bluuebunny/crossref_metadata_2025 huggingface dataset:
On the applicability of electron diffraction to precisely measure temperature in
TEM
Authors: Niekiel Florian , Kraschewski Simon M. , Müller Julian , Butz Benjamin , Spiecker Erdmann
Published: December 2016

With the overwhelming success of
in situ
electron microscopy, fueled by the recent advances in instrumentation, an everlasting question in electron microscopy comes into focus again: the precise determination of the temperature of the sample, especially in
in situ
heating experiments [1]. So far temperature is determined by sensors (thermocouples, resistance thermometers) placed close to the sample. In this work we elaborate on the applicability of parallel beam electron diffraction in TEM to precisely measure temperature directly on the sample and on a local scale.

Well defined metallic particles are applied on the sample surface using a dewetting process after thin film deposition. SAED is used to determine the lattice spacing from ring patterns averaging over a large number of particles. The determined lattice spacing can be translated into temperature using reference data on thermal expansion. To test the performance of this approach, a MEMS‐based sample heating system from
DENSsolutions
is used inside of a double corrected
FEI Titan Themis³ 300
. Various metals (Ag, Au, Pt) are used to cover different temperature ranges. Fig. 1 shows image and diffraction pattern of a typical setup.

To allow for the highest precision, a proper alignment of the microscope is crucial. Therefore a method to assure perfect beam parallelity has been developed in this project, based on the change in diffraction pattern upon changing the sample position relative to the eucentric height. The accuracy of the evaluation based on peak fitting to the azimuthally averaged radial profile critically depends on the determination of the center and correction of astigmatism in the ring pattern. An algorithm has been employed allowing for correction of the astigmatism to the fourth order in the ring pattern (exemplarily shown in Fig. 2). The error due to the evaluation method can be estimated from the results of the evaluation of 100 subsequent diffraction patterns at a constant temperature shown in Fig. 3. The position of the (220) ring of Pt is determined to be 7.27183 ± 0.00023 nm
−1
(corresponding to a temperature accuracy of approximately ± 3.5 K).

The temperature accuracy can be tailored to the particular application by selecting a different metal. Low melting metals show a higher thermal expansion increasing the sensitivity of the temperature measurement, but, on the other hand, limiting the maximum usage temperature because of melting or sublimation. Fig. 4 demonstrates the applicability of the presented approach. Ag particles have been used to measure the temperature during a dynamic
in situ
experiment, showing a very good agreement with the temperature reading from the holder.
Controlled production and growth of hexagonal gold nanostructures during self‐assembly on a Ge(001) surface
Authors: Gauquelin Nicolas , Jany Benedykt , Nikiel Marek , Wilhammar Tom , van Den Bos Karel , van Aert Sandra , Szajna Konrad , Verbeeck Johann , Van Tendeloo Gustaff , Krok Franziszek
Published: December 2016

Self‐organized gold nanostructures on Ge(001) surfaces are currently of special interest due to their applications for mono‐molecular electronic devices and the growth of Ge nanowires. The understanding of electrical as well as physical properties of the system is of great importance and is strongly linked to its atomic structure.

Here, we report on studies concerning post‐annealing induced nanostructure formation after room temperature deposition of a thin film of Au on Ge(001) in Ultra High Vaccuum (UHV). Deposition of 6 monolayers of Au by Molecular Beam Epitaxy (MBE) resulted in the formation of a continuous Au overlayer which was confirmed to be crystalline by Reflection High Energy Electron Diffraction (RHEED). Just after deposition, the samples were post‐annealed in UHV to temperatures ranging from 473 K to 773 K with different cooling rates. The self‐organized structures, in the form of Au nanoislands, were characterized by HR‐SEM and HR‐STEM methods as well as EBSD. It has been found that a preferential island orientation exists along the crystallographic direction of the substrate surface as can be seen in Fig. 1(a),(b). For an annealing temperature close to the eutectic temperature of the Au/Ge system (640 K), a change in size and shape of the Au nanoislands is observed as well as the occurence of the hexagonal phase of gold, indicating eutectic melting of the system as can be seen in Fig. 1. Au(011) orientation of the Au islands with respect to the Ge surface was revealed, independent of the annealing temperature Fig. 1(c),(d). TEM measurements of Au/Ge(001) sample cross sections revealed that the nanoislands created upon annealing at T640 K part of the islands are buried beneath the substrate surface (Fig. 1g), which confirms eutectic AuGe melting. The chemical composition of the Au/Ge interface was uncovered using quantitative atomically resolved HAADF‐STEM and indicates the absence of alloying (Fig. 1f and 1h). The crystallographic structure of the Au islands and the presence of hexagonal gold as well as the Au/Ge interface were studied by quantitative atomically resolved HAADF‐STEM allowing the determination of the structure.

N.G. and J.V. acknowledge funding from the European Research Council under the 7th Framework Program (FP7), ERC Starting Grant 278510 VORTEX. F.K. acknowledges funding from the Polish National Science Center, grant no. DEC‐2012/07/B/ST5/00906. All authors acknowledge financial support from the European Union under the Seventh Framework Program under a contract for an Integrated Infrastructure Initiative (Reference No. 312483‐ESTEEM2).
Probing the heterogeneous nucleation interface of
T
i
B
2 in Al alloys
Authors: Li Jiehua , Hage Fredrik , Ramasse Quentin , Schumacher Peter
Published: December 2016

The grain refinement of Al alloys has been extensively investigated for several decades both in industry and academia, not only through attempts at developing efficient grain refiners, but also with a view to achieve a better understanding of the grain refinement mechanism [1‐7]. The addition of Al‐Ti‐B grain refiners (e.g. Al‐5Ti‐1B, wt. %) during the grain refinement of Al alloys has been widely investigated due to these compounds' higher nucleation potency and wide potential for industrial applications. Various theories regarding the grain refinement mechanisms of Al‐Ti‐B refiners have been proposed [1‐4]. Despite differences between all these theories, it is generally accepted that Ti has multiple roles within the Al melt. One role is to create an enriched Ti region leading to the formation of an Al
3
Ti monolayer necessary for the heterogeneous nucleation of Al on the stable boride substrates (TiB
2
) [5, 6]. The other role is to act as an effective growth restrictor factor [7]. It is the combined effects of the enhancement in nucleation site numbers and of the growth restrictions that result in the formation of desirable, small uniform equiaxed Al grains. It is well accepted that Ti is more likely to segregate to the TiB
2
/ a‐Al interface affecting its structure and thereby the constitutional undercooling at the solid‐liquid interface [5, 6]. The presence of the Al
3
Ti monolayer is still fervently disputed [5‐7]. To resolve this disagreement, an atomic scale experimental investigation on the heterogeneous nucleation interface between TiB
2
and α‐Al in conventional castings (e.g. in alloys containing < 0.15 wt. % Ti that have not been melt spun) would be required.

This paper employs atomic scale high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) to probe the heterogeneous nucleation interface of TiB
2
in Al alloys, with a special focus on the partitioning of solute elements (Ti) to TiB
2
. A significant Ti partitioning to the whole surface of TiB
2
was unambiguously observed in the commercial grain refiner (Al‐5Ti‐1B), as shown in Figure 1 and Figure 2. However, such prevalent Ti partitioning was not observed on the basal planes of TiB
2
in Al‐Si based alloys with high Si concentrations, which could be used to explain why Si poisoning occurs. In order to avoid / reduce the Si poisoning, CrB
2
was added together with TiB
2
. In this case, a significant Cr partitioning to the whole surface of TiB
2
was observed, which may minimize the lattice mismatch with Al and / or improve the stability of a Al
3
Ti monolayer on TiB
2
, as shown in Figure 3. This investigation provides a clearer picture about the heterogeneous nucleation interface between TiB
2
and Al and further develops heterogeneous nucleation theory.
Nanoscale maps of magnetic behavior using
STEM‐EMCD
Authors: Thersleff Thomas , Muto Shunsuke , Spiegelberg Jakob , Rusz Ján , Leifer Klaus
Published: December 2016

Key to the advancement of magnetic materials is the exploitation of emergent magnetic behavior arising from nanoscale confinement. A comprehensive understanding of this behavior requires a technique capable of resolving it and mapping its relationship to parallel nanoscale property domains such as local structural imperfections, chemical environment, and interfacial proximity. The relatively young electron absorption spectroscopy technique known as Electron Magnetic Circular Dichroism (EMCD) [1] promises to meet these criteria, and it has already demonstrated qualitative [2] and quantitative [3, 4] results for parallel electron probe illumination on sample regions in the sub 100 nanometer range. While this already represents a spatial resolution superior to what can be achieved with x‐rays [5], the use of parallel electron illumination means that high spatial resolution can only be achieved through the use of energy filtered diffraction patterns [3, 6] or energy filtered TEM imaging techniques [7].

In this work, we describe our progress in the development of an experimental methodology utilizing convergent electron probes for the purposes of acquiring EMCD datasets. We name this method STEM‐EMCD (see figure 1) and argue that it has two significant advantages over parallel beam illumination schemes. First, the use of a convergent probe allows for the acquisition of arbitrarily large datasets, extending the effective acquisition time on a region of interest well beyond what is feasible for a single‐shot experiment using parallel illumination. This substantially improves the signal to noise ratio of EMCD spectral pairs, as shown in figure 1, and can be employed in such a way to mitigate significant beam damage. Second, the diameter of the electron probe can be reduced to one nanometer or less. If appropriate multivariate statistical methods are used to exploit spectral redundancy in the datacubes, it becomes possible to accurately approximate the raw data using a significantly reduced parameter space, dramatically suppressing the influence of statistical noise. We demonstrate that this allows for sum rules to be applied on individual spectral pairs, enabling real‐space maps of magnetic transitions to be generated with a spatial resolution approaching that of the beam diameter, as shown in figure 2. We conclude with a discussion of some of the challenges still faced by the STEM‐EMCD method as well as its prospects for directly addressing some of the most elusive questions in contemporary research in nanomagnetism.
Accurate and precise measurement of cluster sizes in localisation microscopy images using the Rényi divergence
Authors: Staszowska Adela , Fox‐Roberts Patrick , Cox Susan
Published: December 2016

Localisation microscopy is a super‐resolution imaging technique based on detecting randomly activated single molecules in a sequence of images. A super‐resolution image is then reconstructed as a collection of discrete points, using all of the localised single molecule positions. Clustering analysis of these points can provide quantitative information about sample structure, size of features and/or their number. The information obtained from clustering analysis allows characterisation of the functions or properties of biological systems, for example examining signalling pathways in T‐cells antigen receptors. However, quantitative analysis of clusters in localisation microscopy images is challenging because the clusters are usually small and surrounded by relatively high noise.

The Rényi divergence quantifies differences between two distributions (in this case the observed data and a reference distribution). Its sensitivity to the degree to which one distribution differed from another can be tuned with a scaling parameter α, which allows us to adapt its robustness to noise. We approximated the data distribution by counting all points which were positioned closer to each other than a set threshold and the reference distribution as all the points concentrated in a single cluster. Ripley's K function, which is widely used for performing localisation microscopy analysis, is a special case of the Rényi divergence.

Here we present a comparison of the accuracy and precision of cluster size measurement performed using the Rényi divergence and Ripley's K function. Initial tests involved establishing noise adaptability of the two analysis methods using simulated data sets with characteristics similar to experimental images (with increasing noise levels), and optimising the tunable parameter of the Rényi divergence. We find that the adaptability of the Renyi divergence method is a particular advantage when dealing with localisation microscopy data, in which characteristics can vary a great deal between datasets.
High resolution
EELS
on individual carbon nanotubes by monochromated
TEM
Authors: Senga Ryosuke , Pichler Thomas , Suenaga Kazu
Published: December 2016

Single‐walled carbon nanotube (SWNT) has been known to exhibit a wide range of electronic properties upon its atomic arrangement [1,2]. However it is still difficult to directly correlate the distinct electronic properties with its atomic structure from an individual carbon nanotube. Here, we successfully demonstrate highly localized electronic properties of individual carbon nanotubes with precise atomic structures by means of transmission electron microscopy (TEM) consisting of a monochromator.

We have used a JEOL TEM (TripleC#2) equipped with a Schottky field emission gun, a double Wien filter monochromator and delta correctors. The energy resolution is adjustable from 30 to 200 meV by choosing the energy selecting slits in the dispersion plane of the monochromator. We have performed the electron energy loss spectroscopy (EELS) on individual freestanding SWNTs with the scanning TEM (STEM) mode at 60 kV. The target SWNTs are also imaged by both STEM/TEM modes to fully assign their atomic structures.

Figure 1(a) presents a TEM image of two closely aligned SWNTs (inset) and their C K‐edge (C1s) spectra. The chirality of thicker SWNT (top) and thinner one (bottom) are assigned as (9, 7) and (6, 5), respectively. Each spectrum has several sub‐peaks on the π* response and exhibits completely different features. The line shape analysis [3] suggests that the π* response of (6, 5) tube consists of four sub‐peaks related to the van Hove singularity (vHs) (1s →E
1
*, E
2
*, E
3
* and E
4
*) and a broad π* resonance (Fig. 1(b)). The position of the sub‐peaks fairly consists with the vHs in the shifted ab‐initio DOS [3] (inset in Fig. 1(b)). The relative intensities are possibly influenced by core‐hole effects. The valence‐loss spectra taken from the same SWNTs also exhibit the peaks related to the vHs (E
i
→ E
i
* (i=1,2,…)). However it is difficult to distinguish the two closely aligned SWNTs from the valence‐loss spectra because the large delocalization mixes the peaks for both SWNTs. This means that the core‐loss spectra has a much higher special resolution and reflects more localized electronic structures.

Then, we have experimentally investigated how the core‐loss spectra changes corresponding to nonperiodic structures. Figure 2 shows STEM images of a typical hybrid SWNT and its C K‐edge (C1s) spectra. We have confirmed from TEM image (not shown here) that the hybrid SWNT involves a serial junction between the thinner (11, 1) semiconducting part and the thicker (10, 10) metallic part. The C K‐edges (i to x) presented in Figs. 2(b) and 2(c) are obtained when the electron probe is scanned across the broken lines (i to x) in Fig. 2(a). The π* peaks in the junction part (iv to vii) are different form the spectra for either (10, 10) and (11, 1) and show new peaks (black arrows in Fig. 2(c)) reflecting the distinct electronic structures. Such a highly localized measurement of electronic properties for individual carbon nanotubes has never been realized by any other methods.
New phases in
Cu3Si
solid solution
Authors: Mariana Klementová , Correa Cinthia , Dřínek Vladislav , Brázda Petr , Kopeček Jaromír , Palatinus Lukáš
Published: December 2016

Cu
3
Si is used as a catalyst for the production of technologically highly important chlorosilanes, an intermediate compound in the production of ultrapure silicon for the semiconductor industry [1]. Copper silicides and copper germanides have also been studied as materials for applications as contacts and interconnects in Si and Ge‐Si electronic devices [2]. Different structures of Cu
3
Si and Cu
3
(SiGe) have been reported over the years [3,4,5], however, new aspects have been revealed by this study.

Nanoobjects of various shapes were prepared by the CVD method using organometallic precursors (SiH­­
4
, EtSiH
4
, BuSiH
3
, and their mixtures with H
2
) and copper substrates at temperature of about 500 °C. For comparison and more variability in composition, bulk samples of various compositions (Cu
78
Si
22
, Cu
77
Si
23
, Cu
76
Si
24
, Cu
75
Si
25
, Cu
74
Si
26
) were prepared by arc melting.

Samples were screened by SEM/EDX/EBSD and powder XRD. Selected samples were studied by single‐crystal XRD and TEM. TEM was performed on a Philips CM 120 (LaB
6
, 120kV) equipped with a NanoMEGAS precession unit DigiStar, an Olympus SIS CCD camera Veleta (2048x2048), and an EDAX windowless EDX detector Apollo XLTW. Precession‐assisted electron diffraction tomography (EDT) in microdiffraction setup was used to acquire data for structure characterization of nanoobjects.

In the Cu
3
Si solid solution (Fig. 1), two variants were identified sharing the same average structure (
P
6
3
/
mmc
,
a
=4.06Å,
c
=14.66Å). The structures of the two variants (diagonal (D) and off‐diagonal (O)) differ in the placement of satellite reflections, which are caused by strong modulation of the honeycomb copper layers. The D and O variants are most likely stabilized by composition. The D‐variant was observed in bulk sample with composition of Cu
77
Si
23
and also in the nanoplatelets prepared by CVD on Cu‐substrates, whereas the O‐variant was present in the samples richer in silicon. Moreover, additional periodicity along c‐axis was detected in Cu
3
Si compared to Cu
3
(SiGe) with
c
=7.33Å (Fig. 2). Temperature experiments are currently under progress, and will be also presented.
Atomic scale structure and local chemistry of CoFeB‐MgO perpendicular spin injector
Authors: Tao Bingshan , Devaux Xavier , Barate Philippe , Renucci Pierre , Xu Bo , Frougier Julien , Hehn Michel , Mangin Stéphane , Jaffres Henri , George Jean‐Marie , Marie Xavier , Han Xiufeng , Wang Zhanguo , Lu Yuan
Published: December 2016

The development of spin light emitting diode (spin‐LED) with spin injectors with perpendicular magnetic anisotropy (PMA) is a prerequisite for the conversion of carrier spin polarization to the circular polarization (PC) of photon without magnetic field for practical applications. In our previous study, a maximum PC at zero field (20% at 25K, 8% at 300K) was reported with an ultrathin perpendicular MgO/CoFeB spin injector with Ta capping layer [1]. To achieve a good PMA, post‐annealing is indispensable with a narrow optimal window around 250°C. Recent work shows that the PMA can be increased by 20%, by replacing Ta layer with a Mo layer [2]. Moreover, Mo capping increases the temperature stability of the spin injector, allowing post annealing up to 425°C.

The specific crystal structure, local chemistry and local bonding of all staking layer that make up the perpendicular spin injector remain unclear, hindering the establishment of the relationships between the material properties and the nanoscale structure. The interfacial anisotropy depends critically on the crystal structure. The composition, chemical states, and local defects in CoFeB and in MgO are known to be critical for transport and magnetic properties. Experimentally the structural and chemical issues in CoFeB‐MgO have been addressed utilising HRTEM, EDS, XPS, secondary‐mass spectroscopy. A consistent picture has not emerged yet due to the difficulty of probing local atomic details. In particular there is many contradictory results on the fate of B following annealing, including diffusion into Ta [3], segregation at the CoFe interface [4], B diffusion into MgO forming a magnesium boride phase [5].

Here, we combine HRTEM, aberration corrected STEM (HAADF and BF) and spatially resolved EELS to follow the structure and the local chemistry of MgO\ CoFeB capped with Ta or Mo, before and after annealing up to 400°C. The spin injectors consist in 2.5 nm of MgO / 1.2 nm CoFeB / 5 nm Ta or Mo deposited on a GaAs‐based LED (Fig 1). For FeCoB layer caped with Ta at temperature higher than 250°C, annealing favours the diffusion of B into Ta when CoFe crystallises then Ta diffuses trough the CoFe layer into the MgO barrier (Fig 2). For CoFeB layer caped with Mo, boron stays in the CoFe layer close to the CoFe‐Mo interface (Fig 3). Mo diffusion into the CoFe layer also occurs, but for higher temperature than for Ta diffusion. In extension we'll show that for both structures, annealing has a strong influence on the Fe/Co ratio at the MgO‐CoFe interface and at the CoFe‐capping layer (Fig 2 and 3). The influence of the structure and of local chemical composition on the properties of the spin injector will be discussed.
Colloidal Quantum‐Dot Heterostructures Studied Using Aberration‐Corrected Scanning Transmission Electron Microscopy
Authors: Patriarche Gilles , Pantzas Konstantinos , Pedetti Silvia , Nasilowski Michel , Tessier Mickael , Cassette Elsa , Malher Benoit , Dubertret Benoit
Published: December 2016

Complex colloidal semiconductor quantum‐ dot heterostructures, such as core/shell or core/crown nanoplatelets, can now be readily synthesized [1‐4]. Such heterostructures significantly enhance the optical properties of the colloidal quantum dots. The optical properties of these colloidal quantum dots depend not only on the morphology of the heterostructure – i.e. the size and shape of the core‐, but, more importantly on the chemical nature and the presence of a composition gradient at the heterostructure interfaces, and on the elastic deformation inside the quantum dots that is due to a lattice mismatch between the core and shell/crown materials. The study of these heterostructures through aberration‐corrected Scanning Transmission Electron Microscopy (STEM) provides access to their structure down to the atomic scale. High Angle Annular Dark Field STEM images, in particular, provide direct access to the atomic structure of the nanoparticles, and through the contrast of the atomic columns (“Z‐contrast” images) to their chemical nature. Therefore, atomic resolution STEM images allow one possible to precisely map the strain fields of the heterostructure. Finally, chemical information accessed through the Z‐contrast can be correlated to quantitative STEM‐EDX with a spatial resolution of 1 nm. The present talk summarizes such studies conducted on CdSe/Cd(Zn)S core/shell [1,2], and core/crown CdSe/CdS [3,4] and CdSe/CdTe nanoplatelets.
Investigation of Biofilm Forming Capabilities on Stainless Steel Surfaces of Some Foodborne Pathogens
Authors: Gürsu Bükay Yenice , Dikmen Gökhan , Dağ İlknur
Published: December 2016

Biofilm is a major problem in the food industry produced by pathogenic microorganisms, because adhered cells to biotic or abiotic surfaces are more resistant against antimicrobials and disinfectants than planktonic cells.The retention of bacteria on food contact surfaces is an important in food processing, catering and the domestic environments.
Salmonella
species and
Listeria monocytogenes
are the most important food‐borne pathogenic bacteria. In this study,
L. monocytogenesis
and
Salmonella
species isolated from several food sources in the region of Eskisehir were screened for their biofilm forming ability on the stainless steel material and biofilm development stages were examined with scanning electron microscopy (SEM)

In our study,
L.monocytogenesis
ve
Salmonella spp
isolates were identified by standard microbiological procedures. The biofilm forming capabilities of isolates were tested by microtiter plate and tube methods. Moderate and strong degree of biofilm‐forming organisms on the stainless stain surfaces were taken into electron microscopic procedures. They were examined on 2, 4, 6, 24 ve 48
th
hours for their structure of the biofilm and imaged by SEM (JEOL JSM‐5600LV).

Stainles steel materials are commonly used surfaces in food production, storage and processing processes.
L.monocytogenesis
and
Salmonella spp
. have been shown to adhere to stainless steel surfaces. According to our results, biofilm formation has started from 24
th
hour. Isolation of theese microorganisms from variety foods showed that these foods can be easily infected with bacteria at any stages of food production. It carries risks for public health.
Pre‐Sertoli Cells: A Light And Electron Microscopic Study
Authors: Albayrak Merve , Hürdoğan Özge , Aktar Fadime , Kuntsal Ekin , Tapul Leyla
Published: December 2016

INTRODUCTION

Sry gene expression, starting at 10,5dpc, initiates male sex determination. Sry gene initiates testis differentiation by regulating the differentiation of precursor supporting cells not into Granulosa cells but Sertoli cells (1). Pre‐Sertoli cells are the first cell type to show sex differentiation in gonads. This study aimed to observe the light and electron microscopic features of pre‐Sertoli cells.

MATERIAL AND METHODS

In this study 27 embryos obtained from 6 balb/c type pregnant female mice from 11,5 to 12,5 dpc were used. Sections were observed by using light and electron microscope.

RESULTS

Pre‐Sertoli cells, stained with PAS, were seen as forming a cord around germ cells starting from central parts of gonads (Fig.1). Germ cells and epithelial cells lining the gonadal ridge were PAS (‐). On electron microscope pre‐Sertoli cells were seen mostly disorderly but also clustered and encircled the germ cells at some parts. The nuclei of pre‐Sertoli cells were pulled at one pole of the cells. The cytoplasm at the other pole consisted of granuler and smooth endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria and large amount of glycogen granules (Fig. 2). Lipid granules were also seen in cytoplasm.

DISCUSSION

Pre‐Sertoli cells are found disorderly in gonadal ridges as they are first developed. Shortly after that they proliferate and cumulate to form circular cords around germ cells (2). The accumulation of glycogen starting in pre‐Sertoli cells is responsible for PAS(+) staining. The in vitro study of Matoba et al. stated that, testis specific accumulation of glycogen is a tissue‐otonomous event as it is possible even with no serum or in the absence of adjacent mezonephrosis(4). The same study puts forward that the activation of PI3K‐AKT pathway after Sry gene expression enhances glycogen accumulation in pre‐Sertoli cells. Sox9, Mis, Dhh, Fgf9 are reported as pre‐Sertoli cell marker genes(3). By using the fact that pre‐Sertoli cells are stained PAS(+) because of glycogen they use as energy resource, it can easily be determined if the gonad is developing as male or female, before it is seen morphologically at 12,5dpc.
Exciton and Plasmon Mapping at the Nanoscale
Authors: Nerl Hannah , Winther Kirsten , Hage Fredrik , Thygesen Kristian , Houben Lothar , Ramasse Quentin , Nicolosi Valeria
Published: December 2016

Excitons and plasmonic interactions, which are effectively responsible for the transfer of energy within devices such as solar cells, LEDs and semiconductor circuits, have been understood in theory for decades. However, the photophysical behaviour within materials has always been rather difficult to understand and be directly observed.

Surface structure, localised thickness variations and presence of edges are bound to influence the macroscopic properties of the materials. Understanding the local surface structure and chemistry of these materials at the nanoscale is crucial in order to reach the full potential of the materials for real‐life applications. Hence, there is a need to fully characterise the physical and chemical properties from the bottom up i.e. at the level of individual atoms and to map the optoelectronic properties where they happen.

Due to recent technical improvements we can now access parts of the low loss electron energy‐loss (LL EEL) spectra which had previously been inaccessible. This opens up new possibilities to study nanomaterials not only at unprecedented energy but also – contrary to bulk optical techniques – with a spatial resolution at the nanoscale, as described by Zhou, Dellby [1]. Although some significant progress has been made recently in unravelling the physical origins of the LL EEL features as shown by Tizei, Lin [2], significant gaps in our understanding of the signals and their origins remain. In the study presented here, we used for the first time a combination of experimental monochromated LL STEM EEL spectroscopy and theoretical calculations using time‐dependent density functional theory (TDDFT) as well as the Bethe‐Salpeter equation (BSE) to study the optical properties of MoS
2
at the nanoscale with the aim to understand the origins of the peaks and regional variations of the complete LL EEL spectrum. We report that we identified and resolved as well as mapped mid‐bandgap excitonic signals at ~1.88eV and at ~2.08eV on MoS
2
flakes using monochromated LL EELS (figure 1) and confirmed their origin by BSE calculations; we also identified and mapped several plasmonic peaks (figure 1) using LL EELS combined with TD DFT. Furthermore, we observed great spatial variations in the LL EELS signal when comparing the edge to inner regions of a flake,
i.e
. with increasing number of layers, and we show how these can be largely attributed to beam geometry effects. The effects of the experimental set‐up on the low loss EELS signal will be discussed.
Phase identification of complex grain boundary precipitation in a high
Cr
and
Ni
superalloy upon direct‐aging
Authors: Spadotto Julio Cesar , Watanabe Masashi , Dille Jean , Solórzano Ivan Guillermo
Published: December 2016

The need for corrosion‐resistant alloys applied to support increasingly harsh environments at high temperatures resulted in the development of high chromium‐containing nickel‐base superalloys. It is well established in several complex multicomponent alloy systems, the concurrence of several modes of precipitation phenomena. Perhaps the most intriguing is the occurrence of concomitant general precipitation (GP, homogenous and heterogeneous) and discontinuous mode of precipitation (DP). While the former is controlled by lattice diffusion the latter is driven by grain boundary (GB) diffusion and migration. It is well established that the mechanical and corrosion properties depends critically on the phase stability under service conditions. This study is focused on identification of the different phases precipitated at a specific grain boundary. Here, the precipitation takes place in an high performance superalloy 33 with austenitic matrix and chemical composition (wt.%) of 32,75Cr‐32,53Fe‐31,35Ni‐1,49Mo‐0,54Cu‐0,4N‐0,012C‐0,63Mn‐0,30Si. For this purpose, a JEOL JEM‐ARM200CF aberration‐corrected scanning transmission electron microscope (STEM) has been used at Lehigh.

Figure 1A presents a complex precipitation product at a specific GB in this alloy upon direct‐aging at 700 °C for 100 h. Different phases have nucleated and grown, driven by the diffusion of a moving GB. The two diffraction patterns of Figs 1B and 1D correspondto both grains across the GB and the dark field (DF) TEM image of Fig. 1C shows the adjacent grain being consumed by the advancement of the GB reaction front of the DP. In a previous study [1], X‐ray elemental maps show the degree of partition of different substitutional elements (Fe, Ni, Cr, Mo) and interstitial N. In fact, one can identify more than two phases in this precipitate colony. In general, such complex GB precipitation products depend on the structure and thermodynamic properties of individual GBs [2].

Figure 2 shows a high angle annular dark field (HAADF) image of the region boxed in red in Fig. 1A. This TEM session was conducted in a ChemiSTEM FEI Titan at UFRJ with the foil upside down respect to Fig 1A. This study reveals that the discontinuous precipitation at grain boundary results in three different phases. The precipitate indicated by n° 1 at the GB reaction front itself has been identified as η phase, Cr
3
Ni
2
SiN, with diamond cubic crystal structure. At the original position of the GB, however, two different phases have precipitated: precipitate n° 2 is a M
23
C
6
carbide with FCC structure and precipitate n° 3 is an intermetallic σ phase with tetragonal structure. The precipitation of the latter is associated with embrittlement [3]. XEDS spectra and elemental mapping have corroborated such phase identification [1].
(S)TEM
Study of the Influence of Synthesis conditions on the Nanostructure and Performance of
Au/CeO2
Model Catalysts
Authors: Tinoco Miguel , Fernandez‐Garcia Susana , Lopez‐Haro Miguel , Hungria Ana Belen , Chen Xiaowei , Blanco Ginesa , Perez‐Omil Jose Antonio , Collins Sebastian , Okuno Hanako , Calvino José Juan
Published: December 2016

Ceria nanoparticles exhibiting controlled morphologies have been studied as model supports of gold nanoparticles to establish correlations between surface crystallography and catalytic performance [1]. It is generally assumed that the contacts between Au nanoparticles and support involve the expected ones, i.e. Au//CeO
2
{100} in the case of nanocubes, Au//CeO
2
{110} in nanorods and Au//CeO
2
{111} for nano‐octahedra. Nevertheless, it is important to recall at this respect that: (1) model crystallites involve more than one type of surface plane [2]; (2) previous reports have evidenced that gold nanoparticles anchor preferentially at sites allowing to maximize contact with {111} facets [3]; (3) the surface structure of the model support crystallites may strongly depends on the activation treatments performed on the catalyst prior to the catalytic assay. Therefore, as illustrated in this contribution, a combined 2D and 3D (S)TEM investigation is necessary to reveal the actual nature of the Au//ceria interfaces on these model supports.

CeO
2
nanocubes (CeO
2
NC) were prepared using a hydrothermal method. This support was then treated in an O
2
(5%)/He atmosphere at 600°C for 1 hour to simulate the influence of activation at high temperatures (CeO
2
NC600). Gold was deposited over the two supports by Deposition‐Precipitation method with the objective to anchor 1.5 wt. % of Au on each of these materials. The final gold loadings on those samples were 0.4% and 1.0% respectively (0.4% Au/CeO
2
NC and 1.0% Au/CeO
2
NC600 samples), which clearly indicated a large influence of the activation treatment on the capability of the model support crystallites to anchor the metallic phase on its surface.

HREM and HAADF‐STEM tomography confirmed that the CeO
2
NC surface was a mixture of {100}, {110} and {111} facets, the latter two resulting from truncations of the cubes at edges and corners. In the CeO
2
NC600 support, the {110} surfaces on the edges of the nanocubes, which appeared flat in the CeO
2
NC sample, were fully transformed into a system of {111} nanofacets. Additionally, those edges grew in extent after the calcination process, from less than 1% up to 25% after the thermal treatment. These results suggest that surface nanofaceting significantly promotes the deposition of gold.

In contrast to expectations, STEM studies revealed that Au nanoparticles were always preferentially anchored on {111} surfaces: on the vertices of 0.4% Au/CeO
2
NC (Figures 1a,2a) and on the {111}‐nanofaceted edges in the 1.0% Au/CeO
2
NC600 (Figures 1b, 2b). This result does not only explain the larger metal loading observed on the calcined support but also warns about simplifications about the nanostructure of these systems as well as on the importance of their detailed characterization by STEM.
Electron tomography analysis of
Pt/CeO2
catalyst powders synthesized by solution combustion
Authors: Roiban Lucian , Koneti Siddardha , Epicier Thierry , Nguyen Thanh‐Son , Aouine Mimoun , Morfin Franck , Piccolo Laurent
Published: December 2016

Transmission Electron Microscopy (TEM) or Scanning Transmission Electron Microscopy (STEM) can provide qualitative information on the distribution of metal nanoparticles over a support, as in the example of Fig 1 showing a STEM image of a Pt/CeO
2
catalyst. Nevertheless, as the obtained electron microscopy images are simply 2D projections of the object, they do not provide information on the 3D distribution of the particles which is an essential parameter controlling the catalytic activity. In this particular system, nanopores exist at the surface and a 3D imaging technique such as electron tomography is necessary in order to determine whether metal nanoparticles are anchored on the support surface or,
e.g
., trapped inside the oxide nanopores.

A 1 wt% Pt‐CeO
2
catalyst was prepared by one‐step solution combustion synthesis (SCS) [1], a fast and simple method favoring metal‐support interaction. The sample was analyzed by electron STEM‐HAADF tomography in a FEI environmental TEM (Fig. 2). The analysis was performed at two complementary scales: (i) at a relatively low resolution to gain insight into the ceria pore size and shape distributions, and (ii) at higher resolution to determine the Pt particle size distribution and location with respect to the support [2].

It is found that ceria has a bimodal pore size distribution, with small pores about 10 nm in size between the crystallites and bigger pores around 150 nm formed by winding up of ceria layers. It is highly probable that the synthesis route promotes this peculiar and usnusal microstructure. Noticeably, the present nano‐tomography analysis further demonstrates that only
ca
. 50% of the 6 nm‐sized Pt particles are located at the surface of the ceria, the other 50% being embedded in the support. This implies that only half the particles contribute to catalytic activity, which may have important consequences on the interpretation of catalytic data.
Effect of processing parameters on microstructure and mechanical properties of additively manufactured stainless steel
Authors: Vaideeswaran Kaushik , Sereda Olha , Zangui Youness , Saudan Hervé , Kiener Lionel , Dadras Massoud
Published: December 2016

Additive manufacturing (AM) allows for the building up of bulk structures through the fusion of powder particles layer by layer using a high power laser. This novel technique is practical for the fabrication of complex structures without any mold or tool, but this flexibility is accompanied by the delicate balance of AM processing and post‐processing parameters which are to be optimized to ensure the desired microstructure in order to obtain the required mechanical properties [1‐4]. The current study is aimed at understanding the effect of the AM processing parameters used for the preparation of AM samples on the resulting microstructure, its anisotropy according to growth direction, as well as its implications on the mechanical properties.

Bulk structures of conventional 316L grade stainless steel (with Cr‐16.5‐18.5%, Ni‐10‐13%, Mo 2‐2.5%, traces of Mn, Si, P, S, C) were produced by AM through selective laser melting (SLM), followed by an annealing heat treatment for material internal stress release. Two sets of processing conditions with variations in parameters such as the incident laser energy, the laser spot size and the direction of growth were varied, and the resulting effect on the microstructures both before and after the heat treatment are studied through diverse microscopy techniques such as SEM, EBSD and TEM. The variation in the phase distributions, grain size and porosity are analyzed as a function of the process parameters. Mechanical properties are measured by tensile tests completed by microhardness. Additionally, XRay Diffraction (XRD) has been used for identifying the phases present in the alloy and also for measuring residual stress and crystallographic texture.

The presence of the pores with unmolten particles has been observed in all samples produced with lower laser energy (Fig. 1). Alongside, the layers formed immediately on top of such pores show different microstructure, with the new phase observed consistently on the same side of the porosity in all samples (Fig. 2). The origin of this phase separation is expected to be from the differential heat dissipation (during fabrication) through the pore as opposed to the bulk material. The mechanical properties of the bulk structures (tensile stress, microhardness) showed that increasing the laser power results to an increase in the yield point. Fracture surface (Fig. 3) shows clearly presence of the pores which influences largely the mechanical properties such as ductility.

Overall, through the variation of the process parameters, the trend in evolution of the microstructural and mechanical properties is elucidated aimed at optimizing the parameters for AM products of 316L stainless steel.
Examination Of Retinoic Acid And Oct3/4 Relationship In Gonadal Development
Authors: Albayrak Merve , Tapul Leyla
Published: December 2016

INTRODUCTION

Early developmentof the gonads is monitored in the same morphological appearance in both sexes. Retinoic acid, plays a role in the formation process of mammalian germ cells and is also effective in the selection of male or female identity (2). Oct3/4, which is a transcription factor, is expressed in blastula, morula, inner cell mass of blastocyst and then in the primordial germ cells (8). Retinoic acid has been reported to be one of the possible regulators of Oct3/4 expression (3,7). This study was planned to evaluate the effects of the exogenous retinoic acid on gonadal development in mouse embryos and Oct3/4 expression of primordial germ cells.

MATERIALS AND METHODS

In this study, we used 12 Balb/c pregnant mice. No drug was given to the control group. The experimental group of Balb/c mice were given by oral gavage a dose of 80 mg / kg of retinoic acid dissolved in a mixture of absolute ethyl alcohol‐corn oil (the days of 6.5, 7.5, 8.5). In the meantime, the second control group was formed and given by oral gavage only a suspension of absolute ethyl alcohol‐corn oil for 3 days. Total of 73 embryos 11.5 ‐ 12.5dpc from the control and experimental groups were evaluated.

RESULTS

In fetal gonads of the experimental group (Fig. 1and 2), a smaller number of primordial germ cells was marked with Oct 3/4 immunohistochemically compared to the first and second control groups.

DISCUSSION

A fine set of changes in the levels of retinoic acid are reported to control gonadal development at different stages of embryogenesis (1). Retinoic acid has been reported to have an important role in the sex differentiation of mouse gonads and shows its effect as a meiosis inducing factor (4,5). Suppression of Oct3/4 expression in primordial germ cells that reached and settled in the gonads, is a critical step in the process of embryogenesis. A retinoic acid sensitive element localized in the promoter‐enhancer region has been reported to play a role in suppression of Oct 3/4 in a study of embryonal carcinoma cells(6). The study concluded that, retinoic acid regulates the development and differentiation of primordial germ cells during embryogenesis by suppressing Oct 3/4 expression and the opinion to control this process externally by using activators or inhibitors of retinoic acid receptors, become stronger.
Diagnostic molecular biology with whole genome sequencing versus diagnostic electron microsopy ‐ a change of paradigm in diagnostic
EM
?
Authors: Richter Susanne
Published: December 2016

Starting in the 1960ies, with a common availability of high resolution microscopes and the introduction of negative staining and ultrathin sectioning of microwave embedded infectious tissues, pathogen diagnosis on basis of electron microscopy (EM) has become increasingly important. An EM‐based lab diagnosis turned out to be useful in a wide spectrum of indications like “rapid diagnosis in emerging diseases”, “search for otherwise undetectable agents” (“open view”), the need for “catch‐all‐methods” and/or “rapid differential diagnosis”. Since then, the use of transmission electron microscopy, and to a lesser extent scanning electron microscopy provide a multiplex platform for the detection and differentiation of a wide range of pathogens (Fig. 1‐3). Examples will be given. In past, EM was involved with the detection and identification of broad range of viruses some of which have impacted on human, veterinary and wildlife health. Many of the diseases caused by viruses have emerged from anthropogenic based perturbations of the environment including altered habitat e.g. changes in the number of vector breeding sites and/or host reservoirs, niche invasions, changes in biodiversity, genetic changes of disease vectors or pathogens, and environmental contamination of infectious agents.

However, the use of diagnostic EM declines radically since the late decade of the 20th century which was characterized by a continuous shifting of research interests to molecular biology. With whole genome sequencing some of the indications mentioned above like “catch‐all‐method” or “search for undetectable pathogens ‐ open view” seem to be on first sight no longer existing. Is it now a change of paradigm, a still going onward decline or may diagnostic EM play still an essential role in pathogen diagnosis? The future of diagnostic EM, its constraints and its welfare for the society is discussed. Be aware, since September 11
th
executive authorities have noticed that molecular biology and EM complement each other and most modern diagnostic centres of disease control still execute both techniques in their diagnostic programme; but for how long?. Additionally increased mobility, changes in life style, global trade and social unrest are supporting the spread of emerging or re‐emerging infections. Anyway, we should be aware that molecular biology of today with whole genome sequencing as well as electron microscopy bear a lot of uncertainties in their technical procedure ‐ technical sources of error which should be always be in mind during diagnostic procedure.