Beam Damage Research Articles

Three-dimensional electron ptychography of organic–inorganic hybrid nanostructures

Three dimensional scaffolded DNA origami with inorganic nanoparticles has been used to create tailored multidimensional nanostructures. However, the image contrast of DNA is poorer than those of the heavy nanoparticles in conventional transmission electron microscopy at high defocus so that the biological and non-biological components in 3D scaffolds cannot be simultaneously resolved using tomography of samples in a native state. We demonstrate the use of electron ptychography to recover high contrast phase information from all components in a DNA origami scaffold without staining. We further quantitatively evaluate the enhancement of contrast in comparison with conventional transmission electron microscopy. In addition, We show that for ptychography post-reconstruction focusing simplifies the workflow and reduces electron dose and beam damage.

Ga+-focused ion beam damage in n-type Ga2O3

Focused Ga+ ion milling of lightly Si-doped, n-type Ga2O3 was performed with 2–30 kV ions at normal incidence and beam currents that were a function of beam voltage, 65 nA for 30 kV, 26 nA for 10 kV, 13 nA for 5 kV, and 7.1 nA for 2 kV, to keep the milling depth constant at 100 nm. Approximate milling rates were 15, 6, 2.75, and 1.5 μm3/s for 30, 10, 5, and 2 kV, respectively. The electrical effects of the ion damage were characterized by Schottky barrier height and diode ideality factor on vertical rectifier structures comprising 10 μm epitaxial n-Ga2O3 on n+ Ga2O3 substrates, while the structural damage was imaged by transmission electron microscopy. The reverse bias leakage was largely unaffected even by milling at 30 kV beam energy, while the forward current-voltage characteristics showed significant deterioration at 5 kV, with an increase in the ideality factor from 1.25 to 2.25. The I–V characteristics no longer showed rectification for the 30 kV condition. Subsequent annealing up to 400 °C produced substantial recovery of the I–V characteristics for all beam energies and was sufficient to restore the initial ideality factor completely for beam energies up to 5 kV. Even the 30 kV-exposed rectifiers showed a recovery of the ideality factor to 1.8. The surface morphology of the ion-milled Ga2O3 was smooth even at 30 kV ion energy, with no evidence for preferential sputtering of the oxygen. The surface region was not amorphized by extended ion milling (35 min) at 5 kV with the samples held at 25 °C, as determined by electron diffraction patterns, and significant recovery of the lattice order was observed after annealing at 400 °C.

Focused ion beam preparation of halide perovskite microscopy specimens: evaluation of the beam induced damage

Focused ion beam (FIB) is currently one of the most commonly used methods for preparing transmission electron microscopy bulk specimens. However, for ion beam-sensitive materials such as halide perovskites, the ion beam milling process can easily cause decomposition and structure damage to the specimen. Here we investigate the influence factors of ion beam damage theoretically and experimentally, and successfully obtain the high-resolution transmission electron microscopy image of inorganic halide perovskite sample prepared by FIB. Theoretical investigations indicate that the temperature rises extremely fast for ion beam milling, reaching more than 80% of the highest temperature in less than one picosecond. Experimental investigations of halide perovskites in various forms (nanostructures, thin film devices, and single crystals) suggest choosing appropriate FIB acceleration voltage and beam current together with strategies to reduce the milling time may alleviate structure damage.

Spatial Distribution of the Electron Dose and the Effects on Beam Damage in STEM

Spatial Distribution of the Electron Dose and the Effects on Beam Damage in STEM

Ways to Suppress Electron Beam Damage Using High-Speed Electron Beam Control by Electrostatic Shutter in Sample Observation and Analysis

Ways to Suppress Electron Beam Damage Using High-Speed Electron Beam Control by Electrostatic Shutter in Sample Observation and Analysis

How innovations in methodology offer new prospects for volume electron microscopy

Detailed knowledge of biological structure has been key in understanding biology at several levels of organisation, from organs to cells and proteins. Volume electron microscopy (volume EM) provides high resolution 3D structural information about tissues on the nanometre scale. However, the throughput rate of conventional electron microscopes has limited the volume size and number of samples that can be imaged. Recent improvements in methodology are currently driving a revolution in volume EM, making possible the structural imaging of whole organs and small organisms. In turn, these recent developments in image acquisition have created or stressed bottlenecks in other parts of the pipeline, like sample preparation, image analysis and data management. While the progress in image analysis is stunning due to the advent of automatic segmentation and server‐based annotation tools, several challenges remain. Here we discuss recent trends in volume EM, emerging methods for increasing throughput and implications for sample preparation, image analysis and data management.

Evaluation and degradation mechanism of residual performance of RC beam after drop hammer impact

The residual load-carrying performance after impact is a key index to evaluate the impact-resistant capacity of engineering-used structure member. A multi-functional experimental facility was developed to conduct both the impact test and post-impact static loading test on two types of flexural-failure-dominated RC beam specimens with different tensile reinforcement ratios. Three-dimensional nonlinear finite element(FE) analysis was conducted to reproduce the impact process and to investigate the plastic damage of RC beam in depth. The degradation mechanism of load-carrying performance of RC beam after impact was investigated through fiber-section analysis with uniaxial damaged material models of concrete and reinforcement. The experimental and numerical results demonstrate that the resistance and stiffness of impact-damaged RC beam decrease in different levels. The residual flexural resistance and stiffness ratios are greatly affected by the longitudinal reinforcements. The yield state of compressive reinforcements plays critical effect on the residual performance of RC beam after impact.

A detection method integrating modal deflection curvature difference and natural frequency for structural stiffness degradation

A detection method integrating modal deflection and natural frequency is proposed to locate and quantify the damage of the beam. A damage identification index using modal deflection curvature difference is developed to locate damage. Note that the modal deflection is derived from the flexibility matrix and virtual force. A damage quantification equation is established by the transfer matrix method, which includes the parameters of natural frequencies, damage coefficients and damage location. Since the damage location parameters are determined by the proposed damage identification index, the damage coefficients of the damaged segments can be determined from the natural frequencies according to the damage quantification equation. The proposed damage detection method is verified numerically and experimentally. The results indicate that the proposed method can well locate and quantify the local damage of beams, especially for the beams with non-uniform damage degradation. The proposed damage localization index is more appropriate to locate damage than the index using modal flexibility curvature (MFC) or modal flexibility curvature matrix (MFCM).

Probability seismic demand and fragility analyses of novel SMA-based self-centring eccentrically braced frames

This paper performs the seismic assessment of novel shape memory alloy (SMA)-based self-centring (SC) eccentrically braced frames (EBFs) by using probabilistic seismic demand analysis (PSDA) and probabilistic seismic fragility analysis (PSFA). The structural finite element models are established based on a previous prototype building and verified through test results. The PSDA is based on a set of 176 seismic records, and Sa avg is chosen as the proper intensity measure for max inter-storey drift ratio (MIDR) and max inter-storey residual drift ratio (MIRR); whereas peak ground acceleration is more suitable for peak floor acceleration (PFA). After the PSDA results are obtained, time-history analyses and PSFA are conducted. Compared with traditional steel EBFs, the SMA-based SC-EBF shows a slight weakness in MIDR due to the comparatively small energy dissipation capacity but has an apparent advantage in controlling MIRR due to a good SC capacity provided by SMA angles. Furthermore, although the steel EBF with fixed column bases has the smallest MIDR, the fixed bases cause extra damage in column bases, which will bring other problems in post-earthquake rebuild and deviate from the design target of concentrating damage in link beams. The variability of the PFA is small, showing that the influence of structural forms on PFA is not apparent. Considering the overall structural seismic performances in terms of MIDR, MIRR and PFA, SMA-based SC-EBF can be a promising alternative in future seismic-resistant designs.

Shaking table test of fabricated concrete shear wall structure and study on damage mechanism of strong earthquake

Prefabricated construction technology has the advantages of high quality, high efficiency, low cost, energy saving and environmental protection, and has developed rapidly in China in recent years. Based on the design and construction concept of “equivalent to cast-in-site”, the seismic effect and strong earthquake damage mechanism of the overall structure considering boundary constraints are studied. In order to promote the application and development of high-assembly-rate concrete shear wall structures in high-intensity areas, a reduced-scale structural model of sleeve connection was designed and fabricated based on the Chinese seismic code. Through the multi-level strength-increasing shaking table simulation test, the dynamic characteristics, earthquake response, failure process and strong earthquake disaster mechanism of the model structure are comprehensively analyzed. The research results show that the prefabricated concrete shear wall structure can achieve the predetermined seismic fortification purpose according to the specified construction requirements. Secondly, Under the stepwise excitations of PGA 0.035–0.40 g, the flexural and shear failure of the coupling beam are the main failure mode, and the damage of the coupling beam with a small span-height ratio (1.33) is more serious. Furthermore, Under the stepwise excitations of PGA 0.62–0.90 g, the seismic capacity of the model structure is greatly reduced and there is a risk of collapse. The failure modes of the structure after a strong earthquake include four types: bending-shear composite failure of composite beams, horizontal interface penetration between composite beams and floor slabs, horizontal interface penetration between prefabricated walls and floor slabs, and vertical cracking at the junction surface of prefabricated walls and cast-in-site restraint elements. The latter three are unique forms of fabricated concrete shear wall structures. Finally, according to the whole process data of the test, the bottom shear force and top displacement of the model structure are calculated, and the hysteresis curve, skeleton curve and equivalent lateral stiffness are established. It is hoped that this study can provide a reference for the seismic design of high-rise fabricated concrete shear wall structures.

Induced damage during STEM-EELS analyses on acrylic-based materials for Stereolithography

(Scanning) transmission electron microscopy, (S)TEM, offers a powerful characterization tool based on electron-matter interactions, highly valuable in materials science. However, the possible electron beam induced damage during (S)TEM measurements hinders the analysis of soft materials, such as acrylic resins. Importantly, acrylic resins offer an appealing playground for the development of novel composites with customized properties and convenient processing capabilities for 3D-printing technologies, including Stereolithography (SLA). There are several factors preventing the optimal performance of TEM measurements applied to acrylic resins, among which we focus on the quality of the analyzed specimen (i.e., compromise between thickness and robustness, to achieve electron transparency while keeping the material integrity), particularly challenging when working with soft materials; the electrostatic charging/discharging effects, resulting in sample drift and related noise/artefacts; and the radiolysis and knock-on electron-induced damage, which directly degrade the material under study. We explore and compare different methodologies to obtain resin specimens suitable for (S)TEM analysis, employed for the subsequent study of the electron–beam damage induced during STEM-EELS measurements. Furthermore, we propose likely underlying mechanisms explaining the acrylic resin degradation based on the different EELS monitored signals. On one hand, we assess the evolution of the carbon and oxygen content, as well as the material thinning as a function of the accumulated electron dose. On the other hand, we extract meaningful information from the spectral shape of carbon and oxygen K-edges upon increasing electron doses, unraveling likely degradation pathways. The earned understanding on the electron-beam induced damage and the determination of critical doses provide a useful framework for the implementation of (S)TEM techniques as useful tools to help in the smart engineering of acrylic-based composites for SLA.

Electrical Methods for Sensing Damage in Cement Mortar Beams Combined with Acoustic Emissions.

The temporal variation in terms of the “time-to-failure” parameter of the recordings of the electrical resistance and the acoustic emissions from concurrent measurements in three cement mortar specimens of prismatic shape that were subjected to a three-point bending test until fracture are studied. The novelty of the work at hand lies in the demonstration that the electrical resistance is described by a power law during the last stages of the loading protocols. The onset of the validity of the power law is indicative of the specimens’ imminent fracture, thus providing a useful pre-failure indicator. The above findings are supported by the analysis of the recorded acoustic signals in terms of the F-function and the Ib-value formulations.

AXON Dose: A Solution for Measuring and Managing Electron Dose in the TEM

Abstract: The interaction of the electron beam with materials during TEM/STEM imaging often leads to radiation damage. While a variety of low-dose techniques can help mitigate beam damage, true dose management starts with knowing the precise total accumulated dose and dose rate that a sample has seen throughout an experiment. AXON Dose allows users to calibrate their instruments, track electron dose/dose rate across a sample as a function of time and location, and quantify the impact of dose on individual samples.

Ultrasonic-detected damage and bending behavior of reinforced PP-ECC beams after coupled action of freeze-thaw cycles and constant flexural load

Considering the performance degradation of structures in cold regions, the frost resistance and flexural performance of reinforced PP-ECC beams under the coupled action of freeze-thaw cycles and constant flexural load are investigated in this study. During the coupling test, the ultrasonic wave speed of the beams is recorded and the freeze-thaw damages in different regions of the beam are analyzed. Then, the flexural performance test is conducted on the beams, and the failure mode, number of cracks, maximum crack width, and flexural load-bearing capacity of the beams are measured. It is found that, with the increase of the number of freeze-thaw cycles, the freeze-thaw damage in the PP-ECC beam is more severe, and the flexural load-bearing capacity gradually decreases. Also, the number of cracks and cracking strength of the beams decrease, and the maximum crack width increases. With the increase of the flexural load, the frost resistance of both the tension zone and the bending shear zone of the beam is getting weaker, aggravating the freeze-thaw damage. Applying the constant load with a stress ratio of 0.25 results in the improvement of the frost resistance of the compression zone, thus reducing the freeze-thaw damage and increasing the load-bearing capacity of the beam. However, if the constant load is too large (stress ratio = 0.5), the freeze-thaw damage in the compression zone is aggravated, and the load-bearing capacity of the beam is reduced. Regardless of different degrees of freeze-thaw damage, the ductile failure of the beam is shown.

Atomic-resolution STEM image denoising by total variation regularization.

Atomic-resolution electron microscopy imaging of solid-state material is a powerful method for structural analysis. Scanning transmission electron microscopy (STEM) is one of the actively used techniques to directly observe atoms in materials. However, some materials are easily damaged by the electron beam irradiation, and only noisy images are available when we decrease the electron dose to avoid beam damages. Therefore, a denoising process is necessary for precise structural analysis in low-dose STEM. In this study, we propose total variation (TV) denoising algorithm to remove quantum noise in an STEM image. We defined an entropy of STEM image that corresponds to the image contrast to determine a hyperparameter and we found that there is a hyperparameter that maximizes the entropy. We acquired atomic-resolution STEM image of CaF2 viewed along the [001] direction and executed TV denoising. The atomic columns of Ca and F are clearly visualized by the TV denoising, and atomic positions of Ca and F are determined with the error of ±1 pm and ±4 pm, respectively.

Reducing electron beam damage through alternative STEM scanning strategies, Part II: Attempt towards an empirical model describing the damage process

In this second part of a series we attempt to construct an empirical model that can mimick all experimental observations made regarding the role of an alternative interleaved scan pattern in STEM imaging on the beam damage in a specific zeolite sample. We make use of a 2D diffusion model that describes the dissipation of the deposited beam energy in the sequence of probe positions that are visited during the scan pattern. The diffusion process allows for the concept of trying to ‘outrun’ the beam damage by carefully tuning the dwell time and distance between consecutively visited probe positions. We add a non linear function to include a threshold effect and evaluate the accumulated damage in each part of the image as a function of scan pattern details. Together, these ingredients are able to describe qualitatively all aspects of the experimental data and provide us with a model that could guide a further optimisation towards even lower beam damage without lowering the applied electron dose. We deliberately remain vague on what is diffusing here which avoids introducing too many sample specific details. This provides hope that the model can be applied also in sample classes that were not yet studied in such great detail by adjusting higher level parameters: a sample dependent diffusion constant and damage threshold.

Investigation on Acoustic Emission Parameters due to Fatigue Damage of Concrete Beams with Variable Notched Depth

AbstractAcoustic Emission (AE) application for Structural Health Monitoring (SHM) has undergone a swift advance through research and innovation in recent times. The AE monitoring is widely exploited as a tool for damage detection in materials research and structure monitoring. Various advantages of the AE, such as the potential use in large and complex structures, high-sensitivity, real-time monitoring capability, and potential application across a wide range of field study, has given the technique an edge over other approaches. Nevertheless, most of the reported studies had focused on the interpretation of the results in both quantitative and qualitative perspectives to extend the capabilities and application of AE for damage detection strategy. Eventually, the quantification of the damage level of the concrete structure relative to fatigue loading remained unanswered. Therefore, this study presented the experimental investigation of four types of plain concrete beams with a fixed dimension of 100 × 200 × 600 mm in the different notch-to-depth ratios under cyclic loading. A setup of the instrument consisting of four AE sensors type R6I was employed on each concrete beam sample to ensure a precise measurement for the three-point bending test. The b-value, improved b-value (Ib-value), severity, and intensity analysis methods were applied to quantify the damage level of the concrete structure under fatigue loading. Based on the results, the AE analysis successfully classified the damage levels following the observation made during the increasing cyclic loading on the notched concrete beams, the initiation of cracks, the steady growth of cracks, and beam failure. Valuable insights were recorded throughout the observation, including the progression of the fatigue failure mechanism from the Ib-value results, the intensity chart patterns from the intensity analysis, and the increased severity due to the increased loading cycles from the severity analysis. Conclusively, this study would enable researchers to understand the trend in monitoring the damage level under fatigue loading using the AE technique as well as providing fresh insights for further research.

Experimental Study of Emulative Precast Concrete Beam-to-Column Connections Locally Reinforced by U-Shaped UHPC Shells.

Precast beam–column connections act as vital elements of precast concrete frames. To enhance the resistance to the earthquake-induced damage and environment-induced deterioration of precast beam–column connections, an innovative precast concrete beam-to-column connection locally enhanced by prefabricated ultra-high-performance concrete (UHPC) shells was proposed. For studying the seismic behaviors of these novel connections and the influence caused by the prefabricated UHPC shell length, full-scale precast specimens were experimentally investigated using low-cyclic reversed loading tests. The obtained results were analyzed and discussed, including hysteresis curves, skeleton curves, strength and deformability, performance degradation, energy dissipation capacities, and plastic hinge length. The results reveal that the novel precast concrete beam–column connections with UHPC shells behaved satisfactorily under seismic loadings. The damage in the concrete near the lower part of the beam end is reduced by the prefabricated UHPC shells. The longer prefabricated UHPC shells were more useful for decreasing the damage to the precast concrete components and improved the structural performance. The precast specimen with 600-mm long UHPC shells can achieve a ductility of 4.87 and 4.0% higher strength than the monolithic reference specimen.

Operando Resonant Soft X-ray Scattering Studies of Chemical Environment and Interparticle Dynamics of Cu Nanocatalysts for CO2 Electroreduction.

Understanding the chemical environment and interparticle dynamics of nanoparticle electrocatalysts under operating conditions offers valuable insights into tuning their activity and selectivity. This is particularly important to the design of Cu nanocatalysts for CO2 electroreduction due to their dynamic nature under bias. Here, we have developed operando electrochemical resonant soft X-ray scattering (EC-RSoXS) to probe the chemical identity of active sites during the dynamic structural transformation of Cu nanoparticle (NP) ensembles through 1 μm thick electrolyte. Operando scattering-enhanced X-ray absorption spectroscopy (XAS) serves as a powerful technique to investigate the size-dependent catalyst stability under beam exposure while monitoring the potential-dependent surface structural changes. Small NPs (7 nm) in aqueous electrolyte were found to experience a predominant soft X-ray beam-induced oxidation to CuO despite only sub-second X-ray exposure. In comparison, large NPs (18 nm) showed improved resistivity to beam damage, which allowed the reliable observation of surface Cu2O electroreduction to metallic Cu. Small-angle X-ray scattering (SAXS) statistically probes the particle-particle interactions of large ensembles of NPs. This study points out the need for rigorous examination of beam effects for operando X-ray studies on electrocatalysts. The strategy of using EC-RSoXS that combines soft XAS and SAXS can serve as a general approach to simultaneously investigate the chemical environment and interparticle information on nanocatalysts.

Research on Impact Resistance of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Grid and Engineered Cementitious Composites.

When reinforced concrete structures are subjected to impact loads, they may suddenly yield or fail, or even collapse as a whole. In this paper, the impact resistance of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP) grid and engineered cementitious composites (ECC) was studied. Drop hammer impact tests were conducted on eight beams, then the finite element model was used to simulate the impact test, finally a simplified two-degree-of-freedom (TDOF) model was proposed for CFRP grid reinforced ECC layer strengthened RC beams under impact loading. The results showed that CFRP grid reinforced ECC layer significantly improved the impact resistance of RC beams. When the ECC and CFRP grid were used, the crack development was inhibited after the concrete cracked in the tensile area, avoiding the brittle damage of concrete beams with one crack to the end. Compared with the control beam, the reaction force of RC beams strengthened with CFRP grid and ECC under impact load increased by 16.2%~34.5%, the maximum mid-span displacement decreased by 16.3%~31.6% and the mid-span residual displacement decreased by 36.02%~49.53%. The finite element model and the proposed TDOF mode were demonstrated to effectively simulate the strengthened beam under impact loading.