Ultralow Interfacial Thermal Resistance of Graphene Thermal Interface Materials with Surface Metal Liquefaction

Developing advanced thermal interface materials(TIMs)to bridge heat-generating chip and heat sink for constructing an efficient heat transfer interface is the key technology to solve the thermal management issue of high-power semiconductor devices.Based on the ultra-high basal-plane thermal conductivity,graphene is an ideal candidate for preparing high-performance TIMs,preferably to form a vertically aligned structure so that the basal-plane of graphene is consistent with the heat transfer direction of TIM.However,the actual interfacial heat transfer efficiency of currently reported vertically aligned graphene TIMs is far from satisfactory.In addition to the fact that the thermal conductivity of the vertically aligned TIMs can be further improved,another critical factor is the limited actual contact area leading to relatively high contact thermal resistance(20-30 K mm^(2) W^(−1))of the“solid-solid”mating interface formed by the vertical graphene and the rough chip/heat sink.To solve this common problem faced by vertically aligned graphene,in this work,we combined mechanical orientation and surface modification strategy to construct a three-tiered TIM composed of mainly vertically aligned graphene in the middle and micrometer-thick liquid metal as a cap layer on upper and lower surfaces.Based on rational graphene orientation regulation in the middle tier,the resultant graphene-based TIM exhibited an ultra-high thermal conductivity of 176 W m^(−1) K^(−1).Additionally,we demonstrated that the liquid metal cap layer in contact with the chip/heat sink forms a“liquid-solid”mating interface,significantly increasing the effective heat transfer area and giving a low contact thermal con-ductivity of 4-6 K mm^(2) W^(−1) under packaging conditions.This finding provides valuable guidance for the design of high-performance TIMs based on two-dimensional materials and improves the possibility of their practical application in electronic thermal management.

Retraction note to “Development and characterization of hot dip aluminide coated stainless steel 316L”(J. Cent. South Univ., 10.1007/s11771-018-3937-y)

The Editor-in-Chief has retracted this article [1] because Figures 11 and 12 appear to be identical with Figures 3 and 4respectively from a previously published article [2].Sehrish MUKHTAR,Waqas ASGHAR,Zubair BUTT,Zaheer ABBAS,Mudaser ULLAH and Rana ATTA-UR-REHMAN did not respond to correspondence about this retraction.

Superplastic Behavior of Alumina Composites Mediated by Carbon Nanotubes

The high temperature creep behavior of carbon nanotube(CNT)/alumina was mediated by the surface chemical functionalization used for synthesis of composite powders. Non-covalent functionalized carbon nanotubes make composites ductile, but covalent approach leads composites that are creep-resistant. Oxygen vacancy mechanism is proposed to account for this mediation effect in this communication.

Advances in Li-rich Mn-based Layered Cathode Materials Enable High-performance Li-ion Batteries

In recent decades,lithium-ion batteries(LIBs)have commercially dominated the portable electronics market and gradually evolved into the most encouraging market areas for electric vehicles(EVs).Thanks to the discharge capacity of over 300 mAh g^(-1),Li-rich Mn-based layered cathode materials have emerged as promising cathode materials for developing high-performance Li-ion batteries.

Oxygen-defects evolution to stimulate continuous capacity increase in Co-free Li-rich layered oxides

Though oxygen defects are associated with deteriorated structures and aggravated cycling performance in traditional layered cathodes,the role of oxygen defects is still ambiguous in Li-rich layered oxides due to the involvement of oxygen redox.Herein,a Co-free Li-rich layered oxide Li_(1.286)Ni_(0.071)Mn_(0.643)O_(2)has been prepared by a co-precipitation method to systematically investigate the undefined effects of the oxygen defects.A significant O_(2)release and the propagation of oxygen vacancies were detected by operando differential electrochemical mass spectroscopy(DEMS)and electron energy loss spectroscopy(EELS),respectively.Scanning transmission electron microscopy-high angle annular dark field(STEMHAADF)reveals the oxygen vacancies fusing to nanovoids and monitors a stepwise electrochemical activation process of the large Li_(2)MnO_(3)domain upon cycling.Combined with the quantitative analysis conducted by the energy dispersive spectrometer(EDS),existed nano-scale oxygen defects actually expose more surface to the electrolyte for facilitating the electrochemical activation and subsequently increasing available capacity.Overall,this work persuasively elucidates the function of oxygen defects on oxygen redox in Co-free Li-rich layered oxides.

Rational design of graphene/polymer composites with excellent electromagnetic interference shielding effectiveness and high thermal conductivity: a mini review

The integration and miniaturization of chips lead to inevitable overheating and increasing electromagnetic interference (EMI) problems, which threaten the performance, stability, and lifetime of electroniccomponents. Therefore, it is important to improve the heat dissipation and EMI shielding performancein device packaging for the steady operation of electronic products. In recent years, due to its intrinsic superior thermal conductivity, proper electrical conductivity, light-weight, and structural adjustability,graphene has been widely used as high thermal and conductive fillers incorporated in the polymer matrix to improve the thermal conductivity and electrical conductivity of composites. This review concludesthe recent development of graphene/polymer composites by using graphene as fillers to improve thethermal conductivity and EMI shielding effectiveness (EMI SE). The structure of graphene embedded inthe composites varies from zero-dimension (0D), one-dimension (1D) to two-dimensions (2D). Moreover,highly thermally and electrically conductive fillers with different dimensions were also modified on thegraphene to improve the composite performance. Finally, this review also makes prospects for the development trend of graphene/polymer composites with high thermal conductivity and EMI SE in the future.

Slurry-like hybrid electrolyte with high lithium-ion transference number for dendrite-free lithium metal anode

Lithium metal anode is regarded as the ultimate choice for next-generation energy storage systems,due to the lowest negative electrochemical potential and super high theoretical specific capacity.However,the growth of lithium dendrite during the cycling process is still one of the most critical bottlenecks for its application.In this work,a slurry-like hybrid electrolyte is proposed towards the application for lithium metal anode,which is composed of a liquid electrolyte part and a nanometric silane-Al2O3 particle part.The hybrid electrolyte shows high ionic conductivity(3.89×10-3 S cm-1 at 25℃)and lithium-ion transference number(0.88).Especially,the resistance of hybrid electrolyte decreases compared to that of liquid electrolyte,while the viscosity of hybrid electrolyte increases.It is demonstrated that the hybrid electrolyte can effectively suppress the growth of lithium dendrite.Stable cycling of Li/Li cells at a current density up to 1 mA cm-2 is possible.The hybrid electrolyte helps to uniform the lithium ion flux inside the battery and partly comes from the formation of a rigid and highly conductive hybrid interfacial layer on the surface of lithium metal.This work not only provides a fresh way to stabilize lithium metal anode but also sheds light on further research for electrolyte optimization and design of lithium metal battery system.

316L热浸镀铝不锈钢的研制与表征（英文）

不锈钢316L因其生物相容性而被应用于骨科种植体,但应尽量减少SS 316L种植体可能引起的相关致癌性和炎症效应。本研究采用光学显微镜、能量色散谱(EDS)、纳米压痕和腐蚀测试技术,对SS 316L上Al–Si合金涂层进行表征。采用热浸镀铝工艺,在765℃热浸2 min对SS 316L试样进行热浸镀。一半试样在马弗炉中于550℃扩散4 h,得到SS 316L扩散试样。显微组织观察表明,由于Si的加入,形成了平坦的涂层/基体界面。EDS分析证实涂层/基体界面形成了复杂的金属间化合物,最终提高了涂层的硬度和耐蚀性。

Rational design of graphene structures for preparing high-performance thermal interface materials: A mini review

With the explosive development in integration of electronic components and the increasing complexity of packaging systems,semiconductor chips own extremely high operation temperatures given by the horrible heat accumulation attributed to the drastically increasing power density. Therefore, highly efficient heat dissipation with the help of rationally designed thermal interface materials(TIMs) is the key to maintaining the device performance and lifespan. Graphene exhibits an ultrahigh intrinsic thermal conductivity, which has attracted a large amount of academic interest due to its significant potential for developing high-performance TIMs. In this tutorial review, we summarize the recent advances in graphene-based TIMs, especially emphasizing the determinate effects of graphene structure and alignment in enhancing the heat transfer capacity of corresponding samples,with detailed discussion in the superiorities and limitations of various graphene skeletons. In addition, we also provide prospects for the challenges and opportunities in the future development of graphene-based TIMs.

Spark plasma sintering of damage tolerant and machinable YAM ceramics

Single-phase Y_(4)Al_(2)O_(9)(YAM)powders were synthesized via solid-state reaction starting from nano-sized Al_(2)O_(3) and Y_(2)O_(3).Fully dense(99.5%)bulk YAM ceramics were consolidated by spark plasma sintering(SPS)at 1800℃.We demonstrated the excellent damage tolerance and good machinability of YAM ceramics.Such properties are attributed to the easy slipping along the weakly bonded crystallographic planes,resulting in multiple energy dissipation mechanisms such as transgranular fracture,shear slipping and localized grain crushing.

Enhancement of in-plane thermal conductivity of flexible boron nitride heat spreaders by micro/nanovoid filling using deformable liquid metal nanoparticles

With the fast development of integrated circuit devices as well as batteries with high energy densities,the thermal management of electronic components is becoming increasingly crucial to maintaining their reliable operations.Boron nitride nanosheets(BNNS),which have superhigh thermal conductivity along the in-plane direction while remaining electrically insulating,were widely regarded as an ideal filler for preparing high-performance polymer composites to address the‘‘thermal failure''issue.However,due to the instinctive rigidity of BNNS,the nanosheets are unable to form a tightly interfacial contact between the adjoining fillers,resulting in some micro-and nanovoids within the heat transfer pathways and severely limiting further thermal conductivity enhancement for BNNS-based composites.Herein,soft and deformable liquid metal(eutectic gallium-indium,EGaIn)nanoparticles were employed to fill the gaps between the adjacent BNNS with a rational design of mass ratios of BNNS and EGaIn,leading to a strongly synergistic effect with BNNS on thermal conductivity improvement.As a result,the composite film(BNNS:63 wt%and EGaIn:7 wt%)employing cellulose nanofibers(CNF:30 wt%)as the polymer matrix achieves superhigh thermal conductivity along the in-plane direction of up to(90.51±6.71)W·m^(-1)·K^(-1),showing the highest value among the BNNSbased composites with a bi-filler system as far as we know.Additionally,the film can work as a heat spreader for the heat dissipation of high-power light emitting diodes,outperforming tin foil in cooling efficiency.

Resistive switching effects in oxide sandwiched structures

抵抗切换(RS ) 行为为数据存储由于他们的有希望的潜力吸引了大兴趣。在各种各样的材料之中，基于氧化物的设备看起来就他们有互补金属氧化物半导体技术的方便制造和相容性而言更有益，尽管内在的机制由于 RS 行为的差异仍然是争论的。在这评论，我们集中于基于氧化物的 RS 记忆，工作机制能根据一个所谓的细丝模型的意见基本上在被理解。细丝形成 / 破裂进程，途径发展了检测并且描绘细丝，在基于氧化物的抵抗随机改进 RS 和量传导力行为的表演的几次有效尝试存取存储器(RRAM ) 设备分别地被探讨。

3D Shapeable,Superior Electrically Conductive Cellulose Nanofibers/Ti_(3)C_(2)T_(x) MXene Aerogels/Epoxy Nanocomposites for Promising EMI Shielding

In this work,3D highly electrically conductive cellulose nanofibers(CNF)/Ti_(3)C_(2)T_(x) MXene aerogels(CTA)with aligned porous structures are fabricated by directional freezing followed by freeze-drying technique,and the thermally annealed CTA(TCTA)/epoxy nanocomposites are then fabricated by thermal annealing of CTA,subsequent vacuum-assisted impregnation and curing method.Results show that TCTA/epoxy nanocomposites possess 3D highly conductive networks with ultralow percolation threshold of 0.20 vol%Ti_(3)C_(2)T_(x).When the volume fraction of Ti_(3)C_(2)T_(x) is 1.38 vol%,the electrical conductivity(σ),electromagnetic interference shielding effectiveness(EMI SE),and SE divided by thickness(SE/d)values of the TCTA/epoxy nanocomposites reach 1672 Sm-1,74 dB,and 37 dBmm-1,respectively,which are almost the highest values compared to those of polymer nanocomposites reported previously at the same filler content.In addition,compared to those of the samples without Ti_(3)C_(2)T_(x),the storage modulus and heat-resistance index of TCTA/epoxy nanocomposites are enhanced to 9792.5 MPa and 310.7℃,increased by 62%and 6.9℃,respectively,presenting outstanding mechanical properties and thermal stabilities.The fabricated lightweight,easy-to-process,and shapeable TCTA/epoxy nanocomposites with superior EMI SE values,excellent mechanical properties,and thermal stabilities greatly broaden the applications of MXene-based polymer composites in the field of EMI shielding.

Enhanced tribological properties of aligned graphene-epoxy composites

The random distribution of graphene in epoxy matrix hinders the further applications of grapheneepoxy composites in the field of tribology.Hence,in order to fully utilize the anisotropic properties of graphene,highly aligned graphene-epoxy composites(AGEC)with horizontally oriented structure have been fabricated via an improved vacuum filtration freeze-drying method.The frictional tests results indicated that the wear rate of AGEC slowly increased from 5.19x10^(-6)mm^(3)/(N-m)to 2.87x10^(-5)mm^(3)/(N-m)with the increasing of the normal load from 2 to 10 N,whereas the friction coefficient(COF)remained a constant of 0.109.Compared to the neat epoxy and random graphene-epoxy composites(RGEC),the COF of AGEC was reduced by 87.5%and 71.2%,and the reduction of wear rate was 86.6%and 85.4%at most,respectively.Scanning electron microscope(SEM)observations illustrated that a compact graphene self-lubricant film was formed on the worn surface of AGEC,which enables AGEC to possess excellent tribological performance.Finally,in light of the excellent tribological properties of AGEC,this study highlights a pathway to expand the tribological applications of graphene-epoxy composites.

Microstructure engineering beyond SnSe_(1-x)S_(x)solid solution for high thermoelectric performance

Recently,SnSe has attracted wide attention as a promising environment-friendly IV-VI thermoelectric material.Here,SnS is alloyed with Na-doped SnSe to decrease the thermal conductivity for better thermoelectric performance.Consistent with previous reports,the lattice constant and the band gap change linearly with increasing SnS,suggesting the formation of SnSe1-xSx solid solution.However,SnS nano-precipitations have been clearly observed,indicating the phase separation in the alloys.Moreover,the grain size decreases obviously with increasing SnS amount.The first-principles calculations show that the nano-precipitation is due to the positive formation energies for SnSe1-xSx in the small x region.Due to the structure engineering,the lattice thermal conductivity is greatly reduced in SnSe1-xSx samples,leading to a promising ZT of 1.35 for Na_(0.03)Sn_(0.97)Se_(0.7S0.3)at 816 K.

Pt nanodendrites with (111) crystalline facet as an efficient, stable and pH-universal catalyst for electrochemical hydrogen production

High-performance nanomaterial catalysts for hydrogen evolution reaction via electrochemical water splitting are significant to the development of hydrogen energy.In this work,we report a robust and highly active catalyst fabricated through direct electrochemical deposition of Pt nanodendrites at the surface of activated carbon(Pt NDs).Owing to the large elect roc he mically active area and the exposed(111) facet of Pt,Pt NDs exhibits outstanding activity towards hydrogen evolution reaction with a low requiring overpotential of 0.027 V at 10 mA/cm2 and Tafel slope of ≈22 mV/dec in acidic media.In addition,the hydrogen yield of Pt NDs is 30%-45% larger than that of commercial Pt/C at the same Pt loadings.Moreover,Pt NDs exhibits excellent lo ng-term durability whose hydrogen production efficiency remains unchanged after six-hour hydrogen production,while the efficiency of commercial Pt/C catalyst decayed 9% under the same circumstance.Considering the superiority of catalytic activity and stability,this Pt NDs present great potentiality towards practical hydrogen production application.

Layer-by-layer stacked graphene nanocoatings by Marangoni self-assembly for corrosion protection of stainless steel

Graphene nanosheets are widely used in anti-corrosion polymeric coating as filler,owing to the excellent electrochemical inertness and barrier property.However,as the arrangement of graphene nanosheets is difficult to form a perfect layered structure,polymeric coating with graphene nanosheets usually needs micron-scale thickness to ensure the enhancement of corrosion protection.In this work,layer-by-layer stacked graphene nanocoatings were fabricated on stainless steel by self-assembly based on Marangoni effect.The anti-corrosion property of graphene coatings were studied through Tafel polarization curves,electrochemical impedance spectroscopy and accelerated corrosion test with extra applied voltage.The self corrosion current density of optimized three-layered graphene coated sample was one quarter of that of bare stainless steel.And the self corrosion potential of optimized sample is increased to-0.045 V.According to the results,graphene nanocoatings composed of layered nanosheets exhibits good anticorrosion property.Besides,the self-assembly method provide a promising approach to make layeredstructure coating for other researches about 2 D material nanosheets.

基于马兰戈尼效应制备具有周期性褶皱结构的石墨烯薄膜及其在高灵敏应变探测中的应用

石墨烯薄膜中可控的微纳结构,有利于调控其物理性质并拓宽其在柔性电子器件中的应用.近年来,研究人员致力于控制石墨烯薄膜中褶皱、起伏波纹等微纳结构的形成.但是,在石墨烯薄膜中可控地形成有序的褶皱状结构仍然面临巨大挑战.本文报道了一种简单地制备具有周期性平行褶皱结构的石墨烯薄膜的方法,即通过将溶液表面自组装形成的石墨烯薄膜转移至预拉伸的聚二甲基硅氧烷(PDMS)基底上而得到.制备的石墨烯薄膜中,褶皱的宽度可以简单地通过改变基底的预拉伸形变来控制.当PDMS基底预拉伸应变分别为10%、20%和50%时,薄膜中褶皱的平均宽度分别为3.68、2.99和2.01µm.本文还进一步研究和分析了双层堆叠、褶皱状石墨烯薄膜,在拉伸形变时的形貌结构变化.此外,本文基于该褶皱状石墨烯薄膜,构建了应变传感器.该传感器展现出高灵敏度、宽探测范围和优良的循环稳定性,其在实时运动探测、健康监测和电子皮肤等领域有着广阔应用前景.

A Spiral Graphene Framework Containing Highly Ordered Graphene Microtubes for Polymer Composites with Superior Through-Plane Thermal Conductivity

As the power density of electronic devices increases,there has been an urgent demand to develop highly conductive polymer composites to address the accompanying thermal management issues.Due to the ultra-high intrinsic thermal conductivity,graphene is considered a very promising filler to improve the thermal conductivity of polymers.However,graphene-based polymer composites prepared by the conventional mixing method generally have limited thermal conductivity,even under high graphene loading,due to the failure to construct efficient heat transfer pathways in the polymer matrix.Here,a spiral graphene framework(SGF)containing continuous and highly ordered graphene microtubes was developed based on a modified CVD method.After embedding into the epoxy(EP)matrix,the graphene microtubes can act as efficient heat pathways,endowing the SGF/EP composites with a high through-plane thermal conductivity of 1.35 W·m^(-1)·K^(-1) at an ultralow graphene loading of 0.86 wt%.This result gives a thermal conductivity enhancement per 1 wt%filler loading of 710%,significantly outperforming various graphene structures as fillers.In addition,we demonstrated the practical application of the SGF/EP composite as a thermal interface material for efficient thermal man-agement of the light-emitting diode(LED).

A dense graphene monolith with poloxamer prefunctionalization enabling aqueous redispersion to obtain solubilized graphene sheets

The realization of good aqueous dispersibility of commercial graphene products composed of exfoliated graphene sheets is of significance for downstream applications.However,the tap density of commercial graphene powder is quite low(0.03-0.1 kg/m3),meaning that 1 kg graphene powder occupies about 10-30 m3 in volume during transportation.And,the available content of commercial graphene dispersion/slurry in aqueous medium cannot exceed 5 wt%,although the density is high(≈1050 kg/m3).In this work,a graphene monolith was prepared by oven-drying of graphene sheets prefunctionalized with poloxamer surfactants.Our graphene monoliths not only have a high density(1500 kg/m^3) and high graphene content(≈10 wt%),but also a full capability to be completely redispersed(≈100%) in water by bath sonication to obtain solubilized graphene sheets,whose lateral size and thickness are unchanged compared to as-exfoliated ones.Moreover,a simple empirical method was proposed to predict the redispersion capability of graphene monoliths using different poloxamers by contact angle measurements.Our results provide a universal approach to make exfoliated graphene-based products with better downstream availability and lower transportation cost.