bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of gamma‐irradiation on the photocatalytic activity of undoped and Cu doped titania nanoparticles
Authors: Samet Lolwa , March Katia , Stephan Odile , Chtourou Radhouane
Published: December 2016

Copper doped and undoped TiO
2
powders have been prepared by sol‐gel technique and annealed at 400 °C. The powders were gamma irradiated at ambient temperature and doses between 14 and 60 KGy. The objective of the proposed work is to study the effect of gamma irradiation on the physical properties of undoped and Cu doped TiO
2
photocatalyst. The structural, morphological and optical properties of initial undoped and doped TiO
2
powders have been investigated. The performance of such a system strikingly depends on the insertion of impurities in the TiO
2
structure sublattice and of the disruption brought about. Consequently, this work is mainly focused on a nanoscale electron energy loss spectroscopy (EELS) study, which has been performed on samples with various Cu to Ti molar ratios (0‐12at.%). This study is an attempt to identify at the atomic level, the nature of the dopant insertion in the structure. It also allows evaluation of the composition of the studied TiO
2
powders throughout individual crystallites. In Cu doped TiO
2
sol gel powders, Cu
2+
ion has been found to substitute to Ti
4+
ions. Gamma irradiated samples present a crystalline core and a disordered shell structures (see Figure 2) as a result of the formation of oxygen vacancies. Such oxygen vacancies at the surface of TiO
2
nanocrystals lead to a remarkable enhancement of the photocatalytic activity of Cu doped TiO
2
nanocrystals (see Figure 3). This preparation method by gamma treatement could be potentially used for large‐scale production of high‐surface‐area anatase titania nanoparticles with trapped electrons on oxygen vacancies. Such catalysts show remarkable enhancement in the visible light absorption and photocatalytic activity. The doping and gamma irradiation doses impacts on the structural, optical and photocatalytic efficiencies will be thus highlighted and correlated.
Characterization of Solution‐Annealed and Thermally‐Treated Alloy 600 Intergranular Oxidation using Advanced Analytical Electron Microscopy
Authors: bertali giacomo , Scenini Fabio , Burke Grace
Published: December 2016

The susceptibility of Ni‐Cr‐Fe alloy (Alloy 600) to intergranular stress corrosion cracking (IGSCC) in light water reactor (LWR) primary water environment is well‐known. However, SCC initiation mechanism is still unclear and under debate, especially the key parameters responsible for the general and localised “internal” oxidation susceptibility of Alloy 600 in LWR primary environment require elucidation to develop a mechanistic understanding of the phenomena and to assess their relative importance.

It is well‐known that the precipitation of intergranular M
7
C
3
carbide network improves Alloy 600 Stress Corrosion Cracking resistance in PWR primary water environment. However, the main reason for the beneficial effect of intergranular carbides is still uncertain. In this study, the effect of grain boundary carbides on the preferential intergranular oxidation susceptibility and local grain boundary (GB) migration of Alloy 600 has been studied in detail. Solution‐annealed (SA) and thermally‐treated (TT) Alloy 600 oxidation coupons were exposed for 120 hours in hydrogenated steam environment at 480°C. This oxidation system successfully simulated PWR oxide morphologies [1‐3]. A combination of field emission gun (FEG) scanning electron microscopy (SEM), focused ion beam (FIB) microscopy and analytical electron microscopy (AEM) techniques have been used to characterize in detail the type and extent of preferential oxidation associated with the development of SCC initiation sites.

The surfaces of the oxidized Alloy 600SA and Alloy 600TT specimens were evaluated in an FEI Magellan XHR FEG‐SEM using both secondary electron (SE) and backscattered electron (BSE) modes. High resolution SEM characterization revealed a marked difference between the two thermal treatments especially in terms of HAGB undulations and oxide GB structure, Fig. 1. Surface oxide morphology was correlated with intergranular oxidation susceptibility and local GB migration by using FIB cross‐sections analysis and TEM examination (Fig. 2). Further AEM analyses were performed using the FEI Titan G2 80‐200 aberration‐corrected S/TEM with Super EDX. Detailed scanning transmission electron microscope (STEM) ‐ energy dispersive x‐ray (EDX) microanalysis of FIB TEM lift‐out specimens containing at least one grain boundary revealed the presence of a Cr‐Fe rich oxide at the grain boundaries and a marked microchemical redistribution in the near‐surface region for both SA and TT Alloy 600 (Fig. 3, Fig. 4). However, a noticeable difference in terms of intergranular oxide penetration and local grain boundary migration was observed when comparing the solute segregation/depletion and Intergranular oxidation between the SA and TT specimens.
Nanoscale phase separation and electronic structure of metastable bcc Cu‐Cr alloy thin films
Authors: Liebscher Christian H. , Freysoldt Christoph , Dennenwaldt Teresa , Harzer Tristan , Dehm Gerhard
Published: December 2016

The excellent electrical and thermal transport properties of copper (Cu) make it an attractive material for electronic applications. However, its poor intrinsic mechanical properties and oxidation resistance are strongly limiting the field of application. Alloying Cu with chromium (Cr) is an effective way of increasing the oxidation resistance of such alloys. However, under equilibrium conditions the solubility limit of Cr in Cu is far below 1 at.%. Supersaturated Cu‐Cr alloys can be synthesized by non‐equilibrium thin film deposition techniques. The high cooling rates bring another positive effect of grain refinement that leads to a strong increase of the mechanical properties. In a thin film with nominal composition of Cu
67
Cr
33
(at.%) nanoscale phase separation is characterized by energy dispersive X‐ray spectroscopy (EDS) in an aberration‐corrected scanning transmission electron microscope (STEM). The electronic structure of Cu in body centered cubic (bcc) crystal structure is analyzed by localized electron energy loss spectroscopy (EELS) and experimental spectra are contrasted to spectra calculated by density functional theory (DFT).

Co‐evaporation using molecular beam epitaxy (MBE) obtains metastable Cu‐Cr alloy thin films with nominal thickness of 300 nm and composition of Cu
67
Cr
33
(at.%). Selected area electron diffraction confirms the bcc crystal structure of the thin films with columnar grains of ~50 nm in diameter. Aberration‐corrected STEM in combination with EDS establishes compositional fluctuations within the grains on the order of 1 – 5 nm. The domains adopt the bcc crystal structure shown in the HAADF(High Angle Annular Dark‐Field)‐STEM image of Fig. 1. The chemical phase separation in Cu‐ and Cr‐rich domains with composition of Cu
85
Cr
15
(at.%) and Cu
42
Cr
58
(at.%) is illustrated in Fig. 2. The alignment of the interface between the Cu‐ and Cr‐rich domains shows a preference for {110}‐type habit plane. The electronic structure of the Cu‐Cr thin films is investigated by EELS and is contrasted to an fcc‐Cu reference sample given in Fig. 3. The main differences between bcc‐ and fcc‐Cu are related to differences in van Hove singularities in the electron density of states. In Cu‐Cr solid solutions with bcc crystal structure a single peak after the L
3
‐edge, corresponding to a van Hove singularity at the
N
‐point of the first Brillouin zone is observed. Spectra computed for pure bcc‐Cu and random Cu‐Cr solid solutions with 10 at.% Cr confirm the experimental observations. Changes in electronic structure of supersaturated solid solutions of Cu by alloying with Cr are discussed in detail.
Short time of
Z
n
O
nanoparticles uptake induces
DNA
damage and specific mitochondrial degeneration in human colon carcinoma cells
Authors: Condello Maria , Meschini Stefania , Berardis Barbara De , Ammendolia Maria Grazia , Condello Giancarlo , Pellegrini Evelin
Published: December 2016

Thanks to their unique physico‐chemical properties, ZnO nanoparticles are widely used in consumer and industrial products, due to their higher chemical reactivity, stronger oxidation and corrosion resistance, antimicrobial properties, as compared with larger micro‐sized counterparts (Madhumitha et al., 2016). Recent studies have shown that ZnO nanoparticles can be promising candidates for biomedical applications and therapeutic interventions, and also successful as drug carrier and in targeted gene delivery (Peng et al., 2015; Velmurugan et al.,2015). In our previous in vitro study, ZnO nanoparticles showed to induce oxidative stress in human colon carcinoma cells (LoVo), resulting in significant decrease of cell viability (De Berardis et al., 2010).

In order to gain insight into the mechanism of action at subcellular level, aim of the present investigation was to carry out an ultrastructural study by transmission electron microscopy (TEM) on the subcellular localization of ZnO nanoparticles and a semi‐quantitative analysis of cellular uptake at multiple time points (from a few minutes up to 24 h of exposure). Electron microscopy observations of ZnO treated cells revealed two different mechanisms of cellular uptake, passive diffusion and endocytosis. Control cells show a mitochondria and nuclear normal shape (Fig. 1A). Small particles entry by passive diffusion crossing the plasma membrane without altering its structure (30 min of treatment, Fig. 1B; arrow indicates the nanoparticle in the cell membrane area). After 1h of treatment ZnO nanoparticles are already visible in the mitochondria cristae (Fig. 1C). The induction of the apoptosis is clearly showed in Fig. 1D, after 24 h of treatment. Quantitative analysis of cell death has been performed by flow cytometry.

We also evaluated the intracellular ions release from ZnO nanoparticles, their genotoxic potential by determining 7,8‐dihydro‐8‐oxo‐deoxyguanosine (8‐oxodG) levels, and the expression of phosphorylated histone H2AX (γ‐H2AX). The simultaneous presence of ZnO nanoparticles and Zn
2+
ions in the LoVo cells determined the formation of reactive oxygen species at the mitochondrial and nuclear level, inducing severe DNA damage.

In conclusion, our observations showed that ZnO nanoparticles entered LoVo cells by either passive diffusion or endocytosis or both, depending on the agglomeration state of the nanomaterial. ZnO nanoparticles coming into contact with acid pH of lysosomes altered organelles structure, resulting in the release of Zn
2+
ions. Taken together, the results of this study provide the evidence that damage induced by ZnO nanoparticles in LoVo cells derives from a combined action between intact nanoparticles and Zn
2+
ions, leading new insights into their toxicity.
Momentum‐resolved energy loss spectra from ultra‐thin metal oxide layers obtained at high spatial resolution
Authors: Kinyanjui Michael , Benner Gerd , Kaiser Ute
Published: December 2016

Momentum‐resolved electron energy loss spectroscopy (MREELS) probes the momentum (q) dependence (dispersion) of energy losses from characteristic excitations such as excitons, plasmon, and interband excitations thus probing bandstructures, indirect excitations, and dipole‐forbidden excitations.
1
However, the ability to obtain momentum‐resolved spectra both at high spatial and momentum resolutions has remained difficult. As such, layer‐resolved momentum spectra from ultra‐thin films, heterostructures as well as from nanostructures has not been widely reported.

We present an experimental approach that enables the acquisition of momentum resolved spectra at high spatial resolution down to 2 nm using a nano‐beam electron diffraction approach.
2
Through this approach we have obtained momentum resolved spectra from individual, differently‐oriented nano‐domains in an ultra thin (12 nm) PrNiO
3
layer as well as spectra from different positions in a LaNiO
3
thin film (70 nm).

Figure 1(a) displays a Z‐contrast image of the LaNiO
3
thin layer grown on a LaSrAlO
4
substrate. A nano‐beam electron diffraction pattern from the LaNiO
3
layer is shown in Figure 1(b). A slit is used to select the 200, ‐200 set of diffraction spots (shown by the red rectangle) allowing electrons that have been scattered to certain scattering angles into the spectrometer. This corresponds to the Г‐X direction of the Brillouin zone in the pseudo‐cubic symmetry of LaNiO
3
. The resulting image (ω‐q map) shown in figure 1(c) displays energy losses as function of momentum transfer along the Г‐X (q// [100] ) direction in the reciprocal space. The presented approach will enable the acquisition of momentum resolved spectra from nano‐structured materials, thin films, interfaces, surfaces, and heterostructures at high spatial, energy, and momentum resolutions.
Synthesis of ultra‐small iron‐oxide and cobalt ferrite nanoparticles by a simple thermal decomposition approach
Authors: Piché Dominique , Lozano Juan G , Dillon Frank , Grobert Nicole
Published: December 2016

Ferrite nanoparticles are promising candidates for a range of bio‐medical applications due to their interesting physical and magnetic properties. In order for their nano‐scale properties to be utilised however, synthesis methods which enable fine control over size, shape and composition are required.

In this work we explore the size‐controlled synthesis of iron‐oxide and cobalt ferrite nanoparticles by thermal decomposition and their characterisation by advanced microscopy techniques. The tailored synthesis of the nanoparticles was addressed by exploring the parameters in the reduction of both an iron precursor (Fe(III)(acac)
3
) and a cobalt precursor (Co(II)(acac)
3
) in oleylamine. In this thermal decomposition approach, oleylamine acts as the sole surfactant, reducing agent, and solvent. By controlling the surfactant‐to‐precursor ratio, we have produced ultra‐small nanoparticles with a narrow size distribution. The size, shape and atomic structure of the resulting particles were examined by aberration‐corrected annular dark‐field scanning‐transmission electron microscopy; and the results show that their average size is <3 nm and they are highly crystalline. Electron energy loss spectroscopy was used to analyse the composition of the resulting nanoparticles and the oxidation state of the metals, confirming that they consist of Fe
3
O
4
and CoFe
2
O
4
.

Our results serve to form a solid support for future studies into the size‐dependent interaction of iron‐oxide and cobalt ferrite nanoparticles with cells.
Atomic resolution electron microscopy of cobalt ferrite nanoparticles
Authors: Piché Dominique , Lozano Juan G , Varambhia Aakash , Dillon Frank , Jones Lewys , Nellist Peter D , Grobert Nicole
Published: December 2016

Cobalt ferrite (CoFe
2
O
4
) nanoparticles have recently emerged as a potential candidate for a range of bio‐medical applications due to their interesting physical and magnetic properties. The high magneto‐crystalline anisotropy of CoFe
2
O
4
nanoparticles in particular offers improved efficiency over iron‐oxide nanoparticles, allowing for smaller particles to be used. Synthesis of cobalt ferrite nanoparticles is conventionally achieved using thermal decomposition in oleic acid and oleylamine. Recent methods using oleylamine alone demonstrate greater suitability for biomedical applications, as oleylamine facilitates the phase‐transfer process required to make the nanoparticles water‐soluble. However changing the surfactant is known to have a significant effect on the crystal structure and morphology of metal‐oxide nanoparticles, and the crystal structure of oleylamine‐capped cobalt ferrite nanoparticles has not been studied in detail before. Here we demonstrate the inverse spinel structure of cobalt ferrite nanoparticles synthesised with oleylamine as the sole surfactant, by aberration‐corrected annular dark‐field scanning‐transmission electron microscopy. The crystal structure is resolved with atomic‐level detail which has not been demonstrated with cobalt ferrite nanoparticles previously. Furthermore the distribution of cobalt and iron atoms is shown by atomic‐resolution EELS spectroscopy mapping. This data serves to form a solid support for future studies into the size‐dependent interaction of cobalt ferrite nanoparticles with cells.
Evidence for the dissolution of molybdenum during tribocorrosion of
C
o
C
r
M
o alloy in the presence of serum proteins
Authors: Simoes Thiago , Bryant Michael , Brown Andy , Milne Steve , Ryan Mary , Goode Angela , Porter Alexandra , Neville Anne , Brydson Rik
Published: December 2016

CoCrMo Metal on Metal (MoM) hip implants were designed to be durable, targeting a better quality of life for young, active patients. Current evidence suggests that such implants can release wear particles and metal ions due to a bio‐tribocorrosion process [1,2]. This involves both corrosion of the implant surface itself, which is stimulated by the wear process removing a chromium‐rich passivating film, and also mechanical wear of the surface to produce nanoparticulate wear debris that can be spread by lymphatic circulation and subsequently corrode. Both processes can therefore give rise to the release of metal ions which may have an inflammatory or toxic effect on cells and tissues, notably because certain metal ions can complex with proteins and disable the primary function.

This study focuses on the synthesis and characterization of CoCrMo nanoparticles, which mimic metal‐on‐metal (MoM) wear debris from hip implants. We have used a hitherto unexplored approach of mechanochemical milling to produce a large amount of CoCrMo mimetic wear debris over short time scales [3]. Using TEM, the nanoparticles produced were found to be similar in size, shape and composition to wear debris from CoCrMo hip implants produced both
in‐vivo
and using hip simulators. An efficient separation of nanoparticles from solution prior to free ion concentration analysis by inductively coupled plasma mass spectrometry (ICP‐MS) was developed using centrifugation combined with ultrafiltration (2 kDa ultrafilters; Figure 1). This revised preparation method has allowed the identification of the dissolution of specific alloy elements both in hip simulator lubricant systems and in different biological media and pH environments during both dynamic tribocorrosion studies (using milling) and also during static corrosion (Figure 2). The results indicate a much lower dissolution of cobalt than previously reported. We also identified a significant fraction of Mo ions in solution that could be linked to the preferential binding of Mo by bovine serum albumin (BSA) proteins identified by FTIR and TEM [4; Figure 3]. Electrochemical corrosion tests in the presence of BSA confirm that the proteins play an important role in Mo dissolution from CoCrMo. We suggest that the interaction of Mo‐rich surfaces with amide groups in serum proteins and the possible formation of metal carbonyl complexes are important because both can modify biological molecules, potentially altering the function.

In summary, the role of Mo as well as Co ions should be accounted for in the tribocorrosion of CoCrMo implant alloys, particularly in terms of inflammatory and toxicological responses.
Transmission electron microscopy of unstained
DNA
origami structures on free‐standing graphene
Authors: Kabiri Yoones , Ananth Adithya , van der Torre Jaco , Katan Allard , Malladi Sairam , Hong Jin‐Yong , Kong Jing , Zandbergen Henny , Dekker Cees
Published: December 2016

DNA origami has received great attention in recent years due to its accessible self‐assembly, versatility and potential for single‐molecule biophysical studies. Origami is often imaged in TEM. Monolayer‐thin graphene may provide the ultimate substrate for high‐resolution imaging of DNA origami. However, little is known about interaction of DNA origami and graphene. Here, we report on microscopic observations of the interaction between graphene and DNA origami using transmission electron microscopy (TEM) and atomic force microscopy (AFM). We designed a symmetric origami structure that can be well recognized in imaging, which consists of different features like cavities in the middle, DNA bundles on the side arms and a free dsDNA loop at the bottom (Fig1.a). Fig1.c shows AFM images of these origami structures on highly oriented pyrolytic graphite (HOPG) substrates. The origami structures are observed to be severely distorted upon adsorption onto graphite whereas normal, undistorted adsorption is seen on mica substrates (Fig1.b). Interesting, origami exhibits excellent spreading and no severe distortions on amorphous carbon film (Fig1.d). It thus appears from Fig1.b‐d that DNA origami is particularly distorted on graphite. Next, we investigated these origami structures with TEM experiments on CVD‐grown graphene. We obtained images with uranyl‐stained DNA origami, but interestingly also could obtain good contrast with unstained DNA origami if we employed a focused beam in STEM mode, or with dark‐field microscopy with the stop of central beam (known as DF‐000 technique) – see Fig2.b‐d. The imaging of unstained DNA origami is promising for future applications where possible side effects due to staining with uranyl needs to be avoided. TEM results again showed disruption of the DNA origami structures, suggesting that this is inherent to the interaction between DNA and graphene layer. These distortions may be due to DNA dehybridization caused by favorable interactions between the hydrophobic DNA bases and graphene.
Mathematical modeling of Cajal body formation
Authors: Blazikova Michaela , Malinova Anna , Novotny Ivan
Published: December 2016

In the living cells, there are many structures and organelles enveloped with a membrane that defines their border and controls the communication between the inner and outer environment. In contrast to membrane bound compartment, cells contain numerous membrane‐less structures, whose formation is based on specific interactions among their components. These types of structures include Cajal bodies (CBs), PML bodies and P‐Bodies found in most cell types, stress granules that appear upon environmental stress (heat shock, oxidative stress etc.) or various aggregates that form as result of protein/RNA mutations (e.g. protein inclusions in ALS). The biological role of the membrane‐less structures is a topic of intensive research and the function of several bodies have been revealed. However, little is known about principles that lead to their formation. As an archetypal compartment, we employed the CB (Fig.1), the self‐organizing structure involved in metabolism of various ribonucleoprotein particles. We employed time‐gated Stimulated Emission Depletion (gSTED) microscopy to acquire superresolution microscopy images of the CB and surrounding nucleoplasm. We have visualized the CB scaffolding protein coilin using indirect immunofluorescence in situ. Our preliminary data clearly showed the sub‐resolution structures of the CB (subCBs). Moreover, the substructures are also visible in the surrounding nucleoplasm and indicate that the CB is an aggregate of those basic building blocks (Fig.2‐B). Here, we would like to present our work on a mathematical model based on the fundamental thermodynamic rules of condensation and phase‐separation to describe the formation of membrane‐less bodies. We will present superresolution fluorescence microscopy, photo‐kinetic experiments and fast time‐lapse live cell imaging results and progress of the work on determining of basic biophysical behavior of individual CB components. The project is interdisciplinary and combines advanced fluorescence microscopy techniques and mathematical modeling and simulations.
Subcellular localization of metal pools determined by
TEM
‐
EDS
in embryo Arabidopsis thaliana mutants
Authors: Gillet Cynthia , Mary Viviane , Sanchez Garcia de la Torre Vanesa , Thomine Sébastien , Satiat‐Jeunemaître Béatrice
Published: December 2016

Transmission Electron Microscopy equipped with Energy Dispersive Spectroscopy (TEM‐EDS) is known to be a powerful tool to study metal speciation in biological and environmental samples. The characterisation of different metal pools present in organisms is indeed essential to understand optimal development under various environmental constraints. For instance in plant cells, iron (Fe) is known to be an essential co‐factor for electron transfer in many biological reactions. Fe remobilization by specific membrane transporters in seeds is especially important for germination. In
Arabidopsis thaliana
seeds, the AtVIT1 transporter is involved in Fe influx into perivascular vacuoles whereas the AtNRAMP3 and AtNRAMP4 function in Fe retrieval. The
vit1‐1
and
nramp3nramp4vit1‐1
mutants display an altered Fe pattern.

To examine the subcellular localization of Fe and Mn in cotyledons from wild‐type,
vit1‐1
and
nramp3nramp4vit1‐1
triple mutant dried seeds, we used Energy Dispersive Spectroscopy (EDS) combined with Transmission Electron Microscope (TEM). This technique collects the X‐rays spectrum emitted by plant sample sections bombarded with a focused beam of electrons to obtain a localized chemical analysis (Figure 1). A cartography using STEM‐EDX data complete the characterization of these mutants and open new questions of the iron localization and chemistry in the triple mutant.

Results (Figure 2) show that in
vit1‐1
mutant embryos, Fe and Mn were both concentrated in subepidermal cell globoids, whereas Fe is localized in perivascular globoids in wild‐type. In the
nramp3nramp4vit1‐1
triple mutant Fe was detected at low level in globoids from subepidermal and perivascular cells although
vit1‐1
and
nramp3nramp4vit1‐1
have the same pattern revealed by Perl's/DAB staining (1).

To further localize and quantify metal elements such as Fe or Ni in cells, we also developed a CEMOVIS approach which will allow to perform elemental chemical analysis from lyophilized cryosections observed by STEM‐EDX.
ColorSTEM
‐ A Novel
STEM
Detector for Advanced Materials Analysis in
SEM
Authors: Dluhoš Jiří , Bilík Michal , Petráš Stanislav
Published: December 2016

Performing scanning transmission electron microscopy (STEM) in a scanning electron microscope (SEM) is a popular technique for laboratories without transmission electron microscopy (TEM) capabilities.

The new versatile STEM detector by TESCAN is optimized for both high‐sensitivity orientation contrast as well as materials composition contrast imaging.

Transmitted electrons scattered in different angles represent different types of information that arises within a thin foil in scanning transmission electron microscopy. The new retractable STEM detector design allows maximum manipulation capabilities with the sample, including changes in working distance or eucentric tilt above the detector. Changing the working distance also changes the angular distribution of electrons detected by the detector segments. The sample can be therefore navigated to optimum contrast conditions easily, using changes in the working distance (see Fig. 1).

The redesigned electronics and signal processing apparatus of the detector allows simultaneous acquisition of multiple signals from transmitted and diffracted electrons including bright field (BF), dark field (DF) and high angle dark field (HADF) channels. The newly implemented ColorSTEM concept allows simultaneous acquisition of all channels as a live, color‐coded image with no information loss in either compositional color coding (Fig. 2) or orientation contrast color mode (Fig. 3).

The STEM analysis can be further supplemented with high‐resolution transmission‐EDS or transmission‐EBSD microanalysis. Higher resolution with these techniques is possible by reducing sample thickness thereby minimizing the interaction volume within the sample [1]. This combination takes advantage of the fact that these analytical techniques are already available in the SEM.
Study of Thermally Tunable Coupled Magnetic Vortex Oscillators with Lorentz Transmission Electron Microscopy and Differential Phase Contrast Microscopy
Authors: Wild Johannes , Vogel Michael , Müller Michael , Schwarzhuber Felix , Back Christian , Zweck Josef
Published: December 2016

Magnetic vortex oscillators are an ideal system to study the dynamics of magnetic systems at very small length scales and over a wide frequency range. Their dynamic behavior shows characteristics known from other fundamental physical systems like the harmonic oscillator [1] and is in many aspects well understood. Their lateral dimension vary from a few microns [2] down to the nanometer scale [3]. Due to their flux closure configuration they are magnetically stable and a potential candidate for high density magnetic logic devices and magnonic crystals [4]. The oscillations, which can be obtained in essentially zero external magnetic field (besides the driving field), exhibit a narrow line width and resonance frequencies starting from the MHz range up to GHz frequencies [5]. They can be excited using magnetic field pulses [6] and electric currents harnessing the Spin Transfer Torques (STT) [5].

Recently, the magnetization dynamics in neighbouring magnetic vortex oscillators coupled via their stray fields come into focus of research [7‐10]. The system behaves like damped coupled harmonic oscillators. It has been shown that the dynamics of such systems is strongly influenced by the strength of the magnetostatic interaction given by the distance between the elements and the relative configuration of the core polarizations, e.g., the directions of the out‐of‐plane magnetization components [9].

Here we present a study of coupled vortices with Lorentz Transmission Electron Microscopy (LTEM) and Differential Phase Contrast Microcopy (DPC) at zero magnetic field. We show a novel technique to control the interaction of two or more vortex oscillators by directly influencing their resonance frequencies. The resonance frequencies depend on the saturation magnetization M
s
of the magnetic material, in this case permalloy and is highly dependent on the temperature of the disk. We use Joule heating to electrically manipulate the resonance frequencies of one element to control its excitation by a second neighbouring disk. We systematically mapped the frequency response of both disks for different temperatures to fully understand the behavior of the system.
Examination of inas/insb heterointerfaces in nanowires
Authors: Gejl Aske , Kanne Thomas , Johnson Erik , Denneulin Thibaud , Jäger Wolfgang , Nygård Jesper , Krogstrup Peter
Published: December 2016

Examination of InAs/InSb heterointerfaces in Nanowires

Antimony based semiconductor nanowires (NWs) have been widely studied in recent years due to their large spin‐orbit coupling, high Landé g‐factor, and single subband conductance. They may become a key material in the field of quantum information processing and are currently used in the search for Majorana fermions by electrical transport [1]. Theory predicts that Majorana bound states can be realized in a 1D semiconductor coupled to a superconductor when exposed to an external magnetic field and manipulated by electrostatic gates [2]. Using NWs as a mean to achieve this goal has become even more promising after a recent report on epitaxial semiconductor/superconductor NW interfaces [3,4]. InSb NWs are expected to be the optimal material in this endeavor as the large spin‐orbit interaction, and the possibility to induce superconductivity, in InSb makes it feasible to drive the wires into the topologically protected regime [2,5]. Realization of Majorana bound states in semiconductor/superconductor NWs would open the route to perform quantum information processing in networks by exploiting the unique non‐abelian braiding statistics and non‐trivial fusion rules which are inherent in Majorana Fermions [6].

In this work we present a detailed investigation of the growth of Au‐seeded InSb NWs grown by molecular beam epitaxy (MBE) on (111)B InAs substrate. As InSb has proven difficult to grow directly on InAs substrates, an InAs stem mediates the growth as seen in Fig. 1. In Fig. 2 the growth deformation in this region is analyzed using Geometric Phase Analysis (GPA) and the abrupt interface indicates that the compositional change occur rapidly. To explore the growth dynamics of InSb, the transition region between InAs/InSb is investigated in order to study how incorporation of Sb affects the system. This analysis is performed using HR‐TEM, Dark‐Field Electron Holography (DFEH) [7], and Energy Dispersive x‐ray Spectroscopy (EDS). In Fig. 3 a DFEH image is obtained by interfering the diffracted beam from the InAs part of the NW with that from the InSb part. Using DFEH the in‐plane deformation in the growth direction is shown in Fig. 4. Comparing the results from the aforementioned techniques with parameters used in the MBE during growth gives insight into the incorporation dynamics of Sb in NWs. Understanding the dynamics of NW growth is crucial in order to optimize and utilize these in novel devices. InSb NWs with two‐facet Al shell are also investigated to explore the epitaxy of the interface, since the interface plays the major role in utilizing InSb/Al heterostructures for topological superconductivity and devices.
Analysis of capping with
G
a
A
s
S
b
N
thin layers in (un)coupled
I
n
A
s/
G
a
A
s multi quantum dot layers for enhanced solar cells
Authors: Reyes Daniel F. , Braza Veronica , Utrilla Antonio D. , Ben Teresa , Guzman Alvaro , Hierro Adrian , Ulloa Jose M. , Gonzalez David
Published: December 2016

Nowadays, stacked InAs/GaAs quantum dots (QDs) capped with layers different than GaAs are being applied in photovoltaic and photodetector technologies due to their potential for tailoring the optical properties and enhancing the device efficiency.
1,2
The particular use of GaAsSbN capping layers (CLs) allows controlling the QD size as well as the electron and hole confinement potentials in a wide range.
3
In addition, multi‐coupled QD structures formed by vertically aligned QDs represent a very interesting approach, which enhances the photoluminescence (PL) intensity and reduces the spectral width by utilizing carrier tunneling among QDs. However, in this type of nanostructures the control of the QD composition, size and alignment are important parameters as they affect the electronic coupling and the carrier lifetime. In this work, we analyze the effect of using 2.5 nm‐thick capping layers of GaAs
0.76
Sb
0.2
N
0.04
in an (un)coupled 10 stacked layer structure of InAs/GaAs QD by transmission electron microscopy (TEM) techniques. For this, we have compared three samples: two samples with uncoupled QDs (the spacer thickness is 40 nm) with (
SbN‐u
) and without CL (
Ref
), and a coupled sample with CL and a spacer thickness of 10 nm (
SbN‐c
). PL and photocurrent (PC) data are also used in the discussion.

Cross sectional g200 dark field (DF) images sensitive to composition have been used to obtain a statistic of the buried QD size (Figure 1). For the uncoupled samples, our measurement on more than 90 QDs revealed an unexpected similar height for
Ref
and
SbN‐u
samples (4.7 nm) while the average diameter presents a slight increase in sample
SbN‐u
with respect to
Ref
sample (from 17 to 19 nm). The panorama changes totally for
SbN‐c
sample, where the average height and diameter increases layer by layer from 4.7 to 5.2 nm and from 23 to 34 nm, respectively. The relative volume rises quickly (Figure 1) up to the 4
th
layer, and after slowly, becoming 7 times higher in the upper layer. The shield effect of Sb in the QD decomposition is not appreciated. Indeed, EDX measurements revealed only tiny traces of Sb in the CLs that we related with the typical delay observed in the Sb incorporation due to the CL small thickness. In addition, strain maps from high resolution TEM images acquired on the [110] pole axis were calculated. The comparison between the uncoupled samples discloses that N is incorporated in the CL. The same occurs in the coupled sample where a high compressive strain appears over the QDs (Figure 2). More important, the strain into the QDs decreases in a similar way that the volume increases. Finite element simulations suggest a modification of segregation process during the growth, with an increase of Ga incorporation in the QDs of the upper layers.
Simultaneous Nanoplasmonic Sensing and Transmission Electron Microscopy Characterization
Authors: Iandolo Beniamino , Moss Asger , Nugroho Ferry , Langhammer Christoph , Wagner Jakob
Published: December 2016

We have developed a platform that allows for real time optical sensing based on localized surface plasmon resonance (LSPR) readout inside a transmission electron microscope (TEM). With the TEM, we obtain insight into the structure and composition of materials by performing imaging and spectroscopy with atomic resolution [1]. However, the probed volume is rather small, and the beam‐specimen interaction is often non‐negligible and needs to be taken into account, usually by performing additional experiments. Thus, there is an increasing effort towards enabling simultaneous TEM probing and characterization with complementary techniques. Thanks to the strongly enhanced electric fields generated around metallic nanoantennas, LSPR‐based sensing is a proven tool to study processes at the nanoscale [2], and an ideal complement to TEM since it probes a much larger volume of the specimen.

We have fabricated a TEM specimen holder hosting a miniaturized optical bench [3] that allows for sample illumination and spectroscopic readout. Specimens can be heated up to 1300 ºC, and the holder is compatible with differentially pumped environmental TEM (ETEM), with no prior modification to the microscope required. Comparison between signals obtained simultaneously by TEM and LSPR provides indication of the relevance of electron beam‐induced effects. Moreover, we enable for the first time direct correlation of the LSPR response with changes in physical properties of the specimen. We investigate thermally‐induced sintering of metal nanoparticles, a crucial process in deactivation of catalysts [4]. We envision the combination of LSPR sensing with probing by ETEM to become a versatile tool to study processes at the nanoscale, especially taking place on (photo)catalysts.
Mapping cation‐vacancy ordering and oxygen octahedral distortions in A‐site deficient perovskites by monochromated core‐loss
EELS
Authors: Kepaptsoglou Demie , Hernandez‐Maldonado David , Azough Feridoon , Ophus Colin , Freer Robert , Ramasse Quentin
Published: December 2016

A–site defficient perovskites are of particular interest for a range of engineering applications, such as ionic conductors, batteries and thermoelectric materials. The attraction of these systems lies in particular in their chemically stability over a wide range of compositions and operating conditions. Moreover, they can exhibit different degrees structural ordering, such as cation‐vacancy or oxygen‐octahedral‐tilt‐domain ordering [1,2] which can significantly affect their macroscopic physical properties.

In this work we combine state‐of‐the‐art monochromated core loss electron energy loss spectroscopy (EELS) measurements with advanced image analysis to investigate the interplay between A‐site cation‐vacancy ordering and oxygen octahedral tilting domains in a series of Nd
2/3x
TiO
3
double perovskites, exhibiting different degrees of structural ordering as a function of their heat treatment. [3,4] As a result they exhibit vastly different thermoelectric properties related to the presence of domain boundaries which can suppress the thermal conductivity due to increased phonon scattering. [5,6]

High‐angle annular‐dark‐field (HAADF) imaging and large scale atomically‐resolved EELS maps were used to investigate the chemical ordering of cations on the so‐called A site of the perovskite structure (Figure 1), while pm‐precision annular bright field (ABF) imaging of these compounds reveals the presence of TiO
6
tilting domains, which we show can be correlated with variations in the A‐site occupancy (Figure 2). Furthermore, advanced image analysis of the electron micrographs was used to measure local distortions in the TiO
6
lattice

These local distortions are further investigated using atomically‐resolved monochromated EELS measurements with an energy resolution better than 0.1eV, in a Nion UltraSTEM 100MC. In particular, measurements of the of the Ti L

2,3

edge (Figure 3), reveal local changes of the near‐edge fine structure, usually not discernible with conventional EELS measurements. Changes in the Ti L
2,3
pre‐peak intensity, as well as subtle local variations in the Ti L
3
e
g
/t
g
intensity ratios, clearly observable thanks the relatively high beam current still available at this energy resolution, are indicative of local distortions in the oxygen octahedral sublattice.
Strain at interfaces of the
I
n
A
s/
A
l
S
b heterostructure for quantum cascade lasers
Authors: Vallet Maxime , Claveau Yann , Warot‐Fonrose Bénédicte , Gatel Christophe , Combe Nicolas , Magen Cesar , Teissier Roland , Baranov Alexei , Ponchet Anne
Published: December 2016

Devices based on epitaxially grown multilayers can be highly sensitive to structural and chemical properties at interfaces, especially when the active zones are of nanometric size. The InAs/AlSb system is particularly sensitive to this phenomenon due to the lack of common atomic species between the two materials. While the lattice mismatch between the two material layers is moderate (1.3%), the formation of chemical bonds at interfaces that are different from those existing in layers such as Al‐As or In‐Sb may result in large and very‐localized strains. The lattice parameters of AlAs bonds (
a
AlAs
=0.566 nm) or InSb bonds (
a
InSb
=0.6479 nm), as bulk materials, are 6.6% smaller or 6.9% higher than that of InAs (
a
InAs
=0.6058 nm), respectively. The stress states at interfaces are therefore highly dependent on their dominant bond type, being tensile for AlAs‐like interfaces or compressive for InSb‐like interfaces. In a previous study, a first estimation of the composition at interfaces in the InAs/AlSb system was obtained by combining strain analysis with chemical ones [1]. It was shown that the formation of the tensile AlAs‐type interface is spontaneously favored compared to InSb‐type, which is attributed to its higher thermal stability.

In this work we focused on the meaning of the measured strain at interfaces in order to get quantitative data on their atomic composition and thus to improve the understanding of interface formation. In this perspective, a strain analysis achieved by using the geometrical phase analysis (GPA) was performed on atomically‐resolved Z‐contrast images acquired by HAADF‐STEM (Fig. 1). Experimental strain profiles were then compared to those obtained from simulated images, with a focus on the effect of convolution due to the mask used in the GPA treatment. Very high negative strains at the scale of two atomic planes are observed from experimental images, both at the InAs‐on‐AlSb and at the AlSb‐on‐InAs interfaces. The comparison with simulated strain profiles highlights the strong AlAs‐type character of the interfaces when they are spontaneously formed within the chosen growth conditions (Fig. 2). The strain states at interfaces of these structures were also investigated by using the density functional theory (DFT) and compared to the ones predicted by the theory of linear elasticity (Fig.3).
Cations distribution in synthetic (
MgFe2O4
and
FeAl2O4
) spinels by precession electron diffraction tomography
Authors: NGASSA TANKEU Yvan Georges , Damien JACOB , Pascal ROUSSEL , Mathieu ROSKOSZ , ANDREOZZI Giovanni B.
Published: December 2016

Since recently, a method using precession electron diffraction tomography (PEDT) and dynamical calculations of the diffracted intensities has been developed, allowing the structure determination and refinement at the nanoscale in a TEM [1, 2]. We present the application of this method to the refinement of (MgFe
2
)O
4
and (FeAl
2
)O
4
spinels in order to determine the Fe, Mg and Al cations distributions on specific sites of the structure. This determination is essential for understanding the electrical or magnetic properties of spinels, their chemical reactivity or to retrieve their thermal history in the field of geosciences.

Studied samples were obtained by the flux growth method and for different chemical compositions [3]. Some samples have also been heat‐treated (24 h at 1000°C followed by a rapid quench) in order to intentionally induce some structural disorder associated with Fe, Al and Mg occupancy variations on the tetrahedral and octahedral sites of the structures. Single crystals were large enough to be also studied and refined by X‐ray diffraction. The structures thus deduced serve as model for comparison with the much more local results obtained using PEDT. Thin sections for TEM observations are extracted from the crystals previously studied by XRD via two methods: Focused Ion Beam (FIB) thinning and simple mechanical grinding.

The full refinement method is precisely described in [1]. It is based on the acquisition of a serie of precession (angle varying from 1 to 2°) diffraction patterns continuously acquired for various tilt angles of the sample (+/− 45 to 60°, by step of 1°) as currently done in tomography. The 3D reciprocal space of the structure is then reconstructed (Fig. 1) and experimental

I
hkl

intensities are integrated using the softwares PETS and JANA2006. From the

I
hkl

data set, the structure is solved, using conventional X‐ray methods based on the kinematical approximation implemented in JANA2006, in order to obtain a first reliable structure model (Fig.2). The model is finally accurately refined (atomic position and occupancies) using least‐squares methods based on the comparison of experimental intensities with calculated ones using the multi‐beam dynamical theory, taking into account interactions between diffracted beams for a given thickness and orientation of the sample.

In this work, we will describe and discuss the influence of the various experimental and computational parameters on the accuracy and precision of the PEDT refinement results. These parameters are: i) thinning method (FIB / grinding), ii) precession angle, iii) refinement procedure (including thickness and/or orientation refinement). We will also discuss the need of constraining or not the chemical composition of the samples during the refinement procedure in order to obtain the most reliable results.
Observation of the graphitization process of hollow graphitic spheres
Authors: Pfänder Norbert , Swertz Ann‐Christin , W. Lehmann Christian , Schlögl Robert
Published: December 2016

Introduction

Hollow graphitic spheres (HGS) are interesting support materials for catalytic active metal nanoparticles. HGS can be widely used as tailored mesoporous carbon support with several advantages over other carbon materials.
1
The spheres have a high surface area and a pore system with narrow pore size distribution which makes this material interesting for the impregnation of metal nanoparticles and techniques like the confined‐space alloying of bimetallic nanoparticles.
2
Additionally HGS have a high degree of graphitization what makes the material stable under common catalytic reaction conditions. A typical synthesis route
1
for HGS covers 3 major steps starting with silica spheres coated with a mesoporous silica shell:

‐ Impregnation of the SiO
2
template with iron nitrate and polymer‐precursor

‐ Carbonization/graphitization of the polymer shell

‐ Leaching of the silica to obtain hollow graphitic spheres

Methods

The polymer‐coated SiO
2
spheres were dry‐prepared and heated up to 1000°C with a heating rate of 5 °C min
‐1
. At certain points the temperature was maintained to minimize the thermal drift for the image acquisition.

Results

Starting the thermal treatment at first the activation of iron particles could be observed. Beginning at about 250°C the finely dispersed iron started to agglomerate and formed metallic nanoparticles. By further heating the iron particles became mobile and the graphitization started at about 900°C.