bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
Monochromated Low‐Voltage
EELS
of Optical Resonances in Quantum Materials
Authors: Bell David , VonCube Felix , Rez Peter , Aoki Toshihiro 
Published: December 2016

We have imaged and produced EELS spectra of Vacancy (NV) centers in diamond with our Zeiss Libra TEM [1] with a monochromated electron source and in‐column energy filter, Fig. 1. With monochromated electron energy loss spectroscopy (EELS) we measure the amount of energy loss that an electron undergoes; this includes optical resonances and inter and intra band transitions but also of course the Cherenkov radiation background. The low acceleration voltage of 40 kV directly reduces the background noise of the Cherenkov radiation. According to the photoluminescence spectra, we find a resonance at 1.9 eV (corresponding to 638 nm wavelength). We have also demonstrated an unexpectedly strong surface‐plasmonic absorption at the interface of silver and high‐index dielectrics based on electron and photon spectroscopy [2]. The measured bandwidth and intensity of absorption deviate significantly from the classical theory. Our density‐functional calculation well predicts the occurrence of this phenomenon. It reveals that due to the low metal‐to‐dielectric work function at such interfaces, conduction electrons can display a drastic quantum spillover, causing the interfacial electron‐hole pair production to dominate the decay of surface plasmons. This finding can be of fundamental importance in understanding and designing quantum nanoplasmonic devices that utilize noble metals and high‐index dielectrics.
Depending on the composition, Quantum Materials may act as conductors, insulators, semiconductors or even as superconductors. Combinations of different quantum materials are of high interest to explore new phenomena and act as the foundation for future electronic devices at the nanometer scale. Our quantum materials research is widely spread, reaching from defect formation in graphene to the characterization of hybrid quantum materials. We present our work utilizing Low‐Voltage Monochromated EELS and Low‐Voltage High‐Resolution Electron Microscopy (LV HREM). Together, these often improve the contrast to damage ratio obtained on a large class of samples, such as Quantum Materials.

Fe
3
Sn
2
is a rare metallic Kagome ferromagnet, which synthesis as a single crystal has not previously been reported (Fig. 2). We study this single crystal as well as other topological insulators with the particular interest in the correlated behavior in topologically non‐trivial materials. The (S)TEM images mapped with low voltage EELS show the atomic structure of the layered material(Fig. 2), and the magnetic force microscopy measurements reveal the magnetic anisotropy of the crystal on the surface. Monochromated EELS is the key to all this work, due to increased signal to noise and background and/or ZLP reduction.
Exotic Electron topologies ‐ Knitting with electron vortices
Authors: Clark Laura , Verbeeck Jo 
Published: December 2016

Electron vortex studies have proliferated in the last few years, with many examples of their production, measurement and some examples of application.
However, these studies focus on the more standard cylindrically‐symmetric ideal electron vortex beam. We have recently noted an abundance of exotic vortex behaviours, outwith cylindrical symmetry [1]. Vortex‐antivortex loops were formed and annihilated at many different positions within the beam, with varying sizes. Other studies have shown how a vortex core can wend its way through a crystal lattice, with the vortex always remaining conserved [2].
In the sister field of optical vortices, it has recently been discovered that it is possible, with simultaneous manipulation of holography and careful limiting apertures, to produce 'knots' with the vortex cores [3]. These knots are not knots as known to the layman, but specific forms of multiply interlinked loops. These knots are unusual, and robust topological structures, and take the form of knotted dark threads within the beam [4].
Here, we investigate the feasibility of producing these exotic structures in the rather more confined space of a modern TEM, with finite aperture positioning and strict paraxial limitations. Adjusting the phase hologram technique of Leach et al [3], we have produced a design for a TEM phase mask
(see figure 1 and 2). Such a design is more detailed and technologically challenging than those produced so far in the electron vortex research field [5], but may just be within reach to enable the study of these unusual topological electron structures for the first time.
The interior of the rotavirus capsid
Authors: Estrozi Leandro F. 
Published: December 2016

Rotavirus and other double‐stranded RNA viruses confine and protect their genome inside the capsid even after cell entry, hiding viral ds‐RNA from the cellular immune system. Thus, Rotavirus must be able to perform transcription and replication of its packed genome within a virus core formed by viral proteins by using a complex composed by the viral ds‐RNA and the RNA‐dependent RNA polymerase. For transcription, the resulting mRNAs has to exit the virus through channels in the capsid protein shells. For replication, viral mRNAs must enter the newly formed particles to be used by the polymerases as templates for dsRNA synthesis.
The symmetry mismatch between the symmetric capsid and the asymmetric complex formed by the polymerase and the ds‐RNA was used to reconstruct in 3D the interior of the rotavirus capsid showing for the first time how the ds‐RNA is organized and how it interacts with the polymerase.
Rotavirus has eleven different ds‐RNA segments and 11 to 12 polymerases inside each viral particle. Each polymerase is located underneath each one of the 12 icosahedral vertices [ref1].
The 3D reconstruction with icosahedral symmetry imposed obtained from cryo‐EM images of rotavirus was used to calculate synthetic 2D projections which were subtracted from the corresponding experimental images. This allowed the in‐silico isolation of the asymmetric parts of the structure by signal subtraction (Fig.4). The geometrical relationship between symmetric and asymmetric parts is known (assuming stable relative positioning) and it was is used to convert each one of the views associated to the symmetric 3D reconstruction into 12 sets of 5 views corresponding to the isolated asymmetric parts (5 views per icosahedral vertex). These 5 views were tested by projection matching [ref2] against a low‐resoltuion initial model and only the view giving the highest correlation coefficient was used to reconstruct an asymmetric structure by using the sub‐images without imposing symmetry.
3D
Reconstruction of Crack Formation in Austempered Ductile Cast Iron after an In‐situ Tensile Test
Authors: Tesařová Hana , Dluhoš Jiří , Petrenec Martin , Polák Jaroslav , Krahula Karel 
Published: December 2016

A 3D reconstruction has been performed on a flat specimen after an interrupted in‐situ tensile tests. The sample consisted of austempered ductile cast iron (ADI) alloyed with 2.75% nickel. The analysis was performed by using a dual beam system (FIB‐SEM).
The procedure of this analysis consisted in studying the elastic‐plastic behaviour along with the nucleation and the growing of cracks in ADI at room temperature. For this purpose, a field emission scanning electron microscope (FE‐SEM) equipped with a tensile stage was used.
A systematic observation at the same location on the sample surface was used to clarify the tensile curves which are in agreement with deformation mechanisms. During the testing, decohesion of graphite nodules from the matrix was observed. The cracks initiated mainly at the interface of graphite nodule and the austenitic matrix. The elastic‐plastic region is connected with the plastic deformation of the matrix, growth and linking of microscopic cracks which are connected and finally leading to fracture of the sample.
DPC measurements on annealed cobalt thin films
Authors: Beer Thomas , Schwarzhuber Felix , Zweck Josef 
Published: December 2016

In this work we present the results of differential phase contrast (DPC) [1,2] measurements of micro magnetic field distributions in annealed cobalt thin films. The polycrystalline specimens with a thickness of about 50 nm were produced by thermal boat evaporation under high vacuum conditions. After annealing the average size of individual cobalt crystals is increased and their magnetic properties are changed as shown by G. Herzer in [3] and [4]. Our goal was to determine, if DPC is a suitable technique to investigate how these changes in the crystallographic structure effect the magnetic properties of our specimen. Therefore we performed single DPC measurements as well as DPC tilting series to investigate if and how the magnetic behaviour of the annealed cobalt films is changed.
We investigated 5 different samples. One being the untempered thin film and the others were annealed over one hour with increasing temperatures ranging from 520 K to 820 K. To investigate the magnetic properties we performed a DPC tilt series for each sample. By tilting the specimen relative to the magnetic field of the objective lens we change the effective external in plane field on our samples. This leads to a change of the in plane induction in our cobalt thin films. We started each tilting series at large angles of α=20°, to be sure that all magnetic moments in our specimen are aligned in one direction. Figure 1 shows a DPC measurement of such a saturated state. The homogeneous green colour of the measurement confirms that the magnetic induction is saturated along the direction indicated by the colourwheel. Figures 2‐4 show an excerpt of DPC measurements performed during the tilt series of the specimen annealed at 850 K. It can be seen, that the magnetic structure changes with decreasing α and it seems, that one of the magnetic ripples is pinned to the highlighted crystallites in the center of figures 2 and 3.
By calculating the average direction and strength of the beam deflection for each individual DPC measurement we get information about the dependency between the magnetic induction and the tilting angle respectively the external magnetic field applied. We will present the results of our measurements on the different annealed specimen showing hysteretic behaviour of the magnetic induction and discuss the differences between them.
During our experiments especially the tilt series, which take about 4 hours to obtain, we encountered some difficulties with the DPC technique. In this work we will present these shortcomings and show solutions to some of the problems occured.
Crystal growth of bullet‐shaped magnetite in magnetotactic bacteria of the Nitrospirae phylum
Authors: Li Jinhua , Menguy Nicolas , Gatel Christophe , Boureau Victor , Snoeck Etienne , Leroy Eric , Patriarche Gilles 
Published: December 2016

Magnetotactic bacteria (MTB) are known to produce single‐domain magnetite or greigite crystals within intracellular membrane organelles and to navigate along he Earth's magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on the Earth and they represent a fundamental model of intracellular biomineralization. Moreover, the determination of their specific structure and morphology is essential for paleoenvironmental studies. Yet, the mechanisms of MTB biomineralization remain poorly understood, although this process has been extensively studied in several cultured MTB strains in the Proteobacteria phylum. Here, we present a comprehensive TEM study of magnetic and structural properties down to atomic scales on bullet‐shaped magnetites produced by the uncultured strain MYR‐1 belonging to the Nitrospirae phylum, a deeply branching phylogenetic MTB group. HAADF‐STEM imaging and XEDS elemental mapping revealed a phenotypical heterogeneity among MYR‐1 cells, Phenotype III produces numerous sulfur‐rich globules (fig.1a‐c). Electron tomography (ET) demonstrated that the bullet‐shaped magnetosomes are organized into 3–5 bundles of chains (fig.1d,e). Off‐axis Electron Holography results show that each bundle of MYR‐1 chains appears to behave magnetically as a large uniaxial single domain (USD) magnet that maximizes the net magnetic moment of the cell (fig.1f).
We observed a multiple‐step crystal growth of MYR‐1 magnetite: initial growth forming cubo‐octahedral particles (fig.2), subsequent anisotropic growth and a systematic final elongation along [001] direction (fig. 3). During the crystal growth, one major {111} face is developed and preserved at the larger basal end of the crystal (fig. 4.a). The basal {111} face appears to be terminated by a tetrahedral–octahedral‐mixed iron surface, suggesting dimensional advantages for binding protein(s), which may template the crystallization of magnetite (fig. 4b,c). This study offers new insights for understanding magnetite biomineralization within the Nitrospirae phylum.
A
JEOL
‐based cooling holder with a low specimen drift allowing sub 1Å
STEM
imaging
Authors: Bell David , Zandbergen Henny 
Published: December 2016

With the development of aberration corrected microscopy has come the necessity of more stable sample stages, one area that needs further refinement is cryogenic sample system, both for biological imaging and for sensitive materials samples that would benefit from cryo‐stability. The basic principles of the holder are given in Fig. 1. It shows the main components of the cooling holder, the main coldness losses and the measures taken to create a thermal equilibrium, such that the drift is minimized. This allows for drifts of less than 2 nm/min and sub 1 Å resolution. In the cross‐section of the holder, schematically given in Fig. 1, the outside tube contains a heater close to thermal isolator near the tip, such that the temperature of the outside tube can be regulated to the temperature of the goniometer (or any other temperature). This is done to minimize the drift related to thermal expansion and to prevent any cooling (from the tip of the holder) of parts of the goniometer.
The thermal expansion stability is important since the cooling of the goniometer parts can result in unpredictable (slow) changes in the specimen position, for instance in the electron beam direction resulting in a focus change. In case of the temperature difference between the holder and the goniometer, the heat transfer between the outside rod and the goniometer is uncertain because it depends on the mechanical contact (that can vary with tilt) and the effect of the thermal gradient on each of the relevant components in the goniometer. Likewise the “coldness” influx depends on quite a number of parameters, like the size of the beard, how deep it is in the liquid nitrogen, whether the dewar has a “good” cover to isolate and to prevent turbulence. For that reason we have an option of a heater close to the cryo‐beard. Fig. 2 shows the experimental setup of the JEOL ARM, the holder and the dewar.
Our initial tests with the prototype sample holder on a sample of small gold particles on a thin C film show a resolution stability in HRTEM showing sub 1Å information transfer (Fig. 3). This stability is sufficient to operate the holder in STEM HAADF imaging conditions (Fig. 4) which was acquired at 2k resolution with 17.6 us pixel dwell time. Further work needs to be done to increase the operational duty cycle, however the basic configuration of the holder seems to provide a workable solution for high‐resolution cryo‐imaging.
Low Voltage Imaging of Defects in
2D
‐Quantum Materials
Authors: Bell David , VonCube Felix 
Published: December 2016

The discovery of extraordinary new quantum materials with striking properties has caused great excitement, and promises to transform signal processing and computation. We have performed integrated research on three materials (1) Graphene (G) ‐ electrons that move as massless particles at a constant speed; (2) Topological Insulators (TI) ‐ mobile surface electrons with spins fixed to the direction of motion; and (3) Nitrogen‐vacancy (NV) Centers in Diamond ‐ a single spin stores a bit of quantum information. Remarkably, the quantum phenomena displayed by these materials persists at room temperature, changing the rules for signal processing and computation and opening the way for quantum electronics.
Defects in materials effect the propagation of electrons and holes in graphene and topological insulators act in ways that are totally unlike carriers in conventional semiconductors ‐ they move like two‐dimensional (2D) massless, ultra‐relativistic electrons, except their speed is much less than the speed of light. Because there is no bandgap, an electron can pass through a potential barrier by temporarily turning into a hole, dramatically reducing scattering and improving coherence. In addition, for topological insulators the direction of the spin of a surface electron is tied to its direction of motion, providing an ideal means to transport spin information.
We have imaged and characterized high quality graphene‐like materials, such as hexagonal boron nitride (hBN) and hybrid graphene‐hBN structures (Fig. 1). Compared with mechanical exfoliation, CVD synthesis [1‐2] can provide larger areas, with wafer‐scale monolayer or multilayer graphene sheets. Aberration‐corrected electron microscopy has been used to characterize MBE‐grown films with high resolution at low beam voltages (40 & 80kV) to directly visualize structural defects and relate them to performance.
We use a Cs corrected Zeiss Libra TEM to investigate chemical vapor deposition (CVD) graphene with added copper and mercury defects. With TEM we address the question, where the Hg and Co atoms are placed on the graphene. At the same time, we observe the effect of the copper and mercury on the pi electrons in graphene with Raman spectroscopy. Furthermore, we are interested in graphene based hybrid structures, such as graphene oxide embedded in a vanadium pentoxide nanofiber matrix (Fig. 2). The graphene sheets and the nanofibers have approximately the same thickness, leading to a material with enhanced mechanical performance in comparison to pure vanadium pentoxide and pure graphene oxide sheets.
Application of Low‐Voltage Electron Microscopy and its development and future directions will be presented.