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The thermal conductivity of Al_0.3Ga_0.7As is studied using photoacoustic technique and molecular dynamics simulation. Tersoff's potential is used for the simulation, for the first time, to this alloy. Thermal conductivity, determined experimentally by photoacoustic technique using our experimental setup, agrees well with the molecular dynamics simulation and literature values. The results are compared with the host GaAs and the role of DX centers in thermal property is discussed.

From femtosecond spectroscopy (fs-spectroscopy) of metals, electrons and phonons reequilibrate nearly independently, which contrasts with models of heat transfer at ordinary temperatures ($T>100$ K). These electronic transfer models only agree with thermal conductivity $(k)$ data at a single temperature, but do not agree with thermal diffusivity $(D)$ data. To address the discrepancies, which are important to problems in solid state physics, we separately measured electronic (ele) and phononic (lat) components of $D$ in many metals and alloys over $\sim$290–1100 K by varying measurement duration and sample length in laser-flash experiments. These mechanisms produce distinct diffusive responses in temperature versus time acquisitions because carrier speeds $(u)$ and heat capacities $(C)$ differ greatly. Electronic transport of heat only operates for a brief time after heat is applied because $u$ is high. High $D_{\mathrm{\text{ele}}}$ is associated with moderate $T$, long lengths, low electrical resistivity, and loss of ferromagnetism. Relationships of $D_{\mathrm{\text{ele}}}$ and $D_{\mathrm{\text{lat}}}$ with physical properties support our assignments. Although $k_{\mathrm{\text{ele}}}$ reaches $\sim 20\times k_{\mathrm{\text{lat}}}$ near 470 K, it is transient. Combining previous data on $u$ with each $D$ provides mean free paths and lifetimes that are consistent with $\sim 298$ K fs-spectroscopy, and new values at high $T$. Our findings are consistent with nearly-free electrons absorbing and transmitting a small fraction of the incoming heat, whereas phonons absorb and transmit the majority. We model time-dependent, parallel heat transfer under adiabatic conditions which is one-dimensional in solids, as required by thermodynamic law. For noninteracting mechanisms, $k\cong \mathrm{\Sigma }{C}_i{k}_i\mathrm{\Sigma }{C}_i/(\mathrm{\Sigma }{C}_i^2)$. For metals, this reduces to $k=k_{\mathrm{\text{lat}}}$ above $\sim$20 K, consistent with our measurements, and shows that Meissner’s equation $(k\cong k_{\mathrm{\text{lat}}}+k_{\mathrm{\text{ele}}})$ is invalid above $\sim$20 K. For one mechanism with multiple, interacting carriers, $k\cong \mathrm{\Sigma }{C}_i{k}_i/(\mathrm{\Sigma }{C}_i)$. Thus, certain dynamic behaviors of electrons and phonons in metals have been misunderstood. Implications for theoretical models and technological advancements are briefly discussed.

The present work discusses the study of the transport properties of the PbI₂ single crystal using an indigenously developed photoacoutistic spectrometer. The amplitude photoacoustic signal, being a function of the modulation frequency of the incident optical beam, has been measured by using the front-side detection configuration. The characteristic frequency (f_c) of the single crystal has been found to be 55 Hz. The values of thermal diffusivity, thermal conductivity and thermal effusivity in the case of PbI₂ have been derived experimentally. Their values have been compared with the values reported in a case which studied other materials in the literature. Thermal diffusion lengths have also been calculated at different chopping frequencies from 15 Hz to 90 Hz.

This study sums up the authors recent works^1–6 on steel regarding non-destructive testing and evaluation achieved between 2000 and 2008. The main related items are the establishment of a polynomial correlation⁴ between the thermal diffusivity and the Vickers' hardness HV using the recently established Boubaker polynomial expansion. This correlation is undoubtedly an efficient guide to set an NDT protocol to investigate steel-strengthened surface performance. Special attention is given to carburized steel material,⁶ as the existence of any appropriated NDT photothermal technique is demonstrated^2,5,6 to be unavoidably subjected to some restrictive conditions. The perspectives of the new features of this recent technique are discussed, with special concern with differently treated material like nitrured and nitrocarburized quenched steel.

This paper reports the results of thermal diffusivity measurement on nano Ag added Bi₂Sr₂CaCu₂O₈-Ag_x (with x = 0–1.0) ceramics using an open-cell photoacoustic instrument. The thermal diffusivities were obtained by analyzing the phase of the photo-acoustic signal of thermally thick samples using Calderon's method as well as the analysis of the phase in thermally thick region. We found that the thermal diffusivity increases with the amounts of nano Ag. The values of thermal diffusivity obtained were between 0.01250 ± 0.00128 to 0.01606 ± 0.00230 cm²/s for Ag₀ to Ag_1.0. The electrical resistance versus temperature measurements showed a metal-like behavior for all samples. However, a metal-like transition was observed between x = 0.5 and 0.7 when results of thermal diffusivity and electrical resistance measurements were analyzed together with samples x ≥ 0.7 showing the metallic behavior.

In this study, we define a synthetic parameter: optothermal expansivity as a quantitative guide to evaluating and optimizing both the thermal and the optical performance of PV–T functional materials. The definition of this parameter, ψ_AB (Amlouk–Boubaker parameter), takes into account the thermal diffusivity and the optical effective absorptivity of the material. The values of this parameter, which seems to be a characteristic one, correspond to the total volume that contains a fixed amount of heat per unit time (m³ s^-1) and can be considered as a 3D velocity of the transmitted heat inside the material.

As the PV–T combined devices need to have simultaneous optical and thermal efficiency, we try to investigate some recently proposed materials (β-SnS₂, In₂S₃, ZnS_1-xSe_x|_{0 ≤x<0.5} and Zn-doped thioindate compounds) using the newly established ψ_AB/E_g abacus.

Frequency-resolved thermal lensing (FRTL) is an approach used to measure thermal diffusivity coefficients of liquid samples. The theoretical model of this approach is based on thermal waves and the Fresnel diffraction approximation. This model predicts that only two experimental parameters are needed to estimate the thermal diffusivity of the sample. Experiments performed on pure solvents validate the theoretical predictions and confirm the feasibility of using this approach to thermally characterize liquid samples. The results show that the method is a simple and sensitive approach to determine thermal diffusivity coefficients in liquid samples.

Nano-CdS samples are synthesized by precipitation method and are annealed at 50°C, 82°C and 110°C for 5 h in air. The particle size of these annealed samples is measured by photoacoustic technique and the influence of annealing on the thermal properties are measured and discussed.

As the portable electronics industry continually drives electronic assemblies to higher functionality in smaller form factors, material compatibility and thermal dissipation issues are becoming considerably more acute. Most of the current approaches attempt to marry conventional materials technologies in order to achieve as much leverage as possible out of the established infrastructure. However, concurrent engineering of reliable, high-density electronic assemblies will require the introduction of a new material technology.

A novel base technology that is applicable to all of the major packaging and redistribution elements in an electronic module is presented. A single family of polymer/metal composite conductors can be used for chip packaging redistribution layers, multichip module or multilayer PWB interconnects, and SMT assembly. High-density multilayer circuits with landless blind and buried vias can be fabricated by filling the conductor paste into photoimaged dielectrics and thermal processing. Via layers are prepared directly on the inherently planarized circuit layer in an identical fashion. Building up layers sequentially in this manner results in multilayer circuits built on a single substrate layer and minimizes the number of interfaces between dissimilar materials. Because these composite materials are applied in an additive fabrication method, metal substrates can be employed for high thermal dissipation and excellent CTE control over a wide temperature range. Two variants of the composite conductor can successfully replace solder for surface mount and chip on board assembly. These reliable, highly-thermally and electrically conductive materials are compatible with the standard metal finishes of conventional technologies and can be adopted piecemeal as desired; however, the largest reliability and cost benefit is realized when all of the elements are used in conjunction with one another.

The conductor materials are based on interpenetrating polymer and metal networks that are formed in situ from metal particles and a thermosetting flux/binder. The metal network is formed when the alloy particles melt and react with adjacent high-melting point metal particles. Interaction also occurs between the alloy particles and pad, lead or previous trace metallizations provided they are solderable by alloys of tin. The new alloy composition created by the interdiffusion process within the bulk material has a higher melting point than the original alloy and thus solidifies immediately upon formation. This metallurgical reaction, known as transient liquid phase sintering, is facilitated by the polymer mixture. Integration of the polymer and metal networks is maintained by utilizing a thermosetting polymer system that cures simultaneously with the metallurgical reaction. Although similar in concept and performance to cermet inks, these compositions differ in that their process temperatures are compatible with conventional printed wiring board materials and that the polymeric binder remains to provide adhesion and fatigue resistance to the metallurgical network.

This paper presents the results of experimental measurements of transverse thermal diffusivity for six different industrial Ceramic Matrix Composite materials under the action of in-plane uni-axial mechanical loading. Measurements have also been taken using a one-dimensional Laser Flash technique on 8 mm diameter disc specimens without mechanical load. These results have been used to benchmark data obtained using a three-dimensional Laser Flash rig developed to operate on large mechanical test specimens whilst being loaded in a test machine. The latter facility has been used to measure the degradation of transverse thermal diffusivity with uni-axial strain. For five of the composites tested the degradation of transverse thermal diffusivity was small; and the degradation of transverse thermal diffusivity was linear with strain. One composite showed evidence of fibre pullout, and a decrease of transverse thermal diffusivity to a low value. The different behaviours observed were believed to be associated with the weave type/composite lay-up, and the selection of composite constituent materials, although insufficient data is available to make general conclusions.

A novel transient technique is developed to measure the thermal diffusivity of one-dimensional microscale wires. In this technique, a pulsed nanosecond laser is used to quickly heat the wire. After laser heating, the wire temperature decays slowly. Such temperature decay is sensed and used to determine the thermal diffusivity of the wire. A 25.4 μm thin Pt wire is characterized to verify this technique. The thermal diffusivity of multi-wall carbon nanotube bundles is measured. Based on the measurement result and the inside structure, the thermal diffusivity of individual carbon nanotubes is estimated.

In this study, we define a synthetic parameter, optothermal expansivity, as a quantitative guide to evaluating and optimizing PV–T functional materials in both thermal and optical performance. This parameter, ψ_AB (or Amlouk–Boubaker expansivity), is calculated using both the thermal diffusivity and the optical effective absorptivity of the material. The values of this parameter, which seems to be a characteristic one, correspond to the total volume that contains a fixed amount of heat per unit time (m³s^-1) and can be considered, for future use, as a 3D velocity of the transmitted heat inside the material.

Heat transfer using air jet impingement technique is one of the conspicuous tasks in the looming world of electronic packaging system. Here, the material selection of heat sink becomes one of the prior and important assignments to construct a heat sink with desired characteristic cooling rate. In order to study the material effect of heat sink over the cooling characteristic, the present work takes an initiative in plotting the Nusselt magnitude over the radial distance for different material of heat sink. This is done by computing the flow regime and heat transfer characteristic of a 2D axis symmetric geometry in commercial simulating software, ANSYS CFX. The computation of cooling characteristic in form of Nusselt profile is done using SST + Gamma–theta turbulence model. Since the prediction of heat interaction due to the intermediacy and transition in the flow regime is a unique issue of this problem. The results for Nusselt curve signifies a tangible elevation in local Nusselt value (nonuniformity) with decrease in thermal diffusivity of target surface. Also the nonuniformity is observed to vanish above a critical range (66.76mm²/s) of thermal diffusivity. This happens due to presences of abnormal turbulence of heat flow which occurs inside the target surface. Since the variation in thermal diffusivity causes some imbalance competition between the heat storage and dissipation capabilities. Above all the target surface carrying thermal diffusivity less than 66.76mm²/s possesses a dominating heat storage capability, on behalf of which some heat transfer occurring in near jet and far jet regions are being restricted. These are transferred towards stagnation region in radial direction.

Thermal conductivity and thermal diffusivity of blended clays have been studied with special reference to Ukrainian clay. The blends were made of three different clays available locally in western part of Rajasthan. Thermal conductivity and thermal diffusivity were determined using the transient plane source (TPS) technique at room temperature and normal pressure. It was found that thermal conductivity and thermal diffusivity of the blends reported maximum at temperature 1200° C and near in the values of Ukrainian clay. The thermal conductivity of blend B2 reported maximum value (1.29 W/m-k) in the present study.

The more accurate measurement method for the thermal diffusivity using photothermal displacement spectroscopy was developed. In previous works, thermal diffusivities for materials with a finite thickness were determined by the deformation angle and phase angle as the relative position between the pump and probe beams. In this study, however, a complete theoretical treatment and experimental measurement by the photothermal displacement technique has been performed for semi-infinite solid materials. To verify the developed method, the measurement has been carried out about the pure copper and nickel alloy with a finite and a semi-infinite thickness. In results, the measured values for a semi-infinite materials have the accordance with the literature values within 1% standard deviation, while those for a finite materials show about 3% one. Consequently, the semi-infinite solid model was proposed as a high accurate measurement method for thermal conductivities.