Search

Liquid metals (LMs) are emerging as unique fluids for a variety of applications, but their nanoscale solvation properties remain largely understudied. In this work, a combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations are used to investigate the structure of the interface between the bulk room temperature liquid metal (RTLM) and the LM oxide in nanodroplet systems of gallium, EGaIn (75.5% gallium, 24.5% indium), and Galinstan (68.5% gallium, 21.5% indium, 10% tin). Field's metal (51% indium, 32.5% bismuth, 16.5% tin) is also investigated, which melts at ≈62 °C, as a contrast to the other systems. AFM measurements reveal distinct sub‐oxide nanostructured layering in all three RTLM systems, and Field's metal above the melting point, to differing degrees. EGaIn and Galinstan show multiple penetration events between 20 and 30 nm, with smaller, less complex events in Ga. MD simulations suggest that this layering is a result of the near‐surface ordering of LM atoms beneath the oxide layer. Importantly, the atoms in this region do not behave as solids but are more ordered than in a pure disordered liquid system. The surface nanostructure elucidated here significantly expands the understanding of LM systems and their behavior at interfaces. [ABSTRACT FROM AUTHOR]

Liquid metal nanodroplets are an emerging class of underexplored materials with significant potential in many applications, including catalysis, bio‐therapeutics, and phase‐change materials. These nanostructures are generally synthesized by mechanical agitation via ultrasonication of low‐melting metals like Ga. Once these materials are successfully synthesized, they can be suspended in a vast array of different solvents. However, one major issue arises specifically with liquid metal alloys which are found to de‐alloy in the sonication process. Here, it is demonstrated that this challenge can be overcome by undertaking sonication at high temperatures, suspending nanodroplets within molten sodium acetate (NaOAc). After cooling, the nanostructures become planet‐like nanodroplets which are covered by an interfacial oxide crust, feature a liquid metal mantle, and a solid core. The molten salt solvent can effectively be removed rendering this approach to be ideal, especially for catalysts. The proof‐of‐concept application is demonstrated by carrying out electrocatalytic ethanol oxidation, using the Cu–Ga system. The superior performance of the Cu–Ga nanodroplets highlights potential in catalyzing a vast array of reactions. Aside from the Cu–Ga system, this facile process can be applied to multiple other systems, including Ag–Ga, Zn–Ga, Bi–Ga, In–Cu, and Sn–Cu. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Significant progress has been made in recent years in the development of liquid metal alloy catalysts. This article provides an overview of the state‐of‐the‐art research pertaining to liquid metal alloy catalysis, including alloy synthesis, reactor design, and theoretical calculations. Different alloy synthesis methods are discussed with a focus on strategies that can achieve colloidal intermetallic structures in liquid metal alloys. Current reactors for liquid metal‐based electrocatalytic and thermochemical processes are summarized. The application of theoretical tools, such as machine learning and computational chemistry to further liquid metal alloy design, is discussed. Finally, an outlook on the technological challenges and our perspective on future research opportunities for liquid metal alloy catalysis are presented. [ABSTRACT FROM AUTHOR]

Miniaturization and energy consumption by computational systems remain major challenges to address. Optoelectronics based synaptic and light sensing provide an exciting platform for neuromorphic processing and vision applications offering several advantages. It is highly desirable to achieve single‐element image sensors that allow reception of information and execution of in‐memory computing processes while maintaining memory for much longer durations without the need for frequent electrical or optical rehearsals. In this work, ultra‐thin (<3 nm) doped indium oxide (In2O3) layers are engineered to demonstrate a monolithic two‐terminal ultraviolet (UV) sensing and processing system with long optical state retention operating at 50 mV. This endows features of several conductance states within the persistent photocurrent window that are harnessed to show learning capabilities and significantly reduce the number of rehearsals. The atomically thin sheets are implemented as a focal plane array (FPA) for UV spectrum based proof‐of‐concept vision system capable of pattern recognition and memorization required for imaging and detection applications. This integrated light sensing and memory system is deployed to illustrate capabilities for real‐time, in‐sensor memorization, and recognition tasks. This study provides an important template to engineer miniaturized and low operating voltage neuromorphic platforms across the light spectrum based on application demand. [ABSTRACT FROM AUTHOR]

Imaging sensors with inbuilt processing capability are expected to form the backbone of low‐latency and highly energy efficient artificial vision systems. A range of emerging atomically thin materials provide opportunities to exploit their electrical and optical properties for human vision and brain inspired functions. This work reports atomically thin nanosheets of β‐In2S3 which exhibit inherent persistent photoconductivity (PPC) under ultraviolet and visible wavelengths. This PPC effect enables β‐In2S3‐based optoelectronic devices to optically mimic the dynamics of biological synapses. Based on the material characterizations, the PPC effect is attributed to the intrinsic defects in the synthesized β‐In2S3 nanosheet. Furthermore, the feasibility of adopting these atomically thin synaptic devices for optoelectronic neuromorphic hardware is demonstrated by implementing a convolutional neural network for image classification. As such, the demonstrated atomically thin nanosheets and optoelectronic synaptic devices provide a platform for scaling up complex vision‐sensory neural networks, which can find many promising applications for multispectral imaging and neuromorphic computation. [ABSTRACT FROM AUTHOR]

The alluring electronic, optoelectronic, and photonic properties of low‐dimensional materials have allowed brain‐inspired electronics to evolve in unprecedented ways. With highly efficient neuromorphic devices and architecture being concocted lately, an understanding of the underlying device mechanisms has emerged. The question of what types of materials and physical mechanisms will be used in future neuromorphic hardware is still open for debate. Herein, a critical review of the mechanisms among various configurations in state‐of‐the‐art low‐dimensional neuromorphic devices is presented. The factors are also reviewed that influence the working paradigm of low‐dimensional neuromorphic devices under different stimuli. Finally, a forward‐looking outlook on the challenges and perspectives in analyzing the mechanisms in this emerging research direction to drive next‐generation neuromorphic computing is provided. [ABSTRACT FROM AUTHOR]

Thin film transistors (TFTs) are key components for the fabrication of electronic and optoelectronic devices, resulting in a push for the wider exploration of semiconducting materials and cost‐effective synthesis processes. In this report, a simple approach is proposed to achieve 2‐nm‐thick indium oxide nanosheets from liquid metal surfaces by employing a squeeze printing technique and thermal annealing at 250 °C in air. The resulting materials exhibit a high degree of transparency (>99 %) and an excellent electron mobility of ≈96 cm2 V−1 s−1, surpassing that of pristine printed 2D In2O3 and many other reported 2D semiconductors. UV‐detectors based on annealed 2D In2O3 also benefit from this process step, with the photoresponsivity reaching 5.2 × 104 and 9.4 × 103 A W−1 at the wavelengths of 285 and 365 nm, respectively. These values are an order of magnitude higher than for as‐synthesized 2D In2O3. Utilizing transmission electron microscopy with in situ annealing, it is demonstrated that the improvement in device performances is due to nanostructural changes within the oxide layers during annealing process. This work highlights a facile and ambient air compatible method for fabricating high‐quality semiconducting oxides, which will find application in emerging transparent electronics and optoelectronics. [ABSTRACT FROM AUTHOR]

The structural characteristics of biological specimens, such as wet proteins and fixed living cells, can be conveniently probed in their host aqueous media using soft X‐rays in the water window region (200–600 eV). Conventional X‐ray detectors in this area exhibit low spatial resolution, have limited sensitivity, and require complex fabrication procedures. Here, many of these limitations are overcome by introducing a direct soft X‐ray detector based on ultrathin tin mono‐sulfide (SnS) nanosheets. The distinguishing characteristic of SnS is its high photon absorption efficiency in the soft X‐ray region. This factor enables the fabricated soft X‐ray detectors to exhibit excellent sensitivity values on the order of 104 μCGyVac−1 cm−2 at peak energies of ≈600 eV. The peak signal is found to be sensitive to the number of stacked SnS layers, with thicker SnS nanosheet assemblies yielding a peak response at higher energies and with peak sensitives of over 2.5 × 104 μCGyVac−1 cm−2 at 1 V. Detailed current–voltage and temporal characteristics of these detectors are also presented. These results showcase the excellent performance of SnS nanosheet‐based soft X‐ray detectors compared to existing direct soft X‐ray detectors, including that of the emerging organic–inorganic perovskite class of materials. [ABSTRACT FROM AUTHOR]

Eutectic gallium‐indium (EGaIn) liquid metal droplets have been considered as a suitable platform for producing customized 3D composites with functional nanomaterials owing to their soft and highly reductive surface. Herein, the synthesis of a 3D plasmonic oxide framework (POF) is reported by incorporating the ultra‐thin angstrom‐scale‐porous hexagonal molybdenum oxide (h‐MoO3) onto the spherical EGaIn nanodroplets through ultrasonication. Simultaneously, a large number of oxygen vacancies form in h‐MoO3, boosting its free charge carrier concentration and therefore generating a broad surface plasmon resonance across the whole visible light spectrum. The plasmonic chemical sensing properties of the POF is investigated by the surface‐enhanced Raman scattering detection of rhodamine 6G (R6G) at 532 nm, in which the minimum detectable concentration is 10−8m and the enhancement factor reached up to 6.14 × 106. The extended optical absorption of the POF also allowed the efficient degradation of the R6G dye under the excitation of ultraviolet‐filtered simulated solar light. Furthermore, the POF exhibits remarkable photocurrent responses towards the entire visible light region with the maximum response of ≈1588 A W−1 at 455 nm. This work demonstrates the great potential of the liquid metal‐based POFs for high‐performance sensing, catalytic, and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Chalcohalide semiconductors are an emergent class of materials for optoelectronics. Here, the first work on BiSI chalcohalide thin film photodetectors (PDs) is presented. An entirely new method for the fabrication of bismuth chalcohalide thin films (BiOI and BiSI) is developed. This method circumvents the use of any ligands or counter ions during fabrication and provides highly pure thin films free of carbon residues and other contaminants. When integrated into lithographically patterned lateral PDs these BiSI thin films show outstanding performances and high stability. The direct ≈1.55 eV bandgap of BiSI perfectly accommodates optical sensing over the full visible spectrum. The responsivity (R) of the BiSI PDs reaches 62.1 A W−1, which is the best value reported to date across chalcohalide materials of any type. The BiSI PDs display remarkable sensitivity to low light levels, supporting a broad operational detectivity ≈1012 Jones over four decades in light intensity, with a peak specific detectivity (D*) of 2.01 × 1013 Jones. The dynamics of photocurrent generation are demonstrated to be dominated by photoconductive gain. These results cement BiSI as an exciting candidate for high performance photodetector applications and encourage ongoing work in BiSX (X = Cl, Br, I) materials for optoelectronics. [ABSTRACT FROM AUTHOR]

Atomically thin 2D materials are highly sought for high‐performance electronic and optoelectronic devices. Despite being a widely recognized functional material for a plethora of applications, ultra‐thin nanosheets of zinc oxide (ZnO) at a millimeter‐scale for developing high‐performance electronic/optoelectronic devices have not been reported. This has prevented the exploration of electronic and optical properties of ZnO when it is only a few atoms thick. Here, a liquid metal exfoliation technique is used that takes advantage of the van der Waals forces between the interfacial oxide and the chosen substrate to obtain ZnO nanosheets with lateral dimensions in the millimeter scale and thickness down to 5 nm. Their suitability for applications is shown by demonstrating a visible‐blind photodetector with high figures of merit as compared to other ZnO morphologies. At extremely low operating bias of 50 mV and low optical intensity of 0.5 mW cm−2, the ZnO photodetector demonstrates an external quantum efficiency (EQE), responsivity (R), and detectivity (D*) of 4.3 × 103%, 12.64 A W−1, and 5.81 × 1015 Jones at a wavelength of 365 nm. The trap‐mediated photoresponse in the ZnO nanosheets is further utilized to demonstrate optoelectronic synapses. Versatile synaptic functions of the nervous systems are optically emulated with the ultra‐thin ZnO nanosheets. [ABSTRACT FROM AUTHOR]