Liquid Cell Electron Microscopy Research Articles

Modifying Surface Chemistry of Metal Oxides for Boosting Dissolution Kinetics in Water by Liquid Cell Electron Microscopy.

Dissolution of metal oxides is fundamentally important for understanding mineral evolution and micromachining oxide functional materials. In general, dissolution of metal oxides is a slow and inefficient chemical reaction. Here, by introducing oxygen deficiencies to modify the surface chemistry of oxides, we can boost the dissolution kinetics of metal oxides in water, as in situ demonstrated in a liquid environmental transmission electron microscope (LETEM). The dissolution rate constant significantly increases by 16-19 orders of magnitude, equivalent to a reduction of 0.97-1.11 eV in activation energy, as compared with the normal dissolution in acid. It is evidenced from the high-resolution TEM imaging, electron energy loss spectra, and first-principle calculations where the dissolution route of metal oxides is dynamically changed by local interoperability between altered water chemistry and surface oxygen deficiencies via electron radiolysis. This discovery inspires the development of a highly efficient electron lithography method for metal oxide films in ecofriendly water, which offers an advanced technique for nanodevice fabrication.

Liquid Cell Electron Microscopy of Nanoparticle Self-Assembly Driven by Solvent Drying.

Drying a colloidal solution of nanoparticles is a versatile method to construct self-assembled structures of nanoparticles. However, mechanistic understanding has mostly relied on empirical knowledge obtained from the final structures of self-assembly as relevant processes during solvent drying are likely kinetic and far from equilibrium. Here, we present in situ TEM studies of nanoparticle self-assembly under various conditions, including the concentrations of the initial solution and the types of nanoparticles and substrates. The capability of tracking trajectories of individual nanoparticles enables us to understand the mechanisms of drying-mediated self-assembly at the single-nanoparticle level. Our results consistently show that a solvent boundary primarily affects nanoparticle motions and the resulting self-assembly processes regardless of different conditions. The solvent boundary drives nanoparticles to form two-dimensional assembly mainly through two pathways, transporting scattered nanoparticles by lateral dragging and flattening aggregated nanoparticles by vertical pressing.

Nanobubble nucleation studied using Fresnel fringes in liquid cell electron microscopy

Liquid cell electron microscopy is a useful technique for the observation of chemical, biological, and mechanical processes in liquids at nanometer-scale resolution. This study investigated the generation and growth of nanobubbles using the Fresnel fringe method, which enabled us to determine the location of bubble interface; the nanobubbles were induced in the 600-nm-thick water sample in the cell, by the electron beam. Nucleation occurred first at the solid–liquid interface in the upstream side of electron beam, and this was followed by second-group nucleation at the downstream-side interface; all of the stable nucleations occurred on the solid surfaces. The size of the nucleated bubbles at the moment they became visible depended on the magnification used in the electron microscope, and a higher-energy density in the electron beam induced larger bubbles. The underlying mechanism was also considered in this study.

In situ liquid cell electron microscopy of Ag-Au galvanic replacement reactions.

Galvanic replacement reactions are important as they transform nanoparticle templates into complex porous and hollow metal or alloy nanostructures with interesting properties for a variety of applications. Real-time liquid cell electron microscopy (LCEM) observations of the transformation of solid nanoparticles into hollow shell and cage bimetallic nanostructures are challenging because the high-energy electron beam strongly affects the galvanic process via species such as aqueous electrons and hydroxyl radicals generated through the radiolysis of water in the liquid cell. As a result the galvanic reactions are modified by the introduction of additional pathways that can decouple the oxidation of the nanoparticles from the reduction of the metal ion complexes in solution. Here we demonstrate that changing the pH of the solution provides an effective approach to alter the balance of radiolysis products. In situ observations of the transformation of Ag nanocubes in Au salt containing neutral and acidic aqueous solutions demonstrate that a lowering of the pH by addition of H2SO4 significantly lessens radical-induced modifications of redox reactions by avoiding the excessive reduction of metal-chloro complexes by aqueous electrons (eaq-) and making the process sufficiently slow to be observed. As a result, the different stages of galvanic replacement reactions on nanoparticles can be imaged in real-time by LCEM.

Real-time observation of protein aggregates in pharmaceutical formulations using liquid cell electron microscopy.

Understanding the properties of protein-based therapeutics is a common goal of biologists and physicians. Technical barriers in the direct observation of small proteins or therapeutic agents can limit our knowledge of how they function in solution and in the body. Electron microscopy (EM) imaging performed in a liquid environment permits us to peer into the active world of cells and molecules at the nanoscale. Here, we employ liquid cell EM to directly visualize a protein-based therapeutic in its native conformation and aggregate state in a time-resolved manner. In combination with quantitative analyses, information from this work contributes new molecular insights toward understanding the behaviours of immunotherapies in a solution state that mimics the human body.

Defining the radiation chemistry during liquid cell electron microscopy to enable visualization of nanomaterial growth and degradation dynamics.

We present a critical review of methods for defining the chemical environment during liquid cell electron microscopy investigation of electron beam induced nanomaterial growth and degradation. We draw from the radiation chemistry and liquid cell electron microscopy literature to present solution chemistry and electron beam-based methods for selecting the radiolysis products formed and their relative amount during electron irradiation of liquid media in a transmission electron microscope. We outline various methods for establishing net oxidizing or net reducing reaction environments and propose solvents with minimal overall production of radicals under the electron beam. Exemplary liquid cell electron microscopy experiments in the fields of nanoparticle nucleation, growth, and degradation along with recommendations for best practices and experimental parameters are reported. We expect this review will provide researchers with a useful toolkit for designing general chemistry and materials science liquid cell electron microscopy experiments by 'directing' the effect of the electron beam to understand fundamental mechanisms of dynamic nanoscale processes as well as minimizing radiation damage to samples.

Harnessing Control of Radiolysis during Liquid Cell Electron Microscopy to Enable Visualization of Nanomaterial Transformation Dynamics

Harnessing Control of Radiolysis during Liquid Cell Electron Microscopy to Enable Visualization of Nanomaterial Transformation Dynamics

In Situ EC-TEM Studies of Hyper-Dendritic Zn Growth and Potential Cycling for Secondary Battery Applications

Low cost, durable, and relatively safe electrode materials are highly desirable for secondary batteries, but the implementation of many materials, including zinc, is limited by morphological transformations that take place during potential cycling [1]. The use of zinc in the form of a nanoporous foam fabricated by electrodeposition, known as hyper-dendritic zinc (HD-Zn), can overcome some of the limitations of bulk zinc and act as a useful anode material [1,2]. The HD-Zn structure is composed of sub-hundred nanometer-size Zn crystallites on secondary dendrites in a three dimensional network of highly oriented crystals with high surface area. This structure shows improved capacity retention and more rapid kinetics in alkaline media compared to conventional zinc anodes [1,2]. At present, the growth mechanism and morphological changes taking place in HD-Zn during cycling, which presumably form the basis for its improved performance, are not well understood. Recent advances in in situ electrochemical transmission electron microscopy (EC-TEM), with its unique ability to provide simultaneous temporally and spatially resolved information as well as electrochemical parameters, enable exploration of the underlying physics of the electrochemical reactions that occur at the surface of this structure during cycling [3,4]. In this work, we therefore apply in situ EC-TEM to investigate the electrodeposition process that forms and takes place on HD-Zn. By employing a liquid cell with three electrodes and the capability for liquid flow, we can introduce electrolytes with varying composition of zinc ions and pH, and apply different current and voltage parameters to investigate their effects on the deposited morphology. We track the growth and the potential cycling of HD-Zn, and compare with the deposition of Zn in classical dendrite form onto surfaces. We discuss the effects of additives to the electrolyte, which can change the onset of dendrite formation during Zn deposition. We also compare these flow cell results to static liquid cell experiments in which we have recorded HD-Zn morphology after galvanostatic deposition under the optical microscope, and we will discuss the benefits and pitfalls of flow capabilities for liquid cell electron microscopy for the study of processes during battery operation.

Real-Time Dynamics of Galvanic Replacement Reactions of Silver Nanocubes and Au Studied by Liquid-Cell Transmission Electron Microscopy.

We study the galvanic replacement reaction of silver nanocubes in dilute, aqueous ethylenediaminetetraacetic acid disodium salt (EDTA)-capped gold aurate solutions using in situ liquid-cell electron microscopy. Au/Ag etched nanostructures with concave faces are formed via (1) etching that starts from the faces of the nanocubes, followed by (2) the deposition of an Au layer as a result of galvanic replacement, and (3) Au deposition via particle coalescence and monomer attachment where small nanoparticles are formed during the reaction as a result of radiolysis. Analysis of the Ag removal rate and Au deposition rate provides a quantitative picture of the growth process and shows that the morphology and composition of the final product are dependent on the stoichiometric ratio between Au and Ag.

The Mechanisms for Preferential Attachment of Nanoparticles in Liquid Determined Using Liquid Cell Electron Microscopy, Machine Learning, and Molecular Dynamics

The Mechanisms for Preferential Attachment of Nanoparticles in Liquid Determined Using Liquid Cell Electron Microscopy, Machine Learning, and Molecular Dynamics

Growth dynamics of solid electrolyte interphase layer on SnO2 nanotubes realized by graphene liquid cell electron microscopy

Formation of stable solid electrolyte interphase (SEI) layer is critical to outstanding performance of energy storage devices, because it acts as a passive layer that allows facile transport of ions but forbids electron transport between the electrolyte and electrode. Although much study has been devoted to investigate the morphology and structure of SEI layer using a myriad of analytical devices on past decades, the direct observation of SEI layer on a real time scale has remained as a formidable challenge. In addition, it has been difficult to observe both the decomposition of electrolytes and formation process of stable SEI layer at nanometer scale. Here we utilize in situ transmission electron microscopy (TEM) using graphene liquid cell (GLC) to realize the observation of stable SEI layer formation in a sequential time scale. Upon e− beam irradiation, Li salts in the electrolytes react with reduced electrolytes and form gel-like agglomerates, which are deposited on the surface of the active material as a passivation layer and later stabilized to become more uniform in overall thickness. Additionally, growth dynamics of stable SEI layer were suggested, where the deposition of decomposed electrolytes eventually result in relatively uniform SEI layer. This paper demonstrates that it is possible to observe not only the formation of non-crystalline SEI layer but also the movement of decomposed electrolytes onto the surface of active materials which account for broader understanding of SEI layer, and has the potential to detect important interfacial phenomena in electrochemical devices that were overlooked so far.

Real-Time Imaging of the Formation of Au-Ag Core-Shell Nanoparticles.

We study the overgrowth process of silver-on-gold nanocubes in dilute, aqueous silver nitrate solution in the presence of a reducing agent, ascorbic acid, using in situ liquid-cell electron microscopy. Au-Ag core-shell nanostructures were formed via two mechanistic pathways: (1) nuclei coalescence, where the Ag nanoparticles absorbed onto the Au nanocubes, and (2) monomer attachment, where the Ag atoms epitaxially deposited onto the Au nanocubes. Both pathways lead to the same Au-Ag core-shell nanostructures. Analysis of the Ag deposition rate reveals the growth modes of this process and shows that this reaction is chemically mediated by the reducing agent.

In situ microscopy of the self-assembly of branched nanocrystals in solution.

Solution-phase self-assembly of nanocrystals into mesoscale structures is a promising strategy for constructing functional materials from nanoscale components. Liquid environments are key to self-assembly since they allow suspended nanocrystals to diffuse and interact freely, but they also complicate experiments. Real-time observations with single-particle resolution could have transformative impact on our understanding of nanocrystal self-assembly. Here we use real-time in situ imaging by liquid-cell electron microscopy to elucidate the nucleation and growth mechanism and properties of linear chains of octapod-shaped nanocrystals in their native solution environment. Statistical mechanics modelling based on these observations and using the measured chain-length distribution clarifies the relative importance of dipolar and entropic forces in the assembly process and gives direct access to the interparticle interaction. Our results suggest that monomer-resolved in situ imaging combined with modelling can provide unprecedented quantitative insight into the microscopic processes and interactions that govern nanocrystal self-assembly in solution.

Automated analysis of evolving interfaces during in situ electron microscopy

AbstractIn situ electron microscopy allows one to monitor dynamical processes at high spatial and temporal resolution. This produces large quantities of data, and hence automated image processing algorithms are needed to extract useful quantitative measures of the observed phenomena. In this work, we outline an image processing workflow for the analysis of evolving interfaces imaged during liquid cell electron microscopy. As examples, we show metal electrodeposition at electrode surfaces; beam-induced nanocrystal formation and dissolution; and beam-induced bubble nucleation, growth, and migration. These experiments are used to demonstrate a fully automated workflow for the extraction of, among other things, interface position, roughness, lateral wavelength, local normal velocity, and the projected area of the evolving phase as functions of time. The relevant algorithms have been implemented in Mathematica and are available online.

Opportunities and challenges in liquid cell electron microscopy.

Transmission electron microscopy offers structural and compositional information with atomic resolution, but its use is restricted to thin, solid samples. Liquid samples, particularly those involving water, have been challenging because of the need to form a thin liquid layer that is stable within the microscope vacuum. Liquid cell electron microscopy is a developing technique that allows us to apply the powerful capabilities of the electron microscope to imaging and analysis of liquid specimens. We describe its impact in materials science and biology. We discuss how its applications have expanded via improvements in equipment and experimental techniques, enabling new capabilities and stimuli for samples in liquids, and offering the potential to solve grand challenge problems.

Real-Time Observation of Water-Soluble Mineral Precipitation in Aqueous Solution by In Situ High-Resolution Electron Microscopy.

The precipitation and dissolution of water-soluble minerals in aqueous systems is a familiar process occurring commonly in nature. Understanding mineral nucleation and growth during its precipitation is highly desirable, but past in situ techniques have suffered from limited spatial and temporal resolution. Here, by using in situ graphene liquid cell electron microscopy, mineral nucleation and growth processes are demonstrated in high spatial and temporal resolution. We precipitate the mineral thenardite (Na2SO4) from aqueous solution with electron-beam-induced radiolysis of water. We demonstrate that minerals nucleate with a two-dimensional island structure on the graphene surfaces. We further reveal that mineral grains grow by grain boundary migration and grain rotation. Our findings provide a direct observation of the dynamics of crystal growth from ionic solutions.

Growth of Transition Metal Oxides in Solution under Liquid Cell Electron Microscopy and Electron Beam Effects

Growth of Transition Metal Oxides in Solution under Liquid Cell Electron Microscopy and Electron Beam Effects

(Keynote) Imaging Electrochemical Growth Using Liquid Cell Transmission Electron Microscopy

Transmission electron microscopy is very helpful in measuring structure and composition after electrochemical growth has finished. However, it is also possible to image structures while they are still growing, by carrying out electrodeposition inside the electron microscope. The trick is to confine the electrolyte in a layer that is thin enough to be transparent to the imaging electrons – of the order of a few hundred nanometers – and to include electrodes with a geometry that allows the reaction to be controlled and visualized. To do this, we use microfabrication techniques to build liquid cells with thin windows of silicon nitride. Once filled with electrolyte, a liquid cell is placed in the microscope and controlled by a potentiostat during imaging. We can then relate changes in morphology to electrochemical parameters, providing a detailed probe of growth mechanisms with good temporal and spatial resolution. In this presentation, we first describe practical aspects of liquid cell electron microscopy, particularly the competing requirements of resolution and diffusion – in other words, the extent to which a liquid layer that is thin enough to provide high resolution images can also replicate a process of interest. We then describe measurements of nucleation and growth during the deposition of metal films, and quantify the onset of growth instabilities. We show movies of the interface evolution of galvanostatically deposited Cu from an acidic electrolyte: initially, the kinetics are consistent with kinetic roughening theory, and later, with diffusion limited growth models. Macroscale models appear to predict the behavior over long length and time scales, but short scale behavior differs from spatially averaged measures, affecting the onset of the instability. We demonstrate some control of interface evolution through pulse plating and inorganic additives. We finally discuss liquid cell microscopy of electroless deposition and of corrosion processes in metal films, and combine metal dissolution with reduction by the electron beam to produce nanostructures. Developments in equipment and modelling are making liquid cell microscopy increasingly quantitative, suggesting exciting possibilities for detailed interrogation of a wider range of electrochemical growth physics.

Observation of materials processes in liquids by electron microscopy

Abstract

Determination of redox reaction rates and orders by in situ liquid cell electron microscopy of Pd and Au solution growth.

In-situ liquid cell transmission and scanning transmission electron microscopy (TEM/STEM) experiments are important, as they provide direct insight into processes in liquids, such as solution growth of nanoparticles, among others. In liquid cell TEM/STEM redox reaction experiments, the hydrated electrons e(-)aq created by the electron beam are responsible for the reduction of metal-ion complexes. Here we investigate the rate equation of redox reactions involving reduction by e(-)aq generated by the electron beam during in situ liquid TEM/STEM. Specifically we consider the growth of Pd on Au seeds in aqueous solutions containing Pd-chloro complexes. From the quantification of the rate of Pd deposition at different electron beam currents and as a function of distance from a stationary, nanometer-sized exciting beam, we determine that the reaction is first order with respect to the concentration of hydrated electrons, [e(-)aq]. By comparing Pd- and Au-deposition, we further demonstrate that measurements of the local deposition rate on nanoparticles in the solution via real-time imaging can be used to measure not only [e(-)aq] but also the rate of reduction of a metal-ion complex to zerovalent metal atoms in solution.