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- 2018
- optimization
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- parabolic trough
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- ac-dc difference
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- National Institute of Metrology
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Amorphous silicon and silicates-stabilized ZrO2 hollow fiber with low thermal conductivity and high phase stability derived from a cogon template
摘要： ZrO2 ?bers are used as refractory materials owing to their excellent thermal resistance and thermal stability. Natural cogon ?ber is a type of hollow Gramineae ?ber, and usually contains a small amount of amorphous silicon and silicates, such as SiO2, MgSiO3, CaSiO4, and Al2SiO5, which can e?ectively avoid the phase transition of ZrO2. In this study, hollow ZrO2 ?bers with remarkable thermal insulation and phase stability were synthesized using a cogon ?ber template. The results showed that the ?nal ZrO2 ?bers successfully inherited the hollow structure and amorphous substance from the cogon template. The hollow structure of the biomorphic ZrO2 ?ber helped prevent heat ?ow more e?ciently compared to solid ?bers and reduced the thermal conductivity to a signi?cant extent. In addition, the amorphous silicon and silicates played an important role in the phase stability of tetragonal ZrO2; the transformation from the tetragonal to monoclinic phase was avoided at room temperature and in humid environment.
关键词： Thermal conductivity,Amorphous silicon and silicates,Cogon ?bers,Phase stability,ZrO2 hollow ?bers
更新于2025-09-23 15:23:52
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Color-center formation and thermal recovery in X-ray and electron-irradiated magnesium aluminate spinel
摘要： We have studied the formation of color centers in magnesium aluminate spinel (MgAl2O4) by X-ray and electron irradiations near room temperature (RT). For this purpose, Cu Kα radiation and three electron energies (1.0, 1.4, and 2.5 MeV) were used for variable fluences (up to 4.2 × 10^18 cm^?2). Off-line UV-visible absorption spectra were recorded at RT as well as at low temperature down to 27 K after electron irradiation. The dependence of the production rate of F centers (oxygen vacancies) on the electron energy yields a threshold displacement energy of 190 ± 10 eV for oxygen atoms at RT, which is much higher than the determinations by molecular-dynamics simulations. Such a discrepancy is discussed on the basis of available migration data of point defects in spinel. Equipartition of F0 and F+ centers, i.e., the neutral (VO^x) and singly ionized (VO^.) oxygen vacancies, is reached for high electron fluences. Moreover, the evolution of the width of color-center absorption bands versus temperature is interpreted with the classical theory for F centers (neutral halogen vacancies) in alkali halides. The Stokes shifts are deduced from the temperature dependence of the absorption bandwidths of color centers like for alkali halides and alkaline-earth oxides. Finally, isothermal annealing data for long annealing time show a non-zero asymptotic behavior for both F0 and F+ centers. This uncommon behavior is interpreted by charge exchange processes leading to an equilibrium state between those two color centers.
关键词： thermal recovery,X-ray irradiation,color centers,threshold displacement energy,F centers,electron irradiation,absorption spectroscopy,magnesium aluminate spinel
更新于2025-09-23 15:23:52
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Crystallization kinetics and thermal stability of ZrO <sub/>2</sub> monolithic aerogel improved by SiO <sub/>2</sub> layer
摘要： ZrO2 aerogel modified by SiO2 (ZSA) was synthesized by aging ZrO2 gel in tetraethoxysilane (TEOS) solution using ZrOCl2·8H2O as precursor, and 1,2-propylene oxide (PO) as gelation agent followed by ethanol supercritical fluid drying. Crystallization kinetics and thermal stability of ZSA while calcined at elevated temperature were studied comparing with pure ZrO2 aerogel. The prepared samples were characterized using TG-DSC, N2 adsorption/desorption, SEM and TEM. The results show that thermal stability of ZSA are highly improved due to the SiO2 layer hindering the proliferation, nucleation and growth process of ZrO2.
关键词： ZrO2,thermal stability,aerogel,SiO2,crystallization kinetics
更新于2025-09-23 15:23:52
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Spoof Plasmon Interconnects— Communications beyond RC Limit
摘要： T HE inception of spoof surface plasmon polariton (SSPP) mode realized in planar, patterned conductors to manage light beyond diffraction limit at a chosen frequency garnered significant attention of late. We show that, an SSPP channel can be chosen to act in two distinct ways: first, as a regular RC limited electrical interconnect at low frequencies; and second, as an exotic, beyond RC limit communication channel near its resonant frequency by binding the electromagnetic field on its surface to the elimination of capacitance C. A dynamic transformation between these two modes can constitute an energy economic, tera-scale inter-chip hybrid communication network. We have investigated theoretical limits on the information transfer capability of SSPP interconnects. We show that, a geometry dependent trade-off relation between cross-talk limited bandwidth density and information traveling length emerges in SSPP based communication networks. According to our analysis, a bandwidth density of 1 Gbps/μm is attainable in SSPP communication network with ～ 10 mm information transfer distance, where each channel can carry ～ 300 Gbps information with nominal cross-talk.
关键词： Interconnect,Spoof Plasmon,bandwidth,Terahertz,thermal noise,information capacity
更新于2025-09-23 15:23:52
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Modeling of Radiative Properties of Polystyrene Foams Containing IR-Opacifiers
摘要： The addition of opacifiers in foams considerably reduces the radiative thermal conductivity and consequently enhances the insulation performance of the foams. In this work two different methods were developed to calculate the spectral specific extinction coefficient of opacified extruded polystyrene (XPS) foam material. Cell morphology and thermal conductivity of two identical XPS-foams, one opacified with 3 wt% carbon black as opacifier and one without opacifier, were thoroughly characterized. The experimental results were in a good agreement with the theoretical results obtained from two different computing techniques. These methods allow a good prediction of the specific extinction coefficient of arbitrary opacified foam material.
关键词： Radiative transfer,Radiative thermal conductivity,Complex refractive index,Extinction coefficient,Porous materials,Opacifiers
更新于2025-09-23 15:23:52
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Tuneable thermal expansion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate
摘要： The linear coefficient of thermal expansion for a mixture of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) is calculated using density functional theory and the Debye-Grüneisen model. The linear coefficient of thermal expansion is a key factor in thermal management (thermal conductivity, thermal stress and thermal fatigue) of microelectronic and energy devices, being common applications of the conjugated polymeric PEDOT:PSS system. The obtained value of 53×10-6 K-1 at room temperature can be rationalised based on the electronic structure analysis. The PEDOT and PSS units are bonded by a dipole-dipole interaction between S in PEDOT and H in PSS. A C-C bond in a benzene ring (PSS) or thiophene (PEDOT) is up to 13 times stronger than the S-H bond. By adjusting the population of the S-H bonds by deprotonating PSS, the linear coefficient of thermal expansion can be enhanced by 57%. This allows for tuning the thermal properties of PEDOT:PSS in cutting-edge devices.
关键词： electronic structure,thermal properties,density functional theory,conjugated polymers
更新于2025-09-23 15:23:52
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Air-stable N-doped black phosphorus transistor by thermal deposition of metal adatoms
摘要： In this work, a simple and effective thermal deposition method is described to enhance the stability and achieve n-doping of two-dimensional black phosphorus (BP), resulting the successful fabrication of logic devices. By doping with Al adatoms, the stability of BP against oxidation is enhanced and the transfer characteristics are maintained for several days under ambient conditions. Furthermore, the resulting BP is n-doping showing a negative-shifted threshold voltage and enhanced electron mobility. The mechanism of Al doping is investigated by first-principles calculation and Al induces a downward shift of the conduction band minimum and increases the Femi level. In addition, integration of bare BP and Al-doped BP enables the fabrication of various logic devices such as inverters and p?n diodes. This work reveals a facile strategy to simultaneously enhance the stability and regulate the conductivity of BP by doping with metal adatoms boding well for device applications.
关键词： n-doping,stability,black phosphorus,thermal deposition,first-principles calculation
更新于2025-09-23 15:23:52
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Uniform Cs2SnI6 Thin Films for Lead-Free and Stable Perovskite Optoelectronics via Hybrid Deposition Approaches
摘要： Herein, we synthesized uniform Cs2SnI6 films by two kinds of hybrid deposition methods by considering volume expansion involved during phase transformations. First, oblique thermal evaporation for CsI followed by SnI4 spin-coating resulted in uniform Cs2SnI6 films free of impurity phases. The rapid expansion (within 10 s of spin-coating) from CsI to Cs2SnI6 (ΔV = 106%) was accommodated by porous CsI films inhibiting crack formation. Excess SnI4 on the Cs2SnI6 after spin-coating was effectively removed by toluene washing without any damages to Cs2SnI6, and optimum deposition parameters were suggested in terms of carrier mobility. Second, annealing CsI with SnI4 vapor at 250 °C and post-annealing in the SnI4 and I2 vapor at 300 °C produced Cs2SnI6 film with complete coverage. The slow reaction (70 min for a complete conversion) provided sufficient time for complete diffusion of SnI4 into CsI without crack formation even with compact CsI. The nonradiative recombination path in Cs2SnI6 was suppressed by post-annealing in the SnI4- and I2-atmosphere, as confirmed from the enhanced photoluminescence.
关键词： Lead-free perovskite,Cs2SnI6,Electrical mobility,Oblique thermal deposition
更新于2025-09-23 15:23:52
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Nano-rheology printing of sub-0.2 <i>μ</i> m channel length oxide thin-film transistors
摘要： Down-scaling of the channel length of a fully solution-processed oxide thin-film transistor (TFT) to the nanometer-scale is the key to accessing next-generation devices for Internet-of-Things technology. In this work, we report on the fabrication of an oxide TFT with a channel length of 160 nm, which is far less than those obtained by the current direct-printing techniques, by a newly developed nano-rheology printing (nRP) method. The device had an on/off current ratio, subthreshold voltage, hysteresis, and field-effect mobility of approximately 107, 1.7 V, 0 V, and 0.16 cm2 V s-1, respectively. The key to achieving the sub-micron channel printed TFT is the introduction of a new amorphous La–Ru–O material, which exhibits relatively good conductivity and excellent nRP properties at the nanoscale, for source/drain electrode patterns. Such a short-channel TFT would never be achieved with conventional printing methods, and hence, this approach is highly important for accessing next-generation low-cost, large-area and environmentally friendly printed electronics.
关键词： nano-rheology printing,thermal-imprinting,printed electronics,solution process,oxide thin-film transistor
更新于2025-09-23 15:23:52
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Design and analysis of a multigeneration system with concentrating photovoltaic thermal (CPV/T) and hydrogen storage
摘要： Concentrated photovoltaics (CPV) is an auspicious technology to overcome the high cost problem of highly efficient multi-junction solar cells. However, due to huge concentration of light energy, high heat flux dissipation from a confined space is a challenge. The proposed system here is first of its type to apply and thermodynamically analyze the Nucleate Pool Boiling Heat Transfer (NBHT) for thermal management of CPV. In order to increase overall efficiency of CPV system, a multigeneration system using concentrated photovoltaic thermal (CPV/T) and hydrogen storage is designed and thermodynamically analyzed to fulfill electricity, hot and cold water, heating ventilation and cooling (HVAC) requirement of a residential community with continuous operation. A part of the generated electricity from CPV is used to power the electrolyzer to produce hydrogen and oxygen. The produced gases are stored, and reused by proton exchange membrane fuel cell (PEMFC) to fulfill the system's electrical energy requirement during night time and unfavourable energy conditions in day time. The resultant thermal energy from CPV/T is used for the heating, hot water and cooling requirement of the buildings by employing lithium bromide absorption chiller (AbC). A humidity harvesting system is connected, at the outlet of the absorption chiller, to convert humid air into water and ventilation air requirement of the building. The designed system performs at 67.52% overall energy efficiency, 34.89% of overall exergy efficiency and up to 1862 times concentration ratio at designed steady-state conditions. The results show that with an increase in boiling temperature of NBHT from 353 K to 373 K, the maximum concentration ratio ability increases significantly from 1392 to 2400 times due to increase in critical heat flux, while the electrical efficiency of the CPV system decreases from 28.65% to 27.09% because of increase in cell temperature. To verify the performance of the designed system for different locations, operating conditions and capacities, the effects of Direct Normal Irradiance (IDNI), ambient temperature, relative humidity ratio and the installed capacity are also analyzed by the parametric studies.
关键词： Concentrated photovoltaics,Multigeneration system,Hydrogen storage,Exergy,Solar photovoltaics/thermal system,Electrolyzer and fuel cell
更新于2025-09-23 15:23:52