Microscopy Conference 2023

New method to characterise Li metal and SEI layer with atomic resolution with inert gas transfer and cryo-FIB

IMLB: Late breaking abstracts

MSLB: Late breaking abstracts

Abstract text (incl. figure legends and references) Lithium metal is one of the most promising anode candidate for the next-gen solid state battery. To go through the hurdles for a reliable and cost effective solid state battery, it is crucial to build strong fundamental understandings of different parts of a battery at microscopy level. Techniques such as site-specific DualBeam (FIB-SEM) lamella preparation and subsequent TEM analysis have always been the key steps to unlock atomic resolution for materials science studies. However, due to the air and moisture sensitivity associated with various battery components (Li metal, SEI layer, Solid electrolyte), it used to be a very challenging task to keep sample integrity during the workflow, especially during sample transfer between different instruments. In the current study, an novel IGST (Inert Gas Sample Transfer) workflow solution was used to enable a DualBeam to TEM workflow by protecting both the bulk sample and the prepared lamella in Ar atmosphere with a inert gas transfer module (CleanConnect). Using the CleanConnect module, a bulk Li-metal piece was successfully transferred from glovebox to a DualBeam without signs of surface oxidation. Due to the low melting point of lithium, the entire TEM lamella preparation process, including bulk milling, lift out, attach to TEM grid and final thinning were carried out at cryogenic temperature (-178C) with a LN2 cooled cryo-stage and cryo-nano-manipulator. To achieve minimal ion damage to the final lamella, all the ion milling processes were carried out with Ar plasma focused ion beam. The prepared lamella was then transferred back to glovebox under Ar gas protection using CleanConnect transfer module. Inside the glovebox, the lamella was loaded to a IGST double tilt TEM holder, which allows lamella transfer from glovebox to a CFEG TEM under Ar gas protection. The lamella was then analyzed in TEM. It is evident that the whole workflow successfully protects the lithium metal lamella from oxidation during transfer between multiple instruments. The lithium metal lamella stays crystalline with minimal signs of surface oxidation. Atomic resolution TEM images from lithium metal were successfully acquired. According to literature survey, this could be the first DualBeam prepared lithium lamella which gives atomic resolution in TEM analysis. EELs maps from the lamella were acquired to quantify the amount of oxidation on the Lithium lamella. It was found that the amount of Oxygen were below 1.8 at%, which validates the results. After the TEM analysis, the lamella were delibrately exposed in atomophere for less than 15 sec, significant oxidation were observed after the exposure, which further proves the necessity of the IGST workflow. The study successfully shows the capability of the workflow by achieving atomic resolution from Li-metal, which is one of the most challenging samples in terms of air, moisture, and temperature sensitivity. The success of the workflow also enables new methods to study other trending topics in the battery world such as characterization of SEI layer evolution, post-mortem analysis in higher resolution whilst keeping the sample in its original state.

Poster

Prof. Dr.

Identification of carbides in 28wt.%Cr high chromium cast irons by color etching and electron probe microanalysis

Abstract text (incl. figure legends and references) Introduction As-cast microstructures of high-chromium cast irons (HCCIs) with hypoeutectic composition in range of 27-30wt.%Cr and 2-3wt.%Cr irons consist of primary austenite dendrites with eutectic austenite, partially transformed to martensite, and eutectic M7C3 carbides. Normally, the hardness and wear resistance of these irons depend on the type of matrix and carbide formation. Mo can be added to HCCIs to modify the carbide and to increase the volume fraction of the carbide in their microstructures. The aim of this research is to identify the type of carbides and carbide transformation in 28wt.%Cr cast iron containing Mo additions using color etching techniques and electron probe microanalysis. Materials and methods Carbides in a 28wt.%Cr (R iron), a 28wt.%Cr-6wt.%Mo (Mo6) and a 28wt.%Cr-10wt.%Mo (Mo10) have been characterized by X-ray diffraction, light microscopy with color etching by Groesbeck&quot;s reagent [1], and an Apreo S Thermo Fisher Scientific field emission scanning electron microscope. The chemical composition of the eutectic carbides was analyzed by electron probe microanalysis (EPMA). Results LM and SEM observations shown in Fig. 1 reveal the as-cast microstructures of 28wt.%Cr–2.6wt.%C iron (R iron), and the irons with 6wt.%Mo addition (Mo6) and 10wt.%Mo addition (Mo10). The microstructures consist of primary dendritic austenite (g), eutectic austenite which partly transformed to martensite during cooling and eutectic M7C3 carbides. Mo addition to HCCIs promoted the formation of M6C and M23C6 carbides rather than M7C3 carbides. In the Mo10 iron eutectic M7C3 carbides were not observed and the microstructure contained radiating colonies of M23C6 carbide and lamellar/fish-bone M6C carbide. After color etching, Fig. 1(a-c), M7C3 carbide was colored brown and blue, while austenite matrix remained lighter in contract. The M6C carbide with a lamellar structure/fish-bone had a dark-brown coloration, and the radiating colonies of M23C6 carbide were rainbow colored. At higher magnification, the SEM image in Fig. 1(d) showed that the M23C6 carbide was present as a transition zone between the eutectic M7C3 and M6C in the Mo6 iron, indicating a carbide transition of M7C3 → M23C6 → M6C [2]. SEM-BEI images (Fig. 1(d-f)) revealed that the eutectic M6C carbide in the Mo6 and Mo10 irons had the brightest contrast compared to the M23C6 and M7C3 carbides.Furthermore, Fig. 1(g-i) showing the phase mapping by EPMA, clearly demonstrates that M6C carbide had the highest Mo content, corresponding to the SEM-BEI displaying the brightest contrast due to the high atomic number of Mo. The M7C3 and M23C6 had higher Cr contents. The quantitative elemental analysis can be used to estimate the atomic formulae for M7C3, M23C6 and M6C in the Mo6 iron. Conclusion Color etching with Groesbeck&quot;s reagent can be used to distinguish the M7C3, M23C6 and M6C carbides by brown or blue, rainbow, and dark brown coloration respectively. EPMA analysis suggested the stoichiometric formulae of these carbide in the 28wt.%Cr-6wt.%Mo (Mo6) as (Cr4.7Fe1.8Mo0.1)C3, (Cr14.1Fe6.9Mo1.3)C6 and (Cr1.5Fe3.2Mo1.0Si0.1)C, respectively. References E.C. Groesbeck, Solutions for Carbides, etc., in Alloy Steels, appendix to report of Committee E-4 on Metallography, Proc. ASTM, Vol 26 (Part I), 569 (1926). S. Imurai et al., Effects of Mo on microstructure of as-cast 28 wt.%Cr-2.6 wt.%C-(0-10) wt.% Mo irons. Mater. Charact., Vol. 90, 99-112 (2014).

Prof.

Regularization techniques for 3D surface reconstruction from four quadrant backscattered electron detector images

MS 7: Ceramics and composites

Abstract text (incl. figure legends and references) In scanning electronic microscopy, four quadrants backscattered electron detectors (FQBSD) allow collecting signals from each quadrant separately and combine them to obtain a tridimensional reconstruction of the surface. The main challenge of this operation consists of the integration of the gradient field obtained as the normalized difference of the signal from each pair of opposite quadrants. Owing to the presence of electronic noise that eventually turns into image noise, a least square integration approach is widely adopted for surface reconstruction. However, the reconstructed surface could still be affected by distortions due to sensitivity variations amongst the detector quadrants or an imprecise alignment of the FQBSD with the gun axis, which is quite a common occurrence, particularly in systems equipped with manual retractable FQBSD. In the present work, we demonstrate the possibility of adopting classical regularization techniques to the surface reconstruction from FQBSD images allowing for a substantialimprovement in the 3D surface reconstruction quality. To this purpose, three types of regularization have been explored: background removal by polynomial regression, Dirichlet&quot;s regularization, and Tikhonov&quot;s regularization. The procedures have been experimentally validated on AISI 316L stainless steel polishedsurfaces with microhardness indentation and on laser-patterned aluminum and silicon samples, showing promising results. Concerning the indented samples, Dirichlet&quot;s regularization returned the best result, whereas the other two regularization methods introduced some distortions of the indentation mark. On the other hand, for the laser-processed samples, Tikhonov&quot;s regularization allowed the best reconstruction of surface details, whereas Dirichlet&quot;s reconstruction forced the edges of the sample to be flat, thereby strongly altering the surface profile. This points to the need for an application-driven selection of the regularization technique that is easily implementable in commonly available software. Finally, we will also present paths for further development of the technique to demonstrate the possibility of a quantitative analysis of laser-processed surfaces as an alternative to more expensive and time-consuming optical profilometry and atomic force microscopy.

Real-time multi-dimensional spatiotemporal tracking of single anisotropic nanoparticles in live cells by multifunctional light-sheet nanoscopy

LSLB: Late breaking abstracts

Abstract text (incl. figure legends and references) A wavelength-dependent multifunctional light-sheet nanoscopy (MLSN) was developed to simultaneously track spatial movement (x, y, z), rotational dynamics (azimuth and elevation angles) and transport speed (v) of anisotropic nanoparticles in single live cells, which are referred to as six dimensions (6D) single-particle tracking (SPT). To obtain more detailed information for cell imaging, differential interference contrast, total internal reflection, epifluorescence, and super-resolution radial fluctuation-stream module were combined with the light-sheet nanoscopy. Because of anisotropic optical property, native gold nanorods (AuNRs; 5 nm diameter × 15 nm length) and surface-functionalized AuNRs were used as imaging probes for 6D SPT. s-pol and p-pol light sheets induced by optical polarizer could trigger the asymmetric scattering of AuNRs. Therefore, real-time photoswitching images of AuNRs were achieved for super-resolution images and multi-dimensional SPT. Using this technique, the endocytosis and transport processes of AuNRs at the upper and attaching side membrane regions of single live cells were directly observed. The native and surface-functionalized AuNRs showed various motional behaviors on cell membrane, internalization time and intracellular transport processes due to their different surface properties. This MLSN technology is a promising tool to shed new light on the working mechanism of living cells and to decipher super-resolution imaging of living cells with non-fluorescent imaging probes.

Four-dimensional cuboid multiangle illumination-based light-sheet super-resolution microscopy for minimizing optical illusion

Abstract text (incl. figure legends and references) Light-sheet-based super-resolution microscopy (LSRM) is an excellent detection technique for biological samples because light damage is minimized, but uneven light paths resulting from solid-angle illumination result in optical illusions. A three-dimensional (3D) LSRM limitation is uneven optical obstacles because of the inhomogeneous refractive index in orthogonal illumination. In this study, we introduce a four-dimensional (4D) light-sheet super-resolution microscopy (4D LSRM) with a cuboid prism integrated with a total reflection fluorescence and differential interference contrast microscopy to minimize optical illusions. The rotatable cuboid prism simply overcomes the optical illusion by rotating the specimen on the prism to change the direction of light that comes from illumination lens with super-resolution imaging. In addition, a 4D multiangle illumination-based algorithm was created to select the optimal illumination angle by the combining 3D super-resolution image with multiangle observation. Therefore, the 4D cuboid multiangle illumination-based LSM imaging system developed based on multiangle illumination and 3D imaging can provide the advantages of high-quality whole-cell imaging and single-molecule counting by minimizing optical illusions.

Specification of electrical properties of pyrolyzed 3D Printed Microstructures

IM 7: In situ/operando electron microscopy

Abstract text (incl. figure legends and references) In the era of miniaturization, increasingly smaller devices are being produced that are mainly made of silicon. Beyond silicon, carbon shows suitable properties for applied micro- and nanostructures, such as electrical conductivity, high mechanical and chemical stability and biocompatibility. These properties are especially suitable for biosensors [1]. To realize small structures, pyrolysis can be employed to shrink by up to 90% [1]. However, the holistic pyrolysis mechanism has not yet been studied in detail. So far there is no work that investigates the property change of pyrolyzed microstructures at different atmospheric pressures. Therefore, the investigation of the properties of pyrolyzed microstructures under different atmospheric influences and different temperatures can provide insights into the pyrolysis process. In this work, microstructures are printed on Si substrates by two-photon direct laser writing (DLW) with a commercially available photoresist (IP-Dip). These structures (see Figure 1a) are heated under a high vacuum or an inert Ar atmosphere at various pyrolysis temperatures. After pyrolysis, the shrinkage behavior of the microstructures is characterized by SEM [3], which is dependent on the surface-to-volume ratio [1]. Different geometries are considered, with varying cross-sections connecting the microelectrodes (Figure 1b). It is suggested that the electrical conductivity increases with growing pyrolysis temperature since an increasing sp² hybridization of the C-C bonds in glassy carbon dominate at higher temperatures [2]. The shrinkage behavior of the microstructures under several temperatures and environments, in correlation to the surface to volume ratio [1], is characterized. For the investigation of electrical properties, in situ-SEM nanoprobing with nanomanipulators is used to record voltage-current curves. In the meantime, we study the influence of different environments on the mass loss. In further work, thermogravimetric analysis will be performed to determine the temperature dependent mass loss. The experimental studies will be accompanied by COMSOL simulations to predict the geometrical shrinkage behavior at other temperatures. In summary, the study of pyrolyzed carbonaceous microstructures is an area where much research is still possible. With a better understanding of the pyrolysis process, the processes involved and the properties of glassy carbon, new technologies for medicine and industry can be found. References: [1] Cardenas-Benitez et. al., Microsyst. Nanoeng. 5,38 (2019). [2] Tyler et. al., Adv. Eng. Mater. 23, 2001027 (2021). [3] Sun et. al., Microsc. Microanal. 27 (Suppl 2), 2021. [4] The authors acknowledge financial funding by the German Research Foundation (DFG) under Germany&quot;s Excellence Strategy (EXC-2082/1─390761711).

Detecting charge transfer in defective 2D WS2 with electron ptychography

Abstract text (incl. figure legends and references) Detecting the electron redistribution in a material is a challenging, but important task as it can reveal fundamental information about chemical bondings. Conventional electron microscopy techniques such as annular dark field scanning transmission electron microscopy (ADF-STEM) are only sensitive to the nuclei rather than the electrons. We demonstrate the use of electron ptychography to detect charge transfer in two-dimensional WS2 at atomic resolution. Compared to other phase contrast imaging methods, it has the advantage of higher dose efficiency, correcting residual aberration after data collection as well as distinguishing heavy and light elements with the additional ADF signal. Importantly for this analysis, we introduce a new method to analyse phases which is robust to different experimental parameters. This is crucial as the changes due to charge transfer are very small. We investigate the charge transfer of single layer WS2 by comparing structural potentials obtained using the independent atom model (IAM) and density functional theory (DFT). Based on them, we extract the atomic phases using single side band ptychography (SSB) and compare them with the experimentally obtained phases. The phase extraction is performed via an optimization approach where a simplified simulation of the structure is matched to the target image. The simulation is obtained via convolution of a kernel corresponding to the contrast transfer function of SSB with a 2D point phase model. The method is demonstrated to be robust to noise and sample tilt. We show that charge redistribution can be reliably detected and occurs in the pristine WS2 structure as well as in their defects. While in the pristine structure, Sulphur obtains electrons from Tungsten, S vacancies result in a back transfer of electrons from S to W. Interestingly, the charge transfer is directly related to the density of defects. Our studies open up a new route to analyse charge transfers towards a better understanding of the effects of chemical bonds.

Interfacial structure dependent dynamics of Cu/ZnO during the reverse water-gas shift reaction

Abstract text (incl. figure legends and references) 1. Introduction The active sites for industrial copper/zinc oxide/alumina (Cu/ZnO/Al2O3) catalyzed CO2 transformation have been the subject of intense debate due to the complicated structure together with varied evolution both in activation process and during reaction conditions. Although numerous efforts have been devoted for decades, the precisive identification of desired surface and interface as well as the establishment of dynamic structure-function relationship under catalytic relevant environment still remain a formidable challenge. 2. Objectives The purpose of this study was to establish the dynamic structure-performance relationship of Cu/ZnO under reaction conditions. 3. Materials &amp; methods Cu/ZnO, ACTEM, In-situ Holder, ETEM 4. Results In the current study, the reduction of Cu nanoparticles (NPs) supported on hexagonal ZnO with well-defined nanorod shape (Cu/ZnO) is thoroughly investigated by using the state-of-the-art in-situ spherical aberration corrected transmission electron microscopy (ACTEM) on atomic-scale, while the dynamic feature in subsequent circumstance of reverse water-gas shift (RWGS) reaction is further explored via a combined microscopic and spectroscopic study at technologically interesting temperature range as well as gas composition. The delicate structural information of successfully synthesized Cu/ZnO catalyst after H2 reduction clearly deciphers a semi-spherical morphology of Cu on nonpolar surface of ZnO, whereas an obvious overgrowth of ZnOx moieties alongside faceted Cu NPs on polar terminations. The observed surface changes on catalyst by environmental TEM (ETEM) through increasing the CO2 content under RWGS conditions are accordant to the distribution of intermediates captured by in-situ drift infrared (IR) spectroscopy, which indicates an altered reaction mechanism from "surface-redox" to "formate-Langmuir-Hinshelwood" pathway on the basis of the feed-dependent coverage. In addition, further characterization at low temperature directly elucidates the deactivation of Cu particles on ZnO (10-10) due to the high coverage of accumulated carbon containing species. However, no such poison effect occurs for metallic Cu immobilized on ZnO (0002) and the dynamic behavior derived as the consequence of strong metal-support interaction (SMSI) is verified to play a vital role in facilitating the formation and decomposition of kinetic more favorable metastable species, possible carboxyl on this unique configuration. Hence, the description of dynamic interplay by integrated in-situ approaches could provide fundamental insights into the understanding of structure dependent Cu-ZnO catalytic synergy, and pave the way for rational design of low-temperature catalyst with high efficiency. 5. Conclusion In conclusion, we present an integrated in-situ study for fundamentally understanding the structure sensitivity of Cu as well as the promotion mechanism of Cu-ZnO interaction under RGWS reaction conditions. These intuitive and spatially resolved evidences as an important feature elaborates a complex scenario of surface chemical reactions in conjunction with dynamical changes of Cu/ZnO catalyst, which could add a new perspective to the ongoing discussion regarding the structure of active sites associated with steps in Cu surface and the Cu-ZnO interface, mainly including the incorporation of partly reduced Zn atoms into Cu steps for the conversion of CO2 molecule.

Visualizing demulsification of oil-in-water nano-emulsion in LC-TEM

Abstract text (incl. figure legends and references) Nano-emulsions are known as nano-sized dispersions of at least one immiscible liquid in another liquid, kinetically stabilized by emulsifying agent(s), with vast possible applications [1]. One particular interest for probably all application fields is the stability of nano-emulsions, since their stability goes hand in hand with their functionality. However, generally applied procedures are limited to averaging over a bulk volume or are static. Liquid-cell TEM (LC-TEM) is a door opener to reveal local insights to temporally resolved nano-emulsion stability [2]. The here presented work aims direct visualization of kinetically stabilized oil-in-water nano-emulsions using LC-TEM, evaluating their morphology, dynamics and mechanisms of demulsification. Ultrasonication and homogenization is used to generate droplets with HFE-7500 as the oil dispersed in a Zonyl (surfactant) containing aqueous continuous phase. The average droplet size depends on the applied shear rate and is controlled by dynamic light scattering with a Malvern Panalytical Zetasizer Nano. Protochips&quot; Poseidon LC-TEM holder was used for scanning (S)TEM investigations with Microwell E-chips. (S)TEM studies were performed on a JEOL ARM200F equipped with a cold FEG and Gatan&quot;s Oneview camera. Nano-droplets of the oil phase (initial average diameter approximately 120 nm, as prepared) are directly visualized in both TEM (homogeneous dose rate of 17·106 Gy/s for observation of dynamics) and STEM (averaged dose rate 1·104 Gy/s for overview images) mode. The more strongly scattering oil phase appears brighter in annular dark-field STEM excluding a possible confusion with gas bubbles. Moreover, in closely confined regions at the borders of the used LCs, a destabilization of initial nano-droplets towards a formation of larger ones (average diameter 340 nm) is recognized. Surface charges on the LC membranes may locally change the concentration of surfactants that leads to coalescence. In addition to those static observations, in-situ TEM reveals demulsification by coalescence (figure 1) with a rate of 97·103 nm3/s. This determined demulsification rate is orders of magnitude higher than other reported values from indirect determination methods for similar nano-emulsions, where Oswald ripening was assumed to occur [3]. The difference in mechanism and rate might be caused by strong influences of our experimental conditions, such as electron beam damage of surfactants or electric field trap for surfactants at LC membranes, both decreasing the surfactant concentration in the dispersion and therefore destabilizing the nano-droplets leading to coalescence. Our approach successfully enables studies of oil-in-water nano-emulsions by direct imaging. Demulsification is observed to take place because of a confinement effects in the LC and because of electron beam illuminating effects inducing changes of the surfactant concentration followed by coalescence of nano-droplets. Excluding or reducing those electron beam effects should help to broaden the knowledge on nano-emulsion stabilities and demulsification processes even further. [4] [1] Anton N et al.; Pharm Res 28 (2011) [2] Vratsanos, MA et al.; ACS Nano 16 (2022) [3] Delmas T et al.; Langmuir 27 (2011) [4] Max Planck Society is acknowledged. Figure 1: TEM images of nano-emulsion dynamics. Nano-droplets can immediately identified (a) and merge by coalescence during further electron beam exposure (b)-(d).

Two microscopes are better than one – a unique new Inspection tool for micro/nanostructures by combination of AFM and SEM

IM 3: SEM and FIB developments

Abstract text (incl. figure legends and references) Combining different analytical methods into one instrument is of great importance for the simultaneous acquisition of complementary information. Especially the in-situ combination of two of the most powerful microscopy techniques – scanning electron microscopy (SEM) and atomic force microscopy (AFM) – enables completely new insights in the micro and nano-world. [1,2] In this work, we present a unique inspection tool that seamlessly combines SEM and AFM for inspection and process control of Micro- and Nanostructures (see Figure 1). Due to the self-sensing piezoresistive cantilever technology used for the AFM scanner the cantilever deflection signal can be measured completely electrical and allows for simultaneous acquisition of SEM and AFM data directly at the region of interest. We will present a variety of novel case studies to highlight the advantages this new tool for interactive correlative in-situ nanoscale characterization for different materials and nanostructures. First results will focus on semiconducting BaTiO3-based ceramics with positive temperature coefficient of resistivity (PTCR) that currently gain increased attention due to their application as cabin heater in electrical vehicles. We use electrostatic force microscopy (EFM) in combination with the SEM in order to precisely analyze the grain boundary potential barriers of different BaTiO3-based samples. [3] The grain boundaries were located by backscatter electron detection (BSE) and afterwards measured with in-situ EFM. The barriers were shown to be significantly thinner and more pronounced as the amount of SiO2 was increased from 0 to 5 mol% (see Figure 2). These results can be directly correlated with electron backscatter diffraction (EBSD) measurements to link the AFM and SEM data to the crystallographic microstructure of the different samples. In addition, we will present first results for the in-situ characterization of magnetic micro- and nanostructures for industrial relevant samples (e.g., duplex steel) by combination of SEM and high-vacuum magnetic force microcopy (MFM). SEM enables to the grain boundaries and position the cantilever directly at the region of interest, whereas in-situ MFM allows for the characterization of 3d topography and magnetic properties with nanometer resolution (see Figure 3). Based on the broad variety of applications regarding the inspection and process control of different materials and devices, we anticipate that this new inspection tool to be one of the driving characterization tools for correlative SEM and AFM analysis in the future.

Structural evolution of supported ZnPd/ZnO nanoparticle catalysts studied by environmental STEM

Abstract text (incl. figure legends and references) Methanol Steam Reforming (MSR) is an important reaction converting methanol into hydrogen (CH3OH + H2O à 3 H2 + CO2) holding promise for easy fuel handling in hydrogen based applications like fuel cells. ZnPd/ZnO nanoparticles are promising MSR catalysts due to their high CO2 selectivity, stability and activity.1 It is known that their properties depend strongly on their microstructure and particle size, thus, also on their preparation method.2-5 In order to understand their microstructural evolution during preparation, the calcination of supported Pd(NO3)2 in O2 was studied using in situ high resolution scanning transmission electron microscopy. For additional pre- and post characterisation energy dispersive x-ray spectroscopy and electron energy loss spectroscopy were applied. References Föttinger, K., Van Bokhoven, et al J. Phys. Chem. Lett. 2, 428–433 (2011). O. Jakdetchai, N. Takayama, T. Nakajima, Kinet. Catal. 46 (2005) 56–64 J.-P. Shen, C. Song, Catal. Today 77 (2002) 89–98 R.A. Dagle, Y.H. Chin, Y. Wang, Top. Catal. 46 (2007) 358–362 Y. Wang, J. Zhang, H. Xu, X. Bai, Chin. J. Catal. 28 (2007) 234–238

Prof. Dr. rer. nat. habil.

Twist enables superlubric behavior in bilayer graphene

Abstract text (incl. figure legends and references) The state of vanishing friction known as superlubricity has important applications for energy saving and increasing the lifetime of micro- or nanomechanical systems with sliding components (1). Superlubric behavior has been found in two-dimensional graphene or graphite because of the weak interlayer van der Waals force and shows a strong dependence on twist angle. Experimentally, M. Dienwiebel et al. recognized two narrow angular regions with a distance of about 61 deg. ± 2 deg. showing high friction, whereas nearly zero friction was observed between these two angular regions. This indicates that the ultralow friction is associated with incommensurability between the rotated graphite layers (2). Theoretically, H. Z. Bai et al. revealed the bilayer graphene (BLG) superlubricity with a coefficient of friction of 0.0003 at a twist angle of 3°, and this coefficient of friction is about 26 times lower than a non-superlubric state (3). Despite the insightful theoretical works, the frictional properties within a small twist angle regime and the dynamic twist process during sliding between atomic layers of graphene have not been directly observed in experiments due to the great challenges of such experiments. Here, we report the first time direct observation of dislocation activity and twisting in BLG by in situ straining inside a transmission electron microscopy (Fig. 1A). Combining with the 4D STEM technique, strains and twist angles were evaluated at each strain step (Fig. 1A) and their relationship was established to understand the superlubric properties of BLG. In our experiment, a monolayer-bilayer-monolayer graphene configuration was verified (Fig. 2B). As depicted in Fig. 2B-D, the width of the bilayer region decreased as well as the dislocation network changed during straining. With a BLG change of 22 nm (Fig. 2C), dislocation in BLG converted to the Moiré superlattice configuration, indicating the twist between the two monolayers. When it comes to a BLG width change of 121 nm (Fig. 2D), a higher dislocation density is reached, indicating a further increase in twist angle. The analysis on dislocation types revealed that the predominate screw type dislocations with Burgers vectors and remain, while dislocations with Burgers vectors changed from mixed type to mainly screw type (Fig. 2E-G). Meanwhile, the evaluation of twist angle distribution in BLG shows that the twist angle increases along with the continuous sliding, and these results agree well with the twist angle calculated from the Moiré superlattice periodicity (Fig. 2A). Eventually, the relationship between strain and twist angle reveals a clear decreasing tendency in strain with the increasing of twist angle (Fig. 2B), indicating a gradual change towards superlubric behavior in BLG. In conclusion, we developed an in situ staining method combined with 4D-STEM to realize the direct observation of dislocation activities and investigation of the twist-dependent superlubric behavior in BLG. This method can be taken as a versatile way to study the strain-related physical properties of other 2D materials. (1) S. Kawai et al. Science, , 351, 957 (2016). (2) M. Dienwiebel, et al. Phys. Rev. Lett., 92, 12 (2004). (3) H. Z. Bai, et al. Carbon, 191, 28 (2002). (4) X. Zhou, et al. to be published. Fig. 1 (A) Schematic representation of the straining process and 4D STEM set-up for strain and twist angle evaluation. (B to D) The sequence DF-TEM images taken from the reflection describe the dislocation network and twist in BLG at various strain steps. (E to G) Drawing of the dislocations in the BLG region corresponding to B to D. Fig. 2 (A) Twist angle distribution at various strain steps. (B) Strain-twist angle correlation, showing a decreasing trend of strain with the increasing of twist angle.

EDS nanometric spatial resolution in SEM for bulk material analysis

Abstract text (incl. figure legends and references) Reduced-dimensionality materials are increasingly gathering pace and progress in many important fields of life. For instance, they are undergoing rapid development in energy conversion, solid-state lighting, biological sensing, and information technology. Investigating such nanoscale featured materials became a necessity to achieve better properties and performances. Electron-microscopy chemical mapping is one of the powerful tools to do so. For bulk samples, though, it is very challenging to combine high spatial resolution imaging and spectroscopic analysis at the nanoscale. In response to this challenge, Bruker launched recently the XFlash® 7 EDS detectors. These new detectors offer high spatial resolution by providing excellent output count rates at low probe currents. This ideal combination is obtained thanks to the best solid angle and highest pulse processing speeds ensuring high sensitivity and the highest collection efficiency. In the present work, sub-10 nm EDS-spatial resolution is achieved using low and high kVs and are demonstrated through examples of bulk semiconductor and aerospace materials with challenging element combinations.

Prof.Dr.

Phase contrast in quantum electron microscopy

IM 1: Progress in instrumentation and ultrafast EM

Abstract text (incl. figure legends and references) Quantum Electron Microscopy technique (QEM) is aimed for improvement of electron dose limited resolution by implementing interaction free measurements [1]. One of the QEM approaches is to build a Mach-Zehnder interferometer for electrons using grated mirrors as electron beam-splitters [2]. Earlier, it was shown that a sample with different transparency levels can be imaged by QEM in interaction free manner [3]. Now we consider the case of phase-only sample which represents a typical cryo-EM situation. We conduct theoretical analysis on the dose limited phase resolution of QEM in order to prove it is worthwhile to build. Cryo-Electron Microscopy suffers from sensitivity of biological samples to electron damage. Large proteins and protein complexes can be studied in cryo-EM, while for smaller proteins the X-ray diffraction is still the technique of choice. Modern aberration corrected TEMs and STEMs provide atomic resolution in crystalline samples with illumination doses higher than ~104 e-/A2. Protein structure degrades severely already at doses of two orders of magnitude lower. Novel EM techniques aim for higher dose efficiency that will allow new areas for the cryo-EM investigation. One of such techniques is QEM. In QEM an electron is split into two states, a sample state |S&gt; and reference state |R&gt;, so that initially &lt;S|S&gt; &lt;&lt; &lt;R|R&gt;. The sample state is used as a STEM focused probe while the reference state passes through the empty space. The |S&gt;-state experiences phase shift passing through the sample . After the sample plane, the two states are directed back to the beam-splitter where they exchange some of their amplitudes. This cycle is repeated N times and the electron is taken out to the detector plane to collapse in either the |S&gt;-state or in the |R&gt;-state, with probablity depending on the pahse shift in the sample (see Fig. 1) Phase shift can be tuned such that for a blank sample electrons always arrive in the |S&gt;-state. Then for large the interference on the beam-splitter is inconsistent and probability to find the electron in the |R&gt;-state is overwhelming. The maximal dose is reached at zero phase shift with a value of ≈N/2 representing the fact that electron spends half of the time in the sample arm on average. At large pahse shifts the dose is lower since the |S&gt;-state Figure 1 Phase dependent behavior of a QEM with N=24 cycles. Phase shift in the sample controls collapse probabilities of electrons. For large phase shifts electrons are mostly locked in the initial reference state (blue). For large phase shifts more electrons are detected in the sample sate (red). Electron dose also depends on the phase (black, right axis), with the receiving maximum dose of ≈N/2 (per electron). Using a dose-limited phase resolution as a metric we show that the QEM achieves at least twice as good phase contrast as a TEM for a typical cry-EM protein imaging setup (see Fig. 2). Figure 2 Simulated images (10x10nm2) of a viral protein (PDB DOI: 10.2210/pdb5I4T/pdb) at 200kV tension for aTEM (left panel) and QEM (right panel).The exaggerted doses applied for image clarity.

Miniature components for electron optical instruments with two parallel optical axes

Abstract text (incl. figure legends and references) This poster introduces miniature electron-optical components for e.g. a double mirror corrector or quantum electron microscope [1,2]. Krielaart&quot;s QEM design has two parallel optical axes; a microscope axis and, shifted by typically a millimetre, a mirror axis. A beam separator pair is needed to tilt the entering beam towards the mirror while the reflected exiting beam passes straight, or vice versa. Electrostatic mirrors are needed to cancel aberrations and diffract the beam in a QEM cavity [2]. The components are designed for electron beam energies up to 5 keV. Experimental data on the performance of a beam separator (EBE unit) and a miniature electron mirror will be presented. The EBE unit is a compact bi-axial beam separator with low higher order deflection aberrations [4]. The EBE unit consists of three dipole layers that are placed spatially along the parallel optical axes. This (di)pole arrangement reduces the inherent hexapole fields. In each layer, a mu-metal pole pair provides for deflection in the two lateral directions by either an electric and/or magnetic field. Experiments at E = 2 keV beam energy show a deflection sensitivity of 0.275 mrad/mA and 1.98 mrad/V for magnetic respectively electric excitation. Our miniature mirror unit design combines classic parts machining (e.g., for the holder frame and the liner tube that guides the beam through the mirror electrode plane) with micro-lithographic technologies as developed by the MEMS industry. The high precision of MEMS manufacturing techniques yields well-defined bur-free free-form flat electrodes. These can be used to build low-cost high-quality electrostatic deflectors, stigmators lenses and mirrors. Here, electrostatic mirrors and lenses are made using metalized silicon elements as electrodes, which are sandwiched in between electrically insulating flat quartz spacers. Typical layer thicknesses are a few hundred micrometres. To avoid electrical fields above the breakdown limit of 10 kV/mm, the beam energy is typically limited to 5 keV. Before fixing their position in the full stack, each electron optical element is accurately aligned to both axes using a dedicated 6-DOF Hexapod stacking tool [5]. The beam is injected into the QEM cavity through a grounded metal liner tube, thus offering electrons a field-free passage through the voltage barrier of the mirror and lens electrodes. The beam is shifted from the microscope axis to the mirror axis by a MEMS electrostatic deflector and vice versa by electro-magnetic deflectors in the EBE unit. To set the focal length and aberrations of the mirror, 3-5 accurately stacked electrodes are energized up to ±5 kV [1-3]. In conclusion, when properly designed, aligned and energized, these new compact electron optical components can together conceive a round-trip cavity as needed to coherently build up the signal in a quantum electron microscope. References [1] Dohi, H. and Kruit, P., Ultramicroscopy 189 (2018) 1-23 [2] Krielaart, M.A.R., and Kruit, P., Ultramicroscopy 233 (2022) 113424 [3] M.A.R. Krielaart and P. Kruit, Phys. Rev. A 98 (2018) 063806 [4] Krielaart, M.A.R., Maas, D.J., Loginov, S.V., and Kruit, P., J. Appl. Phys., 127 (2020) 234904 [5] Chapter 5, PhD thesis Zonnevylle, A.C., https://doi.org/10.4233/uuid:23221904-c9c1-4537-af7f-abdbb9df06ed MK, SL and PK acknowledge funding from the Gordon and Betty Moore Foundation. DM gratefully acknowledges support by Hitachi High Technologies.

Event-driven MHz 4D STEM for low dose and in situ electron microscopy

Abstract text (incl. figure legends and references) Four-dimensional scanning transmission electron microscopy (4D STEM) measures 2D reciprocal space diffraction from a focused electron probe scattered at each pixel across a 2D real space area. This high-dimensional dataset allows much richer information to be retrieved than conventional STEM [1]. Particularly the past decade has witnessed the advance of this technique because of the introduction of fast electron-counting detectors [2], which runs at 1-10 kHz continuous readout, while the conventional CCD only works at 1-10 Hz level. However, this "fast" frame rate is still 2-3 orders of magnitude slower than the conventional STEM with single-pixel or segmented detectors. This would prevent at least two kinds of applications which should have been benefited from the versatile 4D STEM measurements. The first is atomic-resolution low-dose phase contrast imaging of sensitive specimens. With a limited amount of dose budget and a fine scanning pixel size (for resolving atomic resolution, unless compressed sensing or ptychography is used), the electron probe current would be impractically low when the diffraction frame rate is only at kHz. As an example, for a total dose of 100 e-/A2 and a pixel size of 0.5 A, the probe current has to reduce to 0.004 pA for 1 kHz detector but can be 4 pA when the detector runs at 1 MHz. Thousandths of pA is either inaccessible in some microscopes or in practice hardly usable in most cases. The second is in situ study of dynamic behavior upon external stimuli. Pushing 4D STEM towards conventional STEM speed or beyond would permit time-resolved investigation of dynamic functionalities of the devices from the rich crystallographic and/or phase contrast information. In contrast to the conventional frame-based detectors, event-driven readout architecture has very recently been applied to electron detection in cryo-EM [3,4], 4D STEM [5,6], as well as coincidence [7,8] and time-resolved [9] spectroscopy. We installed an event-based Timepix3 detector from Amsterdam Scientific Instruments with 2x2 chips (in total 512x512 pixels) on a monochromated and probe-corrected Thermo Fisher Scientific Titan STEM, and tested its performance in 4D STEM experimental setup and applications. Benefiting from its 1.56 ns Time of Arrival (TOA) binning resolution, we can now run 4D STEM measurements at MHz frame rate with reasonable probe current. Digital blanking of detector pixel/area was sometimes used to gain higher probe current within the maximum event rate. We will present three applications that have been tested so far: i) low-dose atomic-resolution phase contrast imaging, ii) large field-of-view crystallography phase mapping, and iii) in situ centre of mass analysis of e-beam-induced charging. Further prospects on programmable scanning path to manipulate the e-beam-induced charging or damage as well as near-real-time analysis of event-driven data based on sparse matrix computation will also be discussed during the presentation. References [1] C. Ophus, Microsc. Microanal. 25, 563 (2019) [2] B. D. A. Levin, JPhys Materials 4, 042005 (2021) [3] J. P van Schayck et al., Ultramic. 218, 113091 (2020) [4] H. Guo et al., IUCrJ 7, 860 (2020) [5] D. Jannis et al., Ultramic. 233, 113423 (2022) [6] P. M. Pelz et al., IEEE Signal Process. Mag. 39, 25 (2022) [7] D. Jannis et al., Appl. Phys. Lett. 114, 143101 (2019) [8] N. Varkentina et al., Sci. Adv. 8, eabq4947 (2022) [9] Y. Auad et al., Ultramic. 239, 113539 (2022)

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Appointment

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Late breaking posters IM