Search Results (132)

Diamond, renowned for its exceptional electrical, physical, and chemical properties, including ultra-wide bandgap, superior hardness, high thermal conductivity, and unparalleled stability, serves as an ideal candidate for next-generation high-power and high-temperature electronic devices. Among diamond-based devices, Schottky barrier diodes (SBDs) have garnered significant attention due to their simple architecture and superior rectifying characteristics. This review systematically summarizes recent advances in diamond SBDs, focusing on both metal–semiconductor (MS) and metal–interlayer–semiconductor (MIS) configurations. For MS structures, we critically analyze the roles of single-layer metals (including noble metals, transition metals, and other metals) and multilayer metals in modulating Schottky barrier height (SBH) and enhancing thermal stability. However, the presence of interface-related issues such as high densities of surface states and Fermi level pinning often leads to poor control of the SBH, limiting device performance and reliability. To address these challenges and achieve high-quality metal/diamond interfaces, researchers have proposed various interface engineering strategies. In particular, the introduction of interfacial layers in MIS structures has emerged as a promising approach. For MIS architectures, functional interlayers—including high-k materials (Al₂O₃, HfO₂, SnO₂) and low-work-function materials (LaB₆, CeB₆)—are evaluated for their efficacy in interface passivation, barrier modulation, and electric field control. Terminal engineering strategies, such as field-plate designs and surface termination treatments, are also highlighted for their role in improving breakdown voltage. Furthermore, we emphasize the limitations in current parameter extraction from current–voltage (I–V) properties and call for a unified new method to accurately determine SBH. This comprehensive analysis provides critical insights into interface engineering strategies and evaluation protocols for high-performance diamond SBDs, paving the way for their reliable deployment in extreme conditions. Full article

The development of an integrated circuit faces the challenge of the physical limit of Moore’s Law. One of the most important “Beyond Moore” challenges is the scaling down of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) versus their increasing static power consumption. This is because, at room temperature, the thermal emission transportation mechanism will cause a physical limitation on subthreshold swing (SS), which is fundamentally limited to a minimum value of 60 mV/decade for MOSFETs, and accompanied by an increase in off-state leakage current with the process of scaling down. Moreover, the impacts of short-channel effects on device performance also become an increasingly severe problem with channel length scaling down. Due to the band-to-band tunneling mechanism, Tunnel Field-Effect Transistors (TFETs) can reach a far lower SS than MOSFETs. Recent research works indicated that TFETs are already becoming some of the promising candidates of conventional MOSFETs for ultra-low-power applications. This paper provides a review of some advances in materials and structures along the evolutionary process of TFETs. An in-depth discussion of both experimental works and simulation works is conducted. Furthermore, the performance of TFETs with different structures and materials is explored in detail as well, covering Si, Ge, III-V compounds and 2D materials, alongside different innovative device structures. Additionally, this work provides an outlook on the prospects of TFETs in future ultra-low-power electronics and biosensor applications. Full article

This study aims to explore the potential of aerogel to optimise the thermal conductivity of mineralised foam materials. Experiments were conducted with (i) addition methods of aerogel, (ii) proportion of aerogels in cement slurry, and (iii) water/cement ratio as influencing parameters for mineralised foam. Additionally, mixed Ordinary Portland Cement (OPC)/Calcium Sulphoaluminate Cement (CSA) slurries were used to test whether a synergy could be achieved. In this study, the defoaming effect of the aerogel and its mitigation to a certain extent by pre-mixing the aerogel with cement slurry were confirmed. The thermal conductivity of the mineralised foams was reduced from 0.049 to 0.036 W/(m·K) when the aerogel was up to 10 wt.% of the cement. In the specimens prepared from the mixed OPC/CSA slurry, a homogeneous circular pore structure was observed under the microscope along with a reduction in the thermal conductivity. The use of aerogels and CSA cements can effectively reduce the thermal conductivity of ultra-low-density mineralised foams to levels comparable with certain plastic foams that dominate the building insulation market. Full article

Enhanced Geothermal Systems (EGS) require thermochemically stable proppant materials capable of sustaining fracture conductivity under harsh subsurface conditions. This study systematically investigates the response of commercial proppants to coupled thermo-hydro-chemical (THC) effects, focusing on chemical stability and microstructural evolution. Four proppant types were evaluated: an ultra-low-density ceramic (ULD), a resin-coated sand (RCS), and two quartz-based silica sands. Experiments were conducted under simulated EGS conditions at 130 °C with daily thermal cycling over a 25-day period, using diluted site-specific Utah FORGE geothermal fluids. Static batch reactions were followed by comprehensive multi-modal characterization, including scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and micro-computed tomography (micro-CT). Proppants were tested in both granular and powdered forms to evaluate surface area effects and potential long-term reactivity. Results indicate that ULD proppants experienced notable resin degradation and secondary mineral precipitation within internal pore networks, evidenced by a 30.4% reduction in intragranular porosity (from CT analysis) and diminished amorphous peaks in the XRD spectra. RCS proppants exhibited a significant loss of surface carbon content from 72.98% to 53.05%, consistent with resin breakdown observed via SEM imaging. While the quartz-based sand proppants remained morphologically intact at the macro-scale, SEM-EDS revealed localized surface alteration and mineral precipitation. The brown sand proppant, in particular, showed the most extensive surface precipitation, with a 15.2% increase in newly detected mineral phases. These findings advance understanding of proppant–fluid interactions under low-temperature EGS conditions and underscore the importance of selecting proppants based on thermo-chemical compatibility. The results also highlight the need for continued development of chemically resilient proppant formulations tailored for long-term geothermal applications. Full article

Polyimide, a class of high-performance polymers, is renowned for its exceptional thermal stability, mechanical strength, and chemical resistance. However, in the context of high-integration and high-frequency electronic packaging, polyimides face critical challenges including relatively high dielectric constants, inadequate thermal conductivity, and mechanical brittleness. Recent advances have focused on molecular design and composite engineering strategies to address these limitations. This review first summarizes the intrinsic properties of polyimides, followed by a systematic discussion of chemical synthesis, surface modification approaches, molecular design principles, and composite fabrication methods. We comprehensively examine both conventional polymerization synthetic routes and emerging techniques such as microwave-assisted thermal imidization and chemical vapor deposition. Special emphasis is placed on porous structure engineering via solid-template and liquid-template methods. Three key modification strategies are highlighted: (1) surface modifications for enhanced hydrophobicity, chemical stability, and tribological properties; (2) molecular design for optimized dielectric performance and thermal stability; and (3) composite engineering for developing high-thermal-conductivity materials with improved mechanical strength and electromagnetic interference (EMI) shielding capabilities. The dielectric constant of polyimide is reduced while chemical stability and wear resistance can be enhanced through the introduction of fluorine groups. Ultra-low dielectric constant and high-temperature resistance can be achieved by employing rigid monomers and porous structures. Furthermore, the incorporation of fillers such as graphene and boron nitride can endow the composite materials with high thermal conductivity, excellent EMI shielding efficiency, and improved mechanical properties. Finally, we discuss representative applications of polyimide and composites in electronic device packaging, EMI shielding, and thermal management systems, providing insights into future development directions. Full article

Fiber–aerogel composites have gained significant attention as high-performance thermal insulation materials due to their unique microstructure, which suppresses conductive, convective, and radiative heat transfer. At room temperature, silica aerogels in particular exhibit ultralow thermal conductivity (<0.02 W/m·K), which is two to three times lower than that of still air (0.026 W/m·K). Their brittle skeleton and high infrared transparency, however, restrict how well they insulate, particularly at high temperatures (>300 °C). Incorporating microscale fibers into the aerogel matrix enhances mechanical strength and reduces radiative heat transfer by increasing scattering and absorption. For instance, it has been demonstrated that adding glass fibers reduces radiative heat transmission by around 40% because of increased infrared scattering. This review explores the fundamental mechanisms governing radiative heat transfer in fiber–aerogel composites, emphasizing absorption, scattering, and extinction coefficients. We discuss recent advancements in fiber-reinforced aerogels, focusing on material selection, structural modifications, and predictive heat transfer models. Recent studies indicate that incorporating fiber volume fractions as low as 10% can reduce the thermal conductivity of composites by up to 30%, without compromising their mechanical integrity. Key analytical and experimental methods for determining radiative properties, including Fourier transform infrared (FTIR) spectroscopy and numerical modeling approaches, are examined. The emissivity and transmittance of fiber–aerogel composites have been successfully measured using FTIR spectroscopy; tests show that fiber reinforcement at high temperatures reduces emissivity by about 15%. We conclude by outlining the present issues and potential avenues for future research to optimize fiber–aerogel composites for high-temperature applications, including energy-efficient buildings (where long-term thermal stability is necessary), electronics thermal management systems, and aerospace (where temperatures may surpass 1000 °C), with a focus on improving the materials’ affordability and scalability for industrial applications. Full article

The shortage of tellurium and toxicity of lead are major obstacles to scaling mid-temperature thermoelectric generators. We engineer quaternary lead chalcogenides with composition (Pb_0.8Ge_0.2Te)_0.95-x(PbSe)_0.05(PbS)_x (0 ≤ x ≤ 0.25), where Pb is lead, Ge is germanium, Te is tellurium, Se is selenium, S is sulfur, and x denotes the molar fraction of lead sulfide (PbS). The primary novelty lies in achieving ultra-low thermal conductivity through controlled phase segregation induced by systematic PbS incorporation. X-ray diffraction analysis reveals single-phase solid solutions up to x ≈ 0.10, with secondary PbS precipitates forming beyond this threshold. These PbS-rich phases create hierarchical microstructures that scatter phonons across multiple length scales, suppressing total thermal conductivity to 0.6 Wm⁻¹K⁻¹ at x = 0.15—approximately 84% lower than pristine lead telluride (PbTe) and approaching glass-like thermal conductivity values. Electrical transport measurements demonstrate sulfur’s role as an electron donor, enabling carrier-type control from p-type to n-type conduction. Despite moderate electrical power factors, the optimized composition (x = 0.20) achieves a peak dimensionless figure of merit ZT ≈ 0.34 at 650 K. This work demonstrates an effective strategy for tellurium-lean, lead-reduced thermoelectric materials through sulfur-induced phase segregation, providing practical design guidelines for sustainable waste heat recovery applications. Full article

Ultrafine fibers from poly(3-hydroxybutyrate) (PHB) and polyvinylpyrrolidone (PVP) and their blends with different component ratios in the range of 0/100 to 100/0 wt.% were obtained, and their structure and dynamic properties were studied. The polymers were obtained via electrospinning in solution mode. The structure, morphology, and segmental dynamic behavior of the fibers were determined using optical microscopy, SEM, EPR, DSC, and IR spectroscopy. The low-temperature maximum on the DSC endotherms provided information on the state of the PVP hydrogen bond network, which made it possible to determine the enthalpies of thermal destruction of these bonds. The PHB/PVP fiber blend ratio significantly affected the structural and dynamic parameters of the system. Thus, at low concentrations of PVP (up to 9%) in the structure of ultra-fine fibers, the distribution of this polymer occurs in the form of tiny particles, which are crystallization centers, which causes a significant increase in the degree of crystallinity (χ) activation energy (E_act) and slowing down of molecular dynamics (τ). At higher concentrations of PVP, loose interphase layers were formed in the system, which caused a decrease in these parameters. The strongest changes in the concentration of hydrogen bonds occurred when PVP was added to the composition from 17 to 50%, which was due to the formation of intermolecular hydrogen bonds both in PVP and during the interaction of PVP and PHB. The diffusion coefficient of water vapor in the studied systems (D) decreased as the concentration of glassy PVP in the composition increased. The concentration of the radical decreased with an increase in the proportion of PVP, which can be explained by the glassy state of this polymer at room temperature. A characteristic point of the 50/50% mixture component ratio was found in the region where an inversion transition of PHB from a dispersion material to a dispersed medium was assumed. The conducted studies made it possible for the first time to conduct a comprehensive analysis of the effect of the component ratio on the structural and dynamic characteristics of the PHB/PVP fibrous material at the molecular scale. Full article

Unconventional hydrocarbon reservoirs with low matrix permeability (<0.3 mD), high temperatures, and sour conditions present significant challenges for stimulation and production enhancement. This study examines field trials for a large oil and gas operator in the UAE, focusing on tight carbonate deposits with reservoir temperatures above 93 °C and high sour gas content. A novel multi-stage chemical stimulation workflow was created, beginning with a pre-flush phase that alters rock wettability and reduces interfacial tension at the micro-scale. This was followed by a second phase that increased near-wellbore permeability and ensured proper acid placement. The treatment’s core used a thermally stable, corrosion-resistant retarded acid system designed to slow reaction rates, allow deeper acid penetration, and build prolonged conductive wormholes. Simulations revealed considerable acid penetration of the formation beyond the near-wellbore zone. The post-treatment field data showed a tenfold improvement in injectivity, which corresponded closely to the acid penetration profiles predicted by modeling. Furthermore, oil production demonstrated sustained, high oil production of 515 bpd on average for several months after the treatment, in contrast to the previously unstable and low-rate production. Finally, the findings support a reproducible and technologically advanced stimulation technique for boosting recovery in ultra-tight carbonate reservoirs using the acid retardation effect where traditional stimulation fails. Full article

The use of CH₄ as an energy source is increasing every day. To increase the efficiency of CH₄ combustion and ensure that the equipment meets ecological requirements, it is necessary to measure the CH₄ concentration in the exhaust gases of combustion systems. To this end, sensors are required that can withstand extreme operating conditions, including temperatures of at least 600 °C, as well as high pressure and gas flow rate. ZnGa₂O₄, being an ultra-wide bandgap semiconductor with high chemical and thermal stability, is a promising material for such sensors. The synthesis and investigation of the structural and CH₄ sensing properties of ceramic pellets made from pure and Er-doped ZnGa₂O₄ were conducted. Doping with Er leads to the formation of a secondary Er₃Ga₅O₁₂ phase and an increase in the active surface area. This structural change significantly enhanced the CH₄ response, demonstrating an 11.1-fold improvement at a concentration of 10⁴ ppm. At the optimal response temperature of 650 °C, the Er-doped ZnGa₂O₄ exhibited responses of 2.91 a.u. and 20.74 a.u. to 100 ppm and 10⁴ ppm of CH₄, respectively. The Er-doped material is notable for its broad dynamic range for CH₄ concentrations (from 100 to 20,000 ppm), low sensitivity to humidity variations within the 30–70% relative humidity range, and robust stability under cyclic gas exposure. In addition to CH₄, the sensitivity of Er-doped ZnGa₂O₄ to other gases at a temperature of 650 °C was investigated. The samples showed strong responses to C₂H₄, C₃H₈, C₄H₁₀, NO_2, and H₂, which, at gas concentrations of 100 ppm, were higher than the response to CH₄ by a factor of 2.41, 2.75, 3.09, 1.16, and 1.64, respectively. The study proposes a plausible mechanism explaining the sensing effect of Er-doped ZnGa₂O₄ and discusses its potential for developing high-temperature CH₄ sensors for applications such as combustion monitoring systems and determining the ideal fuel/air mixture. Full article

Cubic phase SnSe-based materials have great potential in the field of thermoelectricity due to their reduced carrier scattering, increased band degeneracy, and ultra-low lattice thermal conductivity. Nevertheless, systematic studies on the influence of element doping on the thermoelectric properties of cubic SnSe-based materials are still relatively scarce. To enrich the research in this field, this work investigates the effects of Ge doping on the phase composition, electrical and thermal transport properties of cubic Sn_0.50Ag_0.25Bi_0.25Se_0.50Te_0.50 thermoelectric materials. X-ray diffraction (XRD) analysis confirmed that the Ge-doped samples exhibited a single cubic phase structure, while scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed a uniform distribution of elements within the samples. The results indicate that increasing the Ge doping content substantially enhances their electrical conductivity, albeit at the expense of elevated thermal conductivity. By optimizing the content of Ge-doping, the thermoelectric figure of merit (ZT) reached 0.74 at 750 K. Notably, while moderate Ge doping enhances electrical transport properties, excessive doping leads to a significant rise in thermal conductivity, ultimately constraining further thermoelectric performance gains. Full article

Amid the global transition toward sustainable energy, regional power grids with high wind power penetration are increasingly emerging. The implementation of frequency control is critically essential for enhancing the frequency support capability of grid-connected devices. However, existing studies indicate this may induce ULFOs (ultra-low frequency oscillations). Current research on ULFOs have been predominantly concentrated on hydro-dominated power systems, with limited exploration into systems where thermal power serves as synchronous sources—let alone elucidation of the underlying mechanisms. This study focuses on regional power grids where wind and thermal power generation coexist. Eigenvalue analysis reveals that frequency regulation control of doubly-fed induction generators (DFIGs) can trigger ULFOs. Leveraging common-mode oscillation theory, an extended system frequency response (ESFR) model incorporating DFIG frequency control is formulated and rigorously validated across a range of operational scenarios. Moreover, frequency-domain analysis uncovers the mechanism by which inertia control affects ULFO behavior, and time-domain simulations are conducted to validate the influence of DFIG control parameters on ULFOs. Full article

Platinum wires, known for their excellent electrical conductivity and durability, are widely used in high-precision industries, such as aerospace and automotive. These wires are typically coated with polyamide for protection; however, specific manufacturing processes require the coating to be selectively removed. Although traditional chemical stripping methods are effective, they are associated with high costs, safety concerns, and long processing times. As a result, laser ablation has emerged as a more efficient, precise, and cleaner alternative, especially at the microscale. In this study, ultraviolet nanosecond laser ablation was applied to remove polyamide coatings from ultra-thin platinum wires in a water-assisted environment. The presence of water enhances the process by promoting thermal management and minimizing debris. Key processing parameters, including the scanning speed, overlap percentage, and line distance, were evaluated. The optimal result was achieved at a scanning speed of 1200 mm/s, line distance of 1 µm, and single loop in water-ambient, where coating removal was complete, surface roughness remained low, and wire tensile strength was preserved. This performance is attributed to the effective energy distribution across the wire surface and reduced thermal damage due to the heat dissipation role of water, along with controlled overlap that ensured full coverage without overexposure. A thin, well-maintained water layer confined above the apex of the wire played a crucial role in regulating the thermal flow during ablation. This setup helped shield the delicate platinum substrate from overheating, thereby maintaining its mechanical integrity and preventing substrate damage throughout the process. This study primarily focused on analyzing the main effects and two-factor interactions of these parameters using Analysis of Variance (ANOVA). Interactions such as Speed × Overlap and Speed × Line Distance were statistically examined to identify the influence of combined factors on tensile strength and surface roughness. In the second phase of experimentation, the parameter space was further expanded by increasing the line distance and number of loops to reduce the overlap in the X-direction. This allowed for a more comprehensive process evaluation. Again, conditions around 1200 mm/s and 1500 mm/s with 2 µm line distance and two loops offered favorable outcomes, although 1200 mm/s was selected as the optimal speed due to better consistency. These findings contribute to the development of a robust, high-precision laser processing method for ultra-thin wire applications. The statistical insights gained through ANOVA offer a data-driven framework for optimizing future laser ablation processes. Full article

Gallium oxide (Ga₂O₃), as an ultra-wide bandgap semiconducting material, has attracted extensive research interest in recent years. Owing to its outstanding electrical and optical properties, as well as its high reliability, Ga₂O₃ shows great potential in power electronics, optoelectronics, memory devices, and so on. Among all the different polymorphs, ε-Ga₂O₃ is the second most thermally stable phase. It has a hexagonal crystal structure, which contributes to its isotropic physical properties and its suitable growth on low-cost commercial substrates, such as Al₂O₃, Si (111). However, there are far fewer research works on ε-Ga₂O₃ in comparison with the most thermally stable β phase. Aiming to provide a comprehensive view on the current works of ε-Ga₂O₃ and support future research, this review conducts detailed summarizations for the fabrication processes of ε-Ga₂O₃ thin films and the photoelectrical properties of ε-Ga₂O₃-based photodetectors. The effects of different deposition parameters on film phases and qualities are discussed. The forming mechanisms of ε phase prepared by chemical vapor depositions (CVDs) and physical vapor depositions (PVDs) are analyzed, respectively. Conclusions are made concerning the relationships between film microstructures and properties. In addition, strategies for further improving ε-Ga₂O₃ film performance are briefly summarized. Full article

Silica aerogels exhibit exceptionally low thermal conductivity and a low apparent density, as they are unique porous nanomaterials. They are extensively used in thermal insulation in terms of aerospace and building construction, adsorption processes for environmental applications, concentrating solar power systems, and so on. However, the degradation of the silica aerogel’s nanoporous structure at high temperatures seriously restricts their practical applications. Through a comprehensive review of the high-temperature structural evolution and sintering mechanisms of silica aerogels, this paper introduces two strategies to enhance their thermal stability, including heteroatom doping and surface heterogeneous structure construction. In particular, atomic layer deposition (ALD) of ultra-thin coatings on silica aerogel holds significant potential for enhancing thermal stability, while preserving its ultra-low thermal conductivity. Full article