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Conductive particle-containing granular composites with tuneable negative permittivity are being studied to improve the performance of electromagnetic devices, such as shielding materials. In this study, we investigated the relative complex permittivity and electrical conductivity of granular composites of polyphenylene sulfide (PPS) resin and Ag-coated Cu flakes in the radio- to microwave-frequency range and compared them with those of PPS/bare Cu flake composites. Electrical conductivity measurements revealed that the PPS/Ag-coated Cu flake composites have a lower percolation threshold (φc) than the PPS/bare Cu flake composites, whereas the electrical conductivity of the PPS/Ag-coated Cu flake composites in the percolated particle state was higher at the same particle volume fraction. At particle contents above φc, a low-frequency plasmonic state of conduction electrons was achieved in the percolated particle chains in both composites, and negative permittivity spectra were obtained. The percolated PPS/Ag-coated Cu flake composites had a negative permittivity up to a higher frequency than the percolated PPS/bare Cu flake composites. Furthermore, the Drude model was used to analyze the negative permittivity spectra of the composites in the percolated particle state. The plasma frequency of the composites with percolated Ag-coated Cu flakes was higher than that of the composites with percolated bare Cu flakes. Thus, coating Ag on Cu particles improved the conductivity of the composite, leading to negative permittivity up to higher frequencies. This study contributes to the enhancement of the negative permittivity achieved by granular composites, which is useful for microwave technology applications.

The morphology changes in graphite flakes due to the difference in S and Mn contents were analyzed in gray iron samples with a Carbon Equivalent (CE) of 4.0. Although these Mn and S contents are within the range of industrial usage, the morphological characteristics of graphite flakes among the different samples show significant changes in their size and distribution. Graphite flake size was estimated using the Feret diameter, and the flake’s distribution was visually characterized following established standards. As it was observed that graphite flakes also differ in branching, a new procedure was developed to quantify such branching. Based on a skeletonization technique, this new procedure provides data to obtain additional microstructural parameters of the graphite flakes, such as the percentage of branched flakes and the longest shortest path (LSP) of each graphite flake. Microstructural characterization included measuring the eutectic cell count. The results indicate that Feret values and LSP show only weak correlations with concentration estimates from initial S and Mn. The most notable relationships are between sulfur content and Feret or LSP values. In contrast, the branching percentage correlates well with free sulfur at 1150 °C and eutectic cell count and is also linked to graphite distribution types (A or B). Notably, branching percentage offers a straightforward morphological parameter that enhances graphite flake characterization.

In this study, a heat storage–based hybrid greenhouse dryer has been developed and analysed for drying bitter gourd flakes under the climatic condition of Ranchi, India. Proposed heat storage–based hybrid greenhouse dryer consists of a solar air heater with a 2.12-m 2 area, greenhouse dryer and DC fan to induce and force the air. The significant objective of the present study is to analyse the drying efficiency, drying kinetics, property analysis, economic analysis, embodied energy and CO 2 mitigation of the hybrid greenhouse dryer for drying of bitter gourd flakes. An experiment was performed simultaneously on proposed system and open sun drying for the proper comparative analysis. Moisture contents reduced from 88.14 to 10.14% in 6 h in proposed dryer and 88.14 to 11.01% in 15 h for open system. Thus, significant drying time is reduced in proposed system by 8 h as compared to open system. Environmental impact analysis shows that the energy payback time was found to be 0.4907 years only. Cost of the proposed system dryer is 22664.30 INR. The total embodied energy is found 1591.07 kWh and earned carbon credit ranges from 16844.76 to 67379.05 INR, while CO 2 mitigation was 46.28 tonnes for 35 years of expected lifetime. Seven standard mathematical models for drying of bitter gourd flakes were studied. Ahmad and Prakash model was found to be the best as compared to other models. The metal contents of dried bitter gourd flakes were also examined. Bitter gourd dried in proposed dryers possesses superior metal content as compared to open systems. Impact analysis demonstrates that the hybrid greenhouse dryer is more suitable for reducing post-harvest loss with environmental sustainability.

Realization of high-density and reliable resistive random access memories based on two-dimensional semiconductors is crucial toward their development in next-generation information storage and neuromorphic computing. Here, wafer-scale integration of solution-processed two-dimensional MoS 2 memristor arrays are reported. The MoS 2 memristors achieve excellent endurance, long memory retention, low device variations, and high analog on/off ratio with linear conductance update characteristics. The two-dimensional nanosheets appear to enable a unique way to modulate switching characteristics through the inter-flake sulfur vacancies diffusion, which can be controlled by the flake size distribution. Furthermore, the MNIST handwritten digits recognition shows that the MoS 2 memristors can operate with a high accuracy of >98.02%, which demonstrates its feasibility for future analog memory applications. Finally, a monolithic three-dimensional memory cube has been demonstrated by stacking the two-dimensional MoS 2 layers, paving the way for the implementation of two memristor into high-density neuromorphic computing system. Neuromorphic computing requires the realization of high-density and reliable random-access memories. Here, Thean et al. demonstrate wafer-scale integration of solution-processed 2D MoS2 memristor arrays which show long endurance, long memory retention, low device variations, and high on/off ratio.

The two natural allotropes of carbon, diamond and graphite, are extended networks of sp 3 -hybridized and sp 2 -hybridized atoms, respectively 1 . By mixing different hybridizations and geometries of carbon, one could conceptually construct countless synthetic allotropes. Here we introduce graphullerene, a two-dimensional crystalline polymer of C 60 that bridges the gulf between molecular and extended carbon materials. Its constituent fullerene subunits arrange hexagonally in a covalently interconnected molecular sheet. We report charge-neutral, purely carbon-based macroscopic crystals that are large enough to be mechanically exfoliated to produce molecularly thin flakes with clean interfaces—a critical requirement for the creation of heterostructures and optoelectronic devices 2 . The synthesis entails growing single crystals of layered polymeric (Mg 4 C 60 ) ∞ by chemical vapour transport and subsequently removing the magnesium with dilute acid. We explore the thermal conductivity of this material and find it to be much higher than that of molecular C 60 , which is a consequence of the in-plane covalent bonding. Furthermore, imaging few-layer graphullerene flakes using transmission electron microscopy and near-field nano-photoluminescence spectroscopy reveals the existence of moiré-like superlattices 3 . More broadly, the synthesis of extended carbon structures by polymerization of molecular precursors charts a clear path to the systematic design of materials for the construction of two-dimensional heterostructures with tunable optoelectronic properties. A two-dimensional crystalline polymer of C 60 , termed graphullerene, is synthesized by chemical vapour transport, and mechanically exfoliated to produce molecularly thin flakes with clean interfaces for potential optoelectronic applications.

Emergent color centers with accessible spins hosted by van der Waals materials have attracted substantial interest in recent years due to their significant potential for implementing transformative quantum sensing technologies. Hexagonal boron nitride (hBN) is naturally relevant in this context due to its remarkable ease of integration into devices consisting of low-dimensional materials. Taking advantage of boron vacancy spin defects in hBN, we report nanoscale quantum imaging of low-dimensional ferromagnetism sustained in Fe 3 GeTe 2 /hBN van der Waals heterostructures. Exploiting spin relaxometry methods, we have further observed spatially varying magnetic fluctuations in the exfoliated Fe 3 GeTe 2 flake, whose magnitude reaches a peak value around the Curie temperature. Our results demonstrate the capability of spin defects in hBN of investigating local magnetic properties of layered materials in an accessible and precise way, which can be extended readily to a broad range of miniaturized van der Waals heterostructure systems. Hexagonal boron nitride (h-BN) has been used extensively to encapsulate other van der Waals materials, protecting them from environmental degradation, and allowing integration into more complex heterostructures. Here, the authors make use of boron vacancy spin defects in h-BN using them to image the magnetic properties of a Fe 3 GeTe 2 flake.

Through experimental research, the performance of the flake ice machine under different structures of the water distribution pan was comparatively analyzed to enhance performance and optimize the design of the water distribution pan in the evaporation drum. An experimental bench for testing the performance of the flake ice machine was constructed, and the optimal scraping cycle under varying water distribution pan structures was determined. The results revealed a 33% improvement in the ice-making area within the water distribution pan structure, along with a 17.5% reduction in power consumption per unit of ice production, achieved through the optimal operational conditions of the flake ice machine using R404A as the refrigerant. Furthermore, the dry area was enhanced by 40%, leading to an 8% reduction in power consumption per unit of ice production. Notably, for this flake ice machine, the optimal ice-making drying ratio was found to be 1.6.

The use of graphene in a form of discontinuous flakes in polymer composites limits the full exploitation of the unique properties of graphene, thus requiring high filler loadings for achieving- for example- satisfactory electrical and mechanical properties. Herein centimetre-scale CVD graphene/polymer nanolaminates have been produced by using an iterative ‘lift-off/float-on’ process and have been found to outperform, for the same graphene content, state-of-the-art flake-based graphene polymer composites in terms of mechanical reinforcement and electrical properties. Most importantly these thin laminate materials show a high electromagnetic interference (EMI) shielding effectiveness, reaching 60 dB for a small thickness of 33 μm, and an absolute EMI shielding effectiveness close to 3·10 5  dB cm 2 g −1 which is amongst the highest values for synthetic, non-metallic materials produced to date. The properties of graphene/polymer composites are usually limited by the use of discontinuous graphene flakes. Here, the authors report a fabrication method to realise continuous cm-scale graphene/polymer nanolaminates with enhanced electromagnetic interference shielding effectiveness, conductivity and mechanical properties.

Solid-state spin sensors have the capacity to act as quantum microscopes for probing material properties and physical processes. However, so far, these tools have relied on quantum defects hosted in rigid, three-dimensional (3D) crystals such as diamond, limiting their ability to closely interface with the sample. Here we demonstrate a versatile quantum microscope using point defects embedded within a thin layer of the van der Waals material hexagonal boron nitride. To showcase the multi-modal capabilities of this platform, we assemble two different heterostructures of a van der Waals material in combination with a quantum-active boron nitride flake. We demonstrate time-resolved, simultaneous temperature and magnetic imaging near the Curie temperature of a van der Waals ferromagnet, as well as map out charge currents and Joule heating in an operating graphene device. The straightforward integration of the hexagonal boron nitride quantum sensor with other van der Waals materials will yield substantial practical benefits for the design and measurement of 2D devices.Hexagonal boron nitride is a common component of 2D heterostructures. Defects implanted in boron nitride crystals can be used to perform spatially resolved sensing of properties, including temperature, magnetism and current.

MXenes are a large family of two-dimensional materials that have attracted attention across many fields due to their desirable optoelectronic, biological, mechanical and chemical properties. There currently exist many synthesis procedures that lead to differences in flake size, defects and surface chemistry, which in turn affect their properties. Herein, we describe the steps to synthesize Ti 3 C 2 T x —the most important and widely used MXene, from a Ti 3 AlC 2 MAX phase precursor. The procedure contains three main sections: synthesis of Ti 3 AlC 2 MAX, wet chemical etching of the MAX in hydrofluoric acid/HCl solution to yield multilayer Ti 3 C 2 T x and its delamination into single-layer flakes. Three delamination options are described; these use LiCl, tertiary amines (tetramethyl ammonium hydroxide/ tetrabutyl ammonium hydroxide) and dimethylsulfoxide respectively. These procedures can be adapted for the synthesis of MXenes beyond Ti 3 C 2 T x . The MAX phase synthesis takes about 1 week, with the etching and delamination each requiring 2 d. This protocol requires users to have experience working with hydrofluoric acid, and it is recommended that users have experience with wet chemistry and centrifugation; characterization techniques such as X-ray diffraction and particle size analysis are also essential for the success of the protocol. While alternative synthesis methods, such as minimally intensive layer delamination, are desirable for certain MXenes (such as Ti 2 CT x ) or specific applications, this protocol aims to standardize the more commonly used hydrofluoric acid/HCl etching method, which produces Ti 3 C 2 T x with minimal concentration of defects and the highest conductivity and serves as a guideline for those working with MXenes for the first time. Key points MXenes are two-dimensional materials, the best known of which is Ti 3 C 2 T x . Many diverse and unique properties have been described for MXenes, but it is difficult to compare the data because their physical characteristics depend on their synthesis. This protocol provides a detailed guideline for the synthesis of a Ti 3 AlC 2 MAX phase precursor, wet chemical etching of MAX to yield multilayer Ti 3 C 2 T x and its delamination into single-layer flakes. MXenes are two-dimensional materials with diverse optoelectronic, biological, mechanical and chemical properties. This protocol describes how to prepare single-layer flakes of Ti 3 C 2 T x , the most important and widely used MXene, from a Ti 3 AlC 2 MAX phase precursor.