bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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].
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.