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Effects of Hexagonal Boron Nitride Sheets on the Optothermal Performances of Quantum Dots-Converted White LEDs
摘要： Recently, quantum dots-converted white light-emitting diodes (QDs-WLEDs) are attracting numerous attention due to their high luminous efficiency and excellent color quality. As for color conversion material, the quantum dots (QDs) are commonly embedded into a low-thermal-conductivity polymer matrix. In this case, their generated heat during the photoluminescence process can hardly be dissipated into the heat sink, leading to a high working temperature and reduced lifetime. Adding particles with high thermal conductivity to the QDs layer can enhance its thermal conductivity, and thus reduce QDs’ working temperature. At the same time, these particles may affect the optical properties of QDs. However, this problem has still not been deeply studied. In this article, we systematically investigated the effects of the highly thermal-conductive hexagonal boron nitride sheets (hBNSs) on the optothermal performances of QDs/phosphor film in white light-emitting diodes (WLEDs). The thermal conductivity of QDs/phosphor film was significantly increased by 24% after adding 5wt% of 45-μm-diameter hBNS. As for the optical performance, the transparency of the silicone gel film with 45-μm-diameter hBNS was much better than that with 6–9-μm-diameter hBNS under the same weight fraction. Furthermore, the scattering effect of hBNS plays a more important role in enhancing the light conversion performance of QDs than that of phosphor. At last, a color stability test showed the increasing rate of correlated color temperature (IRCCT) of hBNS-added WLEDs are 21% smaller than that of common WLEDs after working 153 h, meaning a better QDs stability in hBNS-added WLEDs.
关键词： light conversion,quantum dots (QDs),Hexagonal boron nitride sheets (hBNSs),thermal conductivity
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Singapore (2018.7.16-2018.7.19)] 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Evaluation of the Thermal Properties for the Design of the Semiconductor Device
摘要： The more semiconductor devices progress, the more importance of caring about heat dissipation from heat generation increase. This is called “Thermal design”. Thermophysical property values like thermal conductivity and thermal expansion coefficient are used as information for thermal design. The specified values in a brochure or literature data of similar materials are usually used as the thermophysical property values for the thermal design. However, when those values are used for simulation, the results may be wrong because an actual measured value such as rate of conduction of heat of an ingredient is different from literature data or the nominal value in many cases. It is thought that there are a lot of cases without considering directionality of an ingredient (anisotropy) and influence of joint interface. We propose that we should measure these values with considering anisotropy, size effect and the bonding state and utilize them for thermal design of electronic materials used in a semiconductor device.
关键词： Thermal diffusivity,Thermal conductivity,Thin film,Thermal resistance,Bonding layer,Anisotropy,Thermal design,Transient thermal measurement
更新于2025-09-10 09:29:36
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Design strategy for ferroelectric-based polar metals with dimensionality-tunable electronic states
摘要： Since LiOsO3 was discovered, obtaining easy-accessible polar metals for research and applications has been challenging. In this paper, we present a multilayer design strategy, which is configured as ferroelectric layer/carrier reservoir layer/isolation layer/substrate, for obtaining polar metals by electrostatically doping a strained ferroelectric material in a more effective way. In the proposed configuration, both 1 unit-cell thick BaTiO3 and PbTiO3 exhibited considerable Ti off-centering with various strains, which should extend the applicability of ferroelectric-based polar metals in ultra-thin devices. Moreover, engineered by the compressive strain and the BaTiO3 thickness, the design strategy effectively achieved polar metallicity and dimensionality-tunable electronic states associated with the modulation of highly anisotropic properties such as electrical and electronic thermal conductivity, which may be helpful for designing ultra-thin, ultrafast, and low-power switch devices.
关键词： BaTiO3,design strategy,highly anisotropic conductivity,polar metal,electronic thermal conductivity,electrical conductivity
更新于2025-09-10 09:29:36
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A suspended 3-omega technique to measure the anisotropic thermal conductivity of semiconducting polymers
摘要： Anisotropic thermal conductivity can complicate the performance of semiconducting polymer thin-films in applications such as thermoelectrics and photovoltaics. Anisotropic measurements of low thermal conductivity polymers are challenging, and there are a limited number of appropriate measurement techniques. Suspended film 3-omega is an appropriate technique but has often required unfavorable microfabrication. Herein, we report on the utility of the suspended 3-omega technique that uses shadow masking, and no other microfabrication techniques, in performing anisotropic (in-plane and through-plane) thermal conductivity measurements of polymer films. We report on the necessary conditions for the validity of the 1D suspended-film heat transfer model and provide experimental guidelines for in-plane thermal conductivity measurements of polymer thin-films. Furthermore, for the first time, we report the anisotropic thermal conductivities of N2200 and a low molecular weight P3HT, which are two common n-type and p-type semiconducting polymers. Measured thermal conductivities are compared with predictions from the conventional Cahill-Pohl model and a recent empirical model that more accurately predicts the temperature dependence.
关键词： semiconducting polymers,thermal conductivity measurements,3-omega technique,anisotropic thermal conductivity,shadow masking
更新于2025-09-10 09:29:36
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Effect of stacking faults and surface roughness on the thermal conductivity of InAs nanowires
摘要： Low thermal conductivity and high power factor are desirable for thermoelectric materials. These properties can be achieved by patterning devices into nano-structures such as nanowires (NWs). The thermal conductivity can be further reduced by altering the NW geometry through the introduction of surface roughness (SR) or stacking faults (SFs). In this paper, relaxation times for scattering of phonons at SFs and SR are developed to accurately compute the impact of both effects on the thermal conductivity of InAs NWs with different diameters. It is found that similar reductions of the thermal conductivity can be obtained with SFs instead of SR. For the shortest possible distance between SFs along a NW, the room temperature thermal conductivity can be reduced to 25% compared to an ideal NW. For a NW with rough surface, a more than 80% decrease of the thermal conductivity is possible for specific roughness profiles. All available experimental data on the lattice thermal conductivity of InAs NWs confirm the theoretical models and simulation results.
关键词： surface roughness,thermal conductivity,phonon scattering,stacking faults,InAs nanowires
更新于2025-09-10 09:29:36
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Anharmonic stabilization and lattice heat transport in rocksalt <i>β</i> -GeTe
摘要： Peierls-Boltzmann transport equation, coupled with third-order anharmonic lattice dynamics calculations, has been widely used to model lattice thermal conductivity (jl) in bulk crystals. However, its application to materials with structural phase transition at relatively high temperature is fundamentally challenged by the presence of lattice instabilities (imaginary phonon modes). Additionally, its accuracy suffers from the absence of higher-than-third-order phonon scattering processes, which are important near/above the Debye temperature. In this letter, we present an effective scheme that combines temperature-induced anharmonic phonon renormalization and four-phonon scattering to resolve these two theoretical challenges. We apply this scheme to investigate the lattice dynamics and thermal transport properties of GeTe, which undergoes a second-order ferroelectric phase transition from rhombohedral a-GeTe to rocksalt b-GeTe at about 700 K. Our results on the high-temperature phase b-GeTe at 800 K con?rm the stabilization of b-GeTe by temperature effects. We ?nd that considering only three-phonon scattering leads to signi?cantly overestimated jl of 3.8 W/mK at 800 K, whereas including four-phonon scattering reduces jl to 1.7 W/mK, a value comparable with experiments. To explore the possibility to further suppress jl, we show that alloying b-GeTe with heavy cations such as Pb and Bi can effectively reduce jl to about 1.0 W/mK, whereas particle size needs to be around 10 nm through nanostructuring to achieve a comparable reduction in jl.
关键词： rocksalt β-GeTe,lattice heat transport,thermal conductivity,phonon scattering,anharmonic stabilization
更新于2025-09-10 09:29:36
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Attaining reduced lattice thermal conductivity and enhanced electrical conductivity in as-sintered pure n-type Bi2Te3 alloy
摘要： Undoped n-type Bi2Te3 bulks were prepared via the liquid state manipulation (LSM) with subsequent ball milling and spark plasma sintering processes. The sample with LSM obtains higher carrier concentration and larger effective mass compared with that without LSM, exhibiting favourable electrical transport properties. More importantly, a much reduced lattice thermal conductivity * 0.47 W m-1 K-1 (decreased by 43%) is obtained, due to the enhanced multiscale phonon scattering from hierarchical microstructures, including boundaries, nanograins and lattice dislocations. Additionally, due to the increased carrier concentration and enlarged band gap, the bipolar effect is effectively suppressed in sample BT-LSM. Consequently, zTmax * 0.66 is achieved in the sample with LSM at higher temperature of 475 K, almost 22% improvement compared with that of the contrast.
关键词： spark plasma sintering,thermoelectric,electrical conductivity,thermal conductivity,liquid state manipulation,ball milling,Bi2Te3
更新于2025-09-09 09:28:46
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[IEEE 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Shanghai (2018.8.8-2018.8.11)] 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Facile Preparation of Silver Nanoparticles Decorated Boron Nitride Nanotube Hybrids
摘要： Blending polymer with thermally conductivity Metal nanoparticles-fillers, which can reducing ITR at a high fillers contents, have recently attracted intense attention. The interfacial thermal resistance (ITR) between fillers at a high filler doping contents causes a limited improvement of thermal conductivity. Fortunately, silver nanoparticles decorated fillers have potential to improve thermally conductivity by reducing ITR between fillers at a high filler content. However, how to fabricate pony-size silver nanoparticles decorated fillers hybrids simply is still a challenge. Herein, we report a facile synthesis of decorating boron nitride nanotube (BNNT) hybrids with AgNP (10-20 nm) by replacing between the Ag+ and -OH on the defect sites of BNNT. This strategy is a viable way to prepare metal nanoparticles-fillers which can be used in highly thermal conductivity.
关键词： boron nitride nanotube,thermal conductivity,hybrids,silver nanoparticles,interfacial thermal resistance
更新于2025-09-09 09:28:46
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On the thermal conductivity of AgSbTe <sub/>2</sub> and Ag <sub/>0.82</sub> Sb <sub/>1.18</sub> Te <sub/>2.18</sub>
摘要： The temperature dependencies of the thermal conductivity of AgSbTe2 and Ag0.82Sb1.18Te2.18 were studied in the temperature range of 5–320 K. The obtained results are compared with quantitative calculations based on a theoretical model of generalized conductivity of heterogeneous systems. It was shown that a rather low value of thermal conductivity of AgSbTe2 and Ag0.82Sb1.18Te2.18 is associated with the disordering of the crystal structure, as well as phonon scattering by point defects and structural components. The presence of the second phase of Ag2Te leads to an increase in the thermal conductivity of AgSbTe2.
关键词： crystal structure disordering,AgSbTe2,thermal conductivity,Ag0.82Sb1.18Te2.18,phonon scattering
更新于2025-09-09 09:28:46
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Electron-phonon anharmonicity and low thermal conductivity in phosphorous chalcogenide ferroelectrics
摘要： The dependence of thermal conductivity with temperature has been studied for Sn(Pb)2P2S(Se)6 ferroelectrics-semiconductors, showing an ultra-low (0.5 W/m K) thermal conductivity above 250 K and the possibility to tune it at lower temperatures playing with the dopant concentration. This behavior has been explained taking into account the combination of different physical mechanisms: hopping heat conductivity in a lattice with strong electron-phonon anharmonicity linked to the stereoactivity of tin and lead cations electron lone pairs together with valence fluctuations in P2S(Se)6 groups. Besides, the presence of an incommensurate phase in the more covalent compounds, the location of tricritical points near 250 K and the peculiarities of the chemical bonding have all been correlated with the experimental behavior observed.
关键词： Ferroelectricity,Bonding,Thermal Conductivity,Structure–Property Relationship,Temperature Dependence
更新于2025-09-09 09:28:46