体心立方(body⁃centered cubic,BCC)金属W作为微型化器件中重要的互连材料,其电迁移行为对小尺寸集成电路的稳定性至关重要。本文利用原位透射电子显微(transmission electron microscopy,TEM)技术,在原子尺度下研究了电迁移诱导BCC金属...体心立方(body⁃centered cubic,BCC)金属W作为微型化器件中重要的互连材料,其电迁移行为对小尺寸集成电路的稳定性至关重要。本文利用原位透射电子显微(transmission electron microscopy,TEM)技术,在原子尺度下研究了电迁移诱导BCC金属W表面结构动态演变过程。结果表明,自由表面是主要电迁移路径;而{110}面和<111>方向分别是优选的迁移面迁移方向;电迁移过程中W表面形成特定的原子台阶或锯齿状结构。对于非低能晶面{002},在电流作用下仍能发生定向迁移,形成新的台阶结构。研究结果揭示了电迁移过程中表面结构的演化规律,为优化BCC金属材料的微观结构设计、提高其在高电流密度环境下的结构性能稳定性提供借鉴。展开更多
We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the ...We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.展开更多
The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to ...The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to polycrystalline tricobalt tetroxide,in the presence of oxygen with a low partial pressure.Numerous cavities(or voids) were formed during the oxidation,owing to the Kirkendall effect.Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law,which was consistent with diffusion-limited kinetics.In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered.The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation,and formed the hollow structure.Irradiation by the electron beam,which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate,played an important role in activating and promoting the oxidations.These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.展开更多
ln-situ transmission electron microscopy in combination with a heating stage has been employed to real-time monitor varia- tions of δ-phase MnO2 nanoflowers in terms of their morphology and crystalline structures upo...ln-situ transmission electron microscopy in combination with a heating stage has been employed to real-time monitor varia- tions of δ-phase MnO2 nanoflowers in terms of their morphology and crystalline structures upon thermal annealing at elevated temperatures up to -665 ℃. High-temperature annealing drives the diffusion of the small δ-MnO2 nanocrystallites within short distances less than 15 nm and the fusion of the adjacent δ-MnO： nanocrystallites, leading to the formation of larger crystalline domains including highly crystalline nanorods. The annealed nanoflowers remain their overall flower-like morphology while they are converted to α-MnO2. The preferred transformation of the δ-MnO2 to the α-MnO2 can be ascribed to the close lattice spacing of most crystalline lattices between δ-MnO2 and α-MnO2, that might lead to a possible epitaxial growth of ct-MnO2 lattices on the 8-MnO2 lattices during the thermal annealing process.展开更多
Heterogeneous catalytic reactions involve the use of highly dispersed active phases such as metal, metal oxide, or metal sulphide nanoparticIes on thermally stable supports. Fluctuations of the reaction temperature du...Heterogeneous catalytic reactions involve the use of highly dispersed active phases such as metal, metal oxide, or metal sulphide nanoparticIes on thermally stable supports. Fluctuations of the reaction temperature during the reactions can induce sintering of the particles. The stability of such small particles represents a crucial parameter in the development of new families of catalysts with high activity in many fields. Here we report the stability of platinum nanoparticles （2-3 nm） on a few-layer graphene （FLG） surface as studied by in situ high temperature transmission electron microscopy.展开更多
文摘体心立方(body⁃centered cubic,BCC)金属W作为微型化器件中重要的互连材料,其电迁移行为对小尺寸集成电路的稳定性至关重要。本文利用原位透射电子显微(transmission electron microscopy,TEM)技术,在原子尺度下研究了电迁移诱导BCC金属W表面结构动态演变过程。结果表明,自由表面是主要电迁移路径;而{110}面和<111>方向分别是优选的迁移面迁移方向;电迁移过程中W表面形成特定的原子台阶或锯齿状结构。对于非低能晶面{002},在电流作用下仍能发生定向迁移,形成新的台阶结构。研究结果揭示了电迁移过程中表面结构的演化规律,为优化BCC金属材料的微观结构设计、提高其在高电流密度环境下的结构性能稳定性提供借鉴。
基金Acknowle dgements This work was financially supported by the National Natural Science Foundation of China （NSFC） （Nos. 10704044 and 50825201）, Fok Ying Tung Education Foundation （No. 111049）, and the National BasicResearch Program of China （No. 2007CB935301）. We thank Qingyu Zhao and Xiaoyang Lin for the help in the STA experiments. RS and SWC acknowledge the support from NSF-CBET （#0625340）. We gratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University.
文摘We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.
基金supported by the National Natural Science Foundation of China(11227403,11327901,51472215,51222202)the National Basic Research Program of China(2014CB932500,2015CB921004)+1 种基金Cyrus Tang Center for Sensor Materials and Applicationsthe resources of the Center of Electron Microscopy of Zhejiang University(ZJU)
文摘The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to polycrystalline tricobalt tetroxide,in the presence of oxygen with a low partial pressure.Numerous cavities(or voids) were formed during the oxidation,owing to the Kirkendall effect.Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law,which was consistent with diffusion-limited kinetics.In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered.The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation,and formed the hollow structure.Irradiation by the electron beam,which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate,played an important role in activating and promoting the oxidations.These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.
基金the Center for Nanoscale Materials, a U.S.Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under contract No. DE-AC02-06CH11357Use of the Electron Microscopy Center for Materials Research and Advanced Photon Source (Beam line 11-ID-C) at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of BasicEnergy Sciences, under contract No. DE-AC02-06CH11357
文摘ln-situ transmission electron microscopy in combination with a heating stage has been employed to real-time monitor varia- tions of δ-phase MnO2 nanoflowers in terms of their morphology and crystalline structures upon thermal annealing at elevated temperatures up to -665 ℃. High-temperature annealing drives the diffusion of the small δ-MnO2 nanocrystallites within short distances less than 15 nm and the fusion of the adjacent δ-MnO： nanocrystallites, leading to the formation of larger crystalline domains including highly crystalline nanorods. The annealed nanoflowers remain their overall flower-like morphology while they are converted to α-MnO2. The preferred transformation of the δ-MnO2 to the α-MnO2 can be ascribed to the close lattice spacing of most crystalline lattices between δ-MnO2 and α-MnO2, that might lead to a possible epitaxial growth of ct-MnO2 lattices on the 8-MnO2 lattices during the thermal annealing process.
文摘Heterogeneous catalytic reactions involve the use of highly dispersed active phases such as metal, metal oxide, or metal sulphide nanoparticIes on thermally stable supports. Fluctuations of the reaction temperature during the reactions can induce sintering of the particles. The stability of such small particles represents a crucial parameter in the development of new families of catalysts with high activity in many fields. Here we report the stability of platinum nanoparticles （2-3 nm） on a few-layer graphene （FLG） surface as studied by in situ high temperature transmission electron microscopy.
