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Nanofilms (NFs) have been widely used in many emerging applications, such as microelectronic devices, spintronics, and optical instruments. Characterizing the thermal conductivity (k) of NFs, kNFs, is nontrivial for both fundamental science and industrial applications. Time-domain thermoreflectance (TDTR) is a powerful technique for thermal characterizations under nano-to-micro-scales. However, both the kNFs and the interface thermal resistance between layers are generally unknown parameters when analyzing TDTR signals. So that an effective thermal resistance model (ETRM) is often utilized, where the impact of heat capacity of NFs, cNFs, has been always ignored. Previous studies have proposed viewpoints on how to validate this assumption, however, which still needs to be verified further by considering the parameters' sensitivities for TDTR signals. In this work, we have highlighted the significance of sensitivity analysis for the investigation of the impact of cNFs with the example experiments on Ni NFs. The error of ETRM has been quantitatively and systematically studied. We found that the application requirements of ETRM in TDTR data analysis rely on the sensitivity relations between kNFs and interface thermal resistance. Finally, suggestions for future characterization of the kNFs have been discussed for reference. Our results and conclusions deepen the understanding of both the transient thermal transport process of multilayer NFs and the ability of TDTR on characterizing kNFs. [ABSTRACT FROM AUTHOR]

Herein, (14,14,14)‐graphyne (GY) supported by silicon substrate is chosen to be the research object. The results demonstrate that the increasing distance between substrate and supported materials (dsub‐sup) results in the enhancement of thermal conductivity (TC) of supported GY, and the TC of supported GY is even higher than that of free‐standing GY when dsub‐sup exceeds a certain value, which means substrate plays an abnormal promoting role in the thermal transport in supported materials (SM). This phenomenon breaks the traditional cognition that the increasing dsub‐sup can only lead to the TC of SM approaching that of free‐standing model. The related mechanism can be seen as the combined impact of weak interaction of long‐dsub‐sup substrate and tensile effect led by lattice mismatch between substrate and GY. Combining with phonon analysis, it can be observed that the influence of substrate shows a closer relationship with phonon scattering, i.e., the anharmonicity, especially the anharmonicity of out‐of‐plane direction. The anomalous promoting effect of long‐dsub‐sup can be also attributed to the weaker scattering of out‐of‐plane phonon, especially the reduced four‐order phonon scattering. This research provides a new idea to suppress the negative effect of substrate on heat dissipation in electronic devices. [ABSTRACT FROM AUTHOR]

Recently, cubic boron arsenide (c-BAs) has attracted global attention due to its higher lattice thermal conductivity (κ L), which is comparable to diamond, and excellent thermal properties. Can c-BAs achieve the leap in κ L after transforming its structure from three-dimensional (3D) to two-dimensional (2D) like diamond to graphene? Previous studies have only investigated the κ L considering three-phonon scattering and isotope scattering, and the calculated results are diverse. In this study, we first calculate second-order interatomic force constants (IFCs) and third-order IFCs to iteratively solve the Boltzmann transport equation (BTE) and to obtain the κ L 3 of monolayer hexagonal BX (X = P, As, Sb), h-BX (X = P, As, Sb), considering only three-phonon and isotope scattering. The corresponding κ L 3 of h-BX are 278.2, 205.7, and 20.2 W/mK at room temperature, and we explain the monotonous change that κ L 3 decreases with the increase of average atomic mass (mavg) different from previous studies. Subsequently we use regular residual analysis (RRA) to determine the necessity of including four-phonon scattering when calculating the κ L of monolayer h-BX. By calculating the fourth-order IFCs, we obtain the κ L 3 + 4 of monolayer h-BX including four-phonon scattering. The values of κ L 3 + 4 at room temperature are 61.12, 37.99, and 5.73 W/mK, which are highly consistent with the κ L ∞ of monolayer h-BX as predicted by the phonon spectral energy density (SED) method. The phonon SED method considers all-order scattering and gives values of 54.05 ± 21.48 W/mK (h-BP), 18.20 ± 4.47 W/mK (h-BAs), and 2.46 ± 0.34 W/mK (h-BSb), respectively. Our results show that the influence of four-phonon scattering on the κ L of monolayer h-BX is significant, and the κ L 3 + 4 and κ L ∞ still undergo monotonic changes after including four-phonon scattering. The main factors that determine the low (ultra-low) κ L of monolayer h-BAs (h-BSb) are large mavg and weaker bonding strength, the existence of intermediate frequency ZO and scattered acoustic branches, the strong anharmonicity caused by the in-plane vibrations of As (Sb) atoms, and four-phonon scattering. This study aims to end the variance within monolayer h-BAs κ L numerical simulation and demonstrate the potential of monolayer h-BSb in thermoelectric field applications. [ABSTRACT FROM AUTHOR]

Tin telluride (SnTe), a promising mid-temperature thermoelectric material, faces limitations due to inherent vacancies and band characteristics. Low-dimensionalization represents one avenue to potentially improve thermoelectric performance. This work explores the SnTe films with varying thicknesses (67–610 nm) and Zn doping concentration (0–12.81%) at high temperature. A 224 nm-SnTe-film exhibits optimal ZT values (0.27 at 600 K), and the Zn-doped films experience impaired thermoelectric properties, with the electrical conductivity reduction being a primary contributor. This study contributes valuable insights for enhancing thin-film SnTe's thermoelectric performance and developing eco-friendly mid-temperature thermoelectric materials. [ABSTRACT FROM AUTHOR]

The investigation of materials' behavior under high-temperature and high-pressure conditions, such as the correlation with structural characteristics and thermal properties, holds significant importance. However, the challenges associated with the experimental implementation have, to a certain extent, constrained such research endeavors. We utilized the ultrafast laser based non-contact thermal measurement method combined with an externally heated moissanite-anvil-cell to characterize the thermal conductivity of [10-10] oriented SiO2 crystals under high temperature (300–830 K) and high pressure (0–15 GPa) conditions. We investigated the impact of extreme conditions on the microstructure from both Raman spectroscopy and thermal perspectives. The presence of kinetic hindrances associated with the transformation of α-quartz to coesite and stishovite was identified and confirmed. It expands the comprehension and application of the SiO2 pressure–temperature phase diagram in this range and provides insights into the intricate relationship between extreme environments and material structure formation through the analysis of thermal characteristics. [ABSTRACT FROM AUTHOR]

The thermal conductivities along the basal and hexagonal directions of α -quartz silica, the low-temperature form of crystalline SiO2, are predicted from the solution of the Boltzmann transport equation combined with the van Beest, Kramer, and van Santen potential for the temperature up to 900 K and the pressure as high as 4 GPa. The thermal conductivities at atmospheric pressure, which show a negative and nonlinear dependence on temperature, are in reasonable agreement with the experimental data. The influence of pressure on thermal conductivity is positive and linear. The pressure (P) and temperature (T) dependences of the thermal conductivity (λ) in basal and hexagonal directions are fitted to a function of the form λ = (b + c P) T a. The thermal conductivity, influenced by temperature and pressure, is analyzed based on phonon properties, including spectral thermal conductivity, dispersion relation, phonon density of states, phonon lifetime, and phonon probability density distribution function. [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]

The application of graphene in high-performance thermal management has received a lot of attention in recent years, which still needs further exploration and development. Here, based on first-principles calculations, the thermal transport is found to be efficiently modulated by enhancing interlayer interactions in bilayer graphene (BLG), showing a different trend compared to graphite. The results of our work suggest that, by enhancing the interlayer force, the "in-plane" anharmonic phonon transport of BLG while the "out-of-plane" harmonic phonon transport of graphite can be effectively tuned. By manipulating interlayer interactions, a controllable and directed parameter (6% out-of-plane compressing deformation of BLG can achieve more than 25% decrement of in-plane thermal conductivity; 10% out-of-plane compressing deformation of graphite can increase out-of-plane thermal conductivity by more than 5 times) for tuning the thermal conductivity can be achieved. The difference in the effect of the interlayer force on thermal conductivity for low-dimensional and bulk materials emphasizes the significance of the anharmonic phonon transport properties of low-dimensional materials with interlayer interaction and thereby provides an important insight for promoting the future application of bilayer graphene and graphite. [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]

Pressure is an effective way to regulate physical properties of ABO3 perovskites, such as thermal conductivity κ of SrTiO3, which can enhance fundamental understanding of structure–property relationships. In this Letter, κ of SrTiO3 was investigated up to ∼20 GPa using high-pressure time domain thermoreflectance together with Raman spectroscopy and first-principles calculations. Our theoretical predictions effectively explain the measured results. In both cubic and tetragonal phases, κ increased with compression, and optical phonons are the dominant heat carriers. The phonon group velocity and relaxation time make prominent contributions to κ with compression in the cubic phase, while the reduction in the anharmonicity of phonon modes and the phonon scattering channels dominates the increase in κ in the tetragonal phase. Especially, during the transition from cubic to tetragonal phases, there is a significant drop in κ, which originally results from the TiO6 octahedral distortion induced by the soft-phonon-mode, which markedly reduces the phonon group velocity. Our results not only help reveal the pressure effect on κ of complex oxides but also pave their way for applications on high-temperature superconductors and spin devices. [ABSTRACT FROM AUTHOR]

The thickness of the metal-transducer nano-film is an essential parameter for high-pressure time-domain-thermoreflectance (TDTR) measurements. In this article, an accurate method was proposed to determine the transducer thickness in high-pressure conditions using the pressure–volume equation of state combined with an image processing method. Both the elastic and plastic deformation of the sample squeezed in diamond anvil cells were considered in this method. High-pressure TDTR measurements on thermal conductivity of MgO and mica were further taken for comparing the influence from different thickness-characterization methods up to ∼18 GPa, and the proposed method accurately captured the effect of plastic deformation on thermal conductivity for the first time. This work can not only help achieve more accurate TDTR measurements under high-pressure but also provide valuable guidance for the diamond anvil cell application in nanoscale research. [ABSTRACT FROM AUTHOR]

The detailed knowledge of the low thermal conductivity of host–guest compounds is essential to improve our fundamental understanding of heat conduction in complex solids and develop high-performance thermoelectric materials. In this Letter, the intrinsic ultralow thermal conductivity (0.44 ± 0.06 W m − 1 K − 1 in 140–190 K) of the tetrahydrofuran (THF) clathrate hydrate is characterized by the time-domain thermoreflectance technique. The underlying heat conduction mechanism is further investigated by non-equilibrium molecular dynamics simulations. We find that trapped THF molecules do harmonic motions and behave as parts of a crystalline structure, thus playing negligible roles in thermal conductivity reduction. The large unit cell and complex cage-like host structure dominate the low thermal conductivity of the THF hydrate. [ABSTRACT FROM AUTHOR]

The van der Waals (vdW) heterostructures of bilayer transition metal dichalcogenide obtained by vertically stacking have drawn increasing attention for their enormous potential applications in semiconductors and insulators. Here, by using the first-principles calculations and the phonon Boltzmann transport equation (BTE), we studied the phonon transport properties of WS2/WSe2 bilayer heterostructures (WS2/WSe2-BHs). The lattice thermal conductivity of the ideal WS2/WSe2-BHs crystals at room temperature (RT) was 62.98 W/mK, which was clearly lower than the average lattice thermal conductivity of WS2 and WSe2 single layers. Another interesting finding is that the optical branches below 4.73 THz and acoustic branches have powerful coupling, mainly dominating the lattice thermal conductivity. Further, we also noticed that the phonon mean free path (MFP) of the WS2/WSe2-BHs (233 nm) was remarkably attenuated by the free-standing monolayer WS2 (526 nm) and WSe2 (1720 nm), leading to a small significant size effect of the WS2/WSe2-BHs. Our results systematically demonstrate the low optical and acoustic phonon modes-dominated phonon thermal transport in heterostructures and give a few important guidelines for the synthesis of van der Waals heterostructures with excellent phonon transport properties. [ABSTRACT FROM AUTHOR]

Generally speaking, for materials with the same structure, the thermal conductivity is higher for lighter atomic masses. However, we found that the thermal conductivity of CaO is lower than that of CaS, despite the lighter atomic mass of O than S. To uncover the underlying physical mechanisms, the thermal conductivity of CaM (M = O, S, Se, Te) and the corresponding response to strain is investigated by performing first-principles calculations along with the phonon Boltzmann transport equation. For unstrained system, the order of thermal conductivity is CaS > CaO > CaSe > CaTe. This order remains unchanged in the strain range of −2% to 5%. When the compressive strain is larger than 2%, the thermal conductivity of CaO surpasses that of CaS and becomes the highest thermal conductivity material among the four compounds. By analyzing the mode-dependent phonon properties, the phonon lifetime is found to be dominant over other influential factors and leads to the disparate response of thermal conductivity under strain. Moreover, the changing trend of three-phonon scattering phase space is consistent with that of phonon lifetime, which is directly correlated to the phonon frequency gap induced by the LO-TO splitting. The variation of Born effective charge is found to be opposite for CaM. The Born effective charge of CaO decreases with tensile strain increasing, demonstrating stronger charge delocalization and lower ionicity, while the Born effective charges of CaS, CaSe, and CaTe show a dramatic increase. Such variation indicates that the bonding nature can be effectively tuned by external strain, thus affecting the phonon anharmonic properties and thermal conductivity. The difference of bonding nature is further confirmed by the band structure. Our results show that the bonding nature of CaM can be modulated by external strain and leads to disparate strain dependent thermal conductivity. [ABSTRACT FROM AUTHOR]

One-dimensional nanomaterials have widely applied in the fields of energy conversion and storage due to their exceptional performance because of the nano-size effect. Herein, we synthesized bamboo-like polymer nanotubes based on cationic polymerization using immiscible initiator nanodroplets that results in a hollow structure. The suspended microelectrode is fabricated to measure the axial thermal conductivity of a single polymer nanotube, which demonstrates that this hollow structure can reduce its effective thermal conductivity. The experimental results show that its effective thermal conductivity is close to 0.03 W m−1 K−1, and decreases to 0.02 W m−1 K−1 with increasing temperature of the heating microelectrode, which may be due to the increasing lattice vibration and inelastic scattering between phonons. Its effective thermal conductivity is smaller than that of air, indicating that the synthetic method is an effective way to fabricate thermal insulating polymer nanotubes by significantly lowering the effective thermal conductivity. Hence, the method offers a new strategy in the fields of thermal insulation and protection. [ABSTRACT FROM AUTHOR]

The in-plane thermal conductivity of semiconductor nanofilm is difficult to be tested due to suspension problem. The thermal boundary resistance (TBR) plays a key role in semiconductor nanoscale structures and nanoscale thermal experiments. By applying alternating current and direct current currents simultaneously on the semiconducting nanofilm on highly insulated substrate, multiharmonics including $$1\upomega $$ , $$2\upomega $$ and $$3\upomega $$ signals originating from the self-heating of nanofilm are measured. The thermal boundary resistance is introduced into the heat diffusion equation in in-plane direction. The expression of temperature oscillation and theoretical analysis of heat transport process show that the in-plane thermal conductivity and TBR can be decoupled from the multiharmonics in frequency domain. Thermal analysis justifies the multiharmonics method according to the effect of in-plane thermal conductivity, TBR between nanofilm and insulated substrate, resistance coefficient of semiconductor nanofilm on temperature oscillation at low frequency. Results show the multiharmonic method sensitivity variations depending on the TBR, the in-plane thermal conductivity, and the electric current frequency. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have been widely developed due to their attractive properties. Here, by using density functional theory (DFT) calculations, for the first time, we explore potential applications of the novel XIS (X = Al, Ga, In) monolayer 2D materials on photocatalytic water splitting. A series of simulations were carried out to predict and study the structural, elastic, phononic, optical and electronic properties of 2D XIS materials. The results show that GaIS and InIS demonstrate low thermal conductivity. For optical properties, AlIS shows strong light absorption coefficients and refractive index only under ultraviolet (UV) light, while GaIS and InIS show stronger performance under both visible light and UV light with the band edge positions spanned the redox potential of water. The reasonable band positions and bandgaps make them promising photocatalysts for water splitting. This work reveals the potential applications of monolayer 2D XIS in thermal, electronic, and photocatalytic water splitting. • A series of stable 2D XIS (X = Al, Ga, In) materials are first reported theoretically. • 2D XIS exhibits high anisotropy in elastic, phononic and optical properties. • 2D GaIS and InIS show enhanced absorption in visible and UV light regions. • 2D XIS demonstrates the potential applications for photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Electrical and thermal management in nanodevices by means of carbon nanotube is highly promising. One main challenge toward CNT-based nanoscale electrical and thermal management devices is the development of effective strategies for reducing the bundle–bundle interface resistance. Here we report a novel strategy, based on the densification of CNT bundles and the functionalization of inter-bundle interfaces for effectively enhanced interfacial electrical and thermal transport. The densification is realized by utilizing the local electrostatic cohesion; and the functionalization is realized by the interface-decorated functional groups. Experiments and theoretical analysis demonstrated obviously enhanced interfacial electrical and thermal conductance originates from: (1) local Coulomb electrostatic cohesion between CNT bundles due to surface-induced dipole moments. This effect can promote both electrical and thermal conductance nearly 2.8 times higher than non-functionalized counterpart. (2) Increased interfacial electron transport channels and thermal vibrations due to surface-decorated functional groups. This effect can bring about up to 75% and 95% improvement for thermal and electrical conductance, respectively. This study provides a new methodology for tunable operation of electrical and thermal properties at inter-bundle interfaces and guidance for design of CNT-based electrical and thermal management devices. [ABSTRACT FROM AUTHOR]

• For the first time, first-principles calculations are used to predict the lattice thermal conductivity of free-standing monolayer XS2 (X = mo and W) and monolayer XS2 supported on SiC (0001) and ZnO (0001) substrates. • The lattice thermal conductivity of monolayer XS2 supported on SiC (0001) and ZnO (0001) substrates show a significant decrease, and the decrease is even greater for the monolayer XS2 supported on ZnO (0001) substrates, reaching about 65–70 %. • The substrate drives softening of the acoustic branch, making the low-frequency phonon group velocity decrease and the three-phonon scattering enhance. • From the perspective of atomic bonding, the substrate breaks the symmetry of bonding of monolayer XS2, which leads to the increase of phonon anharmonicity and ultimately to a decrease in thermal conductivity of monolayer XS2. Thermoelectric materials have properties such as direct conversion of waste heat into electricity and environmental friendliness, which make them promising for renewable energy utilization, however, the lower conversion efficiency limits the large-scale application of thermoelectric materials. Monolayer transition metal dichalcogenides (TMDs) are candidates for thermoelectric materials due to their high power factor, but their higher thermal conductivity (TC) limits the further improvement of the figure of merit (ZT). Here, we employ first-principles calculations and solve the Boltzmann transport equation (BTE) to compare the lattice TC of free-standing monolayer XS 2 (X = Mo and W) and monolayer XS 2 supported on SiC (0001) and ZnO (0001) substrates. We find that the lattice TC of monolayer XS 2 supported on SiC (0001) and ZnO (0001) substrates are sharply reduced. Especially supported on the ZnO (0001) substrate, the lattice TC of XS 2 reduce by 65 %–70 %, which is expected to improve the thermoelectric properties of monolayer XS 2. In addition, we report the underlying cause of this significant reduction in TC. Firstly, the substrate drives softening of the acoustic branch, which leads to a decrease of phonon group velocity in the low-frequency and an enhancement of the three-phonon scattering. Then, the asymmetric bonding of XS 2 is induced by the substrates, which enhance phonon anharmonicity and reduce the phonon lifetime. Our results demonstrate that the lattice TC of monolayer XS 2 can be tuned by adjusting the substrate, which has certain reference values for the thermoelectric design of XS 2. SiC (0001) and ZnO (0001) substrates break the symmetry of the monolayer XS 2 (X = Mo and W) bonding, resulting in an increase in phonon anharmonicity, which reduces the contribution of the low-frequency acoustic branch of monolayer XS 2 to the thermal conductivity. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] The miniaturization of devices makes interfacial resistance to heat dissipation more and more obvious. Therefore, it is important to study interfacial thermal transport systematically. A modified higher harmonic inelastic model is proposed to describe the inelastic scattering at the interface. Combined with this interface model, the thermal transport of interface structures is studied by the Boltzmann transport equation. The results show that the introduction of inelastic scattering enhances the heat flux contribution of low-frequency phonons, changes the phonon distribution near the interface, and enhances the phonon non-equilibrium. This demonstrates the importance of inelastic interfacial scattering in simulations. By analyzing the phonon distribution, it is found that temperature and thickness affect the interfacial heat transport through the redistribution of phonons. The redistribution has the opposite effect on the contribution of inelastic scattering. By studying ballistic phonons in the interface structure, it is found that the ballistic phonons are mainly concentrated in the low-frequency region. Due to the longer mean free path, the phonons with frequencies below 2.5 THz are more likely to maintain a ballistic transport state. Similar to nanoscale hotspots, strong quasi-ballistic transport hinders heat diffusion. The energy fraction of ballistic phonons increases by 49%, and the local effective thermal conductivity drops by 52%. This work studied the mechanism of interfacial thermal transport, and will be useful for future interface simulation. [ABSTRACT FROM AUTHOR]

The weakly van der Waals interactions make monolayer TMDCs straightforward to vertically stack to bilayer systems, which have attracted enormous attention because of their potential applications in optoelectronics and electronic devices. In particular, MoS 2 /WS 2 heterostructure exhibits excellent performance in photodetectors. The thermal transport behavior plays a vital role in life and performance of devices, which have been rarely reported. Here, the thermal properties and thermal transport mechanism of monolayer MoS 2 and WS 2 , bilayer MoS 2 and WS 2 and MoS 2 /WS 2 heterostructure are systematically investigated by first-principles calculations and Boltzmann transport theory. The results indicate that the thermal conductivity of bilayer systems is considerably higher than that of correlated monolayer systems. Most interesting, the thermal conductivity of MoS 2 /WS 2 heterostructure is not only much lower than the thermal conductivity of 2L-WS 2 and 2L-MoS 2 , but also much lower than that of monolayer WS 2 and MoS 2. The harmonic properties mainly including phonon dispersion and anharmonic properties mainly including scattering rate and Grüneisen parameters are used to elucidate the corresponding mechanism. Moreover, the underlying electronic properties mainly including interlayer charge transfer and interlayer coupling play an essential role in thermal transport of MoS 2 /WS 2 heterostructure. The results suggest that the thermal conductivity of TMDCs can be largely tunes by various combinations, such as WS 2 /WS 2 or WS 2 /MoS 2 , which provides an effective way for manipulating the thermal transport properties of MoS 2 and WS 2 for future emerging applications. [ABSTRACT FROM AUTHOR]

• Octadecylamine with a large latent heat is selected as PCM. • The energy storage performance of the MWCNT-enhanced CPCM is experimentally studied. • The CPCM with fast heat storage rate and large heat storage capacity is acquired. • The heat storage power is significantly enhanced by 28.60%. The efficient utilization of the latent heat thermal energy storage (LHTES) system is mainly limited by its underperforming heat storage rate and capacity. Recently, scholars utilized nanoparticles to enhance the thermal conductivity of phase change materials (PCMs). Nevertheless, simultaneous enhancements of thermal conduction and phase change enthalpy have not been realized, much less considering the convective heat transfer. In this study, we selected octadecylamine (ODA) as the PCM; multiwall carbon nanotubes (MWCNTs) were ultrasonically dispersed into the ODA to obtain the uniform-mixed nano-enhanced PCMs (NePCMs). The results show that MWCNTs are conducive to strengthening thermal conduction. Besides, the fusion enthalpy of ODA@0.05 (containing 0.05 wt% of MWCNTs) is 6.45% higher than the pure ODA. However, the addition of MWCNTs improves the viscosities of liquid NePCMs in a non-linear trend, which weakens the convective heat transfer. Considering both heat storage rate and heat storage capacity, we find that the heat storage power of the ODA@0.05 is 22.38% higher than that of the pure ODA. Besides, the heat release power is 14.00% higher than the pure ODA. Consequently, we acquired the composite ODA with fast heat storage/release power and large heat storage capacity, which is an excellent candidate for the LHTES system. This paper sheds some light on the rational utilization of nano-additives to avoid the abuse of nanoparticles. [Display omitted] [ABSTRACT FROM AUTHOR]

• Hydrostatic pressure plays hugely positive role in the thermal conductivities of XC (X=Si, Ge) with zinc blende (ZB) and rock salt (RS) phases, and it also results in an enormous reduction of thermal conductivity when phase transition occurs. • The joint growth of phonon group velocity and phonon lifetime results in the obvious enhancement of thermal conductivity of SiC during the processes before and after phase transition. • During the process before / after phase transition, the abnormal increase of phonon scattering rate / little variation of phonon group velocity offsets the increase of thermal conductivity of GeC caused by phonon group velocity / phonon lifetime, which results in the smaller enhancement of thermal conductivity of GeC. • The thermal transport characteristic of GeC before phase transition is determined by harmonic characteristic and that after phase transition shows a closer relationship with the anharmonic characteristic. • The tremendous reduction of thermal conductivity of SiC during phase transition is caused by the enhancement of the phonon scattering intensity, and that of GeC is leaded by the increase of the number of phonons scattering channels. In this paper, the effect of hydrostatic pressure on the thermal transport properties of silicon carbide (SiC) and germanium carbide (GeC) with zinc blende (ZB) and rock salt (RS) phases at room temperature is investigated by solving the phonon Boltzmann heat transport equation. Studies show that the thermal conductivities of the two materials increase with the raising pressure before the phase transition, however, the enhancement of GeC (40%) is much smaller than that of SiC (100%). Combined with phonon analysis, it is found that this phenomenon originates from the abnormal enhanced phonon scattering rate under high pressure, which partly offsets the increase of phonon group velocity and further suppresses the increase of thermal conductivity. Next, when the phase transition occurs, the thermal conductivities of SiC and GeC decrease sharply by 76% and 86%, respectively, which is mainly caused by the increase of the anharmonic characteristic related to phonon scattering. Finally, after the phase transition, the thermal conductivities of the two materials still show increasing trends with the raising pressure, however, the phonon group velocity of GeC does not change significantly and the variation of its thermal conductivity is mainly determined by the phonon lifetime, which is opposite to the case before phase transition, whose enhancement of thermal conductivity is mainly caused by the increase of phonon group velocity. The results indicate that GeC has a more complex phonon transport mechanism compared with SiC, i.e., its thermal conductivity before phase transition is determined by harmonic characteristic and that after phase transition shows a closer relationship with the anharmonic characteristic. This study provides data and mechanism support for the regulation of thermal conductivity from the perspective of pressure-induced phase transition, and as well as supplies some guiding suggestions for engineering applications in the field of thermal transport regulation. [Display omitted] Hydrostatic pressure plays positive role in the thermal conductivities of XC (X=Si, Ge) during the processes before and after phase transition, and it also plays enormous negative role in the thermal conductivity when phase transition occurs. There are a variety of mutually restrictive phonon mechanisms existed in GeC, which can boost its application in the regulation of TC [ABSTRACT FROM AUTHOR]

Doped silicon (Si) is the key material in semiconductor industries. It is important to fully understand the doping effect on thermal transport properties of single-crystal Si, especially for the thermal management of Si-based electronic devices. In this work, we used a femtosecond-laser time-domain thermoreflectance method to characterize the thermal transport properties of Si with different doping concentrations (1013-1019 cm−3) and doping elements, boron (B) and phosphorus (P). Results show that the thermal conductivity of heavy doped Si (about 2 × 1019 cm−3) by both B and P decreases by about 22% compared with their pure counterparts. Theoretical calculations based on the Boltzmann transport equation were also carried out for comparison with measurement results, and different scattering terms were discussed to find out the main factors for suppressing the thermal transport in doped Si within different doping concentration ranges. Combining with a cryogenic system, the thermal conductivity of doped Si samples and interfacial thermal conductance between Si and aluminum thin films were also measured under low-temperature conditions (down to 160 K). Our systematic studies on the doping effect in the thermal transport of single-crystal semiconductors not only facilitate the understanding of the microscale thermal transport, but also provide references in industrial applications of doped semiconductors. [ABSTRACT FROM AUTHOR]

The thermal boundary resistance (TBR) between SiO 2 -GaN film-sapphire is reconstructed by 3 ω method in the temperature range of 260–480 K. The TBR at SiO 2 /GaN film interface is obtained on different samples with different thickness SiO 2 films at high frequency of 1 KHz–20 KHz and the TBR at GaN film/sapphire interface is isolated by extending the frequency to a wide range. The measured TBR with strong temperature dependence at GaN film/sapphire interface increases with increasing temperature, and is found to be 1.02 × 10 −7 m 2 K W −1 at room temperature. The measured TBR with weak temperature dependence at SiO 2 /GaN film interface decreases with increasing temperature. The temperature dependence of the TBR differs appreciably from the predicted trend by phonon inelastic scattering model and may be affected partially by the lack of some sources of inelastic boundary scattering and the increased diffusive boundary scattering. The predicted results corrected by phonon attenuation process agree well with the experimental values especially at high temperature. The temperature dependence and the larger value of the TBR contain contributions from the near-interface effect including the real boundary between the GaN film and its adjacent layers and the phonon inelastic scattering near the interface region. [ABSTRACT FROM AUTHOR]

Abstract: Thermal conductivities of [mmim]DMP/CH3OH with mole fraction of [mmim]DMP (x =0.00, 0.10, 0.20, 0.30, 0.50, 0.70, 0.85, 1.00) and thermal conductivities of [mmim]DMP/H2O with mole fraction of [mmim]DMP (x =0.025, 0.05, 0.10, 0.20, 0.30, 0.50, 0.70, 0.90, 1.00) at T =298.15K were measured by freestanding sensor-based 3ω technique. The zigzag temperature response curves of the sensor were observed and used to extract the specimen thermal conductivity. The total uncertainty in thermal conductivity measurement and the maximum fitting error were estimated to be within 7.7% and 8.0%, respectively. Intuitively, as increasing the mole fraction of [mmim]DMP, the thermal conductivities of both [mmim]DMP/CH3OH and [mmim]DMP/H2O vary exponentially. Through the comparison with the assuming solutions, the heat transfer performances of [mmim]DMP/CH3OH and [mmim]DMP/H2O solutions were evaluated. [Copyright &y& Elsevier]