bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative analysis of
A
l
N
/
S
i
C
interfaces in
A
l
G
a
N
/
G
a
N
heterostructures grown on
S
i
C
Authors: Gkanatsiou Alexandra , Lioutas Christos B. , Frangis Nikolaos 
Published: December 2016

Wide band gap semiconductors, such as SiC and GaN, exhibit many attractive properties: a unique combination of the wide band gap, high breakdown field, high saturation velocity and the ability to form high quality AlGaN/GaN heterostructures with good transport properties make them ideal candidates for high power and high frequency applications. Hexagonal silicon carbide materials (SiC) are considered to be promising candidates for electronic devices as the third generation key materials for transistors. A typical example of a high performance device is the Al
x
Ga
1‐x
N/GaN heterostructure used as a high electron mobility transistor (HEMT) [1‐2].

As 6‐inch SiC wafers are being introduced into the market, a decrease of the substrate off‐cut for SiC heteroepitaxy is desirable to reduce the manufacturing costs [3‐4]. Therefore, multilayer (5 layers) and multicomponent structures (based on GaN and related materials) were grown on 6H‐SiC (with a misorientation of 1 deg. off from the (0001) plane) substrates using the MOVPE method, for high power applications. The layers were grown epitaxially, as it was confirmed from the corresponding electron diffraction patterns. Several types of interfaces were observed between the layers that either ran parallel to the interface or formed V‐shaped defects (e.g. the SiC/AlN, GaN/AlN, GaN/AlGaN interfaces etc.). Moreover, High Resolution TEM (HRTEM) images showed the existence of steps in the 6H‐SiC/AlN interface. A typical HRTEM image where an atomic scale step is observed is shown in Fig. 1.
In this study, quantitative analysis of the 6H‐SiC/AlN interface is presented based on experimental HRTEM micrographs, showing and proving the steps sites, the layers' sequence and any strain relaxation situation existing. A structural model based on this analysis is proposed and simulated HRTEM images are also obtained. The corresponding atomic models proposed are found to describe well the 6H‐SiC/AlN interface, with the corresponding computer simulation images coinciding with the experimental HRTEM images. An example is shown in Fig. 2, illustrating the monolayer step observed in the 6H‐SiC/AlN interface. In Fig. 3, a characteristic plot shows the phase shift of the fitting of the intensity's distribution along a line that corresponds to the projection of a close‐packing layer revealing the stacking sequence and therefore the starting position of the AlN epilayer. Moreover, the comparison of the sequence clearly shows the height of the step and any alteration on the stacking sequence between the two parts of the image. Finally, the computer simulated image, as shown in Fig. 4, coincides well with the HRTEM image shown in Fig. 1.
Superresolution and depth sensitivity in
HRTEM
through structured illumination
Authors: Van den Broek Wouter , Koch Christoph T. 
Published: December 2016

In the weak phase object approximation the wave function in the objective lens' back focal plane is a convolution of the illuminating wave, ψ
in
, with the projected potential, V, multiplied with the coherent transfer function, H, i.e. ( ψ
in
* ( 1 + σV ) ) H, with σ the interaction constant and * the convolution operator. Therefore, frequencies from above the cutoff‐frequency in H's objective aperture enter the image formation in aliased form, as is illustrated in Fig. 1a. In this abstract, fully dynamical multislice simulations are carried out to investigate if these higher frequencies can be disentangled and superresolution can be achieved.

Simulations of [112] Si are set up with FDES [1], the supercell is 5.12 nm by 5.12 nm wide and is 5 nm thick on the left side and 2.5 nm on the right‐hand side. The in‐plane sampling distance and the slice thicknesses were set to 0.01 nm. Si in the [112] direction displays dumbbells that are 0.075 nm apart, corresponding to a spatial frequency of 13.3 nm‐1 or 33.4 mrad at an acceleration voltage of 200 kV. The imaging is done with illumination that is structured to have random‐but‐known phases and that is bandwidth limited to 20 mrad, see Fig. 1b and Fig. 2a. The objective lens behind the sample is set to Scherzer conditions with an objective aperture of 20 mrad, a defocus of ‐18.8 nm and a spherical aberration of 94.0 µm, thus yielding a point resolution of 0.125 nm that is clearly insufficient for resolving the dumbbells. Eight images are recorded with the simulation shifted by 0.27 nm between consecutive recordings; the first image is shown in Fig. 2b, the others look similar.
A three‐dimensional reconstruction was set up in IDES [2,3] with three slices 2.5 nm apart and a pixel size of 0.01 nm; amplitude and phase of the impinging wave and the settings of the objective lens were assumed known. Multiple scattering was accounted for by propagating the wave between slices with the Fresnel propagator. A Polak‐Ribière conjugate gradient search was used to minimize an error function that was chosen as the sum of absolute differences between measurement and corresponding data simulated from the current object estimate. Contrary to [2,3] no sparse regularization has been applied. In Fig. 3a the middle slice of the reconstruction is shown, displaying a clear separation of the Si‐dumbbells. Furthermore, the lower slice displayed in Fig. 3b shows that depth sensitivity with a resolution of at least 2.5 nm is achieved as the right‐hand side, which by construction does not contain any atoms in its lower half, indeed does not display any. [4]
Quantification of particles in samples of a split‐virion influenza vaccine
Authors: Nicolai Marie‐Claire , Deliot Aurelie , Ronzon Frederic , Cotte Jean‐François , Manin Catherine , Nemecek Daniel 
Published: December 2016

Influenza is an infectious disease caused by
Orthomyxoviridae
viruses that infect 3‐5 million people worldwide during seasonal epidemics. Influenza vaccines must be produced and administred annually to respond to the high rate of mutations and possible exchange of genomic segments between different strains. The vaccines are produced by a well established prodedure in inoculated embryonated eggs. Influenza virions are purified by sucrose gradient and then split by detergent filtered and inactivated by formaldehyde. Samples of split virions contain mainly HA and NP viral proteins.

To monitor quality of produced vaccines, quantitative information about the oligomerization state and molecular assembly of antigens in produced lots is desirable. We have developed a new approach to determine the size distribution of particles in split‐viron influenza vaccine samples by electron microscopy and could thus interpret elution profiles from the asymmetrical flow field‐flow fractionation (A4F) method. Samples were imaged by negative‐stain electron microscopy using organo‐tungstate stain (nanoW, pH 8.0) at 19,000x magnification (5.59 Å/pix) and 4‐μm defocus (Figure 1). About 40‐60 micrographs were initially filtered to remove variations in background and improve signal‐to‐noise ratio [1]. Individual particles were then segmented by a watershed algorithm [2]. Areas of the segmented 2D projections were determined in ImageJ [3] and plotted as histograms of the size distribution. (Figure 2). This approach is able to distinguish among different oligomeric states of HA and NP subunits in the sample, however all larger assemblies and aggregates are not resolved.
In parallel, we analyzed the same samples by A4F. Elution profiles resolved three peaks of small particles (diameter 200 nm). While the first three peaks correspond to the HA and NP oligomers resolved in the size distribution resolved in the analysis by electron microscopy, the latter peaks reflect presence of large lipid vesicles with embedded HA proteins. Interpretation of the A4F elution profiles allows routine screening and monitoring of produced split‐virion influenza vaccines.
This study has been funded by Sanofi Pasteur.
Correlative
SEM
techniques for resolving complex microstructure of
CoCrFeNiZrx
High Entropy Alloys
Authors: Jelen Andreja , Guim Hwanuk , Dolinšek Janez 
Published: December 2016

High‐entropy alloys (HEAs) introduce a new concept of developing advanced metallic materials with properties that conventional alloys, based on one principal element, cannot achieve [1]. Other multi‐component metallic systems are quasicrystals (QCs), complex metallic alloys (CMAs) and bulk metallic glasses (BMGs).
HEAs are multicomponent mixtures of 4 to 9, and occasionally up to 20 chemical elements, in similar concentrations, ranging from 5 to 35 at.% each, where the high entropy of mixing can stabilize disordered solid‐solution phases with simple crystal structures like a body‐centered cubic (bcc), a face‐centered cubic (fcc) and a hexagonal close‐packed (hcp), in competition with ordered intermetallic phases and phase‐segregated mixtures [2]. Though the average crystal structure of a HEA is generally simple, microstructure might be highly complex, as will be shown later in this presentation.

In our research, the HEA series CoCrFeNiZr
x
(x = 0.40, 0.45, and 0.50) has been investigated. Various SEM techniques were employed, including backscattered‐electron (BSE) imaging, EDS point analysis, chemical mapping and EBSD.

The results reveal high complexity of the HEAs' microstructure and helped us to determine the grains' composition. Brief outline is presented in the four figures shown below. Figs. 1 and 2 show BSE SEM images. The coarsest interpretation is that the samples are composed of two different types of microstructures: (1) rounded dark phases and (2) fine interweaving of the light and dark phases. Higher magnification of the image in Fig. 2 shows the “invisible borders”, where the fine microstructure changes its character. EBSD investigations at lower magnification (2.000x) revealed that the “invisible borders” correspond to grain boundaries of larger grains (see Fig. 3 – showing different area than Figs. 1 and 2.), whereas more detailed EBSD results at higher magnification of 10.000x (Fig. 4) explained the fine grain structure inside the main grains. Therefore, grains' sizes at two different scales are present in these samples. The effect of Zr content on the HEA microstructure was thus traceable in great detail.
How dark are dark plasmon modes ‐ a correlative
EELS
and
CL
study on lithographed silver nanodisks
Authors: Schmidt Franz‐Philipp , Losquin Arthur , Hofer Ferdinand , Krenn Joachim R. , Kociak Mathieu 
Published: December 2016

Plasmonic nanostructures enable the concentration of light to the deep subwavelength regime and, thus, are the topic of intense fundamental and application oriented research. Nanoparticles acting as optical antennas are well known for their nanoscale mode volumes, due to the excitation of localized plasmon modes. In this context electron energy‐loss spectroscopy (EELS) in a transmission electron microscope (TEM) became a powerful technique as it enables to map the full modal spectrum of plasmon eigenmodes with unprecedented high spatial resolution [1–3]. Beside EELS, Cathodoluminescence (CL) has also recently been used to gain information about the optical response taking advantage of the same high spatial resolution in a TEM [4]. While it is stated that EELS is linked to the full photonic local density of states (LDOS), the CL signal is related to the radiative LDOS [5].
In this work we present a combined EELS/CL study of plasmon eigenmodes on silver nanodisks, using fast electrons in a TEM. In particular we compare the differences of the EELS and CL response using experimental and simulated data. Precise variation of the disk size is achieved by means of electron beam lithography (Figure 1a), enabling a comprehensive study of plasmon excitations on silver nanodisks.
From theoretical considerations it is known, that for certain particle geometries (and therefore for specific surface charge distributions) there exist so called dark modes, which are “invisible” to photons but “visible” to electrons, and therefore can be measured with EELS but not with light [6]. Here we discuss how dark these dark modes are comparing EELS and CL (figure 1b+c). In particular, radial breathing modes (C in figure 1b+c) were predicted to be dark modes [6], although we will show how comparison between EELS and CL can mitigate this statement. Additionally, limitations for the theoretical predictions will be discussed, when the particle size is increased and therefore retardation effects become more important. In this case we show that dark modes are getting brighter. Furthermore symmetry breaking by the excitation source itself, a focused fast electron beam, will be discussed.
STEM
imaging of atom dynamics: novel methods for accurate particle tracking
Authors: Furnival Tom , Schmidt Eric , Leary Rowan , Knez Daniel , Hofer Ferdinand , Bristowe Paul D , Midgley Paul A 
Published: December 2016

Developments in scanning transmission electron microscopy (STEM) have opened up new possibilities for time‐resolved imaging at the atomic scale. Recent examples include a study of the diffusion of dopant atoms in semiconductors [1] and, using environmental STEM, in situ studies of catalytic reactions [2]. Rapid imaging of single atom dynamics brings with it a new set of challenges. High frame rates and long total acquisition times mean novel methods are needed for handling and processing “big data” sets. Further, the need for short exposure times leads to severe problems with noise, but by exploiting the spatial and temporal correlations between frames, it is possible to considerably improve the signal‐to‐noise ratio using a method known as singular value thresholding [3]. Crucially, by employing robust procedures to automatically estimate the noise and motion characteristics, it is possible to optimize the process with little user input (Figure 1a,b). The identity and positions of individual atoms in the denoised data can then be determined using a newly‐developed intensity‐based classification algorithm. Building on the theme of automation, the classifier can be trained using simulated STEM images to robustly process long image sequences, where manual identification would be prohibitive.
As an example, we have applied these methods to investigate the diffusive behaviour of copper atoms on the (110) surface of silicon. The noise removal and atom identification steps are used along with particle tracking software [4] to extract a set of atomic trajectories from a series of annular dark‐field STEM images (Figure 1c‐e). The form of these trajectories can be related to the underlying silicon substrate, as in Figure 1f, which suggests the existence of preferred pinning sites for copper atoms. The interaction between adatoms and the substrate can be explored with unprecedented spatio‐temporal resolution using rapid imaging, and interpreted by modelling with density functional theory (DFT) calculations (Figure 1g). This highlights the potential for combining time‐resolved STEM with theory, forming a powerful approach to investigating and understanding the dynamic behaviour of materials at the atomic scale.
Atomic‐scale investigation of interface phenomena in two‐dimensionally Sr‐doped
La2CuO4
and
La2CuO4/ La2‐xSrxNiO4
superlattices
Authors: Wang Yi , Suyolcu Y. Eren , Sigle Wilfried , Salzberger Ute , Baiutti Federico , Gregori Giuliano , Cristiani Georg , Logvenov Gennady , Maier Joachim , van Aken Peter 
Published: December 2016

Atomic‐scale investigation of interface phenomena in two‐dimensionally Sr‐doped La
2
CuO
4
and La
2
CuO
4
/ La
2‐x
Sr
x
NiO
4
superlattices

Y. Wang, Y. E. Suyolcu, W. Sigle, U. Salzberger, F. Baiutti, G. Gregori, G. Cristiani, G. Logvenov, J. Maier, and P.A. van Aken
Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
Physics phenomena at interfaces of complex oxide heterostructures have stimulated intense research activity due to the occurrence of a broad range of electric and magnetic functionalities that do not pertain to the constituting single phases alone. Interface effects have been proven to be a powerful tool for improving or even inducing novel functionalities [1, 2]. In the case of interface superconductivity, the interatomic structure relaxation and charge transfer play a key role [3].

In this work, we combine atomic‐resolved quantitative STEM imaging with analytical STEM‐EELS/EDX analysis to investigate the interface effects in La
2
CuO
4
(LCO)‐based hetero‐structures, i.e. superlattices of Sr two‐dimensionally (2D) doped LCO, and LCO/La
2‐x
Sr
x
NiO
4
(LSNO) hetero‐structures, both exhibiting
T
c
up to 40 K, despite its non‐superconducting constituents. HAADF images of the structure are displayed in Fig.1 confirming high‐quality epitaxy. A detailed study of the cation distribution and concentration at the doped interfaces was performed by EDXS and EELS analyses. In the case of Sr‐2D doped LCO superlattices, the analysis shows that Sr cations undergo an asymmetric redistribution, as a result of the MBE growth process. Oxygen
K
‐edge fine structure analysis reveals that the hole concentration profile on the downward side of the nominal SrO layer is clearly decoupled from the Sr‐profile indicating an accumulation of positive charges compensating the negatively charged SrO planes (Fig.2).

These results were supplemented by quantitative analysis of atomic‐resolved high‐angle annular dark‐field (HAADF) and annular bright‐field (ABF) images, which were simultaneously acquired. From these images the local lattice and copper‐apical‐oxygen distortions at the interfaces were evaluated. The relation of these results with the observed
T
c
will be discussed.
Electron tomography: influence of defocus on the determination of reconstructed soot aggregates' surface and volume
Authors: Cabié Martiane , Gailhanou Marc , Ferry Daniel 
Published: December 2016

Aerosols affect the climate system through various physical processes as they can scatter and absorb solar radiation, emit thermal radiation, or act as cloud condensation nuclei that modify the cloudiness coverage, changing then its albedo. Carbonaceous solid aerosols resulting either from anthropogenic processes or biomass burning are one of the most significant contributors to global climate change [1] with respect to their impact on radiative forcing. They are constituted by tiny primary spherules having a diameter typically ranging from a few nanometers to dozens nanometers. These spherules are aggregated to form particles of larger sizes (0.1 to 1 micrometre) showing a complex morphology (Figure 1) that plays an important role on their radiative and transport properties. These soot aggregates are commonly characterized from 2D transmission electron microscopy (TEM) images and their 3D shape is then deduced from TEM projections assuming geometrical models of spheres, cylinders or spheroids. In order to check the validity of the 2D to 3D transition of these geometrical models we investigated bright field (BF) TEM tomography and directly determine 3D soot morphological characteristics.
To be suitable for tomographic reconstruction, images of the tilt series must fulfill the projection requirement and BF TEM images of amorphous specimen, which are dominated by mass‐thickness contrast, can satisfy this assumption. We show in this work that attention must be paid on the influence of defocus, responsible of the appearance of Fresnel fringes, which do not answer the projection requirement and can lead to artefacts that do not ensure a realistic reconstruction of soot aggregates.
To do so, we analyse the effect of defocus both on real and numerical soot particles. Thus the same real soot aggregate is reconstructed (with the SIRT algorithm) from different tilt series obtained at different defocus values. Its surface area and volume are determined by using the Amira software suite after a segmentation step based on the method of Adachi et al [2]. The same procedure (reconstruction, segmentation, surface area measurement) is then applied on an amorphous numerical particle, which is generated using a tight binding model [3] processed with the Nanofabric software developed by Y.Lebouar. Projection series are simulated with the EMS software based on the multislice method [4]. Both experimental and numerical approaches show that defocus drastically modifies the intensity profile of primary particles along their diameter and subsequently affects the shape of the reconstructed aggregate (Figure 2) and leads to overestimated values of their surface area and volume.
A Correlative Methodology based on
SIMS
for Advanced Materials Characterization
Authors: Eswara Santhana , Hu Rong , Yedra Lluís , Audinot Jean‐Nicolas , Schwedt Alexander , Tasan Cem , Mayer Joachim , Raabe Dierk , Wirtz Tom 
Published: December 2016

Development and innovations of modern high‐performance materials rely crucially on the repertoire of characterization methods available. While individual techniques provide information on a specific aspect of the investigated material, a comprehensive understanding requires a correlative approach in which complementary information are needed from exactly the same Region of Interest (RoI). Therefore, correlative methodologies combining several techniques are indispensable in a wide range of scientific disciplines including materials science [1].
In contrast to the traditional EDX and EELS spectroscopies, SIMS is well‐known for high‐sensitivity (ppm), high dynamic range and more interestingly, isotope analysis for all the elements of the periodic table. This presentation will highlight the benefits of correlating SIMS imaging with complementary analysis using Electron Back Scattered Diffraction (EBSD) and Atomic Force Microscopy (AFM). As the SIMS images do not reveal crystallographic orientations of the grains in the microstructure, studies that aim to correlate structural defects such as twinning and grain boundary orientation in a multiphase material require that the strengths of SIMS are coupled with that of EBSD to probe the local crystallographic characteristics. As a first step, we correlate the SIMS with EBSD imaging to complement specific chemical characteristics seen in SIMS with the corresponding crystallographic characteristic captured in EBSD.
To further characterize the material and for correct interpretation, the exact topography of the RoI is required. We do topographic analysis using an AFM on the exact location where SIMS and EBSD analysis are carried out. In this way, a three‐way correlative methodology is developed. As each of these analyses is done on separate instruments, specific methodological strategies are employed to overcome the challenges.

To illustrate this methodology, we selected the topic of hydrogen embrittlement in a TWinning Induced Plasticity (TWIP) steel [2]. As conventional techniques such as EDX are not capable of mapping hydrogen distribution, the SIMS approach brings a particularly strong advantage to this study. Prior to the SIMS analysis, the steel samples were electrochemically charged with deuterium to distinguish it from hydrogen naturally present in the sample. The SIMS images of H
‐
and D
‐
distributions are obtained from a Cameca NanoSIMS50 with a Cs
+
primary ion beam. Then, EBSD and AFM analyses are carried out on the exact location to correlate SIMS chemical characteristics with crystallographic defects such as twins, grain boundaries and sample topography.

In this presentation, we will introduce and demonstrate this correlative paradigm for materials characterization. We will also present the scientific and technical challenges and discuss the strategies to go beyond the current state‐of‐the‐art.