Scaling behavior of thermal conductivity in single-crystallineα-Fe2O3 nanowires

Unveiling the thermal transport properties of various one-dimensional(1D)or quasi-1D materials like nanowires,nanotubes,and nanorods is of great importance both theoretically and experimentally.The dimension or size dependence of thermal conductivity is crucial in understanding the phonon-phonon interaction in the low-dimensional systems.In this paper,we experimentally investigate the size-dependent thermal conductivity of individual single crystallineα-Fe2O3 nanowires collaborating the suspended thermal bridge method and the focused electron-beam self-heating technique,with the sample diameter(d)ranging from 180 nm to 661 nm and length(L)changing from 4.84μm to 20.73μm.An empirical relationship for diameter-/length-dependent thermal conductivity is obtained,which shows an approximately linear dependence on the aspect ratio(L/(1+Cd))at T=300 K,where C is a fitting parameter.This is related to the boundary scattering and diameter effect ofα-Fe2O3 nanowires although rigorous calculations are needed to confirm the result.

Tunable Thermal Conductivity of Ferroelectric P(VDF-TrFE)Nanofibers via Molecular Bond Modulation

Dipoles in ferroelectric copolymer P(VDF-Tr FE)can be driven by electric field,introducing phonon transport modulations via polarizing molecular chains.The thermal conductivity in single 75/25 P(VDF-Tr FE)nanofibers is found to increase with electric field related phonon renormalization,resulted from change in vibrational assignment excited by polarization process.This is evidenced by a direct change of bond energy and bond length in 75/25P(VDF-Tr FE)nanofibers from Raman characterization under polarization electric field.The experimental results provide further intuitive evidences that the size of ferroelectric polymers could directly affect the ferroelectricity from the size-dependent thermal transport measurement.

Suppressed Thermal Conductivity in Polycrystalline Gold Nanofilm:The Effect of Grain Boundary and Substrate

We investigate the electrical conductivity and thermal conductivity of polycrystalline gold nanofilms,with thicknesses ranging from 40.5nm to 115.8 nm,and identify a thickness-dependent electrical conductivity,which can be explained via the Mayadas and Shatzkes(MS)theory.At the same time,a suppressed thermal conductivity is observed,as compared to that found in the bulk material,together with a weak thickness effect.We compare the thermal conductivity of suspended and supported gold films,finding that the supporting substrate can effectively suppress the in-plane thermal conductivity of the polycrystalline gold nanofilms.Our results indicate that grain boundary scattering and substrate scattering can affect electron and phonon transport in polycrystalline metallic systems.

Erratum: A Ubiquitous Thermal Conductivity Formula for Liquids, Polymer Glass, and Amorphous Solids [Chin. Phys. Lett. 37(2020) 104401]

In the Acknowledgement, the following sentence "JH and JL are supported by the National Science Foundation (Award number CBET-1943813) and the Faulty Research and Professional Development Fund at North Carolina State University" should be changed to "JH and JL are supported by the Faulty Research and Professional Development Fund at North Carolina State University".

A Ubiquitous Thermal Conductivity Formula for Liquids, Polymer Glass, and Amorphous Solids

The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time.There have been several approaches to explain the thermal conductivities in these systems,for example,Bridgman's formula for simple liquids,the concept of the minimum thermal conductivity for amorphous solids,and the thermal resistance network model for amorphous polymers.Here,we present a ubiquitous formula to calculate the thermal conductivities of liquids and amorphous solids in a unified way,and compare it with previous ones.The calculated thermal conductivities using this formula without fitting parameters are in excellent agreement with the experimental data.Our formula not only provides a detailed microscopic mechanism of heat transfer in these systems,but also resolves the discrepancies between existing formulae and experimental data.

An innovative way of etching MoS2： Characterization and mechanistic investigation

We report a systematic study of the etching of MoSs crystals by using XeF2 as a gaseous reactant. By controlling the etching process, monolayer MoS2 with uniform morphology can be obtained. The Raman and photoluminescence spectra of the resulting material were similar to those of exfoliated MoS2. Utilizing this strategy, different patterns such as a Hall bar structure and a hexagonal array can be realized. Furthermore, the etching mechanism was studied by introducing graphene as an etching mask. We believe our technique opens an easy and controllable way of etching MoS2, which can be used to fabricate complex nanostructures, such as nanoribbons, quantum dots, and transistor structures. This etching process using XeF2 can also be extended to other interesting two-dimensional crystals.

Thermal transport in organic/inorganic composites

Composite materials, which consist of organic and inorganic components, are widely used in various fields because of their excellent mechanical properties, resistance to corrosion, low-cost fabrication, etc. Thermal properties of organic/inorganic composites play a crucial role in some applications such as thermal interface materials for micro-electronic packaging, nano-porous materials for sensor development, thermal insulators for aerospace, and high-performance thermoelectric materials for power generation and refrigeration. In the past few years, many studies have been conducted to reveal the physical mechanism of thermal transport in organic/ inorganic composite materials in order to stimulate their practical applications. In this paper, the theoretical and experimental progresses in this field are reviewed. Besides, main factors affecting the thermal conductivity of organic/ inorganic compositcs are discussed, including the intrinsic properties of organic matrix and inorganic fillers, topolo- gical structure of composites, loading volume fraction, and the interfacial thermal resistance between fillers and organic matrix.

Measuring the thermal conductivity and interfacial thermal resistance of suspended MoS2 using electron beam self-heating technique

Establishment of a new technique or extension of an existing technique for thermal and thermoelectric measurements to a more challenging system is an important task to explore the thermal and thermoelectric properties of various materials and systems. The bottleneck lies in the challenges in measuring the thermal contact resistance. In this work, we applied electron beam self-heating technique to derive the intrinsic thermal conductivity of suspended Molybdenum Disulfide （MoS2） ribbons and the thermal contact resistance, with which the interracial thermal resistance between few-layer MoS2 and Pt electrodes was calculated. The measured room temperature thermal conductivity of MoS2 is around -30 W/（m K）, while the estimated interracial thermal resistance is around -2 × 10 -6 m-2 K/W. Our experiments extend a useful branch in application of this technique for studying thermal properties of suspended layered ribbons and have potential application in investigating the interracial thermal resistance of different twodimensional （2D） heterojunctions.

Unprecedently low thermal conductivity of unique tellurium nanoribbons

Tellurene,probably one of the most promising two-dimensional(2D)system in the thermoelectric materials,displays ultra-low thermal conductivity.However,a linear thickness-dependent thermal conductivity of unique tellurium nanoribbons in this study reveals that unprecedently low thermal conductivity can be achieved via well-defined nanostructures of low-dimensional tellurium instead of pursuing dimension-reduced 2D tellurene.For thinnest tellurium nanoribbon with thickness of 144 nm,the thermal conductivity is only∼1.88±0.22 W·m^(−1)·K^(−1) at room temperature.It’s a dramatic decrease(45%),compared with the well-annealed high-purity bulk tellurium.To be more specific,an expected thermal conductivity of tellurium nanoribbons is even lower than that of 2D tellurene,as a result of strong phonon-surface scattering.We have faith in low-dimensional tellurium in which the thermoelectric performance could realize further breakthrough.