Atomic Resolution Phase Contrast Imaging and In-Line Holography Using Variable Voltage and Dose Rate

Abstract

The TEAM 0.5 electron microscope is employed to demonstrate atomic resolution phase contrast imaging and focal series reconstruction with acceleration voltages between 20 and 300 kV and a variable dose rate. A monochromator with an energy spread of ≤0.1 eV is used for dose variation by a factor of 1,000 and to provide a beam-limiting aperture. The sub-Ångstrøm performance of the instrument remains uncompromised. Using samples obtained from silicon wafers by chemical etching, the [200] atom dumbbell distance of 1.36 Å can be resolved in single images and reconstructed exit wave functions at 300, 80, and 50 kV. At 20 kV, atomic resolution <2 Å is readily available but limited by residual lens aberrations at large scattering angles. Exit wave functions reconstructed from images recorded under low dose rate conditions show sharper atom peaks as compared to high dose rate. The observed dose rate dependence of the signal is explained by a reduction of beam-induced atom displacements. If a combined sample and instrument instability is considered, the experimental image contrast can be matched quantitatively to simulations. The described development allows for atomic resolution transmission electron microscopy of interfaces between soft and hard materials over a wide range of voltages and electron doses.

Real-time sub-Ångstrom imaging of reversible and irreversible conformations in rhodium catalysts and graphene

“…The finding opens room for the deployment of a weak-excitation approach for electron microscopy that also allows exploring the gray zone between both extremes of Figure 1. It is enabled by a recently developed in-line holography concept with dose rate variations by orders of magnitude at acceleration voltages between 20 kV and 300 kV 29 . The currently obtainable time resolution is in the range of minutes to milliseconds and one can address turn-over-frequencies of chemical reactions for example.…”

Low Dose Characterization of Diamondoid Carbon Nanothreads by Transmission Electron Microscopy

“…Electron diffraction patterns in Figure 1a show a critical electron dose of 150 e-/Å 2 and expansion the lattice of the nanothread lattice. EELS spectra in Figure 1b also reveal a rapid transformation of sp 3 to sp 2 carbon. [2] In this research, we quantify the sp 2 ratio of the carbon present in the nanothreads using low dose spectroscopy techniques.…”

“…In addition, we acquire low dose high resolution imaging by adjusting an electron gun monochromator to reduce the electron dose and minimize beam irradiation and damage while imaging the nanothreads on a high-resolution aberration-corrected transmission electron microscope. [3] High-resolution TEM images in Figure 1c and 1d show the transition from thread-like to amorphous morphology during exposure to high electron dose as an example. This study further analyzes low-dose images of nanothreads in order to compare their fine features with predicted nanothread structures.…”

Nanocatalysis II: In Situ Surface Probes of Nano-Catalysts and Correlative Structure–Reactivity Studies

“…80 kV) and low electron dose exposures (i.e. several electrons per square Angstrom); and thus allow imaging that is free of knock-on atom displacements and ionization effects [69,70].…”