Preparation of high-quality planar FeRh thin films for in situ TEM investigations

The preparation of a planar FeRh thin film using a focused ion beam (FIB) secondary electron microscope (SEM) for the purpose of in situ transmission electron microscopy (TEM) is presented. A custom SEM stub with 45° faces allows for the transfer and milling of the sample on a TEM heating chip, whilst Fresnel imaging within the TEM revealed the presence of the magnetic domain walls, confirming the quality of the FIB-prepared sample

A new thin film photochromic material: Oxygen-containing yttrium hydride

In this work we report on photochromism in transparent thin film samples of oxygen-containing yttrium hydride. Exposure to visible and ultraviolet (UV) light at moderate intensity triggers a decrease in the optical transmission of visible and infrared (IR) light. The photo-darkening is colour-neutral. We show that the optical transmission of samples of 500 nm thickness can be reduced by up to 50% after one hour of illumination with light of moderate intensity. The reaction is reversible and samples that are left in the dark return to the initial transparent state. The relaxation time in the dark depends on the temperature of the sample and the duration of the light exposure. The photochromic reaction takes place under ambient conditions in the as-deposited state of the thin-film samples.Comment: Accepted for publication in Solar Energy Materials and Solar Cell

Electrical characterization and failure analysis using operando TEM

We present here the development of a system that allows for in-situ studies inside the Transmission Electron Microscope (TEM). Functionalized Microelectromechanical Systems (MEMS) used as sample carriers, referred to as Nano-Chips, contain up to eight electrodes used for simultaneous biasing and heating purposes, enabling electro-thermal characterization of various sample types inside the TEM under real life dynamic conditions. This operando approach is an ideal method to study failure analysis of semiconductor materials, performance of resistive switching devices, batteries, fuel cells, piezoceramics and many more

Thermal stability of gas phase magnesium nanoparticles

In this work we present a unique transmission electron microscopy study of the thermal stability of gas phase synthesized Mg nanoparticles, which have attracted strong interest as high capacity hydrogen storage materials. Indeed, Mg nanoparticles with a MgO shell (~3 nm thick) annealed at 300 °C show evaporation, void formation, and void growth in the Mg core both in vacuum and under a high pressure gas environment. This is mainly due to the outward diffusion and evaporation of Mg with the simultaneously inward diffusion of vacancies leading to void growth (Kirkendall effect). The rate of Mg evaporation and void formation depends on the annealing conditions. In vacuum, and at T=300 °C, the complete evaporation of the Mg core takes place (within a few hours) for sizes ~15–20 nm. Void formation and growth has been observed for particles with sizes ~20–50 nm, while stable Mg nanoparticles were observed for sizes >50 nm. Furthermore, even at relative low temperature annealing (as low as 60 °C), void formation and growth occurs in 15–20 nm sized Mg nanoparticles, indicating that voiding will be even more dominant for nanoparticles smaller than 10 nm. Our findings confirm that Mg evaporation and void formation in nanoparticles with sizes less than 50 nm present formidable barriers for their applicability in hydrogen storage, but also could inspire future research directions to overcome these obstacles.

Oxygen Ionic Transport in Brownmillerite-Type Ca2Fe2O5-delta and Calcium Ferrite-Based Composite Membranes

Oxygen ionic transport in mixed-conducting Ca2Fe2O5-delta brownmillerite was analyzed in light of potential applications in the composite materials for oxygen separation membranes and solid oxide fuel cell cathodes. The lattice defect formation and oxygen diffusion mechanisms were assessed by the computer simulations employing molecular dynamics and static lattice modeling. The most energetically favorable oxygen-vacancy location is in the octahedral layers of the brownmillerite structure, which provide a maximum contribution to the ionic migration in comparison with the structural blocks comprising iron-oxygen tetrahedra. The activation energies for the vacancy and interstitial diffusion in the tetrahedral layers, and also between the octahedral and tetrahedral sheets, are several times higher. The calculated values were found comparable to the experimental activation energy for ionic conduction in Ca2Fe2O5-delta, 147 kJ/mol, determined by the steady-state oxygen permeation measurements. The dense membranes of model composite Ca2Fe2O5-delta - Ce0.9Gd0.1O2-delta with equal weight fractions of the components (CGCF5) were sintered and characterized. No critical interdiffusion of the composite constituents, leading to their decomposition, was found by X-ray diffraction and electron microscopic analyses. The electrical conductivity of this composite, with an activation energy of 37 kJ/mol, is intermediate between two parent compounds and is dominantly p-type electronic as for Ca2Fe2O5-delta. Since the ion- and electron-conducting phases are well percolated in the composite ceramics, the oxygen permeation fluxes through CGCF5 are considerably higher than those of both constituents

Metal Electroplating/Stripping and 4D STEM AnalysisRevealed by Liquid Phase Transmission ElectronMicroscopy

Aqueous zinc ion and metal-based batteries have attracted much attention towards the development of an alternative electrochemical energy storage technology beyond lithium ion batteries [1]. There are several advantages of metal-based batteries, including high volumetric capacity (∼8000 mAh/L), low anode potential (∼0.7 V vs. SHE), safety and electrode abundance.However, the problem of metallic dendrite growth during cycling can cause battery short circuit failure, which can result in safetyhazards and severely limit the progress and further commercialization [2, 3]. To this end, direct visualization of dendrite evolutionunder operando conditions is a prerequisite for battery safety and longevity. Among the many operando/in situ techniques, the useof liquid phase transmission electron microscopy (LPTEM) [4] has been very effective in enabling a more detailed understandingof metal plating and stripping, where the ability to locally probe and visualize the key processes governing the dendrite formation.However, it remains challenging to perform high resolution and analytical electron microscopy studies in a liquid cell, especiallyunder liquid flow conditions.In this work, we use LPTEM [5, 6] to directly visualize the electroplating and stripping of metals on micro-electrodes of dedicated MEMS (micro-electro-mechanical system) chips at the nanoscale. By comparing the plating/stripping under different chemical and/or electrochemical environments, including static or flow electrolyte conditions and varying current densities, we showhow metal dendrites can be effectively controlled on electrochemical cycling of the battery, as revealed by our operando LPTEMobservations. In addition, we recently developed a liquid purging approach, which is based on the DENSsolutions unique LiquidSupply System and the on-chip liquid flow capability (Figure 1). This approach enables one to perform 4D STEM electron diffraction analysis on the plating (Figure 2). Following the experimental results, the growth of zinc dendrites can be effectively mitigated and directly minimized by flowing electrolyte into the cell and adjusting the current density, thus, providing new insightsinto the aqueous metal battery’s chemistry and the pathways for further optimization

Metal electroplating/stripping and 4D STEM analysis revealed by liquid phase transmission electron microscopy

Aqueous zinc ion and metal-based batteries have attracted much attention towards the development of an alternative electrochemical energy storage technology beyond Li ion batteries [1]. Although there are several advantages of metal-based batteries, including high volumetric capacity (~8000 mAh/L), low anode potential (~0.7 V vs. SHE), safety and electrode abundance, the problem of metallic dendrite growth during cycling causing battery short circuit and failure, constituting safety hazards, severely limits the progress and further commercial exploitation [2, 3]. To this end, direct visualization of dendrites evolution under operando conditions is prerequisite for battery safety and longevity. Among the many operando/in situ techniques, the use of liquid phase transmission electron microscopy (LPTEM) [4] has been very effective in enabling a more detailed understanding of metal plating and stripping, where the ability to probe and visualize locally the key processes governing the dendrites formation. But it should be mentioned that it is still a challenge to perform high resolution and analytical electron microscopy studies in a liquid cell, especially with liquid flow function.In this work, we use LPTEM [5, 6] to directly visualize the electroplating and stripping of metals on micro electrodes of dedicated MEMS (MicroElectroMechanical System) chips at the nanoscale. By comparing the plating/striping under different chemical and/or electrochemical environment, including static or flow electrolyte conditions, and varying current densities, we show how metal dendrites can be effectively controlled on electrochemical cycling of the battery, as revealed by our operando LPTEM observations. In addition, by employing we recently developed liquid purging approach [7], which is based on the unique liquid supply system and the on-chip liquid flow capability, we are capable to perform 4D STEM electron diffraction analysis on the plating (Figure (a), Orientation mapped STEM image of deposited Zn in liquid by 4D STEM data analysis, Figure (b-e), reconstructed electron diffraction patterns corresponding to each mapped region).Following the experimental results, the growth of Zn dendrites can be effectively mitigated and directly minimized by flowing electrolyte into the cell and adjusting the current density, thus, providing new insights into the Aqueous metal batteries chemistry and the pathways for its optimization

High-resolution and analytical electron microscopy in a liquid flow cell via gas purging

Liquid-phase transmission electron microscopy (LPTEM) technique has been used to perform a wide range of in situ and operando studies. While most studies are based on the sample contrast change in the liquid, acquiring high qualitative results in the native liquid environment still poses a challenge. Herein, we present a novel and facile method to perform high-resolution and analytical electron microscopy studies in a liquid flow cell. This technique is based on removing the liquid from the observation area by a flow of gas. It is expected that the proposed approach can find broad applications in LPTEM studies

Interface Energy Controlled Thermodynamics of Nanoscale Metal Hydrides

Nanoconfined MgH2 is destabilized compared to its bulk counterpart because of an interface energy effect. The hydrogen equilibrium pressure increases by an order of magnitude when decreasing the Mg layer thickness from 10 to 2 nm. This relates to an interface energy change of 0.3 J m−2