Since its discovery, the direct imaging and determination of the crystal structure of few-layer graphdiyne has proven difficult because it is too delicate under irradiation by an electron beam. In this work, the cryst...Since its discovery, the direct imaging and determination of the crystal structure of few-layer graphdiyne has proven difficult because it is too delicate under irradiation by an electron beam. In this work, the crystal structure of a six-layered graphdiyne nanosheet was directly observed by low-voltage transmission electron microscopy （TEM） using low current density. The combined use of high-resolution TEM （HRTEM） simulation, electron energy-loss spectroscopy, and electron diffraction revealed that the as-synthesized nanosheet was crystalline graphdiyne with a thickness of 2.19 nm （corresponding to a thickness of six layers） and showed ABC stacking. Thus, this work provides direct evidence for the existence and crystal structure of few-layer graphdiyne, which is a new type of two-dimensional carbon material complementary to graphene.展开更多
Silver nanoparticles with average particles sizes ranging from 2 to 131nm were manipulatively synthesized starting from silver nitrate using different functional group-containing organic modifiers at room temperature....Silver nanoparticles with average particles sizes ranging from 2 to 131nm were manipulatively synthesized starting from silver nitrate using different functional group-containing organic modifiers at room temperature. The effects of the organic modifiers on the morphology of the resulting silver nanoparticles were strongly dependent on the intrinsic properties of the functional groups and the reducibility of the reductant. Numerous ether bonds （-0-）present in polyethylene glycol and Tween-80 were beneficial to the formation of silver nanoparticles with particle sizes of several nanometers in a narrow size distribution in both weak and strong reducing environments. Cetyltrimethylammonium bromide induced the formation of nanosized silver triangle plates in a weak reducing environment. The crystal growth of the silver nanoparticles with particle sizes of more than lOnm was postulated through an adhesion process of small-sized particles followed by a subsequent coalescence process under the present reaction conditions.展开更多
Because of its high compatibility with conventional microfabrication processing technology, epitaxial graphene （EG） grown on SiC shows exceptional promise for graphene-based electronics. However, to date, a detailed...Because of its high compatibility with conventional microfabrication processing technology, epitaxial graphene （EG） grown on SiC shows exceptional promise for graphene-based electronics. However, to date, a detailed understanding of the transformation from three-layer SiC to monolayer graphene is still lacking. Here, we demonstrate the direct atomic-scale observation of EG growth on a SiC （11^-00） surface at 1,000℃ by in situ transmission electron microscopy in combination with ab initio molecular dynamics （AIMD） simulations. Our detailed analysis of the growth dynamics of monolayer graphene reveals that three SiC （11^-00） layers decompose successively to form one graphene layer. Sublimation of the first layer causes the formation of carbon clusters containing short chains and hexagonal rings, which can be considered as the nuclei for graphene growth. Decomposition of the second layer results in the appearance of new chains connecting to the as-formed clusters and the formation of a network with large pores. Finally, the carbon atoms released from the third layer lead to the disappearance of the chains and large pores in the network, resulting in a whole graphene layer. Our study presents a clear picture of the epitaxial growth of the monolayer graphene from SiC and provides valuable information for future developments in SiC-derived EG technology.展开更多
Direct observation of the dissolution behavior of nanomaterials could provide fundamental insight to understanding their anisotropic properties and stability. The dissolution mechanism in solution and vacuum has been ...Direct observation of the dissolution behavior of nanomaterials could provide fundamental insight to understanding their anisotropic properties and stability. The dissolution mechanism in solution and vacuum has been well documented. However, the gas-involved dissolution and regrowth have seldom been explored and the mechanisms remain elusive. We report herein, an in situ TEM study of the dissolution and regrowth dynamics of MoO2 nanowires under oxygen using environmental transmission electron microscopy （ETEM）. For the first time, oscillatory dissolution on the nanowire tip is revealed, and, intriguingly, simultaneous layer-by-layer regrowth on the sidewall facets is observed, leading to a shorter and wider nanowire. Combined with first-principles calculations, we found that electron beam irradiation caused oxygen loss in the tip facets, which resulted in changing the preferential growth facets and drove the morphology reshaping.展开更多
Solid electrolyte based-resistive memories have been considered to be a potential candidate for future information technology with applications in non-volatile memory, logic circuits and neuromorphic computing. A cond...Solid electrolyte based-resistive memories have been considered to be a potential candidate for future information technology with applications in non-volatile memory, logic circuits and neuromorphic computing. A conductive filament model has been generally accepted to be the underlying mechanism for the resistive switching. However, the growth dynamics of such conductive filaments is still not fully understood. Here, we explore the controllability of filament growth by correlating observations of the filament growth with the electric field distribution and several other factors. The filament growth behavior has been recorded using in situ transmission electron microscopy. By studying the real- time recorded filament growth behavior and morphologies, we have been able to simulate the electric field distribution in accordance with our observations. Other factors have also been shown to affect the filament growth, such as Joule heating and electrolyte infrastructure. This work provides insight into the controllable growth of conductive filaments and will help guide research into further functionalities of nanoionic resistive memories.展开更多
The dynamic behavior of octahedral gold nanopartides （NPs） and nanoparticle clusters （NPCs） in aqueous solution is studied by in-situ liquid-cell transmission electron microscopy （TEM）. The octahedral Au NPs/NPC...The dynamic behavior of octahedral gold nanopartides （NPs） and nanoparticle clusters （NPCs） in aqueous solution is studied by in-situ liquid-cell transmission electron microscopy （TEM）. The octahedral Au NPs/NPCs show preferential orientations in the liquid cell, due to the interaction with the SiNx window. The Au NPs show long-range reversible hopping and three-dimensional （3D） rotational motions in the liquid environment. At the same time, the Au NPCs and NPs perform slow stick-sUp and stick-roU motions, respectivel~ with a centripetal trend. The centripetal motions were explained by a liquid evaporation-induced radial flow model in which the NPCs/NPs trajectories are controlled by Stokes forces and surface friction by the silicon nitride window. The calculated radius-dependent force （Fc） on the NPCs/NPs shows a semi-linear correlation with the distance r between the NPCs/NPs and the center of mass, accompanied with stochastic fluctuations, in agreement with the model predictions. This work thus demonstrates the effectiveness of in situ liquid-cell TEM for the in-depth understanding of complicated liquid flow and force interactions in nanomaterials.展开更多
Comprehensive understanding of the structural/morphology stability of ultrathin （diameter 〈 10 nm） gold nanowires under real service conditions （such as under Joule heating） is a prerequisite for the reliable imp...Comprehensive understanding of the structural/morphology stability of ultrathin （diameter 〈 10 nm） gold nanowires under real service conditions （such as under Joule heating） is a prerequisite for the reliable implementation of these emerging building blocks into functional nanoelectronics and mechatronics systems. Here, by using the in situ transmission electron microscopy （TEM） technique, we discovered that the Rayleigh instability phenomenon exists in ultrathin gold nanowires upon moderate heating. Through the controlled electron beam irradiation-induced heating mechanism （with 〈 100 ~C temperature rise）, we further quantified the effect of electron beam intensity and its dependence on Rayleigh instability in altering the geometry and morphology of the ultrathin gold nanowires. Moreover, in situ high-resolution TEM （HRTEM） observations revealed surface atomic diffusion process to be the dominating mechanism for the morphology evolution processes. Our results, with unprecedented details on the atomic-scale picture of Rayleigh instability and its underlying physics, provide critical insights on the thermal/structural stability of gold nanostructures down to a sub-10 nm level which may pave the way for their interconnect applications in future ultra- large-scale integrated ciroaits.展开更多
Graphene has demonstrated its potential in several practical applications owing to its remarkable electronic and physical properties. In this study, we successfully fabricated a suspended graphene device with a width ...Graphene has demonstrated its potential in several practical applications owing to its remarkable electronic and physical properties. In this study, we successfully fabricated a suspended graphene device with a width down to 20 nm. The morphological evolution of graphene under various electric field effects was systematically examined using an in-situ transmission electron microscope （TEM）. The hourglass-shaped graphene sample instantly broke apart at 7.5 mA, indicating an impressive breakdown current density. The current-carrying capacity was calculated to be -1.6 × 10^9 A.cm-2, which is several orders higher than that of copper. The current-carrying capacity depended on the resistivity of graphene. In addition, atomic volume changes occurred in the multilayer graphene samples due to surface diffusion and Ostwald ripening （OR）, indicating that the breakdown mechanism is well approximated by the electric field. This study not only provides a theory to explain the breakdown behavior but also presents the effects on materials contacted with a graphene layer used as the transmission path.展开更多
Background：Contrast-enhanced ultrasound is a dynamic and continuous modality providing real-time view of vascularization and flow distribution patterns of different organs and tumors.In order to evaluate the diagnost...Background：Contrast-enhanced ultrasound is a dynamic and continuous modality providing real-time view of vascularization and flow distribution patterns of different organs and tumors.In order to evaluate the diagnostic significance of intraoperative contrast-enhanced ultrasound in assessing the resection degree of brain glioma by transmission electron microscopic （TEM） examination,it is important to have specific knowledge about contrast-enhanced ultrasound.Methods：Ultrasound contrast was applied in operations of 120 cases of brain glioma,to evaluate the degree of tumor resection.Biopsy tissues were obtained the suspicious residual tumors surrounding the tumor cavity.The sensitivity and specificity of the residual tumors were determined by the intraoperative ultrasound contrast according to TEM examination results.Results：There were 44 cases of low-grade gliomas and 76 cases of high-grade gliomas.Three hundred and sixty biopsy tissues were obtained.The sensitivity of intraoperative ultrasound contrast in diagnosing the residual tumor was 62.2%,while the specificity degree of it was 92.8%.The consistency coefficient of the ultrasound contrast diagnosis and TEM examination results was 0.584 （Kappa =0.584）,which was between 0.4 and 0.6,therefore it was of medium consistency.Conclusions：Intraoperative ultrasound contrast was of a high sensitivity and specificity in evaluating the excision degree of tumor.The consistency of the residual tumor rate detected,respectively,by ultrasound contrast and TEM examination was of medium consistency.The application of intraoperative ultrasound contrast can improve the resection rate of brain glioma.展开更多
Identification of atomic disorders and their subsequent control has proven to be a key issue in predicting, understanding, and enhancing the properties of newly emerging topological insulator materials. Here, we demon...Identification of atomic disorders and their subsequent control has proven to be a key issue in predicting, understanding, and enhancing the properties of newly emerging topological insulator materials. Here, we demonstrate direct evidence of the cation antisites in single-crystal SnBi2Te4 nanoplates grown by chemical vapor deposition, through a combination of sub-angstr6m-resolution imaging, quantitative image simulations, and density functional theory calculations. The results of these combined techniques revealed a recognizable amount of cation antisites between Bi and Sn, and energetic calculations revealed that such cation antisites have a low formation energy. The impact of the cation antisites was also investigated by electronic structure calculations together with transport measurement. The topological surface properties of the nanoplates were further probed by angle-dependent magnetotransport, and from the results, we observed a two-dimensional weak antilocalization effect associated with surface carriers. Our approach provides a pathway to identify the antisite defects in ternary chalcogenides and the application potential of SnBi2Te4 nanostructures in next-generation electronic and spintronic devices.展开更多
基金This work was financially supported by the National Natural Science Foundation of China （Nos. 11604241, 21790052 and 21331007）, the National Program for Thousand Young Talents of China, the Postdoctoral Science Foundation of China （No. 2015M580209）, the Tianjin Municipal Education Commission, the Tianjin Municipal Science and Technology Commission （No. 15JCYBJC52600）, and the Fundamental Research Fund of Tianjin University of Technology.
文摘Since its discovery, the direct imaging and determination of the crystal structure of few-layer graphdiyne has proven difficult because it is too delicate under irradiation by an electron beam. In this work, the crystal structure of a six-layered graphdiyne nanosheet was directly observed by low-voltage transmission electron microscopy （TEM） using low current density. The combined use of high-resolution TEM （HRTEM） simulation, electron energy-loss spectroscopy, and electron diffraction revealed that the as-synthesized nanosheet was crystalline graphdiyne with a thickness of 2.19 nm （corresponding to a thickness of six layers） and showed ABC stacking. Thus, this work provides direct evidence for the existence and crystal structure of few-layer graphdiyne, which is a new type of two-dimensional carbon material complementary to graphene.
文摘Silver nanoparticles with average particles sizes ranging from 2 to 131nm were manipulatively synthesized starting from silver nitrate using different functional group-containing organic modifiers at room temperature. The effects of the organic modifiers on the morphology of the resulting silver nanoparticles were strongly dependent on the intrinsic properties of the functional groups and the reducibility of the reductant. Numerous ether bonds （-0-）present in polyethylene glycol and Tween-80 were beneficial to the formation of silver nanoparticles with particle sizes of several nanometers in a narrow size distribution in both weak and strong reducing environments. Cetyltrimethylammonium bromide induced the formation of nanosized silver triangle plates in a weak reducing environment. The crystal growth of the silver nanoparticles with particle sizes of more than lOnm was postulated through an adhesion process of small-sized particles followed by a subsequent coalescence process under the present reaction conditions.
基金This work was supported by the National Natural Science Foundation of China （Nos. 51420105003, 11525415, 11327901, 61274114, 11674052, and 11604047） and the Fundamental Research Funds for the Central Universities （Nos. 2242016K41039, MTEC-2015M03, and NJ20150026） and the Natural Science Foundation of Jiangsu Province （No. BK20160694）. W. Z. and F. D. acknowledge the support of Institute for Basic Science, Republic of Korea （No. IBS-R019-D1）. X. W. would like to acknowledge support from the Projects of Science and Technology Commission of Shanghai Municipality （No. 14DZ2260800）.
文摘Because of its high compatibility with conventional microfabrication processing technology, epitaxial graphene （EG） grown on SiC shows exceptional promise for graphene-based electronics. However, to date, a detailed understanding of the transformation from three-layer SiC to monolayer graphene is still lacking. Here, we demonstrate the direct atomic-scale observation of EG growth on a SiC （11^-00） surface at 1,000℃ by in situ transmission electron microscopy in combination with ab initio molecular dynamics （AIMD） simulations. Our detailed analysis of the growth dynamics of monolayer graphene reveals that three SiC （11^-00） layers decompose successively to form one graphene layer. Sublimation of the first layer causes the formation of carbon clusters containing short chains and hexagonal rings, which can be considered as the nuclei for graphene growth. Decomposition of the second layer results in the appearance of new chains connecting to the as-formed clusters and the formation of a network with large pores. Finally, the carbon atoms released from the third layer lead to the disappearance of the chains and large pores in the network, resulting in a whole graphene layer. Our study presents a clear picture of the epitaxial growth of the monolayer graphene from SiC and provides valuable information for future developments in SiC-derived EG technology.
文摘Direct observation of the dissolution behavior of nanomaterials could provide fundamental insight to understanding their anisotropic properties and stability. The dissolution mechanism in solution and vacuum has been well documented. However, the gas-involved dissolution and regrowth have seldom been explored and the mechanisms remain elusive. We report herein, an in situ TEM study of the dissolution and regrowth dynamics of MoO2 nanowires under oxygen using environmental transmission electron microscopy （ETEM）. For the first time, oscillatory dissolution on the nanowire tip is revealed, and, intriguingly, simultaneous layer-by-layer regrowth on the sidewall facets is observed, leading to a shorter and wider nanowire. Combined with first-principles calculations, we found that electron beam irradiation caused oxygen loss in the tip facets, which resulted in changing the preferential growth facets and drove the morphology reshaping.
文摘Solid electrolyte based-resistive memories have been considered to be a potential candidate for future information technology with applications in non-volatile memory, logic circuits and neuromorphic computing. A conductive filament model has been generally accepted to be the underlying mechanism for the resistive switching. However, the growth dynamics of such conductive filaments is still not fully understood. Here, we explore the controllability of filament growth by correlating observations of the filament growth with the electric field distribution and several other factors. The filament growth behavior has been recorded using in situ transmission electron microscopy. By studying the real- time recorded filament growth behavior and morphologies, we have been able to simulate the electric field distribution in accordance with our observations. Other factors have also been shown to affect the filament growth, such as Joule heating and electrolyte infrastructure. This work provides insight into the controllable growth of conductive filaments and will help guide research into further functionalities of nanoionic resistive memories.
文摘The dynamic behavior of octahedral gold nanopartides （NPs） and nanoparticle clusters （NPCs） in aqueous solution is studied by in-situ liquid-cell transmission electron microscopy （TEM）. The octahedral Au NPs/NPCs show preferential orientations in the liquid cell, due to the interaction with the SiNx window. The Au NPs show long-range reversible hopping and three-dimensional （3D） rotational motions in the liquid environment. At the same time, the Au NPCs and NPs perform slow stick-sUp and stick-roU motions, respectivel~ with a centripetal trend. The centripetal motions were explained by a liquid evaporation-induced radial flow model in which the NPCs/NPs trajectories are controlled by Stokes forces and surface friction by the silicon nitride window. The calculated radius-dependent force （Fc） on the NPCs/NPs shows a semi-linear correlation with the distance r between the NPCs/NPs and the center of mass, accompanied with stochastic fluctuations, in agreement with the model predictions. This work thus demonstrates the effectiveness of in situ liquid-cell TEM for the in-depth understanding of complicated liquid flow and force interactions in nanomaterials.
文摘Comprehensive understanding of the structural/morphology stability of ultrathin （diameter 〈 10 nm） gold nanowires under real service conditions （such as under Joule heating） is a prerequisite for the reliable implementation of these emerging building blocks into functional nanoelectronics and mechatronics systems. Here, by using the in situ transmission electron microscopy （TEM） technique, we discovered that the Rayleigh instability phenomenon exists in ultrathin gold nanowires upon moderate heating. Through the controlled electron beam irradiation-induced heating mechanism （with 〈 100 ~C temperature rise）, we further quantified the effect of electron beam intensity and its dependence on Rayleigh instability in altering the geometry and morphology of the ultrathin gold nanowires. Moreover, in situ high-resolution TEM （HRTEM） observations revealed surface atomic diffusion process to be the dominating mechanism for the morphology evolution processes. Our results, with unprecedented details on the atomic-scale picture of Rayleigh instability and its underlying physics, provide critical insights on the thermal/structural stability of gold nanostructures down to a sub-10 nm level which may pave the way for their interconnect applications in future ultra- large-scale integrated ciroaits.
文摘Graphene has demonstrated its potential in several practical applications owing to its remarkable electronic and physical properties. In this study, we successfully fabricated a suspended graphene device with a width down to 20 nm. The morphological evolution of graphene under various electric field effects was systematically examined using an in-situ transmission electron microscope （TEM）. The hourglass-shaped graphene sample instantly broke apart at 7.5 mA, indicating an impressive breakdown current density. The current-carrying capacity was calculated to be -1.6 × 10^9 A.cm-2, which is several orders higher than that of copper. The current-carrying capacity depended on the resistivity of graphene. In addition, atomic volume changes occurred in the multilayer graphene samples due to surface diffusion and Ostwald ripening （OR）, indicating that the breakdown mechanism is well approximated by the electric field. This study not only provides a theory to explain the breakdown behavior but also presents the effects on materials contacted with a graphene layer used as the transmission path.
文摘Background：Contrast-enhanced ultrasound is a dynamic and continuous modality providing real-time view of vascularization and flow distribution patterns of different organs and tumors.In order to evaluate the diagnostic significance of intraoperative contrast-enhanced ultrasound in assessing the resection degree of brain glioma by transmission electron microscopic （TEM） examination,it is important to have specific knowledge about contrast-enhanced ultrasound.Methods：Ultrasound contrast was applied in operations of 120 cases of brain glioma,to evaluate the degree of tumor resection.Biopsy tissues were obtained the suspicious residual tumors surrounding the tumor cavity.The sensitivity and specificity of the residual tumors were determined by the intraoperative ultrasound contrast according to TEM examination results.Results：There were 44 cases of low-grade gliomas and 76 cases of high-grade gliomas.Three hundred and sixty biopsy tissues were obtained.The sensitivity of intraoperative ultrasound contrast in diagnosing the residual tumor was 62.2%,while the specificity degree of it was 92.8%.The consistency coefficient of the ultrasound contrast diagnosis and TEM examination results was 0.584 （Kappa =0.584）,which was between 0.4 and 0.6,therefore it was of medium consistency.Conclusions：Intraoperative ultrasound contrast was of a high sensitivity and specificity in evaluating the excision degree of tumor.The consistency of the residual tumor rate detected,respectively,by ultrasound contrast and TEM examination was of medium consistency.The application of intraoperative ultrasound contrast can improve the resection rate of brain glioma.
文摘Identification of atomic disorders and their subsequent control has proven to be a key issue in predicting, understanding, and enhancing the properties of newly emerging topological insulator materials. Here, we demonstrate direct evidence of the cation antisites in single-crystal SnBi2Te4 nanoplates grown by chemical vapor deposition, through a combination of sub-angstr6m-resolution imaging, quantitative image simulations, and density functional theory calculations. The results of these combined techniques revealed a recognizable amount of cation antisites between Bi and Sn, and energetic calculations revealed that such cation antisites have a low formation energy. The impact of the cation antisites was also investigated by electronic structure calculations together with transport measurement. The topological surface properties of the nanoplates were further probed by angle-dependent magnetotransport, and from the results, we observed a two-dimensional weak antilocalization effect associated with surface carriers. Our approach provides a pathway to identify the antisite defects in ternary chalcogenides and the application potential of SnBi2Te4 nanostructures in next-generation electronic and spintronic devices.
