In order to investigate a gradient nano/micro-structured surface layer on pure copper produced by severe plasticity roller burnishing （SPRB） and grain refinement mechanism, the microstructure characteristics and mat...In order to investigate a gradient nano/micro-structured surface layer on pure copper produced by severe plasticity roller burnishing （SPRB） and grain refinement mechanism, the microstructure characteristics and material properties of sample at various depths from the topmost surface were investigated by SEM, TEM, XRD, OM etc. The experimental results show that the gradient nano/micro-structure was introduced into the surface layer of over 100μm in thickness. The remarkable increase in hardness near the topmost surface was mainly attributed to the reduced grain size. The equiaxed nano-sized grains were in random orientation and the most of their boundaries were low-angle grain boundaries （LAGBs）. The coarse grains are refined into the few micro-sized grains by dislocation activities;deformation twinning was found to be the primary form for the formation of submicron grains;the formation of nanostructure was dominated by dislocation activities accompanied with rotation of grains in local region.展开更多
A1203/5%SIC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed （HIP）, which can subsequently break through the disadvantage of hot-pressing proc...A1203/5%SIC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed （HIP）, which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of A1203 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, A12OJSiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed A1203/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the A1203/5%SIC nanocomposites by pressureless sintering and post HIP process.展开更多
Atomically thin transition-metal dichalcogenide(TMDC) nanostructures are predicted to exhibit novel physical properties that make them attractive candidates for the fabrication of electronic and optoelectronic devices...Atomically thin transition-metal dichalcogenide(TMDC) nanostructures are predicted to exhibit novel physical properties that make them attractive candidates for the fabrication of electronic and optoelectronic devices. However, TMDCs tend to grow in the form of two-dimensional nanoplates(NPs) rather than one-dimensional nanoribbons(NRs) due to their native layered structure. Herein, we have developed a space-confined and substrate-directed chemical vapor deposition strategy for the controllable synthesis of WS2, WSe2, MoSe2, MoS2, WS2(1-x)Se2x NPs and NRs. TMDC NRs with lengths ranging from several micrometers to 100 μm have been obtained and the widths of TMDC NRs can be effectively tuned.Moreover, we found that TMDC NRs show different growth behaviors on van der Waals(vdW) and nonvd W substrates. The micro-nano structures, optical and electronic properties of synthesized TMDC NRs have been systematically investigated. This approach provides a general strategy for controllable synthesis of TMDC NRs, which makes these materials easily accessible as functional building blocks for novel optoelectronic devices.展开更多
Oxidative etching can be a powerful approach to modify the morphology of nanoscale materials for various applications.Unveiling of the etching mechanisms and morphological evolution during etching is critical.Using th...Oxidative etching can be a powerful approach to modify the morphology of nanoscale materials for various applications.Unveiling of the etching mechanisms and morphological evolution during etching is critical.Using the liquid cell transmission electron microscopy,we investigate the etching behavior of gold nanorods under different electron beam dose rates:caseⅠ,3.5×10^9 Gy s^-1;caseⅡ,1.5×10^10 Gy s^-1;caseⅢ,4.5×10^10 Gy s^-1.The Au nanorod develops facets at the tips(caseⅠ)or adopts a transit ellipsoid shape and eventually dissolves(caseⅡ),depending on the dose rate.The rapid etching under an even higher dose rate(caseⅢ)may lead to the formation of Au3+ion-rich intermediates around the nanorod,which further accelerates the lateral etching and unexpectedly increases the aspect ratio of the nanorod.Our quantitative analysis shows that the critical size of the nanorod,below which the etching rate increases significantly with the reduction of nanorod size,may vary subject to the degree that the system is away from equilibrium.These results provide significant insights into the oxidative etching mechanisms and shed light on the rational design and synthesis of nanostructures.展开更多
基金Project(50975095)supported by the National Natural Science Foundation of ChinaProject(2012ZM0048)supported by the Fundamental Research Funds for the Central Universities,China
文摘In order to investigate a gradient nano/micro-structured surface layer on pure copper produced by severe plasticity roller burnishing （SPRB） and grain refinement mechanism, the microstructure characteristics and material properties of sample at various depths from the topmost surface were investigated by SEM, TEM, XRD, OM etc. The experimental results show that the gradient nano/micro-structure was introduced into the surface layer of over 100μm in thickness. The remarkable increase in hardness near the topmost surface was mainly attributed to the reduced grain size. The equiaxed nano-sized grains were in random orientation and the most of their boundaries were low-angle grain boundaries （LAGBs）. The coarse grains are refined into the few micro-sized grains by dislocation activities;deformation twinning was found to be the primary form for the formation of submicron grains;the formation of nanostructure was dominated by dislocation activities accompanied with rotation of grains in local region.
基金Project supported by Pusan National University Research GrantProject(2010-0008-276) supported by National Core Research Center Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology
文摘A1203/5%SIC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed （HIP）, which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of A1203 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, A12OJSiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed A1203/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the A1203/5%SIC nanocomposites by pressureless sintering and post HIP process.
基金supported by the National Natural Science Foundation of China(11974301,11404274,11574395,11702236,61804050)the support from National Natural Science Foundation of China(21673054 and 11874130)+4 种基金the Science and Technology Project of Hunan Province(2019JJ30021,2018JJ3489)Grant from Education Commission of Hunan Province(18B084)Degree and Postgraduate Education Reform Project of Hunan Province(JG2018B045)the Program for Changjiang Scholars and Innovative Research Team in University(IRT13093)financial support from the research project of National University of Defense Technology(ZK18-03-38)。
文摘Atomically thin transition-metal dichalcogenide(TMDC) nanostructures are predicted to exhibit novel physical properties that make them attractive candidates for the fabrication of electronic and optoelectronic devices. However, TMDCs tend to grow in the form of two-dimensional nanoplates(NPs) rather than one-dimensional nanoribbons(NRs) due to their native layered structure. Herein, we have developed a space-confined and substrate-directed chemical vapor deposition strategy for the controllable synthesis of WS2, WSe2, MoSe2, MoS2, WS2(1-x)Se2x NPs and NRs. TMDC NRs with lengths ranging from several micrometers to 100 μm have been obtained and the widths of TMDC NRs can be effectively tuned.Moreover, we found that TMDC NRs show different growth behaviors on van der Waals(vdW) and nonvd W substrates. The micro-nano structures, optical and electronic properties of synthesized TMDC NRs have been systematically investigated. This approach provides a general strategy for controllable synthesis of TMDC NRs, which makes these materials easily accessible as functional building blocks for novel optoelectronic devices.
基金supported by the National Natural Science Foundation of China(51420105003,11327901,61601116 and 61974021)the National Science Fund for Distinguished Young Scholars(11525415)China Scholarship Council(201806090114)。
文摘Oxidative etching can be a powerful approach to modify the morphology of nanoscale materials for various applications.Unveiling of the etching mechanisms and morphological evolution during etching is critical.Using the liquid cell transmission electron microscopy,we investigate the etching behavior of gold nanorods under different electron beam dose rates:caseⅠ,3.5×10^9 Gy s^-1;caseⅡ,1.5×10^10 Gy s^-1;caseⅢ,4.5×10^10 Gy s^-1.The Au nanorod develops facets at the tips(caseⅠ)or adopts a transit ellipsoid shape and eventually dissolves(caseⅡ),depending on the dose rate.The rapid etching under an even higher dose rate(caseⅢ)may lead to the formation of Au3+ion-rich intermediates around the nanorod,which further accelerates the lateral etching and unexpectedly increases the aspect ratio of the nanorod.Our quantitative analysis shows that the critical size of the nanorod,below which the etching rate increases significantly with the reduction of nanorod size,may vary subject to the degree that the system is away from equilibrium.These results provide significant insights into the oxidative etching mechanisms and shed light on the rational design and synthesis of nanostructures.
