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Investigation of Polymer Matrix Nano‐Aluminum Composites with Pulsed Laser Heating by In‐Situ TEM
摘要： Nanocomposites of aluminum and fluoropolymers react rapidly due to highly exothermic aluminum fluorination because of the high specific surface area nanoscale particles. In-situ transmission electron microscopy (TEM) techniques are invaluable for real time monitoring of the reactions in these systems at the nanoscale. Here, we investigated the reactions in nanoscale Al (nAl) and THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride) and nAl-LDPE (low density polyethylene) composites, heated using a pulsed laser in a TEM. Results show that reactions are initiated at about 720 K, when THV starts to decompose, and proceed with the formation and growth of a hollow aluminum fluoride (AlF3) shell. Diffraction patterns revealed that this phase is the rare η-phase AlF3. In contrast, no reactions were observed in the inert nAl-LDPE composites. The experimental and theoretical results reveal that rapid pulsed laser heating and subsequent cooling of a nanoscale sample influences the phases that can form, and can be utilized to investigate other systems.
关键词： Fluoropolymer,Nanoenergetic composites,Laser Heating,In situ TEM
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Structural transformations revealed by in-situ HRTEM observations
摘要： With the recent advance of In-Situ Transmission Electron Microscopy (In-Situ TEM), it has become a very essential technique to understand the structure-property relationships of materials. Here, we demonstrate that the formation mechanism of 1D-Si nanowires is initiated by the atom intrusion into the Si lattice at the interfaces, and the formation process is advanced by the atom intrusion into the Si lattice at the interfaces. The formation mechanism of 1D-Si nanowires is also discussed by the thermodynamic analysis. It is found that the 1D-Si nanowires are formed at the triple junction at the interfaces, and the formation process is advanced by the atom intrusion into the Si lattice at the interfaces. The formation mechanism of 1D-Si nanowires is also discussed by the thermodynamic analysis.
关键词： formation mechanism,atom intrusion,In-Situ TEM,thermodynamic analysis,1D-Si nanowires
更新于2025-09-11 14:15:04
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Kinking effects and transport properties of coaxial BN-C nanotubes as revealed by <i>in situ</i> transmission electron microscopy and theoretical analysis
摘要： The insights into transport behavior and the effects of bending on heterostructures constructed from boron nitride (BN) and carbon (C) nanotubes are important for their flexible device applications because the two systems have equally excellent mechanical but completely different electrical properties. In this work, coaxial BN–C nanotubes have been fabricated and their intrinsic transport properties, as well as structural and electrical response to bending deformation, are studied inside a high-resolution transmission electron microscope. Ballistic, diffusive, and hopping transports within different tube length ranges have been observed. When bending deformation was applied to the tubes, although severe kinking becomes apparent, their transport properties are not notably affected. Meanwhile, both theoretical and experimental analyses confirm that the kink positions depend on the ratio of tube diameter to its length. Possible formation of quantum dots, directly within the kink areas, was predicted through calculations of electron density redistribution between nanotube walls at bending.
关键词： bending deformation,transport properties,BN-C nanotubes,in situ TEM,quantum dots
更新于2025-09-11 14:15:04
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Dumbbell to Core–Shell Structure Transformation of Ni–Au Nanoparticle Driven by External Stimuli
摘要： Conversion of CO2 gas to CO fuels is one of the most promising solutions for the increasing threat of global warming and energy crisis. The efficient catalyst Ni–Au dumbbell converting CO2 into CO at elevated temperatures has high CO product selectivity; however, the accompanied atomic diffusion and subsequent surface reconstruction affect the catalytic efficiency of chemical reaction. Atomic scale characterization of structural evolution of the catalyst, which is essential to correlate the functional mechanism to active catalyst surfaces, is yet to be studied. Here, in situ transmission electron microscopy experiments and atomistic simulations are performed to characterize the structural evolution of Ni–Au dumbbell nanoparticles under two different external stimuli. In the condition of high temperature and vacuum, the Ni–Au nanostructure reveals a clear shape reconstruction from the initial dumbbell to core–shell-like, which is induced by capillary force to minimize free surface energy of the system. The shape transformation involves two stages of processes, initial fast Au diffusion followed by slow source-controlled diffusion. At ambient temperature, the combination of CO2 and electron flux surprisingly induces analogous structural transformation of Ni–Au nanostructure, where the associated chemical reaction and CO absorption stimulate the Au migration on Ni surface. Such surface reconstruction can be widely present in catalytic reactions in different environmental conditions, and the results herein demonstrate the detailed processes of Ni–Au structure evolution, which provide important insights for understanding the catalyst performance.
关键词： core–shell,in situ TEM,catalyst,Ni–Au,gas cell
更新于2025-09-04 15:30:14
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Direct Observation of Curved Surface Enhanced Disordering in Ag <sub/>2</sub> S Nanoparticles
摘要： Surface induced order-disorder phase transition has been widely studied on flat bulk surfaces, while such a transition is poorly understood on curved surfaces in nanoscale. Here, we report a direct observation of the dynamic behaviors of surface-initiated disordering in Ag2S nanoparticles using atomic resolution in-situ transmission electron microscopy. It was found that the disordering behavior is different from the traditional model that the disordered layer follows a logarithmical thickness dependence with temperature. In particular, the disordering is largely enhanced at higher temperature when the radius of the residual order phase is getting smaller. Moreover, the correlation length of disordered phase was found to be several times larger than the typical value for bulk surfaces. This significantly enhanced disordering in nanoparticles could be attributed to the extra driving force provided by the decreasing of order-disorder interface area.
关键词： nanoscale,Ag2S nanoparticles,in-situ TEM,phase transition,surface-initiated disordering
更新于2025-09-04 15:30:14
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In situ TEM Study of the Degradation of PbSe Nanocrystals in Air
摘要： PbSe nanocrystals have attracted widespread attention due to a variety of potential applications. However, the practical utility of these nanocrystals has been hindered by their poor air stability, which induces undesired changes in the optical and electronic properties. An understanding of the degradation of PbSe nanocrystals when they are exposed to air is critical for improving the stability and enhancing their applications. Here, we use in situ transmission electron microscopy (TEM) with an environmental cell connected to air to study PbSe nanocrystal degradation triggered by air exposure. We have also conducted a series of complementary studies, including in situ environmental TEM study of PbSe nanocrystals exposed to pure oxygen, PbSe nanocrystals in H2O using a liquid cell, ex situ experiments, such as O2 plasma treatment and thermal heating of PbSe nanocrystals under different air exposure. Our in situ observations reveal that when PbSe nanocrystals are exposed to air (or oxygen) under electron beam irradiation, they experience a series of changes, including shape evolution of individual nanocrystals with the cuboid intermediates, coalescence between nanocrystals, and formation of PbSe thin films through drastic solid‐state fusion. Further studies show that the PbSe thin films transform into an amorphous Pb rich phase or eventually pure Pb, which suggest that Se reacts with oxygen and can be evaporated under electron beam illumination. These various in situ and ex situ experimental results indicate that PbSe nanocrystal degradation in air is initiated by the dissociation and removal of ligands from the PbSe nanocrystal surface.
关键词： in situ TEM,air stability,ligand removal,degradation,PbSe nanocrystals,oxygen exposure
更新于2025-09-04 15:30:14