bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure‐Thermal Conductivity Relationship in Pressureles Sintered
AlN
Ceramics for Energy Applications
Authors: Turan Servet , Cinar Alper , Kaya Pinar
Published: December 2016

Aluminum nitride (AlN) ceramics are attractive materials for microelectronic packaging due to its high thermal conductivity, low dielectric constant and good matching of thermal expansion coefficient [1‐4]. However, it is difficult to sinter AlN due to its strong covalent bonding. Densification of AlN powder has been attempted by various techniques. For full densification, rare earth and/or alkaline earth oxides are often added as sintering aids during the fabrication of AlN ceramics [4]. To investigate the effect of microstructure on the thermal properties and sintering behaviour, commercially available AN powder (Grade H, Tokuyama Co. Ltd., Japan) was sintered pressureless by using commercially available Sm
2
0
3
and Yb
2
0
3
powders (purity > % 99, Treibacher Industrie, AG, Austria ) as sintering additives and graphene as a secondary phase to improve the thermal properties.

The powder mixture was milled by plenatory ball mill in ethanol for 1.5 hours at 300 cycles / min. Then, the ethanol in the slurry was evaporated. After drying, the powders were pressed by handpress at 50 MPa to obtain pellets. The pellets were cold isostatically pressed (CIP'ed) under 200 MPa. The specimens were then placed into a BN crucible and sintered at 1800 — 1860°C in a graphite furnace with a flowing nitrogen gas.

The heat capacities of the samples were measured by DSC (NETZSCH STA 449F3) whereas the thermal diffusivities of the samples were measured by laser flash technique (Netzsch‐LFA 457). The sintered samples were characterized by employing XRD, SEM and TEM techniques. XRD patterns of the samples were recorded using a (Rigaku Rint 2200, Tokyo, Japan) monochromatic CuKα radiation. Scanning electron microscope (SEM) investigations were carried out using a ZEISS SUPRA 50 VP microscope. For TEM investigations 200 kV field emission TEM (JEOL JEM‐2100F) equipped with STEM high angle annular dark field (STEM‐HAADF) detector (Model 3000, Fischione), electron energy loss spectrometer (EELS) and energy filter (Gatan
TM
GIF Tridiem), and energy dispersive spectrometer (EDS) (JEOL JED‐2300T) was used.

Three different liquid phase addition caused to obtain different intergranular phase formation resulting in a decrease in the thermal diffusivity of the materials with the addition of Yb
2
0
3
(Fig 1a). When the micstructure was investigated with STEM HAADF (Fig 1 (b, c and d)), the grain boundary intergranular films found to have a very different behaviour. In this study, property‐microstructure realtionship for AlN ceramics and AlN‐graphene composites will be presented as a function of different sintering addities, different sinterin conditions and heat treatment procedures.
Identification of core‐shell structures in high active Pt‐alloy catalysts for oxygen reduction by electron spectroscopy
Authors: Deiana Davide , Velazquez‐Palenzuela Amado Andres , Escudero‐Escribano Maria , Masini Federico , Stephens Ifan , Chorkendorff Ib , Hebert Cécile
Published: December 2016

A potential clean alternative to traditional power sources, in particular for the automotive industry, is represented by low temperature fuel cells [1].

The major limitation of this promising technology lies in the high loading of the mostly used catalyst Pt necessary to drive the chemical reactions at the electrodes of the cells, impacting significantly on costs.

Generally, the performance is limited by the sluggishness of the Oxygen reduction reaction (ORR) that occurs at the metal catalyst surface present at cathode. Therefore, a great effort is put in finding catalysts with higher efficiency for the ORR [2][3].

A promising strategy for enhancing the ORR activity is to alloy Pt with other metals [2]. However, commercially available Pt alloys with late transition metals are mostly unstable under the harsh conditions in a fuel cell cathode [4].

Pt‐Gd has been identified as a promising material among a new class of Pt‐lanthanide alloys as highly performing catalyst for the ORR in both activity and stability, surpassing the previously reported Pt‐Y [5‐7].

The experimental results have shown that Pt
x
Gd nanoparticles exhibit an outstanding ORR activity of 3.6 A (mg Pt)
‐1
at 0.9 V with respect to a reversible hydrogen electrode [8].

To fully understand the enhanced performance of these catalysts, the knowledge of the detailed structure and elemental distribution at the nanoparticle level is of extreme importance. Here we present an advanced Scanning Transmission Electron Microscopy (STEM) study of Pt
x
Gd nanoparticle catalyst.

High resolution HAADF‐STEM imaging and STEM‐EDX spectrum imaging has been performed in a double C
s
‐corrected FEI Titan Themis 60‐300 at CIME laboratories, equipped with a monochromated high‐brightness FEG, an EDS SUPER X system with a 0.7 srad of solid angle and a Gatan GIF Quantum ERS high energy resolution EELS spectrometer and energy filter.

Pt
x
Gd nanoparticles have been prepared through a gas aggregation technique in a multi‐chamber ultrahigh vacuum system (Omicron Multiscan Lab) at DTU CINF laboratories.

Figure 1 shows a high resolution STEM micrograph and STEM‐EDX elemental maps of Pt
x
Gd nanoparticles after exposure to ORR conditions during electrochemical tests. From the micrographs the sample presents a polycrystalline structure with a Pt rich shell and a Pt‐Gd core. The formation of the Pt shell is assigned to the initial dissolution of Gd when exposed to the acidic solution of the ORR test.
Assessing chemical and microstructural evolution at interfaces of γ′‐ strengthened superalloys at high temperature by in situ
TEM
heating experiments
Authors: Eggeler Yolita , Enge Daniel , Spiecker Erdmann
Published: December 2016

Single crystal Ni‐base superalloys exhibit outstanding high temperature properties and are used as turbine blade material in advanced gas turbines, where they withstand high temperatures and mechanical loads in harsh environments [1]. Their high temperature properties are associated with their unique two phase γ/γ' microstructure consisting of cuboidal γ′ precipitates, exhibiting the ordered L1
2
crystal structure (vol. frac. ca. 80%) , which are coherently embedded in a solid solution γ fcc matrix. To ensure precipitation hardening at temperatures relevant to gas turbine applications, 700‐1100 °C, the stability of the γ/γ′ phases is of fundamental importance. At high temperatures the γ' ‐ precipitates start to dissolve until a stable γ' ‐ volume fraction is reached [2][3].

In this analysis the microstructural evolution of the γ and γ′ phase towards a new thermodynamic equilibrium, corresponding to a selected temperature, is investigated. In situ TEM studies with chip‐based heating systems (by DENS solution) are performed on a single crystal Ni‐based superalloy, ERBO1. Figure 1 presents a typical ERBO1 lamella, fixed in between the Pt spirals of a high temperature heater chip. The sample is heated to 950°C for different time periods and is subsequently quenched (see heating profile on the right of Figure 1). The elemental distribution was measured by EDXS at room temperature, whereby the sample was tilted close to the [001] zone axis to minimize projection effects. Figure 2 shows the γ/γ' microstructure of the ERBO1 alloy with a black rectangle indicating the region where the ChemiSTEM EDXS measurements were conducted after each heating sequence. The Cr concentration profiles show that the transition towards a new thermodynamic state can indeed be resolved, with progressing time the Cr concentration decreases in the γ phase and increases in the γ′ phase. Such data contain valuable information on the kinetics of interdiffusion in a real superalloy microstructure. Quantitative evaluation of diffusion profiles will enable to simultaneously determine interdiffusion coefficients of various alloying elements. Finally the experimental results will be validated by complementary ex situ experiments on bulk samples employing quenching in a vertical oven. Furthermore, the results will be compared with thermodynamic and kinetic data from theoretical calculations.
Three‐dimensional characterization of
Ni‐Sm0.2Ce0.8O2
‐δ cermet for
SOFC
anodes by high‐resolution
FIB
‐
SEM
Tomography
Authors: Kapun Gregor , Šturm Sašo , Marinšek Marjan , Gaberšček Miran
Published: December 2016

A solid oxide fuel cells (SOFC) technology is one of the most promising energy conversion device due to its high conversion efficiency, low environmental pollution and high flexibility to various fuel types (1). To overcome all challenges concerning materials' long term stability at operating temperatures, current research efforts are aimed at intermediate temperature SOFCs (IT‐SOFCs) (2). From this point of view samaria‐doped ceria (SDC) is a promising ceramic material, with superb ionic conductivity, which can be used as an anode material when combined with Ni in Ni‐SDC cermet (2). To ensure electronic and ionic conductivity as well as gas permeability, anode cermet should exhibit carefully tailored microstructure where metallic Ni, ceramic SDC and pores form continuous phases. In an operating cell fuel gas is electrochemically oxidized at the Ni/SDC/fuel interface, called the triple phase boundary (TPB) region. Therefore, both the activity of Ni‐SDC and their stability are strongly influenced by the cermet's morphology and microstructures such as volume fractions, grain connectivity, grain size, pore size, pore distribution and TPB length (3).

For this purpose, exact and accurate microstructural determination is crucial in predicting material's performances in an operating cell. In such a cermet composite critical topological features such as connectivity and the tortuosity of transport pathways in the pores can only be established based on 3D microstructural information (4). In this work we present quantitative characterization of Ni‐Sm
0.2
Ce
0.8
O
2‐δ
cermets, sintered at 1400°C, using high‐resolution FIB‐SEM tomography. Initially, a layer of platinum was deposited ontop the region of interest to protect the surface and prevent rounding of top edges of cross section during milling. The volume of interest was separated using an optimised U‐pattern pre‐milling procedure to prevent material redeposition and shadowing of the signals used for imaging and microanalysis. The sample was then serial sectioned using an automated slicing procedure with drift correction algorithms to obtain a series of 2D images with narrow and reproducible spacing between the individual image planes (5). Experimental milling and imaging parameters have been optimised in order to obtain a high quality 3D reconstruction with phase contrast information. Individual phases were identified from EDXS elemental maps and further segmented according to their grey level. 3D reconstructed volume is a base for determination of: volume fractions of individual phases, grain connectivity, porosity, tortuosity and TPB length.

The presented analytical method will serve as a tool for quantitative characterization of primary microstructural parameters and complex topological features, during microstructure evolution of Ni‐Sm
0.2
Ce
0.8
O
2‐δ
anode cermets using various sintering procedure.
In vivo calibration of a ratiometric sensor for
pH
and anions concentration in Arabidopsis cells
Authors: Besse Laetitia , Demes Elsa , Angeli Alexis De , Satiat‐Jeunemaître Béatrice
Published: December 2016

In plants, ions fluxes are involved in several physiological processes such as nutrient uptake, signaling pathways, cell elongation and stomata movements. However, little information is available about the intracellular anionic concentrations and anion fluxes among plant cell compartments. In the last years some promising anion concentration sensors have been developed (ClopHensor, Arosio et al. 2010) but have never been used in plant cells. The ClopHensor sensor (Figure 1) is a genetically encoded non‐FRET based sensor developed in mammals cells. It is based on a modified GFP (E²GFP) that is sensitive to chloride and nitrate concentration, and coupled to a DsRed. The DsRed fluorescent protein is used as an internal control for the expression of the construction, because its fluorescence is insensitive to anions concentration and pH, and clearly separated in term of spectral properties. The E²GFP fluorescent protein, excited at 488 nm, is sensitive to pH and anions concentration. But when it excited at 458 nm, the fluorescent signal is only sensitive to anion concentration. Thus, we are able to obtain simultaneously the intracellular pH and anion concentration maps in the cytosol by calculating ratios of fluorescence emission intensity. To do that we used a scanning confocal microscope equipped with an argon laser which provides these laser lines.

In the present collaboration work,
Arabidopsis thaliana
transgenic lines stably expressing ClopHensor in the cytosol were generated by Elsa Demes (phD student). We are currently performing the
in vivo
characterization of the ClopHensor sensor in Arabidopsis cells. Indeed, we are establishing the relationship between the fluorescent signal, and pH or anion concentration values, by generating
in cellulo
calibration curves. This work will lead to the creation of both pH and anions maps to study those parameters at the cell level.
Defocus and probe‐position coupling in electron ptychography
Authors: Cao Shaohong , Li Peng , Maiden Andrew , Rodenburg John
Published: December 2016

One of the most promising applications of electron ptychography is the possibility of converting a conventional SEM, with a relatively poor stability envelope, into a high‐resolution TEM. This is simply achieved by placing a transmission specimen in stage and a CCD camera placed below the specimen [1]. SEM ptychography does not need any image‐forming lenses: the objective lens is only used to generate a conical illumination. Defocusing this into a large area allows for a large ptychographical step size and a very large field of view. High resolution is obtained by solving the phase problem for the high‐angle scattered intensity (lying outside the Ronchigram) via iterative algorithms such as ePIE [2] and DM [3]. See Fig. 2a, where gold atomic fringes in gold nano particles on a carbon support film are clearly visible in a ptychographic reconstruction obtained from a conventional SEM (an FEI Quanta 600 SFEG at 30keV, data from [1]). We also solve for the illumination function, which in the case of conical illumination has a uniform curvature dependent on defocus.

A complication of electron (as opposed to visible light and X‐ray) ptychography is that is normally necessary to solve also for the illumination positions [4] because of errors in the scan coils resulting from magnification calibration inaccuracy and hysteresis. However curvature in the illumination and probe shift are coupled. Figure 1 shows a simplified ray diagram. For any two specimen planes where the ratio of the shift distance () and the ratio of the feature size in the object () equals the ratio of the defocus (), the resulting Ronchigrams will behave identically as the probe is shifted. In fact in the presence of wave interference the correct solution is unique, but for probe position‐searching algorithms that are necessarily guided by the Fourier error metric, the bright intensity of the Ronchigram dominates. When partial coherence is present (so that Fresnel effects in the Ronchigram are supressed) the problem is exacerbated, generally resulting in a distorted probe position lattice (Fig. 3), a wrong estimate of the defocus, and an inconsistent reconstruction in which lattice fringes are strongly delocalised. Of course, delocalisation renders the reconstruction entirely invalid, like an out‐of‐focus conventional TEM image.

We explore the coupled position‐defocus stagnation problem based on both experimental and simulated data. We report progress on various methods that can resolve this important issue.
Electron microscopy characterization of the wear of textured α‐
Al2O3
and κ‐
Al2O3
‐
TiN
multilayer coatings for cutting tool applications
Authors: Coronel Ernesto , Meingast Arno , Rabiei Babak , Persson Jeanette , Lattemann Martina
Published: December 2016

In metal cutting applications, coatings are often applied onto cemented carbide inserts as wear and heat resistant protection layers extending the tool life. A commonly used coating on inserts is Al
2
O
3
which provides chemical stability, thermal and wear protection for the cemented carbide insert. The crater wear and plastic deformation behavior in certain applications can be improved by altering the phase and/or texture of the wear protective coating. Worn (0001)‐textured α‐Al
2
O
3
and κ‐Al
2
O
3
‐TiN multilayer coatings on inserts which had been used in cutting applications have been investigated by means of scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDXS), XRD, electron backscatter diffraction (EBSD) in the SEM and (scanning) transmission electron microscopy ((S)TEM) techniques. The microstructure of the α‐Al
2
O
3
coating can be seen in the SE‐SEM image and its (0001)‐texture is shown in the EBSD orientation map, see Fig. 1a and b. The specimens for (S)TEM characterization were prepared in a Helios NanoLab 650 instrument (FEI Company) equipped with an EBSD detector (NordlysMax
2
, Oxford Instruments), EDXS detector (X‐Max
N
, Oxford Instruments) and AZtec software package (Oxford Instruments). (S)TEM characterization was performed using a Titan
3
60‐300 equipped with ChemiSTEM (FEI Companay). (S)TEM characterization of the worn α‐Al
2
O
3
coating revealed a modified region and EDXS elemental maps showed that this region contains Mg, Ca and Si beside the Al and O, see Fig. 2. Also, small grains of Fe were observed below this modified region. For comparison, (S)TEM characterization was performed on the worn κ‐Al
2
O
3
‐TiN multilayer coating. By determining the elemental distribution and formed phases the chemical wear mechanisms can be described.
Ni
‐based superalloy: crystalline orientation mapping and gamma‐gamma′ phases discrimination with the iCHORD method
Authors: Langlois Cyril , Charpagne Marie‐Agathe , Dubail Sébastien , Douillard Thierry , Bozzolo Nathalie
Published: December 2016

Electron backscatter diffraction (EBSD) is routinely employed as a characterization tool to obtain individual grain orientations, local texture and phase identification. However, in the case of γ ‐ γ′ Ni‐based superalloys, the EBSD technique allows mapping the orientations but fails discriminating the two phases because their diffraction signature is too similar. A coupling with EDX analysis for instance helps to identify the two phases but suffers from the lack of spatial resolution of the EDX maps. Another way to discriminate the two phases is to use the BSE images, sensible to the chemistry, but because of the difference in the geometry of acquisition of the EBSD images and the BSE images, superposition of the two information is complicated by strong spatial distortions. In this context, any new technique that can lead to an easier phase and orientation mapping would be welcome, especially to resolve the fine secondary γ′ precipitates (typically few tens of nanometers).

We proposed recently the iCHORD method (for ion CHanneling ORientation Determination), aiming at constructing orientation maps based on the well‐known channeling contrast phenomenon observed in a rotation series of ionic images (see figure 1) [1]. The proof‐of‐concept of the iCHORD method was established using a titanium nitride specimen (TiN) and further tests were conducted on different metallic materials. In the case of Ni‐based superalloys, the channeling contrast is very strong and allows obtaining quite easily orientation maps comparable in all aspects to the one obtained by the EBSD technique. Furthermore, when using the ion beam to scan the surface, a secondary ion signal can be detected and used for imaging the sample. In the case of γ ‐ γ′ superalloys, this secondary ion signal provides a strong contrast between the γ phase and the γ′ phase (see figure 2). Because of the identical geometry of acquisition for the iCHORD orientation maps and the secondary ion images, both information can be easily superimposed. It allows discriminating between the two phases and giving their crystallographic orientations (see figure 3). Moreover, the spatial resolution of the secondary ion images is around few tens of nanometers, which is far better than the resolution of ~1 µm of EDX maps.

To conclude, the advantages of using ion images to study Ni‐based γ ‐ γ′ superalloys are discussed, particularly the benefits taken from the higher spatial resolution and the ease of mixing orientation and phase information.
Structural and Compositional
EELS
Studies on Doped Carbon Nanostructures used as Cold Field Emitters
Authors: Wang Rongrong , Aurélien Masseboeuf , Neumeyer David , Monthioux Marc , Lopez‐Bezanilla Alejandro , Arenal Raul
Published: December 2016

Nowadays, more and more microscopes are equipped with cold field emission guns (C‐FEG) due to their higher performance. For further improvement of C‐FEGs, new emitter materials need to be explored. In this sense, carbon nanotube (CNTs) related materials are very promising candidates as cold field emitter [1]. However, more recently, carbon cone nanotips (CcNT) [2] have been considered as one of the most applicable form of carbon as field emitter, answering most of the technological problems of CNTs installation in a C‐FEG [3,4]. For a higher performance of C‐FEG, the electronic band structure of carbon nano‐objects (tube or cones) can be modulated through the introduction of heteroatoms into the graphene lattice leading to a lower work function [5,6]. This work is devoted to the doping of these carbon nanostructures by nitrogen and/or boron, the deep study of their structure and atomic composition, and to the evaluation of their cold field emission characteristics. In this contribution, we will focus on our recent results related to doping of carbon nanotubes. HRTEM imaging, spatially‐resolved EELS and X‐ray photoelectron spectroscopy (XPS) studies have been developed on these NTs. After heating treatments, there is no significant structural modification in the CNTs (Fig.1). C‐B and C‐N bonds are identified at macro scale by XPS (Fig.2 (a)) and at local scale by EELS‐STEM (Fig.2 (b), (c)). DFT calculations are also carried out and point out how the CNTs are affected by BN dopants. All these results will be discussed in depth in this contribution.
Ceria ro(a)d to cubes: a combined experiment and
MD
simulation study
Authors: Castanet Uli , Caddeo Francesco , Sayle Dean C. , Majimel Jerome
Published: December 2016

Since the first nanoparticle syntheses, research has focused on producing various nano‐catalysts of different compositions and uses. Over the years, the importance of their shape, hence their exposed facets, grew in interest. The differences between facets, may sometimes remain unclear and controversial, but more and more effects in terms of reactivity and/or selectivity are shown in recent works. In this framework, rod and cubic‐shaped cerium oxide nanoparticles were synthesized using a hydrothermal microwave‐assisted process. Systematic TEM imaging and analysis reveal that rods are progressively replaced by cubes with increasing synthesis time (with fixed temperature and pH). Besides, a more careful look at these cubic‐shaped particles highlights a slight anisotropy ‐ depending on the zone axis they are imaged along ‐ leading us to reconsider their nucleation and growth mechanisms.

These processes were first studied using radiation damages induced in ceria rods' complex microstructures under focussed electron beam. Their periodical packing composed of single crystals aligned along a common low‐index axis were firstly reduced and new nanometer‐sized domains were formed with different (micro)structures. These zones tend to split from the initial rod in case of severe irradiation conditions and may,
in‐fine
, lead to cuboidal particles via a solid‐state transformation process.

As‐synthesized cubes were then characterized by means of high resolution TEM coupled with molecular dynamics simulations. As expected, they exhibit single crystalline structure and {001} lateral facets are enclosed by {111} sharp corners and {011} average flat edges made of alternating {111} steps. More surprisingly, whatever the particle size might be, projected edges and corners width remains constant and corresponds to the diagonal of a four by four square formed by {002} planes. By keeping constant this truncation, surface plane ratios can be tuned only by adjusting ceria particles synthesis conditions.

Further on, when submitted to reducing conditions, both simulations and experiments tend to show a partially reversible flattening of the {011} edges combined with the observation of superlattice reflections and Moiré fringes. This indicates that oxygen anions have been removed from the fluorine CeO
2
structure inducing an ordered oxygen vacancies lattice. Finally, oxygen vacancies movement into the ceria network will be discussed.
Atomic Scale Characterization on
III‐V
Based Heterostructure Nanowire Interfaces
Authors: Venkatesan Sriram , Krogstrup Peter , Scheu Christina , Liebscher Christian , Dehm Gerhard
Published: December 2016

Quasi‐one‐dimensional III‐V semiconducting nanowires attract enormous attention owing to their physical properties such as tunable direct bandgap, high surface to volume ratio, high carrier mobility, tunable structures. Hence they have potential application in next generation electronics, sensors, photonics and photovoltaics. Understanding the details such as, atomic scale structure, local chemical stoichiometry and defects in a sub nanometer scale are inevitable when nanowires are intended for devices.

A systematic interfacial investigation on molecular beam epitaxy grown III‐V based nanowires such as InAs, GaAs,
[1]
in general and in particular, heterostructure nanowires of axially grown Ga
x
In
1_x
As‐InAs and InAs‐InAsSb will be presented.
[2]
In this work, atomic scale structural interfaces and interfacial chemical composition are analyzed using advanced aberration corrected transmission electron microscopy. Atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) and high resolution energy dispersive x‐ray spectroscopy techniques are predominatly used for characterizing the grown nanowires. Our work demonstrates on tailoring the growth, periodicities and the stoichiometry of III‐V nanowire heterostructure containing single/multiple electronic barriers involving In,Ga,As and Sb. We aim to provide understanding on the growth of dissimilar interfaces in heterostructure nanowire (see fig 1). In the InAs‐InAsSb heterostructure wires,
[1]
our work demonstrates the quality of the misfit strained interface in terms of structural abruptness and chemical homogeneity.
Dynamic‐Transmission Electron Microscopy at the Relativistic Electron Gun for Atomic Exploration (
REGAE
) for live cell imaging
Authors: Manz Stephanie , Keskin Sercan , Besztejan Stephanie , Zeitler Benno , Azim Sana , Kassier Guenther , Buecker Robert , Venegas‐Rojas Deybith , Riekeberg Svenja , Zhang Dongfang , Casandruc Albert , Loch Rolf A. , Zhong Yinpeng , Delsim‐Hashemi Hossein , Epp Sascha W. , Floettmann Klaus , Trieu Hoc Khiem , Rentmeister Andrea , Miller R. J. Dwayne
Published: December 2016

With the relativistic electron gun for atomic exploration (REGAE) we seek to observe structural dynamics both in real space imaging and diffraction [1]. REGAE is based on a RF gun accelerator and operates in the range from 2 to 5 MeV. RF gun technology allows high brightness for electron pulses at high energy. The machine is equipped with an RF cavity system, allowing for picosecond bunches with energy spread compensation to prevent limitations by chromatic aberrations and space charge. A custom made lens system for 3 MeV pulse energy system is set in place.

The presentation will include a discussion on space charge induced aberrations in dynamic HVEM, give estimates about the anticipated resolution and discuss the prospects for dynamic transmission electron microscopy of organic samples in environmental cells. Recent results making use of nano‐fluidic cell technology developed in house will be presented as an outlook: DNA – nanoparticle multimers have been studied regarding their dynamic in liquid and stability under electron irradiation during TEM imaging in a conventional 200 keV microscope [2]. First experiments towards imaging dynamics in living cancer cells under environmental conditions in the TEM will be discussed [3].
Transport of Intensity Equation (
TIE
) without filtering and
TIE
videos
Authors: Wild Johannes , Vogel Michael , Schwarzhuber Felix , Back Christian , Zweck Josef
Published: December 2016

In the transmission electron microscope (TEM) almost all specimens are very thin and create mainly phase shifts of the electron beam, hardly any absorption. The phase shift gives a lot of information about the specimen like e.g. thickness modulations, electric fields or magnetic fields. Measuring the phase by conventional imaging techniques is quite difficult as in general only changes in intensity are detected.

One way to get the phase difference between object wave and a reference wave is the transport of intensity equation (TIE) which was initially developed for light microscopes [1]. The most common use of the TIE is to input a linear approximation for the intensity changes which occur when the image is taken at different values of defocus along the z direction and then to solve the equation for the phase. Thus it is possible to calculate the phase in good approximation. From the phase it is e.g. possible to evaluate direction and strength of intrinsic magnetic and electric fields of the specimen.

Recent publications use mainly a commercially available software to perform TIE calculations [2‐4]. This software uses different filter algorithms which are not all known to the user. Therefore it turns out to be difficult to interpret the TIE reconstructions as the the filtering may create measurement artifacts.

Here we present a home written TIE Matlab code to calculate the phase. Our aim was to create a transparent code where the user is aware of all parameters. We use as little filtering as possible to minimize the room for misinterpretations and clearly show where modifications have been made to the original data. We are even able to calculate useful TIE images without any filtering as shown in figure 1.

Our software is capable of calculating magnetic or electric field maps from focal series (in‐focus, over‐focus, under‐focus). Further, it is possible to create automated multiple TIE images for videos to visualize e.g. the temporal development of a magnetic structure. We show one example of a fluctuating skyrmion lattice in Cu
2
OSeO
3
.

We will provide the code as a Matlab applet for everybody interested for free.
Random Beam Scanning Transmission Electron Microscopy and Compressive Sensing as Tools for Drastic Electron Dose Reduction in Electron Tomography
Authors: Trepout Sylvain , Nilchian Masih , Messaoudi Cédric , Donati Laurène , Unser Michael , Marco Sergio
Published: December 2016

Electron tomography is a fantastic tool for deciphering the structural information of complex 3D samples. During the last years, several tools have been developped to improve the 3D reconstruction quality of thick specimens. The direct detector cameras have incredibly increased the SNR and resolution of thin samples 2D projections, bringing electron microscopy resolution at the level of the one of X‐ray diffraction studies. However, the study of thick biological samples in tomography still suffers from the too important electron dose one has to use in order to retrieve high quality images and reconstructions. It has been shown that STEM tomography can generate more accurate reconstructions than TEM tomography while preserving better the sample integrity. Previous uses of compressive sensing enabled the reduction of tilt‐angles in tomography studies, unveiling electron dose reduction. Here, we push further the electron dose reduction thanks to a more effective compressive sensing method which uses incomplete images as incoherent data. The generation of incomplete images being performed at the microscope during the acquisition process where the beam randomly scans the surface of the sample.
STEM
investigation of titania supported gold nanoparticles stabilized by ceria
Authors: Hungría Ana , Tinoco Miguel , Río Eloy Del , Manzorro Ramón , Cauqui Miguel A. , Calvino Jose Juan , Perez‐Omil José A.
Published: December 2016

Gold nanoparticles show an excellent catalytic performance in energy production related processes such as low temperature CO oxidation, PROX and WGS reactions [1‐2]. The effect of the support, like titania or ceria, and/or the presence of different kinds of promoters on the catalytic performance of gold have also been investigated, and a general agreement about the advantages of using reducible oxides is deduced from a revision of the most recent literature. Gold catalysts have also proven to be active in environmental reactions as those occurring in the catalytic converters (TWC) for depuration of exhaust gases in vehicles. The use of gold as a component of the current TWC formulations, substituting the more critical Pt and Pd, would only be feasible if the excellent catalytic properties of this metal could be maintained after exposure at high temperature operating conditions. However due to its relative low melting point gold suffers a severe sintering process starting at temperatures of around 473 K [3].

In order to investigate the stabilization of gold nanoparticles a reference system, 1.5 wt% Au/TiO2World Gold Council catalyst, was modified by depositing on its surface a monolayer of CeO2by incipient wetness impregnation to a final ceria molar loading of 5.4%.Scanning Transmission Electron Microscopy (STEM) studies show that the dispersion of the gold nanoparticles remained unchanged after the impregnation in a value about 36%. Afterwards, both catalysts were tested in consecutive CO oxidation reaction loops at increasing final temperatures. In these cycles, the ceria‐modified catalyst showed not only a higher activity but, more importantly, a largely enhanced stability against deactivation.

Scanning Transmission Electron Microscopy has provided key information to rationalize the origin of the stabilization effect provided by ceria. In particular, STEM‐HAADF images haveclearly revealed the presence of nanometer‐sized ceria rafts, less than 1 nm thick, on the surface of the fresh CeO2(5.4%)/Au(1.5%)/TiO2catalysts. After the CO oxidation test at the highest temperature, 1223 K, the conventional WGC catalyst suffered from a very severe Au nanoparticle sintering, Figure 1(a),whereas Au nanoparticle growth was very much limited in the ceria‐modified catalyst after the same aging test, Fire 1(b).

Cs‐corrected STEM results reveal that a major fraction of the Au nanoparticles (75%), comprising all the smaller ones (< 5 nm), was contacting the ceria nanolayers. This evidences an important stabilizing effect of the proposed surface modification. Moreover, these results open up possibilities for gold catalysts in applications where high temperatures are reached under working conditions.
Is the electronic structure of few layer transition metal dichalcogenides always two dimensional ?
Authors: Yuan Jun , Hong Jinghua , Jin Chuanhong
Published: December 2016

The transition metal dichalcogenides (MoS
2
etc.) are a new class of layered materials that can be prepared in variable layer thickness down to single molecular layer. Compared with the more well‐known graphene, the monolayer version of graphite, the transition metal dichalcogenides are semiconductors and hence can be more useful in applications such as light emission or photovoltaics where an energy gap is essential. Ultra thin transition metal dichalcogenides also show interesting layer thickness dependent physical properties. For example, the semiconductor gap was found to change from indirect to direct when the layer thickness is reduced to monolayer, making monolayer MoS
2
an efficient light emitter.

Here we present investigation of the dimensionality of the joint density of states involved in the interband transition in MoS
2
using angle resolved as well as angle integrated electron energy loss spectroscopy [1]. To aid the analysis, we have extended the theory of joint density of states from three‐dimensional semiconductors to low‐dimensional semiconductors.

Our result and analysis shows not only that the character of the interband transition changes from indirect to direct, as the layer thickness is reduced down to monolayer, as expected, but the indirect band gap retains a three dimensional character down to the monolayer limit. This is compared with the two dimensional character found for the direct bandgap transition in the monolayer MoSe and presumably also in MoS
2.
This raised a question about the condition for observing a true two dimensional electronic structrue even when the atomic structure is reduced to single molecular thickness. We will discuss physical factors might affecting the dimensionality of the electronic density‐of‐states.

Our result has practical implication. For example, it is consistent with the assumption made by Castellanos‐Gomez et al. [2] when interpreting the electrostatic screening effect observed in monolayer MoS
2
, which is very different from that of graphene. Our result also can explain the sensitivity of the indirect interband transition as a function of the layer thickness and the bandgap cross‐over of few layer MoS
2
from indirect to direct.
Hyperbolic Plasmons in the Topological Insulator
Bi2Se3
Authors: Keskinbora Cigdem Ozsoy , Talebi Nahid , Benia Hadj , Koch Christoph , van Aken Peter
Published: December 2016

The surface plasmon excitation is one of the popular field of research due to their high potential to be applicable in sensor
1
or information technologies
2
, cancer research
3
etc. These coherent delocalized electron oscillations are common in metal‐dielectric interfaces. However, recent studies show they also exist in highly doped semiconductors, conducting oxide system or graphene, in summary mostly the systems with high carrier mobility. The next question can be asked for the insulator interfaces.

Bismuth Selenide became popular material system due to its recently discovered topological insulator property, in which it behaves as an insulator in the bulk state and metallic at the surface state. This also makes Bi
2
Se
3
as a potential candidate for surface plasmons,so that the first example of Dirac plasmons on Bi
2
Se
3
was observed in 2013 in 0.5 – 1 eV energy loss region
4
.

The Dirac state is not the only reason of the existence of a plasmon resonance in Bi
2
Se
3
. It is a highly anisotropic with hypabolic dispersion Tetradymites crystal structure, which also makes the dielectric properties highly anisotropic which can allow the plasmon excitation
5
. In this study we would like to show energy filtered transmission electron microscopy (EFTEM) and a finite‐difference frequency‐domain (FDTD) study for investigating Bi
2
Se
3
nanoplates and try to find an explanation for the existing plasmon excitations.

For the experimental observation of Hyporbolic dispersion in Bi
2
Se
3
, EFTEM study was carried out using FEG‐TEM Sub‐Electron‐Volt‐Sub‐Ångstrom‐Microscope (Zeiss SESAM) in the 200 kV equipped with an electrostatic monochromator and the in‐column MANDOLINE filter with 0.2 eV slit width. As shown in Fig. 1 localized excitations exist at surface of Bi
2
Se
3
crystal and they show different collective modes in different energies. These results supported by FDTD simulations to be able to explain the interplay between the edge plasmons and surface plasmons.
Microstructural and chemical characterization of the system
CaO‐Al2O3
using environmental scanning electron microscopy (
ESEM
)
Authors: Berent Katarzyna
Published: December 2016

The calcium and alumina oxide is a highly interesting functional materials. In the binary compound 12CaO·7Al
2
O
3
has a unique crystal structure as a nano‐sized cage with free oxygen anions randomly distributed inside the cages. C12A7 has gained much attention for potential applications in various fields, such as ion conducting solid electrolyte, field and ion emitters, oxidizing catalyst and as a transparent conductive oxide (TCO) in flat panel displays, solar cells and energy conservation (smart windows) devices [1, 2]. The functional properties of electrides are strongly depend on the microstructure. There is in the literature some information about the influence of specific surface area and impurities of alumina on the sintering behaviour of an alumina material. But in this study, the objective is to determine if the various processing techniques have an influence on the microstructure evolution of materials made from alumina and calcium oxide.

Post‐fabrication C12A7 samples were subjected to heat treatment using different processing methods in order to achieve desired crystal structure. The final products were prepared by sintering (1) and melted in an electric furnace (2). Crystalline and amorphous phases were obtained.

The aim of the present study was to evaluate the microstructure of CA ceramics under different melting conditions. The microstructure characteristics were analyzed by means of optical microscopy (OM), X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDXS) and environmental scanning electron microscopy (ESEM).

For scanning electron microscopy (SEM) examination, sintered specimens were cut and polished. ESEM allows the direct examination of specimens without a conductive metallic coating. The application of ESEM could have advantages in the study of ceramic samples due to a reduction in preparation time. The microstructures of bulk materials were observed before and after sintering, and the effect of solution processing parameters and the formation of surface defects was studied. Microstructural differences were observed for the same composition materials under the different processing conditions (Fig. 1). The morphological and compositional properties of the final C12A7 samples are highly affected by their structure and crystallisation.
Discovery of pyridinic nitrogen defects and single atom spin in graphene
Authors: Lin Yung‐Chang , Suenaga Kazu
Published: December 2016

Nitrogen is one of the most important doping elements for carbon materials. N doping was reported to enhance the catalytic ability of carbon materials and can improve the oxygen reduction reaction efficiency. Besides, the N doped graphene are also anticipated for several applications such as n‐type transistor, sensor or lithium battery. Distinct N configurations, i.e., graphitic N and pyridinic N, have been predicted to behave different electronic properties. Therefore, to precisely control the type of N doping is considered a critical issue to realize high performance graphene‐based devices. Though X‐ray photoelectron spectroscopy (XPS) analysis suggests distinct N 1s states for different N configuration, however, the direct link to the specific N defect is still limited by the spacial resolution. Here, we present systematic studies of atomic structures and the atomic EELS studies on graphitic N and pyridinic N defect in graphene by scanning transmission electron microscopy [1]. Figure 1a and 1b show the ADF images and the corresponding atomic models of graphitic and pyridinic N defect in graphene. The energy loss near‐edge structures of the graphitic N and pyridinic N defects are shown in Figure 1c. The graphitic N
K
‐edge shows two sharp peaks at 401.4 eV (π*) and 407.6 eV (σ*), while the π* and σ* peak of pyridinic N exhibits significant down shift to 398.0 eV and 406.6 eV.

Pyridinic N defects are also found highly reactive to attract individual single transition metals (TM) to the defect sites. The spin state of single TM atoms in graphene defect was studied by core‐level electron spectroscopy. Figure 2a and 2b show the ADF images of single Fe atoms anchored at graphene divacancy and at the four pyridinic N defects. We found that the single Fe atom possess high spin at graphene divancacy, while the spin state can be altered to low spin when bonding to pyridinic N (Figure 2c). This work realize the controllable of spin state of an individual TM atom which can be regarded as the smallest component of spintronic devices [2].
Beam exfoliation of
MoS2
layers with a helium ion beam
Authors: Zhang Hongzhou , Maguire Pierce , Fox Daniel S , Zhou Yangbo
Published: December 2016

Precise modification of two dimensional (2D) materials with high resolution will be instrumental in future device fabrication. Such a method is presented here for the removal of layers of MoS
2.
The thickness of selected regions of few layer MoS
2
has been altered with a sub‐nanometre beam of He
+
.
This ‘beam exfoliation’ of MoS
2
has been characterised and controlled. An investigation of annealing and of the modified regions is now underway.

MoS
2
is a material in the transition metal dichalcogenide (TMD) family which undergoes a transition from indirect to direct bandgap when going from multilayer to monolayer. This makes it ideally suited to applications in digital electronics as well as numerous photonic applications such as light emitters, photodetectors and solar cells. Excellent mechanical flexibility also provides potential for use in flexible electronics. Even more interesting than the superlative physical properties of 2D materials is the ability to tune these properties with precision. Considerable alteration of MoS
2
behaviour is already possible by tailoring the crystal structure, stoichiometry and geometry. Since there is such a significant difference between the behaviour of single layer and multilayer MoS
2
, thinning of MoS
2
has been reported in a number of different manners. These include laser ablation and Ar
+
plasma etching.

Few‐layer molybdenum disulphide (MoS
2
) was obtained by mechanical and liquid exfoliation and transferred to a TEM grid. It was irradiated with He
+
at 30 keV in a number of different configurations . In the images presented, thinning is observed in the bright regions where the beam did not penetrate the material.

Figure 1 is a 300kV TEM image which shows a region with intact crystal structure demonstrating a thinned front progressing towards a fully milled region. In addition, the crystal structure is clearly intact.

From previous work, it is known that few layer (one to roughly five or six layers) MoS
2
can be milled (cut through completely) with a minimum dose in the approximate range of 10
17
‐10
18
ions cm
‐2
. In order to perform rudimentary characterisation on the thinning of material SEM was used to measure the minimum helium ion dose at which altered contrast ‐and it is implied, thinning‐ could be observed (of course this does not exclude other possible effects on the complex systems of electron microscope contrast). A variety of SEM operation modes were tested to determine which was the most sensitive to the changes (secondary electron (SE2), Inlens, bright field STEM and dark field STEM). It was found that dark field STEM exhibited the sharpest change in contrast with respect to dose as indicated in figure 2.

Finally figure 3 is a schemtic diagram of the thinning process.