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Direct Observation of Structural Evolution of Metal Chalcogenide in Electrocatalytic Water Oxidation
摘要： As one of the most remarkable oxygen evolution reaction (OER) electrocatalysts, metal chalcogenides have been intensively reported due to their high OER activities during the past few decades. It has been reported that electron-chemical conversion of metal chalcogenides into oxides/hydroxides would take place after OER. However, the transition mechanism of such unstable structures, as well as the real active sites and catalytic activity during OER for these electrocatalysts, has not been understood yet, which urgently needs a direct observation for the electrocatalytic water oxidation process, especially at nano or even angstrom scale. In this research, by employing advanced Cs-corrected transmission electron microscopy (TEM), a step by step oxidational evolution of amorphous electrocatalyst CoSx into crystallized CoOOH in OER has been in situ captured: irreversible conversion of CoSx to crystallized CoOOH is initiated on the surface of electrocatalysts with a morphology change via Co(OH)2 intermediate during OER measurement, where CoOOH is confirmed as the real active species. Besides, this transition process has also been confirmed by multiple applications of X-ray photoelectron spectroscopy (XPS), in situ Fourier-transform infrared spectroscopy (FTIR) and other ex situ technologies. Moreover, based on this discovery, a high-efficiency electrocatalyst of a nitrogen-doped graphene foam (NGF) coated by CoSx has been explored through a thorough structure transformation of CoOOH. We believe this in situ and in-depth observation of structural evolution in OER measurement can provide insights into the fundamental understanding of the mechanism for OER catalysts, thus enabling the more rational design of low-cost and high-efficient electrocatalysts for water splitting.
关键词： structural evolution,XPS,in situ TEM,water oxidation,cobalt chalcogenide
更新于2025-11-14 15:27:09
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Anomalous shape evolution of Ag2O2 nanocrystals modulated by surface adsorbates during electron beam etching
摘要： An understanding of nanocrystal shape evolution is significant for the design, synthesis and applications of nanocrystals with surface-enhanced properties such as catalysis or plasmonics. Surface adsorbates that are selectively attached to certain facets may strongly affect the atomic pathways of nanocrystal shape development. However, it is a great challenge to directly observe such dynamic processes in situ with high spatial resolution. Here, we report the anomalous shape evolution of Ag2O2 nanocrystals modulated by the surface adsorbates of Ag clusters during electron beam etching, which is revealed through in situ transmission electron microscopy (TEM). In contrast to the Ag2O2 nanocrystals without adsorbates, which display the near-equilibrium shape throughout the etching process, Ag2O2 nanocrystals with Ag surface adsorbates show distinct facet development during etching by electron beam irradiation. Three stages of shape changes are observed: a sphere-to-a cube transformation, side etching of a cuboid, and bottom etching underneath the surface adsorbates. We find that the Ag adsorbates modify the Ag2O2 nanocrystal surface configuration by selectively capping the junction between two neighboring facets. They prevent the edge atoms from being etched away and block the diffusion path of surface atoms. Our findings provide critical insights into the modulatory function of surface adsorbates on shape control of nanocrystals.
关键词： surface adsorbates,Ag2O2 nanocrystal,shape evolution,In situ TEM,electron beam etching
更新于2025-09-23 15:23:52
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Inverse size-dependence of piezoelectricity in single BaTiO3 nanoparticles
摘要： The piezoelectric charge coefficients d33 of single BaTiO3 (BT) nanoparticles (NPs) were characterized using a transmission electron microscope (TEM) that is equipped with a precise charge meter and an in-situ TEM indentation holder that enables controlled compression experiments. An exceptionally high d33 of 1775 pC/N was obtained in NPs that are smaller than the critical diameter (D; typically known as < 100 nm) that has been regarded as the lower limit to permit for ferroelectricity in BT. The mechanical conversion efficiency of piezoelectric BT nanogenerators enhanced as D of BT NPs was decreased; this result corresponds with the single-NP compression measurements of d33. This quantification of the effect of D in ferroelectric materials may guide development of efficient and high-powered nanostructured piezoelectric energy devices such as piezoelectric nanogenerators.
关键词： in-situ TEM,size effect,STEM,Ferroelectric,piezoelectric,nanogenerator
更新于2025-09-23 15:23:52
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Gram scale synthesis of monoclinic VO2 microcrystals by hydrothermal and argon annealing treatment
摘要： We report gram scale synthesis of 100 % phase fraction of VO2 (M) monoclinic in powder form with reversible phase transition by combining hydrothermal method and Ar annealing at high temperature. Optimization of single phase VO2 (M) growth and its phase transition characteristics have been analysed systematically by varying growth parameters such as time, synthesis temperature and post growth annealing conditions. Argon annealing of hydrothermally grown VO2 powders at 800°C found to play key role in obtaining VO2 (M) phase in gram scale with characteristic phase transition temperature of 68°C. In-situ TEM has been performed to investigate the microstructure and phase change across the annealing temperature. Detailed characterizations have been carried out to correlate the phases, microstructure and transition temperature of VO2 with respect to growth parameters.
关键词： metal-insulator transition,annealing treatment,monoclinic VO2,in-situ TEM,microcrystals,Scalable synthesis
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - In-situ Characterization of Structure Evolution of Graphene During Field Emission
摘要： The structure stability of graphene field emitter is important for the performance of field emission devices. In this work, high dose electron beam illumination and high current field emission was applied on the graphene field emitter and its structure evolution and field emission characteristics were investigated using an in-situ TEM measurement system. The relation between structure and performance of graphene emitter was demonstrated. The interaction of electron and graphene was also discussed.
关键词： in-situ TEM,structure,field emission,Graphene
更新于2025-09-23 15:21:21
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Direct in situ TEM visualization and insight of the facet-dependent sintering behaviours of gold on TiO?
摘要： To prevent sintering of supported nanocatalysts is an important issue in nanocatalysis. A feasible way is to choose a suitable support. However, whether the metal-support interactions promote or prevent the sintering has not been fully identified due to the lack of confirmed evidences. Herein, we report on completely different sintering behaviours of Au nanoparticles on distinct anatase TiO2 surfaces by in situ TEM. The full in situ sintering processes of Au nanoparticles were visualized on TiO2 (101) surface, which coupled the Ostwald ripening and particle migration coalescence. In contrast, no sintering of Au on TiO2 anatase (001) surface was observed under the same conditions. This facet-dependent sintering mechanism is fully explained by the density function theory calculations. Our work not only offers the direct evidence of the important role of supports in the sintering process, but also provides insightful information for the design of sintering-resistant nanocatalysts.
关键词： in situ TEM,particle migration and coalescence (PMC),sintering,metal?support interaction (MSI),Au-TiO2,Ostwald ripening (OR)
更新于2025-09-23 15:21:01
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Direct in situ TEM visualization and insight of the facet-dependent sintering behaviours of gold on TiO?
摘要： To prevent sintering of supported nanocatalysts is an important issue in nanocatalysis. A feasible way is to choose a suitable support. However, whether the metal-support interactions promote or prevent the sintering has not been fully identified due to the lack of confirmed evidences. Herein, we report on completely different sintering behaviours of Au nanoparticles on distinct anatase TiO2 surfaces by in situ TEM. The full in situ sintering processes of Au nanoparticles were visualized on TiO2 (101) surface, which coupled the Ostwald ripening and particle migration coalescence. In contrast, no sintering of Au on TiO2 anatase (001) surface was observed under the same conditions. This facet-dependent sintering mechanism is fully explained by the density function theory calculations. Our work not only offers the direct evidence of the important role of supports in the sintering process, but also provides insightful information for the design of sintering-resistant nanocatalysts.
关键词： in situ TEM,particle migration and coalescence (PMC),sintering,metal?support interaction (MSI),Au-TiO2,Ostwald ripening (OR)
更新于2025-09-23 15:21:01
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Formation of Gold Nanoparticles in a Free-Standing Ionic Liquid Triggered by Heat and Electron Irradiation
摘要： Ionic liquids (ILs) feature negligibly low vapor pressures and can thus be freely introduced into the high vacuum of a transmission electron microscope. With this extraordinary property, the ILs offer a powerful tool for in situ transmission electron microscopy (TEM) in window-free liquid media at very high resolution. In this work, we use the IL 1-butyl-3-methyl imidazolium chloride in order to study nucleation and growth of gold nanoparticles (NPs) in free-standing liquid droplets by scanning TEM (STEM). The results confirm that the used IL allows for generating Au NP in situ, triggered by electron irradiation and heat. Firstly, the isotropic growth of small, spherical Au NPs was initiated and monitored whereas different growth mechanisms were observed, i.e. growth by monomer attachment, growth through particle coalescence and possible Ostwald ripening events. After the initial growth phase, a second, anisotropic growth process was induced by a moderate temperature increase and continued electron irradiation. As a result, larger, faceted crystals such as tetrahedra, octahedra or decahedra were formed. As all these polymorphs are terminated by {111}-facets, the IL might not only act as liquid medium but in addition as a surfactant which preferentially attaches on the {100}-facets.
关键词： gold,in situ,TEM,heat,nanoparticle growth,ionic liquid
更新于2025-09-23 15:21:01
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[IEEE 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - Berlin, Germany (2019.6.23-2019.6.27)] 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - In-Situ Transmission Electron Microscopy Coupled with Resonant Microcantilever for Comprehensive Evaluating Sulfurization Performance of Zinc Oxide Nanowires
摘要： This paper reports a new technique with in-situ transmission electron microscopy (in-situ TEM) and resonant microcantilever to comprehensively evaluate sulfurization performance of ZnO nanowires. Herein, in-situ TEM is used to real-time observe the sulfurization process of ZnO nanowires under SO2-contained atmosphere. temperature-varying micro-gravimetric method, thermodynamic interaction between ZnO nanowires and SO2 molecules is quantitatively evaluated by resonant microcantilever. By exposing the ZnO nanowires sample to SO2-contained atmosphere, a thick shell layer of ZnSO3 can be formed onto the surface of ZnO nanowires and a novel core-shell nanowire structure of ZnO@ZnSO3 is obtained finally. According to our comprehensive evaluation results, the ZnO nanowires sample with 100 nm diameter exhibits high reactive to SO2 molecules and is suitable for SO2 capture and storage.
关键词： sulfurization process,ZnO nanowires,thermodynamic parameter extraction,In-situ TEM
更新于2025-09-23 15:19:57
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European Microscopy Congress 2016: Proceedings || Defects in as-grown vs. annealed rutile titania nanowires and their effect on properties
摘要： Semiconducting metal oxides play a key role in electrochemical and photo physical applications like photo catalysis and as electrode material in solar cells and Li-ion batteries. Among these metal oxides, hydrothermally grown rutile TiO2 nanowire arrays are promising as the 1 D structure possesses a large surface area and a directed electron path towards the substrate. However, the efficiency of these devices is also influenced by the defects inside the nanowires (dislocations, stacking faults, titanium interstitials and oxygen vacancies). A previous study showed that as-grown nanowires have a high density of lattice defects.[1] However, these defects can be removed by an additional annealing step. Latest findings demonstrate that hybrid solar cells where those annealed nanowires are incorporated have significantly higher power-conversion efficiency.[2] However, the removal of the defects is not fully understood so far. In our present work, transmission electron microscopy (TEM) was used to study the changes within the nanowire during annealing. TEM investigations were performed at 200 kV using a JEOL JEM-2200FS and at 300 kV using a FEI Titan Themis 60-300. First results were obtained by ex-situ TEM analysis of as-grown TiO2 nanowires and nanowires, which were annealed at 500 °C for 4 h. These ex-situ analysis confirm that both, as-grown and annealed nanowires, have the rutile crystal structure. Defects, present in the as-grown state, can be removed by the thermal treatment. Concurrently, a structural transformation inside the nanowires occurs resulting in faceted voids of several nanometer in diameter. Using tilt series from -70° to +70° in high-angle annular dark-field (HAADF) scanning (S)TEM mode and the discrete iterative reconstruction technique (DIRT)[3], a TEM tomograph was obtained, which proved that these voids are solely formed inside the nanowire and not at the nanowire surface (Fig. 1). Further analysis including electron energy loss spectroscopy revealed changes of the oxidation state at the surface region of the voids during annealing, whereas the rutile TiO2 crystal structure was maintained. HAADF-STEM in-situ heating experiments, performed in a JEOL JEM-2200FS with a DENSsolutions heating holder, enabled the direct observation of the structural changes inside the rutile TiO2 nanowires (Fig. 2). Using a slow heating ramp of 3.3°C/min, a sudden formation of these voids at around 500 °C could be observed. Heating at lower temperatures did not affect the structure of the nanowire and also an additional heating after the transformation (600°C, 1h) did not change the size and shape of the voids. These ex-situ and in-situ observations are a decisive step to explain the mechanisms involved in this process in more detail. The results of our TEM investigation were correlated to the properties of as-grown and annealed TiO2 nanowires. Here, we could show that the healing of the lattice defects upon annealing not only increased the performance of hybrid solar cells but also affects other properties of the nanowires e.g. chemical stability.
关键词： in-situ TEM,TiO2 nanowire,defect healing
更新于2025-09-16 10:30:52