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The present work employs density functional theory to explore the structural, optoelectronic, and thermoelectric attributes of the halide-based double perovskite A2GeSnF6 (A = K, Rb, and Cs) compounds. The stable phonon dispersion spectrum affirms dynamical stability, whereas the enthalpy of formation and tolerance factor evaluated collectively verify structural stability. Considering the Tran Blaha modified Becke Johnson potentials (mBJ), the predicted direct band gaps along the symmetry point are 3.19 eV for K2GeSnF6, 3.16 eV for Rb2GeSnF6 and 3.12 eV Cs2GeSnF6. According to an in-depth examination of the optoelectronic features, A2GeSnF6 (A = K, Rb, and Cs), double perovskites are assuring contenders for optoelectronic devices due to their suitable bandgap. The extremely high figure of merit values (0.94–0.97) obtained from the numerical calculation of power factor and thermal conductivity suggest the intriguing prospects of these compositions for thermoelectric devices. These studies offer a perceptive comprehension of the materials for their potential applications in the future. [ABSTRACT FROM AUTHOR]

Earth-adequate quaternary chalcogenides like Cu2NiSnS4 with more complex crystal structures can become non-toxic and cost-effective thermoelectric (TE) materials. TE materials, by employing the energy filtering effect through appropriate energy bandgap, have enhanced their TE efficiency. The composition of CuO in Cu2NiSnS4 matrix has enhanced the Seebeck coefficient (S) and declined the thermal conductivity (κ) simultaneously, due to the decrement of carrier concentration (n), by increasing the wt% of CuO in the composites. The highest power factor of 270.88 μW m−1 K−2 at 573 K is recorded for 30 wt% composites. The 30 wt% composite material thermal conductivity exhibited a low value of 0.442 W m−1 K−1 through stronger phonon scattering at the interface boundaries formed between the Cu2NiSnS4 matrix and CuO compositions. A maximum zT of 0.35 for the Cu2NiSnS4/30 wt% CuO composite was obtained, 75% larger than that of the Cu2NiSnS4 matrix at 573 K. This strategy of introducing metal oxides into the metal sulphide matrix for obtaining efficient TE performance could be extended to other eco-friendly quaternary chalcogenides. [ABSTRACT FROM AUTHOR]

Developing flexible thermal management materials is quite urgent for emerging flexible electronics and wearable devices. Here, a novel strategy is used to prepare hydroxyl-functionalized boron nitride@polyurethane (BNOH@PU) composites with desired BN orientation in the in-plane direction through the foaming process of PU and hot-pressing. BNOH flakes can react with isocyanates to form amido linkages, which is beneficial for reducing interfacial thermal resistance (ITR) between BNOH and PU. In addition, BNOH flakes will be rearranged along the direction of PU backbones through the volume compression of the foaming process and trend to be oriented in the in-plane direction after hot-pressing. The out-of-plane or in-plane thermal conductivities of the composites are 1.69 and 3.19 W m−1 K−1 at 30 wt% BNOH content, and the corresponding thermal conductivity enhancement (TCE) is 1986% and 3838%, respectively. Meanwhile, BNOH@PU exhibited low ITR between BNOH flakes (1.252 × 10−7 K m2/W), good flexibility and stretchability, which was a promising thermal management material for wearable devices. The interfacial thermal resistance (ITR) and the phonon scattering between fillers and polymer matrix could be reduced significantly via the hydroxyl functionalization of BN. In-plane thermal conductivity enhanced BNOH@PU composites with desired BN orientation in the in-plane direction through the foaming process of PU and hot-pressing. [ABSTRACT FROM AUTHOR]

Strain engineering has been proved to be an effective approach to modulate various physical properties in two-dimensional (2D) materials with flexible structures. In this work, based on first-principles calculations, the impact of in-plane biaxial tensile strain on lattice thermal conductivity of bilayer MoSe2, involving different stacking modes, has been systematically investigated by iteratively solving phonon Boltzmann transport equation. Simultaneously, potential regulations of interfacial anharmonic effect in phonon transport via in-plane strain can also be clarified through a comparative study between the monolayer and bilayer cases. Our results indicate that thermal transport in both the monolayer and bilayer MoSe2 is governed by low-frequency phonon branches, and the bilayer exhibits a notably reduced thermal transport capacity due to interlayer interaction existing in van der Waals homogeneous stacks. As the in-plane tensile strain is applied, a significant suppression in thermal transport capacity per layer can be further achieved in both the monolayer and bilayer cases, implying great potential for effective thermal management in 2D MoSe2 via strain engineering. Besides, the role of homogeneous interface in phonon transport of bilayer MoSe2 can also be regulated by the exerted in-plane tensile strain, which slows the decline in thermal conductivity with strain and leads to a larger thermal sheet conductance in the strained bilayer compared to the monolayer. [ABSTRACT FROM AUTHOR]

The effect of defects on the thermal properties of Ψ-Graphene Nanotubes (Ψ-GNTs) is investigated in this study using Molecular Dynamics simulations. The results reveal that the thermal properties of Ψ-GNTs are profoundly impacted by the presence of defects. Specifically, a significant reduction in thermal conductivity is observed with increasing defect concentrations. This reduction is attributed to the scattering of phonons by the defects, which leads to increased phonon–phonon interactions and decreased thermal transport efficiency. Furthermore, the effect of temperature on the thermal properties of defective Ψ-GNTs is investigated. The findings demonstrate a nonlinear decrease in thermal conductivity with increasing temperature. [ABSTRACT FROM AUTHOR]

We critically address the recent experiment by L. Chen et al. [Science 382, 907 (2023)] on nonequilibrium transport and noise in a strange metal YbRh2Si2 patterned into the nanowire shape. In the long device, resistivity, differential resistance and current noise data seem to be consistent allowing us to extract electron–phonon coupling and the temperature dependence of electron–phonon scattering length. The obtained values can be reconciled with the experimental data for the short device only assuming the significant contact resistance. We discuss its possible origin as due to the current redistribution between YbRh2Si2 and its gold covering, and reveal that this redistribution contact resistance should be proportional to the YbRh2Si2 resistivity. We also discuss some subtleties of the noise measurements. Overall, neglecting electron–phonon energy relaxation even in the shortest devices is arguable so that the observed shot noise suppression can hardly be attributed to the failure of quasiparticle concept. [ABSTRACT FROM AUTHOR]

Brillouin scattering in water has been proposed as a method to measure temperature profiles in the ocean. Spontaneous Brillouin scattering can be understood as light scattering on phonons in the water originating from thermal fluctuations. The scattering signal usually features three peaks in its spectrum, of which one is attributed mainly to scattering from suspended particles and shows no frequency shift from the incident light, while the other two are shifted by the phonon frequency leading to a linear dependency of this Brillouin shift to the speed of sound. The speed of sound is dependent on temperature and salinity. To measure temperature and salinity independently, a second measurement parameter is necessary. The spectral width of the Brillouin lines constitutes a measure for the phonon lifetime and depends on various macroscopic water properties. This linewidth was investigated in a laboratory using a scanning FPI (Fabry-Perot interferometer) over a temperature range from 1.8 °C to 35 °C and 13 salinities from 0 ppt to 36 ppt. A strong temperature dependence was confirmed and a weaker, nonlinear dependency on salinity was found. An empirical model was created to describe the data for the purpose of enabling remote sensing of water temperature profile and salinity simultaneously in the future. [ABSTRACT FROM AUTHOR]

Recently, thermoelectric (TE) materials have seized great attention for their role in clean energy conversion applications. Cu2S are p-type super-ionic conductors featuring a narrow band gap of 1.7 eV while exhibiting outstanding thermoelectric characteristics. The Cu2S matrix and the CuO nanoinclusions were successfully synthesized via solvothermal and hydrothermal routes, respectively. The morphological observations made through scanning and transmission electron microscope ensured the homogeneous distribution of CuO nanoinclusions in the Cu2S matrix, hence, the formation of standard Cu2S/CuO composites. In this work, we have introduced a "combined strategy" to boost the figure of merit (zT). The Seebeck coefficient reached the maximum of 271.86 μVK−1 at 573 K for the 20 wt% CuO sample (a 71.45% gain when compared to the pure Cu2S) owing to the filtration of low-energy carriers at the CuO potential barriers (2.5 eV). The Cu2S/20 wt% CuO sample achieved the minimum thermal conductivity values. At 573 K, We recorded a vast power factor value of 952.66 μWm−1 K−2 (32.23% gain) for the Cu2S/15 wt% CuO sample. These values are vastly higher than previously reported for the copper sulfides-based TE materials. Consequently, an optimised zT value of 0.44 (214.29% gain) was accomplished for the Cu2S/15 wt% CuO sample at 573 K. The strategy presented in our study can also be extended to other TE materials, especially for the promising copper chalcogenides to improve their zT values. [ABSTRACT FROM AUTHOR]

In this study, ceramic samples of Bi2Sr2Co2Oy + v wt% B2O3 (v = 0.0, 0.1, 0.2, 0.3, 0.4) were synthesized using the solid state reaction method, and the influence of B2O3 additive on their microstructure and thermoelectric properties were investigated. On one hand, the B2O3 additive acted as a sintering aid, enhancing carrier mobility. On the other hand, B2O3 dispersion served as a nano-second-phase, increasing hetero-interfaces and strengthen phonon scattering, thereby effectively suppressing lattice thermal conductivity. By dual optimization of both electric and thermal transport performance, the Bi2Sr2Co2Oy + 0.3 wt% B2O3 sample achieved a high ZT value (thermoelectric figure of merit) of 0.31 at 923 K, which was improved by approximately 33% compared with the pristine Bi2Sr2Co2Oy sample. [ABSTRACT FROM AUTHOR]

Over the years, Bi2Te3-based alloys have garnered considerable recognition as exceptional thermoelectric materials. Researchers have diligently pursued avenues to enhance the properties of these materials, with a primary focus on reducing thermal conductivity while maintaining optimal electrical performance. Nonetheless, achieving this delicate balance has proven to be a formidable challenge. In this study, we present a novel synergistic optimization approach that entails manipulating the grain refinement and porous structure of the material through precise adjustments in cooling rate and relief temperature during the direct current hot pressing process. By meticulously controlling these parameters, we successfully engineered a multiscale microstructure that effectively promotes phonon scattering. Simultaneously, we optimized carrier concentration. The outcomes of our investigation are truly remarkable, as we attained a peak zT value of approximately 1.23 at 325 K, accompanied by an outstanding average zTave of approximately 1.2 across the temperature range of 300–400 K in the 6.5% porosity-Bi0.35Sb1.65Te3 sample. These findings underscore the efficacy of the multiple synergies employed in our study. Moreover, our research provides a solid foundation for further exploration of complex micro structure modification techniques. [ABSTRACT FROM AUTHOR]

Nano-coatings hold the key to unlocking the vital potential of three-phase nanocomposites by urgently addressing thermal stress concentration. Consequently, the characteristics of double-interfacial heat flux and thermal stress have garnered considerable attention. In this paper, we introduce a set of interfacial conditions aimed at modeling double-interfacial phonon scattering and double-interfacial elasticity in three-phase nanocomposites. We derive closed-form solutions for the thermo-elastic field surrounding a circular nano-inclusion containing the nano-coatings. Through control over the nano-coating thickness and their properties, including thermal conductivity and interfacial phonon scattering coefficient, we can achieve a "neutral inclusions and coatings" temperature field, promoting uniform heat transfer. However, it is important to note that this approach leads to a noticeable increase in thermal stresses at the interfaces and the emergence of stress discontinuities due to the double-interfacial phonon scattering effect. Furthermore, the impact of coating thickness, coating thermal conductivity, and coating thermal expansion coefficient on the maximum interfacial thermal stress exhibits significant variability. Crucially, our findings reveal that adjusting the coating parameters can result in a substantial reduction in the overall thermal stress field's maximum value. This discovery carries significant implications for the design of nanocomposites and holds great promise for various applications. [ABSTRACT FROM AUTHOR]

The effect of inelastic scattering on the transmission of neutrons by a single crystal of Bi4Ge3O12 (BGO) has been investigated experimentally and theoretically. The results of an experiment on measuring the temperature dependence of the transmission of monochromatic neutrons by a BGO single crystal are presented. The dependence obtained in the experiment is well described by a calculation based on consideration of inelastic neutron scattering at phonons. The analysis indicates the existence of a temperature-independent contribution to the total cross section of neutron interaction with a BGO single crystal. It is assumed that this contribution is due to the presence of a small amount of impurities that strongly absorb neutrons in the studied specimen. [ABSTRACT FROM AUTHOR]

Highlights: The flexible composite film presents ultrahigh thermal conductivity and good thermal management performance in electronic devices. An original "self-modified nanointerface" strategy is used to reduce the interfacial thermal resistance between boron nitride and the polymer matrix. The ideal phonon spectrum matching between boron nitride nanocrystals and fillers as well as the strong interaction between self-modified fillers and the polymer matrix are the two major contributors to decrease the interfacial thermal resistance. While boron nitride (BN) is widely recognized as the most promising thermally conductive filler for rapidly developing high-power electronic devices due to its excellent thermal conductivity and dielectric properties, a great challenge is the poor vertical thermal conductivity when embedded in composites owing to the poor interfacial interaction causing severe phonon scattering. Here, we report a novel surface modification strategy called the "self-modified nanointerface" using BN nanocrystals (BNNCs) to efficiently link the interface between BN and the polymer matrix. Combining with ice-press assembly method, an only 25 wt% BN-embedded composite film can not only possess an in-plane thermal conductivity of 20.3 W m−1 K−1 but also, more importantly, achieve a through-plane thermal conductivity as high as 21.3 W m−1 K−1, which is more than twice the reported maximum due to the ideal phonon spectrum matching between BNNCs and BN fillers, the strong interaction between the self-modified fillers and polymer matrix, as well as ladder-structured BN skeleton. The excellent thermal conductivity has been verified by theoretical calculations and the heat dissipation of a CPU. This study provides an innovative design principle to tailor composite interfaces and opens up a new path to develop high-performance composites. [ABSTRACT FROM AUTHOR]

Here, we performed a systematic DFT study assisted by the workflow framework SimStack for the mechanical and thermodynamic properties of the clay mineral lizardite in pristine and six different types of O vacancies configurations. In most cases, the defect caused a structural phase transition in the lizardite from the trigonal (pristine) to the triclinic phase. The results show that oxygen vacancies in lizardite significantly reduce the lattice thermal conductivity, accompanied by an elastic moduli reduction and an anisotropy index increase. Through the P–V relation, an increase in compressibility was evidenced for vacancy configurations. Except for the vacancy with the same crystalline structure as pristine lizardite, the sound velocities of the other vacancy configurations produce a decrease in these velocities, and it is essential to highlight high values for the Grüneisen parameter. We emphasize the great relevance of the punctual-defects introduction, such as O vacancies, in lizardite, since this microstructural design is responsible for the decrease of the lattice thermal conductivity in comparison with the pristine system by decreasing the heat transfer ability, turning lizardite into a promising candidate for thermoelectric materials [ABSTRACT FROM AUTHOR]

Fe-based amorphous coatings were deposited on AZ31B alloy and Q235 steel substrates though detonation spray. Parallel comparison experiments on deposition characteristics, residual stresses, interfacial toughness, bonding strengths, three-point bending behaviors, and tribological behaviors of the coatings were investigated to elucidate the deposition mechanisms and mechanical properties of the Fe-based amorphous coatings on magnesium alloy substrates. The results revealed that the coating on the AZ31B substrate was well bonded via physical and mechanical bonding mechanisms, and the interface was found to be highly resilient against interfacial stresses generated from substrate deformations. However, the high thermal conductivity and low hardness of the magnesium alloy hindered the flattening of the sprayed particles during the deposition process, which compromised the bonding strength of the lamellae layers, thus reducing the cohesive strength and the wear resistance of the AZ31B-substrate coating. [ABSTRACT FROM AUTHOR]

Density Functional-based Tight-Binding coupled with Non-Equilibrium Green Function calculations is used to study the influence of the boron substitutional doping in the Stone–Wales defect on the structural, electronic, and thermoelectric properties of armchair graphene nanoribbons (AGNRs). The cohesive energies and the defect formation energy of all doped structures are estimated in terms of total energies, and it is also shown that the impurity site plays a part in controlling the characteristics of structures where some sites are most energetically favorable. The enhanced scattering at the boundaries will reduce thermal conductivity, the more asymmetry is, the stronger the boundary effect is. Moreover, Stone–Wales defects and boron substitutional doping may increase the scattering of phonons and thus reduce thermal conductivity. It is noted with boron substitution, a complete electron backscattering area is created in doped structures, and the specific placement of that is determined by the doping sites. We discussed the electron and phonon transport characteristics of doped AGNRs. The results propose that substitutional doping play a significant role in altering the thermoelectric properties of AGNRs with topological defects at specific doping locations, providing a roadmap for the synthesis and design of custom-made AGNRs for specific thermoelectricboundary effect is. Moreover, Stone–Wales defects and boron substitutional doping may increase the scattering of phonons and thus reduce thermal conductivity. It is noted with boron substitution, a complete electron backscattering area is created in doped structures, and the specific placement of that is determined by the doping sites. We discussed the electron and phonon transport characteristics of doped AGNRs. The results propose that substitutional doping play a significant role in altering the thermoelectric properties of AGNRs with topological defects at specific doping locations, providing a roadmap for the synthesis and design of custom-made AGNRs for applications. [ABSTRACT FROM AUTHOR]

Exploring the thermal transport properties of the interface structure of low-dimensional nanomaterials contributes to a deeper understanding of the interface phonon modes and may provide theoretical support for efficient chip cooling devices. In this manuscript, we have simulated in detail the effects of system temperature, substrate location, and heat flow density on the thermal transport at the SWCNT/Si interface using the Non-equilibrium Molecular Dynamics approach and predicted the interfacial thermal conductance of SWCNT/Si for second, third and fourth order phonon using the Anharmonic Inelastic model. The results show that the low-frequency acoustic branch of SWCNT is suppressed by phonon scattering from the substrate, and the low-frequency phonon branch of SWCNT is boosted by about 1 THz. The anharmonic channels and inelastic phonon scattering significantly affect the interface phonon modes at higher temperatures, and the anharmonic interactions could increase additional thermal transport channels, which result in an increased number of additional phonon peaks. The increase in temperature gradually consumes the phonons incident at the interface in SWCNT, which enhances the anharmonic scattering and weakens the nonlinear characteristics of the material heterostructure, while the weakening of the acoustic branch accompanied by the temperature increase makes the LA phonon branch thermal conduction rate slower and the interfacial thermal conductance gradually stabilizes, which leads to the weakening of the thermal rectification effect. [ABSTRACT FROM AUTHOR]

Searching for topological superconductors with non-Abelian states has been attracting broad interest. The most commonly used recipe for building topological superconductors utilizes the proximity effect, which significantly limits the working temperature. Here, we propose a mechanism to attain topological superconductivity via forward phonon scatterings. Our crucial observation is that electron-phonon interactions with small momentum transfers favor spin-triplet Cooper pairing under an applied magnetic field. This process facilitates the formation of chiral topological superconductivity even without Rashba spin-orbit coupling. As a proof of concept, we propose an experimentally feasible heterostructure to systematically study the entangled relationship among forward-phonon scatterings, Rashba spin-orbit coupling, pairing symmetries, and the topological property of the superconducting state. This theory not only deepens our understanding of the superconductivity induced by the electron-phonon interaction but also sheds light on the critical role of the electron-phonon coupling in pursuing non-Abelian Majorana quasiparticles. Topological superconductors are deemed to carry great potential of realizing non-Abelian states for fault-tolerant quantum computing. Here, the authors propose a new theoretical mechanism to attain topological superconductivity via forward phonon scattering and hence provide a new possibility for engineering high-temperature topological superconductors. [ABSTRACT FROM AUTHOR]

The phonon-drag effect is useful for improving the thermoelectric performance, especially the Seebeck coefficient. Therefore, the phonon and electron transport properties of Si single crystals at different carrier densities were investigated, and the relationship between these properties and the phonon-drag effect was clarified. Phonon transport properties were determined using nanoindentation and spot-periodic heating radiation thermometry. The electron transport properties were determined based on the electrical conductivity of Si. The diffusive Seebeck coefficient derived from the electron transport properties was in good agreement with previous reports. However, the value of the phonon-drag Seebeck coefficient derived from the phonon transport properties is very low. This phenomenon suggests that phonons with a normal mean free path (MFP) do not contribute to the increase in the Seebeck coefficient; however, phonons with a long MFP and low frequency increase the Seebeck coefficient via the phonon-drag effect. Moreover, the phonon-drag effect was sufficiently pronounced even at 300 K and in the heavily doped region. These features are key in designing thermoelectric materials with enhanced performance derived from the phonon-drag effect. [ABSTRACT FROM AUTHOR]

In the current work we report on the generation of acoustic strains in thin ZnO layers using optoacoustic transduction of ultrashort laser pulses into acoustic waves on an Au thin film transducer. After absorption of energy by the electron system of the metal, energy conversion, thermal expansion and mechanical deformation takes place. The generation and propagation of the induced acoustic strains are monitored in time via a degenerate pump-probe transient reflectivity optical setup at 800 nm, as opposed to most commonly used schemes that employ different wavelengths for the pump and probe beams, mostly in the vicinity of ZnO maximum absorption. The experimental results include energy relaxation times and phonon scattering frequencies and are supported by a thermal vibro-acoustic finite element model. The model is based on the combination of a revised two-temperature approach and elasticity theory, and considers anisotropic properties for the ZnO film and the computation of the elastic wave velocity for the first time. The outcomes are discussed in the context of electron–phonon coupling factors and other material properties. A good agreement between the experimental findings and the results from the numerical simulations has been established, regarding outcomes like the mean velocity of the strain waves, establishing a novel characterization method applicable to a variety of materials and structures. [ABSTRACT FROM AUTHOR]

The electrical conductivity (σ), thermoelectric power (α), Hall coefficient (RH), and thermal conductivity (κ) of unmodified and 0.5 wt % ZrO2-modified extruded samples of the Bi0.85Sb0.15 solid solution have been measured in the range ~77–300 K at a magnetic field strength of up to ~74 × 104 A/m. The results demonstrate that the addition of 0.5 wt % ZrO2 to Bi0.85Sb0.15 reduces the phonon component of its thermal conductivity, leading to an increase in its thermoelectric figure of merit (Z) to ~6.4 × 10–3 K–1. The use of the modified material is expected to considerably improve parameters of related low-temperature thermoelectric converters. At ~77 K, in both the unmodified and ZrO2-modified Bi0.85Sb0.15 solid solutions heat is transported largely by lattice vibrations. [ABSTRACT FROM AUTHOR]

Ti2−xNiCoSnSb (x = 0.125, 0.250, 0.375, and 0.500) half Heusler (HH) high-entropy thermoelectric alloys were synthesized by the arc melting—ball milling—spark plasma sintering route. The impact of secondary phase content on the thermoelectric properties in these alloys was examined. Ni-rich intermetallic (Ni3Sn2, Ni3Sn4) compounds were observed; the intermetallic content increased for lower Ti content, e.g., Ti1.5NiCoSnSb. A Ni-rich full Heusler (FH) secondary phase was also observed. These results were consistent with first-principles calculations that show that the formation enthalpy of Ti1.5NiCoSnSb was higher than that of Ti2NiCoSnSb and the full Heusler (FH) TiNi2Sn phase. In lower Ti content samples, the electrical conductivity increased, and lattice thermal conductivity decreased at the expense of thermopower owing to higher FH and the Ni3Sn2 phase content. Ti1.5NiCoSnSb exhibited lower lattice thermal conductivity of 3.5 W/mK, compared to 5.4 W/mK at 823 K for Ti2NiCoSnSb due to increased phonon scattering at HH/Ni3Sn2 interfaces. But considering the decreasing power factor with lower Ti content, the maximum ZT obtained in Ti1.875NiCoSnSb (0.171 at 973 K) was only marginally higher than the value for Ti2NiCoSnSb. Further, compositional tuning is hence necessary to maximize the power factor. [ABSTRACT FROM AUTHOR]

Non-polar m-plane GaN terahertz quantum cascade laser (THz-QCL) structures have been studied. One is traditional three-well resonant-phonon (RP) design scheme. The other is two-well phonon scattering injection (PSI) design scheme. The peak gains of 41.8 and 44.2 cm−1 have been obtained at 8.2 and 7.7 THz respectively at 300 K according to the self-consistent non-equilibrium Green's function calculation. Different from the usual GaAs two-well design, the upper and lower lasing levels are both ground states in the GaN quantum wells for the PSI scheme, mitigating the severe broadening effect for the excited states in GaN. To guide the fabrication of such devices, the doping effect on the peak gain has been analyzed. The two designs have demonstrated distinct doping density dependence and it is mainly attributed to the very different doping dependent broadening behaviors. The results reveal the possibility of GaN based THz-QCL lasing at room temperature. [ABSTRACT FROM AUTHOR]

Herein, we have conducted a comprehensive study to uncover the thermal transport properties and hydrogen evolution reaction catalytic activity of recently synthesized holey graphyne. Our findings disclose that holey graphyne has a direct bandgap of 1.00 eV using the HSE06 exchange–correlation functional. The absence of imaginary phonon frequencies in the phonon dispersion ensures its dynamic stability. The formation energy of holey graphyne turns out to be − 8.46 eV/atom, comparable to graphene (− 9.22 eV/atom) and h-BN (− 8.80 eV/atom). At 300 K, the Seebeck coefficient is as high as 700 μV/K at a carrier concentration of 1 × 1010 cm-2. The predicted room temperature lattice thermal conductivity (κl) of 29.3 W/mK is substantially lower than graphene (3000 W/mK) and fourfold smaller than C3N (128 W/mK). At around 335 nm thickness, the room temperature κl suppresses by 25%. The calculated p-type figure of merit (ZT) reaches a maximum of 1.50 at 300 K, higher than that of holey graphene (ZT = 1.13), γ-graphyne (ZT = 0.48), and pristine graphene (ZT = 0.55 × 10–3). It further scales up to 3.36 at 600 K. Such colossal ZT values make holey graphyne an appealing p-type thermoelectric material. Besides that, holey graphyne is a potential HER catalyst with a low overpotential of 0.20 eV, which further reduces to 0.03 eV at 2% compressive strain. [ABSTRACT FROM AUTHOR]

Herein, we have first reported the intrinsic properties, including structural, mechanical, electronic, magnetic, thermal, and transport properties of XTiBr3 (X = Rb, Cs) halide perovskites within the simulation scheme of density functional theory as integrated into Wien2k. First and foremost, the structural stability in terms of their ground state energies has been keenly evaluated from their corresponding structural optimizations, which advocate that XTiBr3 (X = Rb, Cs) has a stable ferromagnetic rather than the competing non-magnetic phase. Later on, the electronic properties have been computed within the mix of two applied potential schemes like Generalized Gradient Approximation (GGA) along with Trans-Bhala modified Becke Johnson (TB-mBJ), which thoroughly addresses the half-metallic behaviour with spin-up as metallic and in contrast to opposite spin-down channel signatures the semiconducting behaviour. Furthermore, the spin-splitting seen from their corresponding spin-polarised band structures offers a net magnetism of 2 µB which lends their opportunities to unlock the application branch of spintronics. In addition, these alloys have been characterised to show their mechanical stability describing the ductile feature. Moreover, phonon dispersions decisively certify the dynamical stability within the density functional perturbation theory (DFPT) context. Finally, the transport and thermal properties predicted within their specified packages have also been forwarded in this report. [ABSTRACT FROM AUTHOR]

In this research work, for the first time, the thermal transport properties of the natural Azerbaijani bentonites (Gobu and Atyali) as well as their Multi-Walled Carbon NanoTube/Gobu and Multi Walled Carbon Nano Tube/Atyali ceramic composites were investigated, their application abilities were studied, and the initial mechanism for explaining the thermal properties of these nanocomposites was studied. A laser flash technique was used to determine the thermal conductivity and thermal diffusivity of the prepared nanocomposites. The nanocomposites were prepared by an irreversible dispersion method that was developed by our research group. The highest thermal conductivity and thermal diffusivity were observed for 16% MWCNT-containing nanocomposites. The highest values of thermal conductivity and thermal diffusivity are κ = 1.3 W·(m·K−1) at T = 498 K, a = 1.539 × 10–6 m2·s−1 at T = 543 K for Gobu/x MWCNT (x = 16%) and κ = 0.97 W·(m·K−1) at T = 473 K, a = 1.013 × 10–6 m2·s−1 at T = 300 K for Atyali/x MWCNT (x = 16%) ceramic composites, respectively, and are mostly limited by phonon scattering within the bundles, by MWCNT and natural bentonite ceramic matrix interfaces, formed structure types of MWCNT networks. Experimental results prove that the cross-bar structure of MWCNTs inside Atyali matrices affects thermal conductivity negatively in comparison to the horizontally aligned structure of MWCNTs inside Gobu matrices. The electrical conductivity of these ceramic nanocomposites was significantly increased (for Gobu/x MWCNT (x = 16%) − 284 S·m−1 and for Atyali/x MWCNT 89.8 S·m−1). As these nanocomposites are electrically and thermally conductive at the same time, they can potentially be used as non-corrosive electrodes for electrolysis processes, as substrates like coolers for electronic devices with less heat release, and as heating elements for coveralls and for heating apartments. [ABSTRACT FROM AUTHOR]

Nickel-doped off-stoichiometric bornite Cu5–xNixFeS3.71 0 ≤ x ≤ 1 nanoparticles were synthesized by high-energy mechanical alloying (MA) and subsequent annealing at 653 K for 1 h. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) of the annealed powders revealed low-orthorhombic bornite as the main phase with a minor amount (< 2%) of digenite as the second phase. XRD analysis, scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) results indicated that micro-sized digenite (Cu1.84S) supercells are formed amid bornite nanoparticles after hot-pressing at 673 K. Moreover, for Ni content of x = 0.08 and higher, about 2.6% of Ni3S2 precipitated as a third phase in Cu5–xNixFeS3.71 compounds, suggesting a solubility limit of x ≈ 0.08 for Ni in bornite. The thermal conductivity of the undoped pellet was 0.33 w/m.k at 325 K, which is about 30% lower than similar MA synthesized bornite. The lowest thermal conductivity was obtained for Cu4.96Ni0.04FeS3.71 (x = 0.04) at 473 K (0.19 w/m.k). This ultra-low thermal conductivity is attributed to the synergistic effect of bornite nanoparticles and micro-sized digenite supercells that highly increases phonon scattering at the interfaces. The maximum and minimum electrical resistivity at 325 K was obtained for x = 0.1 (0.106 mΩm) and x = 0.06 (0.137 mΩm) pellets. [ABSTRACT FROM AUTHOR]

In the last few years, a great deal of interest has centred on phonon studies in material science. Therefore, the present study consists of first-principles lattice calculations to comprehend the thermal expansion α (T) and lattice thermal conductivity κ ph of ScAgC. The obtained positive frequencies of phonon dispersion with and without non-analytic term correction (NAC) shows the dynamical stability of ScAgC in FCC structure. The estimated α (T) from quasi-harmonic approximation (QHA) at 300(1200) K is ∼ 4(4.6) × 10 - 6 K - 1 . The predicted value of total κ ph from phonon–phonon interaction (PPI) at 300(1200) K is ∼ 7.4(1.8) Wm - 1 K - 1 . The highest group velocity for acoustic and optical branches (AB and OB) is ∼ 6.7 and ∼ 3.5 km/s, respectively. The predicted average phonon lifetime ( τ λ ) for AB(OB) is ∼ 2.5(1.65) ps at 300 K, whereas it is ∼ 0.6(0.4) ps at 1200 K. The estimated highest heat capacity ( C λ ) at 200 K for AB(OB) is ∼ 23.5 (19.5) meV/K. We fitted the equation A κ T - x κ ( A τ T - x τ ) in the κ ph ( τ λ ) curve to gain a thorough understanding of temperature-dependent κ ph trend. The x τ value due to total AB(OB) is estimated to be ∼ 1.04(1.02), while it is ∼ 1.03 for total branches. The x κ for total branches is calculated to be ∼ 1.02, while it is ∼ 1.04(0.95) for total AB(OB) branches, implying that AB contributes more to the total κ ph . This research could be important for enhancing the properties of ScAgC regarding thermoelectric and photovoltaic applications. [ABSTRACT FROM AUTHOR]

In this work, the first principle approach is used extensively to scrutinize the magneto-electronic properties of ternary A2B2O7 (A = Er and B = Ru, Sn, Ge, Pt) to explore its significance in spintronics applications. The calculations reveal that Er2Ge2O7 is a half-metallic material with a bandgap of 3.74 eV (↑) and Er2(Sn, Pt)2O7 are magnetic semiconductors, which is promising for spintronic applications. Thermoelectric coefficients such as the figure of merit thermal and electrical conductivities, the Seebeck coefficient (S), are also examined to check the possibility of these materials in the field of thermoelectric. The computed value of ZT reflects (ZT ~ 1) A2B2O7 materials and reveals that such type of materials holds a virtuous route towards thermoelectric applicability. [ABSTRACT FROM AUTHOR]

Based on the first-principles calculations of the phonon Boltzmann transport equation (pBTE) under the framework of the three-phonon scattering theory, we characterized the temperature and size dependence of the lattice thermal conductivity of monolayer silicene under the tensile strain. Our research shows that the lattice thermal conductivity of silicene has obvious strain dependence, and demonstrates the great potential of thermal management by applying strain in silicene. The TA phonon mode contributes the most to the thermal conductivity of silicene, while the contribution of the ZA phonon is suppressed. With the increase in tensile strain, the contribution of LA mode phonons to the thermal conductivity increases rapidly, and eventually become the dominant phonon mode of the silicene lattice thermal conductivity. We suspect that this phenomenon is caused by the reduction of the warpage of the silicene and the restoration of the crystal symmetry due to the tensile strain. When the characteristic size is less than 10 nm, the lattice thermal conductivity of silicene is no longer sensitive to temperature, and with the increase in tensile strain, the effective phonon mean free path (MFP) of silicene also increases, and the size effect is more obvious. The characterization of the scattering channel reveals its significant influence on the characteristics of thermal transport capacity of different phonon modes. These findings deepen the understanding of the phonon dynamics of the monolayer silicene-like structure, and provide the reference and theoretical basis for the research on the heat management of the corresponding material combined with strain and size and the development of thermal management technology. [ABSTRACT FROM AUTHOR]

Si–Ge–Sn alloys are offering unusual material properties with a strong potential to add a variety of functionalities to advanced CMOS technology. Being a group IV alloy, SiGeSn can be monolithically integrated on Si. The discovery of a direct band gap at Sn concentration above 8%, the extremely small effective mass for electrons and holes as well as the pronounced phonon scattering are opening new opportunities for Si photonics, high frequency devices and thermoelectrics. Si–Ge–Sn alloys with Sn concentration far beyond the solid solubility limit are metastable, artificial materials, which request challenging growth conditions. In this paper the epitaxial conditions for Si–Ge–Sn alloys to achieve precise control of the Sn content, to manage the lattice mismatch and defects, as well as to fabricate doped layers are discussed. The applied process control allows for epitaxy of group-IV heterostructures, required for typical devices for photonic and electronic applications. In this context, lasers and nanowires MOSFETs are discussed in this paper. In additions, the thermal conductivity is investigated as a critical material parameter to obtain a high thermoelectric figure of merit in GeSn alloys. [ABSTRACT FROM AUTHOR]

In this article, Polarized Raman spectroscopy is being used to determine and validate the crystallographic orientations of Zinc blend crystals. Two crystals of GaAs and ZnTe oriented along (112) are used for Polarized Raman spectroscopic study. To realize the different angles (α) of the in-plane rotation along the surface normal, and the excitation laser polarization is fixed vertically and the sample is rotated. At the scattering side another polarizer is used to get different angles (β) of polarization. Raman spectroscopic technique has been used to study crystallographic plane identification by measuring the Raman scattered intensity using the variation in α and β angles of GaAs crystals while fixing the reference point in the crystal. GaAs crystal showed a different intensity pattern which is fitted by transformation matrix relation to identify the crystallographic plane direction. In ZnTe crystal due to resonance Raman scattering at room temperature and multi-phonon feature with green laser excitation 1LO phonon intensity does not show any variation by varying (α) rotation while rotating the angle at scattering side polarizer (β), LO intensity variation follows the cosine square law. In Resonant and Non-resonant Raman scattering by varying the temperature and laser excitation, the results of ZnTe are found to be different as compared to GaAs. As a result, Polarized Raman spectroscopic study can be done only in non-resonant Raman scattering perhaps using below-band gap excitation to avoid LO multi-phonon scattering. [ABSTRACT FROM AUTHOR]

In this study, we prepared a homogeneous fine powder of barium titanate (BaTiO3, BT) doped with different concentrations of strontium (x = 0, 0.05, 0.125, 0.15, 0.20, and 0.3) and having the composition Ba1-xSrxTiO3 (barium strontium titanate, BSrxT). XRD patterns and Rietveld refinement revealed the existence of a single tetragonal phase structure for BSrxT, x = 0–20%, and a single cubic structure for BSr30%T. The physical properties of the pure and doped mixtures were studied. The results showed that the addition of strontium to the physical properties of BaTiO3, including the apparent porosity, bulk density, linear shrinkage, and water absorption have been changed when increasing the Sr content. Moreover, the inclusion of 15% Sr in BaTiO3 increases the apparent porosity and water absorption of the sample to 6.2 and 28.5%, respectively. The optical properties were investigated by Ultraviolet–visible spectroscopy and it was found that the optical band gap decreases significantly with increasing Sr concentration, from 3.10 for pure BaTiO3 to 2.46 eV for the BSr30%T compound. The thermal conductivity measurements showed that the doping mechanism and the increased temperature have a significant effect on the thermal conductivity results of the fabricated ceramic materials. Therefore, it was found that the value of thermal conductivity increases with increasing Sr doping and at higher temperatures. A correlated behavior of optimum values is observed in band gap energy, absorption, and thermal conductivity which can be exploited for thermo-optical applications. [ABSTRACT FROM AUTHOR]

A method for studying solid dielectrics under conditions of nonstationary propagation of subterahertz phonons is presented. The method analyzes the transport characteristics of thermal phonons in the helium (He) temperature range (2–4 K) in diffusion mode and makes it possible to investigate the following: the kinetic characteristics of thermal phonons in single crystals of solid solutions; the contribution to phonon scattering from the concentration, type, and positions of a substitutional impurity, defects comparable with the wavelength (clusters, phase inhomogeneities, dislocations), low-energy excitations of various nature, including those associated with the formation of an equilibrium configuration of vacancies in the anionic sublattice with respect to substitutional impurity cations; equilibrium criteria in the system of nonequilibrium phonons–low-energy excitations; peculiarities of the phonon spectrum of nanostructured materials; the relationship between the diffusion coefficient of subterahertz phonons and the system of grain boundaries (GB), grain size, conditions for the formation of a "gap" in the phonon spectrum of nanostructured ceramics; spectral properties of GB, their relationship with the technological conditions of synthesis, to evaluate the average thickness and acoustic impedance of GB for a sample; the features of thermal phonon transport in amorphous dielectrics (glasses and glasslike materials) near the thermal conductivity "plateau," the possibility of "gap" formation in the spectrum of phonon states; subterahertz phonon transport in ceramics based on ferroelectrics, electrolyte solid solutions, and cermets. [ABSTRACT FROM AUTHOR]

In recent years, the hybridization of hyperbolic van der Waals heterostructures with plasmonic two-dimensional nano-materials is one of the interesting research areas at THz frequencies due to the coupled features of the hybrid structure. This article investigates the propagation of tunable surface phonon-plasmon polaritons in grounded hybrid graphene-hexagonal Boron Nitride heterostructures. An analytical model is presented for the proposed structure, by applying the boundary conditions for the electromagnetic components in the various regions, to derive an exact dispersion relation. The structure is simulated and the results are reported in the upper Reststrahlen band. A good agreement is seen between simulation and analytical results, which shows the high accuracy of our mathematical relations. The tunability of the heterostructures is shown by studying the effect of chemical potential on the performance of the structure. A high value of the figure of merit, i.e. FOM = 190, is reported at the frequency of 48.3 THz. The presented study can open the way for the design of novel THz devices for future nano-plasmonic applications. [ABSTRACT FROM AUTHOR]

Recent nanoscience and technology are rapidly progressing with both experimental and theoretical surveys to discover and propose new materials in the fields of semiconductors, optoelectronics, etc. So, in this research, titled physical performances of bulk and monolayered gold cyanides (AuCN) were addressed via density functional theory. Wide indirect semiconductor bandgaps of 2.48 eV and 4.06 eV were obtained for bulk and monolayered AuCN, respectively. Obtained optical characteristics were found to be complex in nature depending mostly on crystal structures of bulk and monolayered crystals and the incident polarization direction. Further, both bulk and monolayer counterparts of AuCN intend alternative materials for applied microelectronics due to their low-dielectric constants below 1.5. Both bulk and monolayered AuCN can be also used as possible functional solar cell components because of their infrared (IR) conductivities. Similarly, both structures were found to be good optical absorbents for ultraviolet applications. Unlike monolayered AuCN, bulk AuCN was found to be a high-refractor material for practical IR goals. Calculated phonon dispersion curves with positive frequencies express the potential experimental synthesis of the addressed compounds. High Seebeck coefficients with 2800 × 10−6 V/K for bulk AuCN and 2700 × 10−6 V/K monolayered counterpart promote the possible fabrication of new thermoelectric materials from these compounds. [ABSTRACT FROM AUTHOR]

A model of the dependence of thermal conductivity of liquid mixtures on their concentration is constructed on the basis of a series connection of the thermal resistances of their components. The equivalent resistance model of the "Filaments" type is found to serve as a valid basis for describing the phenomenon of additional thermal resistance obtained in experiments carried out on mixtures. From the model, it follows that the thermal conductivity coefficient of a mixture is not an additive value. The dependence of the additional thermal resistance on the concentration becomes more pronounced with a greater ratio of thermal conductivities of pure components. Taking into account the effect of increasing thermal resistance due to the scattering of phonons on the inhomogeneities of the system, it was possible to obtain a sufficient agreement with experimental data on thermal conductivity for selected mixtures having various natures, including those with a lower critical solution temperature. [ABSTRACT FROM AUTHOR]

Half-Heusler (HH) phase TmNiSb was obtained by arc-melting combined with high-pressure high-temperature sintering in conditions: p = 5.5 GPa, T HPHT = 20, 250, 500, 750, and 1000 ∘ C. Within pressing temperatures 20–750 ∘ C the samples maintained HH structure, however, we observed intrinsic phase separation. The material divided into three phases: stoichiometric TmNiSb, nickel-deficient phase TmNi 1 - x Sb, and thulium-rich phase Tm(NiSb) 1 - y . For TmNiSb sample sintered at 1000 ∘ C, we report structural transition to LiGaGe-type structure (P 6 3 mc, a = 4.367(3) Å, c = 7.138(7) Å). Interpretation of the transition is supported by X-ray powder diffraction, electron back-scattered diffraction, ab-initio calculations of Gibbs energy and phonon dispersion relations. Electrical resistivity measured for HH samples with phase separation shown non-degenerate behavior. Obtained energy gaps for HH samples were narrow (≤ 260 meV), while the average hole effective masses in range 0.8–2.5 m e . TmNiSb sample pressed at 750 ∘ C achieved the biggest power factor among the series, 13 μ WK - 2 cm - 1 , which proves that the intrinsic phase separation is not detrimental for the electronic transport. [ABSTRACT FROM AUTHOR]

Ultra-high temperature ceramics, especially di-borides, are regarded as potential candidates for thermal protection system in hypersonic vehicles by virtue of their high thermal conductivity. However, studies on thermal conductivity behaviour of ultra-high temperature ceramic di-borides exhibit scattered data at high temperatures. Herein, we report a systematic study of a range of di-boride compositions aiming at multiple aspects including the effect of temperature on thermal conductivity of monolithic di-borides (ZrB2 and HfB2), effect of SiC and carbon nanotubes (CNTs) addition on ZrB2 and HfB2 with increasing temperature till 1200 °C, and effect on thermal conductivity with systematic incorporation of ZrB2 and HfB2 into each another. Highest experimental thermal conductivity (63–83 W m−1 K−1) observed in 20 vol% SiC reinforced ZrB2 composite (in the temperature range of 50–1200 °C) witnessed crossover (and drop) than that of monolithic sample (above 900 °C) due to increased phonon–phonon scattering in SiC with the rise in temperature. Concurrently, agglomerated CNT reinforcement further decreased thermal conductivity due to increased inhomogeneity in solid solutioning and enhanced phonon scattering. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenide (TMD) semiconductors are two-dimensional materials with great potential for the future of nano-optics and nano-optoelectronics as well as the rich and exciting development of basic research. The influence of an external magnetic field on a TMD monolayer raises a new question: to unveil the behavior of the magneto-polaron resonances (MPRs) associated with the phonon symmetry inherent in the system. It is shown that the renormalized Landau energy levels are modified by the interplay of the long-range Pekar–Fröhlich (PF) and short-range deformation potential (DP) interactions. This leads to a new series of MPRs involving the optical phonons at the center of the Brillouin zone. The coupling of the two Landau levels with the LO and A 1 optical phonon modes provokes resonant splittings of double avoided-crossing levels giving rise to three excitation branches. This effect appears as bigger energy gaps at the anticrossing points in the renormalized Landau levels. To explore the interplay between the MPRs, the electron-phonon interactions (PF and DP) and the couplings between adjacent Landau levels, a full Green's function treatment for the evaluation of the energy and its life-time broadening is developed. A generalization of the two-level approach is performed for the description of the new MPR branches. The obtained results are a guideline for the magneto-optical experiments in TMDs, where three MPR peaks should be observable. [ABSTRACT FROM AUTHOR]

The recent designs of terahertz quantum cascade lasers usually employ the short periodic length and also the tall barriers for high-temperature operation. In this work, the effect of high-energy lying non-relevant subbands is studied based on nonequilibrium Green's function formalisms model, demonstrating those subbands are probable to play a minor role on the population inversion, but play a major role on the optical gain at high temperatures. The phenomenon can be ascribed to the appearance of leakages crossing neighboring periods via sequential resonant tunneling, and those leakages are inherently created by the specific features of the two-well configuration in this design that the phonon well should be wide enough for performing the phonon scattering to depopulate the lower-laser subband. The narrower periodic length design can strengthen this inter-period leakage. A parasitic absorption between the first high-lying nonrelevant subbands from two laser wells can closely overlap the gain shape and thus significantly reduce the peak gain. [ABSTRACT FROM AUTHOR]

Based on first-principles and Boltzmann transport equation, the electronic structure and thermoelectric properties of derivative TlAgX (X = S, Se) monolayers of KAgSe monolayer are predicted. The results show that the TlAgX (X = S, Se) single layers are indirect bandgap semiconductors. TlAgS and TlAgSe monolayers have the low lattice thermal conductivity of 0.20 and 0.17 W m−1 K−1 at 700 K, respectively. Such ultra-low lattice thermal conductivity is ascribed to the small phonon group velocity, large Grüneisen parameters, and short phonon relaxation time, with greatly suppressed phonon transport. The n-doping TlAgS and TlAgSe monolayers have high ZT values in wide temperature range (300–700 K) and the maximal ZT value reaches 9.1 and 10.3 at 700 K, respectively. The excellent thermal and electrical transport properties and resulting good thermoelectric performance indicate that the TlAgX (X = S, Se) monolayers are good thermoelectric candidate materials. [ABSTRACT FROM AUTHOR]

The specific features of the transport of thermal-frequency phonons at liquid-helium (He) temperatures under the conditions of non-stationary measurements and thermal conductivity in polycrystalline Y3Al5O12 (YAG) ceramic samples, synthesized in different technological regimes, have been studied. The relationship between the phonon diffusion coefficient and the structural features of grains (crystallites) and grain boundaries has been revealed by analyzing the non-stationary measurement data and the thermal conductivity. [ABSTRACT FROM AUTHOR]

In this study, the lattice thermal conductivity of nanostructure material is demonstrated using the non-equilibrium phonon distribution function to solve the Boltzmann transport equation in the relaxation time approximation. This model is compared with the experimental data of silicon nanowires (SiNWs) for a wide diameter and temperature range (20–320 K). Phonon scattering is assumed to be by sample boundaries, impurities and other phonons via Normal and Umklapp processes. The predicted lattice thermal conductivity (LTC) values demonstrate sensible concurrence with experimental measurements. The present analysis can clarify the experimental results on the lattice thermal conductivity of nanostructures. [ABSTRACT FROM AUTHOR]

Polymers are a unique class of materials from the perspective of normal mode analysis. Polymers consist of individual chains with repeating units and strong intra-chain covalent bonds, and amorphous arrangements among chains with weak inter-chain van der Waals and for some polymers also electrostatic interactions. Intuitively, this strong heterogeneity in bond strength can give rise to special features in the constituent phonons, but such effects have not been studied deeply before. Here, we use lattice dynamics and molecular dynamics to perform modal analysis of the thermal conductivity in amorphous polymers. We find an abnormally large population of localized modes in amorphous polymers, which is fundamentally different from amorphous inorganic materials. Contrary to the common picture of thermal transport, localized modes in amorphous polymers are found to be the dominant contributors to thermal conductivity. We find that a significant portion of the localization happens within individual chains, but heat is dominantly conducted when localized modes involve two chains. These results suggest localized modes generally play a key role in thermal transport for different polymers. The results provide an alternative perspective on why polymer thermal conductivity is generally quite low and gives insight into how to potentially change it. Lattice dynamics and molecular dynamics simulations are used to analyze normal modes and thermal conductivity of amorphous polymers. Here, the authors show that the localized modes are dominant, both in mode population and in their contributions to thermal conductivity for all three examples of amorphous polymers studied in this work. [ABSTRACT FROM AUTHOR]

Introducing the nanosecond phase into thermoelectric materials is an effective strategy to improve their thermoelectric properties. In this study, the influence of nano Y2O3 dispersion on the resistivity, Seebeck coefficient and thermal conductivity of Cu2Se + x mol% Y2O3 (x = 0, 0.5, 1.0, 2.0, 3.0) was investigated. Their resistivity and Seebeck coefficient have no obvious change under the combined effects of the microstructure and the energy filtering. Especially, Y2O3 dispersion can inhibit the recrystallization of Cu2Se and make the lamellar grains thinner, thus scattering phonon and reducing the thermal conductivity effectively. When x = 1.0, the thermal conductivity reaches a minimum of 0.65 W/K·m at 923 K. The dimensionless thermoelectric figure of merit (ZT) value of the Cu2Se + 1.0 mol% Y2O3 sample reaches 1.81 at 923 K. The study indicates that nano rare earth oxides are relatively effective second-phase that can reduce thermal conductivity, which may be further promoted for other thermoelectric materials. [ABSTRACT FROM AUTHOR]

Theoretically, nanosecond phase dispersion is an effective method to optimize the performance of thermoelectric materials due to the energy filtering effect and strong phonon scattering. Because of the chemical stability of La2O3, it may be used as a second phase material in Bi2Te2.7Se0.3 matrixes. After the introduction of La2O3, its electric transport performance decreases slightly, but its thermal transport performance increases further. Finally, its thermoelectric performance is optimized. At 455 K, the maximum dimensionless thermoelectric figure of merit (ZT) value of Bi2Te2.7Se0.3 + 0.5 wt% La2O3 reaches 0.97. The experimental results demonstrate that La2O3 dispersion can improve the thermoelectric properties of Bi2Te2.7Se0.3 effectively. [ABSTRACT FROM AUTHOR]

A dual-mode immunoassay strategy based on CdS nanoparticles as signal probes with both of photoluminescent (PL) and multi-phonon resonance Raman scattering (MRRS) properties was developed. Simplified structural design and preparation were achieved due to the intrinsic integration of PL and MRRS dual signals in the single-unit CdS nanoprobes. Human immunoglobulin G (HIgG) was sensitively and specifically detected using the proposed PL-MRRS dual-mode strategy. The linear relationship between the HIgG concentration and the intensity of 707 nm PL peaks/300 cm−1 MRRS peaks under the excitation of 488 nm laser was established. The limit of detection was 0.93 fg mL−1 for PL and 1.10 fg mL−1 for MRRS. In comparison with previous IgG detection methods, the proposed method exhibited prominent advantages in detection sensitivity and working range with good stability and repeatability. An internal self-calibration was realized which ensured the accuracy and reliability of detection results. Both results of specificity experiments and serum sample analysis further confirmed the feasibility of the designed immunoassay strategy in practical serological detection. [ABSTRACT FROM AUTHOR]

Last century, there has been a growing interest in detecting defects in semiconductors, aiming to improve product quality to decrease production costs. Silicon manufacturing is carried out using different methods and procedures. It is crucial to consider quality control in all steps since dislocations, protrusive hillocks, and boron-oxygen complexes, among others, can be produced during the machining process, influencing the final product quality. Optical and electron microscopies are common tools to visualize defects in materials. However, these methods are time-consuming, inaccurate, and expensive. The objective of this work was to propose photothermal techniques as methodology and metrology to detect defects accurately through the knowledge of thermal properties, as these are determined by crystalline structure quality involving defects. Complementary techniques such as X-ray diffraction, FTIR spectroscopy, and the Hall effect established a correlation between the thermal, electrical, and structural properties of p-type Si samples with different carrier concentrations. Local variations in the carrier distribution detected using photocarrier radiometry found recombination by localized electronic defects. The absorption coefficient of B–O, Si–O–Si, and H–C–H bonds were obtained to calculate the concentration of BO-related defects, oxygen, and carbon. Carrier lifetime changes due to scattering processes were computed using the Hall effect, which confirmed structural variations. X-ray diffraction elucidated the effect of doping (boron) concentration on the crystalline quality of Si. Boron inclusions introduced dislocations because of smaller atom sizes than Si. Local variations in thermal diffusivity were detected using photoacoustics, phonon-dislocation scattering was responsible for the changes in this thermal property. The heat capacity, thermal conductivity, and diffusivity decreased owing to the crystalline quality and carrier concentration. Heat transport governed by phonons is extrinsically dependent on carrier concentration since it determines the lattice state. It was set up the photothermal measurements as a low-cost control method in order to improve step by step the quality of modern Si wafers. [ABSTRACT FROM AUTHOR]

HfO2, as a kind of high dielectric ceramic material, has important applications in microelectronic devices. With device miniaturization, the intrinsic thermal conductivity and thermal boundary resistance of ultrathin HfO2 films on Si substrate are becoming increasingly important in thermal management related to heat conduction for gate dielectrics on a few nanometer scales. To study the thickness and temperature dependences of the thermal properties, a series of ultrathin HfO2 films with thickness of 2 nm, 6 nm, 10 nm and 20 nm are grown on Si substrates. The intrinsic thermal conductivities and the thermal boundary resistances are simultaneously measured by the two-color femtosecond pump–probe technique between 300 and 500 K. The intrinsic thermal conductivity of the 2 nm film is about 0.13 Wm−1·K−1, and the thermal conductivity of HfO2 is positive correlated to the thickness. The measured thermal boundary conductance is positive correlated to the temperature. The contributions of elastic and inelastic scattering is determined through the anharmonic inelastic model, and the results show that the inelastic scattering plays a nonnegligible role in interfacial thermal transport. [ABSTRACT FROM AUTHOR]