Microscopy Conference 2023

Prof. Dr.

Session chairs

Prof.

Adaptive probe correction with electrostatic phase plate

Abstract text (incl. figure legends and references) Introduction Scherzer theorem [1] states that to correct spherical aberration of an electron optical system, one needs either electromagnetic lenses that break rotational symmetry, time variant fields, or the existence of space charge. While the effectiveness of the first solution has been widely proven, we implemented the last one as an alternative. In this project, an electrostatic phase plate that creates local electric potential is installed in the microscope, altering the phase of the electron wave. In this manner, the phase plate compensates aberrations to some degree and increases the resolving power of the probe. With this principle, an adaptive aberration correction method is proposed. Objectives To correct the electron probe using phase plate without measuring the aberrations, but through maximizing a chosen quality indicator computed from annular dark field (ADF) images instead. Methods Multiple algorithms are used to search for the best phase configuration, all of them aim to minimize specific loss functions that are coupled with different scanning modes. For line scans, the standard deviation of the intensity is used, while for raster scans, other loss functions can be added, such as BRISQUE image quality assessment [2] and symmetry analysis of the probe. The optimization goes in two steps. In the first step, the resulting image with different phase configurations is acquired by changing the voltage of the phase elements either grouped in rings or as lobes (Fig. 1). To avoid local minima, simulated annealing is used to search rather widely in the space of possible phase configurations. In the second step, gradient descend is applied with complete freedom of possible phase configuration allowed by the phase plate in order to further improve the result from the first step, and thus less symmetric aberrations and local variations in the phase response of the phase plate can be corrected. Results The simulated results (Fig. 1) of the probe and ADF images formed with a circular aperture, phase plate, and corrected phase plate at different stages of the process. The contrast and resolving power increase at each stage, accompanied by sharpening of the probe intensity profile. Conclusion An automatic probe correction scheme with phase plate is presented and experimentally realized on the microscope. Comparing the ADF image generated with the phase plate before and after the process clearer atomic features are observed, even with the unavoidable tail spread-out imposed by the finite fill factor of the phase plate [3]. The project shows a promising method for the probe correction of a less critical optical system and also a significant progress in fully automating electron microscopy experiments. Reference [1] O, Scherzer. "Über einige fehler von elektronenlinsen." Zeitschrift für Physik 101.9 (1936): 593-603. [2] A. Mittal, et al. "Blind/referenceless image spatial quality evaluator." 2011 conference record of the forty fifth asilomar conference on signals, systems and computers. IEEE, 2011. [3] F. Vega Ibáñez, et al. "Can a Programmable Phase Plate serve as an Aberration Corrector in the Transmission Electron Microscope (TEM)?." arXiv e-prints (2022): arXiv-2205. Fig. 1 The probe shape at different stage of probe correction and their corresponding ADF image. The probe gradually converges to a sharp point with increasing resolving power. The sample shown is gold [1 1 1] on amorphous carbon.

IM 1: Progress in instrumentation and ultrafast EM

IM 6: Phase-related techniques & 4D STEM

Poster

Secondary electron imaging in scanning transmission electron microscopy for material science

Abstract text (incl. figure legends and references) (Scanning) transmission electron microscopy ((S)TEM) is a rapidly developing field with a large variety of techniques widely used in modern material science. Signals generated within TEM during electron-matter interaction provide information about the composition, crystallography, mass-thickness, and local electromagnetic fields [1]. Secondary electrons (SEs) are electrons ejected from a sample after electron beam irradiation. SEs originate from the near-surface region of the sample, so these electrons are often exploited in scanning electron microscopy to form images that are sensitive to the surface topology. Topographic information from SEs would greatly aid the interpretation of conventional 2-dimensional STEM images [2], but unfortunately, SE imaging is not available on most conventional STEM instruments. In this work, we demonstrate the capabilities and benefits of SE imaging in STEM as an alternative 3D characterization method. SE images were obtained using an aberration-corrected "cubed" Thermo Fisher Themis Z instrument operated at an acceleration voltage of 200 kV and a beam current of 250 pA. We used a recently proposed methodology to detect SEs using electron beam-induced current (SEEBIC) [3]. A homemade transimpedance amplifier (TIA), electrically connected to the sample via a DENS Solutions Wildfire holder, was used to convert the SEEBIC signal into a voltage signal digitized by the Gatan Digiscan II unit along with the HAADF-STEM detector signal. SE images contain topography information, so they enable revealing the information hidden in conventional HAADF-STEM. We demonstrate this effect on self-assemblies of rounded FexO/CoFe2O4 nanocubes in spherical confinement [4]. Figure 1 shows the five-fold symmetry of an icosahedron, and demonstrates the presence of stacking faults. It should be noted that retrieving the information about such complex morphologies from a single or a few images is very important when the acquisition of tilt series for electron tomography is not possible due to various factors. These approaches are inspired by techniques used in scanning electron microscopy for surface metrology. We demonstrate our first attempts to retrieve 3D information using the shape-from-shading and structure-from-motion algorithms. Another important direction is the investigation of surface facets. The surface nature of the SE signal can greatly aid the understanding of the microscopy data. Figure 1. (a) HAADF-STEM and (b) SEEBIC images of self-assemblies of FexO/CoFe2O4 nanocubes. In conclusion, we have demonstrated the versatility of SE imaging in modern material science for various purposes. The surface origin of the SE contrast enables to extract morphological information that can be hidden in conventional STEM images. The use of novel techniques for 3D reconstructions was discussed as an alternative to conventional electron tomography. The project has received funding from European Research Council (ERC Consolidator Grant 815128, REALNANO). D. B. Williams, C. B. Carter, Transmission Electron Microscopy: A Textbook for Materials Science (2009). C. Mignot, et al., Micros. Today, 26 – 3 (2018). M. Mecklenburg, et al., Ultramicroscopy, 207 – 112852 (2019). D. Wang, et al., Nat. Commun., 9 – 2228 (2018).

IM 7: In situ/operando electron microscopy

Low voltage transmission electron diffraction in SEM as a powerful tool for wide field of view characterization of crystalline materials

Abstract text (incl. figure legends and references) The study of the structure of nanocrystalline materials is often difficult as standard X-ray diffraction techniques break down for sub micrometer particles, especially when occurring in a mixture. Here, we present a tool for structural analysis of a wide range of layered materials and nanosized powder samples based on a conventional scanning electron microscope. An hybrid pixel electron detector below the sample makes it possible to record two dimensional diffraction patterns for every probe position on the sample surface, in transmission mode, thus performing a 4d-STEM (scanning transmission electron microscopy) analysis. This offers a field of view up to 2 mm2, while providing spatial resolution in the nm range, enabling the collection of statistical data on grain size, relative orientation angle, bilayer stacking, strain, etc. which can be mined through a custom-made open-source Python based code. Diffraction pattern acquisition is performed using an Advacam®MiniPix detector with a 300 ?m Si active layer and a 13bit depth dynamic range. We use a standard JEOL JSM-5510 SEM with a W electron source, enabling wide adoption of our proposed setup. Samples are mounted on a Thorlabs 30 mm optical cage system, giving an adjustable sample to detector distance (camera length) ranging from 5 to 50 mm (Fig. 1) [1]. The direct geometrical projection of the diffraction pattern onto the hybrid pixel detector provides a robust calibration of the scattering angles not influenced by lens drift and optical distortions. Fig. 1. (a) Schematic drawing of the experiment, consisting of a layered material and a hybrid pixel detector at the bottom, inside an SEM sample chamber. (b) Picture of the setup. The Thorlabs optical cage system allows camera length adjustment. The authors acknowledge the financial support from EU FLAG‐ERA JTC 2017 GRAPH‐EYE, FWO SBO AutomatED S000121N from the Research Foundation Flanders.

IM 5: Quantitative image and diffraction data analysis

Improving the time-resolution of event-based electron cameras using neural networks trained by femtosecond electron pulse detection

Abstract text (incl. figure legends and references) Introduction In the recent two decades, ultrafast transmission electron microscopy (UTEM) has successfully enabled investigation of ultrafast dynamics on the nanoscale by combining femtosecond electron probe pulses with a synchronized optical sample excitation [1]. With increasing availability of sufficiently fast event-based electron detectors, dynamics down to the nanosecond timescale can also be imaged by continuous-beam TEM. For example, with the TimePix3 chip architecture [2] electron events are registered with a bin width of about 1.6 ns. However, the achievable spatial and temporal resolution in experiments is often limited due to the stochastic electron trajectories in the sensor chip [3]. Neural network approaches have already enabled increased spatial resolution [4]. Objectives Here, we report on the development of a neural network architecture trained by experimental electron pulse data to improve the temporal resolution of the TimePix3 detector. Materials &amp; methods As a high-precision electron arrival time standard, we utilized 200-fs electron pulses (400-kHz repetition rate, 200-keV electron energy, 1.3 electrons/pulse) using the Oldenburg UTEM (Fig. 1a). With a TimePix3 detector (Cheetah T3, Amsterdam Scientific Instruments), we experimentally collected a dataset of electron detection events for 4x106 electron pulses. For accurate synchronization, the TimePix3 detector additionally assigns timestamps to each photoemission laser pulse. For every event, relative detector position, time of arrival (ToA) and time over threshold (ToT) are stored and clustered according to their arrival time and position (on average 6 events per cluster). To predict the arrival time of the primary electron, a fully connected deep neural network model is trained using event data from 1.6x105 time-scrambled event cluster. Results The unprocessed ToA data, using individual unclustered event data, shows a temporal spread of about 10 ns FWHM (Fig. 1b (gray)). Already by identifying event clusters and considering the average ToA in each cluster, the temporal spread in the histogram can be reduced to 7 ns (red). With the neural network, the predicted ToA distribution (for a part of the data not involved in the training) is narrowed to 4.7 ns (FWHM, 2 ns rms, blue). Remarkably, the tailed ToA distribution in the previous cases is transformed to an almost Gaussian distribution by the neural network. An example of imaging data for the unprocessed and neural-network-filtered case is shown in Fig. 1c and d, respectively. Conclusion In conclusion, we demonstrate the application of neural networks trained by femtosecond electron pulse data to predict the accurate ToA, substantially increasing the temporal resolution of the TimePix3 detector. We expect that future versions of the TimePix chip with shorter time bins will likely benefit even more from sophisticated event data analysis. [1] A. Feist et al., Ultramicroscopy 176, 63 (2017). [2] T. Poikela et al., JINST 9, C05013 (2014). [3] F. Pitters et al., JINST 14, P05022 (2019). [4] J. P. van Schayck et al., Ultramicroscopy 218, 113091 (2020). Figure 1: (a) Schematic setup of Oldenburg UTEM with TimePix3 detector. (b) Histogram of the time of arrival for uncorrected (gray), cluster mean corrected ToA (red), and the neural network predicted ToA (blue). (c,d) Image for uncorrected (c) and neural network predicted ToA (d). Color scale: ToA of electron event.

A diffusion model for electron beam damage in STEM

Abstract text (incl. figure legends and references) Even though the advent of the aberration-corrected microscopes has enabled the possibility to perform STEM up to and below 50 pm resolution it is still not trivial to achieve atomic resolved images for each material. This is not because of the optics of the electron microscope but due to the electron beam damage which occurs when the highly energetic incoming electron interacts with the specimen. The common method to reduce the induced damage is by reducing the total dose, by making short exposure times, or reducing the electron beam current. Both result in lower signal-to-noise ratio images limiting the accuracy and precision of the quantified parameters extracted from such data. Experimental evidence has pointed out that not only the dose and dose rate influence the damage which occurs in a specimen during a STEM acquisition but that even the scan sequence and dwell time can modify the induced damage on a specimen [1,2]. One clear experimental evidence is found in the work of Velazco et al. [1] where a substantial decrease in damage is observed on a Linde Type A zeolite when decreasing the dwell time or changing the scan pattern while keeping the total dose and dose rate equal. In the present work, the aim is to qualitatively model the damage observed using a minimal amount of physical parameters (diffusion constant and threshold). A diffusion-based model is chosen since the damage was experimentally found to depend on the scan sequence indicating a non-local component where the induced damage depends on the time at which the neighboring pixels are visited. By only taking the diffusion of a quantity to describe the damage there is no difference in the total induced damage when changing the scan sequence. Therefore, a threshold is introduced below which no damage is induced. Note that no assumption is made on which physical parameter is diffusing and why. Furthermore, the experimental observations observed in Velazco et al. [1] are used to estimate the two parameters of the model and verify the applicability of the model to describe the experiments. By developing such model, it is possible to predict how the scan sequence and dwell time can influence the total induced damage. In the future these predictions could be taken as guidelines to optimize experiments for different samples. References: [1] Velazco A. et al., (2022), Ultramicroscopy, 232, 113398. [2] Jones L. et al. (2018), Microscopy, Issue 67, Pages i98-i113 [3] Jannis, D. et al. (2022), Ultramicroscopy, 240, 113568 [4] Acknowledgment: AB, AV, DJ and JV acknowledge financial support from the Flemish region through FWO grants G093417N and G042920N innovation program under grant agreement No 101017720, FET-Proactive EBEAM

A hamiltonian mechanics framework for straight and curved charge particle optics systems

Abstract text (incl. figure legends and references) Introduction The theoretical formulation of charge particle optics typically concerns the systematic analysis of charge particle trajectories close to some design trajectory / optical axis in a device producing deliberately configured electrostatic and magnetostatic fields. Cornerstone results consider the expansion of path deviations into a hierarchical system of differential equations, which may be solved in an iterative manner to yield paraxial and subsequent aberration optical properties of the system under consideration [1]. Note, however, that considerable technical difficulties arise when analyzing high-order aberrations, e.g., those of curved system, relativistic systems of combined electrical and magnetic fields, which are related to complex expressions, exploitation of symmetries (e.g., symplectic), or numerical implementation. Objectives Here, we seek to develop a particularly compact solution to the charge particle optics program employing Hamiltonian formulation of mechanics. That includes phase space coordinates adapted to (curved) optical axis, systematic expansion into a hierarchy of first order differential equations, simplification of equation system by employing adapted physical gauges, and symplectic symmetries. Finally, we seek to provide compact analysis of archetypal elements such as multipoles or magnetic lenses to high aberration orders. Methods The charge particle optics problem is considered as the propagation of deviation vectors, between design particles moving along the optical axis of a given device and particles in close vicinity to that design particles, along the optical axis [2]. In the Hamiltonian formulation of classical mechanics, these vectors are defined in phase space, i.e., contain both spatial and momentum difference to the design particle. We employ a canonical transformation to transform this conventional phase space into an adapted extended phase space containing time and energy as additional dimensions, which also implies a reparameterization of the trajectory parameter from time to optical axis coordinate. The latter is particularly well suited for description of particle coordinates in planes perpendicular to the optical axis. We finally employ a modified physical gauge (i.e., related to hyperaxial gauge), which is particularly well adapted to the tube-like geometry of the particle pencils around (curved) optical axis. The gauge simplifies expressions considerably and leads to explicit expressions of the potentials in terms of integrals of the physical electrostatic and magnetostatic fields. Last but not least, we also discuss the numerical implementation of this method within the boundary element formalism. Results Employing the above formalism, we set up a compact system of first order differential equations in 6 dimensional extended phase space describing paraxial and aberrational properties of general (curved) optical systems in a hierarchical manner. The equations obey symplectic symmetries at each expansion level, leading, e.g., to interdependencies among error paths or aberration coefficients. We solve these equations for a number of typical optical devices, such as quadrupole and magnetic lens. [1] P.W. Hawkes, E. Kasper, Principles of Electron Optics Vol. 1: Basic geometrical optics, Principles of Electron Optics. [2] F. Kern, J. Krehl, A. Thampi, A. Lubk, Optik 242, 167242. [3] We acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG) (No. 461150024.)

IM 3: SEM and FIB developments

Dealing with carbon contamination as a consequence of wet TEM sample preparation

Abstract text (incl. figure legends and references) Introduction In order to achieve the desired data quality in transmission electron microscopy (TEM) measurements, careful sample preparation forms a crucial step for these experiments. For many samples, dispersing the specimens in solvent and applying the sample as a solution on the grid is a well-suited method. One big obstacle is the formation of carbon contamination on the specimens which can result from organic residues, e.g. solvents. Objectives We investigate the impact of different solvents on TEM measurements and apply cleaning and preparation strategies in order to minimize the carbon contamination during TEM investigations. The amount of accumulated contamination resulting from different solvents was evaluated by high-angle annular dark field (HAADF) measurements and electron energy loss spectroscopy (EELS). The sample preparation in our sample cleaning setup was customized based on the specimens&quot; properties and utilized solvent in order to prevent contamination. Material &amp; Methods Thickness measurements by evaluating HAADF image contrast and EELS analysis were performed with a Thermo Scientific Talos F200X transmission electron microscope. For specific sample pretreatments, a self-made heatable vacuum setup was utilized in order to perform specialized sample preparation methods. All samples were prepared by applying 1 µL of solvent to a holey carbon copper grid and dried for 10 minutes before sample insertion into the TEM. Results HAADF and EELS measurements can be utilized for determining the thickness of deposited carbon contamination. The grids were exposed to the electron beam for different durations immediately after sample insertion and again 30 minutes later. For both toluene and THF as solvents, the determined amount of accumulated carbon showed a linear increase with longer exposure times. When the samples were exposed after 30 min in the TEM vacuum again, the observed carbon layer was significantly less (Fig. 1). In order to prevent solvent outgassing in the microscope environment, a dedicated sample cleaning setup with a cold trap was utilized to prepare the TEM samples by removing solvent residues before sample insertion. Evaluation of decrease in pressure while pumping with a freshly prepared sample grid inserted, gives insight in the necessary drying times in order to reduce contamination during TEM investigations (Fig. 2). Conclusion Our experiments emphasize the crucial impact of the sample preparation in order to achieve best data quality and to keep a clean microscope environment. Based on our experiments, we can prepare our samples in a way resulting in less contamination on the specimen surface and introducing less volatile organic molecules to the microscopes. Fig. 1: Carbon contamination depending on the beam exposure times of toluene (black) and THF (red) immediately after sample insertion (filled in dots) and after 30 min (circles) in the TEM. For each measurement, an area of 173 nm x 173 nm was exposed to the electron beam. Less volatile solvents like toluene lead to far more contamination, though the solvent can outgas in the TEM vacuum. Fig. 2: Pressure measurements of pumping a toluene sample compared to a reference measurement (empty TEM grids). The pressure values are measured above and below a baffle cooler. The pressure difference between the sample and the reference above of the cooler indicates the presence of outgassing molecules.

Prof. Dr. rer. nat. habil.

Study of beam sensitive and nanostructured materials by low-kV and low-dose optimized EBSD

Abstract text (incl. figure legends and references) EBSD analysis on beam sensitive and nanostructured materials demands in many cases low-kV, low-dose or low-vacuum operation with careful beam budget design and sensitive detectors in order to avoid sample degradation, minimize image drift, satisfy spatial resolution requirements and gain sufficient signal-to-noise level for indexable Kikuchi patterns [1-3]. The stated requirements play a major role for the structural characterization of metal-halide-perovskite (MHP) thin films/crystallites, which revolutionized the field of thin-film semiconductor technology, due to their favorable optoelectronic properties and facile solution processing e.g. by inkjet-printing [4]. Best device efficiencies require structural coherence on the atomic scale, which can be achieved by epitaxial growth on lattice matching substrates [4]. In this work, we demonstrate the capability of recent sensitive EBSD cameras for the structural characterization of beam sensitive MHP crystallites (CsPbBr3, FACsPbBr3, MAPbBr3) grown on various substrates (PbS, mica). In particular new direct detection based cameras allow to obtain indexable Kikuchi patterns from MHPs at strongly decreased electron dose at low-kV compared to their indirect detection based counterparts (Figure 1a), which is crucial for a reliable and statistically relevant EBSD characterization. Based on this, we present EBSD results underlining the homogeneous hetero-epitaxial growth over large scale of CsPbBr3 and FACsPbBr3 crystallites on single crystalline PbS substrates fabricated via inkjet-printing and further substantiate the theory of lattice-anchoring and stabilization of the cubic crystal structure of MHPs as indicated in former studies [4, 5] (Figure 1b). Further, we present results on the orientation-dependent growth characteristic of FACsPbBr3 crystallites on flexible and single crystalline mica substrates. Here, various different cubic crystal orientations with characteristic morphologies are observed. Most crystals feature a [101] out-of-plane orientation which is parallel to the [001] axis of the substrate and grow along (110) planes, with a few of them obtaining an in-plane orientation of [101] parallel to the [010] direction of the substrate. Further advantages of low-kV and low-dose sensitive EBSD detectors lie in the achievable spatial resolution, making them perfectly suitable for the analysis of nanomaterials. This benefit evolves particularly in conjunction with low-vacuum operation, since any need for conductive coating of the sample surface, which damps the EBSD signal, but is often required to minimize sample drift, is reduced. Referring to this, we present in Figure 2 EBSD results on the texture analysis on nano-grained and low Z-number thin films (AlN) based on Pt/Ti/SiO2/Si substrates, revealing an average grain size of ~30 nm and a crystal fiber texture with an out of-plane &lt;0001&gt; alignment. Further analyses focus on the local clustering of neighboring grains with similar orientation. Overall, we show that the application of low-kV and low-dose EBSD paves the way for a reliable and efficient structural characterization of beam sensitive and nanomaterials and enables new insights into epitaxial growth and the orientation-dependent growth of MHPs on large scale. [1] Adhyaksa et al., 10.1002/adma.201804792 [2] Leonhard, et al., 10.1002/ente.201800989 [3] Luo et al., 10.1021/acs.jpcc.0c06733 [4] Sytnyk et al., 10.1002/adfm.202004612 [5] Afify et al., 10.1002/adom.202200237

New Performance for SEM with an Annular Switchable Gain BSE Detector Diode

Abstract text (incl. figure legends and references) Using the whole energy spectrum of the SEM has been always an issue by installation of just one Back Scattered Electron Detector (BSD) to get high quality images in each scanning speed and energy range for every application. Despite of the state-of-the-art BSDs with all premium features as a GCE up to 85%, a DCE up to 55% at 1 keV (see Fig. 1), and a high signal to noise (S/N) ratio, there is still lack of a feature which closes the gap between low and high keV range when high scan speed and high throughput are needed. This applies specially for life science and bio science applications where the sensitive samples need to be scanned at low keV conditions but at the same time with high image acquisition. In order to be able to maintain the scan speed relatively high at very low energies, one needs to increase the gain of the BSD collecting as much signal as possible to optimize the signal to noise (S/N) ratio. A typical BSD is not capable of changing the gain once the higher value is needed since the gain is already fixed in the preamplifier. There is no more need to exchange the BSD while working under this situation. Instead with PNDetector&quot;s new Switchable Gain Advanced BSD (SWG-BSD) one can overcome this issue and switch the gain manually to a higher value in a fraction of a second while scanning the sample so that the scan speed is not sacrificed and significantly reduced to get high resolution images. Here we show how the new detector enables this technique. The SWG-BSD is equipped with two preamplification gains in the preamplifier integrated into a compact vacuum compatible housing shown in Fig. 2. The gain values are adjusted to and V/A. The lower value is called &quot;high speed&quot; mode and the higher value is called &quot;high gain&quot; mode. With switching between these two modes one is capable of adjusting the gain while changing the energy in order to maintain the desired scan speed and optimize the S/N. When the SWG-BSD is used in high speed mode the typical rise time achieved by the detector is down to 30ns (the real TV speed) and very high resolution single frame images without smearing can be taken under 0.1 sec with 0.8 MP once the sample is scanned at high energies such as 30keV. The typical example of such application is in semiconductor industry to surf the samples very fast and search for hot spots. Once the spot is found and focused it is now the time to switch to high gain mode and zoom the spot for detail inspection to get an optimized image while reducing the scan speed not that low as it is normally used with traditional BSDs. The SWG-BSD enables the possibility of maintaining the scan speed relatively high under 1000ns rise times and the result will be a superior SEM image of the spot in e.g. 31 sec at 1 keV (see Fig. 3). Other common application for SWG-BSD is observation of sensitive samples like tissues for which very low energies under 1keV are needed to ensure minimal interaction between the electron and the sample and reduce damage and charging. The two gain settings adjusted for SWG-BSD is used in combination with the main amplifier with a Python based GUI software enabling the switch action by a single button designed in the software. The SWG-BSD comes also with the complete motorized retractable system shown in Fig. 2 with all vacuum compatible parts to be installed directly in the SEM. Figure 1. Figure 2. Figure 3. Two SEM images taken by SWG-BSD in (left) high speed and (right) high gain modes.

A ground-potential monochromator design

Abstract text (incl. figure legends and references) Electron energy loss spectroscopy with high energy resolution is interesting for a wide range of applications ranging from analytics of organic matter at very small dimensions to determining the optical properties in two-dimensional materials. In (scanning) transmission electron microscopy ((S)TEM), the energy resolving power of the instrument was determined by the type of the electron source and limited to about 300 meV before the advent of electron monochromators for (S)TEM instruments about two decades ago. In the meantime, several different designs of monochromators have been implemented and can be bought as an option to most high-end microscopes [1‑4]. There are two meaningful positions for monochromators along the optical path: Before or after the accelerator, that is, at high potential or at ground potential, respectively. While most monochromator implementations today are at high potential, ground-potential monochromators have some notable advantages, such as less sensitivity to selection-slit interactions and magnetic stray fields, independence of acceleration voltage instabilities, no performance deterioration from Boersch or Loeffler effect, and the possibility to retrofit it to existing instruments. One of the major general drawbacks in the use of a monochromator for imaging or spectroscopy is the loss of current in the electron beam, and thus, loss of interpretable signal. Therefore, the most interesting parameter besides the actual energy resolution is the available current at this very energy resolution at a certain primary electron energy. Here, we present a design for a ground-potential monochromator that can be retrofit to existing microscope columns. Performance estimates are given for primary electron energies of 300 keV and 30 keV with instruments equipped with a cold field emission electron source. References: [1] H. Rose, Ultramicroscopy 78, 13-25 (1999). [2] P. C. Tiemeijer, Inst. Phys. Conf. Ser. 161, 191-194 (1999). [3] O. L. Krivanek et al., Philos. Trans. R. Soc. London. Sec. A 367, 3683-3697 (2009) [4] M. Mukai et al., Ultramicroscopy 140, 37-43 (2014).

IM 2: Spectroscopy

Optimization and new tools for 3DED data collection

Abstract text (incl. figure legends and references) Introduction 3D Electron Diffraction (3DED), become the &quot;low dose&quot; technique for crystal structure determination of nanocrystals and a wide range of materials. The criteria for a successful crystal structure solution is data completeness while a sufficient refinement is data quality dependent.[1] Several methods for 3DED data acquisition using different hardware have been established, but in order to spread the usage of 3DED a standardization is needed to overcome two major challenges intrinsic in the hardware used.[2] Objectives 3DED needs to become user friendly thanks to automatized data acquisition and diffractometer alignment. Secondly, the uncertainties intrinsically present in our microscopes need to be dumped which make it difficult to measure crystals with domains less than 100nm requiring smaller beam sizes. With these improvements, 3DED will be accessible to a wider community and will show its true potential compared to XRD analysis. Methods The methods currently available use two major approaches, Nano-Beam Electron Diffraction (NBED) and Selected Area Electron Diffraction (SAED). SAED has several advantages, such as beam size down up to 200nm, small crystal shift during the tilt series. Combined with Instamatic, these features enable rapid dissemination of SAED, especially to JEOL users.[3] However, NBED can achieve beam sizes down to a few nm, reduce image dose rates up to 40-fold in STEM images, and use HAADF to generate Z-image contrast. It often shows higher quality datasets compared to SAED and allows multiple datasets acquisition from the same crystal, due to localized beam damage.[4] The concepts of the NBED technique are implemented in Fast-Automated Diffraction Tomography (Fast-ADT), a user-friendly DigitalMicrograph© (DM) script for 3DED acquisition and tracking.[5] Results Here we report our improvement to the 3DED technique. Fast-ADT has been translated and implemented from DM© in Python. The script is based on the Temscript package, allowing use for the majority of the FEI microscopes and future expansion to JEOL microscopes using PyJEM.[6] Fast-ADT allows TEM/STEM SAED and NBED in Precession ED Tomography (PEDT) and Continuous Rotation ED (CRED). This way, FEI machines could use one universal tool for conventional 3DED experiment, with the potential to be deployed and customized to design its personal 3DED experiments. To enhance the 3DED automation, an automatic eucentric height tool is implemented in Fast-ADT, which performs the Z control of the target crystal in a more precise and reproducible way. This is essential for NBED, which plays a role to counterbalance the target drift during data collection and is the major responsible of a 3DED data collection failure. Conclusion With these improvements, one of the last challenges that could be solved by software is the design of a more robust 3DED crystal tracking routine. This implementation is important for NBED because it is easier to lose the target during the tilt series than in SAED, where the beam size is higher. In conclusion, Fast-ADT has the potential to be used more efficiently and be spread easier to all the 3DED labs as a complete package for 3DED data acquisition. [1]https://doi.org/10.1107/S2052520619006711 [2]https://doi.org/10.1021/acscentsci.9b00394 [3]https://doi.org/10.1107/S2052252519007681 [4]https://doi.org/10.1557/PROC-1184-GG01-05 [5]https://doi.org/10.1016/j.ultramic.2020.112951 [6]https://github.com/niermann/temscript

PS 3
Poster session IM 1: Progress in instrumentation and ultrafast EM

Appointment

Session chairs

Programme

PS 3Poster session IM 1: Progress in instrumentation and ultrafast EM

Appointment

Session chairs

Programme

PS 3
Poster session IM 1: Progress in instrumentation and ultrafast EM