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The Structure of Phase-Change Chalcogenides and Their High-Pressure Behavior
摘要： Phase-change materials (PCMs) used in data storage devices have unique structural features and transition properties by thermal heating. Pressure, as another important thermodynamic tool, can also induce a series of interesting phase transitions in PCMs, accompanied by the altering of bonding nature and physical properties. Here, the structure transition as well as property change of prototypical phase-change material Ge–Sb–Te (GST) under hydrostatic pressure has been reviewed. The high-pressure behavior of some other relevant chalcogenides such as GeTe, Sb2Te3, and GeSe, is also discussed. The revealing of structure and property changes due to high pressure sheds light on the underlying physics of many fascinating properties of PCMs, and therefore it will have profound implications on various applications of phase change materials in memory and other fields.
关键词： high pressure,phase-change materials,Ge–Sb–Te,memory materials
更新于2025-09-23 15:23:52
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A Simplified Approach for Obtaining Optical Properties of VO <sub/>2</sub> Thin Films, and Demonstration of Infrared Shape-Shifting Devices
摘要： Micrometer-sized VO2-based devices with integrated resistive heaters of different configurations are fabricated. Quality of the VO2 films is confirmed by measuring the characteristic drop in transmittance and negative differential emissivity for these films. A two-interface model for optical transmittance, reflectance, and absorbance is presented. This method and analytic model presents an advantage over most typically used approaches in that it does not require direct measurements of the material’s optical constants to estimate transmittance. By combining the substrate and the VO2 film into one layer with a reduced optical admittance, the two-interface model is reduced to a single-layer model. Moreover, the present work demonstrates the implementation of the developed VO2-based devices in adaptive camouflage and shape-converting applications. Electrical pulses are used to program different emissivity states to convert geometric shapes inside a fully integrated VO2-based electro-optical window. This results in the reconfiguring of thermal images to either create new shapes, or shift from one to another.
关键词： shape-configuration,hysteresis,programming states,phase-change materials,smart materials
更新于2025-09-23 15:23:52
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Low-loss and broadband non-volatile phase-change directional coupler switches
摘要： An optical equivalent of the field-programmable gate array (FPGA) is of great interest to large-scale photonic integrated circuits. Previous programmable photonic devices relying on the weak, volatile thermo-optic or electro-optic effect usually suffer from a large footprint and high energy consumption. Phase change materials (PCMs) offer a promising solution due to the large non-volatile change in the refractive index upon phase transition. However, the large optical loss in PCMs poses a serious problem. Here, by exploiting an asymmetric directional coupler design, we demonstrate non-volatile PCM-clad silicon photonic 1 × 2 and 2 × 2 switches with a low insertion loss of ~1 dB and a compact coupling length of ~30 μm while maintaining a small crosstalk less than ?10 dB over a bandwidth of 30 nm. The reported optical switches will function as the building blocks of the meshes in the optical FPGAs for applications such as optical interconnects, neuromorphic computing, quantum computing, and microwave photonics.
关键词： Silicon photonics,Non-volatile,Optical switches,Phase-change materials,Reconfigurable photonics,Integrated photonic devices
更新于2025-09-23 15:23:52
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Ag-graphene/PEG composite phase change materials for enhancing solar-thermal energy conversion and storage capacity
摘要： In view of the excellent characteristic of thermal energy storage, phase change materials (PCMs) are of great significance for improving the efficiency of solar thermal energy utilization. However, the direct thermal effect of visible-light (40% of solar radiation) is very low. In order to improve the capabilities of visible-light absorption and photothermal conversion, we reported novel and efficient sunlight-driven PCMs based on polyethylene glycol (PEG) supported by Ag nanoparticle-functionalized graphene nanosheets (Ag–GNS). The multifolded layered structure provides Ag–GNS a large surface area to support PEG for achieving the shape stability before and after phase transition. Meanwhile, based on the local surface plasma resonance effect of Ag, Ag has high visible light selective absorption and infrared reflectance, which can give Ag–GNS enhanced light absorption capacity and reduced thermal radiation. So Ag–GNS/PEG can harvest sunlight and convert light to thermal energy with significantly higher efficiency (η = 88.7–92.0%). Moreover, Ag–GNS/PEG composites exhibit enhanced thermal conductivities (49.5–95.3%), high energy storage densities (> 166.1 J/g), high thermal energy storage/release rates and outstanding form-stable properties. Therefore, this novel sunlight-driven composite can be potentially used for clean and efficient utilization of solar energy.
关键词： Sunlight-driven,Photothermal conversion,Phase change materials,Ag–GNS
更新于2025-09-23 15:23:52
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Development of Graphitic Domains in Carbon Foams for High Efficient Electro/Photo-to-Thermal Energy Conversion Phase Change Composites
摘要： In this research work, hierarchical porous carbon foams (CFs) with high surface area and three dimensionally (3D) interconnected macro/meso/microporous structures were prepared through pyrolysis of stabilized poly(acrylonitrile-co-divinylbenzene) P(AN-co-DVB) polyHIPE foams at 900 °C under nitrogen atmosphere. The prepared CFs revealed high surface area (540 m2 g-1), semi-ordered nanoporosity, high electrical conductivity (470 S m-1) and high graphitization degree. Further, HR-TEM observation of CFs revealed the formation of graphitic domains in the structures. The obtained CFs were employed for encapsulation of phase change materials (PCMs) e.g. paraffin (PA) and polyethylene glycol (PEG). The prepared PCMs composites revealed the excellent reversible thermal/chemical stability after frequent 200 heating/cooling cycles. Black CF/PA and CF/PEG composites can be promising structures to driven either by applying a small voltage (3-3.6 V) with high electric-to thermal efficiency (up to 85%) or by irradiating with sunlight with high photo-to thermal efficiency (up to around 91%).
关键词： paraffin and poly ethylene glycol,carbon foam,phase change materials
更新于2025-09-23 15:23:52
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Mesoporous silica-coated gold nanoframes as drug delivery system for remotely controllable chemo-photothermal combination therapy
摘要： Tumor cells experience higher chemotherapy stress under condition of elevated temperature. As a result, developing novel nanoagents that integrates chemotherapy and thermotherapy holds great promise in biomedicine. Herein, utilizing spatially confined galvanic replacement method, we fabricated a yolk-shell Au@mSiO2 nanoframes with Au NPs and mesoporous silica as yolk and shell, respectively, to sever as an excellent drug nanocarrier with effective photothermal conversion efficiency. Taking full advantage of the high temperature response of the Au@mSiO2 nanoframes, the phase change material 1-tetradecanol (TD) was creatively employed as gatekeepers, intelligently controlling the release of loaded agents. Then, the actively targeted Alanine-Alanine-Asparagine, legumain-recognizable oligopeptides was decorated on the surface of the prepared nanoframes. Upon exposure to near-infrared light, the GC-PtAu@mSiO2-TD nanoframes not only exhibited a high localized temperature response, but also triggered the quick release of loaded cargos, and thus improved the chemotherapeutic efficacy. The in vitro cytotoxicity studies indicated the remarkable synergistic effects. Meanwhile, the laser confocal studies and flow cytometry showed the oligopeptides facilitated the intracellular uptake of GC-PtAu@mSiO2-TD nanoframes in MGC-803 cells. Our study highlighted the great potential of the GC-PtAu@mSiO2-TD nanoframes in drug delivery and the combination of chemotherapy and photothermal therapy.
关键词： Cisplatin,Mesoporous silica-gold nanoframes,Phase-change materials,Photothermal therapy,Controlled release
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE Conference on Antenna Measurements & Applications (CAMA) - Va?ster?s (2018.9.3-2018.9.6)] 2018 IEEE Conference on Antenna Measurements & Applications (CAMA) - Overview On Functional Materials for Frequency Tunable Antennas
摘要： We report the integration of different kind of materials with improved and adapted properties within antenna designs. In this framework, an overview of three frequency tunable antennas will be presented. Two of them are based on radiating slot elements integrating a Ba2/3Sr1/3TiO3 (BST)-based tunable capacitance and therefore present a continuous tunability for the first one while the second one is integrating a VO2-based switch for a discrete tuning. The third design presented in this paper propose a frequency reconfigurable composite GeTe-metal patch antenna operating at the millimeter-waves (24-30 GHz) whose resonant frequency can be tuned and repeatedly changed upon the application of successive laser pulses.
关键词： Frequency tunable antenna,VO2 switches,BST tunable capacitance,Phase Change Materials
更新于2025-09-23 15:23:52
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Role of carbon-rings in polycrystalline GeSb2Te4 phase-change material
摘要： Carbon (C) is used to increase the overall performance of Ge-Sb-Te (GST) phase-change memory material. Yet the C configuration in polycrystalline GST and its microscopic role is unclear. Using the well-studied GeSb2Te4 as an example, this work unravels the microscopic C doping role based on ab initio calculations. Our results reveal that carbon prefers occupying the interstitials at very low C concentrations, while with a roughly critical C concentration of over 2%, carbon atoms will cluster at the grain boundaries, with very few carbon atoms might exist at the interstitials. With further increasing the C concentrations, C atoms tend to form ring-like configurations in the grain boundaries rather than chain-like configurations. This is due to that the covalent bonds in ring-like configurations are stronger than that in chain-like configurations. Further analysis on the lone-pair electrons and electronic densities of states show that C dopants significantly change the number of lone-pair electrons of surrounding atoms, thus affecting the electronic structure. Finally, the diffusion coefficient of C is estimated to be of the order of 10^-13 m^2/s at 400 K, indicating the good stability of C dopants in GeSb2Te4. Our work provides fundamental understanding on the microscopic role of C doping in GST phase-change materials and benefits for improving the properties of the recording materials by controlling the doping concentration.
关键词： Ab initio molecular dynamic simulations,Ab initio calculations,Phase-change materials,Grain boundary,GeSb2Te4,Carbon doping
更新于2025-09-23 15:23:52
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Gate-Tunable Thermal Metal–Insulator Transition in VO <sub/>2</sub> Monolithically Integrated into a WSe <sub/>2</sub> Field-Effect Transistor
摘要： Vanadium dioxide (VO2) shows promise as a building block of switching and sensing devices because it undergoes an abrupt metal-insulator transition (MIT) near room temperature, where the electrical resistivity changes by orders of magnitude. A challenge for versatile applications of VO2 is to control the MIT by gating in the field-effect device geometry. Here, we demonstrate a gate-tunable abrupt switching device based on a VO2 microwire that is monolithically integrated with a two-dimensional (2D) tungsten diselenide (WSe2) semiconductor by van der Waals stacking. We fabricated the WSe2 transistor using the VO2 wire as the drain contact, titanium as the source contact, and hexagonal boron nitride as the gate dielectric. The WSe2 transistor was observed to show ambipolar transport, with higher conductivity in the electron branch. The electron current increases continuously with gate voltage below the critical temperature of the MIT of VO2. Near the critical temperature, the current shows an abrupt and discontinuous jump at a given gate voltage, indicating that the MIT in the contacting VO2 is thermally induced by gate-mediated self-heating. Our results have paved the way for the development of VO2-based gate-tunable devices by the van der Waals stacking of 2D semiconductors, with great potential for electronic and photonic applications.
关键词： 2D materials,field-effect transistor,tungsten diselenide,phase-change materials,vanadium dioxide,metal-insulator transition,van der Waals heterostructures
更新于2025-09-23 15:22:29
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Disorder Control in Crystalline GeSb <sub/>2</sub> Te <sub/>4</sub> and its Impact on Characteristic Length Scales
摘要： Crystalline GeSb2Te4 (GST) is a remarkable material, as it allows to continuously tune the electrical resistance by orders of magnitude without involving a structural phase transition or stoichiometric changes. While well-ordered specimen are metallic, increasing amounts of disorder eventually lead to an insulating state with vanishing conductivity in the 0 K limit, but a similar number of charge carriers. Hence, GST provides ideal grounds to explore the impact of disorder on transport properties. Here, a sputter-deposition process is employed that enables growing biaxially textured GST films with large grain sizes on mica substrates. The resulting films exhibit a systematic variation between metallic and truly insulating specimen upon varying deposition temperature. Transport measurements reveal that their electron mean free path can be altered by a factor of 20, while always remaining more than an order of magnitude smaller than the lateral grain size. This proves unequivocally that grain boundaries play a negligible role for electron scattering, while intra-grain scattering, presumably by disordered vacancies, dominates. These findings underline that the insulating state and the system’s evolution toward metallic conductivity are intrinsic properties of the material.
关键词： metal–insulator transition,electrical properties,phase-change materials,disorder,structural properties
更新于2025-09-23 15:22:29