Katherine Leigh Jungjohann

Controlled Growth of Nanoparticles from Solution with In Situ Liquid Transmission Electron Microscopy

Direct visualization of lead sulfide nanoparticle growth is demonstrated by selectively decomposing a chemical precursor from a multicomponent solution using in situ liquid transmission electron microscopy. We demonstrate reproducible control over growth mechanisms that dictate the final morphology of nanostructures while observing growth in real-time with subnanometer spatial resolution. Furthermore, while an intense electron beam can initiate nanoparticle growth, it is also shown that a laser can trigger the reaction independently of the imaging electrons.

Experimental procedures to mitigate electron beam induced artifacts during in situ fluid imaging of nanomaterials

Scanning transmission electron microscopy of various fluid and hydrated nanomaterial samples has revealed multiple imaging artifacts and electron beam-fluid interactions. These phenomena include growth of crystals on the fluid stage windows, repulsion of particles from the irradiated area, bubble formation, and the loss of atomic information during prolonged imaging of individual nanoparticles. Here we provide a comprehensive review of these fluid stage artifacts, and we present new experimental evidence that sheds light on their origins in terms of experimental apparatus issues and indirect electron beam sample interactions with the fluid layer. A key finding is that many artifacts are a result of indirect electron beam interactions, such as production of reactive radicals in the water by radiolysis, and the associated crystal growth. The results presented here will provide a methodology for minimizing fluid stage imaging artifacts and acquiring quantitative in situ observations of nanomaterial behavior in a liquid environment.

Atomic-scale imaging and spectroscopy for in situ liquid scanning transmission electron microscopy.

Observation of growth, synthesis, dynamics, and electrochemical reactions in the liquid state is an important yet largely unstudied aspect of nanotechnology. The only techniques that can potentially provide the insights necessary to advance our understanding of these mechanisms is simultaneous atomic-scale imaging and quantitative chemical analysis (through spectroscopy) under environmental conditions in the transmission electron microscope. In this study we describe the experimental and technical conditions necessary to obtain electron energy loss (EEL) spectra from a nanoparticle in colloidal suspension using aberration-corrected scanning transmission electron microscopy (STEM) combined with the environmental liquid stage. At a fluid path length below 400 nm, atomic resolution images can be obtained and simultaneous compositional analysis can be achieved. We show that EEL spectroscopy can be used to quantify the total fluid path length around the nanoparticle and demonstrate that characteristic core-loss signals from the suspended nanoparticles can be resolved and analyzed to provide information on the local interfacial chemistry with the surrounding environment. The combined approach using aberration-corrected STEM and EEL spectra with the in situ fluid stage demonstrates a plenary platform for detailed investigations of solution-based catalysis.

Visualizing macromolecular complexes with in situ liquid scanning transmission electron microscopy.

A central focus of biological research is understanding the structure/function relationship of macromolecular protein complexes. Yet conventional transmission electron microscopy techniques are limited to static observations. Here we present the first direct images of purified macromolecular protein complexes using in situ liquid scanning transmission electron microscopy. Our results establish the capability of this technique for visualizing the interface between biology and nanotechnology with high fidelity while also probing the interactions of biomolecules within solution. This method represents an important advancement towards allowing future high-resolution observations of biological processes and conformational dynamics in real-time.

Lithium Electrodeposition Dynamics in Aprotic Electrolyte Observed in Situ via Transmission Electron Microscopy

Electrodeposited metallic lithium is an ideal negative battery electrode, but nonuniform microstructure evolution during cycling leads to degradation and safety issues. A better understanding of the Li plating and stripping processes is needed to enable practical Li-metal batteries. Here we use a custom microfabricated, sealed liquid cell for in situ scanning transmission electron microscopy (STEM) to image the first few cycles of lithium electrodeposition/dissolution in liquid aprotic electrolyte at submicron resolution. Cycling at current densities from 1 to 25 mA/cm(2) leads to variations in grain structure, with higher current densities giving a more needle-like, higher surface area deposit. The effect of the electron beam was explored, and it was found that, even with minimal beam exposure, beam-induced surface film formation could alter the Li microstructure. The electrochemical dissolution was seen to initiate from isolated points on grains rather than uniformly across the Li surface, due to the stabilizing solid electrolyte interphase surface film. We discuss the implications for operando STEM liquid-cell imaging and Li-battery applications.

Phase Boundary Propagation in Li-Alloying Battery Electrodes Revealed by Liquid-Cell Transmission Electron Microscopy

Battery cycle life is directly influenced by the microstructural changes occurring in the electrodes during charge and discharge cycles. Here, we image in situ the nanoscale phase evolution in negative electrode materials for Li-ion batteries using a fully enclosed liquid cell in a transmission electron microscope (TEM) to reveal early degradation that is not evident in the charge-discharge curves. To compare the electrochemical phase transformation behavior between three model materials, thin films of amorphous Si, crystalline Al, and crystalline Au were lithiated and delithiated at controlled rates while immersed in a commercial liquid electrolyte. This method allowed for the direct observation of lithiation mechanisms in nanoscale negative electrodes, revealing that a simplistic model of a surface-to-interior lithiation front is insufficient. For the crystalline films, a lithiation front spread laterally from a few initial nucleation points, with continued grain nucleation along the growing interface. The intermediate lithiated phases were identified using electron diffraction, and high-resolution postmortem imaging revealed the details of the final microstructure. Our results show that electrochemically induced solid-solid phase transformations can lead to highly concentrated stresses at the laterally propagating phase boundary which should be considered for future designs of nanostructured electrodes for Li-ion batteries.

Design of a Heated Liquid Cell for in-situ Transmission Electron Microscopy

Microfabricated, silicon-based chips developed for advanced capabilities in sample holders have recently led to a broad expansion of in-situ transmission electron microscopy (TEM) experiments involving materials’ responses to increased temperature, electrical bias, or mechanical stress. By including freestanding, electron-transparent silicon nitride membranes, a thin environmental chamber for gases or liquids can be created in the TEM allowing new insights into the nanoscale processes involved in electrochemical, catalytic, or biological systems. Heated gas environments in the TEM have been previously demonstrated with microfabricated chips [1-2], but little work has been done with heated liquid environments. With control over the thermal environment, systems that activate at increased temperature (e.g. nanoparticle growth, protein denaturation, corrosion) or systems that degrade with temperature cycling (e.g. battery materials) can be studied.

In Situ and Operando

This topic is a very broad one since it involves everything that has been covered in W&C and then allows the specimen to change while you image it, record the spectra, and/or measure what changes are taking place. We are combining two topics that could be treated separately, namely in-situ experimentation and controlled-environment TEM (which we’ll call an ETEM, but you’ll also see E-TEM or eTEM). The reason for combining the two is that changes in the environment about the sample can change the material as we examine it in the TEM. With TEM, it’s always an in-situ study! We’re also including operando with in situ; operando implies that the material is behaving as it would do in “real life”; the translation is “working.” For example, if a catalyst particle is actually acting as a catalyst when we observe it, it’s an operando study; in general such a particle can’t act as a catalyst unless there is something to catalyze! You are often measuring something (there is a metric) that relates to the performance of the materials – so that you know it’s performing!

Understanding Reaction Mechanisms in Electrochemistry and Corrosion: Liquid-Cell S/TEM

Electrochemical and corrosion studies have greatly benefited from using liquid-cell S/TEM techniques for providing real-time information on the nanoscale mechanisms occurring at solid-liquid interfaces [1]. Within a liquid environment, nanoscale electrodes and metals undergo reactions with the solution creating surface layers and films at the interface. In batteries, these interface layers are known as solidelectrolyte interfaces (SEI). In corrosion experiments, the surface layers are known as scale materials. These systems have related domination of the surface film composition and structure impacting the overall behavior of the electrode and the rate of reaction during corrosion. Therefore, to better understand these material systems and determinant mechanisms, we are investigating using real-time imaging and spectroscopy to characterize these interfaces for initial structural identification, in-situ monitoring of interfacial processes, and post-mortem analysis of electrode/material surfaces.

Steel Corrosion Mechanisms during Pipeline Operation: In Situ Characterization

Pipeline corrosion continues to present challenges to the oil and gas industry, with billions of dollars being spent annually to remediate, repair, and replace steel piping. The corrosion processes of this piping are not well understood, due in part to the seemingly endless environmental and industrial parameters involved in corrosion of the steel. We have applied a nanoscale approach to investigate the initial oilfield corrosion pathways, formation products, and susceptible grain structures of low-alloy carbon steel through the course of corrosion by hydrogen sulfide (H2S) and carbon dioxide (CO2). The goal of the project is to develop a mechanistic understanding of the early onset of corrosion under wellcontrolled environmental conditions in order to develop future strategies to reduce corrosion-related losses. The most aggressive component in these operations is caused by CO2 attack on the steel surface, where an aqueous phase present provides the electrolyte needed for corrosion to occur [1]. Though it is postulated that grain boundaries, material defects, and nanoscale features are likely sites for this mesatype corrosion, predictive relationships have not been adequately demonstrated.