TopoTEM: A Python Package for Quantifying and Visualizing Scanning Transmission Electron Microscopy Data of Polar Topologies.

We have developed a spherical aberration corrected transmission electron microscopy(Cs-corrected TEM) technique that allows us to obtain clearer images in real space than everbefore. We applied this technique to titanium oxide, in which light elements such as oxygenare difficult to observe using TEM because of its small cross section and electronicdamage. In the present study, we successfully observed oxygen atoms in rutileTiO2. In addition, this direct observation of oxygen atoms enabled us to study the Magnéli structure(TinO2n−1), which is caused by oxygen vacancies. These vacancies caused an atomic relaxation of thetitanium and oxygen atoms. The relaxed atoms formed a characteristic shear structureof rutile titanium dioxide phase. This shear structure of the Magnéli structure(TinO2n−1) was visualized with a spatial resolution of 0.119 nm. At the same time, the selected areadiffraction (SAD) pattern of the defect structure was obtained. Additional spots wereshown inside the rutile [110] spot. We made structural models of the shear structureand simulated the diffraction pattern and images using a multi-slice simulation.Additional spots in the simulated diffraction patterns accurately reconstructed theexperimental data. We also considered the possibility of the real-space analysis of localstructures using spherical aberration corrected transmission electron microscopy.

Interaction between single noble metal atoms and graphene edges has been investigated via aberration-corrected and monochromated transmission electron microscopy. A collective motion of the Au atom and the nearby carbon atoms is observed in transition between energy-favorable configurations. Most trapping and detrapping processes are assisted by the dangling carbon atoms, which are more susceptible to knock-on displacements by electron irradiation. Thermal energy is lower than the activation barriers in transition among different energy-favorable configurations, which suggests electron-beam irradiation can be an efficient way of engineering the graphene edge with metal atoms.

Structural and Electronic Properties of BaO/MgO(001)-type Interface Studied via Aberration-corrected Transmission Electron Microscopy and First-principles Calculations

We present a method that allows for a quantitative measurement of the surface self-diffusion on nanostructures, such as nanoparticles, at the atomic scale using aberration-corrected high-resolution transmission electron microscopy (HRTEM). The diffusion coefficient can be estimated by measuring the fluctuation of the atom column occupation at the surface of Au nanoparticles, which is directly observable in temporal sequences of HRTEM images. Both a Au icosahedron and a truncated Au octahedron are investigated, and their diffusion coefficients are found to be in the same order of magnitude, D = 10(-17) to 10(-16) cm(2)/s. It is to be assumed that the measured surface diffusion is affected by the imaging electron beam. This assumption is supported by the observed instability of a (5 × 1) surface reconstruction on a {100} Au facet.

Determining the extent of oxidation in batches of metal nanoparticles is essential to predict the behaviour of the material. Using aberration corrected transmission electron microscopy (TEM) it was possible to detect the formation of an oxide shell, of thickness 3 nm, on the surface of copper nanoparticles. Further analysis showed that this shell actually consists of two layers, both of which were polycrystalline in nature with domains in the size range of 1–2 nm, and having a thickness of 1.5 nm each. Energy dispersive x-ray spectroscopy confirms that the layers arise due to the formation of oxides, but it was not possible to determine their exact nature. Analysis of the intensity variation within images obtained via probe corrected scanning TEM combined with a high angle annular dark field detector indicates that the shell consists of an inner layer of cuprous oxide (Cu2O) and an outer layer of cupric oxide (CuO). This work was complemented by conventional TEM which provided size distribution and revealed that the majority of particles have a core consisting of a single crystal of copper. This demonstrates the ability of TEM to help to determine the oxidation state of nanoparticles and its potential to be applied to a wide range of homogenous and heterogeneous nanoparticles.

In this paper, the recent progress of ferroelectric topologies is briefly reviewed with the emphasis on the important role of state-of-the-art aberration-corrected transmission electron microscopy in revealing the topological features in nanoscale ferroelectric materials. By identifying the ion displacement at a sub-angström level, the corresponding polarization distribution can be determined which uncovers the characteristics of topological structures. The formation mechanisms of ferroelectric topological structures and their evolutions under external fields are summarized from the perspective of strain, screening, and external fields for two prototypical ferroelectric materials, PbTiO<sub>3</sub> and BiFeO<sub>3</sub>. For the PbTiO<sub>3</sub>, its topological structures such as flux-closures, vortices, bubbles, skyrmions, and merons can be well demonstrated in a thickness-strain-screening phase diagram, which could be a guideline for better understanding the topological structures and also for the future exploration. For BiFeO<sub>3</sub>, its topological structures reported are classified as two categories: one is the unscreened topological structure such as vortices and the other is the screened topological structure (center-type domains). Finally, we present the prospects for the future development of the ferroelectric topologies.

Abstract: Contrast transfer function (CTF) is a vital function in transmission electron microscopy (TEM). It expresses to what extent amplitudes converted from the phase changes of the diffracted waves contribute to the TEM image, including the effects of lens aberrations. Simulation is very helpful to understand the application of the function thoroughly. In this work, we develop the CTFscope as a component in the Landyne software suite, to calculate the CTF with temporal and spatial dumping envelopes for conventional TEM and to extend it to various aberrations (up to fifth order) for aberration-corrected (AC)-TEM. It also includes effects on the CTF and imaging due to the objective aperture and image drift for tutorial purposes. The CTFscope has a user-friendly graphical interface for simulation, visualization, saving, and loading of the microscopy conditions and results. It can be used to explore instrumental performance information due to optical aberrations, effects on the resolution of a TEM and AC-TEM, and for teaching electron microscopy courses.

Transmission electron microscopy (TEM) has hit a significant milestone of sub-angstrom resolution. On one hand, electron microscopists and materials scientists are enjoying the highest TEM spatial resolution ever attainable; on the other hand, study of materials in a steady state is hard to meet the increasing demand in new application fields such as nanocatalysts, nanocrystal growth, nanoelectronics, nanosensors, and nanomechanics in which size effect and structural or property responses to stimuli from the surrounding environment are key information to learn. Special attention is thus paid to in-situ TEM. A great deal of effort in developing and improving electron microscopes and specimen holders have resulted in unprecedented progresses in attaining insight into materials in dynamic environments. In many ways, transmission electron microscopes are now functionalized as workstations or nanoscale labs rather than just imaging tools. In this chapter, various types of in-situ TEM technologies are introduced accompanied by application examples. In parallel to the sub-angstrom breakthrough made by the aberration-corrected TEM, atomic resolution is now emphasized in advanced in-situ TEM, advancement on this aspect will be discussed together with other important notes and further challenges.

High-resolution transmission electron microscopy is often used to characterize grain boundaries, but it is usually limited to special high symmetry boundaries with a high density of coincident sites. For these ‘special’ boundaries, both crystals can be brought into a low-index zone-axis with the boundary plane parallel to the incident electron beam. In this case the atomistic structure of the boundary can be solved, which is not possible for other, more general grain boundaries. In the present study, general grain boundaries in SrTiO3 were analyzed using aberration-corrected transmission electron microscopy and scanning transmission electron microscopy. These boundaries included at least one type of disconnection (i.e., defects that can have a step and/or a dislocation component). Since the dislocation component of disconnections along general grain boundaries cannot be fully resolved using the methods currently available, a plane matching approach was used to compare disconnections at different boundaries. Using this approach, the dislocation component of the disconnections was partially characterized and was found to have an edge component mainly parallel to {100} and {110}, close to normal to the macroscopic grain boundary plane. The step component of the disconnections was found to be aligned mainly parallel to the same crystallographic planes ({100} and {110}).

Multimodal in-situ experiments are the wave of the future, as this approach will permit multispectral data collection and analysis during real-time nanoscale observation. In contrast, the evolution of technique development in the electron microscopy field has generally trended toward specialization and subsequent bifurcation into more and more niche instruments, creating a challenge for reintegration and backward compatibility for in-situ experiments on state-of-the-art microscopes. We do not believe this to be a requirement in the field; therefore, we propose an adaptive instrument that is designed to allow nearly simultaneous collection of data from aberration-corrected transmission electron microscopy (TEM), probe-corrected scanning transmission electron microscopy, ultrafast TEM, and dynamic TEM with a flexible in-situ testing chamber, where the entire instrument can be modified as future technologies are developed. The value would be to obtain a holistic understanding of the underlying physics and chemistry of the process-structure–property relationships in materials exposed to controlled extreme environments. Such a tool would permit the ability to explore, in-situ, the active reaction mechanisms in a controlled manner emulating those of real-world applications with nanometer and nanosecond resolution. If such a powerful tool is developed, it has the potential to revolutionize our materials understanding of nanoscale mechanisms and transients.Graphical

Since the invention of the transmission electron microscope (TEM) in 1931 by Max Knoll and Ernst Ruska, modern TEMs underwent remarkable developments in its overall stability and electron optics. In particular, correction of higher-order lens aberrations has facilitated structural characterization of single molecules at atomic resolution. This improvement in resolution has greatly assisted the design and development of new nano-objects in the field of materials and biological sciences. However, taking full advantage of these developments requires high chemical purity in the sample preparation technique and an electron transparent sample support that not only ensures the reliability in structural characterization, but also boosts the signal-to-noise ratio of TEM images. Moreover, the electron beam in TEMs, in addition to image formation, can be used for structural transformation due to the strong interaction of electrons with the investigated material. In this thesis, the structure of mass-selected molecular species, deposited on graphene via electro-spray ion beam deposition (ES-IBD), is investigated by aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) at acceleration voltages between 60 and 80 kV. Due to its impressive electronic and mechanical properties, single- layer graphene (SLG) is used as TEM substrate throughout this work. The transfer methodology of the SLG, obtained by mechanical exfoliation or chemical vapor deposition (CVD), to the TEM grids is presented, followed by thorough structural characterization to analyze the morphology and crystallinity of the transferred SLG using HRTEM. First, beam-sensitive organic molecules such as cytochrome-class hemeprotein (cytochrome-c), chaperonin complex protein molecule (GroEL), copper-pthalocyanine (CuPc) and com- plex molecular magnetic systems in the form of single molecule magnets (SMMs) were investigated. The results showed that despite the presence of the highly conductive substrate and the use of low electron acceleration voltages, small organic molecules did not survive. However, large globular proteins showed some level of electron resistance before suffering radiation damage. Next, the molecular structure of single phosphotungstic acid (PTA) anion molecules deposited by either ES-IBD or the drop-cast method was analyzed and compared. The results showed homogeneous morphology of the samples prepared by ES-IBD. Further- more, by varying coverage and landing energy, it was possible to modify the required morphology. This allowed better control of deposition as compared to the drop cast ap- proach. A main advantage of ES-IBD is the chemical purity during deposition. This is not guaranteed in the drop-cast technique which is performed under ambient conditions. The main part of this thesis deals with the electron-beam-induced transformation of alkali-iodide molecules (CsI, RbI, KI and NaI). The deposited alkali iodide nanoparticles were intentionally exposed to the electron beam to disintegrate them into single ions. It is found that during electron exposure these ions form regular clusters consisting of 4 to 7 atoms, or 2D-crystals. Notably, in the case of CsI, 2D-crystals form only on BLG, whereas on SLG only atomic clusters were formed. HRTEM in combination with electron energy-loss spectroscopy (EELS) is employed to identify the atomic species of the 2D crystals on the atomic scale. In the case of NaI, 2D-crystals form on SLG. Their crystal structure corresponds to the CsCl-type, which has not been reported before. The etching behavior of graphene in the presence of alkali-iodide species is observed in HRTEM experiments for all the deposited species (CsI, RbI, KI, and NaI). By mea- suring the increase in the perimeter of etched holes in SLG, the rate of etching has been calculated. We found that etching was faster in the presence of both alkali and halide ions, as compared to the presence of only one ionic species. First-principles DFT simulation studies were performed to understand the interaction of alkali-iodide dimers on SLG. These calculations yielded quantitative estimates on the charge transfer between the dimer species and the underlying SLG. It was found that adsorption of alkali-iodide on SLG reduces the bonding electron density between the carbon atoms, thus reducing the C-C binding energy. This effect makes the SLG susceptible to damage when exposed to 80-keV electrons, which establishes the catalytic behavior of alkali-iodide species as etchants of SLG.

Quasi‐one‐dimensional III‐V semiconducting nanowires attract enormous attention owing to their physical properties such as tunable direct bandgap, high surface to volume ratio, high carrier mobility, tunable structures. Hence they have potential application in next generation electronics, sensors, photonics and photovoltaics. Understanding the details such as, atomic scale structure, local chemical stoichiometry and defects in a sub nanometer scale are inevitable when nanowires are intended for devices. A systematic interfacial investigation on molecular beam epitaxy grown III‐V based nanowires such as InAs, GaAs, [1] in general and in particular, heterostructure nanowires of axially grown Ga x In 1_x As‐InAs and InAs‐InAsSb will be presented. [2] In this work, atomic scale structural interfaces and interfacial chemical composition are analyzed using advanced aberration corrected transmission electron microscopy. Atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) and high resolution energy dispersive x‐ray spectroscopy techniques are predominatly used for characterizing the grown nanowires. Our work demonstrates on tailoring the growth, periodicities and the stoichiometry of III‐V nanowire heterostructure containing single/multiple electronic barriers involving In,Ga,As and Sb. We aim to provide understanding on the growth of dissimilar interfaces in heterostructure nanowire (see fig 1). In the InAs‐InAsSb heterostructure wires, [1] our work demonstrates the quality of the misfit strained interface in terms of structural abruptness and chemical homogeneity.

This study demonstrates that precise control of nonequilibrium growth conditions during pulsed laser deposition (PLD) can be exploited to produce single‐crystalline anatase TiO2 nanobrush architectures with large surface areas terminated with high energy {001} facets. The data indicate that the key to nanobrush formation is controlling the atomic surface transport processes to balance defect aggregation and surface‐smoothing processes. High‐resolution scanning transmission electron microscopy data reveal that defect‐mediated aggregation is the key to TiO2 nanobrush formation. The large concentration of defects present at the intersection of domain boundaries promotes aggregation of PLD growth species, resulting in the growth of the single‐crystalline nanobrush architecture. This study proposes a model for the relationship between defect creation and growth mode in nonequilibrium environments, which enables application of this growth method to novel nanostructure design in a broad range of materials.

Full 3D Monte Carlo simulation of pit-type defect evolution during extreme ultraviolet lithography multilayer deposition

Journal Article Sparsity and Noise Effects on the Reconstruction of Subsampled Scanning Transmission Electron Microscopy Data Get access Eduardo Ortega, Eduardo Ortega INM - Leibniz Institute for New Materials, Saarbrücken, Germany Search for other works by this author on: Oxford Academic Google Scholar Niels de Jonge Niels de Jonge INM - Leibniz Institute for New Materials, Saarbrücken, GermanyDepartment of Physics, Saarland University, Saarbrücken, Germany Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 2136–2137, https://doi.org/10.1017/S1431927622008273 Published: 01 August 2022