bluuebunny/crossref_metadata_2025 huggingface dataset:
EDS/EBSD
studies and
HR‐EBSD
pattern analysis on pre‐
I
nca ceramic fragments recovered during
S
an
J
osé de
M
oro Archaeology Program
Authors: Dietrich Dagmar , Nolze Gert , Mehner Thomas , Nickel Daniela , Lampke Thomas
Published: December 2016

Pre‐Inca civilizations like the coastal cultures Moche and Nazca (Early Intermediate) and the inland culture Wari (Middle Horizon) were agrarian societies which supported indigenous elites of impressive wealth, power, and organization. With the expansion of the Wari Empire, the polychrome style and technique of Nazca propagated to the other cultures [1, 2]. High status burials, most of the Late Moche Fine Line ceramics and a large corpus of ceramics with Wari‐derived decoration have been recovered in San José de Moro since 1991 [1]. The degree of transfer of procedures in this highly interactive scenario is of special interest: is there a limitation to decoration or is it adopted by the local potters also regarding the formulation of the ceramic bodies? In this context the relative amount, size and type of incorporated non‐plastic inclusions as temper are important.

Two kinds of ceramic artefacts from Peru were compared: fragments of a baker in Wari Viñaque style (Wari, Ayacucho, Peru [3]) and a canteen in Mochica Polícromo style (San José de Moro, Jequetepeque valley, Peru [1]). Bulk composition and elemental distribution were analyzed by combined scanning electron microscopy and energy‐dispersive X‐ray spectroscopy on cross‐sections (Fig. 1). Analyzing appropriate regions of interest in the element maps evidenced composition differences of the fired clay and the mineral inclusions (Fig. 1, 2). On principle, electron backscatter diffraction is appropriate for mineral phase analysis of the artifacts, but apart from quartz the crystallographic identification by automatic indexing commonly fails due to the micro granular aspect and the porosity of the body, weak diffraction patterns and varying composition of the feldspars. Image analysis of the Kikuchi pattern quality maps (Fig. 1) reveals the fractions of silty crystalline inclusions and of micro‐pores in the clayey matrix. However, the clear crystallographic identification of non‐plastic inclusions was possible by setting the electron beam at distinct crystals of interest, averaging accumulated patterns and comparing the resulting analysis with dynamical pattern simulation thereby identifying mostly quartz, ilmenite, magnetite, albite, epidote and kaersutite (Fig. 3), sanidine and apatite. Thus additional indications for the use as well as the provenience of the raw clays, the formulation of the ceramic material and the firing conditions can be provided.
Adiabatic shear loading in thermal spray coatings studied by
EBSD
Authors: Dietrich Dagmar , Cinca Nuria , Sokolowski Pawel , Pawlowski Lech , Guilemany Josep , Lampke Thomas
Published: December 2016

A basic principle during the formation of thermal spray coatings is the phenomenon of “adiabatic shear instability” which influences splat formation, bonding or oxidation of intersplat regions, grain refinement and dynamic recrystallization as result of thermal softening gaining over work hardening upon the impact of accelerated particles of the spray feedstock. Deposits of uniform composition, low porosity and suitable bonding to the substrate are obtained by proper adjusting the window of deposition parameters with respect to the occurrence of adiabatic shear instabilities. However, a lack of knowledge on how low‐ductile intermetallic compounds and hard oxide particles behave at high strain rates obtained during the thermal spray process has to be stated.

The present work shows the interfacial features of several coatings obtained at typical spray parameters. The examples include coatings formed from combinations of ductile or hard particles on hard or ductile substrates [1‐4]. Electron backscatter diffraction (EBSD) was used to show the influence of adiabatic loading on the microstructural evolution. Kikuchi pattern quality maps (Fig. 1a‐d) provide information about dynamic recrystallization and the occurrence of unchanged spherical particles, fragmented shells as well as particles agglomerated by sintering. EBSD kernel average misorientation (KAM) is effective in resolving grain regions subjected to deformation. KAM maps of the next and next‐next neighbor pixels (Fig. 2a‐d) show shear bands and dynamic recrystallization to a different degree in high‐ductile aluminium (a) and low‐ductile iron aluminide (b); hard layers of zirconia (c) and alumina (d) confirm expectedly marginal misorientation, but clearly indicate that the impinging particles induce different alterations of the steel substrates subjected to different pretreatments. Shear bands have been formed on the hills of the laser‐cut structure; dynamic recrystallization occurred on top of the highly disturbed sandblasted surface.
Monitoring Cell Death in Real‐Time/Time‐Lapse Studies
Authors: Edward Roy
Published: December 2016

Personalised medicine, chronic exposure drug toxicity and environmental contaminants amongst others have created the demand for in vitro assays which are more physiologically relevant. One aspect of this may be to run assays for many days and monitor them in real‐time or time‐lapse mode. Therein, it can be useful to assess the general cell survival or perhaps a specific cell death pathway in the context of the treatment or insult under observation.

Depending on the sample under analysis, to date, this can be done by either marking the cells that remain functionally competent or measure release of ATP at a bulk level. It would be preferable if, conversely, only dead/damaged/apoptotic cells were marked in a binary manner, with a convenient and spectrally separated emission signature and with specificity for a predictable intracellular target such as gDNA, and cell‐by‐cell.

To explore this need a novel far‐red DNA binding viability probe, DRAQ7, has been developed. It has been shown to have undetectable toxicity in long‐term / real‐time cell based assays as validated in recent publications (Akagi et al., 2013, Marciniak et al., 2013, Wang et al., 2015, Liang et al., 2015, and internal data) including ultra‐sensitive bioassays for DNA intercalators, ex‐plant tissue culture and nano‐particle toxicity, time‐lapse apoptosis assays and importantly in the presence of toxicants / anti‐cancer compounds. Thus, cells can be exposed to it at any stage of an assay to permit realtime monitoring of loss of membrane integrity (in apoptosis, death). Being DNA specific it allows monitoring cell‐by‐cell while its spectral properties mean it can be incorporated into multi‐colour flow cytometry experiments, or with Hoechst 33342 or CyTRAK Orange (for simple cell health assays) or with mitochondrial membrane potential probes such as TMRM.

DRAQ7 is truly cell impermeant yet retains the DNA targeting and far‐red fluorescence of the parent DRAQ chromophore. Accordingly, it likewise can be used on HCS imaging platforms, fluorescence microscopes, cytometers and sorters. Its spectral properties (long wavelength) are particularly suited to penetrative imaging of multicellular structures and thick ex‐plant tissue sections.

The presentation will focus on the deployment and application of DRAQ7 to demanding real‐time and 3D micro‐tissue assays including patient‐derived samples that enable strategies for personalised medicine, underpinned by core performance data that define its unique properties as a cross‐platform imaging probe for cell viability.
Analysing
J
an
S
teen's pigments using
SEM‐EDX
quantitative
X
‐ray mapping
Authors: Haswell Ralph , Wouters Jesse , Meloni Sabrina
Published: December 2016

The Seventeenth Century Dutch artist Jan Steen is famous for his humorous genre scenes in which he treats life as a vast comedy of manners. However, for such a renowned painter, there is surprisingly little technical information about his paintings. In an effort to correct this deficiency we have carried out a detailed technical examination of the paintings of Jan Steen held at the Mauritshuis as part of the Partnership in Science cooperation between Shell Nederlands B.V. and the Mauritshuis. An important part of this work was the characterisation of paint samples using SEM‐EDX quantitative X‐ray mapping. Compared to measuring individually selected pigment particles this approach has a number of advantages, namely: (i) all particles are measured; (ii) intra‐particle details are discernible; and (iii) by using the spectral imaging method the complete data set is available for retrospective examination.

An example where this approach has proved particularly useful is in the study of Smalt. This is a cobalt containing potash glass that was used widely in Seventeenth Century European oil paintings as a blue pigment. The Smalt used in 12 Jan Steen paintings has been examined. Using quantitative X‐ray mapping we are able to clearly identify the Smalt particles by using a Silicon/Potassium overlay, as shown in Figure 1. It is also possible to determine the composition of each Smalt particle by extracting the X‐ray spectrum associated with each particle and quantifying using standardless methods. Using this approach made it possible to characterise the composition of over 350 Smalt particles. A summary of the results is shown in table I. These reveal that the composition of the Smalt used by Jan Steen did not vary significantly over the course of his career. In addition, by using the mapping approach it is possible to discern differences in the Potassium distribution within individual particles. For example, in Figure 1, a number of the larger Smalt particles have a higher concentration of Potassium in their core which shows up as a region of yellow in the false colour map. To show this variation more clearly a linescan of the Potassium net counts has been extracted from the data which reveals that there is approximately twice as much Potassium in the centre of the particle. In addition, the concentration is constant across most of the centre region of the particle. This could prove helpful in obtaining a more reliable estimate of the original Potassium concentration in these particles so that a better comparison can be made between the degraded and non‐degraded state of the Smalt.

In conclusion, this work shows that quantitative X‐ray mapping has a number of important advantages over measuring particles individually and, crucially, it is now possible to use this approach routinely because with silicon drift detectors it is takes minutes to collect high quality data as compared to the many hours needed with the previous generation of detectors.
How nanoparticles disturb the lipid bilayer vesicles
Authors: Er‐Rafik Meriem
Published: December 2016

Meriem Er‐Rafik*,(1),Khalid Ferji (2), Olivier Sandre (2), Carlos M. Marques (1), Jean‐Francois Le Meins (2), Marc Schmutz (1)

Institut Charles Sadron, Université de Strasbourg‐CNRS UPR 22, 67034 Strasbourg, France

Laboratoire de Chimie des Polymères Organiques (LCPO), Université de Bordeaux, CNRS, 33607 Pessac, France

Innumerous molecules and particles, from simply water to complex proteins or self‐assembled small liposomal carriers, can frequently interact with the cell membrane with possible modification on it. Despite a constant increase of the variety of new particles or molecular assemblies, due to rapid progress in nanotechnology, the molecular features determining how is the membrane behaviour with respect to a given molecule are not yet elucidated.

Here, we will present a new mechanism of the lipid bilayer of liposomes behaviour in presence of nanoparticles investigated by cryo‐electron tomography. Cryo‐electron microscopy is a relevant technique allowing not only to inspect the structure of the membrane, by resolving for instance the two leaflets of the bilayer, but reveals also geometric features of nanoparticles such as size and shape that play an important role for the potential interaction with lipid bilayer (fig. 1). Cryo‐electron tomography resolve in 3D space the relative positions of particles and membranes, providing insight into the interplay between particle‐lipid interactions and the ensuing bilayer transformations.
Oxidation of Carbon Nanotubes Using Environmental
TEM
and the Influence of the Imaging Electron Beam
Authors: Koh Ai Leen , Gidcumb Emily , Zhou Otto , Sinclair Robert
Published: December 2016

Carbon nanotubes (CNTs) can be used as field emission electron sources in X‐ray tubes for medical applications [1, 2]. In a laboratory setting, field emission measurements of CNTs are usually carried out in an ultra‐high vacuum system with base pressure of about 1E‐7 mbar or better. Under less stringent vacuum conditions, CNTs are found to exhibit lower emission currents and reduced lifetimes [3, 4].

Here, we report the direct study on the structural changes in CNTs as we heated and oxidized them
in situ
using an aberration‐corrected environmental TEM [5]. We established a protocol whereby heating and oxidation were performed without an imaging beam and changes on identifiable nanotubes were documented after purging the gas from the chamber, to ensure that they were due to the effect of gaseous oxygen molecules on the nanotubes, rather than the ionized gas species [5]. Contrary to earlier reports that CNT oxidation initiates at the end of the tube and proceeds along its length, our findings show that only the outside graphene layer is being removed and, on occasion, the interior inner wall is oxidized, presumably due to oxygen infiltrating into the hollow nanotube through an open end or breaks in the tube [5]. The CNT caps are not observed to oxidize preferentially [5, 6].

In the environment of an ETEM, interaction between fast electrons and gas leads to ionization of gas molecules and increased reactivity. It is very important to evaluate the results to determine or ameliorate the influence of the imaging electron beam. We found that there is a two orders of magnitude difference in the cumulative electron doses required to damage carbon nanotubes from 80 keV electron beam irradiation in gas versus in high vacuum [7]. We anticipate that experimental conditions that delineate the influence of the imaging electron beam can be established, which will enable us to study the CNT field emission process
in situ
in an ETEM.
STEM
electron tomography of titanium oxide nanotubes surface functionalized by Pt nanoparticles
Authors: Andrzejczuk Mariusz , Roguska Agata , Pisarek Marcin , Lewandowska Małgorzata
Published: December 2016

The titanium oxide nanotubes have become a very attractive material with potential applications in biomedicine, photocatalysis, energy etc. Their properties depend mostly on morphology which is relatively easy to change by controlling the conditions of the anodization like the type of electrolyte used, the voltage and the time of anodization. There is a direct linear relation between the anodization voltage and the average diameter of the formed nanotubes, as the voltage increases the diameter of nanotubes also increases [1,2]. The possibility of the preparation of nanotubes with different size, shape and wall thickness leads to the control of their geometric surface area and specific surface area, which is an important parameter in the development of new substrates for example in heterogeneous catalysis. Nanotube surface functionalization with platinum nanoparticles is a way to fabricate active material for catalysis of oxidation reaction of methanol. Such nanostructured complex materials demand advanced methods for characterization and visualization of real structure, therefore application of TEM and electron tomography techniques is desired.

In this work titania nanotubes were obtained by electrochemical oxidation of pure titanium at voltage of 10 and 25V, that resulted in creation of TiO
2
nanotubes with 40 and 110 nm in diameter, respectively. After anodization the heat treatment was performed at 450
o
C for 1h to change amorphous structure of TiO
2
nanotubes into crystalline anatase structure. A suitable amount of Pt – 0.2 mg/cm
2
on the surface of the nanotubes was deposited using magnetron sputtering. FIB prepared specimens were analyzed in a Hitachi HD‐2700 dedicated STEM (Scanning Transmission Electron Microscopy).

Fig. 1 shows cross‐section SEM images of TiO
2
nanotubes with 0.2 mg/cm
2
Pt deposit on the top. The platinum nanoparticles tend to choose the edges of TiO
2
nanotubes and side walls. A high amount of Pt fills the interior of the nanotubes as shown in Fig. 1b. As nanotubes diameter increases from 40 to 110 nm the depth of deposition into nanotubes also increases (Fig. 1c). Morphology of prepared structures was characterized by scanning transmission electron microscopy tomography. This method provides three‐dimensional structural information at nanoscale based on two dimensional projections acquired at different tilt angles. High angle annular dark field (HAADF) imaging was used for 2D projections. The results have shown distribution of platinum nanoparticles inside the nanotubes. The variations in platinum content introduced into different diameter nanotubes were also examined. Segmented volume of nanotubes was analyzed in terms of specific surface area and volume fraction.
Birch pollen ‐ the key to unlock hidden cases of species hybridization
Authors: Anamthawat‐Jonsson Kesara , Karlsdottir Lilja
Published: December 2016

Normal
Betula
pollen grains are triporate, i.e. having three pores, whereas genetically abnormal or deformed grains are usually not. We collected samples of pollen from 92 individual
Betula
trees/shrubs growing in natural birch woodlands in Iceland. The trees were previously identified as being diploid (2n=28) dwarf birch
Betula nana
(31 plants) and tetraploid (2n=56) downy birch
B. pubescens
(39 plants), whereas 22 plants were found to be triploid (2n=42) hybrids of the two species [1]. The results [2] showed clearly that the two species mostly produced normal triporate pollen, whereas damaged and deformed grains were significantly more frequent among pollen samples from triploid hybrids. The most frequent type of deformity in pollen morphology was pollen with four pores instead of the normal three. Meiosis in the microspore mother cells was also examined and as expected the triploid plants had irregular meiotic figures and produced deformed microspores (unpublished). We therefore investigated the fertility of these triploid trees, by testing pollen viability and assessing seed germination. The results (unpublished) confirmed that the fertility of triploid hybrids was severely reduced. The good news is that triploid hybrids are not completely sterile, and a few individuals under study are even as fertile as the parental species can be. This discovery supports our botanical and molecular studies of introgressive hybridization in
Betula
[1, 3], whereby triploid hybrids serve as a bridge of gene flow across the two species via back‐crossing.

The knowledge that triploid birch hybrids produce abnormal pollen has been utilized in our search for past hybridization events in the Holocene vegetation history of Iceland. Samples from peat were collected in three locations in Iceland: Eyjafjördur (N), Grímsnes (SW) and Thistilfjördur (E). In all three places, periods of elevated proportions of abnormal
Betula
pollen were detected [4 ‐ 6]. By comparison to climate data from the Greenland Ice Core Project, the effect of climate on the birch woodlands can be seen. The hybridisation periods were found to be connected to the advance of woodland‐forming downy birch over dwarf birch habitat in warming climate. Such hybridisation may have taken place in most parts of northern Europe when woodland expanded in the beginning of the Holocene. In Iceland the climate stayed near the lower limits of birch woodland tolerance for most of the Holocene, repeatedly creating conditions that facilitated hybridization. With the warming of climate in the last few decades a new wave of birch hybridisation has started.
The complex structure of catalyst particles used in fluid catalytic cracking
Authors: Krumeich Frank , Diaz Ana , Menzel Andreas , Holler Mirko , Guizar‐Sicairos Manuel , Sanchez Dario Ferreira , Grolimund Daniel , van Bokhoven Jeroen , Shu Yuying , Cheng Wu‐Cheng
Published: December 2016

The refining of crude oil by conversion of its heavy fraction into gasoline and light olefins represents an important industrial process providing a valuable source for fuel and basic chemicals. The catalyst for this reaction, the so‐called fluid catalytic cracking (FCC), is a complex composite of multiple components, including zeolites, clay, and various minor additives with certain catalytic or structural functions. The many reaction and regeneration cycles during long‐term operation change the structure of the FCC particles, leading to a decrease of their catalytic activity. To understand this deactivation, it is essential to derive a three‐dimensional model of an individual catalyst particle, to quantify the porosity, and to identify metal deposition and other structural changes happening during the process. In addition to 3D imaging with high resolution X‐ray tomography [1], we here present the results obtained with different electron microscopy methods that were applied to gain information about the local structure and the elemental distribution with high resolution.

The commercially‐deactivated FCC catalyst studied here is a mixture of a La‐exchanged zeolite type Y, metakaolin clay, an aluminum silicate, and comprises almost spherical particles with diameters between ca. 50 and 100 micrometer (Fig. 1a). For the investigation of the particles' internal structure, cross‐sections were prepared. The spheres were embedded in a resin and the obtained cylindrical blocks cut into slices. For TEM and STEM investigations, these slices were mechanically thinned and finally ion‐milled till a hole in the center was generated [2].

SEM images of these cross‐sections reveal a porous and partly fibrous interior structure that is surrounded by a dense wall (Fig. 1b) which is iron rich according to EDXS mapping, (Fig. 1c). The HAADF‐STEM image (Fig. 2a) was taken at the rim of such a particle. The outermost layer at the left appears bright, dense and two to five micrometer thick. It mainly consists of silicon oxide enriched with iron (Fig. 2b‐d). The loss of porosity in the outermost layer during the catalytic operation originates from the formation of a dense phase there. Furthermore, the EDXS mappings reveal areas in the inner part of the particles that contain mainly Ti, Si and Al. This finding agrees with the results of x‐ray diffraction studies that identified zeolite and titanium oxide in addition to a small amount of crystalline aluminum silicate.

It can be concluded that an equilibrated FCC particle as investigated here is covered by a dense newly‐formed iron‐enriched silicon oxide layer while a freshly prepared, catalytically more active FCC particle has a highly porous outermost shell [3].
Nanoscopic localization of he components of the origin recognition complex during Trypanosome brucei cell cycle
Authors: Lemgruber Leandro , Marques Catarina , McCulloch Richard
Published: December 2016

Origin recognition complex (ORC) architecture has only been explored in depth in the opisthokont supergroup of eukaryotes, which includes yeast and mammals, with little work in protists. The Kinetoplastida is a well‐studied order of eukaryotic microbes and contains several important human parasites, such as
Trypanosoma brucei
. Genome sequencing of
T. brucei
identified only a single ORC‐related protein – TbORC1/CDC6. A number of TbORC1/CDC6‐interacting factors have been identified, raising the possibility that an ORC is present in
T. brucei
. However, many of these interactors are highly diverged in sequence from canonical ORC subunits and none has been shown to have a role in replication. To compare the localization pattern of TbORC1/CDC6 with two of these factors (TbORC1b, and TbORC4), and with a subunit (TbMCM3) of the replicative MCM helicase that ORC is through to recruit, each protein was tagged with 12 copies of the c‐myc epitope (12myc). Analysis of the ratio and morphology of the nucleus (N) and kinetoplast (K) delineates the cell cycle stage of cells within the population: 1N1K for G1 phase; 1N1eK (elongated ‐ replicating ‐ but not yet divided kinetoplast) for S phase; 1N2K cells for S‐G2 phase; and 2N2K cells for postmitosis. Using Super‐resolution structured illumination microscopy (SR‐SIM) we characterized the distribution pattern of each factor using anti‐myc antiserum and compared this with replicating DNA, which was detected with EdU labeling, and with chromatin (DAPI). TbORC1/CDC6 and TbORC4 presented a punctate distribution in non‐replicating cells, and did not localize to a specific region within the nucleus. In early S phase cells there was limited co‐localization between either TbORC1/CDC6 or TbORC4 and EdU, which was also seen in puncta. An overlap in the myc and EdU signals became more pronounced in 1N2K cells, where S phase is more complete, and at that cell cycle stage the protein and replication puncta become more abundant and appeared more diffuse. In 2N2K cells, after completion of replication, localization of TbORC1/CDC6 and TbORC4 returned to a similar pattern to that of 1N1K cells. SR‐SIM imaging revealed that TbORC1B is only seen in the nucleus of S phase cells (1N1eK and 1N2K), where a comparable pattern to TbORC1/CDC6 and TbORC4 was seen, with signal throughout the nucleus in a similarly large number of puncta and with some overlap with EdU. TbMCM3 signal was more abundant and more homogenous in the nucleus that any of the putative ORC‐factors, and displayed little obvious variation in the different cell cycle stages, indicating that each of TbORC1/CDC6, TbORC4 and TbORC1B display distinct sub‐nuclear localisation to that of TbMCM3. SR‐SIM imaging has helped reveal that ORC architecture and regulation appear to be diverged features of replication initiation in
T. brucei
.
Multi scale tomography of materials for Li‐ion battery electrodes
Authors: Maire Eric , Douillard Thierry , Etiemble Aurélien , Roiban Lucian , Vanpeene Victor
Published: December 2016

Increasing energy capacity, power density and cycle life of Li‐ion batteries requires optimizing the composite electrodes microstructure. 3D simulation analysis and modeling have shown that the amount, the size, the shape, the tortuosity and the specific surface area of pores and particles are all key parameters for the improvement of electrode performance.

Recently, the 3D morphologies of various anodes and cathodes for Li‐ion batteries have been evaluated by FIB/SEM and X‐Ray Computed Tomography (XRCT). In addition, 3D imaging softwares allow automatic processing and quantifying measurements by finite element calculations or other numerical models. XRCT is non destructive but routine procedures are limited to rather poor spatial resolution. Combined Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) is destructive but has recently emerged as an established technique for the three‐dimensional imaging at high spatial resolution, inaccessible with laboratory X‐ray tomography. Electron TEM tomography is finally an option to improve the spatial resolution down to several nanometers.

This paper will give examples of different materials used for Li‐ion battery electrodes, analyzed at different scales with all these different 3D tomography techniques. It will be shown that static characterisation of the prestine materials gives the initial morphology of the electrodes.

Samples can then be analysed after electrical cycling and this shows the degradation mechanisms. Some methods even allow to do the observation in operado.
Real‐space mapping of electronic orbitals
Authors: Löffler Stefan , Bugnet Matthieu , Gauquelin Nicolas , Lazar Sorin , Assmann Elias , Held Karsten , Botton Gianluigi A. , Schattschneider Peter
Published: December 2016

The world as we know it is shaped by electronic states. Be it optical, electrical, or magnetic properties, thermal conductivity, or chemical bonding: almost all macroscopic properties can be traced back to the electronic states on the nanoscale. It is all the more surprising that they remained mostly elusive from an experimental perspective so far.

In this work, we show that the mapping of transitions between electronic states in real space with Ångström resolution is indeed possible using state‐of‐the‐art TEM and EELS [1]. As a model system, we used a 20 nm thick rutile sample oriented in [0 0 1] direction. In this system, the Ti L
2,3
edge splits into contributions from states with e
g
and t
2g
symmetry, respectively. Fig. 1 shows the experimental L
2
‐e
g
map extracted from the dataset acquired on a double Cs‐corrected FEI Titan cubed microscope operated at 80 keV after drift‐correction and averaging over 12 unit cells. An asymmetry that is rotated by 90° for nearest neighbors is clearly visible that is caused by the peculiar shape of the e
g
states as shown in the charge density distribution. Furthermore, simulations using the multislice [2] and mixed dynamic form factor [3] approaches were performed. As is evident from fig. 1, the simulations are in excellent agreement with the experimental data.

One crucial prerequisite for such asymmetries to appear lies in the local environment of the atom that is being probed [4]. If the atomic site is invariant under a high symmetry point group, many states will be degenerate and their contributions to the scattered intensity will add up to a circularly symmetric map according to Unsöld's theorem [5]. A prototypical example of this for
p
‐states is shown in fig. 2. Only if the point group symmetry is low enough, the degeneracy is lifted and transitions to individual states can be mapped by selecting a suitable energy window.

This work shows that the mapping of individual electronic states is possible with widely used tools such as TEM and EELS. Thus, it paves the way for exciting new applications such as probing defect states at surfaces and interfaces that could revolutionize material science, as well as our experimental grasp on electronic properties and bonds on the atomic scale.
Actin‐dependent mechanisms during vesicle fusion link exo‐ and endocytosis in synapses
Authors: Arpino Gianvito , Näreoja Tuomas , Sopova Elena , Shupliakov Oleg
Published: December 2016

During the synaptic vesicle fusion at the active zone a fusion pore is formed that results in a formation of an Ω‐shape intermediate structure (Ω‐profile) at the plasma membrane for releasing contents, followed by closure (called kiss‐and‐run) or merging of the Ω‐profile into the plasma membrane (called full fusion). Ω‐profile closure limits vesicular content release and cargo delivery, but recycles vesicles economically. In contrast, Ω‐profile merging allows for rapid, complete content release and cargo delivery, but couples exocytosis to classical endocytosis, involving membrane invagination, Ω‐profile formation and fission, for retrieving merged vesicles. In other words, Ω‐profile merging defines the mode of fusion (full fusion instead of kiss‐and‐run) and the mode of endocytosis (classical endocytosis instead of kiss‐and‐run) [1‐3]. Despite these fundamental roles, the mechanism underlying Ω‐profile merging is unclear in neurons, in which vesicles are less then 50 nm in diameter and fusion takes place rapidly after calcium influx.

Giant presynaptic nerve terminals in lamprey that allow intracellular microinjections of active compounds were used in our experiments to investigate the role of actin dynamics during the synaptic vesicle fusion in synapses. Compounds perturbing the actin dynamics, such as latrunculin A and cytochalasin D, phalloidin and non‐dissociable profilin‐actin directly tagged with fluorescence or along with a fluorescent carrier to monitor microinjections, were introduced into giant synapses stimulated at 5 Hz and 20 Hz and studied by confocal and electron microscopy. Phalloidin labeling was observed at the synaptic active zone and a large number of omega‐shaped membrane invaginations with dimensions corresponded to the size of synaptic vesicles and larger were observed at active zones in synapses microinjected with compounds disrupting actin polymerization as compared to control synapses, injected with dextran or GST and stimulated at the same rate (Fig. 1). In synapses simulated at 20 Hz a larger number of vesicles was observed at active zones at sites of microinjection supporting that SV release was inhibited.

Our results indicate that actin dynamics is involved at stages when synaptic vesicle merges with the active zone and when its membrane relocates to the periactive zone for endocytosis.
Imaging of Electron Beam Triggered Phase Transformations and Chemical Reactions of Organic Molecules by Aberration‐Corrected Low‐Voltage Transmission Electron Microscopy
Authors: Biskupek Johannes , Chamberlain Thomas , Skowron Stephen , Besley Elena , Khlobystov Andrei , Kaiser Ute
Published: December 2016

Direct observation of organic single‐molecules in their pristine state using transmission electron microscopy (TEM) is a challenging task because the electron irradiation during high‐resolution imaging can modify the structure under investigation. However, recent advances in low‐voltage aberration‐corrected high‐resolution transmission electron microscopy (AC‐HRTEM) allow atomic resolution even at accelerating voltages as low as 20kV [1] allowing atomic‐resolution imaging even for light‐element materials with knock‐on damage thresholds below 80kV [3]. However knock‐on damage is not the only damaging process. A reduction of the electron beam‐induced charging and radiolysis effects can be obtained by dedicated sample preparation such as embedding the sensitive material into a chemically inert, conducting, and one‐atom thick container such as a carbon nanotube [3] or in between two layers of graphene [4]. By combining dedicated low‐voltage TEM instrumentation with sophisticated sample preparation, electron irradiation‐induced damage mechanisms slow down or can even be completely turned off which even allows imaging of molecules containing hydrogen‐carbon bonds [5].

In this work we apply low voltage AC‐HRTEM not only to image but also to trigger a previously unknown chemical reaction – the polycondensation of perchlorocoronene (PCC), which leads to the formation of graphene nanoribbons, an exciting polymeric structure with significant potential for electronic applications. The multi‐step mechanism of this reaction was determined by AC‐HRTEM and is both complex and difficult to postulate a priori or from macroscopic observations.  However our time‐series imaging at the single‐molecule level reveals the nature of key intermediates and follows the pathways of their transformations, thus providing the most direct experience of chemical reactions and demonstrating the physical reality of the elusive steric factor in real space. Figure 1a shows a time series of PCC molecules stacked in single walled carbon nanotube and their electron beam induced changes over time as a product of the accumulated electron dose. A close examination of the experimental images (Figure 1b) indicates that intermolecular reactions are possible only when a PCC molecule can change its orientations with respect to the neighbouring molecules: two non‐parallel molecules are able to join together to form angular species which gradually transform into planar species approximately twice the length of the original PCC molecules.
Trapping of helium in nano‐bubbles from 920
Ma
euxenite crystals revealed by
STEM‐EELS
analysis
Authors: Seydoux‐Guillaume Anne‐Magali , David Marie‐Laure , Alix Kevin , Datas Lucien , Bingen Bernard
Published: December 2016

The study of radiation damage resulting from alpha‐decay from U and Th chains in radiocative U‐Th minerals is of tremendous importance. Indeed, this damage critically affects the long term behavior of minerals. It is caused by both the ejection of recoil‐nuclei and alpha‐particles, leading to fundamental modifications in the physical and chemical properties of minerals. If the recoil‐nuclei induced defects have been extensively studied, the consequences of the alpha‐particles ejection have been less investigated. In particular, the (Y,REE,U,Th)‐(Nb,Ta,Ti) oxides, like euxenite, fergusonite, pyrochlore, zirconolite, are known to contain nanometric spherical voids or bubbles, interpreted to contain radiogenic helium. However no direct evidence of the trapping of helium in these voids has been shown up to now. In this study,
in‐situ
analyses by STEM EELS on individual nano‐bubbles from an euxenite crystal, sampled in its host c. 920 Ma old pegmatite in Norway, deliver, for the first time, a positive identification of helium and an estimation of helium pressure in such bubbles. The chemically unaltered euxenite crystal proves amorphous and homogeneously speckled with bubbles ranging from 5 to 68 nm in diameter, around a log‐normal distribution centred at 19 nm. The euxenite contains 9.87 wt% UO
2
and 3.15 wt% ThO
2
. It accumulated a theoretical alpha‐decay dose of 3.46 × 10
20
α/g (i.e. 170 He/nm
3
), at a dose rate of 11926 α/g/s. This corresponds to production of 0.23 wt% He. The density of He inside the bubbles, estimated from EELS data, ranges from 2 to 45 He/nm
3
, leading to a pressure of 8 to 500 MPa. The proportion of produced He trapped in bubbles is about 10%. The bubbles, acting as traps, clearly influence He diffusion. They may contribute to the swelling of euxenite during amorphization and to the fracturing of the host rock. These results suggest that both dose and dose rate are key parameters for the nucleation, growth and coalescence of He bubbles. Simulation of the behaviour of high‐level nuclear waste glasses by extrapolation from actinide doped glass or externally irradiated materials (very high dose rates) may not be predictive on the macroscopic effects (swelling, fracturing), the change of properties of material in which He accumulates, and the presence/size of He bubbles. Furthermore, because alteration is promoted by amorphization, fluid interaction with euxenite crystals saturated with He bubbles will mobilize and redistribute He through the entire rock. Helium may be infused in other minerals, e.g. zircon or apatite, the most utilized minerals for (U‐Th)/He thermochronology, and may completely disturb (U‐Th)/He dating.
Sample preparation for in‐situ biasing
TEM
experiments
Authors: Hömpler Udo , Wagner Tolga , Niermann Tore , Lehmann Michael
Published: December 2016

Knowledge about the potential distribution of semiconductor devices at the nanometer scale is important for the development of new device structures. Electron holography is a technique sensitive to the electrostatic potential with a high spatial resolution up to the sub nanometer scale [1, 2]. The potential especially in semiconductors is highly sensitive to the generation of electron‐hole pairs, damage caused by the electron and ion beam during investigation and preparation [3], and the biasing of the sample. In‐situ Biasing of specimen within the transmission electron microscope (TEM) provides an external stimuli allowing to differentiate between various effects influencing the hologram. A possible investigation is the influence of reverse and forward bias on the width of the depletion region and on the potential difference between p‐ and n‐sides of the diode [4, 5]. For the comparison between the the bulk device and the TEM‐ specimen we monitored the influence of the sample preparation on the electrical behavior.

For these investigations a silicon solar cell was chosen [6]. The used sample geometry is inspired by the experiments of A.C. Twitchett [7]. The first steps are cleaving and grinding of a wedge out of the wafer. Afterwards two copper clamps are bonded with conductive silver on the front and back contacts of the specimen. This is followed by the preparation of a TEM lamella with a focused ion beam (FIB). A sketch of the FIB prepared lamella is shown in Figure 1. The preparation of the biasing sample is finished by bonding of the clamped specimen on a custom build carrier chip with conductive silver. Figure 2 shows the finished sample.

After each preparation step, an IV measurement was performed and the corresponding curves are shown in Figure 3. As result, the influence of the FIB preparation on the whole sample is negligible (solid red and dashed blue). The measurements are not significantly changed before and after inserting the sample holder into the vacuum of the TEM (solid green and dashed orange). In reverse bias direction however a change of the slope after each bonding step is visible. Before bonding the parallel resistance is 70.1 kΩ. After bonding the slope of the current increases. This corresponds to the presence of a parallel resistance. Conductive silver or residues from its solvent might shortcut the device and build a parallel resistance. This parallel resistance decreases from 10.3 kΩ to 1.95 kΩ after the bonding steps.

During investigations within the TEM an influence of the electron beam on the measured shortcut current was recognizable. Illuminating the FIB‐cut lamella portion of the specimen (and partially the thicker parts below it (left of the lamella in Fig. 1) produced a current of ‐2.1 μA, while illuminating the hole near the specimen only produced an current of ‐8.8 nA.
Superstructures In The Scheelite‐Type Rare Earth Doped Tungstate Phases
Authors: Patout Loïc , Hallaoui Abdelali , Taoufyq Aziz , Dominici Christian , Carreiro Campos Andrea Porto , Alfonso Claude , Charai Ahmed
Published: December 2016

Introduction

The aim of the present work deals with the TEM study of scheelite related AWO
4
compounds [1] showing modulated microstructures not revealed with synchrotron XRD investigations. These materials have potential applications in many fields such as photoluminescence, microwave, scintillator materials, humidity sensors and catalysis. Rare earth (RE) tungstate RE
2
(WO
4
)
3
crystal phases are based on a cation‐deficient superstructure of CaWO
4
. Cation substitution of RE are investigated in order to correlate the microstructure to physical properties especially for new potential applications in white‐LEDs and lasers. In our study, a two‐phase powder containing the monoclinic Ce
2
(WO
4
)
3
and orthorhombic Ce
10
W
22
O
81
structures [2], was obtained by complexing method using EDTA and citrate ions. In the latter phase, PED and HRTEM investigations showed a C2/c superspace group (SSG) doubling the smallest
a
cell parameter [3]. Additionally, another cerium tungstate structure substituted with strontium cations was also investigated revealing a (3+2)D incommensurately modulated structure.

Results

Ce

10

W

22

O

81

: polymorphism

ED patterns of highest symmetry (Fig. 1) showed reflection positions paired by a two‐fold axis and indexed in the Pbnm SG (a = 3.6, b = 36 and c = 22.2 Å). A superposition of rows of weak reflections along [010] and present in the Fourier transforms obtained from HRTEM images, led to a doubling of the cell parameter
a
. With PED acquisitions, the superstructure reflections appeared linked together by an inversion center and were related to a C2/c SSG (Fig. 2). The structure was also identified from FFT analyzes of experimental HRTEM projections. The amplitude and phase error values were calculated using the symmetry rules of each plane group. The reconstructed density maps, after imposing the appropriate symmetry projections were used to extract reduced atomic coordinates of Ce atoms, WO
5
, WO
6
and WO
7
groups (Fig. 3). For similar structures, weak satellite reflections, were attributed to partial oxidation of RE elements, short‐range order among the cations and slight changes in the oxygen positions [4‐5]. Synthesized in air, the oxidization of Ce
3+
precursor into Ce
4+
limited to the grain surface, explains the contribution of both structures to the ED patterns.

Sr
2+

substitution in Ce

2

(WO

4

)

3

: (3+2)D incommensurately modulated structure

ED patterns of Ce
0.25
Sr
0.25
WO
4
along main zone axes were indexed in the scheelite tetragonal I4
1
/a unit cell (a
s
= b
s
= 5.44 Å and c
s
= 11.88 Å ≈ 2a
s
). However, lower intensity reflections along [001] (Fig. 4), indicating a partially ordered distribution of vacancies and cations, needed the use of a supercell with 5 digit indices hk0mn corresponding to the diffraction wave vector H = ha* + kb* + lc* + mq
1
+ nq
2
, q
1
≈ 0.57a* + 0.80 b* and q
2
≈ ‐0.80a* + 0.57b* [6].
Insight on the fine structure of semiconductor nanowires down to single atom detection: correlation to their physical properties
Authors: Arbiol Jordi , Genç Aziz , Zamani Reza R. , de la Mata María
Published: December 2016

Nanotechnology allows modifying the structure of nanoobjects down to the atomic scale. Low dimensional quantum structures can be embedded in a nanowire system in order to modify its properties at will. Electronic and optoelectronic devices benefit from the new advances in growth methodologies, with a fine control of the elemental species locally deposited.

In the present work, we will present how an accurate knowledge on the atomic positions, down to single atom detection, may help to deeply understand the improved properties of our complex nanowire heterostructures. We will show how from scanning transmission electron microscopy (STEM), it is possible to obtain precise 3D atomic models that can be used as input for the simulation of its physical properties. Finally, these theoretical properties will be cross‐correlated to the experimental measurements obtained locally on our nanowire systems.

Some of the presented works will include: the effect of the isotope distribution on the phononic behavior of nanowires, the measurement of the internal electric fields in quantum structures and the influence of doping on the compensation of the polarization field, or the influence of polarity and the atomic arrangement on the photonic and electronic properties of single heterostructured nanowires.