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An innovative technique to improve heat transmission is the use of nanofluids. Nanofluids have a significant thermal conductivity for better heat transport. For the thermal behavior of a porous polymer sheet, activation energy assessment is a useful technique for the advancement of the thermal properties of polymers. The governing model is developed for the numerical and physical analysis of heat transfer of porous polymer sheets. The present model is converted into a smooth format for the accuracy of results. The Keller box and Newton–Raphson approaches are used to calculate the thermal properties numerically. The novelty of this research is the depiction of the temperature distributions and heat transfer of chemically reacting thermophoretic nanomaterials along porous polymer stretching sheets. It is noted that the velocity and temperature of thermophoretic nanoparticles decreases and nanoparticle concentration increases as activation energy increases. It is noted that the velocity of nanoparticles increases and concentration decreases as the temperature difference increases. The enhanced heating transfer with maximum thermophoretic transportation was depicted under maximum reaction and activation energy. It is observed that the mass transfer of nanomaterials increases as the Brownian motion of thermophoretic nanomaterials enhances. [ABSTRACT FROM AUTHOR]

This paper introduces an improved Halpin–Tsai model to predict the mechanical, thermal, and electrical properties of silicon-carbide-reinforced polypropylene composites. The model considers the influence of porosity and corresponding silicon-carbide volume fractions and derives relationships between material property shape factors and the aspect ratio, silicon-carbide volume fraction, and porosity. The improved model's predictions exhibit errors of 4.00% for mechanical properties, 2.13% for thermal properties, and 2.24% for electrical properties when compared to finite element analysis. This study demonstrates that the improved Halpin–Tsai model can effectively predict the properties of silicon-carbide-reinforced polypropylene composites, aiding in the design and optimization of these materials. [ABSTRACT FROM AUTHOR]

In this investigation, specimens of magnetic nanoparticles (MNPs) consisting of Fe2O3, Fe3O4, and CoFe2O4 were synthesized in a powdered state through the co-precipitation technique. X-ray diffraction was employed for the purpose of characterizing the dimensions of the sample, yielding the following measurements: t = 64, 10, and 13 nm, respectively. Subsequently, a series of suspensions (S1, S5, S10, S15, and S20) were prepared by introducing varying amounts (x = 1, 5, 10, 15, and 20 mg) of magnetic nanoparticles into 1 ml of distilled water. A low-frequency induction heater was employed to investigate the thermal characteristics of the aforementioned MNPs. The experimental findings indicate that as the concentration of MNPs in the suspension increases, there is a corresponding decrease in the maximum temperature (Tmax) measured in degrees Celsius, the heating rate (∆T/∆t) measured in degrees Celsius per second, and the specific absorption rate measured in watts per gram. Furthermore, the conducted investigation has elucidated that these MNPs exhibit commendable thermal characteristics, thereby signifying their potential utility in the realm of magnetic hyperthermia treatment. [ABSTRACT FROM AUTHOR]

Natural fiber composites are often sought after in industries, such as automotive and aerospace, due to their low density compared to traditional synthetic composites. Sisal and jute are renewable and biodegradable resources, making them attractive from a sustainability standpoint. The effect of carbon nanotube (CNT) insertion of a composed sisal and jute fiber composite material on the thermal and mechanical characteristics is investigated in this study. The primary objective of this research is to determine the exceptional mechanical strength and heat resistance that allows the composite-filled filling CNT to perform better than others. The methodical experimental approach was used to evaluate the effect of sisal and jute matrix and different amounts of CNTs' mechanical and thermal properties. Thermal behavior is found by thermogravimetric analysis, and mechanical performance is used to qualify tensile strength, flexural strength, and impact resistance. The result suggests that CNTs may have reinforcing properties and significant tensile and flexural strength improvement. Impact resistance improved and increased the toughness of the composite material. The 7% CNT composite exhibited improvements in tensile strength of 63.9% and flexural strength of 46.6%, suggesting the synergistic reinforcing effect of CNTs. The high temperature from the use of need resistance shows promise for the composite material based on the tests of its capability for heat absorption and thermal stability. Various technical contexts are potentially useful in focusing on environmentally friendly material creation that exhibits exceptional thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

We have investigated the nonmagnetic impurity effects on magnetic and thermal properties for the spin gap system Ba3CaRu2O9, which has the Ru2O9 dimers composed of two Ru5+ spins (S = 3/2). The measurements of the magnetic susceptibility and specific heat have been carried out for the polycrystalline samples of Ba3Ca(Ru1−xNbx)2O9, where the Ru5+ spins are partially substituted by the non-magnetic Nb5+ ions. We have observed the magnetic behavior of the remained Ru5+ spins derived from breaking the singlet formation by the Nb-doping. These magnetic behaviors can be understood by the S = 3/2 free spin model under an internal magnetic field. Based on the obtained results, the mechanism of the singlet formation of Ba3CaRu2O9 is discussed. [ABSTRACT FROM AUTHOR]

Heat transport in two dimensions is fundamentally different from that in three dimensions. As a consequence, the thermal properties of 2D materials are of great interest, from both scientific and application points of view. However, few techniques are available for the accurate determination of these properties in ultrathin suspended membranes. Here, we present an optomechanical methodology for extracting the thermal expansion coefficient, specific heat, and thermal conductivity of ultrathin membranes made of 2H-TaS2, FePS3, polycrystalline silicon, MoS2, and WSe2. The obtained thermal properties are in good agreement with the values reported in the literature for the same materials. Our work provides an optomechanical method for determining the thermal properties of ultrathin suspended membranes, which are difficult to measure otherwise. It provides a route toward improving our understanding of heat transport in the 2D limit and facilitates engineering of 2D structures with a dedicated thermal performance. [ABSTRACT FROM AUTHOR]

We have investigated the nonmagnetic impurity effects on magnetic and thermal properties for the spin gap system Ba3CaRu2O9, which has the Ru2O9 dimers composed of two Ru5+ spins (S = 3/2). The measurements of the magnetic susceptibility and specific heat have been carried out for the polycrystalline samples of Ba3Ca(Ru1−xNbx)2O9, where the Ru5+ spins are partially substituted by the non-magnetic Nb5+ ions. We have observed the magnetic behavior of the remained Ru5+ spins derived from breaking the singlet formation by the Nb-doping. These magnetic behaviors can be understood by the S = 3/2 free spin model under an internal magnetic field. Based on the obtained results, the mechanism of the singlet formation of Ba3CaRu2O9 is discussed. [ABSTRACT FROM AUTHOR]

With the rise of two-dimensional (2D) materials, their excellent optical, electronic, and thermal properties different from bulk materials make them increasingly widely studied and commercialized. 2D materials' exceptional physical properties and unique structures make them an ideal candidate for next-generation flexible and wearable devices. In this work, we created a manufacturing method to successfully transfer monolayer, bilayer, and trilayer graphene onto the flexible substrate, with trenches of micron size to suspend graphene. Thermal transport measurements have been characterized to prove the suspended region. The achievement of manufacturing 2D materials in suspended condition will allow us to study their intrinsic physical properties at a mechanical strain, as well as contribute to novel flexible and wearable electronic devices and sensors. [ABSTRACT FROM AUTHOR]

For low-temperature thermoelectric applications, a bulk-phase inorganic/organic composite is prepared by introducing a conducting polymer, which is recognized as a potential organic thermoelectric material, into a representative inorganic thermoelectric material (n-type Bi2Te3). A conducting polymer, PEDOT:PSS, was chosen to prepare the Bi2Te3/PEDOT:PSS composite, wherein an intimate interface was formed between Bi2Te3 and PEDOT:PSS. The work function difference between Bi2Te3 and PEDOT:PSS created an energy barrier at the interface, possibly facilitating selective charge carrier transport depending on the energy levels of the carrier (i.e., energy filtering effect), thereby contributing to an enhancement in the Seebeck coefficient. The composite exhibited a completely different bipolar conduction tendency from pristine Bi2Te3, inducing a significant variation in the temperature dependence of the Seebeck coefficient. Furthermore, the interface may affect the carrier and phonon scattering probabilities, resulting in a considerable reduction in thermal conductivity. The composite adjustment was intensively studied to regulate the electrical and thermal properties using the energy filtering effect along with the carrier and phonon scattering probabilities, resulting in a noticeably enhanced thermoelectric performance. The temperature dependence of the performance was effectively adjusted using the bipolar conduction tendency, thereby affording the Bi2Te3/PEDOT:PSS composite exhibiting consistently high ZT values over the wide temperature range of 25–275 °C. The thermoelectric performance of Bi2Te3/PEDOT:PSS was competitive with that of previously reported high-performance n-type Bi2Te3-based analogs. The Bi2Te3/PEDOT:PSS composite is a promising n-type candidate for diverse low-temperature thermoelectric applications as a p-type Bi2Te3 counterpart. [ABSTRACT FROM AUTHOR]

Bulk crystals of β-Ga2O3 were successfully grown by the edge-defined film-fed growth method. The crystalline quality of the obtained crystals was analyzed by the method of x-ray diffractometry. The full width at half maximum of the rocking curve was about 72 arcsec. The optical bandgap was determined by analyzing the optical transmission spectra and amounted to 4.7 eV. The hot disk method was used to obtain the thermal conductivity of the sample along the [001] direction in the temperature range from 30 to 120 °C. The maximum value of thermal conductivity obtained at 30 °C was 9.25 W/(m K). [ABSTRACT FROM AUTHOR]

Cr2W3O12, one of the members of the negative thermal expansion family of A2M3O12, is reported to be prepared by the solid-state method with Cr2O3 and WO3, which was impossible before. Here, the synthesis of Cr2W3O12 is carried out by solid-state sintering. The powder mixture of Cr2O3 and WO3 is obtained using Zn(CH3COO)2 · 2H2O as the catalyst. When Zn(CH3COO)2 · 2H2O (0–25 mol. %) is added to the mixture of Cr2O3 and WO3 with 15 and 20 mol. % of excess WO3, much of the Cr2W3O12 is formed especially because of the addition of 10 and 15 mol. % of Zn(CH3COO)2 · 2H2O. For comparison, commercial ZnO is used as an addition, but its catalytic role is much lower than that of Zn(CH3COO)2 · 2H2O. The roles of addition of Zn(CH3COO)2 · 2H2O and excess WO3 are ascribed to compensate the volatility of WO3 and speed up the reaction of Cr2O3 + 3WO3 → Cr2W3O12 by the catalytic action of Zn(CH3COO)2 · 2H2O, respectively. The prepared Cr2W3O12 samples show positive thermal expansion due to the influence of excess WO3. [ABSTRACT FROM AUTHOR]

Cr2W3O12, one of the members of the negative thermal expansion family of A2M3O12, is reported to be prepared by the solid-state method with Cr2O3 and WO3, which was impossible before. Here, the synthesis of Cr2W3O12 is carried out by solid-state sintering. The powder mixture of Cr2O3 and WO3 is obtained using Zn(CH3COO)2 · 2H2O as the catalyst. When Zn(CH3COO)2 · 2H2O (0–25 mol. %) is added to the mixture of Cr2O3 and WO3 with 15 and 20 mol. % of excess WO3, much of the Cr2W3O12 is formed especially because of the addition of 10 and 15 mol. % of Zn(CH3COO)2 · 2H2O. For comparison, commercial ZnO is used as an addition, but its catalytic role is much lower than that of Zn(CH3COO)2 · 2H2O. The roles of addition of Zn(CH3COO)2 · 2H2O and excess WO3 are ascribed to compensate the volatility of WO3 and speed up the reaction of Cr2O3 + 3WO3 → Cr2W3O12 by the catalytic action of Zn(CH3COO)2 · 2H2O, respectively. The prepared Cr2W3O12 samples show positive thermal expansion due to the influence of excess WO3. [ABSTRACT FROM AUTHOR]

Coordination polymer (CP) glasses have recently emerged as a new glass state. Given the young state of the field, the discovery of concepts that guide the synthesis of CP glasses with targeted thermal and macroscopic properties is at the center of ongoing research. In our work, we draw inspiration from research on inorganic glasses, investigating the impact of Li(C2N3) as a modifier on the thermal properties of the new molecular perovskite [(C3H7)3N(C4H9)]Mn(C2N3)3 (with [C2N3]− = dicyanamide, DCA). We derive the phase diagram and show that Li(C2N3) and [(C3H7)3N(C4H9)]Mn(C2N3)3 form a eutectic mixture, in which the melting temperature is decreased by 30 K. Additionally, for the eutectic mixture at xLiDCA ≈ 0.4, a CP glass forms under slow cooling, opening interesting pathways for scalable synthesis routes of CP glasses. Given the virtually unlimited parameter space of hybrid modifiers, they will play a major role in the future to alter the glass' properties where the availability of rigorously derived phase diagrams will be important to identify material class overarching trends. [ABSTRACT FROM AUTHOR]

As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek a further understanding of the property changes across the phase boundary between "high-entropy" and "entropy-stabilized" phases. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O are investigated across this critical transition temperature via the transient plane-source method, temperature-dependent x-ray diffraction, and nano-indentation. The thermal conductivity remains constant within uncertainty across the multi-to-single phase transition at a value of ≈2.5 W/mK, while the linear coefficient of thermal expansion increases nearly 24% from 10.8 to 14.1 × 10−6 K−1. Mechanical softening is also observed across the transition. [ABSTRACT FROM AUTHOR]

Recent advancements in high-entropy alloys (HEAs) and high-entropy materials (HEMs) show promising potential for different fields of applications. The emergence of HEAs and HEMs has gained significant interest for their exciting nature and properties. As they consist of five or more elements in considerable amounts, properties vary depending on the synergistic effect of combinations of elements. By selecting proper elements and manufacturing methods, better properties can be tuned. Although many unique behaviors of HEAs and HEMs are reported due to their mixing entropy, sluggish diffusion, severe lattice distortion, and multi-metallic cocktail effects, it is necessary to summarize the data to map their feasibility and potential. For example, the combined properties of high thermal stability, thermal fatigue, creep resistance, higher stiffness, and better corrosion resistance for elevated-temperature environments in aerospace applications are pursued. Moreover, gaining the environmental compatibility and longevity of service-life-oxidation behavior of these materials is one of the crucial aspects and, hence, has been recently explored. Therefore, this Research Update aims at summarizing the recent developments and findings in oxidation behavior and highlighting the challenges and controversies for future research perspectives, particularly, on the sustainability for different applications. Moreover, besides the bulk structure, the performance of the HEAs/HEMs coatings is also reviewed. [ABSTRACT FROM AUTHOR]

Two-phase rotating detonation ramjets are considered to be suitable for aerospace applications due to their high thermodynamic cycle efficiency. These engines have an extremely complex internal flow field, in which the liquid fuel undergoes physical and chemical processes such as fragmentation, evaporation, mixing, and combustion; these processes also interact with detonation waves that have significant gradients. This makes it difficult to simulate a three-dimensional (3D) full-process rotating detonation combustion chamber. Here, based on the Euler–Lagrangian simulation method, a 3D numerical combustion chamber was simulated using kinetic theory and the constant thermal physical property parameter (TPPP) calculation method. The accuracy of these methods was then compared with the existing experimental results and theoretical values. Calculating the TPPPs using kinetic theory brought about a relatively high-pressure peak and detonation wave temperature; the detonation wave profile was also finer and more precise. The detonation wave propagation velocity of the two-phase detonation is estimated to be about 60% of the theoretical gas-phase CJ velocity. The calculation method of physical parameters has relatively little influence on the engine's operating frequency and the detonation wave's propagation velocity but has a more significant influence on the peak pressure. Constant TPPPs can be used when the Kelvin–Helmholtz–Rayleigh–Taylor model with insufficient precision is used to consider the breakup of droplets and leads to the acceleration of the propagation speed of two-phase detonation waves. [ABSTRACT FROM AUTHOR]

Two-phase rotating detonation ramjets are considered to be suitable for aerospace applications due to their high thermodynamic cycle efficiency. These engines have an extremely complex internal flow field, in which the liquid fuel undergoes physical and chemical processes such as fragmentation, evaporation, mixing, and combustion; these processes also interact with detonation waves that have significant gradients. This makes it difficult to simulate a three-dimensional (3D) full-process rotating detonation combustion chamber. Here, based on the Euler–Lagrangian simulation method, a 3D numerical combustion chamber was simulated using kinetic theory and the constant thermal physical property parameter (TPPP) calculation method. The accuracy of these methods was then compared with the existing experimental results and theoretical values. Calculating the TPPPs using kinetic theory brought about a relatively high-pressure peak and detonation wave temperature; the detonation wave profile was also finer and more precise. The detonation wave propagation velocity of the two-phase detonation is estimated to be about 60% of the theoretical gas-phase CJ velocity. The calculation method of physical parameters has relatively little influence on the engine's operating frequency and the detonation wave's propagation velocity but has a more significant influence on the peak pressure. Constant TPPPs can be used when the Kelvin–Helmholtz–Rayleigh–Taylor model with insufficient precision is used to consider the breakup of droplets and leads to the acceleration of the propagation speed of two-phase detonation waves. [ABSTRACT FROM AUTHOR]

Phonon transport properties of two-dimensional materials can play a crucial role in the thermal management of low-dimensional electronic devices and thermoelectric applications. In this study, both the empirical Stillinger–Weber (SW) and machine learning interatomic potentials are employed to investigate the lattice thermal conductivity of monolayer GeS and SnS through solving the phonon Boltzmann transport equation. The accuracy of the two types of interatomic potentials and their performance for the evaluation of thermal conductivity are verified by analyzing phonon harmonic and anharmonic properties. Our results indicate that the thermal conductivity can be predicted more accurately with a machine learning approach, while the SW potential gives rise to an overestimated value for both monolayers. In addition, the in-plane anisotropy of thermal transport properties existing in these monolayers can be confirmed by both potential models. Moreover, the origins of the deviation existing in calculated thermal conductivities, including both the effects of interatomic potential models and monolayer compositions, are elucidated through uncovering the underlying phonon transport mechanisms. This study highlights that in contrast to the machine learning approach, more careful verification is required for the simulation of thermal transport properties when empirical interatomic potential models are employed. [ABSTRACT FROM AUTHOR]

For accurate estimation of the thermal characteristics of AlGaN/GaN high electron mobility transistors on diamond, the anisotropic thermal conductivities of polycrystalline diamond (PCD) and GaN with their thickness dependences are included in the finite element simulation model, of which the PCD thermal conductivity kPCD is calculated through detailed analyses of the grain sizes in the directions parallel and vertical to the interface and relative phonon-grain boundary scatterings. In addition, the GaN thermal conductivity kGaN is the result of an approximate solution of the phonon Boltzmann transport equation. To investigate the effects of anisotropic GaN and PCD thermal conductivity, four cases of thermal conductivity models are compared: anisotropic kGaN and kPCD, anisotropic kGaN with constant kPCD, constant kGaN with anisotropic kPCD, and constant kGaN and kPCD. Then the maximum channel temperature simulated from the four above-mentioned models and the errors relative to the case of anisotropic kGaN and kPCD are investigated with respect to thermal boundary resistance, GaN layer thickness, gate pitch, heat source width, and power dissipation. The results show that the combination of anisotropic kPCD and constant kGaN overestimates the maximum channel temperature rise, and using constant kPCD and anisotropic kGaN underestimates the maximum channel temperature rise for almost all the simulations in the text. However, the channel temperature stemming from constant kPCD and kGaN is generally closer to the case with anisotropic PCD and GaN thermal conductivity. [ABSTRACT FROM AUTHOR]

Ferroelectricity and crystallinity of TiN/ZrO2/HfxZr1−xO2 (Hf:Zr = 0.43:0.57; HZO)/SiO2/Si metal–ferroelectric–semiconductor (MFS) capacitors with a top ZrO2 nucleation layer fabricated by low-temperature processes at 300 °C of atomic layer deposition and post-metallization annealing (PMA) were systematically investigated. The HZO (10 nm)-based MFS capacitors without (w/o) and with 2- and 10-nm-thick ZrO2 films (ZrO2-2 nm and ZrO2-10 nm, respectively) were found to form an extremely thin SiO2 interfacial layer (SiO2-IL) with a thickness of one or two monolayers. The HZO film in the TiN/ZrO2/HZO/SiO2/Si capacitors formed the ferroelectric orthorhombic phase even with a low thermal budget of 300 °C; in contrast, that of the w/o capacitor exhibited a predominantly amorphous structure. This result is attributed to the polycrystalline ZrO2 film acting as a nucleation layer for the crystallization of an amorphous HZO film during PMA treatment. Therefore, the remnant polarization (2Pr) increased in the order of w/o (2.2 µC/cm2) < ZrO2-2 nm (6.8 µC/cm2) < ZrO2-10 nm (15 µC/cm2). The endurance properties of the ZrO2-10 nm capacitor were free from the wake-up effect and exhibited less degradation because of the insertion of a thick ZrO2 film of 10 nm at the TiN/HZO interface, which promoted the preferential formation of the ferroelectric orthorhombic phase and prevented the formation of oxygen vacancies at the ZrO2/HZO interface. These results suggest that superior ferroelectricity with wake-up-free properties and higher fatigue resistance of HZO-based MFS capacitors can be achieved by a low-temperature fabrication technique (300 °C) using a top ZrO2 nucleation layer. [ABSTRACT FROM AUTHOR]

Scanning thermal microscopy (SThM) is capable of collecting topography feedback and probing qualitative thermal properties simultaneously. Although topography and thermal feedback signals are obtained from two independent loops without affecting each other, thermal feedback can be distorted by topography feedback, resulting in a topography-related thermal signal, defined as the artifact phenomenon. Based on this situation, the instrument thermal response is no longer accurate, and the intrinsic generation reason and affecting factors of the artifact are still not clear. In this work, different polymeric-based materials were prepared to construct varied contact geometries at the tip/sample contact interface. Identification of the artifact was performed based on the investigation of corresponding topography and thermal feedback. Generation mechanisms of the artifact were further proposed aiming at different contact situations. This work not only clarifies the generation reason and affecting factors of the artifact but also suggests the sample preparation requirements for the eliminated artifact and accurate thermal characterization through SThM. [ABSTRACT FROM AUTHOR]

In this study, we report a facile route to synthesize gelatin-based Single-Walled Carbon Nanotube (gelatin/SWCNT) nanocomposites using a simple solution casting process and investigate the impact of SWCNT filler on the structural, surface morphological, optical, electrical, and thermal features. According to the Fourier transform infrared spectroscopy study, the addition of SWCNTs improves the interaction between gelatin and SWCNTs. The field emission scanning electron microscope images showed the presence of the fillers increased with the increment of SWCNT. The roughness of the samples increased caused by high interfacial interactions between Gel and SWCNTs. The nanocomposite's optical bandgap was observed to be reduced from 2.1 to 1.9 eV as the SWCNT was varied from 0% to 0.5 vol. %. The addition of SWCNTs significantly boosted the DC electrical conductivity of the prepared samples by four orders of magnitude. The incorporation of SWCNT into the gelatin matrix was also observed to improve the nanocomposite's melting enthalpy and degree of crystallinity up to 94.5%. The gelatin/SWCNT nanocomposites were found to be decomposed completely in 4 days in the soil in an open environment. [ABSTRACT FROM AUTHOR]

The observation of the Hanbury Brown and Twiss (HBT) effect with thermal light marked the birth of quantum optics. All the thermal sources considered to date did not feature quantum signatures of light, as they consisted of independent emitters that emit uncorrelated photons. Here, we propose and demonstrate an incoherent light source based on phase-randomized spatially entangled photons, which we coin thermal biphotons. We show that in contrast to thermal light, the width of the HBT peak for thermal biphotons is determined by their correlations, leading to violation of the Siegert relation and breakdown of the speckle-fluctuations interpretation. We further provide an alternative interpretation of the results by drawing a connection between the HBT effect and coherent backscattering of light. Finally, we discuss the role of spatial entanglement in the observed results, deriving a relation between the Schmidt number and the degree of violation of the Siegert relation under the double-Gaussian approximation of spontaneous parametric down conversion. Our work reflects new insights on the coherence properties of thermal light in the presence of entanglement, paving the way for entanglement certification using disorder averaged measurements. [ABSTRACT FROM AUTHOR]

Based on the thermodynamic process of granular matter, considering the influence of temperature on energy dissipation at the mesoscopic level, a thermodynamic constitutive model, which can describe the thermal properties of saturated sand, is proposed in this paper. The model adopts the idea of double entropy theory, which introduces the concept of granular entropy to reflect the energy dissipation at the mesoscopic level. The energy dissipative structure composition and the related migration coefficient relationships are determined theoretically. Combined with the thermodynamic differential equation and the conservation and entropy increase equations, the thermodynamic identity is established; then, the mathematical expression of effective stress, plastic deformation, and granular temperature motion including the temperature effect are deduced accordingly. The relationship between the mesoscopic energy dissipation process caused by temperature change and macro-mechanical behavior is established by means of migration coefficient relationships and the energy function model. In addition, the dilatancy equation considering the state parameters is combined with the model parameters, so the stress–strain behavior of saturated sand considering the temperature effect can be described. The ability of the model to describe the thermal properties of saturated sand is verified by comparing the simulation results with the heating-induced volume change and triaxial undrained shear test results. [ABSTRACT FROM AUTHOR]

Optical and phonon interactions of Ga2O3 thin films with nanocrystalline morphology were studied at extreme temperatures. The films were grown using a sputtering technique and analyzed via temperature response transmission, Raman scattering, and high-resolution deep-UV photoluminescence (PL). Raman modes indicated that the structure corresponds to the β-phase. The optical-gap at the range of 77–620 K exhibited a redshift of ∼200 meV, with a temperature coefficient of ∼0.4 meV/K. The optical-gap at room-temperature is 4.85 eV. The electron–phonon interaction model at that temperature range pointed to a low energy phonon, ∼31 meV, that is involved in the thermal properties of the optical-gap. Detailed Urbach energy analysis indicated that defects are the dominant mechanism controlling the band-edge characteristics even at an elevated temperature regime where phonon dominance is usually expected. Defects are attributed to the disordered forms of graphite that were detected via Raman scattering and to the granular morphology of the film. A deep-UV laser with an above-bandgap exaction line of 5.1 eV was employed to map the PL of the films. The highly resolved spectra, even at room-temperature, show a strong emission of ∼3.56 eV attributed to self-trapped holes (STHs). The STH is discussed and modeled in terms of the self-trapped exciton. Moreover, a very distinct but low-intensity emission was found at 4.85 eV that agrees with the value of the optical-gap and is attributed to bandgap recombination. The intensity ratio between the STH and that of the bandgap was found to be 6:1. [ABSTRACT FROM AUTHOR]

Back in 2008, Panofsky gave an empirical formula, T = 1 1.5 W 2 / 3 , for turkey baking time, T, in hours vs turkey weight, W, in pounds, the so-called Panofsky formula or Panofsky constant. Compared to the previously existed recipes that are based on the simple linear relationship between turkey weight and baking time, the Panofsky formula provides a more accurate estimate for the baking time. For instance, a general guideline of 13–20 min/lb was widely recommended in all previous turkey baking recipes. In this work, we conduct a comprehensive study of the turkey baking process that leads to a mathematical derivation of the Panofsky formula under some approximations. We also generalize the Panofsky formula to define a general Panofsky formula, T = 1 P W 2 / 3 , where P is defined as the Panofsky constant. Under spherical approximations, we then apply an accurate physical solution of the heat transfer equation and use the rigorous solution with numerical methods to study the generalized Panofsky formula and the Panofsky constant. We found that the generalized Panofsky formula can be perfectly applied to all turkey baking scenarios for baking time calculations. Furthermore, we did a careful analysis of the Panofsky constant, which equals 1.5 in the original Panofsky formula. The dependency of the new Panofsky constant on thermal properties of the turkeys and other initial parameters of baking, e.g., initial and final center temperature of the turkeys, oven temperature, thermal conductivity, specific heat, and turkey's density, was carefully analyzed and mapped out. The Panofsky constant, P, could vary from 1.1 to 1.9 depending on these thermal parameters. [ABSTRACT FROM AUTHOR]

Flexible electronic technology is now widely developed in wearable products for humans and the detection of physiological characteristics, track tracking, and analysis of the living environment for animals and plants. In these application scenarios, flexible electronic devices (FEDs) may work outdoors for a long time and may be exposed to strong solar radiation, which may cause the temperature of FEDs to be too high and affect their stability. Hence, a quantitative description of the thermal properties of FEDs is helpful to provide a reference for the design of related FEDs. This paper establishes a three-dimensional thermal analysis model, verified by the finite element method and experiments, to analyze the temperature increase in the interface of the device under solar radiation and generated by the device itself, and analyzes the parameters that have an influence on the temperature increase in the interface, including the thickness of the substrate and the encapsulated layer and the power of the device. On this basis, the contributions for these parameters to the temperature increase in the interface are further compared. [ABSTRACT FROM AUTHOR]

Bio-degradable and eco-friendly plasticized starch/reduced graphene oxide (PS/rGO) nanocomposites were made by a simple aqueous casting method. The effect of the rGO nanofiller on the structural, surface-morphological, mechanical, thermal, and electrochemical properties of the nanocomposite was studied. rGO enhances the thermal stability and significantly improves the mechanical strength of the polymer nanocomposite. The PS/rGO nanocomposite exhibits improved electrochemical performance and a specific capacitance as high as 42.25 F/g at a current density of 0.1 mA/cm2, which is about 20 times higher than that of PS (2.51 F/g). These improved thermal, mechanical, and electrochemical properties of the PS/rGO may be attributed to the good interfacial interaction and preferential orientation of rGO sheets in the nanocomposites. The PS/rGO nanocomposites with improved thermal and mechanical properties together with enhanced electrochemical performance produced from an easy and low-cost process will provide a sustainable way for the fabrication of eco-friendly energy storage devices. [ABSTRACT FROM AUTHOR]

Structural, electronic, optical, and thermal properties of undoped and metal, M (Ni, Cu, and Zn), doped cadmium iodide (CdI2) were studied using a generalized gradient approximation of density functional theory. Lattice constants found from the theoretical studies of the structure of the undoped and doped CdI2 are in good agreement with those found in the available experimental and theoretical investigations. A strong mixing of I 5p and M 3d states is found after the doping of 3d M in CdI2, which alters the bandgap from positive to negative. Among all M (Ni, Cu, and Zn), Ni doped CdI2 with a narrow negative bandgap evolve the quantum dot level. Due to interactions between the Cd 4d and M 3d states, the measured optical and thermal properties of the doped system assessed with pure CdI2 indicate unusual behaviors, which suggest that the material can be used in different nano-electronic and electrochemical applications and in biological levels such as detection of COVID-19 pathogens. [ABSTRACT FROM AUTHOR]

In this study, the thermal properties of the powder sample of Fe3O4 magnetic nanoparticles prepared by the co-precipitation method and characterized by x-ray diffraction and transmission electron microscopy have been reported. An induction heater was used to determine the thermal properties of the sample coated with gum arabic (GA) in various concentrations, viz., X = 0, 20, 40, 60, and 80 mg/ml. The results show that the thermal properties of the sample depend on the concentration of GA. Furthermore, it was found that the specific heat capacity (CG) of the GA solution decreased with the increase in the concentration of GA. [ABSTRACT FROM AUTHOR]

A four parameter exponential-type potential known as the deformed and modified Morse potential model was proposed. The solution of the one-dimensional radial Schrӧdinger equation was obtained in the presence of the proposed potential for an arbitrary ℓ-state using a parametric Nikiforov–Uvarov method. The energy equation was used to obtain the eigenvalues for the cesium molecule and tin carbide for various states. The effects of the deformed parameter on the eigenvalues were studied. The result for the Morse potential was obtained by fixing the deformed parameter to zero. Finally, the thermal properties of the proposed potential and the Morse potential were studied in detail. The result obtained revealed that the behavior of the energy eigenvalue for the deformed and modified Morse potential with the deformed parameter (b) equals one, is same as the behavior of the energy eigenvalue for the actual Morse potential. [ABSTRACT FROM AUTHOR]

Viscosity and phase transitions were studied in the (KF-KCl)eut.-(10 mol. %)K2SiF6 system. Synchronous thermal analysis (STA) was used to study the phase transformations in the system in the temperature range of 298–1113 K. The (KF-KCl)eut.-(10 mol. %)K2SiF6 melt was found to be homogeneous at 903–993 K. The viscosity of the system under study was investigated by the rotational viscometer FRS 1600. The results may be described by linear function in coordinates ln(η) – 10 000/T at 898–984 K when viscosity changes from 2.8 to 2.1 mPa s. The melt's nonhomogeneity at 984–1055 K is manifested by the change of the temperature dependence slope. The correlation of viscosity and STA data allows determining the decomposition mechanism of K2SiF6 in the melt under study. The decomposition results in the formation of KF and SiF4. The viscosity of the investigated system was measured during the crystallization process at 876–898 K. The melt at the temperatures below 898 K was found to be in the form of suspension, which is illustrated by the deviation of the linear dependence in ln(η) – 10 000/T coordinates. At 876–898 K, the viscosity rises from 2.8 mPa s to 85.1 Pa s as temperature decreases. [ABSTRACT FROM AUTHOR]

We report systematic measurements of thermal transport properties of a Ni–Co-based superalloy at temperatures ranging from room temperature to around 800 K. In this temperature range, the thermal diffusivity and conductivity of the superalloy monotonically increase with an increase in the temperature, while the specific heat capacity is almost temperature-independent. We found that the observed thermal conductivity of the Ni–Co-based superalloy is higher than the electronic thermal conductivity expected from the Wiedemann–Franz law, indicating the substantial contribution of phonon thermal conductivity. The temperature dependence of the phonon thermal conductivity for the Ni–Co-based superalloy was observed to be weaker than that for other Ni-based alloys, which can be qualitatively explained by enhanced phonon scattering due to small γ′-phase precipitates in the superalloy. This result suggests possible tuning of the thermal conductivity of the superalloy based on phonon transport engineering. [ABSTRACT FROM AUTHOR]

Premix membrane emulsification is a quick and efficient method to prepare emulsion. Pre-emulsion was prepared by dissolving 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and cellulose acetate butyrate (CAB) in ethyl acetate, and the mixture was added to an aqueous solution containing a surfactant. Then, the droplet uniform emulsion through the transmembrane was formed. The composites with the core–shell structure were obtained after evaporating the solvent. The results displayed that the morphological structure of CL-20 based composite could change from the dumbbell-shaped structure to spherical structure with an increase in the CAB content. Based on the impact sensitivity and thermal properties, the composite enhanced the safety. Meanwhile, a remarkable enhancement in the decomposition peak temperature (Tp0) and the critical temperature of the explosion (Tb) at a relatively low content of CAB (3 wt. %, 5 wt. % and 10 wt. %) was also noted. This approach provides a faster way for the design and preparation of polymer composites. [ABSTRACT FROM AUTHOR]

An advanced multiphysics EDA (Electronic Design Automation) methodology is presented for analyzing thermal and thermomechanical problems during chip assembly and operation. The tool-prototype, which was built on the basis of this methodology, employs an anisotropic effective thermal-mechanical property methodology that replaces building complex geometries in finite element analysis simulations, thereby enhancing accuracy and performance significantly. With multiscale capabilities enabled, the tool-prototype first performs full chip stress and temperature analyses and detects hotspots. Then, a detailed analysis is performed in the selected regions of interest, with the resolution adjusted to a feature-scale by adopting a finer grid for extracting effective properties, and enables one to address feature-scale stress-induced issues such as back-end-of-line cracking or stress-induced mobility degradation of transistors. When the tool-prototype is linked with power analysis and layout EDA tools, it can perform the reliability check within the design flow. The assessment procedure will help to design power efficient chips by avoiding thermal and stress hotspots that compromise chip performance and reliability. [ABSTRACT FROM AUTHOR]

Using the first-principles calculations and combining with the phonon Boltzmann transport equation, we systematically investigated the phonon thermal transport properties of II–VI group graphenelike materials (BeO, MgO, CaO, SrS, and SrSe). The lattice thermal conductivities κ L 's of 118.68, 42.48, 11.13, 3.33, and 3.09 W/mK are obtained at 300 K in BeO, MgO, CaO, SrS, and SrSe, respectively, which is much lower than that of graphene. Strikingly, the κ L of SrS and SrSe is lower than most two-dimensional materials. Further analyses revealed that (i) the lower phonon group velocity of SrS and SrSe caused by a larger atomic mass reduces the κ L and (ii) strong anharmonicity and more available phonon scattering channels enhance phonon anharmonic scattering, resulting in lower κ L. By means of the relationship between κ L and the phonon mean-free path and the width of nanowires, the size dependence of lattice thermal conductivity is investigated as well, which provides a theoretical basis for the design of thermoelectric nanostructures. [ABSTRACT FROM AUTHOR]

The effects of the intercalated ion concentration on the cross-plane thermal conductivity and the thermal boundary conductance in the graphite/lithiated graphite interface are investigated from molecular dynamics simulations. At low ion concentration, the cross-plane thermal conductivity of the lithiated graphite is lower than that of the pristine graphite. However, as the intercalated ion concentration increases, the cross-plane thermal conductivity increases rapidly, even exceeding that of the pristine graphite at high ion concentration. By analyzing the variations of the cross-plane elastic constants and phonon dispersion relation with the intercalated ion concentration, it is found that the intercalated ions significantly increase the phonon irradiation heat flux along the cross-plane direction. Our study further shows that the variation of the intercalated ion concentrations can also modulate the thermal boundary conductance in the graphite/lithiated graphite interface. The non-equilibrium molecular dynamics simulations show that the thermal boundary conductance between graphite and lithiated graphite decreases as the lithiation level increases, which would worsen the thermal performance of Li-ion batteries. A one-dimensional atomic chain model is proposed to elaborate on how the effective spring stiffness of material influences the interfacial transmission of phonons with different frequencies. This work provides a quantitative calculation of the cross-plane thermal conductivity and thermal boundary conductance in intercalated graphite samples and is also extremely important for the thermal management and structural design of lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Humic acid (HA) was first loaded on single-walled carbon nanotubes (SWCNTs) and then the HA-loaded SWCNTs (FSWCNTs) were further incorporated into polylactic acid/poly-β-hydroxybutyrate (PLA/PHB) composites (with a weight ratio of 60/40) to synthesize the FSWCNT/PLA/PHB blend, which is designed to prepare a fully biodegradable film. Further research to assess the morphological, mechanical, barrier, and hydrophobic properties of blends was carried out. HA was successfully attached to SWCNTs by investigating the microstructure of FSWCNTs and SWCNTs. Meanwhile, the samples showed two different melting peaks, which demonstrates that the blend was immiscible. Interestingly, the crystallization of PHB was gradually accelerated by increasing the content of FSWCNTs. The blend also exhibited an effect on the oxygen barrier. Most importantly, a small amount of the FSWCNT could greatly improve the ductility of the FSWCNT/PLA/PHB composite, with the maximum tensile strength increased by 236% and the elongation at break improved by 790%. Additionally, the tensile strength, compatibility, thermal stability, and barrier abilities of the films were improved for an FSWCNT content within the range of 0.1 wt. %–0.2 wt. %. From this study, it can be observed that PLA/PHB blended with small portions of FSWCNTs may further expand the application of environmentally friendly resources to diverse applications such as flexible films, agricultural films, and so on. [ABSTRACT FROM AUTHOR]

A simple yet innovative approach has been made through a powder metallurgy route for the synthesis of aluminum–graphene (Al–Gr) composite materials for commercially viable solar thermal collectors. The Al–Gr composite (with 1 wt. % of graphene filler content) recorded an enhanced thermal conductivity of ∼280 W/mK, which is higher than that of pristine Al (∼124 W/mK), at room temperature. It has also been found that the prepared composite has a lower coefficient of thermal expansion. The structures and morphologies of the composites have been investigated in detail with the help of X-ray diffraction technique, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, etc. Furthermore, the density measurements showed that the composites retain ∼97.5% of the density of pristine aluminum even after the sintering treatment. X-ray micro-computed tomography revealed the structural integrity and non-porous nature of the samples, free from any defects and deformations. The thermal fusing of Al-based composite materials at 630 °C is found to be satisfactory with the required strength, and the composites showed at least ∼125% increase in the thermal conductivity than that of pristine Al. These results suggest that the Al–Gr composites can be deployed as solar thermal collectors and heat sink materials for thermal dissipation. [ABSTRACT FROM AUTHOR]

High concentration (>100 mM) wormlike micellar (WM) fluids are non-Newtonian with micelle lengths in the tens of nanometers. The viscoelastic properties of the fluid are affected by the structure and entanglement of the micelles and thus structural phase transitions can be indirectly studied using mechanical shear waves. Although these structural phase transitions have been extensively studied as a function of concentration, comparably less work is available on the temperature dependence. In this study, shear wave speeds (SWS) were studied as a function of temperature in a cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal)-based wormlike micellar fluid as an indicator of micellar structural changes. The heat capacity and thermal conductivity were also measured as these can be expected to change with structural phase transitions. Discontinuities in SWS were observed between 12 °C and 14 °C indicating the existence of a possible structural phase transition at this temperature. Gradual variation of the thermal properties was observed during controlled heating and cooling, while during autonomous heating from crystallization to fluid, a dramatic increase in both thermal properties peaking near 13.5 °C was observed. [ABSTRACT FROM AUTHOR]

Stability and duration of ultrasonic phantoms are still subjects of research. This work presents a tissue-mimicking material (TMM) to evaluate high-intensity therapeutic ultrasound (HITU) devices, composed of gellan gum (matrix), microparticles (scatterers), and chemicals. The ultrasonic velocity and attenuation coefficient were characterized as a function of temperature (range 20 °C–85 °C). The nonlinear parameter B/A was determined by the finite amplitude insertion substitution (FAIS) method, and the shear modulus was determined by a transient elastography technique. The thermal conductivity and specific heat were determined by the line source method. The attenuation was stable for 60 days, and in an almost linear frequency dependence (0.51f0.96 dB cm−1), at 20 °C (1–10 MHz). All other evaluated physical parameters are also close to typical soft tissue values. Longitudinal ultrasonic velocities were between 1.49 and 1.75 mm μs−1, the B/A parameter was 7.8 at 30 °C, and Young's modulus was 23.4 kPa. The thermal conductivity and specific heat values were 0.7 W(m K)−1 and 4.7 kJ(kg K)−1, respectively. Consistent temperature increases and thermal doses occurred under identical HITU exposures. Low cost, longevity, thermal stability, and thermal repeatability make TMM an excellent material for ultrasonic thermal applications. The TMM developed has the potential to assess the efficacy of hyperthermia devices and could be used to adjust the ultrasonic emission of HITU devices. [ABSTRACT FROM AUTHOR]

To study the effects of emulsifier content on the structure and thermal properties of encapsulated phase change materials (PCMs), four kinds of paraffin/chitosan (CS) macroencapsulated PCMs with different emulsifier contents were fabricated via the piercing–solidifying method. The effects of emulsifier content on macro-profile, micromorphology, thermal energy storage properties, and thermal durability of the as-prepared composite, as well as the structure of the optimal capsules, were investigated. The results show that the non-spherical degree, average diameter, and compressive strength decreased first and then increased with increase in emulsifier content, resulting in thermal energy storage capacity's increase at first and then its decrease. The optimal macro-capsules, fabricated at the critical micelle concentration of the emulsifier, present a regular spherical surface and microencapsulated paraffin wax inside. The paraffin content is as high as 85%, with a phase change latent heat of 112.6 J g−1 for melting and 118.7 J g−1 for solidification. The melting enthalpy and weight loss ratio of the optimal paraffin/chitosan composite after 600 heating/cooling cycles only changed to 0.71% and 1.17%, respectively. These results not only suggest that the piercing–solidifying method can be employed to fabricate macro-capsules with high heat storage performance and excellent thermal stability but also reveal that paraffin/CS can be used in thermal management at low temperature. [ABSTRACT FROM AUTHOR]

C6F12O (heptafluoroisopropyl pentafluoroethyl ketone) has been considered as a potential eco-friendly gas insulating medium to replace SF6, the most potent greenhouse gas, used in medium-voltage equipment. In this paper, we explored the compatibility between the C6F12O-air gas mixture and metals such as copper and aluminum to evaluate the long-term behavior of the new gas. Aging tests for the C6F12O-air gas mixture and metal were conducted, and the composition as well as the microstructure was analyzed. It was found that the interaction between C6F12O-air and copper results in the decomposition of C6F12O and corrosion of copper. Several by-products including CO2, C3F6, C4F8O, and C6F12 can be detected. Obvious color modifications and corrosion points exist after interaction. The compatibility between C6F12O-air and aluminum is superior to that between C6F12O-air and copper. Their interaction did not lead to the corrosion of aluminum. As for engineering applications, anticorrosion measures should be taken on copper to avoid the occurrence of negative chemical interactions. [ABSTRACT FROM AUTHOR]

This study aims to observe the changes in the structural characterization and physical properties of calcium-praseodymium-cobalt oxide thermoelectric materials with graphene doping. Structural characterizations were examined via X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), and Fourier Transformed Infrared Spectroscopy (FTIR) measurements. Temperature-dependent thermal conductivity and Seebeck coefficient were measured by Physical Properties Measurement System (PPMS). In the SEM images, the samples were observed to be crystalline and showed enhanced fusion with graphene doping. There were no impurities in the samples according to the EDX results and all sample components were observed in these results. The properties and structures of the bonds in the XRD results were also visible in the FTIR results. According to the PPMS results, it was determined by measurements and graphs that graphene doping provided a significant and changeable effect to the thermoelectric materials. [ABSTRACT FROM AUTHOR]

Using infrared absorption spectroscopy of hydrogen passivated β-Ga2O3 the temperature dependence of the dominant O – H vibrational line was measured between 5 and 300 K. With increasing temperature, the vibrational line shifts by Δω = 7.8 cm-1 to lower frequency. This is accompanied by a broadening of the vibrational line from Γ = 0.61 to 8.18 cm-1. The data are discussed in terms of elastic and inelastic phonon scattering and exchange coupling. Moreover, the perturbation of the hydrogen potential is evaluated. [ABSTRACT FROM AUTHOR]

While over the past decade architected cellular materials have been shown to possess unique mechanical properties, their thermal properties have received relatively little attention. Here, we investigate thermal transport in hollow nickel microlattices as a function of temperature and mechanical loading using infrared thermography. The effective thermal conductivity of hollow nickel microlattices with 99.9% porosity and 1 µm layer thickness is as low as 0.049 W m−1 K−1 at 320 K and increases to 0.075 W m−1 K−1 at 480 K, an increase we attribute to internal thermal radiation. By measuring the emissivity and using the Stephan-Boltzmann law, we estimate the contribution of thermal radiation in the effective thermal conductivity to range from 20% at 320 K to 49% at 480 K. The high porosity of microlattices strongly limits solid conduction and makes surface radiation very important in thermal transport. We further explore the impact of the strut surface condition by comparing hollow doped nickel microlattices with a smooth surface to those with a rough surface: the emissivity increases from 0.24 to 0.43, leading to increased thermal radiation contributions of 41% at 320 K to 58% at 480 K. Under mechanical loading, as the strain increases from 0% to 50%, decreasing the angle between the struts and the horizontal plane from 60° to 38°, the effective thermal conductivity decreases from 0.049 W m−1 K−1 to 0.016 W m−1 K−1. These findings indicate that architected cellular materials provide an excellent platform to control thermal properties independently on mechanical properties and to potentially develop thermal and thermomechanical metamaterials. [ABSTRACT FROM AUTHOR]

Using infrared absorption spectroscopy of hydrogen passivated β-Ga2O3 the temperature dependence of the dominant O – H vibrational line was measured between 5 and 300 K. With increasing temperature, the vibrational line shifts by Δω = 7.8 cm-1 to lower frequency. This is accompanied by a broadening of the vibrational line from Γ = 0.61 to 8.18 cm-1. The data are discussed in terms of elastic and inelastic phonon scattering and exchange coupling. Moreover, the perturbation of the hydrogen potential is evaluated. [ABSTRACT FROM AUTHOR]

The equiatomic high-entropy alloy Cr20Mn20Fe20Co20Ni20 high-entropy alloy has a valence-electron-concentration of 8 electrons/atom which is equivalent to that of Fe. The alloy being FCC is therefore electronically equivalent to FCC-Fe. We show through the thermal expansion properties that the alloy carries similar anti-Invar properties as FCC-Fe, but unlike FCC-Fe it is stable throughout its solid-state temperature-range. Therefore, by exploiting the anti-Invar property and expanding the lattice of the alloy by introducing interstitial carbon, we make Cr20Mn20Fe20Co20Ni20 ferromagnetic with a Curie temperature lying above room temperature. [ABSTRACT FROM AUTHOR]

Creating micro/nanoscale systems with one dimension substantially larger than the others is relatively straightforward, and convenient for studying thermal energy transport. This paper reports the theory for a novel noncontact micro/nanoscale temperature measurement technique named Suspended ThermoReflectance (STR). Here, the heat diffusion equation is applied to a cantilever beam of micro and nanoscale dimensions with Neumann and Dirichlet Boundary Conditions. The Neumann condition takes on constant, decaying, and periodic forms leading to steady-state, transient and harmonic solutions, respectively. Though general solutions are presented for multiple length to width ratios (L/w) in terms of geometry as well as thermal properties, silicon is studied due to its continued technological importance. The analytical solutions are compared to a 3D Finite Element Model to determine at what L/w ratio the analytical solutions accurately represent a 3D microcantilever beam. Thermal conductivity is determined using the steady-state solution. The transient solution yields the overall thermal diffusivity of the system irrespective of any frequency change, while the harmonic solution provides the phase difference along the length of the cantilever beam leading to a thermal diffusivity and the frequency dependent heat capacity. The analytical model can be used to analyze the aforementioned thermal properties for STR measurement at 4% accuracy for the system with length to width ratio of 20 and at 1% accuracy for length to width ratio of 100. [ABSTRACT FROM AUTHOR]

We have fabricated two-dimensional nanometer-scale hole array structures on GaAs doubly-clamped microelectromechanical system (MEMS) beam resonators to modulate their thermal properties. Owing to the reduction in the thermal conductance of the MEMS beams by introducing the hole array structures, the nano-porous MEMS bolometers show 2-3 times larger thermal sensitivities than the unpatterned reference sample. Furthermore, since the heat capacitance of the MEMS beams is also reduced by introducing the hole array, the thermal decay time of the patterned MEMS beams is increased only by about 30-50%, demonstrating the effectiveness of the hole array structures for enhancing the thermal sensitivities of bolometers without significantly deteriorating their operation bandwidths. [ABSTRACT FROM AUTHOR]