In-situ SEM can intuitively observe the changes in microstructure and microcrack initiation during the deformation process of the specimen.In this paper,the microstructural evolution,mechanical properties,and damage n...In-situ SEM can intuitively observe the changes in microstructure and microcrack initiation during the deformation process of the specimen.In this paper,the microstructural evolution,mechanical properties,and damage nucleation modes of DP1180 laser welded joints were systematically discussed by the trans-mission electron microscope(TEM),focused ion beam(FIB),and in-situ tensile test.The precipitation of carbides and disappearance of dislocations tangles deteriorated the mechanical properties of tempered martensite in the sub-critical heat affected zone(SCHAZ),which caused its microhardness slightly de-creased(∼27 HV)and also called the softened zone.The joints fractured in the SCHAZ during the tensile and Erichsen cupping tests and microcracks initiated from the tempered martensite,while the microc-rack initiation of base material(BM)occurred at the ferrite/martensite interface.The dominant damage nucleation mode of the joint was tempered martensite cracking,and that of BM was ferrite/martensite interface decohesion during tests.展开更多
Number concentration and distribution of airborne particles in the size range 5.6 to 560 nm diameter were measured in Beijing for a 15-d period in winter 2005. Dally average number concentrations of nucleation mode （...Number concentration and distribution of airborne particles in the size range 5.6 to 560 nm diameter were measured in Beijing for a 15-d period in winter 2005. Dally average number concentrations of nucleation mode （5.6-20 um）, Aitken mode （20-100 um）, and accumulation mode （100-560 um） particles, and total particles were 17500, 32000, 4000, and 53500 cm^-3, respectively. Average particle size distribution was monomodal with a mode diameter of about 40 um at night and bimodal with mode diameters of about 10 and about 40 um during the daytime. New particle formation events, which were connected to diurnal variation of nucleation mode particles, were observed in more than half of the observation days. The events often started around 10：00-11：00 Chinese Standard Time （CST） and ended up after 3-4 h. Concentrations of Aitken and accumulation mode particles increased from midnight and reached their maxima at about 10：00 CST, and then decreased and became the lowest in the afternoon. Analysis of diurnal cycles in traffic volume and meteorological parameters revealed that the accumulation of the particles in Aitken and accumulation modes in the morning was influenced by formation of an inversion and increase in vehicle emission, and dispersion of such particles in the afternoon was associated with more effective vertical mixing and higher wind speed.展开更多
Two-dimensional(2D)semiconductors offer an atomic thickness that facilitates superior gate field penetration and enables transistors to maintain shrinking with suppressed short-channel effects,thereby being considered...Two-dimensional(2D)semiconductors offer an atomic thickness that facilitates superior gate field penetration and enables transistors to maintain shrinking with suppressed short-channel effects,thereby being considered as channel materials for future transistors in the post-Moore era.As a member of high-mobility 2D semiconductors,the air-stable Bi_(2)O_(2)Se with a moderate bandgap has drawn significant attention.Distinguished from other 2D materials,Bi_(2)O_(2)Se can be oxidized layer-by-layer to form a high-k native-oxide dielectric,Bi2SeO5,with an atomically sharp interface,similar to Si/SiO2 in the semiconductor industry.These characteristics make Bi_(2)O_(2)Se an ideal material platform for fabricating various devices with excellent performance,such as transistors,thermoelectrics,optoelectronics,sensors,flexible devices and memory devices.To realize advanced applications of 2D Bi_(2)O_(2)Se,it is essential to develop scalable and high-quality preparation methods with relatively low cost.Chemical vapor deposition(CVD)has shown promise in meeting these requirements.Over the past years,CVD has been widely used to synthesize 2D Bi_(2)O_(2)Se despite some remaining challenges.In this review,we summarize the recent progress in the controlled growth of 2D Bi_(2)O_(2)Se via the CVD method.We begin by introducing the crystal structure and properties of Bi_(2)O_(2)Se.Next,we focus on the morphology control of 2D Bi_(2)O_(2)Se,including various nucleation modes and different dimensionalities by carefully manipulating the CVD process.In terms of nucleation modes,in-plane and vertical epitaxial growth of Bi_(2)O_(2)Se,achieved by controlling the interaction between epitaxial layer and substrate,are reviewed.Wafer-scale continuous Bi_(2)O_(2)Se film facilitates the device integration while vertical 2D fins pave the way for fabricating high-performance fin field-effect-transistors(FinFET).As for the dimensionality control,the transition from 2D nanoplates to 1D nanoribbons is investigated.Parameters such as precursor ratio,growth temperature and types of catalyst play a key role in such transition.We then discuss the construction of ordered arrays of Bi_(2)O_(2)Se with the above morphology by selective growth and post treatment for potential device integration.In addition,we highlight the electrical quality improvement of the grown material via defect control and strain release.For example,both the Se poor growth condition and the out-of-plane strain-free growth contribute to higher mobility of Bi_(2)O_(2)Se.Lastly,we propose potential strategies for precise control of Bi_(2)O_(2)Se structures and quality.In order to meet the demands of advanced electronic applications,more efforts are expected to made to achieve uniform,transferable and site-specific preparation of high-quality single-crystal Bi_(2)O_(2)Se on a large scale.展开更多
Rapid solidification in undercooled Ni-18.7 at.%Sn eutectic melts was observed in-situ by a high-speed high-resolution camera and the microstructures were characterized in detail by electron backscattering diffraction...Rapid solidification in undercooled Ni-18.7 at.%Sn eutectic melts was observed in-situ by a high-speed high-resolution camera and the microstructures were characterized in detail by electron backscattering diffraction.For the first time,the exact crystallographic orientation relations(ORs)between HCP-Ni_(3)Sn(α-Ni)subsets were analyzed.For HCP-Ni_(3)Sn,the{1121}<1126>and/or{1122}<1123>twin ORs(i.e.,HCP-Ni_(3)Sn twins)hold independently on undercooling,whereas forα-Ni,the{111}<112>twin OR is the case at low undercooling and would hold initially at intermediate and high undercooling.The roles of twinning and allotropy transformation(i.e.,FCC-Ni_(3)Sn→HCP-Ni_(3)Sn)were integrated to reveal the formation mechanism of HCP-Ni_(3)Sn twins,and a reversed OR transition analysis was carried out for rep-resentative samples from low to high undercooling.Consequently,novel twin-assisted eutectic growth was found to occur all along.On this basis,we showed that the single nucleation mode of Herlach is followed,and speculated that primary and secondary coupled eutectic dendrite growth and un-coupled growth ofα-Ni and FCC-Ni_(3)Sn might all be the origins of anomalous eutectics.This work would shed some lights on the long-time controversies about the nucleation mode and the formation mechanism of anomalous eutectics in undercooled eutectic alloys.展开更多
In the present work,the focus has been shifted to the relationship between the PANI morphology and the physicochemical properties,controlled by the amount of added ionic liquids,of the polymerization medium instead of...In the present work,the focus has been shifted to the relationship between the PANI morphology and the physicochemical properties,controlled by the amount of added ionic liquids,of the polymerization medium instead of focusing on the structure of the ionic liquids as used to be in the litterature.For that reason,PANI has been synthesized in different weight ratio of[Pyrr][PTS]/water following the standard experimental process.The addition of[Pyrr][PTS]into the polymerization medium controls the morphology of PANI without affecting its structure.Moreover,[Pyrr][PTS]promotes a viscous reaction system without the need of an external source.The viscosity of the polymerization system restricts the diffusion of species that leads to the predominance of the homogeneous nucleation mode during the course of polymerization and,thus,nanostructuring of PANI morphology.As for the ionic conductivity,it reflects the mobility of the ions of the polymerization medium and,thus,the way of its interference with the formed PANI that affects the arrangement and the shape of formed PANI fibers.This relationship between PANI morphology and the physicochemical properties,adjusted by adding ionic liquids,of the polymerization medium is prelaminar and promising.The effect of the ionic liquids on the viscosity as well as on the mobility of the polymerization medium have to be taken into consideration to choose the ionic liquids,which lead to the PANI with desired morphology.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.51871010 and52005022).
文摘In-situ SEM can intuitively observe the changes in microstructure and microcrack initiation during the deformation process of the specimen.In this paper,the microstructural evolution,mechanical properties,and damage nucleation modes of DP1180 laser welded joints were systematically discussed by the trans-mission electron microscope(TEM),focused ion beam(FIB),and in-situ tensile test.The precipitation of carbides and disappearance of dislocations tangles deteriorated the mechanical properties of tempered martensite in the sub-critical heat affected zone(SCHAZ),which caused its microhardness slightly de-creased(∼27 HV)and also called the softened zone.The joints fractured in the SCHAZ during the tensile and Erichsen cupping tests and microcracks initiated from the tempered martensite,while the microc-rack initiation of base material(BM)occurred at the ferrite/martensite interface.The dominant damage nucleation mode of the joint was tempered martensite cracking,and that of BM was ferrite/martensite interface decohesion during tests.
基金Project supported by the National Natural Science Foundation of China(No.20477020)the National Science Fund for Distinguished Young Scholars(No.20625722).
文摘Number concentration and distribution of airborne particles in the size range 5.6 to 560 nm diameter were measured in Beijing for a 15-d period in winter 2005. Dally average number concentrations of nucleation mode （5.6-20 um）, Aitken mode （20-100 um）, and accumulation mode （100-560 um） particles, and total particles were 17500, 32000, 4000, and 53500 cm^-3, respectively. Average particle size distribution was monomodal with a mode diameter of about 40 um at night and bimodal with mode diameters of about 10 and about 40 um during the daytime. New particle formation events, which were connected to diurnal variation of nucleation mode particles, were observed in more than half of the observation days. The events often started around 10：00-11：00 Chinese Standard Time （CST） and ended up after 3-4 h. Concentrations of Aitken and accumulation mode particles increased from midnight and reached their maxima at about 10：00 CST, and then decreased and became the lowest in the afternoon. Analysis of diurnal cycles in traffic volume and meteorological parameters revealed that the accumulation of the particles in Aitken and accumulation modes in the morning was influenced by formation of an inversion and increase in vehicle emission, and dispersion of such particles in the afternoon was associated with more effective vertical mixing and higher wind speed.
文摘Two-dimensional(2D)semiconductors offer an atomic thickness that facilitates superior gate field penetration and enables transistors to maintain shrinking with suppressed short-channel effects,thereby being considered as channel materials for future transistors in the post-Moore era.As a member of high-mobility 2D semiconductors,the air-stable Bi_(2)O_(2)Se with a moderate bandgap has drawn significant attention.Distinguished from other 2D materials,Bi_(2)O_(2)Se can be oxidized layer-by-layer to form a high-k native-oxide dielectric,Bi2SeO5,with an atomically sharp interface,similar to Si/SiO2 in the semiconductor industry.These characteristics make Bi_(2)O_(2)Se an ideal material platform for fabricating various devices with excellent performance,such as transistors,thermoelectrics,optoelectronics,sensors,flexible devices and memory devices.To realize advanced applications of 2D Bi_(2)O_(2)Se,it is essential to develop scalable and high-quality preparation methods with relatively low cost.Chemical vapor deposition(CVD)has shown promise in meeting these requirements.Over the past years,CVD has been widely used to synthesize 2D Bi_(2)O_(2)Se despite some remaining challenges.In this review,we summarize the recent progress in the controlled growth of 2D Bi_(2)O_(2)Se via the CVD method.We begin by introducing the crystal structure and properties of Bi_(2)O_(2)Se.Next,we focus on the morphology control of 2D Bi_(2)O_(2)Se,including various nucleation modes and different dimensionalities by carefully manipulating the CVD process.In terms of nucleation modes,in-plane and vertical epitaxial growth of Bi_(2)O_(2)Se,achieved by controlling the interaction between epitaxial layer and substrate,are reviewed.Wafer-scale continuous Bi_(2)O_(2)Se film facilitates the device integration while vertical 2D fins pave the way for fabricating high-performance fin field-effect-transistors(FinFET).As for the dimensionality control,the transition from 2D nanoplates to 1D nanoribbons is investigated.Parameters such as precursor ratio,growth temperature and types of catalyst play a key role in such transition.We then discuss the construction of ordered arrays of Bi_(2)O_(2)Se with the above morphology by selective growth and post treatment for potential device integration.In addition,we highlight the electrical quality improvement of the grown material via defect control and strain release.For example,both the Se poor growth condition and the out-of-plane strain-free growth contribute to higher mobility of Bi_(2)O_(2)Se.Lastly,we propose potential strategies for precise control of Bi_(2)O_(2)Se structures and quality.In order to meet the demands of advanced electronic applications,more efforts are expected to made to achieve uniform,transferable and site-specific preparation of high-quality single-crystal Bi_(2)O_(2)Se on a large scale.
基金This work was financially supported by the National Natural Science Foundation of China(No.51975474)the Fundamental Research Funds for the Central Universities(No.3102019JC001)Haifeng Wang is very grateful to Prof.D.M.Herlach(1949-2022)for his inspiring suggestions and continuous support on the work of rapid solidification.
文摘Rapid solidification in undercooled Ni-18.7 at.%Sn eutectic melts was observed in-situ by a high-speed high-resolution camera and the microstructures were characterized in detail by electron backscattering diffraction.For the first time,the exact crystallographic orientation relations(ORs)between HCP-Ni_(3)Sn(α-Ni)subsets were analyzed.For HCP-Ni_(3)Sn,the{1121}<1126>and/or{1122}<1123>twin ORs(i.e.,HCP-Ni_(3)Sn twins)hold independently on undercooling,whereas forα-Ni,the{111}<112>twin OR is the case at low undercooling and would hold initially at intermediate and high undercooling.The roles of twinning and allotropy transformation(i.e.,FCC-Ni_(3)Sn→HCP-Ni_(3)Sn)were integrated to reveal the formation mechanism of HCP-Ni_(3)Sn twins,and a reversed OR transition analysis was carried out for rep-resentative samples from low to high undercooling.Consequently,novel twin-assisted eutectic growth was found to occur all along.On this basis,we showed that the single nucleation mode of Herlach is followed,and speculated that primary and secondary coupled eutectic dendrite growth and un-coupled growth ofα-Ni and FCC-Ni_(3)Sn might all be the origins of anomalous eutectics.This work would shed some lights on the long-time controversies about the nucleation mode and the formation mechanism of anomalous eutectics in undercooled eutectic alloys.
基金funded by RESCOLL French society and the Lebanese University。
文摘In the present work,the focus has been shifted to the relationship between the PANI morphology and the physicochemical properties,controlled by the amount of added ionic liquids,of the polymerization medium instead of focusing on the structure of the ionic liquids as used to be in the litterature.For that reason,PANI has been synthesized in different weight ratio of[Pyrr][PTS]/water following the standard experimental process.The addition of[Pyrr][PTS]into the polymerization medium controls the morphology of PANI without affecting its structure.Moreover,[Pyrr][PTS]promotes a viscous reaction system without the need of an external source.The viscosity of the polymerization system restricts the diffusion of species that leads to the predominance of the homogeneous nucleation mode during the course of polymerization and,thus,nanostructuring of PANI morphology.As for the ionic conductivity,it reflects the mobility of the ions of the polymerization medium and,thus,the way of its interference with the formed PANI that affects the arrangement and the shape of formed PANI fibers.This relationship between PANI morphology and the physicochemical properties,adjusted by adding ionic liquids,of the polymerization medium is prelaminar and promising.The effect of the ionic liquids on the viscosity as well as on the mobility of the polymerization medium have to be taken into consideration to choose the ionic liquids,which lead to the PANI with desired morphology.
