bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic Behavior of
Fe‐Ni‐C
Martensitic Steels during Aging at Room Temperature
Authors: Curelea Sergiu , Cazottes Sophie , Epicier Thierry , Danoix Frédéric , Zapolsky Héléna , Lavrskyi Mikola , Maugis Philippe , Chentouf Sara , Goune Mohamed
Published: December 2016

The kinetic behavior of a Fe–24 Ni–0.4 C (weight percent) martensitic steel during aging at room temperature has been investigated by transmission electron microscopy. Electron diffraction, coupled with imaging techniques in a transmission electron microscope, including high resolution studies, have been used at various stages during the aging process, in order to characterize the microstructural features of the analyzed samples.

Rapid cooling (quenching) in liquid nitrogen of the austenitic state of the above‐mentioned material leads to the formation of a martensitic phase which, at room temperature (RT), begins to transform, through a process called spinodal decomposition. As a result of this process, a modulated structure is formed, in which carbon‐rich regions (precipitates) occur in a periodic manner throughout the matrix, leading to the presence of diffuse streaks or satellite spots around each fundamental (matrix) reflection on the electron diffraction patterns, see Figure1. This process is thus accompanied by a reduction of the tetragonality of the martensitic phase (
bct
), which evolves towards the formation of a cubic structure (
bcc
), see Figure2, corresponding to alpha‐iron (ferrite). After long ageing times, Fe3C is observed. The presence and structure of intermediate carbides is also studied.

The microstructure of the carbon‐rich phase is also analyzed by electron diffraction. The evolution of the tetragonality with time, translated as the c/a ratio, which is also function of the carbon composition, is studied. Moreover, the variation of the distance between the carbon‐rich precipitates (in fact, the periodicity of the modulated structure), along with the evolution of their width and length, are also observed.

Thanks are due to the Clym ( Centre Lyonnais de Microscopie) for the access to the TEM 2010F.
Influence of
Cu
content on the structural and morphological features of
TixCuy
intermetallic thin films for biosignals acquisition
Authors: Lopes Claudia , Koneti Siddhardha , Roiban Lucian , Borges Joel , Epicier Thierry , Vaz Filipe , Steyer Philippe
Published: December 2016

Thin films synthesized by Physical Vapor Deposition (PVD) are currently studied to be used in different types of sensors [1,2]. Among these, sensors and electrodes used for biomedical devices are particularly important since they allow converting one or more measured signals of any living tissue into other quantities, usually an electrical signal. Beyond the electrical response, a biomedical sensor should also be biocompatible and totally innocuous for the patient. Additionally some degree of antibacterial effect is considered as a further asset for the sensor. The Ti‐Cu system perfectly meets such requirements, Ti being biocompatible, while Cu is relevant for its antibacterial character. Objective of this study is to deeply characterize the nature and microstructure of Ti‐Cu films in order to better understand and optimize the sensor response.

Films are deposited by a PVD magnetron sputtering process from a composite Ti‐Cu target. Their chemistry, morphology and fine microstructure are characterized by X‐Ray diffraction, Rutherford Backscattering Spectrometry, Scanning and Transmission Electron Microscopies.

Results show that three main zones were distinguished, in relation with the Cu/Ti atomic ratio into the films. SEM reveals that the morphology of micrometer‐ thick films changed from a columnar to an amorphous‐like microstructure. XRD diffraction indicated that the hcp‐Ti structure dominates for low Cu/Ti ratios. For higher Cu contents, formation of Ti‐Cu intermetallic phases was noticed which becomes more clear and obvious for the third zone (Cu contents above 75 at.%). HR‐TEM and STEM observations confirm the presence of nanocrystallites embedded into an amorphous matrix (Fig. 1). A further chemical characterisation allowed identifying the nature of intermetallics, which contributed to explain sensors' electrical behaviours (Fig. 2).
Probing structural and electronic properties of h‐
BN
by
HRTEM
and
STM
Authors: Mouhoub Ouafi , Ricolleau Christian , Wang Guillaume , Amara Hakim , Andrieux Amandine , Dorval Nelly , Fossard Frédéric , Lavenus Pierre , Lagoute Jerome , Pham Van Dong , Wu Pai Woei , Loiseau Annick , Alloyeau Damien
Published: December 2016

After the discovery of graphene and its consequences in the field of nanoscience and nanomaterials, there has been a growing interest in 2D materials and also their vertical stacking due to unique properties and potential applications.[1] For instance, it was shown the transport properties of exfoliated graphene supported by hexagonal boron nitride (h‐BN) could approach the intrinsic graphene limits.[2] Nevertheless, studying the structural properties of 2D materials and 2D heterostructures is crucial to understand their physical and chemical properties. Our motivations have been to exploit state of the art aberration‐corrected high resolution transmission electron microscopy (HRTEM) and scanning tunneling microscopy (STM) to study the structure and electronic properties of graphene (G), h‐BN and G/h‐BN heterostructures.

HRTEM analyses were conducted with a JEOL ARM microscope equipped together with a cold FEG, an aberration corrector for the objective lens and a One view camera (Gatan). Notably, we used high‐speed atomic‐scale imaging to study with unprecedented dynamics (up to 25 fps) the nucleation and growth mechanisms of triangular holes in h‐BN under beam irradiation (Figure 1). The direct observation of B and N atom sputtering and surface reconstruction processes allow understanding how the triangular shape and orientation of holes are maintained during the growth. Interestingly, by studying the effects of the electron dose and the number of BN layers, we demonstrate that these atomic‐scale processes are simultaneously driven by kinetic and thermodynamic effects. Further works are in progress to study the stability of h‐BN/G stacking under electron‐beam irradiation.

STM analyses were carried out with low temperature STM at 4 K, on 2D heterostructures that consist in a few layers of graphene doped with nitrogen on thick exfoliated flakes of BN deposited on SiO
2
. Remarkably, we show that STM allows identifying and characterizing ionization defects within the BN flakes below the graphene layers (Figure 2). This study opens new avenues to probe the electronic interactions between this two stacked materials.
Examination of semiconducting properties of oxides in the vicinity of metal‐oxide interfaces for selected alloys
Authors: Vanta Radovan , Abolhassani Sousan , Dadras M
Published: December 2016

Radovan Vanta
1
,

Sousan Abolhassani
1
, Shiv Ashish Kumar
2
,

Massoud Dadras
2
, Adrienn Baris
1
, Guillaume Boetsch
3
,

Harry Brandenberger
4
,

Andreas Rummel
5

1

Laboratory for Materials Behaviour, Paul Scherrer Institut, 5232 Villigen‐PSI, Switzerland,

2

Service of Microscopy and Nanoscopy, IMT, University of Neuchâtel, Neuchâtel, Switzerland,

3

Imina Technologies SA, EPFL Innovation Park, Bâtiment E, 1015 Lausanne, Switzerland,

4

Gloor Instruments AG, Schaffhauserstrasse 121, 8301 Kloten, Switzerland,

5

Kleindiek Nanotechnik GmbH, Aspenhaustr. 25, 72770 Reutlingen, Germany,

This paper provides a brief overview of the studies performed on semi‐conducting properties of oxides and the change of these properties, for specific materials. A direct method is developed to measure the properties of the oxide by means of micromanipulators, in the SEM.

The interest of this method is to evaluate the role of such change of properties in the vicinity of interface of metal‐oxides and to correlate the properties to the oxidation behavior and also to the hydrogen uptake of the alloy.

In a previous study the properties of a material has been measured by means of micromanipulators, outside of the microscope. This study has been performed in the SEM. The present study reports the properties of two families of alloys. It shows that an alloy with a sub‐stoichiometric oxide in the vicinity of the interface has a lower resistivity. The method consists of using a fine micromanipulator installed in the SEM; a surface is created by FIB micromachining and the measurements are made by means of the micromanipulators inside the SEM, in this manner an accurate positioning is possible.

As it can be observed in Figure 1, the oxide in alloy Zr2.5%Nb is sub‐stoichiometric near the metal oxide interface [1]. Figure 2 presents the results of measurements of the Zr2.5%Nb and low‐tin Zircaloy‐4. The results of measurements and the comparison of the two alloys show that the second alloy having a stoichiometric oxide does not show such variation in resistivity in the vicinity of the metal‐oxide interface. The results will be discussed to confirm the role of the different properties of the oxide, on the oxidation behavior.
Electron energy loss spectroscopy (
EELS
) fingerprints of p‐ and n‐type doping in graphene
Authors: Kepaptsoglou Demie , Hardcastle Trevor , Seabourne Che , Bangert Ursel , Zan Recep , Amani Julian , Hofsäss Hans , Nicholls Rebecca , Brydson Rik , Scott Andrew , Ramasse Quentin
Published: December 2016

Doping is a great way to make nanomaterials suitable for use in nanoscale devices and electronics. Dopant atoms supply mobile charge carriers in the form of electrons (n‐type) or holes (p‐type) whilst leaving the material neutral, and the physical interface between p‐ and n‐type materials ‐ the pn junction diode ‐ is a fundamental building block of electronic circuits. There is a general consensus that moving beyond the (mainly) Si‐, Ge‐ and GaAs‐based technology of the last seventy years is highly desirable, so there is currently lots of interest in finding superior replacements for next‐generation electronics. Graphene's discovery [1] lies at the root of this renewed interest, and it now seems likely that graphene, or nanomaterials inspired by graphene, will find their way into consumer and industrial electronics in some significant form quite soon.

To make progress, we need information about the electronic structure of the material of interest, and how doping affects that electronic structure. Atomic‐resolution electron energy loss spectroscopy (EELS) is a great way to achieve this because it can reveal the bonding around an individual dopant atom. This insight can then be directly compared with theoretical electronic structure calculations in the form of density functional theory (DFT) to yield a detailed understanding of the electronic structure and the potential implications for use in nanoscale devices.

In this talk I shall present atomic‐resolution
K
‐edge EEL spectra for the case of substitutional B and N dopants in graphene synthesised using low‐energy ion implantation, and I shall explain how a careful comparison with theoretical DFT calculations indicates that the EELS data is in fact the first direct experimental evidence of p‐ and n‐type doping in graphene. [2] This approach demonstrates how potentially very lucrative information can be extracted from joint studies of experimental and theoretical EELS, and it could be readily extended to other nanomaterials.
TEM
investigation of
Li2MnSiO4
microstructure at different states of charge of
L
i‐ion battery cell
Authors: Gajewska Marta , Świętosławski Michał , Molenda Marcin
Published: December 2016

The study concerns dilithium manganese orthosilicate nanomaterial (Li
2
MnSiO
4
‐ LMS), which is a promising new candidate for cathodes in Li‐ion systems. The material is characterized by high theoretical capacity, working voltage and low production costs. Unfortunately, LMS material cannot be successfully applied in commercial systems yet, due to its structural instability in initial charging/discharging cycles of a battery cell. The reasons of structural changes (amorphization) of the material, that occur during electrochemical reaction in the cell, are still not clear. In order to find a stage of the electrochemical process in which a destruction of long‐range ordering in LMS crystalline structure occurs, we conducted ex‐situ TEM observations at different states of charge of a battery cell. To facilitate microscopic observations of particular LMS grains, a working electrode was prepared by using TEM support grid as a current collector. Thanks to that, the same sample could be used in TEM observations and in potentiostatic charging/discharging processes. Our study (Fig.1) shows that destruction of Li2MnSiO4 crystalline structure takes place at potentials lower (e.g. 3.5 V) than oxidation reaction of manganese ions (i.e. 4.2 V). It suggests that, in opposition to previous literature reports, amorphization process of the material is connected with other, and not yet specified, electrochemical reactions.
The highest characterization potentialities of sub‐20
meV
spatially resolved
STEM‐EELS
Authors: March Katia , Scarabelli Leonardo , Liz‐Marzán Luis M. , Aoki Toshihiro , Rez Peter , Cohen Hagai , Crozier Peter A. , Krivanek Ondrej L. , Stéphan Odile , Kociak Mathieu
Published: December 2016

Recent developments in monochromator technologies have demonstrated electron microscope resolution of infrared features, by electron energy loss spectroscopy (EELS) carried out with an energy resolution of ~10 meV [1]. In this contribution, we will present two experiments in nanoplasmonics and phonon spectroscopies performed on the NION HERMES scanning transmission electron microscope (STEM) at Arizona State University with a spectral resolution better than 16 meV. EELS in a STEM is an invaluable technique for mapping optical excitations with a nanometer spatial resolution, with a clear interest in mapping surface plasmons [2] now down to plasmon energies as small as 170 meV thanks to new advances in monochromators [3]. We will go to show on the case of long plasmonic bimetallic nanorods (Fig 1.) the interest of increased spectral resolution such as the one provided by the HERMES for plasmonic studies. For the same reason, recording EEL spectra showing vibrational features of hydrogen‐containing biological samples is now possible, resolving the characteristic C–H, N–H and NH
2
vibrational signatures, with no observable radiation damage (Fig 2.) [4]. These two examples will illustrate the HERMES performances to show how such increases in performance may unveil new physical effects.
Three‐dimensional nanomechanical spectroscopy of soft matter‐liquid interfaces
Authors: Garcia Ricardo
Published: December 2016

This contribution is devided in two sections. The first section is devoted to examine some relevant issues regarding force microscopy imaging of biomolecules such as spatial resolution, molecule deformation and quantitative mapping of mechanical properties. Specifically, we present a method to obtain the stress‐strain curve of a single protein in liquid. The second section is devoted to present an advanced AFM method to genearte three dimensional maps of solid‐liquid interfaces. We develop a force microscope method to map the 3D structure of solid‐liquid interfaces. The maps provide atomic‐scale spatial resolution images of the formation of hydration layers and the adsorption of ions on solid‐liquid interfaces. Some applications include to resolve the atomic structure of hydration layers generated from alkali chloride solutions on an atomically flat mica surface.
Strain‐driven oxygen deficiency in multiferroic
SrMnO3
thin films
Authors: D. Rossell Marta , Agrawal Piyush , Hébert Cécile , Passerone Daniele , Erni Rolf
Published: December 2016

In the last decade, multiferroic materials exhibiting simultaneous magnetic and ferroelectric order with strong magnetoelectric coupling above room temperature have attracted great interest. This is motivated by the expectation of integrating them into low‐power spintronic nanodevices, where the magnetic order is controlled by low energy consuming electric fields instead of magnetic fields. Manganese‐based perovskite oxides are particularly promising for this purpose. Recently, it was suggested that strain‐driven multiferroicity associated with spin‐phonon coupling should arise in strained SrMnO
3
(SMO): under epitaxial strain a polar instability in the ferromagnetic phase leads to a substantial energy lowering, which stabilizes the ferromagnetic‐ferroelectric multiferroic phase over the bulk antiferromagnetic‐paraelectric phase [1]. Thus, the spontaneous polarization is driven by the off‐centering of the magnetic Mn
4+
cations from the MnO
6
octahedra and increases by expansion of the lattice.

However, the SMO structure tends to incorporate oxygen vacancies, which makes it very difficult to synthesize fully stoichiometric SMO samples. Moreover, for SMO films, a small biaxial tensile strain of 2% is predicted to increase the oxygen vacancy concentration by one order of magnitude at room temperature [2]. Understanding the role of the oxygen non‐stoichiometry in this material is of fundamental importance for the development of multiferroic SMO thin films as perfectly stoichiometric highly resistive samples are required.

Here, we focus on the structural and electronic properties of several SMO thin films grown on different substrates, namely LSAO, LAO, LSAT, STO and DSO, by using aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and electron energy loss spectroscopy (EELS). The structural parameters of the SMO films are obtained by geometrical phase analysis of HAADF‐STEM images and are plotted as a function of nominal strain in Fig. 1. EELS data were acquired for all the samples: the obtained oxygen
K‐
edge spectra show pronounced peak‐height changes and energy shifts as a function strain (Fig. 2). The experimental results are interpreted with the aid of the all‐electron density functional theory (DFT) code WIEN2k (see Fig. 3). Thus, the effect of oxygen vacancies on the O
K
and Mn
L
2,3
electron energy‐loss near‐edge structures (ELNES) is theoretically investigated [3].
Dissecting the neuronal microtubule cytoskeleton using optical nanoscopy
Authors: Kapitein Lukas
Published: December 2016

Cellular organization depends on the cytoskeleton, a mechanical network of biopolymers that controls cell shape and strength, as well as on motor proteins that can move over these biopolymers to deliver cargo to specific subcellular compartments. Nevertheless, the precise mechanisms that control cytoskeletal organization, the function and dynamics of different motor proteins, and the precise functions of subcellular positioning are still poorly understood. In my lecture, I will highlight novel probes and methodology for the super‐resolution imaging of the cytoskeleton. These approaches allow us to better resolve cytoskeletal organization in dense cellular compartments, such as the axons and dendrites of neurons. These technologies hold great promises for exploring cellular organization in health and disease.
Native machinery of membrane‐associated protein synthesis
Authors: Pfeffer Stefan , Englmeier Robert , Foerster Friedrich
Published: December 2016

A large fraction of ribosomal synthesis occurs at organellar membranes. At the endoplasmic reticulum (ER), the inner mitochondrial, and the thylakoid membrane, nascent proteins are co‐translationally inserted or transported into other compartments. Here, we structurally study membrane‐bound ribosomes and their associated machineries in their native settings using cryo‐electron tomography (cryo‐ET) in combination with subtomogram analysis (Fig. 1).

Studies of ribosomes associated to isolated rough ER vesicles reveal the structure of the native ER translocon, as well as its compositional variability. Core components of the ER translocon are the protein‐conducting channel Sec61, the translocon associated protein complex (TRAP), and the sub‐stoichiometric oligosaccharyl transferase complex (OST), which all bind to the ribosome. Subnanometer resolution subtomogram averages indicate that the ribosome alone, even without a nascent chain, is sufficient for lateral opening of Sec61, contrary to recent mechanistic models. To elucidate the structures and functions of TRAP and OST in detail, we make use of mutations involved in congenital disorders, as well as their evolutionary diversity across different organisms. Analysis of cryo‐tomograms from focused‐ion‐beam‐milled whole cells allows studying the compositional variability of the ER‐translocon and the relative arrangement of ER‐associated ribosomes
in vivo
, which reveals a highly characteristic polysome organization.

Mitochondrial ribosomes specialize on the synthesis of few, very hydrophobic membrane proteins. Cryo‐electron tomographic analysis of mitochondria isolated from
Saccharomyces cerevisiae
reveals the binding mode of mitoribosomes to the inner mitochondrial membrane, as well as their molecular organization into polysomes. The structures of mammalian mitoribosomes differ dramatically from their fungal counterparts and we study the consequences of these differences on membrane association and polysome organization. State‐of‐the‐art phase plate imaging helps to overcome the contrast limitations set by the extremely dense and optically barely electron transparent mammalian mitochondria.

Chloroplast ribosomes constitute the third realm of eukaryotic ribosomes. We analyzed the
in situ
structure and intracellular distribution in green algae. The interaction mode of ribosomes with the thylakoid membrane appears to be much less defined than those of their cytoplasmic and mitochondrial counterparts.

In summary,
in situ
studies using cryoelectron tomography put atomic‐level structural information of ribosomal complexes into context with their associated organellar membranes and their respective co‐translational processing machineries, revealing high evolutionary diversity for organelles and organisms.
Dynamics of magnetic domain walls and skyrmions studied by high resolution
XMCD
‐
PEEM
microscopy
Authors: Pizzini Stefania , Vogel Jan , Rougemaille Nicolas , Sirotti Fausto , Cesar Julio , Chaves Dayane , Mentes Onur , Foester Michael , Aballe Lucia , Locatelli Andrea , Boulle Olivier
Published: December 2016

Photoemission electron microscopy combined with x‐ray magnetic circular dichroism (XMCD‐PEEM) is a powerful synchrotron radiation technique that can be used to observe magnetic configurations of nano‐objects with high spatial resolution. Combined with time resolution, using stroboscopic detection, the magnetisation dynamics of such objects can be studied with sub‐nanosecond resolution.

We will describe the study of domain wall (DW) dynamics and magnetic skyrmions in multilayers of composition Pt/Co/MOx (M=Al, Mg), characterised by a large perpendicular magnetic anisotropy (PMA) and anti‐symmetric exchange interaction (Dzyaloshinskii‐Moriya interaction, DMI). Such interaction favours non‐collinear magnetic textures such as chiral Néel walls and magnetic skyrmions.

In systems with large DMI, such as Pt/Co/AlOx with ultrathin Co, domain walls acquire a Néel chiral structure and move at large speeds when driven by current pulses. Most microscopic studies of domain wall dynamics have been performed using quasi‐static measurements, where the DW position and structure are imaged before and after the excitation pulse. In order to better understand the details of the interaction between current and DW magnetisation, we have observed DWs
during
the application of the current pulses, by synchronising the current pulses with the x‐ray pulses, in stroboscopic mode. The measurements reveal that the DWs move without inertia, showing a practically vanishing mass. The negligible inertial effects can be explained taking into account  the narrow domain wall width induced by the large PMA, the large damping parameter and the stabilising effect of the longitudinal field associated to the Dzyaloshinskii‐Moriya interaction.

Magnetic skyrmions are nanometer scale whirling spin configurations, predicted in the 80's but only recently observed with high resolution magnetic microscopies. Their small size, topological protection and the fact that they can be moved by very small current densities call for applications to novel memory and logic devices where skyrmions are the information carriers. Here we report on the experimental observation of magnetic skyrmions in Pt/Co/MgO sputtered ultrathin magnetic nanostructures, stable at room temperature without applied magnetic field. XMCD‐PEEM measurements allowed us to observe such skyrmions and to demonstrate their chiral Néel structure. The skyrmion sizes are typically of the order of 120 nm. Our experimental observations are well reproduced by micromagnetic simulations and numerical modelling. This allows the identification of the physical mechanisms governing the size and stability of the skyrmions, which are keys for the design of devices based on their manipulation.
Structure of the bacterial type 3 secretion system in action
Authors: Kudryashev Mikhail
Published: December 2016

Pathogenic bacteria commonly use the conserved type 3 secretion system (T3SS or Injectisome) to deliver virulence factors into the target eukaryotic cells in order to manipulate their functions. Injectisome is a multi‐protein nanomachine assembled at the bacterial membranes containing the periplasmic basal body, cytoplasmic sorting platform and export apparatus
1
. A hollow needle extends from the periaplasmic part to the extracellular face serves as a channel for the secreted molecules. The high resolution structure of the components of the injectisome is well understood: structure of the basal body at subnanometer resolution
2
in combination with computational molecular analysis
3
demonstrated the inter‐subunit interaction interfaces and suggested a conserved oligomerization mechanism for the assembly. The cytoplasmic ATPase SctN (according to the general nomenclature) is structurally similar to the F‐ and V‐ type ATPases and is believed to be responsible for detachment of chaperones and unfolding the exported substrates
4
.

Recent fluorescent studies in
Yersinia enterocolitica
showed turnover of SctQ; the turnover was faster for secreting injectisomes therefore the injectisome was suggested to be a highly dynamic nanomachine
5
. Additionally, upon activation of secretion newly formed injectisomes are established next to the existing ones
6
. Interestingly, trapping the exported substrate in the isolated needle complex (made of the basal body and the needle) results in only small conformational changes distant from the secretion path
7
. It is highly interesting to visualize the mechanics of substrate secretion happening inside the cell and understand the intermediate steps of this exciting process.

During my talk I will present the structural analysis of the injectisomes in
Yersinia
and
Chlamydia
performed by cryo electron tomography and subtomogram averaging. Surprisingly, the basal bodies of injectsomes of
Yersinia enterocolitica
can vary in length up to 20%
8
. This flexibility it attributed to the flexible domains of the proteins of the basal body. In
Chlamydia
the basal bodies of injectisomes strongly contract upon contact with the host cell membrane. This contraction is coupled to a structural stabilization of the cytoplasmic part of the injectisome
9
. This “pumping action” likely constitutes a general mechanism related to the injection of effectors. Higher resolution structural analysis
in situ
combined with mutagenesis will generate the clearer understanding of the mechanics of the T3SS action.
Understanding of atomic structures of nanoparticles on surfaces
Authors: Li Ziyou
Published: December 2016

Metallic nanoparticles occupy special places in fundamental research and practical applications, not only because they bridge the gap between atoms and bulk matter but more importantly because some fascinating phenomena appear only at nanoscale level. Research has shown that the properties of nanoparticles are strongly affected by their size, shape, chemical composition as well as their supports. Hence it is essential to gain full knowledge of their three‐dimensional atomic structures, which is still a challenging task for nanoclusters and nanoalloys.

After a brief overview of the current status of structure research on clusters and nanoalloys, I will discuss what an aberration‐corrected scanning transmission electron microscopy (STEM) can offer in this area through an atom counting approach. I will then present two case studies from our recent work: (1) on control and manipulation of the size and atomic structure of Au clusters, formed via gas phase condensation and deposited on amorphous carbon films and MgO(100) surfaces; and (2) on structures of TiO
2
(110) supported Au‐Rh nanoalloys, prepared through solution based chemical synthesis method, under effects of various thermal treatments. In both cases, direct evidence of atomistic details of the clusters, nanoalloys as well as nanoparticle‐support interfaces will be presented and their possible mechanisms will be discussed, together with computer modeling studies. Our emphasis will be on understanding the relationship between nanoparticle structures and their thermodynamics or kinetics.
Cathodoluminescence and
EBIC
study of widegap semiconductors and devices
Authors: Sekiguchi Takashi
Published: December 2016

Cathodoluminescence (CL) and electron‐beam‐induced current (EBIC) are versatile techniques to characterize semiconductor materials and devices. In this talk, we review our achievement on the study of widegap semiconductors, GaN and SiC.

The major defects in GaN are dislocations. GaN wafers on sapphire include dislocations of 10
9
to 10
7
cm
−2
due to lattice mismatch. Fig. 1 shows the secondary electron (SE) and CL images of GaN wafer with different thickness. Such dislocations may agglomerate and form the hexagonal pits of micrometer size. These defects are detrimental for the device performance. Homoepitaxial GaN wafer take over the dislocations of 10
6
cm
−2
from the seeds. We have performed CL study to distinguish dislocation characters and to clarify the effect of dislocations.

The major defects in SiC are threading screw dislocations (TSD) and stacking faults (SF). TSD act as the killer defects due to the surface roughness at the dislocation core region. SF may be generated and expanded due to e‐beam irradiation. EBIC is very effective to characterize these defects in SiC. The e‐beam enhanced defect generation of SF (Fig.2) will be reviewed.

At the end, we demonstrate 3D spectra imaging of CL, which is very promising to analyze the details of extended defects.

This work was supported from “GaN project”, Study of Future Semiconductors for Sustainable Society in MEXT, Japan.
Functionalized Carbon Nano‐onions as Imaging Probes for Cancer Cells
Authors: Giordani Silvia , Frasconi Marco , Marotta Roberto
Published: December 2016

Multimodal imaging probes based on carbon nano‐onions (CNOs) have emerged as a platform for bioimaging because of their cell‐penetration properties and minimal systemic toxicity. [1‐3] We have developed a synthetic multi‐functionalisation strategy for the introduction of different functionalities (receptor targeting unit and imaging unit) onto the surface of the CNOs. The modified CNOs display high brightness and photostability in aqueous solutions and their selective and rapid uptake in two different cancer cell lines without significant cytotoxicity is demonstrated. The localization of the functionalized CNOs in late‐endosomes cell compartments is revealed by a correlative approach with confocal and transmission electron microscopy. [4] Understanding the biological response of functionalized CNOs with the capability to target cancer cells and localize the nanoparticles in the cellular environment, will pave the way for the development of a new generation of imaging probes for future biomedical studies.
Extreme Nanowires: The Smallest Crystals in the Smallest Nanotubes
Authors: Sloan Jeremy , Kashtiban Reza , Marks Sam , Beanland Richard , Sanchez Ana , Brown Sam , Vasylenko Andrij , Brommer Peter , Morawiec Krzysztof , Kret Slawomir , Medeiros Paulo , Wynn James , Spencer Joe , Smith David , Ramasse Quentin , Liu Zheng , Suenaga Kazu , Morris Andrew , Quigley David , Faulques Eric
Published: December 2016

A logical extension to fabrication of monolayer 2D materials such as graphene is creation of ‘Extreme Nanowires’ (i.e. Fig. 1), down to a single atom column in width.[1,2] In this limit, crystals have fundamentally different physical characteristics and properties.[3‐5] We and others have created atomically regulated nanowires by confining them within the smallest diameter carbon nanotubes (i.e. either single walled carbon nanotubes (SWNTs) or double walled carbon nanotubes (DWNTs)), and are investigating their structural and electronic properties. These materials also provide an ultimate benchmark for testing the most sensitive characterisation methodologies which, when corroborated with suitable theory, will provide new data on physics at the most fundamental length scale accessible to nanomaterials fabrication. The most powerful investigative tools for structural investigation are aberraton‐corrected Transmission Electron Microscopy (ac‐TEM) and Scanning Transmission Electron Microscopy (ac‐STEM) and, here, we describe the application of these methods to a variety of Extreme Nanowire systems.

One of the most crucial aspects of the role of electron microscopy in our investigation is the 2D and 3D elucidation of the structure of quasi‐ or true 1D nanowires formed in SWNTs as these form the primary source of information for density functional theory (DFT) and other ab initio theoretical approaches to both structure and properties elucidation. When combined with real physical measurements, this combined approach becomes even more powerful as we can start to piece together how the fundamental physics of a crystalline nanowire changes once we constrain its width down to one or two atoms in cross section. For example we recently record Raman Spectra from 2x2 atom thick HgTe nanowires embedded within 1.2‐1.4 nm SWNTs[4] and found that we are able to model the Raman‐measured lattice phonons of this system based on a simple structural model previously determined from two pairs of Exit Wave Reconstruction images which we also used to make DFT predictions about the altered electronic structure of this system which is predicted to change from a ‐0.3 eV semi‐metal to a ~1.2 eV band gap semiconductor.[3] Following on from the exciting recent work of Senga et al.[2] who imaged the first true 1D crystals of CsI in DWNTs we are now modeling single atomic chain coils of tellurium formed within narrow SWNTs (Fig. 2).[6]
Characterizing Localized Surface Plasmons using Electron Energy‐Loss Spectroscopy
Authors: Li Guoliang , Cherqui Charles , Wu Yueying , Rack Philip , Masiello David , Camden Jon
Published: December 2016

Localized surface plasmon resonances (LSPRs) are the coherent and collective oscillations of conduction band electrons at the surface of metallic nanoparticles. LSPRs are known to localize far‐field light to a sub‐diffraction‐limited length scale, yielding an intense electric field at the particle surface. This effect has been harnessed to dramatically enhance light‐matter interactions, leading to a variety of applications such as surface‐enhanced Raman spectroscopy (SERS), photothermal cancer therapy and solar energy harvesting. Though a variety of near‐ and far‐field optical methods are used to probe LSPRs, the spatial resolution of these methods is on the order of tens of nanometers, limiting their effectiveness. In contrast, electron energy loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM) combines sub‐nanometer resolving power with the capability to excite both optical‐accessible and –inaccessible plasmon modes and therefore has emerged as one of the leading techniques (Figure 1). In this presentation, I will briefly introduce the STEM/EELS technique and demonstrate the power of STEM/EELS in the characterization of LSPRs. In addition to the traditional use of STEM/EELS for LSPR imaging, we have recently demonstrated that STEM/EELS can also be used to spatially map LSP‐semiconductor energy transfer at the nanoscale. The future of STEM/EELS as a window into the nanoscopic world is especially promising, and we expect continued advances in the molecular, optical, materials, information, and energy sciences as a result.
Atom probe tomography of early stage clustering in
Al
alloys
Authors: Pogatscher Stefan , Dumitraschkewitz Phillip , Gerstl Stephan S.A.
Published: December 2016

Nano‐scaled early stage Si or Mg containing clusters in Al‐Mg‐Si alloys are experimentally extremely difficult to observe and atom probe tomography (APT) is the only technique to visualize and chemically measure these clusters today. Two examples for the technological importance of understanding clustering during natural aging in the Al‐Mg‐Si system are presented. First, a quenching procedure is shown to significantly alter the overall excess‐vacancy concentration consequently altering solute clustering kinetics. Second, trace element additions are shown to trap excess‐vacancies and hence to reduce the freely available vacancy concentration, which results in decreased solute clustering. The modification and understanding of early stage clustering is commercially important since it has strong implications on the strength evolution during industrial heat treatments. However, restrictions remain in achieving the ultimate quantification of such small solute aggregates by APT. Especially the surface migration of Si atoms is an open issue. However, an accurate adjustment of measurement and analysis parameters is known to minimize this problem. Nevertheless, clustering directly after quenching has not been possible to investigate because of the time required for sample preparation and sample transfer into the analysis chamber. Here we present a new strategy how the measurement of as‐quenched conditions and very early stages of natural aging can be realized via APT. This can be accomplished via sample production at cryogenic temperatures to suppress diffusion. The shown procedure includes cryogenic focused ion beam (FIB) preparation and direct cryogenic transfer of fresh APT samples into the analysis chamber of an atom probe. Results on as‐quenched and in‐situ naturally aged Al‐Mg‐Si alloys are presented. Furthermore, the effect of FIB induced clustering at cryogenic temperatures is discussed.
Ultrastructural analysis of spindle architecture in C. elegans
Authors: Müller‐Reichert Thomas
Published: December 2016

Mitosis and meiosis are essential mechanisms for any eukaryotic cell in order to divide and propagate. During both processes, microtubules are reorganized to assemble into bipolar spindles and align the condensed DNA in preparation for chromosome segregation. While the dynamic aspects of spindle assembly have been intensively studied by light microscopy, detailed ultrastructural analyses of spindle organization are largely missing. For an in depth understanding of both mitotic and meiotic spindle architecture, a quantitative 3‐D analysis of spindles is urgently needed. Using the early
C. elegans
embryo as a model system, the aim of our work is to better understand the functional organization of bipolar spindles. We apply dual‐axis, serial‐section electron tomography to quantitative analyze spindle parameters. This approach takes advantage of imaging embryos at about 5‐8 nm resolution and a genetically amenable model system, in which background structure and a genome‐wide screen for factors involved in cell division has been completed.
From core and valence excitations to orbital mapping: a theorist's perspective
Authors: Draxl Claudia
Published: December 2016

Ab initio
spectroscopy is a powerful combination of quantum‐based theories and computer simulations, covering a wide range of theoretical and computational methods that incorporate many‐body effects and interactions showing up in the excited state. This framework, combining density‐functional theory (DFT) with many‐body perturbation theory, not only allows for analyzing data obtained by experimental probes, but also for shining light onto the underlying physics. I will demonstrate this with a series of selected materials and excitation processes:

Oxygen K‐edge spectra from the wide‐gap semiconductor Ga
2
O
3
will reveal how signals from atoms located in a particular environment can be selectively enhanced or quenched by adjusting the crystal orientation [1]. These results suggests ELNES, combined with
ab initio
many‐body theory, to be a very powerful technique to characterize complex systems, with sensitivity to individual atomic species and their local environment.

With the example of self‐assembled phases of functionalized azo‐benzene it will be shown, how excitonic effects in core and valence excitations can be tuned by molecular packing [2], and how this may affect the switching functionality of the molecules.

Finally, I will discuss how transmission electron microscopy can be used for mapping atomic orbitals, exploring its capabilities by a first principles approach [3]. For defected graphene, exhibiting either an isolated vacancy or a substitutional nitrogen atom, different kinds of images are to be expected, depending on the orbital character (see Figure 1).
Combining advanced
TEM
techniques for full characterization of extended defects in creep‐deformed single crystal superalloys
Authors: Spiecker Erdmann , Müller Julian , Eggeler Yolita M. , Lenz Malte
Published: December 2016

Single crystal superalloys are used for turbine blades in the hottest parts of gas engines, where they have to withstand high stresses at temperatures exceeding 1000°C. This is only possible because of the well‐known γ/γ′‐microstructure of these alloys, forming the basis for excellent creep properties [1]. One of the research objectives is to gain a microscopic understanding of the elementary deformation mechanisms and defect processes that govern high‐temperature creep and to use this knowledge for further improvement of single crystal superalloys. Beside Ni‐base superalloys which are well established in applications new Co‐base superalloys have attracted a lot of research interest since the discovery of stable γ/γ′‐microstructure in these alloys in 2006 [2]. Research on Co‐base superalloys is still in its infancy, meaning that there is strong need for fundamental studies on elementary deformation mechanisms and defect processes.

In this contribution we give an overview of our recent research on extended defects that form upon high‐temperature creep in Ni‐ and Co‐base superalloys. We demonstrate that the combination of advanced transmission electron microscopy (TEM) techniques, employing dedicated diffraction, high‐resolution and analytical methods, is generally required for full characterization of such extended defects and for obtaining a complete picture of their role in elementary creep processes.

Figure 1 illustrates an example of full characterization of superdislocations in a Ni‐base superalloy. First, large‐angle convergent beam electron diffraction (LACBED) is employed for reliable determination of the Burgers vector [3], overcoming the well‐known problems of conventional Burgers vector analysis of such dislocations. Secondly, using a new FIB cross‐sectioning technique [4], the core structure of the same dislocation is studied by high‐resolution scanning TEM (HRSTEM). This approach enables scale‐bridging characterization of complex superdislocations on the micrometer and atomic scale.

Figures 2 and 3 summarize advanced TEM studies on extended faults that form upon creep of Ni‐containing Co‐base (CoNi) superalloys [5]. Inside of γ′ precipitates a characteristic defect configuration is observed in which superintrinsic stacking fault (SISF) loops are fully embedded in antiphase boundaries (APB). LACBED is used to determine the full Burgers vector (including sign and magnitude!) of the partial dislocation loop [5]. Pronounced segregation of alloying elements at SISF and APB is revealed by HRSTEM and energy‐dispersive X‐ray spectroscopy (EDXS). Based on these and other results, an elementary creep mechanism is proposed which is characterized by ½<112> slip involving a SISF→APB transformation [5]. Atomic diffusion at creep temperature appears to be a rate limiting step by gradually changing the fault energies which control the kinetics of the transformation.
Three‐dimensional maps of full‐length huntingtin and linkage to development of Huntington's disease
Authors: Jung Taeyang , Seong Ihnsik , Song Ji‐Joon , Hebert Hans
Published: December 2016

Among neurodegenerative diseases causing serious medical and social problems, in particular in association with an aging population, Huntington's disease (HD) is classified as a representative one of nine polyglutamine (polyQ) tract disease families. The polyQ diseases cause dominantly inherited neurodegenerative disorders that typically manifests itself during midlife with motor, psychiatric and cognitive symptoms leading to death in 15‐20 years after onset (Fig. 1). They evolve from an expansion of the CAG repeat tract in single responsible genes.

HD results from polyQ expansion at the N‐terminal in the huntingtin protein (3,144 amino acid protein). The longer the repeat is, the earlier the onset of disease. A metastudy showed that the prevalence of HD in Europe, North America and Australia was 5.7 per 100 000
1
.

Genetic studies showed that huntingtin knock‐out cause embryonic lethality implicating the important role of huntingtin during development
2
. Despite that huntingtin was identified to be responsible for HD two decades ago, little is known about its biological function nor the molecular mechanism of the pathogenesis. Even if the polyQ expansion in huntingtin occurs close to the N‐terminus it is imperative to investigate the function of huntingtin in full‐length context as the expansion is likely to modulate activities of the full‐length protein. Huntingtin has several HEAT motifs without any known functional domain. Therefore, huntingtin was predicted to adopt an extended shape as shown in other HEAT repeat proteins.

For the present structural studies, allelic series of huntingtin with various polyQ lengths were successfully expressed and purified. We have obtained the overall structure of full‐length huntingtin having 23 (Q23) and 78 (Q78) glutamines at medium‐resolution by negatively‐stained single‐particle electron microscopy (EM) showing the protein adopts a spherical shape
3
(Fig. 2). CD spectra were consistent with a predominant α‐helical secondary structure. The position of the polyQ region could be mapped onto the structure following antibody‐bound amino‐terminal FLAG‐tags of the Q23‐ and Q78‐huntingtins. Furthermore, cross‐linking mass spectrometry analysis revealed a modulated network of intramolecular contacts that together with the EM data suggests that huntingtin is composed of five structural domains. Thus, in a large size protein like huntingtin, HEAT repeat domains can be folded back to form a closed helical solenoid with functional sites in the internal cavity. The difference in structures of the EM maps of Q23 and Q78 huntingtin and between cross‐linking patterns of the two species suggest modulation of the overall structure with increasing polyQ lengths.