Real-time imaging of nanoscale electrochemical Ni etching under thermal conditions

In Situ Transmission Electron Microscopy of Electrocatalyst Materials: Proposed Workflows, Technical Advances, Challenges, and Lessons Learned

In situ electrochemical liquid phase transmission electron microscopy (LP-TEM) measurements utilize micro-chip three-electrode cells with electron transparent silicon nitride windows that confine the liquid electrolyte. By imaging electrocatalysts deposited on micro-patterned electrodes, LP-TEM provides insight into morphological, phase structure, and compositional changes within electrocatalyst materials under electrochemical reaction conditions, which have practical implications on activity, selectivity, and durability. Despite LP-TEM capabilities becoming more accessible, in situ measurements under electrochemical reaction conditions remain non-trivial, with challenges including electron beam interactions with the electrolyte and electrode, the lack of well-defined experimental workflows, and difficulty interpreting particle behavior within a liquid. Herein a summary of the current state of LP-TEM technique capabilities alongside a discussion of the relevant experimental challenges researchers typically face, with a focus on in situ studies of electrochemical CO2 conversion catalysts is provided. A methodological approach for in situ LP-TEM measurements on CO2R catalysts prepared by electro-deposition, sputtering, or drop-casting is presented and include case studies where challenges and proposed workflows for each are highlighted. By providing a summary of LP-TEM technique capabilities and guidance for the measurements, the goal is for this paper to reduce barriers for researchers who are interested in utilizing LP-TEM characterization to answer their scientific questions.

Abnormal Silicon Etching Behaviors in Nanometer-Sized Channels

Modern semiconductor fabrication is challenged by difficulties in overcoming physical and chemical constraints. A major challenge is the wet etching of dummy gate silicon, which involves the removal of materials inside confined spaces of a few nanometers. These chemical processes are significantly different in the nanoscale and bulk. Previously, electrical double-layer formation, bubble entrapment, poor wettability, and insoluble intermediate precipitation have been proposed. However, the exact suppression mechanisms remain unclear due to the lack of direct observation methods. Herein, we investigate limiting factors for the etching kinetics of silicon with tetramethylammonium hydroxide at the nanoscale by using liquid-phase transmission electron microscopy, three-dimensional electron tomography, and first-principles calculations. We reveal suppressed chemical reactions, unstripping phenomena, and stochastic etching behaviors that have never been observed on a macroscopic scale. We expect that solutions can be suggested from this comprehensive insight into the scale-dependent limiting factors of fabrication.

Temperature Dependent Nanochemistry and Growth Kinetics Using Liquid Cell Transmission Electron Microscopy

Liquid cell transmission electron microscopy has become a powerful and increasingly accessible technique for in situ studies of nanoscale processes in liquid and solution phase. Exploring reaction mechanisms in electrochemical or crystal growth processes requires precise control over experimental conditions, with temperature being one of the most critical factors. Here we carry out a series of crystal growth experiments and simulations at different temperatures in the well-studied system of Ag nanocrystal growth driven by the changes in redox environment caused by the electron beam. Liquid cell experiments show strong changes in both morphology and growth rate with temperature. We develop a kinetic model to predict the temperature-dependent solution composition, and we discuss how the combined effect of temperature-dependent chemistry, diffusion, and the balance between nucleation and growth rates affect the morphology. We discuss how this work may provide guidance in interpreting liquid cell TEM and potentially larger-scale synthesis experiments for systems controlled by temperature.

Liquid cell electrochemical TEM: Unveiling the real-time interfacial reactions of advanced Li-metal batteries

Li metal batteries (LMBs) reveal great application prospect in next-generation energy storage, because of their high energy density and low electrochemical potential, especially when paired with elemental sulfur and oxygen cathodes. Complex interfacial reactions have long been a big concern because of the elusive formation/dissolution of Li metal at the solid-electrolyte interface (SEI) layer, which leads to battery degradation under practical operating conditions. To precisely track the reactions at the electrode/electrolyte interfaces, in the past ten years, high spatio-temporal resolution, in situ electrochemical transmission electron microscopy (EC-TEM) has been developed. A preliminary understanding of the structural and chemical variation of Li metal during nucleation/growth and SEI layer formation has been obtained. In this perspective, we give a brief introduction of liquid cell development. Then, we comparably discuss the different configurations of EC-TEM based on open-cell and liquid-cell, and focus on the recent advances of liquid-cell EC-TEM and its investigation in the electrodes, electrolytes, and SEI. Finally, we present a perspective of liquid-cell EC-TEM for future LMB research.

A temperature-tuned electrochemiluminescence layer for reversibly imaging cell topography

Investigating electrochemiluminescence (ECL) scenarios under different temperatures is important to expand its imaging scope near an electrode surface. Here, we develop a temperature-tuned ECL layer by recording the evolution of shadow regions of adherent cells. Finite element simulation and experimental results demonstrate that the thickness of the ECL layer (TEL) is reversibly regulated by electrode temperature (T _e), so that single cell topography at different heights is imaged. The TEL in two ECL routes shows different regulation ranges with elevated T _e, thus providing a flexible approach to adjust the imaging scope within specific heights. In addition, a heated electrode significantly improves the image quality of cell adhesion in heterogeneous electrochemical rate-determined situations. Thus, the contrast in cell regions shows a reversible response to T _e. This work provides a new approach to regulate the TEL and is promising for monitoring transient heat generation from biological entities.