bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative
STEM
analysis of multiscale
CNT
assemblies
Authors: Gnanasekaran Karthikeyan , de With Gijsbertus , Friedrich Heiner
Published: December 2016

Carbon nanotubes (CNTs) and their macroscopic assemblies have shown their potential as advanced conductors. The assembly of individual CNT's into hierarchical structures is determined either by their interactions (bottom‐up self‐assembly) or during the fabrication process (top‐down strategy). Hence, to tailor the macroscopic functional properties (e.g. electrical conductivity or porosity) of assemblies, a detailed understanding on how interactions create multiscale morphologies and finally function is required. STEM is widely employed for the nanoscale analysis of (in)organic materials. However, (S)TEM imaging of hierarchical CNT assemblies has several limitations. For instance, CNT/polymer composites are only composed of light elements which results in low contrast between the phases. Moreover, they are beam sensitive. We have optimized the contrast between the CNT's and the polymer phase combining experiments and simulations at limited electron dose [1]. In addition, a hierarchical morphology extends across several length scales, hence, depending on the area of imaging, interpretations could vary, questioning the representativeness of the analysis. Our approach to imaging of representative volumes of hierarchical materials included the development of a toolbox to acquire large‐areas at high‐resolution, which in essence brings STEM closer to a bulk characterization technique [2].

With these technical developments and relevant image analysis tools, the processing‐structure‐property relationship of porous CNT assemblies and CNT/polymer composites (PNCs) have been studied on a scale that was previously impossible. We will illustrate the potential of the methodology on examples of: 1) CNT compacts where the final structure and electrical conductivity can be controlled by the polydispersity and aspect ratio of the CNT population (Figure 1) [3]; 2) CNT/polymer composites where residual CNT‐CNT interactions during compounding lead to inhomogeneous but highly conducting CNT networks [4]; and 3) CNT alignment can be induced by spin‐coating of polymer latex‐CNT mixture which exhibit directionally varying electrical conductivity (Figure 2) [5]. In above investigations it has becomes clear that CNT‐CNT contacts play a crucial role in the formation of least resistance pathway. At present we are investigation such contacts in details employing electron tomography combined with template matching to deduce the contact number and contact area per unit volume. In summary, we are developing (S)TEM towards bulk characterization tool for the analysis of beam sensitive hierarchical materials over multiple length scale which are materials of scientific and technological importance.
Surface Atomic Structure and Growth Mechanism of {1 0 0}‐Faceted Perovskite Oxide Nanocubes
Authors: Du Hongchu , Jia Chun‐Lin , Mayer Joachim
Published: December 2016

Monodisperse faceted nanocrystals, with controllable shapes and sizes, have been becoming increasingly important for applications in catalysis, gas sensing, and energy conversion. Such highly shape sensitive and selective physical and chemical properties inherently stem from the atomic and electronic structures on the faceted surfaces. For elemental nanocrystals, the atomic structure on the surfaces is determined by the geometric shape itself. However, for compound materials such as alloys and complex oxides, the compositional segregation and different terminating lattice planes on the surfaces have to be taken into account. In order to understand the unique property and growth mechanism of these nanocrystals, atomic details on the faceted surfaces need to be studied on the atomic level.

Strontium titanate (SrTiO
3
), strontium zirconate (SrZrO
3
) and their solid solutions (SrTi
1−x
Zr
x
O
3
) are important members in the class of perovskite structures with a general formula ABO
3
(Figure 1a). These materials are of great technological and fundamental importance not only because of their interesting properties, but also because of their ability to combine and to adjust these properties by chemical substitution with a wide variety of cations. However, despite the success of the synthesis of the {1 0 0}‐faceted BaTiO
3
, SrTiO
3
, and Ba
1−x
Sr
x
TiO
3
nanocubes, whether the {1 0 0} facets of the nanocubes are terminated with AO (SrO) or BO
2
(TiO
2
) is a question which still remains open for speculation and investigation. A comprehensive understanding of the growth mechanisms of these faceted nanocubes has not been achieved. Direct experimental evidence for the atomic structure on these nanocube surfaces has become one of the key steps in exploring the growth mechanisms.

In this work, we report on detailed studies of monodisperse {1 0 0}‐faceted nanocubes of SrTi
1−x
Zr
x
O
3
(x = 0.25 to 0.5) which were synthesized using the oil‐water two‐phase solvothermal method. The surface atomic structure of the monodisperse faceted nanocrystals is determined by means of aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM). On the basis of the structural features on the faceted surfaces, a deeper insight into the growth mechanisms could be obtained.
On the diffusion‐mediated cyclic coarsening and reversal coarsening in an advanced
Ni
‐based superalloy
Authors: Chen Yiqiang , Prasath Babu Rajan , Slater Thomas , Mitchell Robert , Ciuca Octav , Preuss Michael
Published: December 2016

Polycrystalline nickel‐based superalloys for turbine disc applications typically employ complex alloy chemistry in order to produce a high volume fraction of gamma‐prime (γ′) precipitates for the optimisation of mechanical properties [1]. The precipitate coarsening causes a gradual loss of coherency between γ′ precipitates and γ matrix when materials serving elevated temperatures, therefore resulting in the degradation of its mechanical performance [2]. In this work, we report new experimental observations for diffusion‐mediated secondary γ′ precipitate coarsening (See Fig. 1) within a near‐zero misfit alloy RR1000 in a cyclic manner that these precipitates coarsen and split periodically [3].

Using absorption‐corrected energy‐dispersive X‐ray (EDX) spectroscopy within the scanning transmission electron microscope (STEM) [4], compositional variations for secondary γ′ precipitates as a function of coarsening behaviour under have been investigated. We have observed clear cyclic variations in the elemental concentrations of Co, Ti and Al within the secondary γ′ as a function of ageing time. STEM/EDX spectrum imaging and electron tomography on individual secondary γ′ have revealed local enrichment of Co within the core of secondary γ′ (See Fig. 2). STEM‐EDX analysis of the γ‐γ′ interface revealed nanoscale enrichment of Co and Cr and a depletion of Al and Ti within the γ matrix region near the γ‐γ′ interface (See Fig. 3). Our experimental results, coupled with complementary modelling and synchrotron X‐ray diffraction analysis, demonstrate the importance of elastic strain energy resulting from local compositional variations for influencing precipitate morphology. In particular, we show that elemental inhomogeneities, produced within both matrix and precipitates, are induced by complex interactions between thermodynamics and diffusion kinetics. These elemental inhomogeneities will likely affect the kinetics of coarsening and therefore must be taken into account when predicting the microstructure likely to be produced when the material is exposed to different heat treatment regimes. More generally, our findings suggest the importance of considering diffusion kinetics when attempting to understand the microstructural evolution of advanced superalloys. Our discovery renders the potential to retain the overall γ‐γ′ coherence in nickel‐based superalloys when exposed to elevated temperatures, and therefore to improve its creep properties.
A potential therapeutic effects of
BMN673
, a novel
PARP
inhibitor, on Triple Negative Breast Cancer
Authors: Eskiler Gamze Guney , Cecener Gulsah , Egeli Unal , Tunca Berrin
Published: December 2016

Triple negative breast cancer (TNBC) is the most aggressive and lethal subtype of breast cancer due to a higher rate of early recurrence, distant metastases and also heterogeneity in the molecular levels. Thus, there is a urgent need for effective therapies. In the recent years, PARP inhibitors have drawn considerable attention for especially BRCA‐associated sporadic TNBC patients. In the present study, we aimed to determine the cytotoxic and apoptotic effects of BMN 673, which is a novel and highly potent PARP inhibitor, on TNBC cell line.

Triple‐negative BRCA1‐defective HCC1937 breast cancer cell line was treated with BMN673 and the cytoxoxicity effects was evaluated by WST‐1 analysis. The apoptotic effects was evaluated using Annexin V‐propidium iodide (PI) and cell cycle analysis. The double stained with acridine orange/ethidium bromide of these cells was observed under the fluorescence microscope.

Initial cytotoxicity screening showed that BMN673 displayed the anti‐proliferative effect, with in time (6–12 days) and dose‐dependent (0.01, 0.1, 1 and 10 nM) (p<0.05). The maximum inhibition rate was measured 19.54%, 24.21%, 49.91% and 58.0% at 0.01, 0.1, 1 and 10 nM of BMN673 at 12 days, respectively (p<0.05). There was an increase of apoptotic cell death and cell cycle progression in all concentrations compared to the untreated control. Treatment with doses of 0.01, 0.1, 1 and 10 nM BMN673 significantly induced total apoptotic cells (6.2%, 23.45%, 47.95% and 61.28%, respectively) and a significant block at the G
2
/M phase. Additionally, we observed a loss of membrane integrity, chromatin condensation and increasing vacuole formation in HCC1937 cells when treated with the maximum concentration of BMN673.

In conlusion, this study has revealed that BMN673 inhibits cell proliferation and induces cell cycle progression and apoptosis within the minimum concentration. Thus, BMN673 could represent a potentially therapeutic strategy for especially, BRCA‐defective TNBC.
Spatially Mapping the Plasmon Resonances of Hollow
1D
Nanostructures: Hybrid
A
u
A
g Nanotubes
Authors: Genç Aziz , Patarroyo Javier , Sancho‐Parramon Jordi , Arenal Raul , Bastus Neus G. , Puntes Victor , Arbiol Jordi
Published: December 2016

Morphological control at the nanoscale paves the way to fabricate nanostructures with desired plasmonic properties. We present the nanoengineering of plasmon resonances in 1D hollow nanostructures of two different AuAg nanotubes; completely hollow nanotubes (Figure 1) and hybrid nanotubes comprising the sequential formation of solid Ag parts and hollow AuAg parts (Figure 2). Spatially resolved plasmon mapping by electron energy loss spectroscopy (EELS) revealed the presence of high order resonator‐like modes and localized surface plasmon resonance (LSPR) modes in both nanotubes. Experimental findings are accurately correlated with the boundary element method (BEM) simulations, where both experiments and simulations revealed that the plasmon resonances are intensely present inside the nanotubes. Based on the experimental and simulated results obtained in the present study, we show that the novel hybrid AuAg nanotubes possess two significant features: (i) LSPRs have been generated distinctively from the hollow and solid parts of the hybrid AuAg nanotubes which opens the way to control a broad range of plasmon resonances with one single nanostructure and (ii) the periodicity of the high order modes are disrupted due to the interaction of solid and hollow parts.
Design and characterization of mesopores in photocatalytically active oxynitride single crystals using structural and chemical
TEM
analysis
Authors: Pokrant Simone , Dilger Stefan , Landsmann Steve
Published: December 2016

Mesoporous single crystals have been a matter of intense discussion in the last years in the context of solar energy harvesting, since it is expected that this material class can contribute significantly to the improved design of highly efficient solar energy conversion devices [1]. Especially for photocatalytic or photoelectrochemical hydrogen generation high surface area and good charge‐transport properties are key features to enhanced device performance [2, 3]. Good conductivity is usually obtained in large defect free structures such as single crystalline materials, where consequently the surface area is small. High surface area, however, is obtained best by porous agglomerates of nanoparticles, where the conductivity is low because of multiple grain boundaries. The possibility to achieve performance improvement by combining both concepts has been demonstrated via the fabrication of large single crystals on the micrometer scale with a mesoporous structure using a template based approach [4]. In comparison to nanocrystalline materials, the improved charge carrier conductivity has been shown in this material class as well as its competitive surface area. Moreover, other template‐free synthesis routes are known, where porous structures in solids are formed spontaneously. One example is the solid‐gas phase reaction carried out for the synthesis of oxynitrides, i.e. thermal ammonolysis [5]. However, the control of pore size and density requires a detailed understanding of the reaction mechanisms during synthesis.

Some of these oxynitride materials i.e. LaTiO
2
N (LTON) or LaTaON
2
are photocatalytically active [6‐8]. The main characterization techniques used to evaluate the pore quantity and quality have been powder techniques (for example physisorption), giving information about the open porosity, and qualitative scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which suggested that open and closed pores are formed [6‐8]. However, little is known about the size and shape distribution especially of the closed porosity or about the pore formation process.

In this contribution we will focus on microscopic pore characterization of LTON as a function of the synthesis method by combining several TEM techniques (Figure 1, 2) [9,10]. The pores themselves were explored mainly by electron tomography and by scanning TEM (STEM) with an high angle annular dark field (HAADF) detector, while the crystallinity was investigated using a combination of high resolution transmission electron microscopy (HREM), selected area diffraction (SAD) and nanobeam diffraction. The local chemical composition was studied by electron energy loss spectroscopy. With the improved understanding of the pore formation mechanism in LTON we enabled porosity tuning in large oxynitride single crystals leading to enhanced performance in photocatalytic and photoelectrochemical water‐splitting.
High energy resolution
EELS
of copper phthalocyanine crystals
Authors: Kurata Hiroki , Fujiyoshi Yoshifumi , Tomisaki Yuriko , Nemoto Takashi , Haruta Mitsutaka
Published: December 2016

Recent developments of a monochromator for transmission electron microscopy provide a new tool for chemical analysis in local area of materials. Owing to the improved energy resolution, the energy range probed by electron energy‐loss spectroscopy (EELS) has been extended to visible or infrared region, allowing vibrational spectroscopy in the electron microscope [1, 2]. Moreover, one can also measure the fine energy‐loss near‐edge structure (ELNES) by exciting electrons in relative shallow inner‐shells like a carbon K‐edge, being an advantage in the analysis of organic compounds. In the present work, we demonstrate the high energy resolution EELS study of copper phthalocyanine (Fig. 1) crystals performed by a JEM‐ARM200F equipped with a double Wien filter [3] and spherical aberration correctors.

Figure 2 shows the carbon K‐edge ELNES measured from the thin film crystals of copper phthalocyanine (CuPc) and chlorinated one (Cl
16
CuPc). Since the radiation damage is serious for the CuPc crystal compared to the Cl
16
CuPc one, its ELNES is rather noisy due to the limited electron dosage (0.5 C/cm
2
). However, the chlorination effects are clearly observed in the change of ELNES, which is attributed to the chemical shift of 1s level of carbon atoms because the molecule has four independent carbon atoms with a different 1s binding energy. From the orientation dependence of ELNES intensity, the peaks (a) to (d) can be assigned to the transitions from 1s to π* unoccupied molecular orbitals. The peak (a) is related to the excitations of the carbon atoms forming a benzene ring in CuPc, while the peak (c) in the spectrum of Cl
16
CuPc is assigned to the excitations of carbon atoms bonding to chlorine atoms having a large electronegativity. The intensity of peak (a) in the spectrum of CuPc rapidly decreased with the increase of electron dosage as shown in Fig. 3. This means that the primary damage process is C‐H bond scission. Figure 4 shows the low‐loss spectra of CuPc extended to the infrared region, in which the C‐H stretch excitation is observed at 376 meV as a shoulder peak. This peak also disappeared when an electron dosage increased. The low‐loss spectra obtained from these crystals will also be presented and compared to the optical measurements.
InAs/InSb
: From Nanowires to Nanomembranes
Authors: de la Mata María , Leturcq Renaud , Plissard Sébastien R. , Rolland Chloé , Magén César , Caroff Philippe , Arbiol Jordi
Published: December 2016

The control over crystalline defects is of extreme importance when growing functional materials, since their presence may alter the final behavior (opto‐electronic properties) and evolution of the growing system (orientation and shape). In the present work we address both phenomena in the particular case of InSb related nanostructures.

On one hand, heterostructured architectures may show interfacial dislocations if reaching the coherency limit, which is dependent on geometrical constrictions of the systems in addition to the mismatch between phases. In this context, it is usually assumed that the mismatch strain in axial heterostructured nanowires is mainly relaxed by elastic distortion of the lattice, although theoretical calculations predict the formation of misfit dislocations[1]. It is remarkably important unveiling whether the partial/total lattice relaxation takes place through elastic and/or plastic mechanisms since both will affect the material performance. Interestingly, the location and shape of the heterointerfaces, as well as possible diffusion phenomena involved, may hinder the understanding of the actual relaxation mechanism, as we show in the case of axial InAs/InSb nanowires[2]. Contrary to most reported works, we find out the presence of misfit dislocations at the core of the system while there is a huge plane bending through the edges of the nanowires.

On the other hand, we correlate the systematic observation of a lateral twin boundary with the morphological transition from nanowires to membrane‐like systems, called nanosails. Based on the experimental data gathered, consisting on SEM and aberration‐corrected STEM measurements, including polarity determination[3], we are able to establish the underlying defect‐driving growth mechanism leading to the formation of membrane‐like structures growing aside InAs/InSb nanowires[4], showing excellent transport properties. Possible instabilities during the growth may promote the sinking of the catalytic droplet to wet one sidewall, leading to the nucleation of the lateral twin that opens the way for the broadening of the system.
Advanced characterization of colloidal semiconductor nanocrystals by
2D
and
3D
electron microscopy
Authors: Bladt Eva , Goris Bart , Hutter Eline , van der Stam Ward , Moes Relinde , de Mello Donega Celso , Vanmaekelbergh Daniël , Bals Sara
Published: December 2016

Due to the specific size‐dependent photoluminescence spectra of semiconductor nanocrystals (NCs), their use is promising as building blocks for new electronic and optical nanodevices such as light‐emitting diodes, solar cells, lasers and biological sensors.
1,2
In order to design these NCs with tailored properties for specific applications, a high level of control over their synthesis is of key importance. Therefore, it is of great importance to characterize both the shape as the composition of these systems. Here, a range of different colloidal semiconductor NCs are characterized using 2D and 3D electron microscopy techniques.

We will discuss, 2D semiconductor CdSe nanoplatelets (NPLs), both flat as helical shaped
3
, which are investigated using electron microscopy techniques. The aim is to retrieve structural information using high resolution imaging which enables us to study the growth mechanism of these NPLs. The flat NPLs have mainly {100} edges (Figure 1.A) and only a thickness of 4 to 5 atomic layers (Figure 1.B). The analysis of the helical NPLs shows that they are zinc blende and that the helices are folded uniquely around the ⟨110⟩ axis (Figure 1.D). In order to retrieve the helicity of the ultrathin helical shaped platelets, electron tomography is applied. The three‐dimensional tomographic reconstructions confirm that the observed helices fully rotate over a diameter of ∼25 nm and that they are not preferentially left‐ or right‐handed (Figure 1.C).

Furthermore, heteronanocrystals (HNCs) are studied as they improve the stability and, thereby, the surface passivation of the NCs when overgrown with a shell of a second semiconductor with a higher bandgap. In this manner, the robustness of the system and the photoluminescence quantum yield of the core is increased.
4
In order to understand the growth process of HNCs, both the 3D structure as the position of the core inside that structure is of key importance. We investigate two types of CdSe/CdS core/shell HNCs, with either a nanorod or bullet shape. High resolution HAADF‐STEM microscopy enables us to investigate the crystal structure of the core‐shell nanostructure (Figure 2.A,C). Advanced electron tomography based on novel reconstruction algorithms
5
is used to investigate the 3D shape and to reveal the position of the CdSe core in the CdS shell (Figure 2.B,D). For the CdSe/CdS core/shell bullets, the presence of two types of morphologies was revealed (Figure 2.D). High resolution STEM imaging was used to characterize the surface facets of both morphologies, which enabled us to compare the surface energy of both morphologies. For the CdSe/CdS nanorods, a sequential topotactic cation exchange pathway that yields CuInSe
2
/CuInS
2
nanorods with near‐infrared luminescence is further investigated
6
.
Deep investigation of antiphase‐boundaries defects in rare‐earth nickelates
Authors: Mundet Bernat , Jareño Júlia , Gázquez Jaume , González Juan Carlos , Obradors Xavier , Puig Teresa
Published: December 2016

Transition metal oxides (TMO's) are highly sensitive systems to external fields due to strong electron correlations and high polarizability of the metal‐oxygen bond. This makes it possible to tune their macroscopic properties by inducing slight distortions at their unit cell structure. A paradigmatic example is the rare earth (RE) nickelates, which present a tunable metal‐to‐insulator transition (MIT) and resistive switching (RS) effect, placing them as a new plausible alternative for current non‐volatile memories. Here, we use aberration‐corrected Scanning Transmission Electron Microscopy (STEM) combined with Electron Energy Loss Spectroscopy (EELS) to correlate both structure and electrical properties as a function of the RE cation specie (La, Sm, or Nd), substrate mismatch and film thickness. Nanoscale investigations show that Nikelate thin films require chemical and structural reconstructions in the form of antiphase boundaries (APBs) to compensate the mismatch with the substrate. This 2D defect suppresses one Ni‐O plane either in the in‐plane or in the out‐of‐plane direction, changing locally the lattice spacing. The APBs landscape is evaluated on RE‐nickelate epitaxial thin films grown by chemical solution deposition onto LaAl(LaAlO
3
)
0.3
‐(Sr
2
AlTaO6)
0.7
(LSAT), SrTiO
3
(STO) or LaAlO
3
(LAO) substrates with thicknesses that range from 6nm to 50nm, as shown in Figure 1 and 2. This structural study is also complemented with electrical and advanced XRD measurements that reveal a sharp MIT transition which is shifted when substrate, thickness or RE ionic radius is modified.
The concept of quantum electron microscopy
Authors: Kruit Pieter , Berggren Karl , Hommelhoff Peter , Kasevich Mark
Published: December 2016

Following a recent suggestion [1] that interaction‐free measurements are possible with electrons, we have analyzed the possibilities to use this concept for imaging of biological specimen with reduced damage. We have also made preliminary designs for an atomic resolution interaction‐free electron microscope, or “quantum electron microscope” [2], for one example see figure 1.

The idea of interaction‐free measurements follows Elitzur and Vaidman [3], who proposed that an opaque object may be observed by detecting a photon that did not interact with that object. This concept uses a Mach‐Zehnder interferometer in which one branch of the particle wave passes through the specimen (“specimen beam”) while the other part follows another path (“reference beam”). For a substantial reduction of the interaction, the amplitude of the wave passing through the specimen must be small and the interaction must be repeated many times. To implement this concept in an electron microscope would require a number of unique components not found in conventional transmission electron microscopes. These components include a coherent electron beam‐splitter or two‐state‐coupler, and a resonator structure to allow each electron to interrogate the specimen multiple times. A two‐state‐coupler has the function of moving the electron wave slowly between the reference beam and the specimen beam, as in a Rabi‐oscillation. We have come up with four different choices for this: a thin crystal, a grating mirror, a standing light wave and an electro‐dynamical pseudopotential.

Figures 2 shows a typical example of the theoretical output of a measurement, where for each pixel there is signal in the reference beam, the specimen beam and the inelastic channel, possibly detected in an energy loss measurement. Figure 3 shows the advantage of interaction free measurement in the detection of the presence of a dark pixel as compared to dark field microscopy. In the analysis of the image contrast that interaction‐free microscopy can create, our tentative conclusion is that transparent specimen can be detected, but different transparencies cannot be distinguished [4]. Other modes of operation of a microscope with multiple interactions with the specimen, however, may enable this.
Misfit of coherent precipitate phases in
Al
alloys measured by scanning transmission electron microscopy
Authors: Wenner Sigurd , Holmestad Randi
Published: December 2016

The age‐hardenable Al–Mg–Si alloy system is strengthened by needle‐shaped β″ phase precipitates that develop during heat treatment. The phase is fully coherent with the Al matrix, and induces a considerable strain field in the Al matrix, which is key to its hardening property. The lattice parameters of β″ have been measured as an average over many precipitates using electron diffraction [1], but never systematically for specific precipitate shapes. Transmission electron microscopy is ideal for this task, although one must take care to avoid image distortions when accurate distances are to be measured. Multi‐exposure scanning transmission electron microscopy (STEM) image series were processed to correct drift and scan distortions [2]. With such datasets, we can investigate the detailed atomic structure and ensure the precipitates to be defect‐free, and at the same time measure relative atomic distances accurately. This enables the measurement of the misfit between the β″ phase and the Al matrix, for which we employ the geometric phase analysis (GPA) technique [3]. As the misfit in the long direction of the particles is negligible, we concentrate on the
a
([100]
β″
) and
b
([001]
β″
) directions, which lie in the cross‐sectional plane.

24 precipitates with 15 distinct geometries were investigated [4]. Fig. 1 shows images of representative particles together with the average measured misfits for each geometry. The misfit is found to vary significantly between particles, in the range 1–7%. The misfit in either direction is inversely proportional to the particle width in that direction, as seen in Fig. 2(a). This works as an energy minimization mechanism, as the strain in the Al matrix is distributed evenly in its cross‐sectional plane. The elasticity of the β″ phase is similar to that of the Al matrix, which is in accordance with related literature [5]. The relative β″–Al misfit area is independent on particle shape, as shown in Fig. 2(b), and has a value of about 7%. A particle will grow during heat treatment until the strain from these extra 7% becomes too much to handle, and the particles loses coherency.

The measured misfits give a good match to reported density functional theory (DFT) simulations for a β″ phase with composition Mg
5
Al
2
Si
4
within a range of precipitate geometries [6,7]. Two other likely compositions were tested, but were found not to fit with the shape‐misfit relationship of the experimental data. The conclusions in this study will contribute to improving models for precipitation hardening from atomic to macroscopic scales.
In situ study of
Au‐Rh
nanoalloys
Authors: De Clercq Astrid , Piccolo Laurent , Giorgio Suzanne
Published: December 2016

Introduction:

Au‐Rh nanoalloys were prepared from colloidal solution [1]. The growth mechanism was studied
in situ
by TEM in a graphene liquid cell [2‐3]. Then, in an environmental sample holder [4],the influence of oxygen or hydrogen adsorption on the structure of AuRh/TiO
2
catalysts was observed at a pressure of a few mbar and at room temperature.

Growth mechanism:

The colloidal solution was encapsulated in a graphene oxide liquid cell and directly observed in a standard electron microscope. The particle growth was initiated under the electron beam.

The same area was observed during about 80 s and images were recorded every 5 s. The average particle size increases until 4 nm. The density number plotted in fig. 1, indicates a maximal density after 25 s, then a drop after 50 s, corresponding to a growth mechanism by direct adsorption of the monomers. This process is followed by coalescence of the particles, as directly seen in fig. 2.

Segregation in hydrogen:

Au‐Rh nanoparticles with an homogeneous structure, and supported on rutile TiO
2
nanorods powders, were observed during oxidation‐ reduction cycles in an environmental sample holder. In the largest NPs, core‐ shell formation was clearly observed during hydrogen adsorption, as seen in figure 3. On the other hand, the observation of Au‐Rh NPs annealed
ex situ
in H
2
at 400 °C, also shows the core‐ shell contrast which was not visible before H
2
treatment.

The strong interaction between hydrogen and Rh is certainly responsible for the surface segregation of Rh.
Sirtuin 1 Downregulation Exacerbates Fibrosis and Inflammation in Obese Mice Liver
Authors: Stacchiotti Alessandra , Favero Gaia , Giugno Lorena , Lavazza Antonio , Sanchez‐Ramos Cristina , Prieto Ignacio , Monsalve‐Perez Maria , Rezzani Rita
Published: December 2016

Non‐alcoholic fatty liver (NAFLD) occurs as simple hepato‐steatosis and its evolution into severe non‐alcoholic steatohepatitis (NASH) is strictly connected to obesity, but the pathogenesis is still obscure. Recently, a multiple hit theory suggested that from gut and adipose tissue different adipokines and inflammatory markers influenced the liver where steatosis, collagen deposition and inflammation might occur. Sirtuin 1 (Sirt1) is a NAD‐dependent enzyme involved in longevity and in the regulation of multiple cellular functions and metabolism. Here we hypothesized that Sirt 1 down‐regulation might exacerbate liver damage and mitochondrial lesions in hepatocytes in dietary‐induced obesity in mice. To best analyse these events, we studied male C57BL/6 mice (WT) and Sirt 1 deficient heterozygous mice (HET) (by an established colony in CSIC generated from founders from Dr David Sinclair laboratory, Harvard University, Boston, USA). Animals housed in calorimetric rooms on a 12h: 12h light/dark cycle were placed for 16 wks, from 12 to 28 wks of age, on a standard rodent diet (8% fat ‐13.0 kJ/g) or on a high fat diet (HFAT‐ 35% lard‐18.8kJ/g Tekland Research Diet–TD03584). Body weight was monitored at the beginning, at 3wks and at 16 wks before euthanasia. Livers were fixed in 4% paraformaldehyde overnight for histopathology, immunohistochemistry or in Karnowsky mixture (4% paraformaldehyde and 1% glutaraldehyde) then post‐fixed in 1% osmium tetroxide for transmission electron microscopy analysis (TEM). By H&E, Masson trichrome and Sirius red staining at bright and polarized microscopy significant increase in steatosis and fibrosis in HET mice received HFAT diet vs WT fed HFAT diet were detected (Fig.1 and Fig.2). Interstitial collagen type I, type III, and basal membrane associated collagen type IV fibres were detected in pericentral vascular wall, intermediate lobular area and in thickened sinusoidal wall at light microscopy and at TEM (Fig.3). In contrast, WT or HET animals fed standard diet (as control groups) displayed negligible liver changes. Remarkably, HET mice fed HFAT diet showed abnormal giant mitochondria and activated Kupffer cells, strongly positive to Perls Prussian Blue iron staining, that were lacking in other groups. Finally, in HET obese mice myofibroblasts immersed in an abundant extracellular matrix and fibrous debris were observed by TEM (Fig.4). To highlight the crucial role of oxidative damage and caspase 1 complex in the progression to NASH, we analysed 4HNE and pro‐caspase 1 expressions. Remarkably, strong 4HNE and moderate caspase 1 signals were present in pericentral and midzonal hepatocytes in HET HFAT diet mice but weak in WT HFAT diet group and absent in controls. All these data suggest that Sirt 1 is critical to limit fibrogenesis and inflammation associated to irreversible NASH in HFAT diet induced obesity in mice.
Optimisation of
TEM
preparation in metallic materials using low voltage ions
Authors: Legras Laurent , Lescoat Marie Laure , Jublot‐Leclerc Stephanie , Gentils Aurélie
Published: December 2016

TEM samples of metallic materials can be prepared by mainly two ways: Electrothinning and ion thinning either by ion milling systems or Focused Ion Beam (FIB). In both cases, very thin lamellae can be obtained but residual artefacts are always present on their surfaces. Depending on which information is needed, those artefacts can limit and even prevent us from observing the samples properly. In the general case, electrothinning induces a residual oxide layer, mostly amorphous, that can evolve during TEM observations (Fig.1). On the other side, ions milling and FIB induce amorphous layers, irradiation defects and ions implantations although new FIB systems give the possibility to clean the specimens at low kV.

In this study, we show that ion polishing systems with low acceleration voltage can greatly improve the quality of electrothinned and FIB lamellae. Various cleaning conditions were tested using Precise Ion Polisher (PIPS I from GATAN) and with the new Precise Ion Polisher (PIPS II GATAN
2012
). Compared to PIPS I, PIPS II provides a better control of the ion beam at an acceleration voltage down to 100V. The sputtering kinetic was measured on various alloys (316L, Ni based alloy 600, oxidized and quenched Zr alloy). To do so, thickness maps were acquired with a FEI TECNAI OSIRIS equipped with an energy filtered imaging system (GIF Quantum from GATAN). Even though macroscopic dusts can be removed after Ar+ cleaning at 500V, thinning and decrease of amorphous layer is only slightly effective in PIPS I. To get a significant thinning rate in PIPS I, an accelerating voltage higher than 1kV has to be used but evidences of irradiation defects were seen on 316L. PIPS II experiments were conducted on various alloys with various ion thinning conditions, on both electrothinned and FIB lamellae. The kinetic rates measured are plotted on Fig.2 showing an effective thinning of lamellae even at 100V. When comparing the lamellae as‐electrothinned and as‐cut at 30kV by FIB to PIPS II cleaned lamella, a clear decrease of amorphous layer is observed and the quality of the lamellae is greatly improved. To be sure that no irradiation defects are induced by such thinning, we studied PIPS II cleaning on an Au+ pre‐implanted 316L. Cross sectioned lamellae were prepared at 30kV in a Helios Nanolab Dual Beam from FEI. The effect of low voltage cleaning on the lamellae is showed on Fig.3. No irradiation defects were seen in non Au+ implanted area. However, a few nanometres thick layer of amorphous is still present on both surfaces. These results show that the thickness and the quality of metallic TEM samples (either prepared by electrothinning or by FIB) can be easily improved by using a complementary thinning/cleaning with low voltage Ar+ ions in PIPS II.

Experiments on 316L received a financial support from the French National Research Agency through the project CoIrrHeSim ANR‐11‐BS09‐006.
Self‐assembly characterization of Saccaharomyces Cerevisiae and Drosophila Melanogaster septins by cryo‐electron microscopy and tomography
Authors: Taveneau Cyntia , Cicco Aurelie Di , Levy Daniel , Bertin Aurélie
Published: December 2016

Septins are a highly conserved

1

family of proteins in eukaryotes required for cell division. These proteins are recognized as the fourth component of the cytoskeleton. They promote membrane remodelling by a specific phosphoinositide binding

2

. Consequently, septins are multi‐tasking proteins and have prominent role in cytokinesis

3

, establishing diffusion barriers for membrane‐bound proteins

4

, neuron morphogenesis

5

and contribute to the development of neurodegenerative diseases (Alzheimer, Parkinson

6

) as well as tumor formation. Thus, recent years have seen renewed for the study of septins.

Septins are GTPases proteins which are bound to the inner cell membrane. As opposed to other cytoskeletal proteins, they polymerize in a non‐polar fashion into paired filaments

2,7

. They display a remarkable plasticity, both in term of binding partners (several proteins, membranes) and self‐assembly organizations. Indeed, the filaments have a potential to self‐assemble into higher‐order structures including rods, filaments, rings and gauzes

2,7,8

.

We focus our interest in understanding how septins self‐assembly in distinct ultra‐structures. To this end, we are using cryo‐electron microscopy and tomography. Thus, we are now characterizing (i) liposome remodelling by septins (ii) septins organizations in the different ultra‐structures (iii) physico‐chemical conditions required for the formations of the ultra‐structures and their functions (type of lipid, membrane curvature…). So far, we concentrate our study on
Saccaharomyces Cerevisiae
septins and recently on
Drosophila Melanogaster
ones, which is one of the first septins ultra‐structure characterization in higher eukaryotes.
Precision and application of atom location in
HAADF
and
ABF
Authors: Wang Yi , Zhou Dan , Sigle Wilfried , Suyolcu Y. Eren , Müller‐Caspary Knut , Krause Florian F , Rosenauer Andreas , van Aken Peter
Published: December 2016

Precision and application of atom location in HAADF and ABF

Yi Wang
1
, Dan Zhou
1*
, Wilfried Sigle
1
, Y. E. Suyolcu
1
, Knut Müller‐Caspary
2
, Florian F. Krause
2
, Andreas Rosenauer
2
, Peter A. van Aken
1

1
Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569, Stuttgart, Germany

*
Current: Materials Science and Engineering, University of Wisconsin‐Madison, 1509 University Avenue, Madison, WI 53706, USA

2
Institut für Festkörperphysik, Universität Bremen, Otto‐Hahn‐Allee 1, 28359 Bremen, Germany

The multifaceted magnetic, electrical, and structural functionalities of perovskite oxides are underpinned by the distortions of the crystal lattice [1]. These distortions include the displacement of cations, deformation of oxygen octahedra (BO
6
, where B is a transition metal atom), and collective tilts of the octahedral network. Controlling and engineering these distortions in the constituent oxides are crucial in designing and fabricating heterostructures with novel functional properties that are absent in the bulk form. Atomistic understanding of these distortions and elucidation of their influence on the final properties requires imaging and measuring of atomic positions of both cations and oxygen. With the application of spherical aberration (
C
s
) correctors, sub‐Angstrom atomic resolution is nowadays regularly achievable in both TEM and STEM. The recent application of the annular bright‐field (ABF) imaging technique in perovskite oxides has become increasingly popular, as it enables simultaneous imaging of heavy and light elements and allows for simultaneous acquisition of other signals [2, 3].

Here, we report the development of a software tool, written in Digital Micrograph scripting language [4], to extract quantitative information of the crystal lattice and of oxygen octahedron distortions of perovskite oxides from high‐angle annular dark‐field (HAADF) and ABF STEM images. Center‐of‐mass and two‐dimensional (2D) Gaussian fitting methods are implemented to locate positions of individual atom columns. As shown in Fig.1, under daily reproducible working conditions, e.g. sample drift and contamination present, the precision is in the range of 3–4 pm. Applications of this tool will be presented.

The accuracy of atom location by ABF can be significantly influenced by atom‐column tilts introduced by inadequate alignment by the operator or by strain near crystal defects. The influence of such tilts was quantitatively analyzed using image simulations. Figure 2 shows exemplarily simulated HAADF and ABF images for 0 and 10 mrad tilt [5].
Covalent functionalization of Single‐Wall Carbon Nanotube by ferrocene derivatives : localisation and identification of a single molecule
Authors: Devaux Xavier , Allali Naoual , Mamane Victor , Dossot Manuel
Published: December 2016

Depending on the rolling vector, single‐wall carbon nanotubes (SWCNTs) can present metallic or semi‐conducting properties, which is of strong interest for potential applications in electronic devices and sensors. Consequently, SWCNTs have been recognized as interesting candidates for developing electrochemical biosensors for several years. They are described as promoters of electron transfer between electrode and target molecules, increasing reaction rate and decreasing electrode response time [1,2]. To realise efficient bio‐electrochemical sensor of D‐glucose, ferrocene derivatives were covalently grafted on purified SWCNTs. Ferrocene active electrochemical center was separated from carbon nanotube by polyethylene glycol linkers of different chain length (3 to 5 etoxy links).

The functionalized SWCNTs were studied using an aberration‐corrected STEM working at accelerating voltage of 80 kV (Jeol ARM200) to assess the efficiency of the functionalization and explore the selectivity of the grafting.

High‐resolution HAADF and BF images were simultaneously recorded to determine the structure of the SWCNTs. By analysing the Fourier‐transform of the images the chiral indices of a SWCNT can be determined using the same method than for ED pattern [3]. The comparison of information obtained from HAADF and BF images at different focus and simulations using QSTEM [4] shows that the chiral indices of a SWCNT can be assigned by measuring the tube diameter on HAADF and the chiral angle from BF images, for a focus range of a few nm. The simultaneous use of both detectors may allow for a lowering the dose of electrons for the recording of relevant data and so limit the irradiation damages, especially for small‐diameter SWCNTs.

On HAADF, the strong signature of atoms heavier than carbon, at the end of a tiny over‐contrast of about 1.4 nm long can be seen on some SWCNTs, as it is shown in the figure, in the red square. The structure of this SWCNT of 1.1 nm in diameter was determined as a chiral tube with (11,6) indices. QSTEM simulation of a single ferrocene‐polyethylene‐glycol molecule grafted on (11,6) CNT shows contrasts that match well with that of the experimental image. EELS spectrum images were realised to track oxygen K and iron L2‐3 signals. As it can be seen in the figure, two iron atoms were detected in the area of analysis. Their localisation corresponds to that of the two strong contrasts in the HAADF image. In the EELS spectra the energy of the Fe L
2‐3
edges (close to 708 eV and 721 eV) is consistent to that usually recorded with XPS for Fe (II) in ferrocene groups [5]. Oxygen signal was also detected along the chain that links the iron atom to the SWCNT. The analysis of about thirty SWCNTs shows that the functionalization method affects both semiconducting and metallic tubes.
Structural evolution of strontium titanate nanocuboids under in‐situ electron irradiation and heating
Authors: Liberti Emanuela , Kim Judy , Lin Yuyuan , Kirkland Angus
Published: December 2016

Annealing thermal treatments are routinely used in the synthesis of nanoparticles to tailor their size and shape. To control particle growth at elevated temperatures, understanding the dynamics behind surface evolution is of primary importance. Time‐resolved, in‐situ, aberration‐corrected high‐resolution transmission electron microscopy (HRTEM) has been successfully used to image structural modifications of nanoparticles in response to thermal annealing, including, for example, surface faceting and sintering [1].

This study reports the structural evolution of SrTiO
3
nanocuboids [2] in response to thermal annealing at high temperature (≥ 500 °C) using HRTEM imaging. In‐situ experiments were performed using a dedicated heating holder, in a JEOL 2200MCO microscope, operating at 200 keV, under low (4 × 10
6
e/nm
2
) and high (10
10
e/nm
2
) electron dose conditions. Imaging at low electron doses reveals structural modifications to the nanoparticles that can be ascribed to heating only. At low dose, the effect of beam irradiation on the surface structure is negligible even for direct exposure times longer than 30 min. An example is illustrated in Figure 1, where a typical flat {001} facet remains unchanged after 2 min of direct beam exposure. By comparison, electron irradiation at high electron dose triggers the growth of TiO islands within a few seconds, consistent with previous observations by Lin and co‐workers [3]. Figure 2 illustrates the formation of TiO islands after 3 s exposure at high electron dose (a), and the subsequent sputtering of surface atoms after 1 h 20 min of direct irradiation (b).

Following in‐situ thermal treatment at 800 C, surface faceting is observed at low dose (arrows in figure 3 (b)). The formation of the new facets is triggered by diffusion of the surface atoms, driven by the elevated temperature. Furthermore, atomic migration induces sintering of the particle (Ostwald ripening). For longer annealing times at higher temperatures, phase transformation of the facets is expected to take place, and TiO
x
islands will eventually start to grow [4]. In‐situ thermal annealing of the particles at higher temperatures is currently under investigation, and the results will be also reported.