantable medical device applications are integral for the embedded systems employed to these ends. The Bluetooth protocol is of major interest given its ubiquitous nature in consumer electronic devices. Here the effectiveness of Bluetooth in such applications is examined with a custom-designed Bluetooth system. The radio frequency (RF) attenuation testing was conducted in a variety of different media, including water, meat, ballistic gel, and fat. The RF signal attenuation was found to be the highest in meat and ballistic gel, less in water and least severe in fat. The measured distances at which signal integrity was still maintained provide necessary information for designing and implementing Bluetooth based medical devices and function as evidence for the feasibility of Bluetooth enabled systems for such communications.

A number of design challenges are associated with in-body devices, especially ingestible capsules, including selection of operation frequency and antenna design. Operation frequency, miniaturization, gain, and interference with the environment and the internal components of ingestible capsules are all challenging factors. In this work, we design and measure the performance of miniature antennas that can be included in ingestible capsules. The meandering pattern designs are implemented with a 433 MHz center frequency which is within one of the industrial, scientific and medical (ISM) bands. The antenna patterns are rolled into cylinders to reflect their configuration inside a capsule. The effects of different antenna design features, environmental dielectric changes, and the battery locations relative to the antenna traces are explored. We show that the optimized antenna can offer acceptable performance even when the center frequency shifts due to the modulation of the dielectric constant of the media and by the insertion of batteries. Both simulations and measurements provide insight into how the meandering antenna should be designed for the desired frequency that can be expanded to other ingestible and implantable systems.

The presence of strong inter-layer interactions has hindered the synthesis efforts towards large-area and highly crystalline monolayer SnS. Here, the authors report synthesis of large-area monolayer SnS using a liquid metal-based technique, and fabricate piezoelectric nano-generators with average peak output voltage of 150 mV at 0.7% strain.

The combination of metallurgy concepts and nanotechnology with liquid metal processing has been largely unexplored. Here the authors use liquid-phase ultrasonication to produce a model system of catalytically active nano-alloys, demonstrating electrocatalysis and photocatalysis.

Abstract Cytokines are critical mediators that oversee and regulate immune and inflammatory responses via complex networks and serve as biomarkers for many diseases. Quantification of cytokines has significant value in both clinical medicine and biology as the levels provide insights into physiological and pathological processes and can be used to aid diagnosis and treatment. Cytokines and their clinical significance are introduced from the perspective of their pro‐ and anti‐inflammatory effects. Factors affecting cytokines quantification in biological fluids, native levels in different body fluids, sample processing and storage conditions, sensitivity to freeze‐thaw, and soluble cytokine receptors are discussed. In addition, recent advances in in vitro and in vivo assays, biosensors based on different signal outputs and intracellular to extracellular protein expression are summarized. Various quantification platforms for high‐sensitivity and reliable measurement of cytokines in different scenarios are discussed, and commercially available cytokine assays are compared. A discussion of challenges in the development and advancement of technologies for cytokine quantification that aim to achieve real‐time multiplex cytokine analysis for point‐of‐care situations applicable for both biomedical research and clinical practice are discussed.

Summary: The power conversion efficiency (PCE) of metal halide perovskite solar cells (PSCs) has improved dramatically from 3.8% to 25.5% in only a decade. Gas quenching is a desirable method for fabricating high-efficiency cells as it does not consume antisolvents and is compatible with large-area deposition methods such as doctor blading and slot-die coating. To further improve PCEs for gas-quenched PSCs, here, we develop complementary bulk and surface passivation strategies by incorporating potassium iodide (KI) in the perovskite precursor and applying n-hexylammonium bromide (HABr) to the perovskite surface. We show that (1) KI induces a spatial-compositional change, improving grain boundary properties; (2) KI and HABr reduce traps, especially at levels close to the mid-gap; and (3) HABr greatly improves the built-in potential of the device, thereby improving voltage output. The champion device achieves a steady-state PCE of 23.6% with a VOC of 1.23V, which is, to the best of our knowledge, the highest for PSC by gas quenching to date.

While CO2 reduction proves an appealing means to convert greenhouse emissions to high-value products, there are few materials capable of such a conversion. Here, the authors demonstrate a liquid-metal electrocatalyst to convert CO2 directly into solid carbon that can be used as capacitor electrodes.

Two-dimensional piezoelectric materials hold promise for nano-electromechanical technologies, yet it is challenging to prepare them in large areas with high sample homogeneity. Syed et al. surface print GaPO4 sheets with unit cell thickness over centimetres using a liquid metal-based synthesis process.

Abstract Two-dimensional (2D) transition metal oxide and chalcogenide (TMO&C)-based photocatalysts have recently attracted significant attention for addressing the current worldwide challenges of energy shortage and environmental pollution. The ultrahigh surface area and unconventional physiochemical, electronic and optical properties of 2D TMO&Cs have been demonstrated to facilitate photocatalytic applications. This review provides a concise overview of properties, synthesis methods and applications of 2D TMO&C-based photocatalysts. Particular attention is paid on the emerging strategies to improve the abilities of light harvesting and photoinduced charge separation for enhancing photocatalytic performances, which include elemental doping, surface functionalization as well as heterojunctions with semiconducting and conductive materials. The future opportunities regarding the research pathways of 2D TMO&C-based photocatalysts are also presented.

One of the key challenges 2D materials still face is their uniform wafer-scale deposition. Here, the authors present a deposition method for post-transition metal dichalcogenides, based on transformation of an ultra-thin oxide layer on the surface of liquid elemental gallium onto an oxide-coated substrate.

The control over the motion and deformation of liquid droplets is essential to many microfluidic and actuation systems. Zavabeti et al. demonstrate that applying a pH or ionic gradient across a droplet of liquid metal alloy of gallium results in its motion due to a breaking of the surface charge symmetry.

We fabricated large-area atomically thin MoS2 layers through the direct transformation of crystalline molybdenum trioxide (MoO3) by sulfurization at relatively low temperatures. The obtained MoS2 sheets are polycrystalline (~10–20 nm single-crystal domain size) with areas of up to 300 × 300 µm2, 2–4 layers in thickness and show a marked p-type behavior. The synthesized films are characterized by a combination of complementary techniques: Raman spectroscopy, X-ray diffraction, transmission electron microscopy and electronic transport measurements.

The original version of this Article contained errors in the author affiliations. Affiliation 1 incorrectly read ‘School of Chemical Engineering, University of New South Wales (UNSW), Sydney, NSW 2031, Australia’ and affiliation 4 incorrectly read ‘School of Engineering, RMIT University, Melbourne, VIC 3001, Australia.’ This has now been corrected in both the PDF and HTML versions of the Article.

Ga⁻Sn⁻Zn eutectic alloy is a non-toxic liquid metal alloy which could be used in a multitude of applications, including as a heat transfer agent, in gas sensing, and in medicine. Alloys containing gallium readily oxidise in air, forming a thin oxide layer that influences the properties of liquid metals and which has not been studied. In this study, the oxide layer formed on Ga⁻Sn⁻Zn alloy was transferred at room temperature onto three substrates—quartz, glass and silicon. The contact angle between the liquid alloy and different substrates was determined. The obtained thin oxide films were characterised using atomic force microscopy, X-ray photon spectroscopy, and optical and transmission electron microscopy. The contact angle does not influence the deposition of the layers. It was determined that it is possible to obtain nanometric oxide layers of a few micrometres in size. The chemical composition was determined by XPS and EDS independently, and showed that the oxide layer contains about 90 atom % of gallium with some additions of tin and zinc. The oxides obtained from the eutectic Ga⁻Sn⁻Zn liquid alloys appear to be nanocrystalline.

Nature Communications 8: Article number: 14482; published: 17 February 2017; Updated: 22 March 2017 The original version of this Article contained a typographical error in the spelling of the author Omid Kavehei, which was incorrectly given as Omid Kevehei. This has now been corrected in both the PDF and HTML versions of the Article.

Active droplets play important roles in microfluidics, robotics, and micro-electromechanical systems. As a special class of active droplets that are conductive, reactive, and of high surface tension, liquid metal droplets (LMDs) can be driven by electric-field-induced surface (Marangoni) flows to function as reconfigurable components in actuators, sensors, catalytic reactors, and antennas. Stimulating LMDs using an electric field induces concurrent electro-hydrodynamic flows and electrochemical surface oxidation (passivation). It is however difficult to decouple these two effects which brings complexity in controlling LMD motions. To address this challenge, pulse time modulation (PTM) signals are used. PTM enables controlled LMD displacement by propelling the droplets forward during the voltage-on phases and facilitating surface recovery from oxidation during the voltage-off phases. Counterintuitively, by taking such intermittent "rests", the LMDs effectively inhibit the unfavorable impact of oxidation, granting high motion controllability. Combining high-speed imaging, motion tracking, machine learning, and electrochemical analysis, the study reveals how electro-hydrodynamic flows and surface oxide formation/dissolution interplay to generate well-defined motion regimes. The study further develops a quasi-analytical model to describe droplet motions and designs a rotary LMD motor to showcase the versatility of the approach. This work provides the fundamental framework and viable strategy for designing innovative liquid metal-based systems. [ABSTRACT FROM AUTHOR]

A microfluidic dielectrophoresis platform consisting of curved microelectrodes was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a quartz substrate, which has insignificant Raman response, and integrated with a microfluidic channel that was imprinted in poly-dimethylsiloxane (PDMS). We will show that this novel integrated system can be efficiently used for the determination of suspended particle types and the direct mapping of their spatial concentrations. We will also illustrate the system's unique advantages over conventional optical systems. Nanoparticles of tungsten trioxide (WO3) and polystyrene were used in the investigations, as they are Raman active and can be homogeneously suspended in water. [ABSTRACT FROM AUTHOR]

Atomically thin WO3is fabricated using a three-step process, involving wet-chemical synthesis of hydrated-WO3, mechanical exfoliation of fundamental layers and dehydration by annealing at 300 °C. Atomic force microscopy reveals that the minimum resolvable thickness of the hydrated flakes to be ∼1.4 nm, which corresponds to the unit-cell height. The subsequent annealing temperature determines the degree of dehydration and thereby the crystallographic structure of the resultant WO3. The hydrated and dehydrated flakes are characterized by Raman spectroscopy to reveal spectroscopic fingerprints of flake thickness. Thin flakes are also shown to have higher propensity for lithium intercalation, which is also evidenced in Raman planar peak intensity. [ABSTRACT FROM AUTHOR]

Abstract Electrocrystallization is a promising method for controlled charge‐transfer complex (CTC) deposition on microfabricated electrodes for gas sensing applications. However, there remains a gap in our understanding of CTC electrodeposition. In this study, we focus on investigating the electrocrystallization of cobalt tetracyanoquinodimethane (Co‐TCNQ) on a microdisk electrode to elucidate and control the process. Leveraging the microelectrode technique, we conduct steady‐state measurements to observe nucleation and crystal growth dynamics, particularly in the early stages of electrocrystallization. We use cyclic voltammetry and chronoamperometry to examine Co‐TCNQ electrocrystallization under various electrolytic conditions. We identify electrocrystallization kinetics, ranging from electrokinetic to diffusion‐limited growth, governing the nucleation and growth of Co‐TCNQ crystals. Notably, we pinpoint the applied overpotential and precursor concentration range necessary for a single nucleation site on the microelectrode. Moreover, we demonstrate control over crystal orientation and morphology. Our findings reveal a nonclassical growth pathway for Co‐TCNQ crystals characterized by oriented attachment of small crystallites along the conductive long axis. Importantly, electrodeposited Co‐TCNQ on patterned microelectrodes exhibits selective sensing capabilities for nitrogen dioxide gas. Overall, this study sheds light on CTC electrodeposition through a proof‐of‐concept demonstration involving Co‐TCNQ electrodeposition on microelectrodes, presenting potential applications across diverse materials.