bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying magnetism on the nanometer scale:
EMCD
on individual
FePt
nanoparticles
Authors: Schneider Sebastian , Pohl Darius , Löffler Stefan , Kasinathan Deepa , Rusz Jan , Schattschneider Peter , Schultz Ludwig , Rellinghaus Bernd
Published: December 2016

Electron energy‐loss magnetic chiral dichroism (EMCD), which is the electron wave analogue of X‐ray magnetic circular dichroism (XMCD), offers the possibility to study magnetic properties at the nanoscale in a TEM. The relatively young method of EMCD [1] was already refined to such an extent that it is possible to probe magnetic moments of thin films of a variety of ferromagnets [2, 3, 4]. By now, these measurements already surpass the resolution of XMCD experiments. However, quantitative EMCD measurements are so far only reported on thin films rather than on nanoparticles, which are expected to reveal distinct magnetic properties due to their reduced dimensions and enhanced surface to volume ratio.

We report on EMCD measurements on a single FePt nanoparticle (cf. Figure 1) and compare our experimental findings with simulations. L1
0
ordered FePt is a particularly interesting material since it offers the highest magneto‐crystalline anisotropy among the oxidation‐resistant hard magnets [5]. It is therefore a promising material for future high density magnetic data storage media. The L1
0
ordered FePt nanoparticles on a STO substrate were prepared by sputtering. Prior to the spectroscopic measurements, samples in plan view geometry were subjected to mechanical thinning and grazing incidence Ar
+
ion milling in order to obtain 10 nm thick substrate‐free nanoparticles.

The experiments were performed on a FEI Titan
3
80‐300 microscope equipped with an image C
S
corrector. The sample was oriented in three beam condition with the [001] easy axis of L1
0
FePt oriented (close to) parallel to the electron beam. Binned‐gain acquisition of the EEL spectra was used to optimize the S/N ratio [6]. Particular attention was paid to the analysis of the EEL spectra. A measurement route is presented that allows for the extraction of a dichroic signal from spectra that still suffer from non‐optimal S/N ratio. Our experiments are supported by simulations of EEL spectra utilizing the WIEN2k program package [7] in combination with Bloch‐wave (BW) methods. These simulations are used to (pre‐)determine optimal experimental parameters, that provide for the highest EMCD signals [8, 9]. The experiments reveal a small but reproducible dichroic signal (cf. Figure 2) that agrees well with the results of the theoretical calculations. From these experimental spectra, a ratio of angular to spin magnetic moment m
l
/m
s
= 0.08 ± 0.08 is for the first time quantitatively derived for individual FePt nanoparticles [10], which agrees well with the XMCD result m
l
/m
s
= 0.09 for a large ensemble of L1
0
ordered FePt nanoparticles [11].
Utilising correlative 3D imaging to understand creep cavitation in stainless steel
Authors: Slater Thomas , Bradley Robert , Geurts Remco , Bertali Giacomo , Burke Grace , Haigh Sarah , Withers Philip , Burnett Timothy
Published: December 2016

The role of grain boundary orientation and secondary phase precipitation on creep cavitation in a stainless steel sample has been investigated using a correlative tomography
1
approach. A number of different 3D imaging techniques are combined on the same sample in order to understand the initiation and progression of cavitation.

Correlative imaging has become an important tool in both biology
2,3
and materials science
4
, where it provides 2D information of the same sample area at multiple length scales. Correlative tomography describes the extension of correlative imaging to three dimensions via a range of techniques, which also provides the opportunity to probe sub‐surface volumes
1
.

The position, size and morphology of cavities on three grain boundaries in a stainless steel sample taken from a power station steam header were examined using X‐ray computed tomography (CT)
5
. X‐ray CT demonstrates that the presence of cavities, as well as their size and shape, varies for each of the grain boundaries examined in this study (Figure 1). Subsequently, FIB‐SEM slice and view provides a higher‐resolution analysis of the same sample to resolve and identify the precipitates decorating the cavitated grain boundaries. Additionally, 3D electron backscatter diffraction (EBSD) mapping reveals the misorientation at grain boundaries and thus offers some insight in to why certain boundaries may possess cavities and whether grain boundary misorientation affects the size and shape of cavities.

Furthermore, a 200 nm diameter pillar was sectioned from one of the cavitated boundaries in order to perform scanning transmission electron microscope (STEM) – energy dispersive X‐ray (EDX) tomography
6,7
. STEM‐EDX tomography reveals the distribution of elements at nanometre scale in three dimensions (Figure 2). This high‐resolution chemical information aids understanding of precipitate formation and provides accurate characterisation of precipitate morphology.

The correlative 3D imaging approach applied here gives unprecedented insight in to cavitation in stainless steels and is also applicable to a wide range of other materials that display characteristic features at a number of different length scales.
Structural and chemical characterization and
3D
modelling of metal oxide core‐shell nanoparticles with complex morphology
Authors: Martí‐Sánchez Sara , Genç Aziz , Luo Zhishan , Ibáñez Maria , de la Mata María , Cabot Andreu , Arbiol Jordi
Published: December 2016

A wide variety of metal oxide manganite and ferrite core‐shell nanoparticles (NPs) with adjustable composition were characterized by means of Transmission Electron Microscopy related tools in order to precisely understand their composition, the arrangement of the different chemical species and cation valence state variation along the nanoparticles.

The nanoparticles were produced at low temperature and ambient atmosphere using a one‐pot two‐step synthesis protocol involving the cation exchange of Mn or Fe by Co or Ni in preformed Mn
3
O
4
or Fe
3
O
4
NPs, allowing the formation of a core shell structure. These nanoparticle systems present a complex 3D structure, which has been modelled with Rhodius software [1] and simulated with the STEM‐CELL packages [2], giving rise to a fine determination of the studied systems.

Special attention has been paid on manganite – cobalt systems. By selecting the proper cobalt precursor, CoO crystallites could be simultaneously nucleated on the NP surface to form Mn
3
O
4
@CoMn
2
O
4
–CoO (Figure 1). In this latest case, heterostructured NPs exhibited improved performance and durability as bifunctional catalysts for the oxygen reduction and evolution reactions (ORR, OER) over commercial Pt and IrO2‐based catalysts and over previously reported spinel electrocatalysts in alkaline solution.
In Situ Study of Internal Structure of Spherical Polyelectrolyte Complex Capsules Using
ESEM
Authors: Nedela Vilem , Bucko Marek , Tihlarikova Eva , Krajcovic Tomas , Gemeiner Peter , Navratilova Eva , Hudec Jiri
Published: December 2016

Polyelectrolyte complex (PEC) capsules/beads are very important for biotechnological applications such as drug delivery and bacterial whole‐cell biocatalyst development. The very beam‐sensitive bio‐polymer capsules are laboratory produced as a uniform with a controlled shape, size, membrane thickness, permeability and mechanical resistance [1]. PEC capsules are very sensitive to any treatment and samples could be inspected in their fully native and functional state to prevent any misinterpretation. Characterization and study of PEC capsules properties is possible using thermodynamically stabile and fully wet state, precisely reached after very slow changing of conditions in the specimen chamber of ESEM. The morphological study using low current ESEM was already presented [2]. The internal structure can be in solvent, semisolid or solid state, depend on capsule type and manufacturing process [3], nevertheless it was not described in its native state yet. Study of inner part as well as surface morphology of PEC capsules using classical SEM or cryo‐SEM can be misleading due to requirement of dry resp. freeze sample. The aim of this work is in‐situ study of internal structure of PEC capsules in fully wet state and demonstration of state of matter of PEC capsules core.

PEC capsules has been produced by air‐stripping nozzle via polyelectrolyte complexation (20 min) of sodium alginate and cellulose sulphate (CS) as polyanions, poly(methylene‐co‐guanidine) as a polycation, CaCl
2
as a gelling agent and NaCl as an antigelling agent [1] without the use of a multiloop reactor. Due to the high beam sensitivity of samples and its relatively big size (800 μm in diameter), a combination of our published method [4] and special improvement of our ionization detector of SE were used. The gentle and slow sample chamber pumping procedure [4] and our ionization detector of SEs [2] (beam current up to 40 pA) enhanced for larger field of view (850 μm) were combined Samples were observed in conditions of vapor pressure 684 Pa, stage temperature 2°C, humidity 97%, acc. voltage 20 kV and probe current 35 pA.

Fully wet and well preserved PEC capsule with visible surface microstructure is presented in Fig. 1A. PEC capsules are very sensitive to beam impact which was used to in‐situ disruption of outer shell. Afterwards the liquid core slowly rose by capillary action on the PEC capsules wall simultaneously with capsule collapsing due to its emptying, see Fig. 1B. Due to different temperatures between the sample and the Peltier cooling stage, the liquid core was dried and crystalized on the PEC capsule surface, see Fig. 1C. First results provide promising information leading to statement that the inner structure of this type of PEC capsules is viscous liquid.
A complex prokaryotic endomembrane system
Authors: Heimerl Thomas , Flechsler Jennifer , Wanner Gerhard , Rachel Reinhard
Published: December 2016

Compartmentation is generally considered a feature of eukaryotic cells. One exception in the “prokaryotic world” is the marine hyperthermophilic Crenarchaeon
Ignicococcus
that exhibits a large inter‐membrane compartment (IMC) between an inner (cytoplasmic) and an outer (cellular) membrane (CM and OCM) [1]. In addition,
I. hospitalis
supports the propagation of another archaeon ‐
Nanoarchaeum equitans ‐
on its surface [2]. Cryopreparation in combination with 3D methods (serial sectioning, FIB/SEM and electron tomography) enabled us to deliver a comprehensive insight into the anatomy of
I. hopitalis
and its contact to
N. equitans
. The 3D‐models obtained, reveal a highly complex and dynamic endogenous membrane system with putative secretory function: The IMC makes up ~40% of the whole cell volume on average, but in few cells, it can reach an extent much larger than the volume of the cytoplasm. In the IMC, elongated protrusions of the cytoplasm are present. Apparently, these structures can constrict from or fuse with the CM or themselves. We also observed interactions of these protrusions with the OM via macromolecular, cylindrically shaped complexes. All interacting structures are connected via thin filaments (~3‐6 nm in diameter), that span through the whole IMC and are presumably responsible for membrane dynamics. In addition, homologues in sequence and/or structure to eukaryotic proteins can be found in
Ignicoccus
, that are putatively involved in the system like their eukaryotic counterparts: small GTPases (Sar1/Arf like), Coatomer proteins, Sec61ß, proteins of the ESCRT‐III system, a tethering complex component (Bet3) and the ATPase CDC48/p97 [3, 4]. Since
Ignicoccus
belongs to the recently proposed TACK superphylum, that is considered a sister group of eukaryotes [5], it is also tempting to speculate about a prokaryotic origin of the eukaryotic endogenous membrane system. Regarding the contact of
N. equitans
to
I. hospitalis,
a fusion of cytoplasms of both organisms was revealed, providing an important complement and explanation to recent proteomic [4], transcriptomic [6] and metabolomic [7] studies on this inter‐archaeal system.
Investigating the loss spectrum of individual carbon nanotubes at high energy resolution in real and momentum space
Authors: Hage Fredrik S. , Ramasse Quentin M.
Published: December 2016

Over the last quarter of a century Electron Energy Loss Spectroscopy (EELS) has proved itself as an excellent tool for investigating the plasmonic [1‐5] and electronic [1, 3, 4] response of carbon nanotubes: either by attaching a spectrometer to a Scanning Transmission Electron Microscope STEM [4, 5] or using a purpose built stand‐alone spectrometer [1‐3]. While STEM‐EELS provides superior spatial resolution to that of a stand‐alone spectrometer, it was not until recent improvements in electron source monochromation that the energy resolution of the two techniques became comparable. This was demonstrated by Sato and Terauchi [4] who used TEM –EELS to identify peaks in the loss spectrum of individual CNTs attributable to inter‐band transitions between van Hove singularities (vHs) in the CNTs' electronic density of states.

As an extension of the work of Sato and Terauchi [4], the present study is focused on the spatial and momentum dependence of the loss spectrum of individual CNTs. Fig. 1A shows loss spectra acquired from the single walled CNT in Fig. 1B using both a penetrating (1) and an aloof beam geometry (2), (3). The spectra in Fig. 1A are primarily characterised by peaks attributed to vHs (black arrows) [1, 3, 4], and, the π and π+σ plasmon resonances [1‐5]. The apparent red‐shift of the two plasmon peaks with increasing distance to the tube centre is consistent with literature [5]. Note the lack of a comparable red‐shift for the “vHs peaks” as well as a significant change in fine structure of the high energy shoulder of the π plasmon peak.

Resolving the CNT loss spectrum in momentum space allows for access to information not readily available in real space. Specifically, the momentum resolved spectra in Fig. 1C reveal that the vHs peaks are non‐dispersive (no peak shift with increasing momentum transfer), consistent with a reported measurement of a “bulk” sample of purified single wall CNTs [1]. Furthermore, it is shown that the “π peak” comprises two distinct plasmon modes: “π
1
“ and “π
2
”. The π
1
peak is non‐dispersive, thus indicating confinement perpendicular to the CNT axis, while the π
2
peak is dispersive, which in turn indicates significant plasmon propagation along the CNT axis [2, 3].
Analysis of
GaAs
compound semiconductors and the semiconductor laser diode using electron holography, Lorentz microscopy, electron diffraction microscopy and differential phase contrast
STEM
Authors: Sasaki Hirokazu , Otomo Shinya , Minato Ryuichiro , Yamamoto Kazuo , Hirayama Tsukasa , Yamasaki Jun , Shibata Naoya
Published: December 2016

In order to develop and manufacture semiconductor devices which are key components of the optical telecommunication products, such as the semiconductor laser diode, it is essential to confirm whether it is manufactured as designed. Electric potential distributions of the semiconductor devices are designed in nanoscale, so two dimensional methods to evaluate the electrical potential in the semiconductors with a high spatial resolution are necessary for product management. The observation of the gallium arsenide (GaAs) model specimen was carried out by using the electron holography and Lorentz microscopy [1].

Lorentz images and intensity profiles are shown in FIG 1 (a)‐(f). The p‐n junctions are clearly seen in both the 0.6 mm under‐focused and over‐focused images, but hardly any interfaces of different dopant concentration can be observed in the images. FIG 2 shows the electron holographic reconstructed phase image. The p‐ and n‐type regions are clearly seen as areas of dark and bright contrast, and some differences in the changing dopant concentrations can also be seen.

A phase image of semiconductor laser diode by the electron holography is shown in FIG 3 [2]. In FIG 3(a), the interface region is approximately 5 μm. And the spacing between interface fringes is approximately 30 nm. Next, in order to observe the pn junction near the active layer in a high spatial resolution, the photograph was taken by changing the interference fringes conditions. The expanded phase image of a part of FIG 3(a), surrounded by a dotted line, is shown in FIG 3(b). Since the interference region is approximately 1.5 μm, and the interference fringe spacing is 5 nm, the spatial resolution is approximately 15 nm. As can be recognized from the phase image, we can understand that more detailed structure can be observed in the higher spatial resolution in comparison with the phase image in FIG 3(a). Here, the designed location of the pn junction was positioned at the dotted line, but it was found from the electron holography observation results that the pn junction did not exist in the original position. This semiconductor laser diode could not have the expected output characteristics. The structural defect of the pn junction, found out in this observation, is considered to be the cause.

For other semiconductor electric voltage evaluation methods by TEM, electron diffraction microscopy [3] which is one method of phase reconstruction method, differential phase contrast [4] (DPC) which is one method of STEM are also effective and possible to be utilized complementarily with the electron holography. We will discuss about these methods applied for semiconductor in this presentation.
3D
Elemental and interdependent reconstructions based on a novel compressed sensing algorithm in electron tomography
Authors: Printemps Tony , Bernier Nicolas , Robin Eric , Saghi Zineb , Hervé Lionel
Published: December 2016

Electron Tomography (ET) is a key technique to perform 3D characterization at the nanometer scale [1]. 2D projections at different tilt angles are first acquired in an electron microscope, then an inversion algorithm is used to reconstruct the 3D volume of the sample from the dataset. Classically, ET is performed in a HAADF STEM mode in materials science leading to 3D Z‐contrast reconstructions. 3D elemental mapping based on EELS or EDS acquisitions is also possible in reconstruction theory [2]. Yet, reconstruction theory needs several hundreds of projections and 2D chemical mapping needs an important acquisition time and electron dose, therefore 3D elemental mapping is challenging. Nowadays, microscopes improvements limit the acquisition time of 2D chemical mapping. Moreover, powerful state‐of‐the‐art reconstruction algorithms make possible the reconstruction from a limited dataset of a few dozens of projections only. As a consequence 3D elemental mapping is now possible with a reasonable acquisition time of a day or less.

New reconstruction algorithms add prior knowledge on the object to compensate for the lack of information due to limited number of available projections. The prior knowledge can be a limited number of possible grey levels in the reconstruction to perform discrete tomography [3]. This correspond to a limited number of known materials in the sample. In the case of Compressed Sensing (CS) algorithms [4], the prior knowledge is a sparsity of the object expressed in a particular basis. A special case of CS reconstruction is the use of the gradient sparsity of the object to perform Total Variation Minimization (TVM) algorithms [5]. In that case, objects constant by parts are preferably reconstructed.

We propose a mixed approach suited for EDS acquisition. That mixed approach combines both projection denoising [6] and a TVM based algorithm that uses the reconstructions of each element all together. This new approach leads to higher reconstruction accuracy since a new kind of prior knowledge is used. Indeed, reconstructions of different elements should not be independent since a variation of an element is most of the time correlated to a variation of at least another element. The algorithm will be introduced. Simulations using projections with high Poisson noise and strong misalignment will be used to show the accuracy of our approach. Experimental results for a GaN‐TiAl intermetallic sample in EDS tomography will also be presented.

This work was supported by the French “Recherche Technologie de Base” (RTB) program. The authors acknowledge access to the nanocharacterization platform (PFNC) at the Minatec Campus in Grenoble. The authors thank Alphonse Torres from CEA Leti for providing the intermetallic specimen.
Improvement of
3D
atom probe tomography reconstruction integrating transmission electron microscopy information
Authors: Mouton Isabelle , Estivill‐Stroud Robert , Grenier Adeline , Gregoire Magalie , Juhel Marc , Barnes Jean Paul
Published: December 2016

We propose to improve atom probe tomography (APT) reconstruction methods to increase the reliability and the accuracy of the resulting 3D volumes. Currently, 3D reconstructions are done iteratively atom by atom, to convert the ion sequence (
#N
) and the detected position (

X
D

,

Y
D

) into atomic coordinates (
x,y,z
). To obtain a more realistic reconstruction, a better estimation of the main reconstruction parameters (e.g. image compression factor, detection efficiency, evolution of the tip radius) is required [1].

Some techniques have already been developed in order to estimate the reconstruction parameters. Those calibrations are based on voltage curve, tip image, field ion microscopy or desorption images. Most of these techniques have been shown to give accurate results on homogenous or metallic materials (in this case, the crystallographic pole or atomic planes can easily be observed) [2]. Unfortunately, these techniques are poorly suited for semiconductor materials, since the projection laws and the physics of field evaporation affect the reconstruction parameters, especially in the case of multiphase materials where evaporation fields are different from one phase to another.

In this study, we aim to correlate the information obtained by transmission electron microscopy (TEM) with atom probe tomography to improve the current reconstruction model. We focused on high‐K multilayer materials where the evaporation field is very different between each layer. As we can see on figure 1, the original sample contains flat and chemically well‐defined interfaces, whereas those interfaces are strongly distorted (figure2.a) when a classic reconstruction algorithm (with cone angle consideration) is used. This distortion comes from the assumption that two atoms arriving one after the other on the detector were close to one another in the tip, which is not the case in wide field of view APT.

In our model, the reconstruction is performed by dealing separately with different (and previously defined) areas of the detector surface. The ions are labeled independently in every sub‐detector, allowing different reconstruction parameters for each subdetector and therefore a better match of the theoretical thickness of every layer. The new reconstruction (figure 2.b) shows homogenous atom density, flat interfaces and more accurate layer thicknesses, making the chemical quantification more reliable. This study could be extended to 3D objects, where the microstructural features observed in TEM could be used to constrain the resulting APT volume.

This work has been funded by the French ANR Recherche Technologique de Base (RTB) programme. The experiments were performed on the Nanocharacterisation platform (PFNC) at MINATEC.
Structural, chemical and strain features of misfit dislocation cores in ultrathin
La0.7Sr0.3MnO3
epitaxial films deposited on
LaAlO3
Authors: Bagués Núria , Santiso José , Esser Bryan D. , Williams Robert E. A. , McComb David W. , Konstantinovic Zorica , Pomar Alberto , Balcells Lluís , Sandiumenge Felip
Published: December 2016

Heteroepitaxial interfaces in thin film complex oxides have attracted considerable attention in recent years due to their influence on the physical properties of these materials, in particular due to the possibility of tuning bulk functional properties [1]. The most common strain relaxation mechanism between lattice mismatched heterostructures is the formation of misfit dislocation arrays at the interface. These misfit dislocations play an interesting role as they can form self‐organized patterns on the nanometre scale which can behave differently from bulk material [2]. An understanding of the structural and chemical consequences associated with the strain fields of dislocations at oxide interfaces is important as they may determine the functionality of these oxides in ultrathin films and multilayers.

In this work, misfit dislocations in epitaxial films of La
0.7
Sr
0.3
MnO
3
(LSMO), a half‐metal ferromagnet, grown on [001] LaAlO
3
(LAO) single crystal substrates were investigated. A detailed study of atomic‐scale structural and chemical changes associated with the strain field of dislocations was performed using aberration‐corrected scanning transmission electron microscopy (STEM) combined with atomic resolution spectroscopy techniques; electron energy‐loss (EELS) spectrum imaging and energy dispersive x‐ray (EDS) spectral mapping. Special attention was paid to ultrathin films of only a few nanometers thickness where the strain field of the dislocations affects surface topography and current [3].

A STEM high angle annular dark field (HAADF) of a cross‐section of a 7nm film exhibiting dislocated interface is shown in Figure 1a, where spacing between dislocations around 20 nm can be observed. A STEM‐HAADF image of the dislocation core structure with the Burgers circuit yielding a Burgers vector bx = a
LAO
[100], parallel to the interface, is shown in Figure 1b. The lattice strain maps (Figure 1c), taken from the experimental images using the Geometrical Phase Analysis (GPA) method [4], show core splitting in two partials, along with compressive and tensile regions extending into the substrate and the film, respectively. Spectroscopy analyses of cross‐sections reveal a chemically rough interface between the substrate and film and show that the dislocations are not located at the interface but one or two unit cells above the interface with the substrate. Analysis of the EELS spectrum images suggest that the lanthanum composition at the vicinity of the dislocation core is enhanced (Figure 2).

These results provide an insight into how the intrinsic strain associated with a defect, in this case misfit dislocations, may produce chemical changes which may be useful in the development of ordered functional patterns in complex oxide thin films.
Three‐dimensional visualization of Tick‐borne encephalitis virus‐cell interactions
Authors: Bily Tomas , Palus Martin , Vancova Marie , Ruzek Daniel , Nebesarova Jana
Published: December 2016

Tick‐borne encephalitis virus (TBEV) is the etiological agent of Tick‐borne encephalitis, a serious neurological human infection. The endemic region is Europe and Asia with more than 10,000 clinical cases every year. We used electron tomography (ET) technique for visualization of neural cells infected with TBEV prepared by high‐pressure freezing followed by freeze substitution and embedded into epoxy resin [1, 2]. Images of three dimensional volume of the section enables better to understand alterations of neural cells caused by TBEV than 2D Transmission electron microscopy (TEM) projection images, where the visibility of structures depends crucially on section thickness. Here, we showed how to 3D visualization influenced an interpretation of obtained TEM results. Next, we discuss our experience with settings of optimal imaging conditions, appropriate resolution given by Crowther criterion [3], elongation factor [4] and necessity of using of the single or dual tomography. ET was done like a single/dual axis using JEOL 2100F equipped with high tilt stage and Gatan camera Orius SC 1000 controlled with Serial EM software. Tomograms were aligned and reconstructed using IMOD software package. 3D models were generated by manually masking of the area of interest by means of IMOD or Amira.

Our results depicted mainly changes in organisation of rough endoplasmic reticulum (RER) induced by TBEV and a formation of virus‐induced sub‐compartments of RER called smooth membrane structures including a presence of pores. We found that cisterns of RER are often arranged into two tightly apposed cisterns. Depending on the type of host cells, used TBEV strains and length of infection, we described proliferation of RER with harboured sites of replication (3 days post infection) which are reorganised during the extensive infection stress (12 days post infection) into whorls with central part having features of an autophagosome [2]. In primary neurons infected by TBE strain Neudoerfl, virus‐induced tubule‐like structures (18 – 22 nm in diameter) were frequently observed inside of reorganised RER. Most of these structures were connected to the TBEV and run either in parallel lines or in different directions. In several cases, these tubule‐like structures were surrounded with other tubules of 43.8 ± 4.3 nm (N = 7) in diameter [2]. Finally, we imaged vacuoles containing individual virions with nucleocapsids associated with host microtubules [2].
The comparison of grain boundaries in a nanostructured austenitic stainless steel annealed conventionally and under high hydrostatic pressure
Authors: Krawczynska Agnieszka , Gierlotka Stanisław , Palosz Bogdan , Lewandowska Malgorzta
Published: December 2016

Nanostructured metals and alloys are known to behave differently during annealing comparing to their micrograined counterparts. They exhibit lower thermal stability and often abnormal grain growth occurs. In the present work, the combination of severe plastic deformation processing followed by subsequent conventional annealing and annealing under high hydrostatic pressure was applied. Samples were subjected to the heat treatment at 700°C for 10 minutes either under atmospheric or hydrostatic pressures of 2 or 6 GPa. The recrystallization process is investigated in TEM observations using HD2700 Hitachi. In samples after deformation one can notice a high density of nanotwins inside nanograins (Fig 1 and 2). In samples after annealing nanograins appear, the smallest of about 50 nm in the diameter (Fig 1 and 3). The main question refers to the differences in the microstructure after conventional annealing and annealing under high pressure. At this stage, one can predict that diffusion processes are suppressed by high pressure. The question arises as to what information about the grain boundary migration mechanisms can be drawn from high pressure studies. There are only a few papers where influence of high pressure on the grain growth [1] and migration of individual grain boundaries [2] was studied. It was found, that the activation energy and activation volume for grain boundary migration in aluminium bicrystals are larger than that for grain growth in aluminium polycrystals and depend on the grain boundary crystallography. Moreover, the high pressure had greater impact on the movement of high‐angle grain boundaries than low‐angle grain boundaries [3]. These theories refer to microstructural materials and they will be verified in the case of nanostructured materials.
Atoms in Motion: Electron beam induced dynamics in experiment and simulation
Authors: Knez Daniel , Volk Alexander , Thaler Philipp , Ernst Wolfgang , Hofer Ferdinand
Published: December 2016

With the availability of aberration‐correctors, scanning transmission electron microscopy (STEM) has become one of the most versatile tools for the characterization of nanostructured materials. In combination with electron energy loss spectrometers (EELS) and energy dispersive X‐ray (EDX) detectors in principle chemical information can be extracted at atomic resolution. Due to the high current densities occurring in a highly focused electron beam, however, STEM has to be classified as destructive method in many cases.
[1]
This is especially true for small metallic clusters with a high percentage of low‐coordinated atoms, which are interesting in particular for heterogeneous catalysis.

In this work electron beam induced dynamics was studied via transient STEM HAADF image sequences for different nanostructured material systems like bimetallic alloys and clusters. All clusters were synthesized by means of the superfluid helium droplet method, which guarantees their high purity.
[2]
Furthermore, we present a methodology for the simulation of elastic electron damage processes using an algorithm based on molecular dynamics and Monte Carlo techniques.
[3]
Figure 1a shows simulation results for a bimetallic AuAg‐cluster which exhibits selective Ag‐sputtering and a rapid change of morphology during electron radiation. In Figure 1b HAADF image time series of an Au‐CrO
x
core‐shell nanowire can be seen. Due to electron beam enhanced diffusion of Au atoms in CrO
x
, significant morphology changes of the Au core can be observed after a few seconds of electron beam exposure, even at 60 keV electron energy.

Deeper understanding of electron beam induced dynamics can not only help to develop strategies to prevent sample damage, which is important especially for analytical and quantitative STEM analysis. Electron induced motion of single atoms on the surface or inside crystalline materials may also be useful to estimate surface energies, analyse defect generation and investigate diffusion processes.
[4,5]
Figure 1c shows the electron beam mediated diffusion of Au atoms on and inside an Al‐matrix, for instance.

Moreover, electron beam induced chemical reactions can be used to tailor nanostructures with properties not obtainable otherwise. We show how Ni clusters transform into single crystalline, hollow and toroidal NiO clusters, consisting of less than 3000 Ni atoms, during electron exposure (see Figure 1d and e). The transformation is mediated by adsorbed water and driven by a nanoscale Kirkendall effect. We studied the oxidation process via HAADF time‐lapse series and EELS analysis.
Using the Deben Enhanced Coolstage for in‐situ
(E)SEM
freeze‐drying & high resolution imaging of polymer latices
Authors: Tkaczyk Marzena , Dragnevski Kalin , Edwards Gary
Published: December 2016

A
‘simple
’ methodology, combining the use of Environmental Scanning Electron Microscopy (ESEM) and the recently introduced DEBEN Enhanced Coolstage was successfully developed and not only used to study dynamic processes, e.g. different stages of latex film formation, but also for high resolution imaging of
‘freeze‐dried’
structures. By using the extended temperature capability of the DEBEN Enhanced Coolstage (−50 to +160
°
C) it is possible to easily convert any (E)SEM chamber into what essentially can be described as a freeze‐drying facility. By using this method it is also possible to preserve the structure and features of the studied system with minimum shrinkage and distortion and in the case of polymer latices at a desired stage of film formation. Moreover, specimens can then be readily imaged, without the need of conductive coatings and at much lower chamber gas pressures, thus minimising the beam skirting effects and allowing higher resolutions to be achieved. In this study this is clearly demonstrated (
Figure 1 & 2
) using a model poly‐methyl methacrylate based latex dispersion; under ‘wet’ (partially dehydrating) conditions, whilst the individual particles can be seen it is difficult to distinguish them and any associated boundaries and/or arrangements, whether cubic or hexagonal; better images, as shown can be obtained from air‐dried specimens, but this limits the time‐frame of possible observations. However, subsequent freeze drying, as expected, resulted in the observation of a well‐defined and more stable (in imaging terms) structure; it was also possible to image individual particles and their interactions at much higher resolutions. It is strongly believed that the methodology can be applied to other material systems, including biologicals and pharmaceuticals.
Playing around with shape and composition of nanoparticles for various applications
Authors: Parlinska‐Wojtan Magdalena , Gruzel Grzegorz , Roga Elzbieta , Depciuch Joanna , Kowal Andrzej
Published: December 2016

Nowadays, nanoparticles with sizes between 2 to 50 nm become more and more popular, because they can be applied in various fields such as materials science, chemistry, catalysis, medicine or biology. In particular nanoparticles with fancy shapes gain a lot of attention, also because of the low‐cost synthesis methods. This study is focused on several types of catalytic nanoparticles (NPs), silver nanoparticles synthesized using green chemistry methods and in particular on their morphological and chemical analysis using HR(TEM). Three‐dimensional (3D) catalysts [1] being promising for application in fuel cells were studied. These nanoparticles have a dodecahedron shape with Pt skin at the edges and a Ni core, Figure 1(a). When etching away the core, the remaining empty Pt frame offers a much larger active surface compared to spherical nanoparticles. The morphology of these 3D PtNi particles strongly depends on the synthesis parameters allowing fabricating dodecahedrons, Figure 1(a), core‐shell or even dendritic structures, Figure 1(b).

SnO
2
nanoparticles are excellent supports for noble metal NPs, as their combination exhibits good catalytic activity towards ethanol oxidation reaction [2]. Various synthesis routes including polyol and microwave assisted methods allowed producing different SnO
2
NPs, Figure 2(a). The break of the C=C bond in the ethanol molecule occurs at the interface between PtRh and SnO
2
particles, Figure 2(b). Therefore their physical contact is imperative for the effectiveness of the catalyst. Structural aspects and chemical analysis by TEM characterization techniques of the PtRh/SnO
2
/C catalysts were analyzed.

Green synthesis method using camomile extract was applied to synthesize silver nanoparticles in order to tune their antibacterial properties merging the synergistic effect of camomile and Ag [3]. Scanning transmission electron microscopy (STEM) revealed that camomile extract (CE) consisted of porous globular nanometer sized structures, which were a perfect support for Ag nanoparticles, Figure 3(a). The Ag nanoparticles synthesized with the camomile extract (AgNPs/CE) of 7 nm average size, were uniformly distributed on the CE support, Figure 3(b). The EDX chemical analysis showed that camomile terpenoids, Figure 3(c) act as a capping and reducing agent being adsorbed on the surface of AgNPs/CE, Figure 3(d), enabling their reduction from Ag
+
and preventing them from agglomeration. Antibacterial tests using four bacteria strains, showed that the AgNPs/CE performed five times better compared to CE and AgNPs/G samples, reducing totally all the bacteria in 2 hours, Figure 4.
Characterization of Branched Carbon Nanostructures
Authors: Malik Sharali , Nemoto Yoshihiro , Hongxuan Guo , Katsuhiko Ariga , Hill Jonathan
Published: December 2016

Branched carbon nanostructures such as branched‐Multi‐Walled Carbon Nanotubes (b‐MWCNTs, Fig. 1) are exotic types of carbon nanostructures whose technological potential have not yet been fully explored. Although MWCNTs have been used to improve the properties of composite materials, there are currently still two main problems remaining to be solved before MWCNT/composite materials can realize their full potential:‐

(1) adequate dispersion of the nanotube‐reinforcement material, and

(2) strong enough interfacial bonding between the nanotube‐reinforcement elements and the composite matrix.

These problems can be addressed by utilizing branched‐carbon nanostructures as it is known (from theory and simulation experiments) that branched fibres greatly enhance interfacial bonding e.g. the ancient process of adding straw to mud to make stronger bricks. It is well known that, in the case of carbon nanotube networks, junction resistance is the dominant limiting factor and so, a network of branched‐carbon nanostructures would significantly reduce this network resistance. . Therefore, in addition to potential improvements in composite applications, the electrical properties of networks made of branched‐carbon nanostructures could have major benefits to the existing commercial application of CNT/CNF reinforced composites in Conductive Static Dissipation (ESD) as well as potential use in Supercapacitors, Solar Cells and Li‐Ion batteries.
In‐liquid
TEM
to visualize multimerization and self‐assembly of
DNA
functionalized gold nanoparticles
Authors: Keskin Sercan , Besztejan Stephanie , Kassier Guenther , Manz Stephanie , Buecker Robert , Riekeberg Svenja , Trieu Hoc Khiem , Rentmeister Andrea , Miller Dwayne
Published: December 2016

Base‐pairing stability in DNA‐gold nanoparticle (DNA‐AuNP) multimers along with their dynamics under different electron beam intensities was investigated with in‐liquid transmission electron microscopy (in‐liquid TEM) using custom developed silicon nitride based liquid cells. Multimer formation was triggered by hybridization of DNA oligonucleotides to another DNA strand (Hyb‐DNA) related to the concept of DNA origami. We analyzed the degree of multimer formation for a number of samples and a series of control samples to determine the specificity of the multimerization during the TEM imaging. DNA‐AuNPs with Hyb‐DNA showed an interactive motion and assembly into 1D structures once the electron beam intensity exceeds a threshold value. These findings indicate that DNA base pairing interactions are the driving force for
in situ
multimerization and DNA‐metallic NP conjugates provide excellent models to understand structure‐function correlation in biological systems with nanometer spatial resolution (Keskin et al., 2015, 10.1021/acs.jpclett.5b02075).
Structural Mechanism of Assembly and Maturation of the
HBs
Antigen
Authors: Deliot Aurelie , Nicolai Marie‐Claire , Buosi Vanessa , Thion Laurent , Sepulcri Patricia , Nemecek Daniel
Published: December 2016

Hepatitis B surface antigen (HBsAg) is overexpressed in great excess during hepatitis B (HBV) infection in the form of noninfectious (DNA‐free) subviral particles. These particles greatly outnumber mature virus particles (virions) and presumably function as decoys for the immune system to facilitate infection by the DNA‐containing virions. These properties are exploited in the current HBV vaccine, in which recombinant HBsAg is used as a potent antigen capable to induce a strong immune response and long‐term immunological memory. Several studies have implicated that HBsAg consist of a lipid bilayer with embedded HBs subunits [1‐3]. The particles appear as pleomorphic spheres with an average diameter of ~23 nm and an empty internal cavity. Particles produced for the vaccine contain monomeric HBs subunits that subsequently cross‐link via formation of disulfide bridges within the HBsAg particles.

We employed cryo‐electron tomography to image individual HBsAg particles in their native environment at different times of maturation. Reconstructed 3D tomograms showed different kinds of HBsAg particles that could be classified into three groups: (i) small spherical particles of ~16 nm in diameter, (ii) spherical particles of ~25 nm in diameter with an internal cavity and (iii) elongated oval particles with an internal cavity of ~20 nm diameter and 25‐30 nm length. The electron‐dense shell of HBsAg particles is about 5 nm thick and likely represents the lipid bilayer. The shell contains short protrusions with higher density (Figure 1) that are spaced 5‐6 nm apart and likely represent lipid‐embedded HBs subunits.

Parallel measurements of proton NMR spectra indicated significant structural changes in protein backbone and aliphatic side chains of lipids during HBsAg particles maturation. Those variations support a decreased flexibility and suggested more rigid structure of the lipid bilayer during HBsAg maturation [4].

We analyzed size distribution of HBsAg particles and densities corresponding to HBs subunits within the particles to assess the molecular architecture of particles during maturation. The results provide insights into how structural changes in the lipid bilayer and cross‐linking of HBs subunits affect the molecular architecture of HBsAg particles that is directly related to immunogenicity of the HBV vaccine.

This research has been funded by and performed at Sanofi Pasteur.
Characterization of multicomponent
Al
alloys by
TEM
,
HAADF‐STEM
,
EELS
and
DFT
Authors: Mørtsell Eva , Andersen Sigmund , Marioara Calin , Røyset Jostein , Friis Jesper , Holmestad Randi
Published: December 2016

Light, environmentally friendly and recyclable materials are of increasing importance, such as in the automotive industry where the age‐hardenable Al‐Mg‐Si alloys are of high interest. By understanding better how microstructure responds to changed processing or composition, costs can be cut and macroscopic properties tailored for particular applications. For example, by reducing the solute amount a softer material will allow higher extrusion speeds, however, on the expense of material strength. Recently, it was shown how adding back a lower at% of ‘exotic’ elements like Li, Cu, Ag and Ge compensates such strength loss [1]. Age hardening is ascribed to dislocation resisting strain‐fields set up in the aluminium during nucleation and growth of the metastable, nanoscale, semi‐coherent precipitate needles in the three <100> Al directions [2]. The replacement elements change precipitate structure and growth conditions.

Precipitate statistics based on transmission electron microscopy (TEM) can elucidate how material strength is related to precipitate number densities, sizes and volume fractions; see example a bright field TEM micrograph in Fig. 1 (a) used for this purpose. The elemental contrast in probe Cs corrected high angle annular dark field scanning TEM (HAADF‐STEM) greatly assists structural characterization of individual precipitate cross sections [3], enabling identification of precipitate type and the composition of individual atomic columns. See example of a
β’’
precipitate in Fig. 1 (b).

Because elements with similar atomic number (Z) express very small intensity differences, electron energy loss spectroscopy (EELS) elemental mapping has been applied to aid resolution. It became clear that EELS in combination with HAADF‐STEM can resolve the hexagonal network of Si columns [4] well, see Fig. 2. It was also found that a significant proportion of the other atomic columns were mixed.

A pressing matter in material design is enhanced control with precipitate characteristics which vary strongly with alloy composition and processing. Density functional theory (DFT) simulations have a great potential for broadening the understanding concerning precipitate nucleation, growth and final microstructure, and how they are connected. Here we have investigated binding between solute atoms and to vacancies, along with volume misfits (see Fig. 4) in the Al lattice, in a venture to relate these parameters to precipitation.