Dose-rate-dependent damage of cerium dioxide in the scanning transmission electron microscope

Abstract

Beam damage caused by energetic electrons in the transmission electron microscope is a fundamental constraint limiting the collection of artifact-free information. Through understanding the influence of the electron beam, experimental routines may be adjusted to improve the data collection process. Investigations of CeO2 indicate that there is not a critical dose required for the accumulation of electron beam damage. Instead, measurements using annular dark field scanning transmission electron microscopy and electron energy loss spectroscopy demonstrate that the onset of measurable damage occurs when a critical dose rate is exceeded. The mechanism behind this phenomenon is that oxygen vacancies created by exposure to a 300 keV electron beam are actively annihilated as the sample re-oxidizes in the microscope environment. As a result, only when the rate of vacancy creation exceeds the recovery rate will beam damage begin to accumulate. This observation suggests that dose-intensive experiments can be accomplished without disrupting the native structure of the sample when executed using dose rates below the appropriate threshold. Furthermore, the presence of an encapsulating carbonaceous layer inhibits processes that cause beam damage, markedly increasing the dose rate threshold for the accumulation of damage.

Sub-nanometer surface chemistry and orbital hybridization in lanthanum-doped ceria nano-catalysts revealed by 3D electron microscopy

“…Notably, the Ce post-edge energy window showed substantially reduced plural scattering effects in the core spectrum. The M 5 / M 4 ratios were 1.14 and 0.89 for the shell and core, respectively, consistent with the Ce 3+ and Ce 4+ limiting cases for the Ce cation oxidation state 20, 22 . The M 45 line ratios indicated clear phase segregation in the core-shell analysis, with an optimum shell thickness of 1.3 nm.…”

Atomic‐Scale Valence State Distribution inside Ultrafine CeO2 Nanocubes and Its Size Dependence

“…For this purpose, the distribution of Ce 3+ cations in CeO 2 NCs was studied based on STEM‐EELS analysis. The irradiation effect on the valence state of cerium cations was considered and was avoided by using a low dose electron beam and short acquisition time to obtain the EELS spectra . Indeed, for the first time, we succeeded in acquiring an EELS spectrum across a single CeO 2 NC perpendicular to its {100} exposed facet layer‐by‐layer based on the atomic‐resolution HAADF‐STEM images.…”

“…The EELS spectra were recorded using a Gatan Enfinium camera system with an energy spread Δ E of ≈0.3 eV. A low dose rate and short acquisition time of 2.5 s were used for each box scanning to avoid beam irradiation …”

Atomic scale insights into structure instability and decomposition pathway of methylammonium lead iodide perovskite

“…2 and 3, the dose rate is estimated to be 220–360 e Å −2 s −1 which is calculated by dividing the screen current (6 ~ 10 pA) by the area of the raster 49 . To get a satisfactory STEM image, we need to carefully align the zone axis and adjust the astigmatism and the focus before image acquisition, which is time-consuming and costs about 5–10 min.…”