Liquid Cell Transmission Electron Microscopy Research Articles

Evaluation of correlated studies using liquid cell and cryo-transmission electron microscopy: Hydration of calcium sulphate and the phase transformation pathways of bassanite to gypsum.

Insight into the nucleation, growth and phase transformations of calcium sulphate could improve the performance of construction materials, reduce scaling in industrial processes and aid understanding of its formation in the natural environment. Recent studies have suggested that the calcium sulphate pseudo polymorph, gypsum (CaSO4 ·2H2 O) can form in aqueous solution via a bassanite (CaSO4 ·0.5H2 O) intermediate. Some in situ experimental work has also suggested that the transformation of bassanite to gypsum can occur through an oriented assembly mechanism. In this work, we have exploited liquid cell transmission electron microscopy (LCTEM) to study the transformation of bassanite to gypsum in an undersaturated aqueous solution of calcium sulphate. This was benchmarked against cryogenic TEM (cryo-TEM) studies to validate internally the data obtained from the two microscopy techniques. When coupled with Raman spectroscopy, the real-time data generated by LCTEM, and structural data obtained from cryo-TEM show that bassanite can transform to gypsum via more than one pathway, the predominant one being dissolution/reprecipitation. Comparisons between LCTEM and cryo-TEM also show that the transformation is slower within the confined region of the liquid cell as compared to a bulk solution. This work highlights the important role of a correlated microscopy approach for the study of dynamic processes such as crystallisation from solution if we are to extract true mechanistic understanding.

Inactivation of Fluorescent Lipid Bilayers by Irradiation With 300 keV Electrons Using Liquid Cell Transmission Electron Microscopy

Liquid cell transmission electron microscopy allows for imaging of samples in a fully hydrated state at high resolution and has the potential for visualizing static or dynamic biological structures. However, the ionizing nature of the electron beam makes it difficult to discern real physiological dynamics from radiation induced artifacts within liquid cell samples. Electron flux thresholds for achieving high resolution structures from biological samples frozen in ice have been described extensively by the cryo-electron microscopy field, while electron flux thresholds which do not result in a functional change for biological samples within the hydrated environment of a transmission electron microscope liquid cell is less clear. Establishing these functional thresholds for biologically relevant samples is important for accurate interpretation of results from liquid cell experiments. Here we demonstrate the electron damage threshold of fluorescently tagged lipid bilayers by quantifying the change in fluorescence before and after electron exposure. We observe the reduction of fluorescent signal in bilayers by 25% after only 0.0005 e−/Å2 and a reduction of over 90% after 0.01 e−/Å2. These results indicate that the loss of function occurs at irradiation thresholds far below a typical single high resolution (scanning) transmission electron microscopy image and orders of magnitude below fluxes used for preserving structural features with cryo-electron microscopy.

Metastable hexagonal close-packed palladium hydride in liquid cell TEM.

Metastable phases-kinetically favoured structures-are ubiquitous in nature1,2. Rather than forming thermodynamically stable ground-state structures, crystals grown from high-energy precursors often initially adopt metastable structures depending on the initial conditions, such as temperature, pressure or crystal size1,3,4. As the crystals grow further, they typically undergo a series of transformations from metastable phases to lower-energy and ultimately energetically stable phases1,3,4. Metastable phases sometimes exhibit superior physicochemical properties and, hence, the discovery and synthesis of new metastable phases are promising avenues for innovations in materials science1,5. However, the search for metastable materials has mainly been heuristic, performed on the basis of experiences, intuition or even speculative predictions, namely 'rules of thumb'. This limitation necessitates the advent of a new paradigm to discover new metastable phases based on rational design. Such a design rule is embodied in the discovery of a metastable hexagonal close-packed (hcp) palladium hydride (PdHx) synthesized in a liquid cell transmission electron microscope. The metastable hcp structure is stabilized through a unique interplay between the precursor concentrations in the solution: a sufficient supply of hydrogen (H) favours the hcp structure on the subnanometre scale, and an insufficient supply of Pd inhibits further growth and subsequent transition towards the thermodynamically stable face-centred cubic structure. These findings provide thermodynamic insights into metastability engineering strategies that can be deployed to discover new metastable phases.

Liquid cell transmission electron microscopy reveals C-S-H growth mechanism during Portland cement hydration

We report the first application of in-situ liquid cell transmission electron microscopy (LC-TEM) to research hydration reactions of nano OPC, providing nanoscale insight into early reaction mechanisms. We demonstrate that the formation and growth of C-S-H precipitates starts through lateral growth of planar silicate sheets, but soon continues in all directions resulting in a 3D microstructure. Furthermore, nanocrystalline C-S-H structures with sizes between 5 nm to 10 nm were observed inside the amorphous or highly disordered C-S-H matrix, denoting that C-S-H growth is conformed to layered structure model. Crack formation and propagation inside C-S-H precipitates confirms the presence of increasing lattice strain due to growing defects that limits the growth of a fully crystalline structure by buckling and separating the sheets. The rolling up and crumbling of C-S-H sheets promotes the formation of new embryos, leading to the growth of precipitates in all direction and finally their coalescence.

Organic solution-phase transmission electron microscopy of copolymer nanoassembly morphology and dynamics

Direct imaging of the dynamics of polymeric assemblies in organic solvents is an outstanding challenge. Herein, we apply liquid cell transmission electron microscopy (LCTEM) to study polymeric nanomaterials in organic solvents. LCTEM is distinct from other TEM methods as it can be applied to characterize the morphology of nanomaterials in organic solvents. To enable this demonstration, we examined electron-solvent interactions for two common organic solvents, N,N-dimethylformamide and methanol, and compared these solvents to water. For each solvent, we developed Monte Carlo simulations and kinetic radiolysis models, providing scattering and chemical insight, respectively. Guided by theoretical results, we applied LCTEM and postmortem mass spectral imaging of poly(styrene)-b-poly(4-vinylpyridine) assemblies in each solvent. Then, a worm-to-micelle transformation in poly(styrene)-b-poly(4-vinylpyridine) was triggered via organic solvent mixing during LCTEM, enabling an experiment not possible through a cryogenic TEM time series. Our work provides a pathway for an expanded examination of nanomaterials in organic solvents via LCTEM, a neglected research area despite the obvious prevalence of such materials across chemistry and materials science.

Liquid-cell transmission electron microscopy for imaging of thermosensitive recombinant polymers

Various polymers used in controlled release applications exhibit solution-based thermal responses. Unfortunately, very few characterization and imaging techniques permit resolution of individual polymers during their thermally-triggered phase transitions. Here, we demonstrate the use of temperature-ramp liquid-cell transmission electron microscopy (LCTEM) for real-time evaluation of the solution and interfacial behavior of elastinlike polypeptides (ELPs) and their self-assembled nanostructures over a temperature range incorporating their intrinsic lower critical solution temperatures (LCSTs). Individual polymers and supramolecular assemblies were discriminated dependent upon solubility states. The recombinant polymers were shown to adsorb to the silicon-nitride chip window from the buffered saline solution and desorb in a temperature-dependent manner. Silk-elastinlike protein block copolymers (SELPs) (composed of repeat peptide motifs of silk and elastin) differed from ELPs in thermal behavior. While both polymers were shown to cluster, only SELPs formed robust amyloid-like fibers upon heating.

Insight into ultrasensitive and high-stability flocculation-enhanced Raman spectroscopy for the in situ noninvasive probing of cupping effect substances.

The aggregation of nanoparticles is the key factor to form hot spots for the flocculation-enhanced Raman spectroscopy (FLERS) method. However, the structure of flocculation is still not clear. It is therefore necessary to explore and analyze the aggregation process of nanoparticles more carefully, so as to realize a better application of FLERS. Here, we report the application of in situ liquid cell transmission electron microscopy (TEM) combined with an in situ high-speed camera to analyze the particle behaviors. The results showed that flocculation can exist stably and the gap between the nanoparticles in the flocculation always remained at 7-9 nm, which ensured the high stability and sensitivity of the FLERS method. We successfully applied FLERS to the in situ noninvasive probing of cupping effect substances. The results indicated the scientific principle behind the traditional Chinese medicine method to some extent, which thus provides a new and effective method for the in situ dynamic monitoring of biological systems.

Possible embryos and precursors of crystalline nuclei of calcium carbonate observed by liquid-cell transmission electron microscopy

Several different building blocks or precursors play an important role in the early stages of the crystallization of calcium carbonate (CaCO3). Many studies have been conducted over a long period to elucidate the fundamental processes involved in this crystallization. Here, we report the role of an amorphous phase and embryo at the beginning of the nucleation of CaCO3 from solutions of relatively low supersaturation. Prenucleation crystals formed in amorphous calcium carbonate (ACC) at a significantly large formation rate of 2 × 1022 m-3 s-1, suggesting that a low interfacial energy exists between the ACC and crystals. Only one calcite crystal exceeded the size for a critical nucleus (∼104 molecules) in 150 pre-nucleation crystals. Each pre-nucleation crystal might consist of a different polymorph, and ACCs have a similar composition and structure. A particle-detection algorithm, used in conjunction with machine learning, suggested that an embryo with a characteristic structure exists in solution and might play a crucial role in nucleation. No similar embryonic structure could be observed immediately after the dissolution of pre-nucleation particles, implying that their dissolution process is not simply the reverse process of their growth. This method should provide a new approach to understanding nucleation processes.

Formation and Growth of Cerium (III) Oxalate Nanocrystals by Liquid-Cell Transmission Electron Microscopy

Formation and Growth of Cerium (III) Oxalate Nanocrystals by Liquid-Cell Transmission Electron Microscopy

Applications of in situ electron microscopy in oxygen electrocatalysis

Oxygen electrocatalysis involving the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) plays a vital role in cutting-edge energy conversion and storage technologies. In situ studies of the evolution of catalysts during oxygen electrocatalysis can provide important insights into their structure - activity relationships and stabilities under working conditions. Among the various in situ characterization tools available, in situ electron microscopy has the unique ability to perform structural and compositional analyzes with high spatial resolution. In this review, we present the latest developments in in situ and quasi-in situ electron microscopic techniques, including identical location electron microscopy, in situ liquid cell (scanning) transmission electron microscopy and in situ environmental transmission electron microscopy, and elaborate their applications in the ORR and OER. Our discussion centers on the degradation mechanism, structural evolution and structure - performance correlations of electrocatalysts. Finally, we summarize the earlier discussions and share our perspectives on the current challenges and future research directions of using in situ electron microscopy to explore oxygen electrocatalysis and related processes.

Coordination Cage-Based Emulsifiers: Templated Formation of Metal Oxide Microcapsules Monitored by In Situ LC-TEM.

Metallo‐supramolecular self‐assembly has yielded a plethora of discrete nanosystems, many of which show competence in capturing guests and catalyzing chemical reactions. However, the potential of low‐molecular bottom‐up self‐assemblies in the development of structured inorganic materials has rarely been methodically explored so far. Herein, we present a new type of metallo‐supramolecular surfactant with the ability to stabilize non‐aqueous emulsions for a significant period. The molecular design of the surfactant is based on a heteroleptic coordination cage (CGA‐3; CGA=Cage‐based Gemini Amphiphile), assembled from two pairs of organic building blocks, grouped around two Pd(II) cations. Shape‐complementarity between the differently functionalized components generates discrete amphiphiles with a tailor‐made polarity profile, able to stabilize non‐aqueous emulsions, such as hexadecane‐in‐DMSO. These emulsions were used as a medium for the synthesis of spherical metal oxide microcapsules (titanium oxide, zirconium oxide, and niobium oxide) from soluble, water‐sensitive alkoxide precursors by allowing a controlled dosage of water to the liquid‐liquid phase boundary. Synthesized materials were analyzed by a combination of electron microscopic techniques. In situ liquid cell transmission electron microscopy (LC‐TEM) was utilized for the first time to visualize the dynamics of the emulsion‐templated formation of hollow inorganic titanium oxide and zirconium oxide microspheres.

Dynamic processes of hybrid nanostructured Au particles/nanobubbles in a quasi-2D system by in-situ liquid cell TEM

Recently hybrid structure of hydrogen nanobubble (HNB) and gold nanoparticles (GNP) have attracted a great deal of interest in many potential applications including ultrasound contrast agent, cancer therapy and drug delivery. For the first time, here we reported interaction of high energy electron beam with sodium citrate catalyzes a highly stable hybrid super structure (HNB ∈ Au) where sub-nanometer sized GNPs are decorated on the HNB surface. The formation mechanism of HNB ∈ Au has been in-depth studied in this work. This electron radiation technique is the easiest method for the large-scale production of environmentally benign sub-nanometer sized GNP and HNB at room temperature. We have successfully demonstrated the HNB can serve as a substrate or a template for attracting Au nano-clusters onto its surface by in-situ transmission electron microscopy in liquid environment. The kinetics of multiple coalescence process of merging ultra-small GNP and HNB has been analyzed with Mehl-Avrami-Kolmogorov (JMAK) scheme. It suggests that the growth modes for HNB and GNP in the formation process of HNB ∈ Au are 2D and 3D, respectively. Here we have also calculated the momentum transferred to the GNP from the incident electrons and surrounding liquid molecules. It indicates that the incident electrons can trigger the GNP sliding on HNB surface at relatively high dose rate.

In Situ Observation of the Early Stages of Rapid Solid-Liquid Reaction in Closed Liquid Cell TEM Using Graphene Encapsulation.

In situ liquid cell transmission electron microscopy (TEM) is a very useful tool for investigating dynamic solid–liquid reactions. However, there are challenges to observe the early stages of spontaneous solid–liquid reactions using a closed-type liquid cell system, the most popular and simple liquid cell system. We propose a graphene encapsulation method to overcome this limitation of closed-type liquid cell TEM. The solid and liquid are separated using graphene to suspend the reaction until the graphene layer is destroyed. Graphene can be decomposed by the high-energy electron beam used in TEM, allowing the reaction to proceed. Fast dissolution of graphene-capped copper nanoparticles in an FeCl3 solution was demonstrated via in situ liquid cell TEM at 300 kV using a cell with closed-type SiNx windows.

Real-space imaging of nanoparticle transport and interaction dynamics by graphene liquid cell TEM.

Thermal motion of colloidal nanoparticles and their cohesive interactions are of fundamental importance in nanoscience but are difficult to access quantitatively, primarily due to the lack of the appropriate analytical tools to investigate the dynamics of individual particles at nanoscales. Here, we directly monitor the stochastic thermal motion and coalescence dynamics of gold nanoparticles smaller than 5 nm, using graphene liquid cell (GLC) transmission electron microscopy (TEM). We also present a novel model of nanoparticle dynamics, providing a unified, quantitative explanation of our experimental observations. The nanoparticles in a GLC exhibit non-Gaussian, diffusive motion, signifying dynamic fluctuation of the diffusion coefficient due to the dynamically heterogeneous environment surrounding nanoparticles, including organic ligands on the nanoparticle surface. Our study shows that the dynamics of nanoparticle coalescence is controlled by two elementary processes: diffusion-limited encounter complex formation and the subsequent coalescence of the encounter complex through rotational motion, where surface-passivating ligands play a critical role.

Dynamic transformation of cubic copper catalysts during CO2 electroreduction and its impact on catalytic selectivity

To rationally design effective and stable catalysts for energy conversion applications, we need to understand how they transform under reaction conditions and reveal their underlying structure-property relationships. This is especially important for catalysts used in the electroreduction of carbon dioxide where product selectivity is sensitive to catalyst structure. Here, we present real-time electrochemical liquid cell transmission electron microscopy studies showing the restructuring of copper(I) oxide cubes during reaction. Fragmentation of the solid cubes, re-deposition of new nanoparticles, catalyst detachment and catalyst aggregation are observed as a function of the applied potential and time. Using cubes with different initial sizes and loading, we further correlate this dynamic morphology with the catalytic selectivity through time-resolved scanning electron microscopy measurements and product analysis. These comparative studies reveal the impact of nanoparticle re-deposition and detachment on the catalyst reactivity, and how the increased surface metal loading created by re-deposited nanoparticles can lead to enhanced C2+ selectivity and stability.

Thermoresponsive polymer assemblies via variable temperature liquid-phase transmission electron microscopy and small angle X-ray scattering

Herein, phase transitions of a class of thermally-responsive polymers, namely a homopolymer, diblock, and triblock copolymer, were studied to gain mechanistic insight into nanoscale assembly dynamics via variable temperature liquid-cell transmission electron microscopy (VT-LCTEM) correlated with variable temperature small angle X-ray scattering (VT-SAXS). We study thermoresponsive poly(diethylene glycol methyl ether methacrylate) (PDEGMA)-based block copolymers and mitigate sample damage by screening electron flux and solvent conditions during LCTEM and by evaluating polymer survival via post-mortem matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). Our multimodal approach, utilizing VT-LCTEM with MS validation and VT-SAXS, is generalizable across polymeric systems and can be used to directly image solvated nanoscale structures and thermally-induced transitions. Our strategy of correlating VT-SAXS with VT-LCTEM provided direct insight into transient nanoscale intermediates formed during the thermally-triggered morphological transformation of a PDEGMA-based triblock. Notably, we observed the temperature-triggered formation and slow relaxation of core-shell particles with complex microphase separation in the core by both VT-SAXS and VT-LCTEM.

Pitfalls in Electrochemical Liquid Cell Transmission Electron Microscopy for Dendrite Observation

The growth of dendrites on the electrodes during charge–discharge cycles can lead to short‐circuit and potential ignition, which limit the capacity and application of the rechargeable batteries. With the development of in situ electrochemical liquid cell transmission electron microscopy, the growth process of metallic dendrites can be observed in real‐time. However, there remains a great challenge to operate the electrochemical liquid cell experiments successfully and repetitively. Herein, the lithium‐ion battery electrolyte system and the other electrolyte system of silver nitrate with sodium nitrate aqueous solution are adopted in our experiments to demonstrate the problems in conducting electrochemical liquid cell experiments. Influence factors are summarized, including the tube residual, cleanliness of electrodes, bubbles in the liquid cell, and the stability of the electrochemical system. All these aspects affect the electrochemical liquid cell experiments, and understanding these influencing factors is beneficial to improve the success rate of experiments. This work may offer guidance for the wide application of in situ electrochemical liquid cell transmission electron microscopy in observing the growth of dendrites in batteries.

Challenges and Opportunities in Understanding Proton Exchange Membrane Fuel Cell Materials Degradation Using In‐Situ Electrochemical Liquid Cell Transmission Electron Microscopy

AbstractEnvironmental pollution at the current state of fossil fuel consumption has led clean energy devices like proton exchange membrane fuel cells (PEMFCs) to emerge as alternative energy generation solutions. However, the performance, durability, and efficiency limitations of PEMFCs have hindered their widespread adoption. Improving their performance and durability can be achieved by fundamentally understanding and tuning their catalyst layer structures and compositions. Transmission electron microscopy and scanning transmission electron microscopy have proven to be among the best characterization tools available to analyze the microstructural features of the catalyst layers of PEMFC devices. The ability to directly observe changes in catalyst materials during operation with high spatial and temporal resolutions by the means of In‐situ techniques can accelerate material development in the PEMFC field. In this article, structure, properties, and performance of PEMFC materials are reviewed, and their known degradation mechanisms are introduced. Available In‐situ TEM techniques are presented to guide the selection of suitable methods and approaches for studying the PEMFC systems. Finally, the current literature is presented on PEMFC research that has used In‐situ electrochemical liquid cell TEM to study materials evolution and degradation, highlighting the specific challenges and opportunities for applying the technique in the PEMFCs’ field.

Dipeptide Nanostructure Assembly and Dynamics via in Situ Liquid-Phase Electron Microscopy.

In this paper, we report the in situ growth of FF nanotubes examined via liquid-cell transmission electron microscopy (LCTEM). This direct, high spatial, and temporal resolution imaging approach allowed us to observe the growth of peptide-based nanofibrillar structures through directional elongation. Furthermore, the radial growth profile of FF nanotubes through the addition of monomers perpendicular to the tube axis has been observed in real-time with sufficient resolution to directly observe the increase in diameter. Our study demonstrates that the kinetics, dynamics, structure formation, and assembly mechanism of these supramolecular assemblies can be directly monitored using LCTEM. The performance of the peptides and the assemblies they form can be verified and evaluated using post-mortem techniques including time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Simulating Current Distribution of Oxygen Evolution Reaction in Microcells Using Finite Element Method

A three-dimensional finite element method (FEM) model simulating the electrochemical behaviour of Pt coplanar thin-film electrodes used for liquid cell transmission electron microscopy measurements was developed. The model included reaction kinetics and it was applied for the oxygen evolution reaction (OER). Kinetic parameters of OER in the liquid cell were experimentally acquired and applied to the FEM model. Comparison between the experimental and simulated polarization curves demonstrated the reliability of the FEM predictions. The simulations were used to produce maps of the potential and current density distributions of the working and counter electrodes as well as for calculating the distribution of the current density in the liquid electrolyte. Two distinctive electrode geometries were evaluated with the FEM model. It was predicted that non-symmetrical electrode designs can cause unexpected electrochemical behaviour with respect to the electrolyte current density between working and counter electrodes accompanied by the presence of hot spots. The findings suggest that FEM simulations could be key to designing well-performing electrochemical microcells for liquid phase electron microscopy experiments.