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Ovonic threshold switching in polycrystalline zinc telluride thin films deposited by RF sputtering
摘要： Chalcogenide materials of the amorphous phase with low band gaps were reported to show Ovonic threshold switching (OTS), making them suitable for selection devices in cross-point memory arrays. Herein, we report that ZnTe films with polycrystalline structures show OTS behavior. Nearly stoichiometric ZnTe thin films were deposited by an RF sputtering method. X-ray diffraction analysis indicated that the films were polycrystalline. The optical band gaps of the ZnTe films were estimated as 2.2 eV from UV-visible spectroscopy transmittance measurements. Photoluminescence measurements indicated the existence of deep-level defects in the ZnTe thin films. Although these ZnTe films have a polycrystalline structure with a relatively high band gap, I-V profiles show OTS characteristics, with a selectivity of over 104, fast threshold switching time in the sub-10 ns scale, and thermal stability up to 400°C. ZnTe also shows switching endurance for more than 109 cycles without Vth drift, maintaining its selectivity of 104. Thus, we improved the threshold switching characteristics by using a wide-band-gap and polycrystalline-structured ZnTe-based chalcogenide material. Post-annealing experiments indicated that the thermal budget of the ZnTe thin film was sufficient for stacked cross-point array structures, thereby overcoming a previous limitation of chalcogenide switching materials. This material is promising for application in high-density cross-point memory arrays as the selection device.
关键词： crystalline,ovonic threshold switching,selection device,thermal stability,zinc telluride
更新于2025-09-19 17:15:36
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Optical spectroscopy of thermal stable Na2ZnP2O7: Sm3+/ (Li+, K+) phosphors
摘要： Na2ZnP2O7 pyrophosphates doped with different concentrations of Sm3+ were synthesized successfully via a solid-state reaction process. A vibrational Raman-IR spectroscopic and diffraction analysis has been performed. The Na2ZnP2O7: Sm3+ powders were crystallized in a tetragonal lattice with P42/mnm space group. The photoluminescence (PL) emission and PL excitation (PLE) spectra were studied as a function of Sm3+ concentration. The optimal Sm3+ doping concentration in Na2ZnP2O7 host matrix is determined to be 1 mol%. In order to enhance the luminescent intensity of these phosphors, the compensator charge Li+ and K+ ions were introduced in the Na2ZnP2O7 host. Furthermore, the luminescence of Na2ZnP2O7: Sm3+ indicates good thermal stability at high temperatures. The chromaticity diagram of the Commission International de l'Eclairage (CIE) was investigated, indicating a bright orange-red emission. Hence, the obtained results indicate that the as-prepared phosphor can be a potential candidate for application in Light Emitting Diodes (LEDs).
关键词： thermal stability.,Orange-red phosphor,Na2ZnP2O7,Luminescent material
更新于2025-09-19 17:15:36
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High thermal stability and fast speed phase change memory by optimizing GeSbTe with Scandium doping
摘要： Phase change materials along the GeTe-Sb isoelectronic tie line are proved to be promising host material for optimization, based on which the well-known golden composition is developed. Here, Sc doped Ge2Sb1Te2 has been proposed for phase change memory (PCM) application, showing higher thermal stability and faster operation speed than those of the golden composition. The fast speed of 40 ns, high 10-year data retention of 160 °C, and good endurance of 6×105 cycles have made Sc0.2Ge2Sb1Te2 a promising candidate for PCM application. The impact of Sc on the microstructure is believed to be essential for those improvements in PCM.
关键词： Ge-Sb-Te alloys,High thermal stability,Fast speed,Phase change memory
更新于2025-09-19 17:15:36
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On the Decomposition of Carbonate-Based Lithium-Ion Battery Electrolytes Studied Using Operando Infrared Spectroscopy
摘要： A novel infrared diagnostic for operando measurements of electrolyte decomposition is reported. The diagnostic was used to study the decomposition of LiPF6/EC/DEC electrolyte in LCO/graphite Li-ion cells. During formative cycles spectra revealed electrochemical reduction of the EC carbonyl group, which corresponded to simultaneous SEI formation on the graphite anode. This observation supplements current theories of EC decomposition during SEI formation. Operating LCO half-cells at voltages above 4.2 V caused permanent battery capacity loss but no observable electrolyte degradation, indicating the LCO electrode is degraded at high voltage. Infrared thermometry was used to measure the temperature of the electrolyte during heated tests. Operating cells at temperatures above 70°C resulted in SEI and electrolyte decomposition. Operando spectra collected during heating revealed EC ring-opening as the mechanism of thermal degradation, which resulted in permanent capacity loss. EC thermal decomposition was identical in all cells tested, indicating a homogeneous decomposition reaction independent of electrode material or potential. Thermal stability decreased with increased salt concentration indicating that decomposition is likely catalyzed by LiPF6 decomposition products. Thus, thermal decomposition is not caused by continued reduction reactions on the anode due to SEI failure, as EC reduction and EC thermal decomposition have different mechanisms.
关键词： SEI formation,operando infrared spectroscopy,thermal stability,lithium-ion batteries,electrolyte decomposition
更新于2025-09-19 17:15:36
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Thermally Superstable Cellulosic-Nanorod-Reinforced Transparent Substrates Featuring Microscale Surface Patterns
摘要： The recent rapid expansion of thin-film, bendable, and wearable consumer (opto)electronics demands flexible and transparent substrates other than glass. Plastics are the traditional choice, but they require amelioration because of their thermal instability. Here, we report the successful conversion of a soft and thermally vulnerable polymer into a highly thermally stable transparent nanocomposite material. This is achieved by the meticulous choice of a polymer with a glass-transition temperature below 0 °C that gives stable mechanics above room temperature, reinforcing the polymer with a load-bearing hierarchical network of the incredibly strong and stable natural material: cellulose nanorods. Owing to the Pickering emulsification process, the nanocomposites inherit the self-assembled structural hierarchy from the cellulose nanorod-encapsulated resin droplets. The ameliorated nanocomposites have highly desirable high-temperature endurance (～150?180 °C) in terms of the thermomechanical, thermodimensional, and thermo-optical performance. Any photonic nano- or microstructures can be directly molded on the surface of the nanocomposites in high precision for better light management in photonic and optoelectronic applications. The highlight of this work is the demonstration of a highly thermally stable microlens array on the ameliorated transparent nanocomposite.
关键词： thermal stability,polymer nanocomposites,flexible electronics,Pickering emulsion,microlens array,nanocellulose
更新于2025-09-19 17:15:36
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Fluoroalkyl POSS with Dual Functional Groups as a Molecular Filler for Lowering Refractive Indices and Improving Thermomechanical Properties of PMMA
摘要： The dual-functionalized polyhedral oligomeric silsesquioxane (POSS) derivatives, which have the seven fluorinated alkanes and the single acrylate ester on the silica cube, were designed as a filler for lowering the refractive index (RI) and improving thermomechanical properties in poly(methyl methacrylate) (PMMA). The desired dual-functionalized POSS fillers were prepared, and because of its high miscibility, homogeneous films were readily obtained, by the casting method, with the mixture solutions containing the modified POSS and the polymers. From optical measurements, it was found that the larger effects of lowering the RIs of the PMMA matrices were observed from the modified POSS than those of the octa-substituted POSS derivatives with the homogeneous substituents. It should be mentioned that the degradation temperatures and the storage moduli were able to be greatly elevated by loading the present POSS fillers. Finally, it was demonstrated that the methacrylate ester-tethered POSS should be the most effective filler for modulating PMMA (?n = ?0.020, ?Td20 = +53 °C, ?E’/E’ = +72%).
关键词： low refractive material,thermal stability,fluoropolymer,filler,POSS
更新于2025-09-19 17:15:36
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Oxygen Atmosphere Annealing Effect on the Thermal Stability of TiO<sub>2-x</sub> Based Films for Shutter-Less Infrared Image Sensors
摘要： In the present study, we examine the thermal stability of TiO2-x (TiO) and Nb:TiO2-x (TNO) films at different exposing temperatures for the as-deposited and oxygen-atmosphere annealed samples. In order to attain the good thermal stability characteristics, lower resistance of the TiO and TNO samples were annealed in oxygen gas atmosphere at a high flow rate (5 lit/min) of oxygen gas and annealing time (25 min). From the structural studies, it can be confirmed that the annealing process gives the incorporation of oxygen atoms to its vacant sites and the phase transition improvement from the amorphous to rutile structure. The annealed samples reveal the high resistivity and temperature coefficient of resistance (TCR) values than as-deposited samples. Furthermore, it was confirmed that the annealed samples exhibits a significant improvement of thermal stability compared to the as-deposited samples. As a result, the annealed TNO sample exhibits outstanding thermal stability as well as better bolometric performance. Consequently, this study reveals that the annealed TNO sample is appropriate for shutter-less infrared image sensor devices.
关键词： TiO2-x film,Bolometric properties,Thermal stability.,Annealing
更新于2025-09-19 17:15:36
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Thermal Stability of WB2 and W–B–N Films Deposited by Magnetron Sputtering
摘要： The work is mainly to study the thermal stability including the phase stability, microstructure and tribo-mechanical properties of the AlB2-type WB2 and W–B–N (5.6 at.% N) films annealed in vacuum at various temperatures, which are deposited on Si and GY8 substrates by magnetron sputtering. For the WB2 and W–B–N films deposited on Si wafers, as the annealing temperature increases from 700 to 1000 °C, a-WB (700 °C) and Mo2B5-type WB2 (1000 °C) are successively observed in the AlB2-type WB2 films, which show many cracks at the temperature ≥ 800 °C resulting in the performance failure; by contrast, only slight α-WB is observed at 1000 °C in the W–B–N films due to the stabilization effect of a-BN phase, and the hardness increases to 34.1 GPa first due to the improved crystallinity and then decreases to 31.5 GPa ascribed to the formation of α-WB. For the WB2 and the W–B–N films deposited on WC–Co substrates, both the WB2 and W–B–N films react with the YG8 (WC–Co) substrates leading to the formation of CoWB, CoW2B2 and CoW3B3 with the annealing temperature increasing to 900 °C; a large number of linear cracks occur on the surface of these two films annealed at ≥ 800 °C leading to the film failure; after vacuum annealing at 700 °C, the friction performance of the W–B–N films is higher than that of the deposited W–B–N films, while the wear resistance of the WB2 films shows a slight decrease compared with that of the deposited WB2 films.
关键词： AlB2-type WB2 films,Thermal stability,W–B–N films,Magnetron sputtering,Mechanical properties
更新于2025-09-19 17:15:36
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Structure, thermal stability and chromaticity investigation of TiB2 based high temperature solar selective absorbing coatings
摘要： Transition metal titanium diboride (TiB2) is a promising material for the solar selective absorbing coatings due to its favorable spectral selectivity and thermal stability. In this research, spectrally selective TiB2/Al2O3 tandem absorber is deposited on stainless steel (SS), which exhibits a high solar absorptance (αs = 0.93) and a low thermal emissivity (ε = 0.11). In this tandem absorber, the TiB2 acts as the main absorber layer and the Al2O3 acts as an antire?ection layer. The tandem absorber coating is systematically characterized by ultra-high resolution scanning electron microscope (SEM), UV–vis-NIR spectrophotometer, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Micro-Raman techniques. The thermal stability in vacuum of the SS/TiB2/Al2O3 tandem absorber coatings is investigated in the temperature range of 400–800 °C for 2 h and 100 h, respectively. SEM and Raman spectra indicate that the change of surface morphology and chemical composition for the coating result in the degradation of optical performance. With the di?erent annealed temperature, the SS/TiB2/Al2O3 tandem absorber coatings exhibit di?erent color, which is further investigated using chromaticity diagram.
关键词： Chromaticity,Titanium boride,Structure,Thermal stability,Solar selective absorbing coatings
更新于2025-09-19 17:15:36
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Comparative Intrinsic Thermal and Photochemical Stability of Sn(II) Complex Halides as Next Generation Materials for Lead-Free Perovskite Solar Cells
摘要： Here we present a systematic study of the thermal and photochemical degradation pathways for a series of complex tin-based halides ASnX3 (X=I, Br) with organic (CH3NH3+, H2NCHNH2+) and inorganic (Cs+) univalent A-site cations. Thin films of tin-based perovskites were exposed to continuous light soaking and/or thermal annealing in the dark under inert atmosphere, which simulate pragmatic anoxic operation conditions of solar cells with the absorber layer isolated from the (re)action of oxygen and moisture by appropriate encapsulation. Using a set of complementary techniques such as optical spectroscopy, AFM microscopy, XRD and XPS we have elucidated that hybrid tin halide perovskites undergo rapid thermal and light-induced degradation with a complete elimination of organic cations and the formation of some volatile decomposition products and Sn(IV) halide species. On the contrary, all-inorganic compositions comprising CsSnBr3 and, particularly, CsSnI3 showed much superior thermal and photochemical stability with respect to both light and elevated temperatures. Unfortunately, all investigated complex tin halides suffer from heat- and light-induced Sn(II) disproportionation with the formation of Sn(IV) species and, presumably, metallic Sn0. This facile disproportionation and chemical degradation pathway reduces dramatically the intrinsic stability of Sn(II) complex halides and limits their potential for practical application. While this problem can be addressed using additional stabilizing additives and crystal lattice engineering approaches, the analysis of the comprehensive sets of our results solidifies further rational design approaches for development of lead-free absorbers for inorganic perovskite-based solar cells with enhanced stability for efficient and durable PV systems.
关键词： photochemical stability,perovskite solar cells,tin-based halides,Sn(II) disproportionation,thermal stability
更新于2025-09-19 17:13:59