In Situ Observation of Au Nanostructure Evolution in Liquid Cell TEM

Gold nanostructures (NSs) have been widely investigated due to their unique properties. Understanding their growth behaviors during synthesis will be beneficial in designing and applying to many functional nanodevices. It is important to enrich the fundamental science and technology of the synthesis and characterization through real time evolution. In this work, we observed the dynamic growth of Au NSs by using liquid in situ transmission electron microscopy (TEM). The solution was sealed in a liquid cell, and the results indicated that the thicker solution layer tended to form multi-twinned decahedral NSs; in contrast, nanoplates easily formed in the thinner solution layer. The silver halide model, relying on side-face structures, and the Wulff construction can be used to explain the formation of NSs. Additionally, we analyzed the growth rate of different morphologies to elucidate their growth behaviors. The growth mechanism and formation kinetics of different shapes of Au NSs were systematically studied, which provided direct evidence toward and extended the study of reaction kinetics for modifying the morphology of NSs

In Situ Observation of Au Nanostructure Evolution in Liquid Cell TEM

Gold nanostructures (NSs) have been widely investigated due to their unique properties. Understanding their growth behaviors during synthesis will be beneficial in designing and applying to many functional nanodevices. It is important to enrich the fundamental science and technology of the synthesis and characterization through real time evolution. In this work, we observed the dynamic growth of Au NSs by using liquid in situ transmission electron microscopy (TEM). The solution was sealed in a liquid cell, and the results indicated that the thicker solution layer tended to form multi-twinned decahedral NSs; in contrast, nanoplates easily formed in the thinner solution layer. The silver halide model, relying on side-face structures, and the Wulff construction can be used to explain the formation of NSs. Additionally, we analyzed the growth rate of different morphologies to elucidate their growth behaviors. The growth mechanism and formation kinetics of different shapes of Au NSs were systematically studied, which provided direct evidence toward and extended the study of reaction kinetics for modifying the morphology of NSs

Observing Growth of Nanostructured ZnO in Liquid

Hydrothermal synthesis is commonly used to produce a large area of ZnO nanowires because of its simple and inexpensive process. However, the mechanism of hydrothermal synthesis remains unknown. In this work, zinc acetate and HMTA dissolved in deionized water as a precursor solution were sealed in a liquid cell for observation by <i>in situ</i> transmission electron microscopy. The growth of ZnO nanowires was classified into two steps. The first step was the nucleation and growth of ZnO nanoparticles. The ZnO nanoparticles grew as a result of either isotropic monomer attachment on the {21̅1̅0} and {01̅10} surfaces or coalescence of nanoparticles in the same crystal arrangement. The second step was the anisotropic growth of ZnO nanoparticles into nanowires on the (0001) surface. Because the (0001) surface is Zn-terminated with positive charges that can attract the negatively charged monomers, i.e., [Zn­(OH)₄]^2–,the monomers tended to deposit on the (0001) surface, resulting in ZnO nanowires growing along the [0001] direction. Moreover, the growth of ZnO nanowires was identified to be a reaction-controlled system. The direct observation of the dynamic process sheds light on the hydrothermal synthesis method

Revealing Controllable Nanowire Transformation through Cationic Exchange for RRAM Application

One dimensional metal oxide nanostructures have attracted much attention owing to their fascinating functional properties. Among them, piezoelectricity and photocatalysts along with their related materials have stirred significant interests and widespread studies in recent years. In this work, we successfully transformed piezoelectric ZnO into photocatalytic TiO₂ and formed TiO₂/ZnO axial heterostructure nanowires with flat interfaces by solid to solid cationic exchange reactions in high vacuum (approximately 10^–8 Torr) transmission electron microscope (TEM). Kinetic behavior of the single crystalline TiO₂ was systematically analyzed. The nanoscale growth rate of TiO₂ has been measured using in situ TEM videos. On the basis of the rate, we can control the dimensions of the axial-nanoheterostructure. In addition, the unique Pt/ ZnO / TiO₂/ ZnO /Pt heterostructures with complementary resistive switching (CRS) characteristics were designed to solve the important issue of sneak-peak current. The resistive switching behavior was attributed to the migration of oxygen and TiO₂ layer served as reservoir, which was confirmed by energy dispersive spectrometry (EDS) analysis. This study not only supplied a distinct method to explore the transformation mechanisms but also exhibited the potential application of ZnO/TiO₂ heterostructure in nanoscale crossbar array resistive random-access memory (RRAM)

Phosphorus-Doped p–n Homojunction ZnO Nanowires: Growth Kinetics in Liquid and Their Optoelectronic Properties

For wide-ranging applications in nanoscale electronic devices, durable and reproducible p-type nanostructures are essential. In this work, simple ZnO nanowire (NW) p–n homojunctions were grown using a two-step hydrothermal synthesis method. P₂O₅ served as a doping source to obtain p-type ZnO NWs. The morphology of the ZnO NW arrays was examined using field emission scanning electron microscopy. The high-resolution transmission electron microscopy (HRTEM) image indicated that the ZnO NW p–n homojunction is single-crystalline with a ⟨0001⟩ growth direction. The distribution of P element was analyzed using energy-dispersive spectroscopy. The dynamic growth observation was conducted using liquid in situ TEM to investigate the ZnO nucleation and growth mechanism. We divided the ZnO nanocrystal precipitation into three processes. Whether two adjacent particles grow stably or not was found to be related to the distance. Moreover, the temperature-dependent photoluminescence spectra revealed that two extra emission peaks located at 416 and 435 nm were emitted from the ZnO NW p–n homojunction, which resulted from donor–acceptor recombination. In addition, the electron transport properties confirmed the rectification behavior of the multi ZnO NW p–n homojunctions. The turn-on voltage and the current were approximately 2.8 V and 10^–4 to 10^–5 A, respectively, under forward bias. The results indicate the potential application of ZnO NW p–n homojunctions as nanoscale light-emitting diodes

Phosphorus-Doped p–n Homojunction ZnO Nanowires: Growth Kinetics in Liquid and Their Optoelectronic Properties

For wide-ranging applications in nanoscale electronic devices, durable and reproducible p-type nanostructures are essential. In this work, simple ZnO nanowire (NW) p–n homojunctions were grown using a two-step hydrothermal synthesis method. P₂O₅ served as a doping source to obtain p-type ZnO NWs. The morphology of the ZnO NW arrays was examined using field emission scanning electron microscopy. The high-resolution transmission electron microscopy (HRTEM) image indicated that the ZnO NW p–n homojunction is single-crystalline with a ⟨0001⟩ growth direction. The distribution of P element was analyzed using energy-dispersive spectroscopy. The dynamic growth observation was conducted using liquid in situ TEM to investigate the ZnO nucleation and growth mechanism. We divided the ZnO nanocrystal precipitation into three processes. Whether two adjacent particles grow stably or not was found to be related to the distance. Moreover, the temperature-dependent photoluminescence spectra revealed that two extra emission peaks located at 416 and 435 nm were emitted from the ZnO NW p–n homojunction, which resulted from donor–acceptor recombination. In addition, the electron transport properties confirmed the rectification behavior of the multi ZnO NW p–n homojunctions. The turn-on voltage and the current were approximately 2.8 V and 10^–4 to 10^–5 A, respectively, under forward bias. The results indicate the potential application of ZnO NW p–n homojunctions as nanoscale light-emitting diodes

Twin-Boundary Reduced Surface Diffusion on Electrically Stressed Copper Nanowires

Surface diffusion is intimately correlated with crystal orientation and surface structure. Fast surface diffusion accelerates phase transformation and structural evolution of materials. Here, through in situ transmission electron microscopy observation, we show that a copper nanowire with dense nanoscale coherent twin-boundary (CTB) defects evolves into a zigzag configuration under electric-current driven surface diffusion. The hindrance at the CTB-intercepted concave triple junctions decreases the effective surface diffusivity by almost 1 order of magnitude. The energy barriers for atomic migration at the concave junctions and different faceted surfaces are computed using density functional theory. We proposed that such a stable zigzag surface is shaped not only by the high-diffusivity facets but also by the stalled atomic diffusion at the concave junctions. This finding provides a defect-engineering route to develop robust interconnect materials against electromigration-induced failures for nanoelectronic devices

Twin-Boundary Reduced Surface Diffusion on Electrically Stressed Copper Nanowires

Surface diffusion is intimately correlated with crystal orientation and surface structure. Fast surface diffusion accelerates phase transformation and structural evolution of materials. Here, through in situ transmission electron microscopy observation, we show that a copper nanowire with dense nanoscale coherent twin-boundary (CTB) defects evolves into a zigzag configuration under electric-current driven surface diffusion. The hindrance at the CTB-intercepted concave triple junctions decreases the effective surface diffusivity by almost 1 order of magnitude. The energy barriers for atomic migration at the concave junctions and different faceted surfaces are computed using density functional theory. We proposed that such a stable zigzag surface is shaped not only by the high-diffusivity facets but also by the stalled atomic diffusion at the concave junctions. This finding provides a defect-engineering route to develop robust interconnect materials against electromigration-induced failures for nanoelectronic devices

Twin-Boundary Reduced Surface Diffusion on Electrically Stressed Copper Nanowires

Surface diffusion is intimately correlated with crystal orientation and surface structure. Fast surface diffusion accelerates phase transformation and structural evolution of materials. Here, through in situ transmission electron microscopy observation, we show that a copper nanowire with dense nanoscale coherent twin-boundary (CTB) defects evolves into a zigzag configuration under electric-current driven surface diffusion. The hindrance at the CTB-intercepted concave triple junctions decreases the effective surface diffusivity by almost 1 order of magnitude. The energy barriers for atomic migration at the concave junctions and different faceted surfaces are computed using density functional theory. We proposed that such a stable zigzag surface is shaped not only by the high-diffusivity facets but also by the stalled atomic diffusion at the concave junctions. This finding provides a defect-engineering route to develop robust interconnect materials against electromigration-induced failures for nanoelectronic devices

In Situ TEM Investigation of the Electrochemical Behavior in CNTs/MnO₂‑Based Energy Storage Devices

Transition metal oxides have attracted much interest owing to their ability to provide high power density in lithium batteries; therefore, it is important to understand the electrochemical behavior and mechanism of lithiation–delithiation processes. In this study, we successfully and directly observed the structural evolution of CNTs/MnO₂ during the lithiation process using transmission electron microscopy (TEM). CNTs/MnO₂ were selected due to their high surface area and capacitance effect, and the lithiation mechanism of the CNT wall expansion was systematically analyzed. Interestingly, the wall spacings of CNTs/MnO₂ and CNTs were obviously expanded by 10.92% and 2.59%, respectively. The MnO₂ layer caused structural defects on the CNTs surface that could allow penetration of Li⁺ and Mn⁴⁺ through the tube wall and hence improve the ionic transportation speed. This study provided direct evidence for understanding the role of CNTs/MnO₂ in the lithiation process used in lithium ion batteries and also offers potential benefits for applications and development of supercapacitors