Abstract:Functional behavior can be initiated and captured in series of images with previously unknown details using a successful effort to effectively control beam-sample interactions in high-resolution transmission electron microscopy. The approach uses tunable electron dose rates that can be chosen to be as low as attoamperes per square-Ångstrom to delay sample degradation to an unexplored end. Dose rates can be systematically increased to stimulate and observe dynamic object responses. Observations can be made in r… Show more
“…However, unlike the abrupt onset of knock-on damage in bulk materials, this onset is continuous and occurs at much lower energies because of the distribution of reduced binding energies of atoms at surfaces, interfaces, or defects [24, 25]. In fact, surface effects entirely dominate if the sample dimensions shrink to the range of single-digit nanoparticles, where entire particles can become unstable in the electron beam [20, 26]. Fig.…”
This article summarizes core aspects of beam-sample interactions in research that aims at exploiting the ability to detect single atoms at atomic resolution by mid-voltage transmission electron microscopy. Investigating the atomic structure of catalytic Co3O4 nanocrystals underscores how indispensable it is to rigorously control electron dose rates and total doses to understand native material properties on this scale. We apply in-line holography with variable dose rates to achieve this goal. Genuine object structures can be maintained if dose rates below ~100 e/Å2s are used and the contrast required for detection of single atoms is generated by capturing large image series. Threshold doses for the detection of single atoms are estimated. An increase of electron dose rates and total doses to common values for high resolution imaging of solids stimulates object excitations that restructure surfaces, interfaces, and defects and cause grain reorientation or growth. We observe a variety of previously unknown atom configurations in surface proximity of the Co3O4 spinel structure. These are hidden behind broadened diffraction patterns in reciprocal space but become visible in real space by solving the phase problem. An exposure of the Co3O4 spinel structure to water vapor or other gases induces drastic structure alterations that can be captured in this manner.
“…However, unlike the abrupt onset of knock-on damage in bulk materials, this onset is continuous and occurs at much lower energies because of the distribution of reduced binding energies of atoms at surfaces, interfaces, or defects [24, 25]. In fact, surface effects entirely dominate if the sample dimensions shrink to the range of single-digit nanoparticles, where entire particles can become unstable in the electron beam [20, 26]. Fig.…”
This article summarizes core aspects of beam-sample interactions in research that aims at exploiting the ability to detect single atoms at atomic resolution by mid-voltage transmission electron microscopy. Investigating the atomic structure of catalytic Co3O4 nanocrystals underscores how indispensable it is to rigorously control electron dose rates and total doses to understand native material properties on this scale. We apply in-line holography with variable dose rates to achieve this goal. Genuine object structures can be maintained if dose rates below ~100 e/Å2s are used and the contrast required for detection of single atoms is generated by capturing large image series. Threshold doses for the detection of single atoms are estimated. An increase of electron dose rates and total doses to common values for high resolution imaging of solids stimulates object excitations that restructure surfaces, interfaces, and defects and cause grain reorientation or growth. We observe a variety of previously unknown atom configurations in surface proximity of the Co3O4 spinel structure. These are hidden behind broadened diffraction patterns in reciprocal space but become visible in real space by solving the phase problem. An exposure of the Co3O4 spinel structure to water vapor or other gases induces drastic structure alterations that can be captured in this manner.
“…Here, S/TEM electron probes also interact with the environment (gas or liquid) itself and care has to be taken to avoid uncontrolled changes of the in situ condition (local heating, ionization of gas, radiolysis damage to liquids, local chemistry/pH changes, etc.) [1,17,49,55,57,65,69,[75][76][77]143,164]. When using gaseous environments in MEMS cartridges lattice resolution in S/TEM have been reported [170], while, when using liquid environments, nanometer spatial resolution seems to be the current limit [57,69,164].…”
Section: Observe Structural Evolution Of Interfaces In Gaseous and LImentioning
confidence: 99%
“…However, these illumination conditions might be unsuitable for studying atomic arrangements at interfaces -with lower bond energies compared to regular atomic coordination. We need to pay attention to beam -sample -local environment interactions [17,37,39,55,64,76,77] to maintain the potential of comparing in situ S/TEM results with information achieved from other in situ experiments as well as data from ex situ or post mortem investigations. Structural reorganization caused by electron beam need to be avoided or at least be controlled and specified [65].…”
Section: Maintaining Inherent Atomic S/tem Resolution In In Situ Expementioning
“…Nevertheless, the probing radiation still actively alters the genuine structure of surfaces, interfaces and small atom clusters because unavoidable beam-sample interactions remain relevant if binding energies are lowered compared to bulk values and the onset of atom displacements is soft without exhibiting a pronounced threshold. In atomic resolution images with single atom sensitivity such alterations are readily visible [5].As heterogeneous materials scale below 5-10 nm, interfaces and small atom clusters allow tailoring unprecedented materials properties and it becomes essential to explicitly address their sensitivity to any probing radiation. For a detection of single atoms in these circumstances, we recently introduced low dose-rate in-line holography [3 -5], which allows operating electron microscopes with dose rates that are comparable with best practices in biological applications while achieving single atom sensitivity by the acquisition of large image series.…”
mentioning
confidence: 99%
“…Nevertheless, the probing radiation still actively alters the genuine structure of surfaces, interfaces and small atom clusters because unavoidable beam-sample interactions remain relevant if binding energies are lowered compared to bulk values and the onset of atom displacements is soft without exhibiting a pronounced threshold. In atomic resolution images with single atom sensitivity such alterations are readily visible [5].…”
Exploring the abilities of aberration-corrected electron microscopy, it is now established that single atoms can reliably be detected across the Periodic Table of elements. This capability enables electron tomography from single projections [1], spectroscopy studies of catalytically active edge sites in 2D-materials [2] or even the observation of single atom dynamics [3] to name a few new and exciting applications. However, the detection of single atoms comes with a "price tag": Unlike images from atom columns that can be captured with varying electron doses and signal-to-noise (S/N) ratios (Figure 1a), the contrast from a single atom can only be visualized if the total electron dose is large (10 3 -10 5 electrons/Å 2 , Figure 1b) even if a S/N ratio of only 2 is desired. Absolute values depend on the efficiency of the electron detection modes and the atomic number Z of an element (Figure 1c,d) [4]. It has become accepted that the related high beam currents in the range of 1A/cm 2 -100 A/cm 2 may allow maintaining bulk material properties if acceleration voltages are suitably varied between 60 kV and 300 kV. Nevertheless, the probing radiation still actively alters the genuine structure of surfaces, interfaces and small atom clusters because unavoidable beam-sample interactions remain relevant if binding energies are lowered compared to bulk values and the onset of atom displacements is soft without exhibiting a pronounced threshold. In atomic resolution images with single atom sensitivity such alterations are readily visible [5].As heterogeneous materials scale below 5-10 nm, interfaces and small atom clusters allow tailoring unprecedented materials properties and it becomes essential to explicitly address their sensitivity to any probing radiation. For a detection of single atoms in these circumstances, we recently introduced low dose-rate in-line holography [3 -5], which allows operating electron microscopes with dose rates that are comparable with best practices in biological applications while achieving single atom sensitivity by the acquisition of large image series. In this manner, structural materials integrity can be better maintained to an unexplored end. This talk highlights recent achievements including the radiation sensitivity of catalytic materials where the occurrence of an amorphous phase is radiation induced [6] and an Oswald ripening of 3 nm large catalysts that is stimulated by the electron beam (Figure 2) [7].References:[1] F-R. Chen et al, Nature Comm.,
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