bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation of Graphene and its Conversion to Single Walled Carbon Nanotube revealed
Authors: picher matthieu , Pin Ann Lin , Gomez Ballesteros Jose L. , Balbuena Perla , Sharma Renu
Published: December 2016

During catalytic chemical vapor deposition, the chirality of single wall carbon nanotubes is determined when the growing graphene nucleus wraps around the catalyst and converts into a tubular structure. Elucidating this critical process is required to develop deterministic bottom‐up strategies aiming at better chiral distribution control. Direct observations of carbon nanotube growth, and theoretical modeling and simulations of the nucleation have been published but experimental atomic‐resolution evidence of single‐walled carbon nanotube nucleation has, until now, eluded us.

The main obstacle is that nucleation involves a few atoms only and a short time scale, thus requiring a combination of high spatial and temporal resolution for direct observation. Here, we overcome the temporal resolution constraint by reducing the growth rate in order to match the temporal resolution of our recording medium. We employ an environmental scanning transmission electron (ESTEM), equipped with an image corrector and a digital video recording system, to follow SWCNT growth using Co‐Mo/MgO catalyst and acetylene (C
2
H
2
) as a carbon source (see Methods). We present atomic‐resolution movies that reveal the nucleation of graphene on cobalt carbide nanoparticles followed by its transformation to a single‐walled carbon nanotube. We find that the surface termination of the faceted catalyst nanoparticles regulates the nucleation of the graphene sheet and its conversion into a nanotube. Additional density functional theory calculations show that the disparity in adhesion energies for graphene to different catalyst surfaces is critical for nanotube formation: strong work of adhesion provides anchoring planes for the tube rim to attach, while weak work of adhesion promotes the lift‐off of the nanotube cap (Fig. 1). [1]
Microstructural and mechanical properties of hyper‐deformed surfaces: In‐situ micro‐pillar compression and
EBSD
investigations in α‐iron
Authors: TUMBAJOY‐SPINEL David , JOAO Sergio SAO , MAEDER Xavier , DESCARTES Sylvie , BERGHEAU Jean Michel , MICHLER Johann , KERMOUCHE Guillaume
Published: December 2016

The mechanical surface treatments confer better local mechanical properties against wear or fatigue service conditions. In the case of impact‐based treatments, a local microstructure refinement in the near surface is produced by a severe plastic deformation of the material, leading to a progressive reduction of the grain size over a few tens of microns, and consequently an increase of the hardness and mechanical properties. These zones are commonly known as Tribologically Transformed Surfaces (TTS). In this project, the micro‐structural transformation in the near surface is produced on pure α‐iron samples using a repetitive impact‐based procedure: Micro‐percussion treatment. In this technique, every impact is effectuated on the same position with a rigid conical indenter (tungsten carbide), controlling the number, angle and velocity of impacts. The resulting imprint (figure 1) is characterized by a significant grain size refinement and consequently a graded strengthening as a function of distance to the impacted surface. Moreover, several in‐situ micro‐pillar compression tests are carried out in the cross‐section of the hyper‐deformed surface (figure 2) in order to quantify this mechanical property gradient in‐depth. However, the yield strength increment observed with this technique does not reveal the different micro‐structural contributions (grain size effect, dislocation hardening, etc…) on the increase of mechanical properties. Indeed, the main purpose of this work is to correlate the mechanical properties gradient with the local microstructural evolution produced by the impact‐based severe plastic deformation. For these purpose, EBSD mapping (figure 1) is used to determine the grain size distribution and the local “Kernel Average Misorientation” (KAM) in the cross section. A qualitative estimation of the geometry necessary dislocation density could be done from this latter estimation. With this analysis, the Hall‐Petch and dislocation strengthening contributions could be correlated and compared with the experimental results from micro‐pillar compressions (figure 2).
Advantages and pitfalls for transmission electron microscopic studies in the identification of extracellular vesicles
Authors: Kittel Agnes , Osteikoetxea Xabier , Sódar Barbara , Pálóczy Krisztina , Baranyai Tamás , Giricz Zoltán , Buzás Edit Irén
Published: December 2016

Although the story of extracellular vesicles (EVs), these cell‐derived submicron structures started about 70 years ago, we had to wait for the first transmission electron microscopic (TEM) evidence of their existence till 1981.

By now it has been proved that the release of membrane vesicles is a process conserved in both prokaryotes and eukaryotes. Compelling piles of evidence support the significance of exosomes, microparticles/microvesicles or ectosomes and apoptotic bodies in a broad range of biological processes including e.g. intercellular communication, signaling processes, the transfer of genetic information, and also in case of pathological events, from inflammation till tumor development. Not surprisingly, the possibility of EV‐related biomarker and therapeutic applications made this research field attractive for clinical and pharmaceutical research, too.

However, in spite of growing interest, the classification of EVs is still under debate. The numerous protocols, applied by the different research teams, made the comparison of the results more complicated; moreover several frequently used and up‐to‐date particle enumeration techniques such as nanoparticle tracking analysis or tunable resistive pulse sensing are not suitable to distinguish vesicles and e.g. protein aggregates in similar size. Falsified experimental results may occur easily, especially in case of body fluid samples or culture media, in which protein aggregates, which share biophysical parameters with EVs, may contaminate vesicle preparations.

Purity and type of the fractions should be investigated with different techniques depending on the size range of the investigated vesicle population. For detection of exosomes, the frequently used flow cytometry is not the best choice, while by means of AFM, dynamic light scattering, MS techniques or microfluidic device, mentioned only few among the applied possibilities, can reveal several features of the investigated vesicle samples. However, even the most sophisticated combination of different techniques cannot be complete without transmission electron microscopy. It is the only technique which is able to visualize vesicular and non‐vesicular particles in the whole size range of the vesicle population, and if we want to use EVs for research and therapy, we have to learn, how TEM can be applied for their accurate characterization.
In situ
TEM
observation of electromigration in Ni nanobridges
Authors: Kozlova Tatiana , Zandbergen Henny W.
Published: December 2016

Using
in situ
scanning transmission electron microscopy (STEM) (FEI Titan microscope operating at 300 keV), a microelectromechanical system (MEMS) chip and a dedicated biasing and heating sample holders, built in‐house, we investigated electrical and thermal properties of 15‐nm‐thick Ni nanobridges. These techniques allow to visualize nanobridge morphology transformations down to atomic scale while electrical current is passed. If thin metallic wire is subjected to high current density, the material transfer can start which results in the wire break. This phenomenon is called electromigration
1
.

Ni nanobridges with a length of 500 – 1000 nm and a width 200 – 500 nm were produced by e‐beam metal evaporation onto a 100‐nm‐thick freestanding silicon nitride membrane and patterned using electron beam lithography (Fig. 1a). Contacts to the nanobridges were made with a 100‐nm‐thick layer of Au and a 3‐nm‐thick adhesion layer of Cr. Initial resistance of the structures, including bridge, contact pads and leads, is in the range of 160 – 250 Ohm. More details of the sample preparation can be found elsewhere
2
. Using electrical setup
3
,
I–V
measurements were performed in bias‐ramping mode. Voltage is gradually increased (with a speed of 15 mV/s) from 0 V to a predefined value of 500–600 mV, followed by a decrease back to 0 V, after which a new cycle with higher maximum voltage was performed (Fig. 1f).

Fig.1 shows STEM images of Ni nanobridge with 10‐nm‐thick Al
2
O
3
oxidation‐protective layer on top taken before electromigration and after each bias‐ramping cycle with maximum voltages 500 mV, 520 mV, 540 mV and 580 mV. Fig. 2f shows corresponding
I–V
curves for four voltage cycles applied in a row. Sample temperature prior to voltage apply was 100 K. During electromigration experiments in Ni material transfer was shown to be voltage polarity dependent: Voids initially form near the cathode contact pad of the bridge, as in the majority of metals due to electron‐wind force, but at the end bridge breaks near the anode side.

Also, we visualised morphological transformations in polycrystalline Ni film (deposited on top of the heater with 20‐nm‐thick windows in Si
3
N
4
membrane) during substrate heating up to 400°C (Fig. 2) and estimated the bridge temperature achieved in electromigration experiments due to the Joule heating to be around the Curie point. In order to enhance the contrast between grains, annular dark‐field STEM imaging was used
4
.

Enriched with oxygen bubbles formation was found due to Ni nanobridges oxidation after a month of their storage at atmospheric pressure. In order to prevent samples oxidation, 10‐nm‐thick Al
2
O
3
layer was used as a protective layer. The place of bridge break near the anode side was shown to be independent on the ambient pressure and substrate temperature.
In situ
SEM
dynamic investigation of charging kinetics in insulating materials
Authors: Sao Joao Sergio , Mekni Omar , Goeuriot Dominique , Damamme Gilles
Published: December 2016

Dielectric breakdown constitute an important limitation in the use of insulating materials since it causes its damage. This catastrophic phenomenon (Figure 1) is obviously an important failure in the levels of equipment requiring some insulation safety or ensuring their proper functioning. This causes some technological problems associated with the manufacture and use of insulating materials in several industrial sectors like in microelectronics, high voltage electric energy transport and spacecraft. The choice of insulating material for those applications is related to the corresponding breakdown voltage value which limits their use. To improve the resistance to dielectric breakdown, it is imperative to understand and control the cause of this damage process reducing the reliability of some instrumentation. It is well known that breakdown is correlated with the presence of space charge within the insulators. Indeed, breakdown is related to a fast relaxation (detrapping) of trapped charge. Commonly, this space charge can be determined by the SEMME method (Scanning Electron Microscope Mirror Effect) which quantifies the final trapped charge amount. The purpose of this work is to develop a technique using a specific arrangement in the SEM chamber (Figure 2) in order to characterize the trapped charge dynamic by ICM (Induced Current Method). This technique allows enhancing the understanding of trapping phenomenon, spreading and stability of trapped charges

The experiments were carried out in a FESEM (Field Emission Scanning Electron Microscope) Carl Zeiss SUPRA 55 VP using a specific configuration in the SEM sample holder (Figure 3). It permits to measure separately and simultaneously the influence current and the conduction current and tracing back to the trapped charge temporal evolution during (charging) and after (charge decay) electrons irradiation (Figure 4). Thereafter, the used technique of two injections separated by a pause time was a powerful method for monitoring and understanding the dynamics of the trapped and released charges in insulating materials. These results open the way for the establishment of a conventional characterization procedure, which will be useful in different contexts of use of insulating materials. The studied materials are α‐alumina and Yttria Stabilized Zirconia (YSZ) polycrystalline ceramics. Since the dielectric and electrical properties of an insulating material are highly dependent on its microstructure, the grain size effect and MgO doping effect are then studied and discussed. Via the developed technique, the microstructure ‐ dielectric rigidity correlations could be well justified.
The Role of Interfacial Structure and Defects in Precipitation Pathways in Aluminium Alloys
Authors: Bourgeois Laure , Zhang Zezhong , Zhang Yong , Chen Yiqiang , Rosalie Julian , Li Jiehua , Dwyer Christian , Medhekar Nikhil
Published: December 2016

Precipitation hardening in aluminium alloys provides well‐known examples of how identical materials can develop very different microstructures through different processing conditions or the addition of trace alloying elements. Desirable microstructures for useful materials properties such as high mechanical strength often involve the precipitation of metastable phases from a supersaturated solid solution. A textbook case is the precipitation of Guinier‐Preston (GP) zones in Al‐Cu alloys [1] and the subsequent formation of θ' and θ' metastable phases [2]. More than 75 years after the original work by Guinier and Preston, the atomic‐scale mechanisms behind the solid‐solid phase transformations associated with the nucleation and growth of those phases remain unknown. Such an understanding is required if one is to move towards rational design of new high‐performance alloys aided by modern computational techniques.

In the last eight years aberration‐corrected scanning transmission electron microscopy (STEM) has enabled significant progress in the determination of bulk and interfacial structures of alloy precipitates. Here we present recent work combining STEM observations and computer simulations for the structural and energetics characterisation at the atomic scale of precipitate phases and their interfaces. We will show that even classic binary alloy systems such Al‐Cu, Al‐Au and Al‐Ag can reveal surprising characteristics. For example, the two isostructural phases θ' (Al
2
Cu) and η (Al
2
Au) display vastly different interfacial structures (see Fig. 1) [3‐5]. These differences can be explained by the calculated defect energies for Cu and Au solute in aluminium [5]. Another unexpected finding was that of a new intermediate phase, denoted Z, in the Al‐Ag system. This phase is coherent with the Al matrix and consists of alternating bilayers of Ag and Al (see Fig. 2) [6]. The structure of the Z phase is analogous to that of Ag segregating on θ' precipitates (see Fig. 3) [7]. Finally, we will present examples of precipitation pathways being altered through the introduction of certain alloying additions or lattice defects.

The authors acknowledge funding from the Australian Research Council (DP150100558 and LE0454166), computational support from the Monash Sun Grid cluster, the National Computing Infrastructure and Pawsey Supercomputing Centre funded by the Australian Government, and the use of facilities within the Monash Centre for Electron Microscopy.
Image‐Based Analysis of a Human Neurosphere Stem Cell Model for the Evaluation of Potential Neurotoxicants
Authors: Larson Brad , Sherman Hilary , Gitschier Hannah , Wolff Alexandra , Luty Wini , Brechet Damien
Published: December 2016

Developmental neurotoxicity (DNT) of environmental chemicals has long been identified as a threat to the health of the human population, as the developing nervous system is particularly susceptible to toxicant exposure. The resulting neurological deficits can have long‐term effects on families and society both financially and emotionally. Current DNT testing guidelines involve the use of animal models; primarily rodents. The testing strategy incorporates large numbers of animals, which can be extremely time‐ and cost‐intensive; particularly due to the backlog of chemicals needing to be tested (Lein
et al.
, 2005). This demand, in addition to current and future proposed regulations on the use of animals for testing makes it imperative that new models be found to reduce animal experimentation while providing a suitable method to test new chemicals.

Three‐dimensional cell models, which incorporate human neural stem cells (hNSCs) aggregated into neurospheres, have been proposed as a viable alternative for DNT testing. The in vitro system has the ability to recapitulate the processes of brain development, including proliferation, migration, differentiation and apoptosis (Salma
et al
., 2015). Inclusion of human cells, as opposed to murine, also meets recommendations to circumvent the drawback of species differences between in vivo testing and actual exposure effects.

Here we will demonstrate the use of a 3D neurosphere model, composed of hNSCs, to conduct toxicity testing of potential neurotoxicants. A spheroid microplate was used to create and maintain cells in the 3D model. 3D neurosphere proliferation, multipotency, along with the continued capacity to differentiate into neurons, astrocytes, and oligodendrocytes was initially validated. Neurotoxicity testing was then performed using neurospheres maintained in the 3D spheroid plate. Detection of induced levels of oxidative stress, apoptotic, and necrotic activity within treated neurospheres, compared to negative control spheres, was evaluated. Monitoring of cell proliferation, differentiation, multipotency and experimental testing was performed using a novel cell imaging multi‐mode reader.
Influence of metal additive
Nb
on the morphology of Vanadium Phosphorus Oxide Catalysts
Authors: Miao Xiaopei , Huang Wenqing
Published: December 2016

Vanadium phosphorus oxide (VPO) catalysts have been considered as the most effective industrial catalysts for the oxidation of n‐butane to maleic anhydride. The preparation methods of the catalyst, and reaction conditions and other factors will have different effects on the catalyst properties. In order to improve the performance of VPO catalyst, we often add co‐catalyst: metal additives can not only improve the activity and selectivity of the catalysts to some extent, but also play important roles in reducing reaction conditions and prolonging the reaction time. The VPO catalyst precursors have been prepared through reducing pentavalent vanadium in organic phase, and then introducing the Nb element whose radius is similar to V
4 +
ionic by the co‐precipitation method. The effect of Nb additive on the morphology of VPO catalyst was studied by SEM and TEM, and the morphology of the catalyst was compared with that of the VPO catalyst without additive in the figure below.

SEM and TEM images of VPO catalyst precursor showed sheet structure with irregular size, and the transmission diffraction pattern suggested amorphous structure in Fig.1a‐a'. Although there was a small amount of hexahedral structure for the VPO activated catalyst, the main morphology was granular structure different in size. After the addition of Nb additive, configuration of VPO precursor was regular diamond‐shaped as shown in Fig.1c‐c'. This kind of crystal takes the thickness of about 200nm, but the crystal size is reduced to 40nm for the Nb‐VPO activated catalyst. It suggests that: the broken of tabular crystal is helpful to improve the specific surface area, thus to provide more active sites for the catalytic reaction and increase the catalytic activity. In addition, the catalyst will expose more crystal defects after fragmentation, and provide necessary conditions for the separation of the catalyst active site. Therefore, crushing effect by adding Nb into the organic phase is beneficial to improve the selectivity of maleic anhydride. On the basis of the previous work, a comparative analysis on the morphology VPO catalyst before and after the addition of Nb, we can draw a conclusion: the crystal phase of VPO precursor containing the Nb additive is VOHPO
4
·0.5H
2
O, which is preferred to grow along the (001) crystal face. So the rhombic structure is more regular. For the Nb‐VPO activated catalyst, phase composition is still (VO)
2
P
2
O
7
, but there has been little VOPO
4
phase. The synergy of V
+4
and V
+5
species in two crystal phases is the key to improve catalytic activity of VPO catalyst. The catalytic selectivity has been greatly increased after the addition of Nb.
Quantitative
3D
analysis of huge nanoparticles assemblies
Authors: Zanaga Daniele , Bleichrodt Folkert , Altantzis Thomas , Winckelmansa Naomi , Palenstijn Willem Jan , Sijbers Jan , de Nijs Bart , van Huis Marijn A. , Liz‐Marzán Luis M. , van Blaaderen Alfons , Batenburg K. Joost , Van Tendeloo Gustaaf , Bals Sara
Published: December 2016

Nanoparticle assemblies attract increasing interest because of the possibility of tuning their properties by adjusting the overall size and shape, the stacking of the individual nanoparticles, and the distances between them.[1]

Transmission electron microscopy is an important technique to characterize materials at the nanometer scale and below. However, it conventionally only allows for the acquisition of two‐dimensional (2D) projections of three‐dimensional (3D) objects, which is not sufficient for a quantitative characterization of complex 3D nanostructures. Electron tomography has therefore been developed to overcome this strict limitation, becoming a versatile and powerful tool, increasingly used in the field of materials science.[2]

For the characterization of nano‐assemblies, electron tomography is nowadays a standard technique, yielding a 3D description of the morphology and inner structure.[3] Despite the valuable information that can be obtained, as the synthetized systems become more complex, an accurate characterization of the structure becomes more demanding. For example, 3D reconstructions based on classical algorithms, suffer from a number of restrictions that hamper an accurate characterization of closed‐packed nanoparticles assemblies.

Here, we present a novel approach that enables us to determine the coordinates of each nanoparticle in an assembly, even when the assembly consists of up to 10,000 (spherical) particles.[4, 5] This technique will have a major impact as it enables a straightforward quantification of inter‐particle distances and 3D symmetry of the stacking. Furthermore, the outcome of these measurements can be used as an input for modelling studies that predict the final 3D structure as a function of the parameters used during the synthesis.
Effect of trace elements on the material properties of an aluminium casting alloy
Authors: Schroettner Hartmuth , Pabel Thomas , Petkov Tose , Mertschnigg Sabrina , Rossmann‐Perner Anita
Published: December 2016

The aim of the project is to determine the fundamentally effects of impurities and individual micro‐alloying elements (eg. as vanadium V, titanium Ti, calcium Ca, zirconium Zr, potassium K, phosphorus P and others) or combinations of these trace elements in aluminum alloys and their impact on the quality of aluminum castings.

As a result, limit values and tolerances for individual impurities (trace elements) should be defined and determined. Further on practical study methods should be developed that support on the one hand a reliable series production of high‐quality alloys and castings and on the other hand the procurement of aluminum alloys by the foundries.

The casting trials in industry‐related standards were performed on the base of a high purity alloy AlSi7Mg0,3 with systematic addition (30ppm, 300ppm, 3000ppm) of micro‐alloying elements, controlled by chemical analysis with an emission spectrometer.

Technological properties as flowability, hot crack susceptibility and shrinkage cavity formation were evaluated. Static and dynamic material testing, like tensile tests, hardness measurements and Woehler curves was implemented. The thermo‐physical properties as specific heat capacity, thermal expansion, temperature conductivity, density and heat conductivity were measured.

Phase calculations by ThermoCalc‐Software, to simulate the formation of intermetallic phases and their impact on the microstructure are compared to classical metallography and additional SEM/TEM‐investigations.

SEM/EDXS/EBSD‐measurements for the micro‐characterization of the structure and the composition of the intermetallic phases are made on cross sections (figures 1‐4).

Out from regions/phases of interest TEM‐lamellas are prepared with the FIB‐technique and transferred to TEM for using EDXS/EELS/EFTEM and diffraction methods for the nano‐characterization of these phases.
Transmission imaging of biological tissue with the Delft multi‐beam
SEM
Authors: Zuidema Wilco , Ren Yan , Hoogenboom Jacob , Hagen Cees , Kruit Pieter
Published: December 2016

A major bottleneck for large‐scale and volume EM is the imaging speed. The total acquisition time needed for a single sample can easily take days, or even weeks using standard single‐beam SEM's. Multi‐beam microscopes have been developed to increase imaging speed[1,2], but it remains a challenge to achieve electron detection similar to a regular SEM in terms of signal type, contrast and resolution.

We have developed a SEM employing 196 electron beams using a standard column of a FEI Nova NanoSEM 200. The 196 electron beams are generated from a single high‐brightness Schottky electron source, making use of a square aperture lens array grid of 14 by 14 holes. Modified source optics allows focusing of all beams in the sample plane, with the same probe current and probe size as in a single‐beam SEM. Both secondary and transmission electron signals can be detected in the system, of which an overview is shown in figure 1. For the detection of the transmitted electrons, the sample of interest is placed on a scintillating screen and the light generated by each beam is collected through an optical objective lens. This light is focused on a CMOS camera placed outside the SEM chamber and the image is produced through online processing of the intensity of each beam. An example of rat pancreas tissue imaged by this method is shown in figure 2. The secondary electrons are focused on a scintillating screen in the variable aperture plane, making use of a retarding lens and the electron optics used for the focusing of the primary beams. This signal is again focused on a CMOS camera and the same process for imaging is performed as for the transmitted electrons.

We present proof‐of‐principle results showing that sub‐10nm resolution can be obtained for transmission imaging of stained rat pancreas tissue. We will discuss our efforts towards improving the detection methods and the data processing speed. Furthermore, work will be shown on quantifying and comparing the signals obtained from secondary, transmitted and backscattered electrons on stained tissue sections, as imaged by a conventional SEM.
Quantitative low‐voltage spherical and chromatic aberration‐corrected high‐resolution
TEM
analysis of beam‐specimen interactions in single‐layer
MoS2
and
MoS2
/graphene heterostructures
Authors: Lehnert Tibor , Biskupek Johannes , Köster Janis , Linck Martin , Kaiser Ute
Published: December 2016

Sub‐Angstrom resolution at medium accelerating voltages of 200‐300 kV is routinely achieved in standard transmission electron microscopes by hardware correction of the spherical aberration of the imaging lenses [1, 2]. At such voltages, defective, very thin and/or light‐element materials very often suffer from knock‐on damage, demanding experiments at the lower voltage ends of the microscopes, which are by default 80kV resp. 60kV with a resolution limited to approximately 2Å. Often, however, the achievable resolution at these voltages is not sufficient to understand the electron beam‐matter interactions. Consequently, there is a demand for instrumentation that allows atomic‐resolution at much lower voltages [3]. Using a standard field‐emission electron source, the resolution is strongly limited by the chromatic aberration of the imaging lens requesting hardware aberration corrector that corrects for both, spherical and chromatic aberrations of the objective lens [4, 5].

Here, we report results towards understanding voltage‐dependent electron beam‐sample interaction for single‐layer MoS
2
and MoS
2
‐graphene heterostructures using our newly developed Cc/Cs – corrected Sub‐Angstrom Low‐Voltage Electron Microscope (SALVE) operating at voltages between 20‐80kV [6]. Damage cross‐sections are determined by directly counting the vacancies produced during the high‐resolution TEM experiments obtained at defined voltages and with defined electron doses. As the vacancies are created by different damage mechanisms as knock‐on damage, radiolysis, ionization, and chemical etching, we discuss our results in the light of these mechanisms, with the aim to separate their contributions. Similar 80kV Cs‐corrected HRTEM studies have been performed earlier albeit with much lower resolution [7]: in this case the resolution is about half the resolution obtained at 30kV (Cc/Cs) (see for comparison Figure 1). As the knock‐on threshold energy for sulfur atoms in MoS
2
has been calculated to be about 90 keV [8], the measured increase in the damage rates from 80 to 30 kV is attributed to radiolysis and ionization effects because of increased scattering cross‐sections [9].
The value of in situ transmission electron microscopy in studding ferroelectric materials
Authors: Zakhozheva Marina , Schmitt Ljubomira Ana , Pivak Yevheniy , Acosta Matias , Zuo Kun , Xu Qiang , Kleebe Hans‐Joachim
Published: December 2016

Ferroelectrics play an important role in today's modern life. A large variety of applications including piezoelectric actuators, sensors, dielectric capacitors, memory devices, etc. are based on these materials. Recently, scientific interest has been given to the Ba(Zr
0.2
Ti
0.8
)O
3
‐x(Ba
0.7
Ca
0.3
)TiO
3
(BZT‐xBCT) perovskite ferroelectric, that exhibits superior electrical and mechanical properties. It is known that domain morphology plays a significant role in electromechanical properties of ferroelectrics. As the external electric field induces domain wall motion or domain switching, it is important to perform direct observations of domain structure evolution under electric field.

In the present study in situ transmission electron microscopy (TEM) was employed to reveal the evolution of ferroelectric domains under electric field and temperature in BZT‐xBCT. It is shown that in situ TEM is an extremely powerful tool in order to visualize the real‐time microstructural evolution in these materials. During the in situ electric field TEM experiments, a multiple‐domain state (A) → nanodomain state → single‐domain state transformation occurred during the poling process. With further increase in the applied field a multiple‐domain state (B) appeared. This state could be associated with strain incompatibility between neighbouring grains under the electric field. The displacement of the domain walls and changes in the domain configuration during electrical poling indicated a high extrinsic contribution to the piezoelectric response in lead‐free BZT – xBCT. The temperature induced ferroelectric → paraelectric phase transition in the BZT – xBCT is also investigated. On heating and cooling a microstructure evolution in BZT – xBCT system was observed. Irregular domains with curved walls appeared in BZT – xBCT due to internal stresses associated with coexistence of rhombohedral and tetragonal domains within one grain.
Microscopy Image Browser: an open‐source platform for segmentation and analysis of multidimensional datasets
Authors: Belevich Ilya , Joensuu Merja , Kumar Darshan , Vihinen Helena , Jokitalo Eija
Published: December 2016

Understanding the structure – function relationship of cells and cell organelles in their natural context requires multidimensional imaging. Recent technical advances especially in multimodal 3D‐5D imaging techniques have enabled a new insight into the morphology of tissues, cells and organelles. As the performance and access to such techniques are improving, the amounts of collected data are growing exponentially posing a question about effective processing, visualization, and analysis of these large datasets. Quite often the detailed analysis of multidimensional data is impossible without segmentation of objects of interest out of the volume (creating of a model). Usually the segmentation is the most time consuming and challenging part of the image analysis routine. For example, it may take up to a month to properly segment a single electron tomogram. The slowness of the process is caused by two main factors: limited number of good software tools (even commercial ones) and segmentation algorithms that can be applied to facilitate the modeling. As a result, the real potential of the collected data is not completely realized.

Here, we present a free user‐friendly software package (Microscopy Image Browser, MIB) for effective segmentation and image processing of multidimensional datasets that improves and facilitates the full utilization of acquired data and enables quantitative analysis of morphological features. MIB is written in Matlab language which is familiar to many researchers and available for main common operating systems (Windows, Mac and Linux); alternatively MIB is also distributed as a standalone package for both Windows and Mac OS. The access to the code and the open‐source environment enables fine tuning and possibility of adding new plug‐ins to customize MIB for specific needs of any research project.

Even though the focus of the program is 3D segmentation of electron microscopy datasets, MIB is rather universal and can be used to perform segmentation, analysis and visualization of 2D‐4D datasets obtained by light microscopy.

We already utilized MIB in more than 10 scientific research projects, where it allowed us to facilitating the segmentation part of the image processing workflow significantly. Here we demonstrate its successful application by presenting results of segmentation and quantification of cells and different cellular organelles imaged using various electron and light microscopy techniques.
Cryo‐
TEM
observations and Xray mapping of polyoxometalate / polystyrene hybrid nanoparticles with surface reactivity
Authors: de La Haye Jennifer Lesage , Guigner Jean‐Michel , Hasenknopf Bernold , Lacôte Emmanuel , Rieger Jutta
Published: December 2016

Polyoxometalates (POMs) are metal‐oxygen clusters which can store electrons without altering their structure, so they are suitable for application in catalysis and materials science. In this project, we wished to synthesize surface catalytically active polystyrene‐polyoxometalate (PS‐POM) composite latexes through radical emulsion polymerization of styrene in water in the presence of amphiphilic POMs.

We used TEM analyses to demonstrate that polystyrene nanoparticles were stabilized by the POMs cluster at their surface. First, cryo TEM was used in order to determine the nanoparticles' shape and size. Secondly the photo‐catalytic activity of the POMs was evaluated. Upon UV irradiation, POMs can be photo‐reduced, in presence of organic molecules (acting as sacrificial electrons donors). According to the literature, the POMs attached to the PS surface should be able to transfer their captured electrons to metal ions, such as silver ions, to generate metals nanoparticles. We tested this benchmark reaction in the presence of our hybrid latexes. By Cryo TEM, we observed that nanoparticles were formed as expected in short reaction times, and that they were only present at the surface of PS‐POM composite latexes. In addition, Xray mapping at room temperature confirmed the presumed structure of the hybrid particles: POM clusters were only located at the particle surface by the detection of W atoms present in the used POM.
Gas
TEM
holder for in‐situ biasing and heating experiments
Authors: Vicarelli Leonardo , Zandbergen Henny
Published: December 2016

We present our custom designed Gas Transmission Electron Microscopy (TEM) holder for in‐situ electrical, gas and heating experiments. The holder is currently compatible with FEI machines, but it can be easily redesigned for other transmission electron microscopes. The holder has a sliding cassette at the sample position (Figure 1, left side), which can be manually opened and closed through a rotating knob, located at the opposite end of the TEM holder. Closing the cassette will ensure complete gas sealing around the sample, up to a pressure difference of 1 atm (respect to the microscope vacuum). One gas line is used for both inlet and outlet.

The beam is blocked when the cassette is closed, meaning that it is not possible to acquire live imaging during the gas flow. However, this configuration is very practical from the point of view of sample loading and unloading, as it only takes a few minutes to replace the sample, without any O‐rings or complicated sealing mechanisms. Moreover, the sample does not need to be exposed to air after the gas reaction, which gives a relevant advantage over ex‐situ measurements.

The TEM holder also has 10 electrical feedthroughs, which can be used for in‐situ electrical biasing experiments. Four of these electrical contacts can be used for in‐situ heating, in combination with our custom made MEMS heaters [1] (Figure 1, right side), capable of reaching 1000 K in vacuum and 700 K in 1 atm Argon environment.

As a first application of our gas TEM holder, we exposed freestanding multilayer graphene to 1 atm of Hydrogen and simultaneously heated the sample at 550 K for a few minutes. As we can see from Figure 2, this high‐pressure hydrogen annealing resulted in isotropic etching of graphene, with formation of round holes, approximately 80 nm in diameter. Further experiments will be performed to evaluate the etching rate and the isotropicity/anisotropicity as function of temperature, pressure and gas composition.
In situ study of
CeO2
microspheres sintering using
HT‐ESEM
Authors: Nkou Bouala Galy Ingrid , Podor Renaud , Lechelle Jacques , Dacheux Nicolas , Clavier Nicolas
Published: December 2016

Sintering could be defined as the transformation of a powdered compact into a cohesive material under heating at high temperature. It appears as a key‐step in the preparation of ceramic materials such as UOx and MOx nuclear fuels. The sintering is usually described through three different stages. The initial stage involves the elaboration of necks between the grains and leads to the cohesion of material while the intermediate and final stages are dedicated to the elimination of porosity between the grains by the means of grain growth mechanisms
[1]
. Presently, only few experimental works are devoted to the kinetics of necks elaboration (i.e. first stage of sintering), and this stage is mainly described through numerical simulation of 2 to 4 spherical grains in contact
[2]
.
A morphological approach for texture detection, application to SEM stereo reconstruction
Authors: Drouyer Sébastien , Beucher Serge , Bilodeau Michel , Moreaud Maxime , Sorbier Loïc
Published: December 2016

3D surface reconstruction from multiple SEM images has been widely addressed in the scientific literature. Different approaches exist, most of them use variants of Digital Image Correlation (DIC) [1][2].

DIC methods perform well on textured areas of images but provide limited results on uniform or flat zones. Approaches using segmentation techniques, that match discernible regions of images, provide a solution to solve this problem on low‐textured regions [3]. However, these methods are more computationally expensive and are less accurate than DIC on textured areas. Our objective is therefore to combine these two methods. One preliminary step is to differentiate textured areas, where DIC can be used, from low‐textured areas, where segmentation techniques are needed. This step will be addressed in this paper, and we propose a new approach using morphological operators to do that.

Our approach uses the watershed operator with morphological gradient and markers obtained with h‐minima [4]. On each region, average gradient value is computed. Automatic thresholding and post processing using opening by criteria [5] is then performed to differentiate textured areas from low‐textured ones.

Comparison of our approach with more standard methods of texture detection such as local entropy of local variance calculations [6] will be presented.

A major benefit of our approach is that transition between textured areas and low‐textured ones strongly follow real contours of flat zones, limiting interpolation problems between DIC and methods using segmentation techniques.

We will illustrate our texture detection algorithm by applying it on 3D surface reconstruction with SEM images of crystals of zeolites and catalyst with alumina supports.
Transmission Electron Microscopy of a Poorly Soluble Drug, Felodipine
Authors: S'ari Mark , Cattle James , Brown Andy , Rik Brydson , Hondow Nicole , Blade Helen , Cosgrove Steve , Hughes Les
Published: December 2016

Many drugs that are currently in development exhibit poor dissolution properties due to low solubility. To increase the solubility of these drugs different technologies have been developed including solid dispersions, nano‐crystals and lipid formulations. Use of solid dispersions can increase solubility by dispersing a drug within an amorphous polymer matrix, inhibiting re‐crystallisation from the amorphous phase. This can be achieved by hot‐melt extrusion (HME), spray drying and co‐precipitation [1].

Transmission electron microscopy can be used to analyse different phases and morphologies within a solid dispersion which may not be found using conventional bulk techniques such as powder X‐ray diffraction, differential scanning calorimetry and Fourier transform infra‐red spectroscopy [2]. However, organic compounds can be easily damaged when exposed to the electron beam causing structural change, so low dose exposure is necessary to limit any damage that occurs [3].

The research here investigates a model system involving the drug felodipine and the copolymer copovidone. Solid dispersions of 15% and 50% felodipine were prepared by HME and then milled to form a powder. This powder was then dispersed in water, 3‐4 droplets were placed onto separate copper continuous carbon TEM grids and left to dry. These were then examined by TEM, operated at 200kV, equipped with a CCD camera. The electron flux was set between 0.007 ‐ 0.040 e
−
Å
2
s
−1
to limit any damage which may be caused by the high energy electrons [3].

The results show that within the 50% solid dispersions different morphologies and phases can be found, most areas show near amorphous diffraction patterns (Figure 1) but some show single crystal patterns (Figure 2). This suggests that the felodipine and copovidone are not always molecularly mixed and that small amounts of the felodipine had recrystallised after the initial HME process. Similarly, the 15% mixture had areas with varied morphologies and showed some signs of phase separation. The next step will be to quantify the identified phase fractions (amorphous, single crystal and nano‐crystalline) within these solid dispersions.
Quasi‐Nanofluidic liquid cell for in situ liquid Trasmission Electron Microscopy
Authors: Lagana Simone , Mikkelsen Esben Kirk , Sun Hongyu , Marie Rodolphe , Mølhave Kristian
Published: December 2016

In this work we present a new microfabricated nanochannel device for in situ liquid TEM based on wafer bonding (Fig.1a). A schematic depiction of the chip cross section is presented in Fig.1b. The cell system was fabricated with a new direct bonding technique linking the adhesion properties of Silicon Rich Nitride (SiNx)/Stoichiometric Silicon Nitride (Si
3
N
4
) within atomic layer deposition (ALD) of Al
2
O
3
tuned for this application to provide low temperature bonding. The liquid vessel is designed with multiple nanochannels on a suspended membrane area, with tunable liquid layer thickness ~100 nm and silicon nitride windows ~ 50 nm. The channel design of the system improves the control of the top and bottom membrane bulging compared to commercial liquid cell devices and is hence expected to improve the area with high spatial resolution achievable in liquid TEM imaging.  Our nanofluidic system together with a custom‐made flow holder will give further control of liquid conditions dynamically varying experimental conditions.

The liquid cell was first tested by optical fluorescence microscopy using a solution of 10 nm quantum dots (QD) and as depicted in Fig.2. Flow and diffusive motion of the QDs could be followed. In a Tecnai TEM at 200 kV, a solution of 30 mM HAuCl
4
was sealed in the channel with epoxy glue and upon TEM irradiation gold particles in average size between 5 and 15 nm were nucleated along the channels (Fig.3a). Sometimes rocking particle motion was observed, confirming their enclosure within the liquid layer (Fig.3b). In our design membranes are inner bending on each other and plastically deformed due to the extremely high (>12 bar) capillary force. Thus, a thin layer of water < 100 nm is trapped among the membranes. In contrast with other  recent liquid vessels
[1]
, our nanofluidic system points toward higher resolution since liquid thickness  [2], biomineralization synthesis
[3]
, liquid phase displacement and in liquid holography.