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.

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Age-hardening in Al alloys has been used for over a century to improve its mechanical properties. However, the lack of direct observation limits our understanding of the dynamic nature of the evolution of nanoprecipitates during age-hardening. Using in-situ (scanning) transmission electron microscopy (S/TEM) while heating an Al-Cu alloy, we were able to follow the growth of individual nanoprecipitates at atomic scale. The heat treatments carried out at 140, 160, 180 and 200 °C reveal a temperature dependence on the kinetics of precipitation and three kinds of interactions of nano-precipitates. These are precipitate-matrix, precipitate-dislocation, and precipitate-precipitate interactions. The diffusion of Cu and Al during these interactions, results in diffusion-controlled individual precipitate growth, an accelerated growth when interactions with dislocations occur and a size dependent precipitate-precipitate interaction: growth and shrinkage. Precipitates can grow and shrink at opposite ends at the same time resulting in an effective displacement. Furthermore, the evolution of the crystal structure within an individual nanoprecipiate, specifically the mechanism of formation of the strengthening phase, θ′, during heat-treatment is elucidated by following the same precipitate through its intermediate stages for the first time using in-situ S/TEM studies.

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In-situ TEM studies using an environmental cell (nanoreactor) play an important role in not just giving an understanding the corrosion mechanisms at a sub-micron scale, but also on the influence of heat-treatment on the microstructural change and corrosion behaviour of these alloys. One of the main requirements of for these in-situ TEM studies is the leak tightness of the nanoreactor. This is achieved by gluing the top and the bottom chips together with water glass or commercially available cyanoacrylate compounds. The drawback of this method is the chips are inseparable after the in-situ TEM study, making it impossible to carry out any further investigations on the same specimen. To overcome this drawback, we worked on upgrading the nanoreactor by redesigning the TEM holder to avoid gluing. This made it possible not only to assemble the nanoreactors in a more reliable way but also separate the two halves after the in-situ TEM study. This has opened up opportunities to carry out investigations like tomography, AFM measurements and other surface characterization studies on the same specimen, adding more to the mechanisms observed from the in-situ TEM studies.@en

We present a new approach to study the three-dimensional compositional and structural evolution of metal alloys during heat treatments such as commonly used for improving overall material properties. It relies on in situ heating in a high-resolution scanning transmission electron microscope (STEM). The approach is demonstrated using a commercial Al alloy AA2024 at 100-240 degrees C, showing in unparalleled detail where and how precipitates nucleate, grow,or dissolve. The observed size evolution of individual precipitates enables a separation between nucleation and growth phenomena, necessary for the development of refined growth models. We conclude that the in situ heating STEM approach opens a route to a much faster determination of the interplay between local compositions, heat treatments, microstructure, and mechanical properties of new alloys.@en

We show that by operating a scanning transmission electron microscope (STEM) with a 0.1 nm 300 kV electron beam, one can sculpt free-standing monolayer graphene with close-to-atomic precision at 600 degrees C. The same electron beam that is used for destructive sculpting can be used to image the sculpted monolayer graphene nondestructively. For imaging, a scanning dwell time is used that is about 1000 times shorter than for the sculpting. This approach allows for Instantaneous switching between sculpting and imaging and thus fine-tuning the shape of the sculpted lattice. Furthermore, the sculpting process can be automated using a script. In this way, free-standing monolayer graphene can be controllably sculpted into patterns that are predefined in position, size, and orientation while maintaining defect-free crystallinity of the adjacent lattice. The sculpting and imaging processes can be fully computer-controlled to fabricate complex assemblies of ribbons or other shapes.@en

Localized corrosion in AA2024-T3 specimens was investigated by ex situ transmission electron microscopy (TEM) studies to determine an experimental window for real in situ TEM corrosion studies. In the as-prepared specimens, intermetallic phases leading to local galvanic couples were classified based on the size and composition. The corrosion behavior of the TEM specimens was investigated in two kinds of corrosive environments, 1M NaCl and oxygen bubbled through aqueous HCl of pH=3. In the specimens exposed to a NaCl environment for a duration of 30min, remnant copper-rich particles as a result of de-alloying were observed and energy filtered TEM (EFTEM) oxygen maps revealed the pitting of the oxide film at grain boundaries. In addition, severe deposition of NaCl crystals on the specimen surface was detected, making NaCl environment unsuitable for in situ TEM studies. Exposure to oxygen bubbled through aqueous HCl for durations of 20, 40, and 60min gave insights into different stages of localized corrosion in this alloy. EFTEM elemental maps confirmed that the remnants formed during the de-alloying were Cu rich, whereas most of the corroded regions had oxygen-rich corrosion products. The corrosion behavior of the AA2024-T3TEM samples showed to be in agreement with corrosion of bulk material reported in the literature. Thus, oxygen bubbled through aqueous HCl is considered a suitable environment for carrying out in situ corrosion experiments in the TEM.@en

In this article, we present novel sample preparation methods using a helium ion microscope (HIM). We report the possibility of reshaping, at room temperature, thin metal lines on an electron-transparent membrane: A set of platinum bridges with standard geometry (300 x 200 x 15 nm) was modified at room temperature into different shapes using focused helium (He)-ion beam. Also the applicability of the HIM as a tool for precise modification of silicon (Si) and strontium titanate (SrTiO3) lamellae is shown and discussed. We demonstrated that in situ heating (e. g., at 600 degrees C) of the samples during He-beam illumination by use of a specially developed heating stage enables production of thin Si and SrTiO3 samples without significant artifacts. The quality of such cuts was inspected by transmission electron microscopy with high-resolution imaging, and the diffraction patterns were analyzed.@en

A quasi in situ method using a specially developed holder is presented to follow electrochemically induced microstructural changes on a nanometre scale using analytical transmission electron microscopy (TEM). By following a specific specimen area after repeated exposure to oxygen bubbled through aqueous HCI of pH = 3, de-alloying of a grain-boundary precipitate of similar to 200 nm was observed by monitoring the changes in the EELS copper L-2,L-3-edge and EFTEM elemental maps. These results, supporting the existing models of de-alloying of copper rich precipitates in aluminium alloys, demonstrate the effectiveness of the quasi in situ specimen holder for analytical TEM studies of corrosion.@en

An approach to carry out chemical reactions using aggressive gases in situ in a transmission electron microscope (TEM), at ambient pressures of 1.5 bar using a windowed environmental cell, called a nanoreactor, is presented here. The nanoreactor coupled with a specially developed holder with platinum tubing permits the usage of aggressive chemicals like hydrochloric acid (HCl).@en