bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of nanocatalysts for ethanol oxidation
Authors: Roga Elzbieta , Gruzel Grzegorz , Depciuch Joanna , Kowal Andrzej , Parlinska‐Wojtan Magdalena
Published: December 2016

Nowadays limited resources of fossil fuels and environmental concerns increase interest in alternative sources of energy [1]. Recently, fuel cells became very popular and interesting as a good solution for this problem. However, it should be remembered that the oxidation reaction between the catalyst and the fuel (ethanol) occurring in fuel cells is complex and generates a lot of by‐products. This whole process does not promote a better efficiency of the cell, on the contrary, it leads to poisoning of the catalyst, decreasing the efficiency of the device. Therefore the key challenge for this branch of science is primarily the development of the appropriate type of catalysts [1]. Recently promising technology seem to be ternary nanocatalysts containing platinum, rhodium, and tin oxide (IV) [2].

The motivation for our work is a better understanding of the synergistic effect between these three components in nanocatalysts, replacing the rhodium by rhenium and determining their selectivity for total oxidation of ethanol to CO
2
.In the present study we used three methods of synthesis: polyol [3], citrate [4] and microwave assisted [5].

The obtained nanoparticles were characterized by Photon Correlation Spectroscopy (PCS), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR).

The HAADF STEM structural analysis showed that the nanoparticles obtained by all three methods have similar dimensions ‐ about 2 nm. In the case of the citrate and polyol methods the nanoparticles were strongly agglomerated, which was visible not only in the TEM images, but also confirmed by the results obtained by the PCS. On the other hand, nanoparticles obtained by the microwave assisted synthesis did not show such a strong agglomeration as those obtained by the two other methods. All SnO
2
samples had a crystalline structure, which was confirmed by HRSTEM images (Fig. 1). Additionally fourier transform infrared spectroscopy (FTIR) was applied to determined the structure of tin oxide obtained in the two differences synthesis (microwave and polyol assisted). It was found, that in the infrared spectrum of Sn oxide synthesized by polyol methods, a stretching modes of Sn‐O from Sn(OH)
4
was not observed. Moreover, in this samples, more stretching modes of O‐Sn‐O (Sn
4+
) was noticed, whereas the samples synthesized by microwave methods, characterized by larger amounts of Sn‐O (Sn
2+
) stretching modes (Fig. 2). The size of the nanoparticles varied from 2 to 12 nm, depending on the synthesis parameters.

The next step is the synthesis of PtRh and PtRe nanoparticles on the obtained SnO
2
supports.

Our research confirmed that the crystalline structure, particle size and shape, and surface properties are highly dependent on the chosen method of synthesis.
Structure and Energetics of Double‐Wall Carbon Nanotubes
Authors: Ghedjatti Ahmed , Fossard Frédéric , Wang Guillaume , Flahaut Emmanuel , Amara Hakim , Lauret Jean‐Sébastien , Loiseau Annick
Published: December 2016

Single‐walled carbon nanotubes (SWNTs) have shown oustanding capabilities in the realization of new functional devices but are extremely sensitive to any slight changes in their environment, altering their physical properties. A strategy to overcome this difficulty is to use double‐walled carbon nanotubes (DWNTs), consisting of two concentric tubes. In order to better know the basic properties of this kind of tubes in linkage with their structure, we have developed a systematic and robust procedure using acHR‐TEM (aberration corrected Transmitting High Resolution Electron Microscopy) to determine the atomic structure over one hundred DWNTs [1]. This procedure includes several steps which are summarized in Fig.1. Statistical analyses of their diameters and twist angle between inner and outer tubes shown in Fig.2 and Fig.3, reveal that some configurations are strongly favored whereas some others are never observed. These results reveal the existence of strong coupling between the two concentric tubes in a DWNT for the smaller diameters lower than 2 nm. To complete this analysis, we performed Monte Carlo calculations with an empirical energetic model in order to understand the nature of the coupling and explain the selectivity of observed patterns [2].
Tracing acetylcholine binding‐proteins microscopically in tissues of the snail Biomphalaria glabrata
Authors: Treiber Daniela , Kokkinopoulou Maria , Lieb Bernhard , Markl Jürgen
Published: December 2016

The nicotinic acetylcholine receptors (nAChR) are members of the Cys‐loop receptor superfamily. Playing important neurophysiological roles they are in the focus of biomedical research. The acetylcholine binding proteins (AChBP) in the hemolymph of gastropods are structural and functional homologues of the ligand binding domain of nAChR. In contrast to the membrane‐bound nAChR, AChBP is water soluble. Therefore, AChBP is a very efficient surrogate for indirect investigations of nAChR functions [1]. AChBP is based on 25 kDa polypeptides. Like nAChR (Fig. 1A), AChBP is usually a pentamer (Fig. 1B,C). However, in the hemolymph of the planorbid snail
Biomphalaria glabrata
(vector snail of the schistosomiasis parasite) it exists as a pentagonal dodecahedron (12 pentamers), 25 nm in diameter (Fig. 1D). This large size and high symmetry makes it well accessible to 3D electron microscopy [2]. Moreover, in
B. glabrata
two different AChBP polypeptides (designated as
Bg‐
ACHBP1 and
Bg‐
AChBP2) were detected, recombinantly expressed, and reassembled to functional oligomers [2]. Recombinant
Bg
‐AChBP1 readily formed dodecahedra, whereas recombinant
Bg
‐AChBP2 formed only pentamers and dipentamers [2]. The existence of hetero‐oligomers could be excluded, but not the possibility that in the hemolymph also
Bg
‐AChBP2 might be present as dodecahedra. Agonist and antagonist binding properties of AChBP and nAChR are comparable [1]. Concerning biological functions of AChBP in snails, several possibilities have been discussed (for references, see [1,2]): (i) suppressor of cholinergic transmission; (ii) regulator of CaCO
3
crystallization (shell growth); (iii) binding agent of algal toxins.

Here we show by
in situ
hybridization that in
B. glabrata
, AChBP is expressed in the mantle epithelium (Fig. 2A). In this context, it should be remembered that the molluscan shell is secreted by the mantle. Transmission electron microscopy revealed ultrastructural details of this epithelium (Fig. 2B). The applied cDNA probe was inefficient to discriminate between
Bg
‐AChBP1 and
Bg
‐AChBP2, but immunofluorescence microscopy using isoform‐specific rabbit antibodies revealed the presence of
Bg
‐AChBP1 and the absence of
Bg
‐AChBP2 in the mantle epithelium (not shown). Therefore,
Bg
‐AChBP1 might be involved in regulating shell growth. Although these data are preliminary, they suggest that the two
Bg
‐AChBP isoforms significantly differ in their biological functions within the snail. We now perform CaCO
3
crystallization experiments in the presence of
Bg
‐AChBP1.
In situ
UHVEM
observation of atomic ordering in magnetic nanoparticles using a direct detection camera
Authors: Sato Kazuhisa , Yasuda Hidehiro
Published: December 2016

Recent demands for ultrahigh density magnetic storage technology require the development of recording media with higher magnetocrystalline anisotropy energy in order to ensure thermal stability of magnetization as well as ultrahigh recording density. For such a purpose, equiatomic CoPt alloy nanoparticles (NPs) are one of the candidate materials [1]. The hard magnetic property of this alloy is attributed to the tetragonal L1
0
‐type ordered structure; the anisotropy energy is dependent on the degree of order of the ordered phase. Therefore, formation of the L1
0
ordered phase is the key issue for practical applications. In this study, we hence intend to observe atomic ordering of CoPt NPs by ultra‐high voltage electron microscopy (UHVEM) equipped with a direct detection camera.

Thin films of disordered CoPt alloy NPs were synthesized by co‐deposition of Co and Pt targets using rf‐magnetron sputtering onto NaCl(001) substrates kept at 620 K. After the deposition of Co and Pt, surface of the NPs were coated by an amorphous carbon (a‐C) thin film. The specimen films were removed from the NaCl substrate by immersing the substrate in distilled water, and then floating films were mounted onto microgrids for electron transparency. Structure and composition of the NPs were characterized using a JEOL JEM‐ARM200F TEM (200 kV). Electron irradiation experiments and the simultaneous in situ heating observation were carried out using a JEOL JEM‐1000EES UHVEM (1 MV) equipped with a Gatan K2‐IS electron direct detection CMOS camera newly installed at the Research Center for UHVEM, Osaka University [2].

Figure 1 shows a selected area electron diffraction (SAED) pattern and a TEM image of as‐sputtered CoPt alloy NPs with disordered fcc structure. As seen, (100)‐oriented CoPt alloy NPs with sizes of ~15 nm are dispersed. Average alloy composition was Co‐45at%Pt as determined by EDX analysis (Fig. 1(c)).

Figure 2 shows two successive TEM images of a CoPt NP acquired in situ with a frame rate of 1/400 s. The observation was made at 583 K under electron irradiation at 1 MV with a dose rate of 1.5 × 10
25
e/m
2
s. In Fig. 2(a), disordered phase with the fcc structure is seen. After 2.5 ms, the ordered fringes suddenly appeared as shown in the middle of the NP surrounded by the square (Fig. 2(b)). The atomic ordering can also be confirmed by appearance of weak 001 superlattice reflection in the attached Fast Fourier Transform (FFT) pattern. The observed kinetic ordering temperature of 583 K for binary CoPt NPs is lower than that reported in the previous study (> 800 K) [3]. The low temperature atomic ordering can be attributed to the enhancement of atom migration by high‐energy electron irradiation [4].
3‐D reconstruction of surface topography inSEMby means of energy filteredSEandBSE
Authors: Kupreenko Stepan , Rau Eduard , Tatarintsev Andrey , Zaytsev Sergey
Published: December 2016

The reconstruction of surface topography based on the detection of backscattered or secondary electrons in SEM has found increasing interest during long time [1‐5].

For more accurate reconstruction one should know angular dependecies of secondary electron emission (SE) coefficient δ and backscattered electron (BSE) coefficient η, which, in general, are quite well investigated and defined [6]. But for increasing sensitivity in determination of local surface slopes it is offered to detect BSE and SE not integrally, as in previous works, but differentially by energy, i. e. by value of signal detected in narrow energy range of emitted electrons. As it was shown in our experiments, sensitivity increases in times in such formulation of experiment. Experiments were carried out in LEO‐1455VP (Zeiss) equipped with a two‐channel toroidal electron spectrometer [7]. We measured energy spectra of SE and BSE for various angles of incidence α (Fig. 1). SE spectra are slightly deformed because of applying negative bias Vs=‐33 V to stage (electrons leave surface nonisotropically). Comparison of integral and differential coefficients is depicted on Fig. 2. Values of integral coefficients δ and η were calculated by formulas from [8] (by substituting R to Rcosα [9]) and [10] respectively. Values of integral coefficient at fixed angle of detection θ were obtained by simple integration of measured spectra. LineScans of Ti‐ball, obtained as difference signal between two symetrically mounted detectors at fixed energy of electrons, are depicted on Fig. 3.

Obtained results allow us to conclude that secondary electrons are best suited for proplem of surface relief reconstruction than backscattered electrons.

This work was funded thanks to the support of RFBR (grant 15‐02‐01557)
In situ
TEM
electrical biasing studies on defect based crystal‐amorphous transformation in
GeTe
nanowire devices
Authors: Nukala Pavan , Agarwal Ritesh
Published: December 2016

Germanium telluride (GeTe), a phase‐change material, switches rapidly and reversibly between crystalline and amorphous phase. The crystalline to amorphous transformation pathway is based on melting the crystalline phase and quenching it to amorphize in nanoseconds timescale. However, this is inefficient and energy consuming, and it is necessary to look for alternate pathways to carry out this transformation.

Using in situ TEM electrical biasing experiments on GeTe nanowires, we discovered a defect‐assited low energy pathway for crystal‐amorphous transformation. GeTe is both ferroelectric (FE) and inherently defective (Ge vacancies) metallic material, an unusual combination of properties in any material system. We show through dark‐field TEM movies that interaction between extended defects of different origins (ferroelectric and metallic) can result in a pathway towards amorphization. In the “forming stage”, voltage pulses applied on metallic GeTe act as heat shocks creating anti‐phase boundaries (APB) by coalescing and quenching Ge vacancies in a Ge plane. These APBs interact with the pre‐existing 71° ferroelectric domain boundaries converting them into 109
o
boundaries. The partial dislocations surrounding the APBs migrate in the direction of the electrical wind‐force, only to be impeded by the 109° boundaries. Eventually, the mobility of the partial dislocations becomes zero, analogous to a scenario of traffic jam on a highway. Accumulating more extended defects at the jam, eventually collapses the crystallinity ‘nucleating’ an amorphous phase with medium range order, in a very local region that cuts across the cross‐section of the nanowire. The amorphous mark can be recrystallized via another electrical pulse which heat it beyond the crystallization temperature.
Environmental tomography of liquid latex suspensions in
STEM
Authors: Xiao Juan , Roiban Lucian , Foray‐Thevenin Genevieve , Masenelli‐Varlot Karine
Published: December 2016

ESEM (Environmental Scanning Electron Microscopy) allows the observation of liquids under specific conditions of pressure and temperature. Moreover, when working in the transmission mode,
i.e
. in STEM (Scanning Transmission Electron Microscopy), nano‐objects can be analyzed inside a liquid. Those acquired images are quite similar to those obtained in TEM (Transmission Electron Microscopy) using a closed cell [1]. By implementing a Peltier stage in the tomography device which was developed for the characterization of the 3D structure of non‐conductive and low‐contrast materials [2], the acquisition of image series of wet samples (wet‐STEM tomography) [3]. Moreover,
in situ
evaporation of water can be performed to study the materials evolution from the wet to the dry state.

In our experiment, SBA‐PMMA, a copolymer derived from styrene and metacrylic acid esters in aqueous solution, is chosen as the sample. A 3% PMMA shell, which plays the role of steric surfactant, has already included in the SBA particles. Some other surfactants can be introduced to further stabilize the latex for some special applications [4].

We first present measurements of the sample temperature using different experimental conditions, to show that the sample can be preserved in the dry state. Then, we show series of tilted images that are acquired during
in situ
hydration / dehydration experiments. Reconstructed volumes are obtained using the image processing softwares
etomo
and
Fiji
(see Figure 1), and the resolution is calculated using Fourier Shell Correlation (FSC). The influence of irradiation damage on the reconstructed volumes are discussed.

Afterwards, the volumes are segmented (see Figure 2) and quantified to follow the evolution of the microstructural parameters during water evaporation.  This shows the potentialities of wet‐STEM tomography for the characterization of suspensions from the wet to the dry state.
Quantitative compositional characterisation of fuel‐cell catalysts using EDX ionisation cross sections
Authors: MacArthur Katherine , Slater Thomas , Haigh Sarah , Ozkaya Dogan , Heggen Marc , Nellist Peter , Lozano‐Perez Sergio
Published: December 2016

Hydrogen fuel‐cells are a ‘zero emission’ technology because they only release H
2
O, making them a very attractive source of clean electric power. Unfortunately, fuel‐cells such as the polymer exchange membrane (PEM) fuel‐cell are heavily reliant on a platinum catalyst at both the anode and cathode in order for the reaction to proceed at the low operating temperatures. It is largely the cost of this platinum metal which limits their more wide‐scale manufacture and use.

In light of this, the search is on for more active catalysts with lower platinum content. A great deal of success has been seen in the research of bimetallic alloy catalysts where the expensive platinum metal is combined with a much less expensive metal such as nickel or cobalt. Such catalysts not only provide a reduction in the amount of platinum used but also an increase in the activity, which may be due to the compressive strain that the alloying element introduces.

In order to develop these catalysts further and make them a viable alternative to platinum, we need to understand what is happening at the nanometre and even sub‐nanometre scales. For this we need to be able to characterise our catalysts at high resolution, understanding both the composition and structure. A new method for quantitative energy dispersive x‐ray (EDX) [1] analysis in the scanning transmission electron microscope (STEM) has been developed with this in mind.

In the same way that the scattering cross section, σ, can be calculated from ADF image intensity and for ionisation edges in EELS, it is possible to calculate an EDX partial cross section using an approach that demonstrates similarities with the ζ‐factor method. Rather than the ratio approach provided by the traditional k‐factor method, this is a direct measurement which yields the number of atoms of each element after quantification, as such thickness can easily be extracted as well. This quantification method was applied to PtCo alloy nanoparticles that have been acid‐leached to provide platinum enrichment (or rather cobalt depletion) at the particle surface [2]. It is possible to quantify the levels of cobalt depletion in the first few atomic layers of the particle, showing that the leaching produces a localised surface depletion that can only be determined by this high resolution EDX quantification.
Magnetic coupling of 4f and 3d moments by
EMCD
: application to DyFe2‐based superlattices
Authors: Fu Xiaoxiao , Warot‐Fonrose Bénédicte , Dumesnil Karine , Arras Rémi , Serin Virginie
Published: December 2016

The emerging technique EMCD, Energy‐Loss Magnetic Chiral Dichoism, aims to measure the element‐specific magnetic moment of solids at a nanometer scale using electron energy‐loss spectroscopy in a transmission electron microscope (TEM) [1‐3]. The magnetic moment information is carried in the electron energy‐loss spectra obtained from two specific positions of particular electron diffraction patterns. In the last few years, EMCD has been extensively applied to probe 3
d
moments in 3
d
transition metal. Our work explores its application to both 4
f
moment and 3
d
moment by investigating Dy‐M
4,5
edges and Fe‐L
2,3
edges respectively in DyFe
2
/YFe
2
superlattice.

As illustrated in figure 1, DyFe
2
and YFe
2
layers appear alternatively to form a superlattice with a specific bilayer repeat distance. Both DyFe
2
and YFe
2
crystalize in the same structure, making the superlattice actually a single crystal. For EMCD experimental setup, a specific three‐beam condition has been settled in the TEM to detect the signals of Fe‐L
2,3
edges and Dy‐M
4,5
edges in the same condition. Spectra and dichroic signals are shown in figure 2. The influence of the dynamic diffraction effect on the Fe‐L
3
and Dy‐M
5
EMCD signal amplitudes is precisely analyzed, and it will be shown in this presentation that the opposite sign of these two peaks unambiguously proves the antiparallel alignment of net Fe 3
d
and Dy 4
f
moments. In addition, EMCD sum rules specified for M
4,5
edges have been derived and their application conditions to Dy‐M
4,5
edges will be discussed in detail.

This work evidences that the EMCD technique is an effective tool to probe 4f moment and to study magnetic moment coupling in magnetic materials.
Controlling the grain size of polycrystalline TiO2 films grown by atomic layer deposition
Authors: Kavre Piltaver Ivna , Badovinac Ivana Jelovica , Saric Iva , Peter Robert , Ambrozic Gabriela , Omerzu Ales , Petravic Mladen
Published: December 2016

Titanium dioxide (TiO
2
) is a widely used material for photocatalytic, optical, electrical and medical applications. Atomic layer deposition (ALD) represents an excellent technique for the synthesis of thin films due to its precise thickness control, simplicity, high conformity of obtained films and reproducible growth of defect‐free films.

It was shown recently that photo‐catalytic TiO
2
films grown on cellulose‐based and porous substrates can be used in water purification systems [1]. Its photo‐catalytic activity strongly depends on the crystal structure and the grain size of the film, i.e. the TiO
2
films must have a well‐defined anatase phase with large polycrystalline grains [2]. It was recognized that plasma enhanced ALD (PEALD) growth of the TiO
2
film can produce the anatase phase even at low deposition temperatures [3]. This result is important for the growth of thin polycrystalline films on temperature‐sensitive materials, such as organic substrates. On the other hand, the grain size is shown to depend critically on the type and the morphology of substrates [4].

We have investigated the effects of thin intermediate layers, grown by ALD on silicon substrates, on the grain size of the TiO
2
films, grown by thermal ALD and PEALD technique in a wide temperature range, from room temperature up to 300°C. Amorphous TiO
2
films were obtained with thermal ALD for temperatures below 150°C, while the anatase phase with crystalline aggregates has been identified on films synthesised with PEALD at low temperatures. We show that the size of crystallites can be greatly enlarged if grown on an intermediate layer of amorphous Al
2
O
3
. The films were characterised by a range of analytical techniques, including scanning electron microscopy with energy dispersive x‐ray spectroscopy, secondary ion mass spectrometry, x‐ray photoelectron spectroscopy and x‐ray diffraction.
Study of the interaction of Macrobrachium rosenbergii Nodavirus and its virus‐like particles (M
r
NV
‐
VLP
s
) in Sf9 insect cells: the dependence upon caveolin‐mediated endocytosis and the possible existence of a capsid ligand domain
Authors: Somrit Monsicha , Watthammawut Atthaboon , Weerachatyanukul Wattana , Guerardel Yann
Published: December 2016

Macrobrachium rosenbergii Nodavirus (MrNV) causes white tail disease (WTD) in the giant freshwater prawn
M. rosenbergii
. In our past studies, we generated
Macrobrachium rosenbergii
Nodavirus virus‐like particles (MrNV‐VLPs) that were capable of being “nanocontainers” through the uptake of foreign plasmids after viral capsid disassembling/reassembling treatment. Nevertheless, the studies into the binding and internalization of this particular virus into susceptible host cells have been lacking; therefore our team has utilized live MrNV and recombinantly synthesized MrNV‐VLPs as a tool to examine viral entry mechanisms in Sf9 insect cells; whereby revealing the dependence upon the caveolin‐mediated endocytotic pathway for internalization and infection. Furthermore, viral capsid protein subunit modeling and capsid enzyme digestion were performed for revealing viral protrusions/ligands.
Can quantum wave filters outperform image processing?
Authors: Clark Laura , Verbeeck Jo
Published: December 2016

As electron microscopists, we are often limited by both low contrast, and high‐noise levels for beam‐sensitive materials. The contrast is a function of the imaging technique, and the sample under study. The noise level of the image is a fundamental property of the finite electron dose, which must remain limited, to avoid damaging the sample.

As a result of these, one route to improving microscopy images lies in developments of novel imaging techniques. Image post processing techniques are commonly used for example, to remove noise in images or increase the contrast of specific features of interest. These methods perform well in specific cases, but one can wonder whether this post processing approach is the most optimal in terms of electron dose efficiency.

The primary source of noise in electron micrographs is Poisson noise due to the electron counting process occurring at the point of detection.

However, if we can manipulate the coherent electron wave prior to its detection, implementing a specific operator acting on the wave, noise will occur on the detected processed image rather than prior to the processing.

Such a setup can be obtained by using phase plates in the diffraction plane. Ideally, these phase plates affect the phase of the passing electron wave without invoking a detection process, effectively acting as a quantum filter.

We discuss and compare three primary examples of such quantum wave filtering, and the results they have on the noise behaviour of the resulting images: vortex filtering as an edge enhancement filter [1], wave background removal [2], and tuneable wave background reduction. We find each method improves the image signal‐to‐noise ratio compared to image post processing implementing a similar filter. We show that each quantum wave filter has different advantages which may be used to enhance certain image features of interest.

Removal of the background in the wave decreases noise specifically in image regions of low intensity, reducing the variance of the noise in the image, allowing more precise measurements. Reduction rather than removal of the background however, enables a noise decrease, while avoiding contrast reversals due to sign changes in the wave, improving direct interpretability. The vortex‐ filtering method provides robust directional, or isotropic edge detection, with high contrast possible.

We demonstrate each of these options on a selection of different model samples, and discuss their noise properties, required dose levels and their possible implementation.
‘Slice & View’ nano‐tomography of porous media using
FIB‐SEM
Authors: Liu Yang , Le Fur Pierre , van Huis Marijn , Plümper Oliver
Published: December 2016

Research on porous media is of major importance to many fields varying from catalysis to Earth science. Characterizing such media in 3D is expected to provide information on surface and volume rendering, which is required for understanding fluid transport. In the present study, electron tomography performed in the FIB‐SEM (Focused Ion Beam ‐ Scanning Electron Microscope) [1] is applied to a highly porous Diatomaceous Earth material. Representative volumes (Figure 1) have been obtained and treated in Fiji and Avizo software, the pore volume and pore connections are studied and quantified to generate the pore network [2–5]. Next, the data is used for fluid simulation through Computational Fluid Dynamics (CFD) methods, in order to study and analyze flow and diffusion properties in the obtained pore network (Figure 2). The geometry of pores is also evaluated to study how it influences transport properties in the sample. Furthermore, the effects of image correction and segmentation on the simulation are also examined.
Impact of high energy electrons on nitrides for nanocathodoluminescence
Authors: Griffiths James , Zhang Siyuan , Lhuillier Jeremy , Zhu Dandan , Wallis David , Howkins Ashley , Boyd Ian , Stowe David , Humphreys Colin , Oliver Rachel
Published: December 2016

Nitride quantum well (QW) light emitting diodes (LEDs) exhibit high efficiencies relative to traditional lighting sources. The quantum wells serve to confine carriers and lead to higher device efficiencies. To achieve the highest device efficiencies requires optimisation of the active quantum wells and hence experimental observations of the structural and optical characteristics. Recently, by imaging the cathodoluminescence (CL) in a scanning transmission electron microscope (STEM), the structural and optical properties were correlated with a spatial resolution of a few nanometres [1], an approach referred to as nanoCL. NanoCL has also been used to reveal quantum confinement in high brightness LEDs [2], and optimise the device structure to achieve the highest device efficiency.

Whilst the improved spatial resolution associated with nanoCL can reveal optical characteristics on the nanoscale, the higher electron energies can lead to structural damage. Here we investigate the effect of high energy electrons on the luminescent intensity. An exponential decline in the luminescent intensity is observed over time with exposure to the electron probe. Spectral time profiles are performed over a range of accelerating voltages from 80 to 200 keV to study the variation in the luminescence with the electron energy. We observe that the luminescent intensity is substantially more stable at lower accelerating voltages and predict a threshold for damage below which there is no damage. NanoCL can thus potentially provide a reliable approach to the study of functional optoelectronic devices.
Compressed sensing for beam sensitive materials imaging in
S
canning
T
ransmission
E
lectron
M
icroscopy
Authors: Béché Armand , Goris Bart , Freitag Bert , Verbeeck Jo
Published: December 2016

Transmission electron microscopy (TEM) is a very powerful technique to investigate materials down to their atomic components. Its versatility allows quantifying samples from their shape to the nature of their constituents and surroundings. However, the strong interaction of the electron beam with matter potentially induces damages in samples under investigation, especially for those composed of soft matter such as zeolites, metal organic frameworks (MOFs) and most life science samples. Current workarounds involve the reduction of the beam intensity, such as in the so‐called low dose imaging, or increase of the detector performances as provided e.g. by direct electron detectors.

Recently, improvement in signal processing lead to the development of compressed sensing [1, 2], a numerical algorithm based on the assumption that real life images are sparse in some particular well‐chosen basis. Images can then be expressed with much less components than what required by the Nyquist sampling theorem. By extension, not all pixels in a given image are necessary and only a random selection of them is sufficient to retrieve the original image with fidelity. By definition, compressed sensing is a very dose efficient technique as only parts of the sample need to be exposed to the electron beam to reconstruct a faithful image. So far, only theoretical implementations of compressed sensing were investigated in the TEM community, focused mostly on the case of tomographic reconstructions [3].

Very recently, we demonstrated the first physical implementation of compressed sensing in a Scanning TEM (STEM) based on the use of a solenoid as a fast beam blanker [4]. The solenoid is placed in the condenser plane of a STEM in a specially designed condenser aperture holder with feedthrough electrical contacts. By synchronizing the STEM signal with the current source driving the solenoid, we successfully acquired compressed images by shifting the beam away from the region of interest on blanked pixels. The case of both medium scale imaging (Fig.1) and high resolution imaging (Fig. 2) was investigated and reconstructed using the SPGL1 algorithm [5] with a signal compression of 80%. The present setup, although still quite far from low dose imaging conditions, has lead to successful imaging of a cross grating and a SrTiO
3
sample. Latest results revealed that a checkerboard pattern, the most demanding pattern for the fast beam blanker, could be acquired with a dwell time of 40 µs and a beam deflection of 225 nm, as shown in Fig. 3.

By further improving the experimental setup, we expect reducing the acquisition dwell time to values within the µs range. Such improvements will offer possibilities for realizing improved images and tomography experiments of electron beam sensitive materials.
Understanding the in vivo reactivity of metal orthopaedic implants
Authors: Koronfel Mohamed , Goode Angela , Weker Johanna , Simoes Thiago , Drummond‐Brydson Richard , Hart Alister , Toney Michael , Porter Alexandra , Ryan Mary
Published: December 2016

CoCr alloys became commonly used in orthopaedic implants, especially for younger patients, owing to their superior wear and corrosion resistance. However, severe inflammation resulted in unexpectedly high failure rates, leading to the withdrawal of some CoCr devices from the market, and lawsuits were filed in the US. Simulation studies show that, despite exhibiting lower volumetric wear, CoCr implants produce more, smaller (50 nm‐3 µm), particles; up to
one trillion nanoparticles (NPs)
can be produced in each patient annually. The observed inflammation in patients is believed to be caused by these wear‐produced NPs. CoCr NPs have been observed in macrophage cells in periprosthetic tissue. While CoCr is extremely corrosion resistant in bulk form, Co
2+
ions have been observed in blood and other organs such as the liver and spleen raising question on the mechanism of the dissolution of the CoCr NPs particles
in vivo
.

Ex situ
studies of CoCr NPs in simulated biological environment have been performed in our lab with the use of an applied electrochemical potential to simulate the oxidising environment generated during inflammatory response. Electron microscopy showed morphological changes in the particles as they developed into a porous sponge‐like structures (
e.g
. shown in Figure 1). This phenomena has not been observed in CoCr alloys before, revealing a new mechanism of dissolution of these alloys at the nanoscale. This research suggests that new testing criteria are required for implant materials, in particular where there is wear debris generated, where
bulk
form testing must be accompanied with studying reactivity of materials at the nanoscale.

The morphological changes apparent at the nanoscale, through electron microscopy, was correlated with chemical changes through the high energy resolution of Transmission X‐ray Microscopy/X‐ray Absorption Spectroscopy at Stanford Synchrotron Light Source. This was done at both the Co and Cr X‐ray absorption edges, to reveal the points of oxidation of Co and Cr in the particles.
Radial and Axial Interfaces in
III
‐
V
Heterostructured Nanowires
Authors: Zamani Reza R. , Lehmann Sebastian , Hage Fredrik S. , Ramasse Quentin M. , Dick Kimberly A.
Published: December 2016

Nanoscale heterostructures are promising candidates with potential in several applications such as optoelectronics and electronics. III‐V nanowires, in this context, are excellent examples as they offer an ample range of possibilities for modulating the properties.
1
In addition, their morphology allows accommodation of different compounds with larger lattice mismatch compared to bulk.
2
In this work, we study a heterostructured GaSb‐InAs system in which InAs grows both radially and axially on the GaSb.

Nanowires are grown by metal organic vapor phase epitaxy (MOVPE) using size‐selected Au aerosol particles,
3
as catalysts, which were deposited onto B‐oriented GaAs wafers. The nanowire growth was carried out in an AIXTRON 3x2″ close coupled showerhead MOVPE growth reactor at set temperatures of 510°C for GaAs and GaSb and 460°C for InAs, respectively. Firstly GaAs stems were synthesized. Then GaSb axial segments were grown on GaAs stems followed by an InAs growth step which led to formation of a radial shell on the GaSb segments as well as an axial segment on top of GaSb.

The axial and radial heterointerfaces are thoroughly studied by means of aberration‐corrected scanning electron microscopy (STEM) and atomic‐resolution electron energy loss spectroscopy (EELS). We demonstrate that the sharpness of the interfaces is different and hence they exhibit different charge transport properties in axial and radial directions. In Figure 1, the atomic‐resolution EELS maps at the radial interface are shown.
4

Moreover, the polarity of the nanowires is determined by means of medium‐/high‐angle annular dark‐field (MAADF/HAADF‐STEM) imaging. It is shown that each accommodating material inherits the polarity from its base. An As‐polar GaAs segment grows on the GaAs (111)B substrate. Then GaSb accommodates with Sb polarity, the heavier element is on top in the dumbbell units; and the InAs shell grows with As polarity (lighter element on top). Therefore, as shown in Figure 2, a switch in the intensity along the dumbbell units is observed along the diameter of the nanowires caused by the change in the chemical composition (from GaSb core to InAs shell). The EELS compositional maps also confirm this change.
4
Characterization of the microstructure of composite
Ti6Al4V
‐
AA
2519 obtained by explosive welding
Authors: Bazarnik Piotr , Cantoni Marco , Śnieżek Lucian , Lewandowska Małgorzata
Published: December 2016

A composite which combines good thermal resistance and high mechanical properties of titanium alloys with good plasticity and low density of aluminium alloys seems to be a promising materials for airspace applications. However, welding of titanium and aluminium is difficult because they are extremely chemically reactive with oxygen and nitrogen at high temperatures. In this concept, the explosive welding (EXW) is one of most promising solid‐state welding methods because it gives an opportunity to form the bonding on over the entire junction surface. In order to understand the phenomena taking place at joined surfaces, the detailed microstructural analysis is required, which was a prime goal of the present work.

Ti6Al4V and AA2519 plates 5 mm in thickness were joined via EXW with a detonation speed of 2000 m/s. The samples for scanning electron microscopy (SEM) observations were prepared by using HITACHI IM‐4000 ion milling system, which is a damage‐less polishing process and allows to see the structure on SEM through the channelling contrast. SEM observation was carried out in a HITACHI SU‐70 field emission Schottky scanning electron microscope at 10 kV accelerating voltage with the in‐lens back‐scatter electron (BSE) mode at 7mm working distance to get as much as possible surface contrast and resolution. Careful observations of selected areas were carried out on CS‐corrected dedicated scanning transmission electron microscope (STEM) Hitachi HD‐2700 operating at the accelerating voltage of 200 kV. The STEM thin foilswere prepared via in‐situ lift‐out in Hitachi NB 5000 focused ion beam. Precise EDX analysis were carried out on FEI Tecnai Osiris 200 kV microscope using Super‐X EDX detectors.

Figure 1a shows an overview of a Ti‐Al interface. EXW caused a high grain refinement in aluminium plate. The interface zone can be divided into two sections. The first one is 5 µm thickness zone consisted of nano‐sized grains of three intermetallic phases: TiAl
3
, TiAl
2
and TiAl which were identified by X‐ray analysis and electron diffraction. The second zone consist of a small aluminium grains and a white (BSE) Cu rich net around them (Figure 1b). These intermetallic inclusions were often accompanied by nano‐cracks (Figure 1b). Figure 2a shows the magnified structure of this interfacial area in High‐Angle Annular Dark‐Field (HAADF)‐STEM mode. The high resolution imaging (Figure 2b) shows that the copper net region have a crystalline structure. EDX mapping presented on Figure 3 shows the distribution of Ti, Al and Cu in the matrix and a gradient distribution of these alloying compounds in the structure. Copper net phenomenon was explained by the breaking or dissolving of big rich in copper equilibrium particles during explosive welding. Supersaturated solid solution of aluminium cannot contain all dissolved copper, so its excess was secondarily separated in the grain boundaries.
A mechanism for the introduction of threading dislocations in
III
‐nitride epitaxial layers from closed basal stacking fault domains
Authors: Smalc‐Koziorowska Julita , Bazioti Calliope , Albrecht Martin , Dimitrakopulos Georgios
Published: December 2016

The crucial issue of extensive threading dislocation (TD) introduction in III‐nitride compound semiconductor epitaxial layers remains unresolved so far since their densities cannot be justified on the basis of operation of Matthews‐Blakeslee dislocation glide on pyramidal planes. This concerns primarily the TDs with
a
‐type 1/3<11‐20> Burgers vectors which constitute the principal TD population. Mosaicity is another reason for TD introduction due to the need for accommodation of small misorientations between nucleated islands. However, high TD densities have persisted despite the advancements in mosaicity suppression through growth involving two‐dimensional step flow.

Based on transmission electron microscopy (TEM) observations, we propose a mechanism for the nucleation of
a
‐type TD half loops from closed domains bounded by two superimposed intrinsic basal (0002) stacking faults (BSFs) of I
1
type [1]. We have employed both diffraction contrast TEM and high resolution TEM (HRTEM) in cross sectional and plan‐view geometries in order to verify the generality of the proposed mechanism by experimental observations on InGaN, AlGaN, and InAlGaN epilayers, as well as on multi‐quantum wells (MQWs) grown by the MBE and MOVPE methods. Defect characterization was performed by the circuit mapping [2] and geometrical phase analysis (GPA) methods.

We have found that depending on the relative orientation of the sphalerite structural units that comprise the I
1
BSFs, the BSF closed domain may be dislocation‐free (Fig. 1) or may be surrounded by a 1/3<10‐10> partial dislocation loop (Fig. 2). In the former case the structural units are mirror related, whereas in the latter they are oriented in parallel as shown in Figs. 1(a) and 2(a) respectively. Such closed domains are hexagonally‐shaped with sides along the
m
‐type <10‐10> directions. When defected, they become unstable in response to the strain environment caused by the interfacial misfit or by the compositional grading. As a result they re‐arrange in order to contribute to the strain relief through a Burgers vector reaction, so that the total in‐plane Burgers vector of the loop is not zero, but corresponds instead to a misfit dislocation segment. Such a reaction requires a concurrent emanation of an inverse TD half loop from nodes localized at two of the hexagon's vertices, in agreement with the experimental observations. The I
1
BSF superposition eliminates any Burgers vector component along the [0001] growth direction thus resulting in pure
a
‐type TDs. The emanation of such TD half loops has been thoroughly verified by extensive observations.
Concepts for an electrostatic phase shifting device
Authors: Wagner Tolga , Niermann Tore , Berger Dirk , Lehmann Michael
Published: December 2016

The advantage of providing amplitude and phase information of an object exit‐wave makes off‐axis electron holography a powerful tool for analyzing field and potential distributions up to an atomic scale. The ability to selectively manipulate the phase of the incoming electron wave additionally opens doors to new possibilities and  microscopic methods, such as the direct interferometric measurement of the coherence length of an electron wave packet [1, 2] or energy‐loss magnetic chiral dichroism (EMCD) based investigations [3].

In principle, a selective phase shifting device is realized by directing one of two coherent electron beams through an electrostatic potential surrounded by a grounded electrode to shield stray fields, while the other beam propagates undisturbed in the vacuum. We present two different concepts to create such a device.

The first one is a variation of an experiment G. Moellenstedt suggested in 1980 [1] and was first realized in 1985 by H. Schmid [2]. Instead of using two concentric tubes, we realized a setup with two separated and electrically isolated 1 mm long micro tubes on an especially developed modular carrier chip (M1) to electrify them (figure 1).

The second concept includes two perforated metallic plates (20 µm X 20 µm X 3 µm) in a distance of 3 µm to each other. The micro device shown in figure 2 was produced with focussed ion beam (FIB) allowing both a selective phase shift as well as the investigation of influences of stray fields.

We performed first in‐situ biasing TEM experiments with the phase shifting micro tubes. A big and necessary achievement was the enlargement of the hologram width from 2 µm to more than 25 µm. This was realized by using solely the TL22 lens of the image Cs corrector as objective lens of the FEI Titan 80‐300 Berlin Holography Special TEM. However, the micrographs in figure 3 show strong artefacts which we attribute to beam tilting due to charging effects of the tube surfaces. These artefacts manifest in a bending‐like projection of a biprism beneath the micro tubes.
Microscopy of thin
AlN
layers grown by
MBE
on (111) silicon
Authors: Cora Ildikó , Kovács András , Mansurov V.G. , Malin T.V. , Galitsyn Yu.G. , Zhuravlev Kostya , Pécz Béla
Published: December 2016

After the discovery of graphene many other materials were subject of research in a 2D form among them some of them showed bandgap at room temperature. There were a lot of theoretical papers which predicted the properties of the appropriate candidates.

AlN layer is widely used as a buffer layer for the epitaxial growth of III‐Nitrides on SiC, Si and Al
2
O
3
substrates. In this work, the formation of a few monolayers thick graphene‐like AlN (g‐AlN) layer on a (111)‐oriented silicon substrate in ammonia molecular beam epitaxy (MBE) has been studied using various transmission electron microscopy (TEM) techniques.

Flat, ultrathin layer of AlN was deposited on an ammonia treated (111) Si substrate (1). Two samples with thick (15‐25 monolayer) and thin (3‐4 monolayer) AlN were prepared. Cross sectional TEM specimens were prepared using the conventional mechanical polishing and low‐energy (<1 keV) low‐angle Ar ion milling. TEM images (not shown) used to measure the AlN layer thicknesses as X and Y nm in the two samples. The chemical composition of the interface structure between the AlN and Si substrate was studied by spectrum imaging; combining energy dispersive X‐ray spectroscopy (EDXS) and scanning TEM (STEM) in an aberration‐corrected FEI Titan 80‐200 ChemiSTEM microscope. Figure 1 shows the Si and N map of the sample containing 15‐25 AlN monolayers. The elements distribution across the interface extracted as linescans and shown in Fig. 1b suggests nitrogen enrichment between the Si and AlN. The interface structure was further studied by aberration‐corrected TEM using an FEI Titan 80‐300 kV TEM operated at 300 kV. Figure 2 shows the boundary structure very clearly, where ‐ based on the measured distances (3.3 Å and 1.9 Å) ‐ we suppose that two layers of Si
3
N
4
phase were grown onto the silicon probably due to the ammonia treatment prior the AlN deposition. The first three sheets of AlN was measured to be as 2.86 Å and 2.60 Å that are higher than the wurtzite‐type AlN (2.5 Å) suggesting that the AlN does not immediately follow the wurtzite‐type stacking.

The results promise not only the formation of few layer AlN with different properties from the thick layers, but also their possible integration into the silicon device technology.