Polymer/conductive filler composites have been widely used for the preparation of self-limiting heating cables with the positive temperature coefficient (PTC) effect. The control of conductive filler distribution and ...Polymer/conductive filler composites have been widely used for the preparation of self-limiting heating cables with the positive temperature coefficient (PTC) effect. The control of conductive filler distribution and network in polymer matrix is the most critical for performance of PTC materials. In order to compensate for the destruction of the filler network structure caused by strong shearing during processing, an excessive conductive filler content is usually added into the polymer matrix, which in turn sacrifices its processability and mechanical properties. In this work, a facile post-treatment of the as-extruded cable, including thermal and electrical treatment to produce high-density polyethylene (HDPE)/carbon black (CB) cable with excellent PTC effect, is developed. It is found for the as-extruded sample, the strong shearing makes the CB particles disperse uniformly in HDPE matrix, and 25 wt% CB is needed for the formation of conductive paths. For the thermal-treated sample, a gradually aggregated CB filler structure is observed, which leads to the improvement of PTC effect and the notable reduction of CB content to 20 wt%. It is very interesting to see that for the sample with combined thermal and electrical treatment, CB particles are agglomerated and oriented along the electric field direction to create substantial conductive paths, which leads to a further decrease of CB content down to 15 wt%. In this way, self-limiting heating cables with excellent processability, mechanical properties and PTC effect have simultaneously been achieved.展开更多
Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model,...Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model, based upon which a two-dimensional cylindrical kinetics model is developed for the oxidation of silicon nanowires and is extended for tungsten. In the model, diffusivity is affected by the expansive oxidation reaction induced stress. The dependency of the oxidation upon curvature and temperature is modeled. Good agreement between the model predictions and available experimental data is obtained. The de- veloped model serves to quantify the oxidation in two-dimensional nanostructures and is expected to facilitate their fabrication via thermal oxidation techniques.展开更多
Atomic layer deposition(ALD) as a flexible surface-controlled fabrication technique has attracted widespread interest in numerous nanotechnology applications, which can obtain ultrathin or two-dimensional molybdenum d...Atomic layer deposition(ALD) as a flexible surface-controlled fabrication technique has attracted widespread interest in numerous nanotechnology applications, which can obtain ultrathin or two-dimensional molybdenum disulfide(2D MoS2) films.The ALD technique possesses the characteristics of precise thickness control, excellent uniformity, and conformality, relying on the self-limiting surface reaction. In this mini-review, the knowledge about the fabrication mechanisms and applications of ALD prepared MoS2 films is reviewed. The surface reaction pathway about ALD synthesis MoS2 is elaborated, and the corresponding factors causing saturation adsorption are discussed. Two possible growth mechanisms of ALD-MoS2 film based on the building blocks and MoS2 islands are compared. For both, the deposition process of MoS2 can be divided into two stages, heterogeneous deposition stage and homogeneous deposition stage. The mismatch between the as-deposited MoS2 in the heterodeposition and the lattice structure of the substrate surface is a key factor leading to the poor crystallinity of as-deposited MoS2. In addition, the extensions of ALD MoS2 technique to improve the as-deposited film quality are discussed. Finally, the applications of ALD deposited MoS2 film are summarized, and future perspectives are outlined.展开更多
The sodium(Na)metal battery has the prospect of promising high energy density and sustainable tech-nology for low-cost energy storage.However,the soft texture and high reactivity of Na cause it easy to structure colla...The sodium(Na)metal battery has the prospect of promising high energy density and sustainable tech-nology for low-cost energy storage.However,the soft texture and high reactivity of Na cause it easy to structure collapse and produce side reactions with organic electrolytes.Inspired by ancient Chinese ar-chitecture,a structural engineering strategy is introduced to conquer the above issues.PVDF film-covered stainless steel mesh(SMPF)embedded in the obverse of Na metal to form a“self-limiting”Na/electrolyte interface and bare stainless steel mesh(SM)with high electronic conductivity embedded in the reverse of Na metal to form a uniformly electronic distributed Na/collector interface.Based on the electric field simulation and in-situ optical tests,the well-designed structure of the SM@Na@SMPF electrode can re-strict the dendrite growth and slow down the bubbles release.The above strategies provide important technical support for the large-scale application of flexible Na metal batteries.展开更多
Understanding of metal oxidation is very critical to corrosion control,catalysis synthesis,and advanced materials engineering.Metal oxidation is a very complex phenomenon,with many different processes which are couple...Understanding of metal oxidation is very critical to corrosion control,catalysis synthesis,and advanced materials engineering.Metal oxidation is a very complex phenomenon,with many different processes which are coupled and involved from the onset of reaction.In this work,the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics(MD)simulations using a reactive force field(ReaxFF).We show that oxygen transport is the dominant process during the initial oxidation.Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titanium(0001)surface and further prevented oxidation in the deeper layers.The mechanism of initial oxidation observed in this work can be also applicable to other self-limiting oxidation.展开更多
With the development of the third generation of semiconductor devices,it is essential to achieve precise etching of gallium nitride(GaN)materials that is close to the atomic level.Compared with the traditional wet etc...With the development of the third generation of semiconductor devices,it is essential to achieve precise etching of gallium nitride(GaN)materials that is close to the atomic level.Compared with the traditional wet etching and continuous plasma etching,plasma atomic layer etching(ALE)of GaN has the advantages of self-limiting etching,high selectivity to other materials,and smooth etched surface.In this paper the basic properties and applications of GaN are presented.It also presents the various etching methods of GaN.GaN plasma ALE systems are reviewed,and their similarities and differences are compared.In addition,the industrial application of GaN plasma ALE is outlined.展开更多
文摘Polymer/conductive filler composites have been widely used for the preparation of self-limiting heating cables with the positive temperature coefficient (PTC) effect. The control of conductive filler distribution and network in polymer matrix is the most critical for performance of PTC materials. In order to compensate for the destruction of the filler network structure caused by strong shearing during processing, an excessive conductive filler content is usually added into the polymer matrix, which in turn sacrifices its processability and mechanical properties. In this work, a facile post-treatment of the as-extruded cable, including thermal and electrical treatment to produce high-density polyethylene (HDPE)/carbon black (CB) cable with excellent PTC effect, is developed. It is found for the as-extruded sample, the strong shearing makes the CB particles disperse uniformly in HDPE matrix, and 25 wt% CB is needed for the formation of conductive paths. For the thermal-treated sample, a gradually aggregated CB filler structure is observed, which leads to the improvement of PTC effect and the notable reduction of CB content to 20 wt%. It is very interesting to see that for the sample with combined thermal and electrical treatment, CB particles are agglomerated and oriented along the electric field direction to create substantial conductive paths, which leads to a further decrease of CB content down to 15 wt%. In this way, self-limiting heating cables with excellent processability, mechanical properties and PTC effect have simultaneously been achieved.
基金financial support of this work by the National Natural Science Foundation of China(11472149)the Tsinghua University Initiative Scientific Research Program(2014z22074)
文摘Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model, based upon which a two-dimensional cylindrical kinetics model is developed for the oxidation of silicon nanowires and is extended for tungsten. In the model, diffusivity is affected by the expansive oxidation reaction induced stress. The dependency of the oxidation upon curvature and temperature is modeled. Good agreement between the model predictions and available experimental data is obtained. The de- veloped model serves to quantify the oxidation in two-dimensional nanostructures and is expected to facilitate their fabrication via thermal oxidation techniques.
基金supported by the National Natural Science Foundation of China(Grant No.51822501)the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20170023,BK20181274)+8 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.3202006301,3202006403)the Qing Lan Project of Jiangsu Provincethe International Foundation for Science,Stockholm,Swedenthe Organization for the Prohibition of Chemical Weapons,The Hague,Netherlands,through a grant to Lei Liu(F/4736-2)the grants from Top 6 High-Level Talents Program of Jiangsu Province(Grant No.2017-GDZB-006,Class A)the Tribology Science Fund of State Key Laboratory of Tribology(Grant No.SKLTKF15A11)Open Research Fund of State Key Laboratory of High Performance Complex Manufacturing,Central South University(Grant No.Kfkt2016-11)Open Research Fund of State Key Laboratory of Fire Science(Grant No.HZ2017-KF05)Open Research Fund of State Key Laboratory of Solid Lubrication(Grant No.LSL-1607)。
文摘Atomic layer deposition(ALD) as a flexible surface-controlled fabrication technique has attracted widespread interest in numerous nanotechnology applications, which can obtain ultrathin or two-dimensional molybdenum disulfide(2D MoS2) films.The ALD technique possesses the characteristics of precise thickness control, excellent uniformity, and conformality, relying on the self-limiting surface reaction. In this mini-review, the knowledge about the fabrication mechanisms and applications of ALD prepared MoS2 films is reviewed. The surface reaction pathway about ALD synthesis MoS2 is elaborated, and the corresponding factors causing saturation adsorption are discussed. Two possible growth mechanisms of ALD-MoS2 film based on the building blocks and MoS2 islands are compared. For both, the deposition process of MoS2 can be divided into two stages, heterogeneous deposition stage and homogeneous deposition stage. The mismatch between the as-deposited MoS2 in the heterodeposition and the lattice structure of the substrate surface is a key factor leading to the poor crystallinity of as-deposited MoS2. In addition, the extensions of ALD MoS2 technique to improve the as-deposited film quality are discussed. Finally, the applications of ALD deposited MoS2 film are summarized, and future perspectives are outlined.
基金financially supported by the National Natural Science Foundation of China(No.51901205)the Natural Science Foundation of Zhejiang Province(No.LY21E010003)+2 种基金the College Leading Talents Training Program of Zhejiang Provincethe Re-search Initiation Fund in Ningbo Universitythe K.C.Wong Magna Fund in Ningbo University.
文摘The sodium(Na)metal battery has the prospect of promising high energy density and sustainable tech-nology for low-cost energy storage.However,the soft texture and high reactivity of Na cause it easy to structure collapse and produce side reactions with organic electrolytes.Inspired by ancient Chinese ar-chitecture,a structural engineering strategy is introduced to conquer the above issues.PVDF film-covered stainless steel mesh(SMPF)embedded in the obverse of Na metal to form a“self-limiting”Na/electrolyte interface and bare stainless steel mesh(SM)with high electronic conductivity embedded in the reverse of Na metal to form a uniformly electronic distributed Na/collector interface.Based on the electric field simulation and in-situ optical tests,the well-designed structure of the SM@Na@SMPF electrode can re-strict the dendrite growth and slow down the bubbles release.The above strategies provide important technical support for the large-scale application of flexible Na metal batteries.
基金Support of this work from the National Natural Science Foundation of China(Grant No.51361009)Work at Ames Laboratory was supported by the US Department of Energy,Basic Energy Sciences,Division of Materials Science and Engineering under Contract No.DE-AC02-07CH11358,including a grant of computer time at the National Energy Research Scientific Computing Centre(NERSC)in Berkeley,CA.
文摘Understanding of metal oxidation is very critical to corrosion control,catalysis synthesis,and advanced materials engineering.Metal oxidation is a very complex phenomenon,with many different processes which are coupled and involved from the onset of reaction.In this work,the initial stage of oxidation on titanium surface was investigated in atomic scale by molecular dynamics(MD)simulations using a reactive force field(ReaxFF).We show that oxygen transport is the dominant process during the initial oxidation.Our simulation also demonstrate that a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Titanium(0001)surface and further prevented oxidation in the deeper layers.The mechanism of initial oxidation observed in this work can be also applicable to other self-limiting oxidation.
基金This work was supported by the Key Projects of Ministry of Science and Technology of the People’s Republic of China(Grant No.SQ2020YFF0407077)the Industry-University-Research Cooperation Project of Jiangsu Province(Grant No.BY2020462)+1 种基金the National Foreign Experts Bureau High-end Foreign Experts Project(Grant No.G20190114003)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.2021XKT1206).
文摘With the development of the third generation of semiconductor devices,it is essential to achieve precise etching of gallium nitride(GaN)materials that is close to the atomic level.Compared with the traditional wet etching and continuous plasma etching,plasma atomic layer etching(ALE)of GaN has the advantages of self-limiting etching,high selectivity to other materials,and smooth etched surface.In this paper the basic properties and applications of GaN are presented.It also presents the various etching methods of GaN.GaN plasma ALE systems are reviewed,and their similarities and differences are compared.In addition,the industrial application of GaN plasma ALE is outlined.
