Identifying corrosion initiation events in metals and alloys demands techniques that can provide temporal and spatial resolution simultaneously. Transmission electron microscopy (TEM) enables one to obtain microstructural and chemical descriptors of materials at atomic/nanoscopic level and has been used in corrosion studies of many metal-electrolyte combinations. Conventionally, ex situ and quasi in situ TEM studies of pre- and post-corroded samples were performed, but possible experimental artifacts such as dehydrated surfaces might not fully represent the real interfacial conditions as compared to those when actually immersed in the electrolyte. Recent advances in liquid cell transmission electron microscopy (LC-TEM) allows for in situ monitoring morphological and even compositional evolutions in materials resulting from interaction with gas or liquid environments. Corrosion science, as a challenging field of research, can benefit from this unparalleled opportunity to investigate many complicated corroding systems in aqueous environments at high resolution. However, “real life” corrosion with LC-TEM is still not straightforward in implementation and there are limitations and challenging experimental considerations for conducting reliable examinations. Thus, this study has been devoted to discussing the challenges of in situ LC-TEM wherein state-of-the-art achievements in the field of relevance are reviewed.@en

Lithium leaching coatings have recently been developed as eco-friendly active corrosion protection technology for aerospace aluminium alloys (AAs) by the formation of a conversion layer at coating defects. While general conversion layer formation characteristics were studied and reported before, here we study the local layer formation process with sub-micron resolution at and around intermetallic particles (IMPs) in AA2024-T3. Top- and cross-sectional-view morphological electron micrograph observations along with open circuit potential (OCP) measurements are performed, mimicking coating defect conditions upon lithium carbonate leaching from the coating matrix. The results revealed five stages of the conversion process in which the alloy matrix and different IMPs evolve morphologically, compositionally, and electrochemically. Besides, we found a correlation between the OCP response of the AA2024-T3 system and the morphological and compositional evolutions of the alloy matrix and IMPs at different stages of exposure. Passive layer and alloy matrix dissolution leading to surface Cu-enrichment and S-phase dealloying occur at early stages of exposure. They precede the formation of a columnar layer on the alloy, followed by the establishment of a dense-like layer at the final stage. Dealloying of Al2CuMg can assist the conversion process by providing local supersaturation. Through complementary experiments in a sodium carbonate solution and besides X-ray diffraction analysis, we found out that lithium plays a critical role in stabilising the corrosion product throughout the conversion process.@en

Liquid-phase transmission electron microscopy (LP-TEM) has provided corrosion scientists with a unique opportunity to directly correlate nanoscopic morphological and compositional evolutions to the corresponding electrochemical response of corroding thin TEM specimens. Electrochemical liquid cell designs are key components of a LP-TEM study towards an implementation which is representative for realistic exposure conditions of bulk samples. However, the application of commercially available liquid cells in corrosion studies brings along an important shortcoming of galvanic coupling effects due to the inevitable connection of the TEM specimens with Pt patterned electrodes. Here, we introduce an approach of fabricating electrochemical liquid cells to alleviate the current cell design challenge for corrosion studies. Besides, we present a protocol for preparing thin specimens to be electrochemically investigated with our home-made electrochemical liquid cell. We finally confirm the effectiveness of this methodology by electrochemically evaluating thin specimens of AA2024-T3 in an open-cell configuration through open circuit potential and potentiodynamic polarisation measurements.@en

In this study, we report on a combined microscopic, analytical and electrochemical characterization of the nanoscopic passive layer on a tungsten‑molybdenum-containing super duplex stainless steel. We used scanning transmission electron microscopy/energy dispersive X-ray spectroscopy, scanning Kelvin probe force microscopy, scanning tunneling spectroscopy, and Mott–Schottky electrochemical impedance spectroscopy analysis to correlate the local chemical composition and electronic properties of passive layers on austenite and ferrite phases. The passive layer on the ferrite phase contains a higher amount of Mo, W, and Cr, which accommodates a higher nobility of ferrite and a higher local energy of the band gap compared to those on the austenite. The two aforementioned phases exhibit a different composition and semi-conductive properties of their passive layers leading to dissimilar local corrosion susceptibility. These findings are of pivotal importance in further studies of austenite and ferrite phase resolved corrosion resistance of duplex stainless steel demanding a dedicated alloying strategy.@en

Dealloying is involved in materials science responsible for fabrication of nanoscale structures beneficially but for corrosion degradations detrimentally. Detailed understanding related to the latter is critical for designing corrosion-resistance alloys and dedicated inhibition systems. Thus, direct nanoscopic observations of nano-structural and compositional evolutions during the process are essential. Here using liquid phase-transmission electron microscopy (LP-TEM), for the first time, we show dynamic evolution of intricate site-specific local corrosion linked to intermetallic particles (IMPs) in aerospace aluminium alloys. To thoroughly probe degradation events, oxidation direction is controlled by purposefully masking thin specimens, allowing for observing top-view surface initiation to cross-sectional depth propagation of local degradations. Real-time capturing validated and supported by post-mortem examinations shows a dealloying-driven process that initiates at IMPs and penetrates into the depth of the alloy, establishing macroscopic corrosion pits. Besides, controversial mechanisms of noble-metal redistribution are finally elucidated.@en

While graphene may appear to be the ultimate support membrane for transmission electron microscopy (TEM) imaging of DNA nanostructures, very little is known if it poses an advantage over conventional carbon supports in terms of resolution and contrast. Microscopic investigations are carried out on DNA origami nanoplates that are supported onto freestanding graphene, using advanced TEM techniques, including a new dark-field technique that is recently developed in our lab. TEM images of stained and unstained DNA origami are presented with high contrast on both graphene and amorphous carbon membranes. On graphene, the images of the origami plates show severe unwanted distortions, where the rectangular shape of the nanoplates is significantly distorted. From a number of comparative control experiments, it is demonstrated that neither staining agents, nor screening ions, nor the level of electron-beam irradiation cause this distortion. Instead, it is suggested that origami nanoplates are distorted due to hydrophobic interaction of the DNA bases with graphene upon adsorption of the DNA origami nanoplates.@en

Nanoscopic characterization of heterogeneous intermetallic particles (IMPs) which microstructurally and compositionally evolve during local corrosion is crucial in unravelling the mechanisms and sequence of initial and local corrosion events. Herein, we study site-specific initiation events focused on microscopic constituent intermetallic compounds and nanoscopic dispersoids in AA2024-T3 at the nanoscale using a combined quasi in-situ and ex-situ analytical TEM approach. Our findings show a dealloying-driven local corrosion initiation at the studied IMPs that have been considered as cathodic phases traditionally. Besides, local degradation which is a result of galvanic interactions between dealloyed regions of IMPs and their adjacent alloy matrix is largely governed by the intrinsic electrochemical instability of intermetallic compounds.@en

Staining compounds containing heavy elements (electron dyes) can facilitate the visualization of DNA and related biomolecules by using TEM. However, research into the synthesis and utilization of alternative electron dyes has been limited. Here, we report the synthesis of a novel DNA intercalator molecule, bis-acridine uranyl (BAU). NMR spectroscopy and MS confirmed the validity of the synthetic strategy and gel electrophoresis verified the binding of BAU to DNA. For TEM imaging of DNA, two-dimensional DNA origami nanostructures were used as a robust microscopy test object. By using scanning transmission electron microscopy (STEM) imaging, which is favored over conventional wide-field TEM for improved contrast, and therefore, quantitative image analysis, it is found that the synthesized BAU intercalator can render DNA visible, even at the single-molecule scale. For comparison, other staining compounds with a purported affinity towards DNA, such as dichloroplatinum, cisplatin, osmium tetroxide, and uranyl acetate, have been evaluated. The STEM contrast is discussed in terms of the DNA–dye association constants, number of dye molecules bound per base pair, and the electron-scattering capacity of the metal-containing ligands. These findings pave the way for the future development of electron dyes with specific DNA-binding motifs for high-resolution TEM imaging.@en

High-yield and continuous synthesis of ultrapure inorganic nanoparticles (NPs) of well-defined size and composition has invariably been one of the major challenges in nanotechnology. Employing green techniques that avoid the use of poisonous and expensive chemicals has been realized as a necessity for manufacturing NPs on an industrial scale. In this communication, we show that a newly developed high-frequency spark (HFS) quenched by a high-purity gas yields a series of monometallic and bimetallic NPs in large quantities, with well-defined (primary) particle size (sub-10 nm) and chemical composition. The mass production rate is linearly dependent on the operating frequency, and can reach up to 1 g h−1, providing a universal and facile technology for producing multicomponent hybrid NPs. Considering also that the methodology requires neither any specialized machinery, nor any chemical reagents, product purification, or any further waste processing, it provides a green, sustainable and versatile platform for manufacturing key building blocks toward industrial scale production.@en

Many theoretical studies predict that DNA sequencing should be feasible by monitoring the transverse current through a graphene nanoribbon while a DNA molecule translocates through a nanopore in that ribbon. Such a readout would benefit from the special transport properties of graphene, provide ultimate spatial resolution because of the single-atom layer thickness of graphene, and facilitate high-bandwidth measurements. Previous experimental attempts to measure such transverse inplane signals were however dominated by a trivial capacitive response. Here, we explore the feasibility of the approach using a custom-made differential current amplifier that discriminates between the capacitive current signal and the resistive response in the graphene. We fabricate well-defined short and narrow (30 nm × 30 nm) nanoribbons with a 5 nm nanopore in graphene with a high-temperature scanning transmission electron microscope to retain the crystallinity and sensitivity of the graphene. We show that, indeed, resistive modulations can be observed in the graphene current due to DNA translocation through the nanopore, thus demonstrating that DNA sensing with inplane currents in graphene nanostructures is possible. The approach is however exceedingly challenging due to low yields in device fabrication connected to the complex multistep device layout.@en

This work focuses on the cross-sectional characterization of the protective conversion layer formed on AA2024-T3 by lithium-leaching from a polyurethane coating in a corrosive environment. The layer shows a multi-layered arrangement comprising nanoscopic local phases. Transmission electron microscopy (TEM) and complementary high-resolution secondary ion mass spectroscopy (SIMS) were employed to observe the cross-sections of the entire layer formed at different locations of a 1-mm-wide scribe, in terms of morphology, structure and chemical composition. The conversion layer was comprised of two ubiquitous sublayers; a thin dense layer (i.e. 150 nm) adjacent the alloy substrate and a porous layer. The former represents an amorphous lithium-containing pseudoboehmite phase, Li-pseudoboehmite, whereas the latter is composed of amorphous and crystalline products; an outer columnar layer merely seen on the peripheral region is also crystalline. Through a sandwich structure and the d(003) basal spacing, the crystalline phases were identified as Li-Al layered double hydroxide. Although lithium was found uniformly spread within different regions, the local phases with no/low concentration of lithium were revealed with energy filtered TEM and confirmed with SIMS analysis.@en

High-fidelity and facile ex situ transmission electron microscopy (TEM) characterization of lithium−oxygen (Li−O2) batteries is still limited by challenges in preserving the native environment of Li−O2 discharge products. The extreme reactivity and moisture sensitivity of the discharge products means that they are quickly altered during sample retrieval from cycled batteries and transfer for TEM analysis, resulting in loss of original information. We here demonstrate that by using a TEM specimen grid directly in Li−O2 batteries as both support electrode and sample collector overlaid on a standard oxygen diffusion electrode, discharge products that are formed on the grid can be kept pristine.@en

olling Contact Fatigue (RCF) is very high-cycle fatigue process, leading to the formation of so-called butterfly cracks around non-metallic inclusions. The purpose of this study is to describe the crack initiation and microstructural changes around butterfly cracks in the hardened and tempered bearing steel with artificially introduced Al2O3 inclusions. This paper presents results from investigations using state-of-art electron imaging techniques such as Transmission Electron Microscopy (TEM), Electron Backscattered Diffraction (EBSD) and Focused Ion Beam (FIB). EBSD measurements showed high level of local grain mis-orientation at Al2O3/steel matrix interface which suggests possible locations for microcracks initiation. The TEM samples, containing the cracks, were selected from specific locations using precise FIB preparation process, allowing the TEM analyses of the large microstructural changes between the butterfly crack (formation of ultra fine nano-crystalline ferrite) and the steel matrix (tempered martensite). It was found that the butterfly crack growth and microstructural changes (formation of nano-crystalline ferrite) are simultaneous processes as a result of low-temperature recrystallization@en

olling Contact Fatigue (RCF) is very high-cycle fatigue process, leading to the formation of so-called butterfly cracks around non-metallic inclusions. The purpose of this study is to describe the crack initiation and microstructural changes around butterfly cracks in the hardened and tempered bearing steel with artificially introduced Al2O3 inclusions. This paper presents results from investigations using state-of-art electron imaging techniques such as Transmission Electron Microscopy (TEM), Electron Backscattered Diffraction (EBSD) and Focused Ion Beam (FIB). EBSD measurements showed high level of local grain mis-orientation at Al2O3/steel matrix interface which suggests possible locations for microcracks initiation. The TEM samples, containing the cracks, were selected from specific locations using precise FIB preparation process, allowing the TEM analyses of the large microstructural changes between the butterfly crack (formation of ultra fine nano-crystalline ferrite) and the steel matrix (tempered martensite). It was found that the butterfly crack growth and microstructural changes (formation of nano-crystalline ferrite) are simultaneous processes as a result of low-temperature recrystallization@en

Fe2C plays a crucial role in the precipitation of iron carbides. Jack's structural models for epsilon-Fe2C, and non-stoichiometric epsilon-Fe2.4C, are analyzed using first-principles calculations. Several new configurations of epsilon-Fe2C with even higher stability are found. We show how epsilon-Fe2C transforms into eta-Fe2C, and address the structural relationships with the chi-Fe5C2, theta-Fe3C and Fe7C3 phases. The relative occurrence of these phases in steel, as well as their probable evolution during tempering of quenched steels, is discussed.@en

Nanopores-nanosized holes that can transport ions and molecules are very promising devices for genomic screening, in particular DNA sequencing. Solid-state nanopores currently suffer from the drawback, however, that the channel constituting the pore is long, similar to 100 times the distance between two bases in a DNA molecule (0.5 nm for single-stranded DNA). This paper provides proof of concept that it is possible to realize and use ultrathin nanopores fabricated in graphene monolayers for single-molecule DNA translocation. The pores are obtained by placing a graphene flake over a microsize hole in a silicon nitride membrane and drilling a nanosize hole in the graphene using an electron beam. As individual DNA molecules translocate through the pore, characteristic temporary conductance changes are observed in the ionic current through the nanopore, setting the stage for future single-molecule genomic screening devices.@en

Nanopores-nanosized holes that can transport ions and molecules are very promising devices for genomic screening, in particular DNA sequencing. Solid-state nanopores currently suffer from the drawback, however, that the channel constituting the pore is long, similar to 100 times the distance between two bases in a DNA molecule (0.5 nm for single-stranded DNA). This paper provides proof of concept that it is possible to realize and use ultrathin nanopores fabricated in graphene monolayers for single-molecule DNA translocation. The pores are obtained by placing a graphene flake over a microsize hole in a silicon nitride membrane and drilling a nanosize hole in the graphene using an electron beam. As individual DNA molecules translocate through the pore, characteristic temporary conductance changes are observed in the ionic current through the nanopore, setting the stage for future single-molecule genomic screening devices.@en

A long-standing challenge in physics is to understand why cementite is the predominant carbide in steel. Here we show that the prevalent formation of cementite can be explained only by considering its stability at elevated temperature. A systematic highly accurate quantum mechanical study was conducted on the stability of binary iron carbides. The calculations show that all the iron carbides are unstable relative to the elemental solids, alpha-Fe and graphite. Apart from a cubic Fe23C6 phase, the energetically most favorable carbides exhibit hexagonal close-packed Fe sublattices. Finite-temperature analysis showed that contributions from lattice vibration and anomalous Curie-Weis magnetic ordering, rather than from the conventional lattice mismatch with the matrix, are the origin of the predominance of cementite during steel fabrication processes.@en