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.

A new route to fabricate flexible,breathable composites with advanced thermal management capability for wearable electronics

Wearable electronics with miniaturization and high-power density call for devices with advanced thermal management capabilities,outstanding flexibility,and excellent permeability.However,it is difficult to achieve these goals simultaneously due to the conflict between high thermal conductivity and permeability and flexibility.Here,we report an approach to fabricate flexible,breathable composites with advanced thermal management capability by coating the boron nitride nanosheets(BNNSs)layer with high thermal conductivity on the grids of patterned electrospun thermoplastic polyurethane(TPU)fibrous mats.The composite exhibited a significant enhancement of thermal conductivity and preserved instinctive breathability simultaneously.When the composite was integrated into flexible devices,its saturating operating temperature dropped significantly compared to that of pure Ecoflex packaging.Moreover,the surface temperature fluctuation was less than 0.5°C during more than 2000 cycles bendingreleasing process.Finally,a prototype to fabricate wearable electronics with advanced thermal management capability was proposed.

Research on the Relationship Between Macroeconomic Indicators and Stock Market Value

The article first addresses the following questions:“Why does gross domestic product(GDP)rises,but the stock market value falls?”;“Among the macroeconomic factors,which factor has a greater impact on the promotion of investment value in the securities market?”.With these questions in mind,we put forward a hypothesis emphasizing on the impact of macroeconomic factors on the value of the stock market based on existing research and used the regression method to verify this hypothesis.The following conclusions were drawn:(1)variables that have a positive nonlinear relationship with stock market value include balance of payments surplus,rising GDP level,M1,the whole society’s fixed asset investment,and national per capita disposable income;(2)variables that have a negative nonlinear relationship with stock market value include deposit,loan interest rate,new RMB loan amount,consumer price index(CPI),and producer price index;(3)deposit reserve ratio has an S-shaped curve relationship with stock market value;(4)exchange rate has an inverted U-shaped curve relationship with stock market value.

具有分级界面的纳米纤维增强聚合物复合材料:用于高温介电储能应用

陶瓷纳米填料增强的柔性聚合物基复合材料在先进电子电气系统中显示出巨大的储能应用潜力.但如何在高于150℃的条件下提高其能量密度和效率仍然是一个挑战.本文中我们采用氮化硼-钛酸钡(BNBaTiO_(3))非均质纳米纤维作为填料,耐高温的聚醚酰亚胺(PEI)为基体,使复合材料的介电常数和击穿强度同时提高.分级结构的BN/BaTiO_(3)/PEI界面提升了材料的陷阱密度和能级,可进一步抑制传导损耗.在此基础上,复合材料在150℃,能量效率高于90%时展现出5.23J cm^(-3)的超高能量密度,这是迄今为止纳米纤维增强聚合物复合材料中最高的能量密度.研究表明,分级界面是提高材料高温储能的有效策略,对介电材料在高温下的应用具有重要意义.

一种提升六方氮化硼抗氧化性的洁净干转移方法

六方氮化硼(h-BN)是一种具有出色热稳定性和化学惰性的二维材料,在苛刻条件下应用广泛.然而,表面金属催化剂会使其抗氧化性显著降低.对于通过化学气相沉积制备的样品,常规通过湿法蚀刻金属基底的转移方法不可避免地会引入金属残留.我们这里提出了一种针对铜表面生长的单层h-BN薄膜的洁净干转移方法.空气环境下界面氧插层和表面铜氧化导致界面粘附能量显著降低,因而h-BN薄膜可以从基底上被直接机械剥离开.与湿法转移制备的薄膜形成鲜明对比,干法转移得到的h-BN薄膜几乎没有金属(铁)污染,使其抗氧化性提高了50–100℃,甚至接近其本征性能.在干法转移的单层h-BN薄膜保护下,单层石墨烯在空气中的耐受温度提高到700℃,展示了这一干转移方法的优势.

半导体薄膜表面粘附的非对称性偏压调控

电调控表面粘附对微机电系统是至关重要的,同时相对于外加电压极性常具有对称性.本文以二硫化钼为研究对象,以石墨烯、氮化硼和n型硅为参照组展示半导体薄膜表面的非对称粘附行为.研究主要通过导电原子力显微镜和理论模拟来揭示金探针与金基底上二硫化钼之间的偏压调控粘附力的行为.结果反映二硫化钼表面偏压对粘附的调控能力远大于参照组材料,这种非对称行为主要来源于半导体薄膜与背电极之间形成的肖特基结中的内建电场.

Non-affinity:The emergence of networks from amorphous planar graphs

The primary research of physics is to reveal the underlying law of the physical world.However,for a complex system consisting of multiple components,even if we know every details of each component,we still cannot predict the collective behavior due to the emergence phenomenon.The amorphous networks of mass points hinged by springs belong to such a complex system.Owing to the non-affinity,one of the emergence phenomena of the network,the displacements field of the internal mass points under the external load tends to be chaotic,and there is no well-established theoretical framework to describe these points’collective behavior analytically.The non-affine mechanical responses of the amorphous networks are very common,whereas the affine response is rare and it occurs only in those lattices with one site per unit cell.The network’s non-affinity prevents us from further investigating the relationship between its intrinsic properties(such as the contact number,local structure,and topological characteristics)and the mechanical behaviors.As a result,it is very complicated and difficult to predict the responses of an amorphous network to an imposed strain.Interestingly,a sort of amorphous network derived from the jammed particles is reported to have almost perfect affine mechanical behavior,in a stark contrast with the general perception.These findings may shed light on uncovering the structural factors that affect the network’s affinity.This article will give a short review of the latest advances in this area.

Flexible and highly-sensitive pressure sensor based on controllably oxidized MXene

Conductive Ti_(3)C_(2)T_(x)MXenes have been widely investigated for the construction of flexible and highly-sensitive pressure sensors.Although the inevitable oxidation of solution-processed MXene has been recognized,the effect of the irreversible oxidation of MXene on its electrical conductivity and sensing properties is yet to be understood.Herein,we construct a highly-sensitive and degradable piezoresistive pressure sensor by coating Ti_(3)C_(2)T_(x)MXene flakes with different degrees of in situ oxidation onto paper substrates using the dipping-drying method.In situ oxidation can tune the intrinsic resistance and expand the interlayer distance of MXene nanosheets.The partially oxidized MXene-based piezoresistive pressure sensor exhibits a high sensitivity of 28.43 kPa^(-1),which is greater than those of pristine MXene,over-oxidized MXene,and state-of-the-art paper-based pressure sensors.Additionally,these sensors exhibit a short response time of 98.3 ms,good durability over 5000 measurement cycles,and a low force detection limit of 0.8 Pa.Moreover,MXene-based sensing elements are easily degraded and environmentally friendly.The MXene-based pressure sensor shows promise for practical applications in tracking body movements,sports coaching,remote health monitoring,and human–computer interactions.

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.

Probing interactions at two-dimensional heterointerfaces by boron nitride-wrapped tip

Non-covalent interactions are important for two-dimensional heterointerfaces but challenged to be accurately determined,especially when the dielectric hexagonal boron nitride(BN)is involved.Here,we present a comprehensive quantitative investigation on the interactions at the interfaces of BN-BN,BN-molybdenum disulfide,and BN-graphite using a BN-wrapped atomic force microscope tip and first-principle theory.The critical adhesion forces at BN-molybdenum disulfide and BN-graphite interfaces are measured to be 1.107±0.062 and 0.999±0.053 times that at BN-BN interface,respectively,while increase to 1.195±0.076 and 1.085±0.075 a.u.after exposure of the tip to radiation in scanning electron microscopy,with data repeatability higher than 86%.The result with non-radiated tip agrees with the van der Waals interactions predicted by the state-of-the-art density functional theory-based vdW2D method,whereas the effect of radiation comes from the introduced charges in the tip,indicating the crucial roles of both dispersion and electrostatic interactions in construction,manipulation and device application of two-dimensional heterostructures.