bluuebunny/crossref_metadata_2025 huggingface dataset:
Developing new electron interferometry configurations in
I2TEM
thanks to electron optics simulations
Authors: Kubo Yudai , Gatel Christophe , Taniguchi Yoshifumi , Snoeck Etienne , Houdellier Florent
Published: December 2016

The
In situ
Interferometry Transmission Electron Microscope (I2TEM), is a microscope designed to easily performed new electron interferometry experiment [1,2,3]. The microscope is equipped with a 300kV cold field emission source, one electrostatic Möllenstedt biprism (BP) installed before the three condenser lenses, two goniometer stages situated respectively above and inside the objective lens pole piece (namely high resolution stage and Lorentz stage) and finally three BPs placed between the intermediate lenses. The strength of this microscope lies in its wide optical flexibility, which can be used to develop new configurations very difficult to obtain using standard TEM. On the other hand, this flexibility increases the optical complexity of the operation and implies being able to simulate the electrons trajectories as a function of the various optical conditions (lenses excitations, High voltage, gun lens ratio, …) to predict “a priori” the hologram properties which will be obtained (width, interference fringes, …).

To perform such simulations, all lenses strengths have been calculated using finite element modelling software COMSOL multiphysics (see figure 1) [4], as a function of their ampere‐turns excitations. These results are then used in SIMION software (see figure 2) [5] to compute the complete electron trajectories starting from the FE tip through the biprism to finish in the detector plane.

The simulations are finally compared to experimental data in order to calibrate the model.
Quantifying the hole distribution in cuprates: Atomic‐resolution near‐edge fine‐structures of the superconductor
Sr3Ca11Cu24O41
Authors: Bugnet Matthieu , Radtke Guillaume , Löffler Stefan , Schattschneider Peter , Hawthorn David , Dabkowska Hanna A. , Luke Graeme M. , Sawatzky George A. , Botton Gianluigi A.
Published: December 2016

Sr
14‐x
Ca
x
Cu
24
O
41
is a fascinating member in the family of cuprates, not only because of its peculiar crystal structure where two distinct units, corner‐shared CuO
2
chains and edge‐shared Cu
2
O
3
ladders, coexist within the unit cell but also because it is the only known superconductor with a non two‐dimensional CuO
2
plane structure. Indeed, the superconducting state theoretically predicted by E. Dagotto and T.M. Rice [1] was first observed experimentally in Sr
0.4
Ca
13.6
Cu
24
O
41.84
below T
c
= 12 K and for pressures starting from 3 GPa [2].

Independently of the Ca composition, Sr
14‐x
Ca
x
Cu
24
O
41
is an intrinsically hole‐doped compound with 6 holes per formula unit, leading to an average Cu valence of +2.25. A central issue for understanding the mechanisms leading to superconductivity in this compound is therefore to measure accurately the carrier distribution among CuO
2
chains and Cu
2
O
3
ladders. This task has been undertaken shortly after the discovery of superconductivity in this system [3] but is still a matter of intense debate due to the very scattered nature of the results. For instance, depending on the technique, reported hole concentrations in the ladder layers of Sr
3
Ca
11
Cu
24
O
41
vary from ~1 to ~4.5 holes/formula unit [4,5].

All these results have been obtained with techniques that have a relatively poor spatial resolution ranging from several hundred nanometers to a few micrometers. In this work, we exploit the unmatched spatial‐resolution of STEM‐EELS to measure local hole concentration in superconducting Sr
3
Ca
11
Cu
24
O
41
at the atomic scale and provide, for the first time, a real‐space measurement where spatial separation between chains and ladders is achieved [6]. As shown by F.C. Zhang and T.M. Rice [7], in doped cuprates, the hole strongly binds to the four O atoms surrounding the central Cu through Cu
3d
‐O
2p
in‐plane sigma hybridization within the CuO
4
plaquettes. As such, the local hole concentration can be monitored very efficiently through the O‐K pre‐edge structures as shown in Figure 1. These experimental results, combined with inelastic scattering calculations, demonstrate unambiguously that holes lie preferentially within the CuO
2
chains of the structure.

In summary, this work illustrates how the combination of near‐edge fine‐structure analyses with atomic resolution in the aberration corrected STEM can improve the understanding of the electronic properties of complex oxides, such as Cu‐based superconductors [8].
Quantitative measurement of the charge distribution along a tungsten nanotip using transmission electron holography
Authors: Zheng Fengshan , Migunov Vadim , Ramsperger Urs , Pescia Danilo , E.Dunin‐Borkowski Rafal
Published: December 2016

Off‐axis electron holography can be used to measure the electron‐optical phase shift associated with a charge density distribution in the transmission electron microscope (TEM). The charge density can then be recovered either by integrating the Laplacian of the reconstructed phase
1
or, equivalently, by applying a loop integral
2
. Whichever approach is used, the perturbed reference wave
3
does not affect the measurement of the projected charge density inside the specimen so long as it does not itself contain any charges. Here, we study a W nanotip, in which the charge density distribution is of interest for applications in field emission and atom probe tomography. We assess artefacts and noise in the measurements.

Figure 1(a) shows an off‐axis electron hologram of a W nanotip recorded at 300 kV using an FEI Titan 60‐300 TEM. The interference fringe spacing is 0.318 nm, the nominal magnification is 140 000 and the voltage applied to the electrostatic biprism is 90 V. The apex of the nanotip has a diameter of approximately 5 nm and is covered with a layer of tungsten oxide. A voltage of 50 V was applied between the nanotip and a flat electrode positioned approximately 3 µm away from it. In order to remove the contribution to the phase shift from the mean inner potential, two holograms with and without a voltage applied to the nanotip were recorded. The difference between the two phase images was then evaluated after sub‐pixel alignment. Figures 1(b) and (c) show the resulting unwrapped phase before and after adding phase contours of spacing 2π/3 radians. Figure 1(d) shows the charge distribution calculated by applying a Laplacian operator to a median‐filtered version of the phase image. Figure 1(e) shows cumulative charge profiles along the nanotip determined both using a loop integral and by applying a Laplacian operator to either an unwrapped phase image or the original complex image wave. The integration region is marked by a green dashed rectangle in Fig. 1 (b). The measured charge profile is consistent between the three approaches. Figure 1(f) shows an evaluation of noise in the measurement obtained by performing a similar integration in a region of vacuum indicated by the red dashed rectangle in Fig. 1(b). Results such as those shown in Figs. 1(d) and (e) can be used to infer the electric field and electrostatic potential around the tip. Future work will involve comparing the present approaches with using a model‐based technique for determining the charge density from a recorded phase image.
Excitonic Properties of Inorganic‐Organic Hybrid Perovskites and Nanophotonic Devices
Authors: Xiong Qihua
Published: December 2016

Excitonic Properties of Inorganic‐Organic Hybrid Perovskites and Nanophotonic Devices

Qihua Xiong

School of Physical and Mathematic Sciences & School of Electrical and Electronic Engineering

Nanyang Technological University, Singapore, 637371

Abstract:
In this talk, we present investigations of vapor phase synthesis of purely inorganic or organic‐inorganic perovskites nanoplatelets by a van der Waals epitaxy mechanism and their excitonic properties. Those crystals exhibit 2D well‐faceted triangular, hexagonal or square geometry with thickness range of tens to hundreds of nanometers. Optical spectroscopy investigations suggest that the crystals have large exciton binding energy, high external quantum efficiency and long diffusion lengths. The naturally formed high‐quality planar whispering‐gallery mode cavities ensure adequate gain and efficient optical feedback for low‐threshold optically pumped in‐plane nanolasers ranging from ultraviolet and near‐infrared, with an exceptionally high quality factor (>4000) in purely inorganic perovskite square‐shaped crystals. Our findings open up a new class of wavelength tunable nanomaterials potentially suitable for on‐chip integration and flexible optoelectronic devices. Progress in light‐emitting diode and laser cooling will also be discussed.
Analysis of Food Packaging Layered Polymers by
SEM/EDS
and Raman
Authors: Konopka John , Thompson Keith
Published: December 2016

Food packaging can consist of many layers of materials each engineered for different purposes. The layers may be very thin, in some cases much less than one micron. Principally composed of polymers layers may be composed of inorganics and inorganic particles may be embedded by design or as artifacts. Analysis for quality assurance or failure analysis is difficult due to the complex nature of the sample.

Raman can easily identify the polymers used in these products. Raman mapping has a resolution of one micron or better. SEM imaging easily achieves a resolution of ten nanometers and can distinguish different polymers by their appearance in electron imaging. EDS achieves a spatial resolution of a few tens of nanometers. It can identify all elements present here except hydrogen.

Together these techniques provide complementary information. In addition imaging and elemental mapping with SEM/EDS may be faster than Raman mapping.

For this work a JEOL JSM‐7610F FESEM equipped with a Thermo Scientific NS7 EDS analyzer and 60mm2 area Ultradry silicon drift detector were used for the SEM/EDS data. A Thermo Scientific DXRxi Raman spectrometer with optical microscope was used for the Raman spectroscopy.

The SEM conditions were 10 kV acceleration voltage and about 3 nA beam current.

The sample used here is a cross section of a commercially available potato chips bag. The sample was sectioned by a fresh razor blade. For SEM/EDS the sample was carbon coated.

Figure 1 compares the results from both SEM/EDS and Raman. In this view the interior of the package is towards the top of the image. The right image shows a Backscatter Electron (BSE) image of the cross

section overlaid by elemental maps for Al, Ti, Si and O. Twelve layers were identified by inspection ranging from about 25 microns to approximately 175 nm thick. Some are not visible at this low magnification view. An Al layer about 200 nm thick was seen. A 175 nm thick layer containing S and Cl was found (not shown in the figure). Several layers contained Ti rich particles. Some particles of silicon oxide, possibly artifacts, were seen. The live time for this map was 931 seconds.

The image at left in Figure 1 shows the results of the Raman mapping analysis. The identified polymers layers and their thicknesses are labeled. In general the two techniques agree well on the overall composition of the sample. The Raman analysis identifies the polymers making up each of the layers which was not possible by SEM/EDS. It also found the inorganic rutile particles embedded in some of the layers. It did not find any of the sub 200 nm layers seen in the SEM.
Comparison of propagation‐based phase contrast tomography and full‐field optical coherence tomography on bone tissue
Authors: Di Tommaso Sylvaine , Rositi Hugo , Langer Max , Frindel Carole , Olivier Cécile , Peyrin Françoise , Rousseau David
Published: December 2016

The current huge development of new 3D microscopic techniques (synchrotron microtomography, optical coherence tomography, light sheet microscopy, …) opens a large variety of new perspectives for life sciences. The contrasts of these new microscopies are mostly well understood on samples of known material content such as those used in physics or instrumentation studies. The situation is different when it comes to the interpretation of the contrasts observed with complex heterogeneous media found in biology. Therefore determining which 3D microscopy technique is suited for which biological question is a topic of current interest (see [1,2] for instance in our group).

In this communication, we propose a comparison of the contrast observed with full‐field optical coherence tomography (OCT) and propagation‐based phase contrast tomography (PCT) on bone tissue at similar spatial resolution. A first comparison of OCT with standard absorption microtomography was given in [3] for bones and we extend this comparison to PCT which is known to provide enhanced contrast on bones at multiple scales [4]. The contrast of both these techniques are a priori interesting to be compared since they both rely on discontinuities of refraction index. This produces phase shift in PCT which operates in the X‐ray domain with a monochromatic beam (generated by a synchrotron) while this generates direct intensity reflexion with OCT which only resorts to white light in the visible domain.

As visible in Figure 1, we specifically focussed our attention on the contrast observed in both techniques around the same bone structural unit, a so‐called osteon, at a microscopic scale with images of same spatial resolution (voxel size 3.5µm). It happens that the osteons are visible in PCT while they are not perceptible with conventional absorption micro computed tomography. Also, concentric lamellae, corresponding to the so‐called Harvers system, appear clearly visible in OCT while they are not perceptible with PCT at this spatial resolution. The contrast between the osteon and the surrounding bone tissue, is found in terms of homogeneous regions in PCT. However, this less spatially resolved contrast in PCT is constant throughout the sample while it is spatially variable in OCT where a continuous degradation of the contrast is observed along the direction Z of the propagation of light. We found, as given in Figure 2, that a certain spatial average of some 30 µm along Z was able to improve optimally the contrast across the concentric lamellae when inspected at the surface (up to 500 µm depth) of the sample with OCT. This contributes to establish quantitatively the complementarity of OCT and PCT for the characterization of bones at the microscopic scale.
Unusually high iron enrichment in hard dental tissues of coypu
Authors: Srot Vesna , Salzberger Ute , Bussmann Birgit , Deuschle Julia , Watanabe Masashi , Pokorny Bostjan , Turinek Ida Jelenko , Mark Alison F. , van Aken Peter A.
Published: December 2016

Living organisms possess a unique capability to form complex bio‐minerals with very diverse compositions and structures. Organic matrix and crystalline constituents are closely linked together in unique material constructions that are formed under conditions of moderate temperature, pressure and pH value. Many of these bio‐minerals show excellent physical and mechanical properties [1, 2] that cannot be reproduced in the laboratory.

Rodents have long opposing pairs of continuously growing incisors that are worn down by gnawing. The front surface of the incisors is enamel consisting of 96 wt% of inorganic material; the inner part is softer dentine that forms the bulk of the teeth [3]. The surfaces of incisors of different rodent species show a characteristic orange‐brown color and are identified with the presence of iron [4].

In our study, the microstructure and the chemical composition of continuously growing incisors from the coypu (
Myocastor coypus
Molina) were investigated in detail using energy‐dispersive X‐ray spectroscopy (EDX) and electron energy‐loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM) imaging at high spatial as well as high energy resolution. VG HB501UX, Zeiss SESAM and Jeol ARM200F microscopes were used and the resulting data were combined with knowledge obtained from mechanical testing experiments.

A layer with variable thickness, which has not been observed before, was detected on the outer surface of the incisors as marked on the optical micrograph image (Fig. 1). An annular dark field (ADF)‐STEM image of a cross‐sectional view showing the interface between the Fe‐rich surface layer (Fe‐SL) and Fe‐rich enamel (Fe‐E) is shown in Figure 2a. Analytical investigations of this surface layer showed much higher amounts of iron compared to the concentration values reported in the literature up to now. Within the iron‐rich surface layer we surprisingly detected multiple iron containing varieties where iron is present in predominantly the 3+ valence state, as revealed by studies of electronic structure. O‐K fine structural features suggest the presence of different intermixing levels of Fe phosphate and Fe oxide/hydroxide (Fig. 2b).

The present discoveries will greatly enhance the understanding of the function of the incorporation of iron at the nanoscale level and its effect on the microstructural properties.
Analytical
STEM
Study of Dy‐doped
Bi2Te3
Thin Films
Authors: Srot Vesna , Schönherr Piet , Bussmann Birgit , Harrison Sara E. , van Aken Peter A. , Hesjedal Thorsten
Published: December 2016

Breaking the time‐reversal symmetry (TRS) in three‐dimensional (3D) topological insulators (TIs) [1,2] is crucial for unlocking exotic physical states and exploring possible device application. Doping the prototypical 3D‐TI Bi
2
Te
3
with transition metal ions can lead to ferromagnetic ordering at low temperatures [3,4]. We present the study of incorporation of dysprosium (Dy) into Bi
2
Te
3
with the intent to achieve higher ferromagnetic ordering temperatures and higher magnetic moments [5].

Dy‐doped thin films were grown on c‐plane sapphire substrates by molecular beam epitaxy (MBE) [6]. Samples with a Dy concentration of
x
≤ 0.113 were selected for high‐angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) and energy‐dispersive X‐ray spectroscopy (EDX‐) STEM investigations [5]. A (Dy
0.113
Bi
0.887
)
2
Te
3
film was carefully detached from the substrate using a droplet of glue, and thin TEM lamellae were cut in cross‐sectional geometry using an ultramicrotome. Thin sections were obtained using an oscillating water‐filled diamond knife to cut approximately 40 nm thick slices that were captured on Cu grids covered with a lacey carbon film.

A high crystallinity (Dy
0.113
Bi
0.887
)
2
Te
3
thin film acquired at 60 kV is shown in an HAADF‐STEM image in Figure 1. The characteristic crystal structure consisting of stacked quintuple layers separated by van der Waals gaps is clearly recognizable. A higher magnification HAADF‐STEM image with the overlaid structural model is presented in Figure 2a. EDX line‐scans were acquired traversing the van der Waals gap between the adjacent quintuple layers (see arrow in Fig. 2a). The corresponding intensity profiles of Bi‐M, Te‐L and Dy‐L X‐ray emission lines along the arrow (in Figure 2a) are presented in Figure 2b. The intensity of the Dy‐L signal is precisely following the Bi‐M signal, indicating the substitutional incorporation of Dy atoms on Bi sites and the absence of Dy in the van der Waals gaps. No evidence for cluster formation or local phase segregations could be detected [7].
Using cryomethods around
SEM
technologies to characterize waxes on the petals surface of Rosa damascena
Authors: Fernandez Eric , Rose Christophe , Marull‐Tufeu Sylvie
Published: December 2016

The rosaceae is one of the major family of flowering plants with 3200 species in 115 genera. The genus Rosa encompasses approximately 190 species and more than 18 000 cultivar forms of the plant have been identified [1]. The species
Rosa damascena
is well known for its intensely fragrant flowers.In the cosmetic field, essential oils and waxes are two major components which are extracted from therose flower. Rose essential oils are very often used in fine fragrances whereas waxes can be used as active components to play a major role in the skin physiology.

Rose petals' surfaces have already been studied by conventional SEM technologies. The rose scent compounds are emitted by both epidermal layers [2]. Residues of secretory substances have already been observed on both surfaces [2,3]. The wax components are localized in the cuticle on the surface of the epidermal cells. The cuticle of floral organs presents a micro‐relief defined as cuticular patterns [4]. Although the shape of epidermal cells is variable between both the petal rose faces, the cuticle presents some common patterns which results in parallel folds. Circular wax patterns were also observed on the abaxial surface [2,3,5].

The aim of our study was principally to characterize more precisely the wax aspect at thesurface of petals of the
Rosa damascena
. Wax microstructures are fragile and to avoid sample preparation artifacts we decided to work on fresh hydrated specimens and innovate by mixing cryomethods with different observation modes in SEM.

In a first approach we manually plunged the petal sample into liquid nitrogen and transferred it into the SEM chamber equipped with Peltier freezing stage. The surface analysis using SE and BSE detectors in variable pressure mode allowed us to distinguish two shapes of epidermal cells on the abaxial face. Both are elliptical but one of them shows globular structures (Figure 1). This latter shape would appear to be associated with circular wax models. In a second time, the cryofixation was carried out with a semi‐automated plunge freezing device. The specimen was etched, coated and then transferredfrom the cryo preparation chamber onto a SEM‐FEG cryo‐stage. High resolution imaging with an in‐lens SE detector at low voltage permitted us to analyse the extreme surface of petals and observe the structure of the rose petal waxes.

We confirmed by this study the interest of mixing cryomethods to preserve the rose petal wax patterns as close as their native state. In addition using numerous and complementary detectors in different vacuum modes allowed us to collect new information on the wax aspect at thesurface of petals of the
Rosa damascena
. The optimizing protocols of cryomethods can also be an opportunity to have a better understanding of the scent molecules release from the epidermal cells though the cuticle. Our first observations in this direction are encouraging.
Structure resolution of the new phase
Ba19Cr12O48
Authors: Lepoittevin Christophe , Jeanneau Justin , Toulemonde Pierre , Nunez-Rugueiro Manuel
Published: December 2016

After nearly 30 years of research on the superconducting cuprates, the discovery of high T
c
superconductivity in related iron based pnictides in 2008
1
has stimulated the search of new superconducting compounds. In particular, phases presenting 2D squared planes of 3d transition elements with antiferromagnetic interactions, like the famous cuprate YBa
2
Cu
3
O
7‐
d
, are of great interest. In that sense, the n=1 (Sr
2
CrO
4
(Sr214)) and n=2 (Sr
3
Cr
2
O
7
(Sr327)) members of the Sr
n+1
Cr
n
O
3n+1
Ruddlesden‐Popper (RP) series, synthesized by J.A. Kafalas and J.M. Longo under high pressure ‐ high temperature for the first time in 1972 are interesting
2
. Only recently this Sr‐Cr‐O system has been revisited by Baikie
et al.
and E. Castillo‐Martinez & M.A. Alario‐Franco
3,4
.

To explore new Cr‐based systems where superconductivity could potentially be induced by changing doping and Cr‐Cr interactions, we have synthesized new chromates by replacing Sr with other alkaline earth elements.

The replacement of Sr by a smaller Ca alkaline earth has given rise to a new Ca‐based chromate Ca
3
Cr
2
O
7
(Ca327) RP phase synthesized at 4 GPa and 1000°C
5
. When a bigger alkaline earth element, such as Ba, was used, a new unknown phase was isolated instead of the traditional RP‐type phase in this conditions of synthesis; the low pressure Ba
2
CrO
4
orthorhombic phase was first obtained from the solid state reaction of BaCO
3
and Cr
2
O
3
at 1000°C under Ar flow, then this Ba‐based precursor was treated at 1000°C under 6 GPa for 30 minutes.

Since it was impossible to solve ab initio the crystallographic structure of this new phase from powder X‐ray diffraction, electron diffraction (ED) appeared to be the most suitable method. First of all the selected area electron diffraction highlighted a big cubic cell with the cell parameter a = 13.6 Å, as illustrated by the two [110] and [111] zone axis electron diffraction patterns on figure 1. The extinction conditions are consistent with a body‐centered lattice. Then an ED tomography was performed manually by executing a rotation of the sample holder from +50° to ‐50° and recording an ED pattern each 1° step, with the application of a 1° precession. The reflections picking, 3D reciprocal space reconstruction, cell determination and reflection intensities extraction were realized with the software PETS
6
, and the structure model was obtained using charge flipping on JANA2006
7
. All the cations were properly determined as well as most of the oxygens, and the remaining oxygens were identified by fast Fourier transform difference. Then the structure was successfully refined from powder X‐ray diffraction data using Rietveld method. On the final structure presented on figure 2, all Cr are situated in face‐sharing octahedra.
Cell surface properties of probiotic Escherichia coli strains
Authors: Pepoyan Astghik , Balayan Marine , Manvelyan Anahit , Isajanyan Marianna , Tsaturyan Vardan , Hovnanyan Margarita , Hovnanyan Karlen
Published: December 2016

Background.Beneficial effects of probiotic Nissle 1917 on the host health have been shown in a range of investigations(1). During our previous studies the positive effects ofE. coli 2‐1on human and animals organism have also been described(2), and the liquid‐crystal state of cell walls from theE. colicells was shown by the x‐ray diffraction method under the small and large angles (Fig. 1).

Taking into account that solid‐liquid interfaces could have a considerable effect on host bacterial physiology(3) we aimed to investigate the cell surface hydrophobicities of probiotic strainsE. coli M‐17andE. coli 2‐1strains.

Methods. The probiotic strainsE. coli 2‐1from the probiotic formulation ASAP (Armenia) andE. coli M‐17from the probiotic formulation Colibacteron (Armenia) were used during these investigations. The twenty‐four gut commensalE. colistrains from the four healthy volunteers were used as controls. The cell surface hydrophobicities of theE. colistrains were determined by a MATH test according to Koss and coauthors(4 ), and the crystallization levels of cell walls (35 % water suspensions) from these strains were assessed semi‐quantitatively at 25'C with polarizing microscopy MIN‐8 with Bertrán's prism and increase x 300. The determination of the sizes of structural units carried out by a standard way with the help an eyepiece ‐ a micrometer; the +150W halogen lamp was a light source.

Results. Comparative MATH test experiments show that both investigated probiotic strains' cells surfaces are more hydrophobic than the bacterial surfaces of strains from the normal gut microbiota. At the same time, the low crystallization levels of cell wall proteins for probioticE. colistrains were described. Most probably, the comparative hydrophobic structure of bacterial membranes from probiotic strains regulates “probiotic‐characteristics” ofE. coli M‐17andE. coli 2‐1strains.
3D‐
TEM
microstructure analyses of anisotropic and isotropic aerogels of
TiO2
nanoparticles
Authors: Gramm Fabian , Tervoort Elena , Sologubenko Alla , Minas Clara , Rechberger Felix , Bouville Florian , Studart Andre , Niederberger Markus
Published: December 2016

Aerogels are fascinating materials with low density and high surface area with great application potential in battery materials, fuel‐ and solar cells and many more.(1‐3) These porous structures are conventionally prepared by sol‐gel chemistry and subsequent supercritical drying.(4) In the case of TiO
2
nanoparticles, the ability of the crystalline nanoparticles to undergo oriented attachment is fundamentally important for the self‐assembly into three‐dimensional interconnected networks. Such structures (Fig.1) are prepared by destabilizing highly concentrated dispersions of well‐defined TiO
2
nanocrystals. The gelation results in a percolating network of ultrafine structures which is preserved by supercritical drying. This processing technique allows for the preparation of crystalline, isotropic and translucent aerogels with broad pore size distributions and disordered pore arrangements (Fig.1).(5)

The aim of our study is to produce structures from destabilized dispersions and subsequent unidirectional freeze‐drying. Compared to the aerogel route, this process results in a different macro‐ and microstructure consisting of about 3 µm large units of compacted aerogel structures. Here, the pores are of a more ordered nature due to the freeze drying procedure.

In this work, aerogels prepared by supercritical drying and structures made via freeze‐drying were analyzed microstructurally. Using TEM tomography, we study the morphology of the 3D networks of the nanocrystals within both structures. Critical performance parameters like pore size, connectivity and tortuosity of those structures are analyzed.
New design of Möllenstedt electrostatic biprism setup for off‐axis electron holography
Authors: Cours Robin , Marcelot Cécile , Houdellier Florent
Published: December 2016

Many different forms of electron holography have been explored or imagined. The off‐axis configuration that uses a post‐specimen electrostatic Möllenstedt biprism (BP) is the most widespread. It can be easily set up in a modern transmission electron microscope (TEM) thanks to the general introduction of field emission guns. The
In situ
Interferometry Transmission Electron Microscope (I2TEM), is a microscope designed to easily performed electron holography experiment [1,2,3]. The microscope is equipped with a 300kV cold field emission source, one biprism (BP) installed before the three condenser lenses, and three biprisms placed between the intermediate lenses.

Regarding the high numbers of biprisms used in this microscope, their quality, their stability, and their easy servicing are one of the major concerns to maintain the performance of the machine. A wire surrounded with a ground anode basically constitutes commercial biprisms. The wire is, in most of case, produced by coating ultrasmall quartz fibers with noble metals. The resulting biprisms, although they are quite small by most fabrication standards (approximately 700 nm in diameter), can have various mechanical, electrical, structural … properties. Furthermore, their preparation methods are, in general, not very reproducible.

We have developed a new method to produce biprism in a more reproducible way, maintaining the best mechanical and electrical performance of the wire. Regarding the H‐bar shape of these new wires, due to the FIB preparation, the electric field that appears between the wire and the ground electrode, could be strongly affected by the system geometry. Finite element models using Comsol Multiphysics [4], have been used to better understand this effect which can, combining with the biprism holder shape, strongly influence the final hologram performance. We have then proposed a new biprism holder, which overcome all these drawbacks, and test these news holders, with new FIB prepared wires inside the I2TEM microscope.
Tag‐free labeling of tubulin in live cells with fluorescent organic dyes
Authors: Schvartz Tomer , Alush Noa , Nachmias Dikla , Arbely Eyal , Elia Natalie
Published: December 2016

High‐resolution fluorescence imaging, combined with the latest labeling techniques available today have yet been able to provide the necessary spatiotemporal resolution to record all cellular processes in live cells. Substituting the bulky fluorescent protein tags (such as GFP) currently used in live‐cell applications with much smaller fluorescent dyes that possess superior photophysical characteristics will markedly improve these advanced imaging techniques. Genetic code expansion and bioorthogonal labeling offer, for the first time, a non‐invasive way to specifically and directly attach such fluorescent dyes to proteins in live cells. Here we employ this strategy to directly tag α‐tubulin in live mammalian cells. By screening different conditions we have optimized the system for quantitative high‐resolution recording of microtubules in live cells. We will present data demonstrating the feasibility and efficiency of the approach and will discuss the advantages and limitations of using genetic code expansion for quantitative high‐resolution microscopy.
Model calculations for low‐lossEELspectra of2Dmultilayer systems
Authors: Mohn Michael , Hambach Ralf , Wachsmuth Philipp , Kaiser Ute
Published: December 2016

Collective electronic excitations (plasmons) in single‐layer and few‐layer graphene have been studied extensively in the past few years. In particular, the dispersion and nature of the π plasmon peak in free‐standing single‐layer graphene was investigated by means of momentum‐resolved electron energy‐loss spectroscopy (MREELS) [1‐3]. Besides, it was also studied how the transition from mono‐ to multilayer graphene changes the shape of EEL spectra. Within a layered electron‐gas (LEG) model, this transition can be modeled very precisely [4,5].

For other 2D materials such as transition metal dichalcogenides (TMDs), however, this approach may be highly inaccurate. We therefore evaluate more precise model calculations for multilayer systems. Our calculations are based on time‐dependent DFT calculations for the individual monolayers. The plane‐wave pseudopotential DFT code abinit [6] is used to simulate the ground state within local density approximation (LDA). The linear response is then calculated within random‐phase approximation (RPA) using the dp‐code [7]. Compared to the LEG model where the monolayers are assumed to be perfectly 2‐dimensional and homogeneous, we preserve the layers' microscopic structure in our calculations.

We demonstrate that only by taking the finite thickness of the constituent monolayers into account, the spectra of multilayer MoS2can be modeled correctly (see the figure). Our calculations can be also applied to arbitrary van‐der‐Waals heterostructures. Our results are directly compared to MREEL spectra recorded with a Zeiss Libra 200 based TEM prototype (“SALVE I”, [8,2]) equipped with a monochromator and an Ω type in‐column energy filter. This allows for the verification of our calculations over a large range of energy losses (0‐40 eV) and different momentum transfers within the Brillouin zone. [9]
Local Information Powers Heterogeneous Catalysis Research:TEMInvestigation of Industrial Relevant Cu/ZnO/Al2O3 Catalysts for Methanol Synthesis
Authors: Lunkenbein Thomas , Frei Elias , Schumann Julia , Behrens Malte , Willinger Marc Georg , Schlögl Robert
Published: December 2016

In a simplified picture a heterogeneous catalyst can be described as a high energy material, which is composed of two important parts: bulk and surface. The bulk is defined by a certain crystal and electronic structure as well as defect concentration, and reflects the real structure of the catalyst. It is responsible for the formation and stabilization of the active surface. Although physical and chemical information on the real and surface structure can be obtained by integral methods, important local fluctuations from the ideal structure, which are essential for the catalytic performance, in the catalyst composition may be overlooked.1This highlights the significance of transmission electron microscopy (TEM) as the tool for the local description of the nano‐ and/or mesoscale of heterogeneous catalysts.

Here, we focus on a transmission electron microscopic (TEM) description of the local nano‐ and mesoscale of industrial relevant Cu/ZnO/Al2O3catalyst for methanol synthesis. Methanol, one of the most important industrial chemicals, is produced from syngas (CO, CO2, H2) at high pressure (50‐80 bar) and elevated temperature (240‐280 °C) and is considered as a prospective key‐compound for chemical energy and hydrogen storage. The working mechanisms of this industrial methanol catalyst have been investigated extensively.2However, its actual active phase is still debated controversially. On the one hand, the catalytic odyssey may be caused by material, pressure and time gaps, which often do not mirror industrial relevant conditions. On the other hand, the diversity of results indicates the difficulty of investigating and understanding this complex catalyst system, in particular due to the lack of visual local information.

Our local observations tackle a detailed description of the mesostructure of the catalyst, the real structure of Cu nanoparticles and the formation of a special polymorph of layered ZnO on top of the Cu nanoparticles after reductive activation on industrial relevant ternary Cu/ZnO/Al2O3catalyst.1bIn addition, we will highlight the temperature, gas and time dependent evolution of this metastable layered ZnO polymorph from minutes to months (Figure 1).3

In conclusion, the results demonstrate the power of local TEM investigation in heterogeneous catalysis research. In combination with complementary integral data, they allow a detailed understanding of the system, which would be otherwise hard to obtain. The findings illustrate that methanol synthesis can be considered as an interface mediated process between Cu and ZnO.
In situ compression experiments of fused silica pillars in the
TEM
and
SEM
Authors: Mačković Mirza , Przybilla Thomas , Herre Patrick , Romeis Stefan , Paul Jonas , Barthel Etienne , Teisseire Jeremie , Schrenker Nadine , Peukert Wolfgang , Spiecker Erdmann
Published: December 2016

While fused silica is known for its brittleness on macroscopic scale [1], it exhibits an amount of plasticity on microscale [2]. Thermally‐treated Stöber‐Fink‐Bohn (SFB)‐type silica spheres are known to approach the structure of vitreous silica and show size‐dependent mechanical properties [3,4]. Adequate electron‐beam (e‐beam) irradiation can be used to induce enormous ductility during compression of nanoscale silica spheres [5–7], and to alter their Young's modulus (
E
) [7]. While a controlled introduction of structural anisotropy by cooling of glass melts under load [8–10] was shown to enhance the mechanical properties of glass fibers [11], we recently showed that e‐beam‐assisted quenching under load (turning off the e‐beam during compression) inside the transmission electron microscope (TEM) may also lead to structural anisotropy and affects the mechanical properties of nanoscale silica spheres [12]. Here we prove the potential of e‐beam‐assisted quenching under load on fused silica pillars and further investigate their size‐dependent mechanical behavior.

Fused silica pillars are prepared by two different methods from bulk fused silica, namely (1) reactive ion etching (RIE) and (2) focused ion beam (FIB) milling in combination with a charge neutralizer system (FEI Company). Mechanical testing was performed with the Hysitron PI95 TEM Picoindenter
TM
in the TEM and a custom‐built indenter in the scanning electron microscope (SEM) [6]. Both, RIE and FIB milling lead to pillar structures with reproducible geometry and suitable for in situ mechanical experiments in TEM and SEM (Fig. 1). In situ compression of RIE pillars to high strains in the SEM eventually results in fracture with characteristic star‐like fracture pattern (Fig. 2). In situ compression experiments at smaller strains carried out on FIB‐prepared pillars in the TEM at beam‐off conditions reveal a fully elastic deformation behavior, as exemplarily shown in Fig. 3. Thereby, an
E
= 78 GPa and compressive strength of ≥ 8 GPa are achieved. While
E
is slightly higher, the compressive strength clearly exceeds the one known for bulk fused silica [1], and the one of microscale fused silica pillars [2]. Further compression experiments on pillars in the TEM and SEM are planned, with the aim to explore their overall size‐dependent mechanical behavior in direct relation to our work on nanoscale glass spheres [4,7]. Finally, we expand our recently reported e‐beam‐assisted quenching under load approach [12] also on fused silica pillars, with the aim to get a generalized picture of the mechanical properties of nanoscale glasses upon quenching under load in the TEM.
Environmental(S)TEManalysis of Fe nanoparticles under oxygen atmosphere
Authors: Lari Leonardo , Carpenter Robert , Lazarov Vlado , Gai Pratibha , Boyes Ed
Published: December 2016

Fe and Fe‐oxide nanoparticles (NPs) have a number of promising potential applications in physical and medical sciences. These include magnetic storage devices, catalysis, sensing, contrast enhancement in magnetic resonance imaging and magnetic hyperthermia [1–3]. Understanding of the metallic Fe NPs formation and the oxidation processes down to atomic scale is paramount for the control of the quality and the optimization of their applications. Although metals oxidation has been studied for decades on bulk and thin film materials [4], there is still a lack of studies on the oxidation of metallic iron at the nanoscale. A recently modified double aberration corrected JEOL 2200FS (S)TEM [5] has demonstrated the possibility of the analysis of metallic nanoparticles in gas environment at temperature allowing single atom visualisation by HAADF STEM in controlled gas reaction environment [6]. In this study, thin films of Fe were deposited by sputtering ex‐situ on C films supported by standard TEM Cu grids. Nanoparticles were produced by annealing in vacuum within the microscope column the pre‐sputtered iron thin films (see Figure). Nanoparticle formation and size distribution was monitored in‐situ as a function of time and temperature by HAADF STEM imaging. After annealing, nanoparticles were shown to consist of single crystal metallic Fe. The Fe nanoparticles interaction with the Oxygen atmosphere was studied in‐situ at 300 °C with an Oxygen partial pressure at the specimen in the range of 2*10−2Pa to 2 Pa. The interaction of the nanoparticles with the gas will be discussed in terms of the oxidation mechanism as well as the changes in nanoparticle geometry, composition, size distribution, and crystallinity.
Energy dispersive x‐ray analysis of platinum‐nickel nanoparticles embedded in hollow graphitic spheres used as fuel‐cell catalysts
Authors: Swertz Ann‐Christin , Mezzavilla Stefano , Pfänder Norbert , Schüth Ferdi , Lehmann Christian W.
Published: December 2016

Introduction

Proton Exchange Membrane Fuel Cells (PEM‐FCs) are known as potential energy conversion devices in transportation systems. For the efficiency of these fuel cells a highly efficient and stable catalyst is needed. Platinum‐Nickel bimetallic nanoparticles embedded in hollow graphitic spheres (HGS) have been proven as highly active catalyst for the oxygen‐reduction reaction which plays a key role in the efficiency of PEM‐FCs.
1

These catalysts are synthesized via the confined‐space alloying approach. The synthesis of PtNi@HGS starts with the impregnation of HGS with the metal precursors. After high temperature annealing treatments metallic nanoparticles with a small size (3.5 nm) and a narrow particle size distribution encapsulated in the pores of the HGS can be obtained.
2

Methods

In this study the PtNi@HGS synthesized via confined‐space alloying were analyzed using different electron microscopy methods like HAADF‐STEM, EDX line scan and elemental mapping. Especially the electrochemically degraded samples were of great interest questioning the distribution of the two metals in the metallic nanoparticles.

To confirm the experimental results and to explain the structure of the nanoparticles after degradation theoretical EDX line scan profiles were calculated using Monte‐Carlo‐simulations
3
.

Results

In HR‐STEM images the structure of this catalyst system can be seen clearly: The crystalline metallic nanoparticles are encapsulated in pores of the hollow graphitic spheres (fig. 1). The EDX elemental mapping shows that the metal nanoparticles contain Pt and Ni. EDX line scans with a high spatial resolution clearly evidence a 0.5‐1 nm thick Pt‐rich outer shell and Pt‐Ni core after electrochemical degradation of the catalyst.

To confirm the experimental results and to explain the structure of the nanoparticles theoretical EDX line scan profiles were calculated using Monte‐Carlo simulations. Simulated line scans of PtNi@Pt particles (0.5 nm shell and 3 nm core) show profiles similar to the experimental data as shown in figure 2. This excellent agreement supports the formation of core shell particles during the electrochemical degradation of the catalyst.
Synchrotron Infrared Microspectroscopy, an innovative approach to investigate tissue chemical changes in mouse model of Pompe of disease (glycogenosis type
II
) and to assess efficiency in gene therapy
Authors: Dubreil Laurence , Hordeaux Juliette , Deniaud Johan , Lagalice Lydie , Bey Karim , Sandt Christophe , Jamme Frederic , Colle Marie‐Anne
Published: December 2016

Pompe disease is an autosomal recessive disorder caused by the deficiency of the lysosomal enzyme acid alpha‐glucosidase (GAA). The disease is characterized by lysosomal glycogen storage in heart and muscles, and manifests as a fatal cardiomyopathy in infantile form. Cardiac correction by enzyme replacement therapy (ERT) has recently prolonged the lifespan of these patients, revealing a new natural history. The emergent neurologic phenotype and the poor correction of skeletal muscles in survivors are currently partly attributed to central nervous system (CNS) glycogen storage, uncorrected by ERT. A gene therapy strategy using AAV vectors delivered to cerebrospinal fluid has been set up to restore GAA activity into the CNS. We demonstrate the use of Infrared Micro spectroscopy with synchrotron light as an innovative tool to map glycogen at the subcellular level in motor neurons and cardiac fibers. Principal Component Analysis (PCA) of infrared spectral data from motor neurons and cardiac fibers show that both treated and wild‐type animals are merged in the same cluster whereas infrared spectra obtained from untreated Pompe mice are characterized by increase of the bands assigned to the carbohydrates of glycogen.

This new analytical approach that allows an highly sensitive and resolutive direct probing of tissue glycogen is required to explore early biochemical change at a subcellular level and therefore to assess therapeutic efficiency for Pompe disease.