In situ off-axis electron holography of metal-oxide hetero-interfaces in oxygen atmosphere

Abstract

Off-axis electron holography has been extended to in situ observations in gas atmospheres. The Yttria-stabilized zirconia (YSZ)-Pt hetero-interface was characterized by electron holography at high temperature in a vacuum and in an oxygen atmosphere. Analysis of the phase shift profiles revealed high mobility of anions in the oxide in the vicinity of the interface in the oxygen atmosphere. This would compensate for any increase in the number of oxygen vacancies in YSZ through the metal interface.

In Situ Transmission Electron Microscopy of Ionic Conductivity and Reaction Mechanisms in Ultrathin Solid Oxide Fuel Cells

“…Figure 2b shows a corresponding phase image reconstructed from the central area of the electron hologram, as shown by the red-dashed rectangle in Figure 2a. The sign convention used in Figure 2 corresponds to the phase in vacuum being higher than that in the specimen (Tavabi et al, 2011 a ). A similar approach was used to acquire phase images from both the half and the complete cells in different environments.

Figure 2 Representative off-axis electron holography results from an ultrathin half solid oxide fuel cell.

…”

“…This W layer was considered to be a catalytically inactive electrode in the half-cells. The specimens were mounted either on conventional Mo FIB grids (EM Japan Co. Ltd., Tokyo, Japan) for energy dispersive X-ray spectroscopy (EDS) mapping and electron energy-loss spectroscopy (EELS) or on Ta ribbons, which served as heating devices (Tavabi et al, 2011 a ) for in situ electron holography, before final thinning. The specimen temperature on the Ta ribbon was calibrated using a homemade alumel–chromel thermocouple in a vacuum chamber, as shown in Supplementary Figure 3.…”

“…In situ off-axis electron holography observations were performed using a Hitachi HF-2000 cold-field emission TEM (Hitachi Ltd., Japan) equipped with an electrostatic biprism close to a conjugate image plane of the microscope and a home-built environmental system for the introduction of gas into the objective lens pole-piece gap (Tavabi et al, 2011 a ). The oxygen atmosphere was raised up to 5E-4 mbar at the specimen area.…”

“…A TEM specimen holder with four electrodes and a Ta heating ribbon was used to study specimens at elevated temperature in a gas environment (Moritomo et al, 2006). Half and complete SOFCs that had been prepared using FIB microsampling were mounted in this holder (Tavabi et al, 2011 a ). Electron holographic phase images were reconstructed using custom scripts written in Digital Micrograph software (Gatan Inc., Pleasanton, CA, USA).…”

“…An important challenge for the observation of gas–solid reactions using electron holography is scattering of the electron beam by the gas, which can reduce beam coherence. We have recently shown that it is possible to perform in situ off-axis electron holography in a gas atmosphere (Tavabi et al, 2011 a ). Here, we apply in situ off-axis electron holography to study a Gd-doped ceria (GDC) solid oxide electrolyte that has an interface with a Pt electrode (in a half-cell).…”