bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic scale studies of
La/Sr
ordering in
La2‐2xSr1+2xMn2O7
single crystals
Authors: Roldan Manuel , Oxley Mark , Li Qiang , Gray Kenneth , Mitchell John , Pennycook Stephen , Varela Maria
Published: December 2016

Many fascinating properties of materials depend strongly on the local chemical environment. This is the case for many complex oxides, such as materials with colossal magnetoresistance, where small variations of composition at the atomic scale can affect drastically the macroscopic properties. The main objective of the present work is to analyze the local chemical composition with atomic resolution and to find out if any underlying chemical order is in any way connected to the magnetic properties of double perovskite La

2
‐
2
x

Sr

1+2
x

Mn
2
O
7
(LSMO) manganite oxides. For these compounds, charge and orbital ordering are observed for some doping values near x = 0.50 [1, 2].

For this purpose, we have use aberration corrected scanning transmission electron microscopy (STEM) combined with electron energy‐loss spectroscopy (EELS) measurements and also theoretical simulations. We have compared different compositions within three distinct magnetic regions of the phase diagram: a ferromagnetic metallic sample with x=0.36, an insulating, antiferromagnetic (AF) x=0.56 and an additional AF x=0.50 sample which also exhibits charge ordering.

High angle annular dark‐field (HAADF) images, also known as Z‐contrast, confirm that our single crystals exhibit high crystal quality. No secondary phases or defects are observed. Figure 1 displays an atomic resolution image obtained with the
c
‐axis perpendicular to the electron beam of a x=0.50 sample. The perovskite (P)‐like planes and the rock salt (R)‐like planes are clearly observed, highlighted in green and red, respectively, on the image. The P‐like planes exhibit a slightly high contrast, suggesting a possible La enrichment. EELS atomic resolution maps (inset) support a high degree of La segregation on those planes, while R‐like planes are Sr rich. However, due to dechanneling of the beam, detailed image simulations are essential to accurately quantify the local chemical composition in an atomic column‐by‐atomic column fashion. For all our samples, we find a significant degree of long‐range chemical ordering, which increases in the AF range. However, ordering is not complete and it cannot explain by itself the macroscopic electronic ordering phenomena [3].
The 3‐D organisation of the plant endomembrane system
Authors: Hawes Chris , Kittelmann Maike , Hughes Louise
Published: December 2016

Recent advances in high resolution field emission scanning electron microscopy combined with the ability to section resin blocks within the microscope specimen chamber have revolutionised our ability to study cell structure in three dimensions. Serial Block Face Scanning Electron Microscopy (SBFSEM) permits the collection of large three dimensional data sets from resin embedded material. One of the major limitations of the technique is generating sufficient contrast in the specimen prior to resin embedding to permit sequential collection of relatively high magnification images. We use selective staining of membranes using the zinc iodide/osmium tetroxide impregnation technique to selectively highlight membranes of the secretory pathway. In this way the organisation of nuclear envelope, endoplasmic reticulum and Golgi membranes can be studied through reconstructions of data sets obtained from the Gatan 3‐View system and reconstructed using Amira or Imaris. Here we will describe the use of this technique to investigate the organisation of the endoplasmic reticulum in dividing root meristematic calls and the relationship between Golgi bodies and the tubular endoplasmic reticulum.
Multiphase material sample preparation using broad‐beam Ar ion milling for
EBSD
analyses
Authors: Nowakowski Pawel , Schlenker James , Ray Mary , Fischione Paul
Published: December 2016

When compared to monophase materials, multiphase materials can offer an improvement in properties or introduce new properties. For example, tungsten, carbides, and nitrides do not have many applications as monophase materials; these metals are brittle, which can override their other desirable properties, such as hardness, high temperature stability, and wear. However, when these materials are dispersed in a soft matrix, such as low‐carbon steel, nickel, or cobalt, and form a composite, the multiphase materials are then characterized by desirable mechanical properties, such as ductility, strength, and resistance to creep and fatigue [1,2]. Other types of multiphase materials are protective surface coatings, such as tribological and antioxidation applications, and microelectronics devices [3].

Knowledge of the phases present in the material, their distribution, and their fractions is fundamental to materials characterization. A common investigative approach for engineered materials is electron backscatter diffraction (EBSD) combined with energy dispersive spectroscopy (EDS). EBSD provides information about crystallographic orientations or misorientations and allows the study of grain boundaries, deformation, and recrystallization. EDS can define the chemical composition of the materials. When combined, these techniques permit phase identification with high accuracy [4].

Sample preparation of multiphase materials for EBSD and EDS can be challenging, especially when the different phases have very different characteristics. For example, if one phase is hard and brittle and the second phase is soft and ductile, the rate of material removal during mechanical polishing can vary widely. In addition, the hard particles removed from the first phase can act as a grinding medium and tear the soft matrix of the second phase. The result is a surface inappropriate for EBSD analyses. Electrolytic etching is another sample preparation technique that is not ideal for multiphase materials; it often requires the use of toxic or dangerous chemicals, it can cause differential etching of the sample surface, and it can give the sample surface a varied topography, which will produce a shadowing effect in the EBSD/EDS analysis.

The goal of this work is to illustrate how the use of low energy, broad‐beam argon ion milling can improve and facilitate multiphase material sample preparation. Several examples are discussed, including hard particles within a soft matrix and a multiphase protective layer on a metal substrate.
Topological insulator
Sb2Te3/Bi2Te3
heterostructures: structural properties
Authors: Luysberg Martina , Lanius Martin , Kampmeier Jörn , Weyrich Christian , Kölling Sebastian , Schall Melissa , Schüffelgen Peter , Neumann Elmar , Mussler Gregor , Koenrad Paul M. , Schäpers Thomas , Grützmacher Detlev
Published: December 2016

In a topological insulator (TI) the bulk electronic band structure behaves like an ordinary band insulator. However, at the surface topologically protected surface states occur, which give rise to a spin‐locked, dissipation‐less electronic transport. Hence, topological insulator materials, such as Sb
2
Te
3
or Bi
2
Te
3
, are of great interest for spintronic devices or quantum computing. In order to achieve the dissipation‐less transport, the Fermi level has to be exactly tuned within the Dirac cone like band structure at the surface. To date intrinsic doping by vacancies or antisite defects renders Sb
2
Te
3
and Bi
2
Te
3
p‐ and n‐type, respectively, which results in hole or electron transport in the bulk. Recently we solved this problem by growing p‐n junctions made of Sb
2
Te
3
and Bi
2
Te
3
[1]. In this approach the carrier concentration at the surface is reduced by formation of the space charge layer at the buried heterointerface.

Structure‐wise the X
2
Te
3
(X=Bi, Sb) rhombohedral unit cell consists of three Te‐X‐Te‐X‐Te quintuple layers, which are linked by van der Waals forces. In order to achieve layers of high structural perfection on Si(111) substrates careful control of the growth parameters of the molecular beam epitaxy is required. In particular, we could demonstrate that the suppression of twin domains, which are the most prominent structural defects, is possible by van der Waals epitaxy [2].

Here we report on advanced scanning transmission electron microscopy and energy dispersive X‐ray studies on MBE grown Sb
2
Te
3
/Bi
2
Te
3
heterostructures. Figure 1 displays STEM bright‐field and dark‐field images, where the quintuple layers within the heterostructures and a highly perfect interface to the Si substrate are atomically resolved. The EDX measurement in Figure 2 reveals, that at the heterointerface a Sb and Bi gradient extends over about 4 nm, effectively introducing a ternary compound as interlayer. Corresponding electrical transport measurements demonstrate the tunability of the intrinsic carrier concentration by variation of the thickness of the individual films [3].
Direct estimation of
3D
atom positions of simulated
Au
nanoparticles in
HAADF
STEM
Authors: De Beenhouwer Jan , Lobato Ivan , Van Dyck Dirk , Van Aert Sandra , Sijbers Jan
Published: December 2016

The most commonly used algorithms to reconstruct HAADF STEM data such as Filtered Back Projection (FBP) and iterative reconstruction algorithms such as ART, SART and SIRT assume a linear image formation model. However, the linearity assumption is only a crude approximation of the non‐linear behaviour of the real image formation model. Moreover, the limited angular range results in smearing in the reconstruction along the missing wedge and the typically small amount of projections creates a largely undersampled problem. The reconstruction can therefore be regarded as a limited data problem for which a regular SIRT reconstruction was not designed. One way to solve this problem is to reduce the number of unknowns by adding prior knowledge to the reconstruction algorithm. We present a simulation study for the use of a 3D Gaussian atomic model as a prior in the iterative reconstruction method developed in [1] using the ASTRA toolbox [2]. Our algorithm starts from an initial SIRT reconstruction that typically does not reveal the crystal structure but does agree relatively well with the projection data. In the subsequent iterations of our algorithm we combine this initial reconstruction with a gradually refined estimation – both in image space and projection space – of the 3D atom grid. For a quantitative validation we simulated 26 projection images (pixel size 16 pm) for two Au nanoparticles consisting of 1415 and 6525 atoms respectively with a frozen phonon approach using the MULTEM software [3]. The angular range was limited to 100 degrees, resulting in a large missing wedge and Poisson noise was added to obtain a signal to noise ratio of 10. The average distance between atom positions in the phantom and the reconstruction was found to be less than 6 pm in the direction of the missing wedge for both particles and 3 to 5 pm in the other dimensions for the 1415 atom particle (Fig. 1) and the 6525 atom particle (Fig. 2) respectively, resulting in subpixel accuracy for the recovered atom positions (Fig. 3). The recovery of the 6525 atom positions took approximately 20 minutes.
Direct imaging of hydrogen atomic columns in hydride phases in titanium grade 2
Authors: Daněk Kamil , Gärtnerová Viera , Němec Martin
Published: December 2016

Despite diligent work on titanium hydrides the crystal structures of some titanium hydride phases are still not well established. Transmission electron microscopes (TEMs) can support crystallographic data by direct imaging of unknown structures with superior resolution. Direct imaging of hydrogen atomic columns is extremely challenging due to their weak scattering. However, an introduction of TEMs with corrected spherical aberration has made such experiments feasible. In this work, direct imaging of hydrogen atomic columns in titanium hydrides was performed in order to provide additional support to incomplete crystallographic data for titanium hydrides.

The commercially pure titanium grade 2 annealed at 900 °C for 1 h was examined in this work. Samples for transmission electron microscopy (TEM) were prepared by mechanical grinding of 3 mm discs and subsequent thinning by twin‐jet electropolishing in perchloric acid solution using Struers TenuPol‐5. The titanium grade 2 contains 0.24 at.% of hydrogen, which can create hydride phases. Face‐centered tetragonal γ‐hydride phase was found in a lentil‐like shape in the α‐Ti matrix and in a shape of long thin lamellae at either the α‐Ti matrix/β‐Ti phase interface or originating at α‐Ti matrix grain boundaries. This phase introduces hydrogen‐induced diffracted reflections that do not coincide with the diffracted reflections coming from Ti atoms. For that reason, the presence of the hydrogen can be observed even using the selected area electron diffraction (SAED) technique. The hydrogen‐induced reflections translate also to a phase‐contrast pattern (PCP). Compared to the titanium columns, the hydrogen columns produce much broader peaks/dips that enable us to differentiate between the positions filled with hydrogen and the vacant columns in the structure.

Annular bright‐field scanning transmission electron microscopy (ABF‐STEM) and high resolution transmission electron microscopy (HRTEM) techniques were employed. As both techniques rely on phase‐contrast imaging, they can produce imaging artifacts that can be easily mistaken for genuine structural features caused by the presence of the hydrogen. To increase robustness of our results we support them with simulations based on theoretical models of the hydrides. Multislice method was used to simulate the dynamic scattering effects. This helped us to find optimal imaging conditions with regard to resolution, maximal contrast for the hydrogen positions and the absence of imaging artifacts for a wide range of thickness and defocus values.
Quantification of the
HAADF
contrast from the nanometer scale down to the single atomic column: application to quantum cascade lasers
Authors: Pantzas Konstantinos , Patriarche Gilles , Largeau Ludovic , Amanti Maria , Vasanelli Angela , Sirtori Carlo , Beaudoin Grégoire , Sagnes Isabelle
Published: December 2016

The emission wavelength of quantum cascade lasers can potentially be continuously tuned from the short (2µm) to the long (15µm) infrared, making them an ideal candidate for infrared emitters in a region where materials with the appropriate gap are scarce. The challenge with QCLs lies in the complexity of the epitaxial structure. Indeed, in a typical InGaAs/InAlAs/InP structure the active region is often comprised of thirty stages, each stage containing an alternation of twenty or more InGaAs wells and InAlAs barriers, the thicknesses of which range between 7 and 40 Angstrom. Properly optimizing the epitaxial process therefore requires feedback on the thickness and, most importantly, the composition of each individual well and barrier in the layer, as even small deviations can make or break the end device. Currently, even in the most advanced transmission electron microscopes, equipped with state of the art EDX systems it is not possible to obtain quantitative information on the composition of layers that are thinner than 15 Angstrom. Quantifying the chemical information in the Z‐Contrast of HAADF images [1] therefore provides the only solution to obtain the kind of quantitative feedback required for QCLs. The present paper discusses how to obtain such chemical mappings in InGaAs/InAlAs QCLs by combining HAADF‐STEM, EDX and also X‐ray Diffraction and how the information collected from these mappings is used to optimize the QCL structure [2]. The paper also discusses how this information is fed to numerical models to model the performance of the end device and optimize the QCL design. Finally, the paper forays into the quantification of the contrast of single atomic columns, ultimate step in the analysis.
Impact of water and oxidation states in the galvanic replacement formation of hollow oxide nanoparticles
Authors: Besa Pau Torruella , López‐Ortega Alberto , Roca Alejandro , Petrecca Michelle , Estradé Sónia , Peiró Francesca , Puntes Victor , Nogués Josep
Published: December 2016

Metal‐oxide hollow nanoparticles are appealing structures from the applied and fundamental viewpoints. The synthesis of bi‐phase metal‐oxide hollow nanoparticles has been reported based on galvanic replacement using an organic‐based seeded‐growth approach, but with the presence of H2O. Here we report on a novel route to synthesize hollow core‐shell MnOx/FeOx nanoparticles by galvanic replacement without the use of H2O. We demonstrate that the role of H2O in the MnOx/FeOx galvanic replacement synthesis is to oxidize the MnO/Mn3O4 seeds into pure Mn3O4 in order to obtain the suitable oxidation state so that the Mn3+→Mn2+ reduction by the Fe2+ ions can occur. Thus, if no H2O is added, onion‐like MnO/Mn3O4/Fe3O4 nanoparticles are obtained, while whenMn3O4 seeds are used, hollow core‐shell MnOx/FeOx are achieved. Thus, a critical step for galvanic replacement is the existence of proper oxidation states in the seeds so that the chemical reduction by the shell ions is thermodynamically favoured.
Imaging by Zernike phase plates in the
TEM
Authors: Edgcombe Chris
Published: December 2016

Abbe lens theory can be used to calculate the images produced by a system made up of a simple phase object, a round lens and a Zernike phase plate. When all these have rotational symmetry, 1D Fourier‐Bessel transforms are suitable.

Given a disc object producing a uniform phase shift over its diameter and a phase plate providing a simple step in phase by α at a defined spatial frequency q
0
, the resulting image intensity can be defined for any size of object phase change. The distortion of the image by the central hole in the Zernike plate depends on a parameter B which is proportional to the product of the diameter of the object and q
0
and also depends on the lens focal length; when B is less than 1, the distortion is small (Fig. 1). The range of object phase that produces a monotonic variation of intensity is found to depend strongly on the phase change α introduced by the phase plate, being greatest when α is between π and 2π (Fig. 2).

For this object and plate, the weak phase approximation (WPA) is useful in giving an indication of the radial distribution of intensity. It does not predict well the range of monotonic variation of intensity with object phase.

In the search to reduce the ‘ringing’ in the image produced by large objects with a stepped plate, we analysed also the behaviour when the phase change at the plate increases to its maximum value α over a range of radius (instead of a step). When the phase change is proportional to radius for q < q
0
, we find that as object diameter increases, the intensity is reduced gracefully when α ∼ π/2, but that contrast reversal can occur when α ∼ 3π/2.

The intensity has also been calculated in WPA for an object phase distribution typical of a spherical object. With this object, the image intensity varies continuously with object radius, as expected, and is reduced as B increases above 1. The behaviour when the phase profile of the plate is ramped is similar to that for the disc object with the same phase profile for the plate (Fig. 3).

The advantages for different kinds of objects offered by plates with phase shifts α either less than or greater than π suggest that in practical use it will be desirable for phase plate holders to be fitted with plates of both thicknesses.
Size and orientation effects on the mechanical response of a
Ni‐Ti‐Al‐Nb‐Hf
alloy
Authors: Ding Rengen , Zheng Lijing , Chiu Yulung
Published: December 2016

NiTi‐Al based alloy is considered as a potential high temperature structural material [1]. The addition of Nb is able to improve the oxidation resistance of NiTi‐Al based alloys at ~ 800°C [2] and also their strengths at room and elevated temperatures [3]. A Ni‐43Ti‐4Al‐2Nb‐2Hf alloy has been demonstrated to be a promising lightweight high‐temperature structural material [4]. It is thus of significance to understand the effect of crystal orientations on its mechanical behaviours. In the past, mechanical testing of single crystal metals was performed on large crystal. However, the preparation of single crystals of this class of alloys is very difficult. Meanwhile, understanding material behaviour with decreasing sample size is necessary for exploring the potential application in nano‐technologies. In this study, electron backscattered diffraction (EBSD) was used to identify the grain orientations (e.g. close to [001], [011] and [111] directions) of a directional solidified Ni‐43Ti‐4Al‐2Nb‐2Hf alloy. Pillars with diameters ranged of 0.5 mm ~ 4 mm were machined using a focussed ion beam (FIB) microscope. Compression tests were performed using a Hysitron PI85 picoindenter. Specimens for transmission electron microscopy (TEM) were prepared along longitudinal direction of the pillars by FIB, and then examined in an FEI Tecnai F20 microscope.

The results show that its strength depends on the crystal orientations and the size of pillars (Fig. 1). The pillars were plastically deformed via dislocation gliding (Fig. 2) and twinning.
Structural evolution of
Pt/CNF
nanocomposites as a part of fuel cell's gas‐diffusion electrodes
Authors: Zhigalina Victoria , Zhigalina Olga , Ponomarev Igor , Ponomarev Ivan , Razorenov Dmitriy , Skupov Kirill
Published: December 2016

A search of new nanostructural materials (such as gas‐diffusion layers, electrodes, catalysts, membranes etc.) for a polybenzimidazole‐membrane fuel cell remains a crucial task nowadays. Reducing of noble metals content has become one of the most significant goals in development of fuel cells while a balanced union of electron and ion conductivity along with gas permeability and catalytic activity of electrodes serves as an essential condition of the hydrogen‐air fuel cell efficiency [1].

In this study carbon nanocomposites of nanofiber nonwoven mats, produced by electrospinning and decorated with Pt, after work inside membrane electrode assembly as gas‐diffusion cathode at 160‐180 °C were investigated by analytical TEM and STEM methods [2].

Initially a nanofiber surface is evenly covered with a thick layer of Pt nanoparticles of anisotropic elongated shape with a number of sub angstrom atomic steps on their surface (
Fig. 1a
). This type of defects plays an important part in platinum catalytic activity [2,3].

The investigations of such a nanocomposite after work as a gas‐diffusion cathode in a fuel cell revealed significant changes in the structure of the platinum layer. After several hours of work at a standard fuel cell working temperature (160 °C) the structure of metal nanoparticles changes slightly (
Fig. 1b
). Metal nanoparticles preserve their shape elongated in direction and specific distribution on fibers surface same as in initial nanocomposites. However, in this case platinum is covered with a thin amorphous layer. Some of the platinum nanocrystals demonstrate the signs of partial melting and a loss of initial acicular shape as well as the decrease of surface defects.

After several days of work at standard and high fuel cell working temperature (160‐180 °C) the structure of catalyst changes considerably (
Fig. 1c
) and can be observed as melted conglomerates of unspecified shape and size of 40‐100 microns (
Fig. 2
) with a cover of thin (5‐10 nm) amorphous layer.
Cryo‐Electron Tomography of Protein Nanocrystals
Authors: Toots Maert , Skoglund Ulf
Published: December 2016

Knowing the structure of biological molecules plays a key role in understanding their function. To date there is no single structure determination method that would always work for every biological molecule. Instead there exists a plethora of complementary methods each with their specific advantages and disadvantages. Small but difficult to crystallize proteins have proven to be a particularly hard target for many of the conventional methods. However, proteins that do not crystallize to large well‐diffracting crystals, could still form tiny nanocrystals in many cases, which could be completely invisible under regular light microscope or mistaken for amorphous precipitate when inspecting a crystallization drop.

Using cryo‐electron tomography we demonstrate in this work that real space imaging can be successfully used for structural studies of proteins that have been crystallized to nanocrystals. In this proof of principle research we have used cryo‐electron tomography to image lysozyme (molecular weight 14 kDa) nanocrystals in the size range of 100 nm. We show that by exploiting crystallographic symmetry inherent in the tomogram and taking advantage of other possibilities provided by real space imaging we can achieve resolution in the range of 15Å.

To achieve this result we have used in‐house software for 3D reconstruction and subsequent refinement of the reconstruction using maximum entropy regularization algorithm together with contrast transfer function deconvolution. For processing crystalline data we have developed a toolkit for necessary 3D image processing tasks, such as peak detection, crystallographic lattice parameter search and refinement, and 3D image averaging and space group symmetrization.

Nano‐crystal tomography could become an established method in structural biology complementing the existing methods by firstly being applicable on small and difficult to crystallize proteins, but secondly on any general 3D reconstruction that includes crystallographically related parts. On top of studying one single averaged molecule, this method can also be used to analyze the nano‐crystal as a whole and study the distribution of disorder within the crystal.
Monitoring of Dynamic Live Brain Tumor Cells using
SICM
and its Future Applications
Authors: Myung‐Hoon Choi , Goo‐Eun Jung , Cho Yong‐Sung , Cho Sang‐Joon
Published: December 2016

The high resolution monitoring of live cell membranes in physiological conditions has been the homework for centuries for biologists. Visualization and Understanding of cell membrane activities could give precious insight upon how cells interact with outer environment. Scanning ion conductance microscopy (SICM) can provide the surface morphology of biological soft materials in liquid directly. The SICM uses ionic current as feedback signal by detecting it through the nano‐size opening of glass pipette. The dedicated SICM operating mode called approach and retract scanning (ARS) makes SICM imaging stable in liquid environment. The SICM three‐dimensional topographical image is generated by composing the recorded height information at each pixels. The in‐liquid imaging capability without physical contact allows using SICM for various cell study topics in live status such as cell division, fusion, and other fundamental physiological phenomena.

In this study, we examined cell‐to‐cell interaction and cell's plasma membrane transformation. By imaging live brain tumor cell with SICM at the connective position between two cells, we successfully acquired the interactive morphological changes of cell's adhesion molecule at the edge in sequence. From the series of non‐invasive cell morphological images, acquired in three dimension, we also calculated and monitored the velocity of membrane transformation and membrane holes volume changes.
Electron beam‐induced etching of carbon nanotubes by environmental transmission electron microscope
Authors: Tomita Yuto , Yoshida Hideto , Takeda Seiji
Published: December 2016

It is crucially needed to develop a novel process to cut and connect nanomaterials artificially for further progress in nanotechnology. Gas‐mediated electron beam‐induced etching (EBIE) is promising to carve nanomaterials via electron beam‐induced chemical reactions between the nanomaterials and precursor gases. In this study, we have investigated the EBIE process of multi‐walled carbon nanotubes (CNTs) in oxygen gas using environmental transmission electron microscopy (ETEM).

Commercially available multi‐walled CNTs (NanoIntegris Inc.) were supported on a Cu micro grid with a carbon supporting film of 3 mm in diameter. A grid with multi‐walled CNTs was fixed on a specimen holder and transferred to an ETEM (FEI Tecnai F20 equipped with an environmental‐cell [1]) operated at 200 kV. As a precursor gas for EBIE, oxygen gas (99.9999%) was introduced into the ETEM. To carry out the EBIE of multi‐walled CNTs, a focused electron beam (about 0.2 nm in diameter) was repeatedly scanned across multi‐walled CNTs in oxygen gas of 100 Pa at room temperature in scanning TEM (STEM) mode.

Figure 1 shows the EBIE process of a multi‐walled CNT in oxygen gas. A focused electron beam was scanned repeatedly along a white dotted line in Fig. 1(a) with the rate of 103 s
−1
. STEM images and TEM images of the multi‐walled CNT were recorded after every 62 scans. The electron dose was estimated and shown in each image in Fig. 1. As the electron dose increases, the multi‐walled CNT is etched gradually. Figures 1(b), 1(c), 1(f), and 1(g) clearly show that the etching proceeds from the outer walls to inner walls of the multi‐walled CNT. Finally, the multi‐walled CNT is cut completely along the scanning direction (Fig. 1(d), (h)). The cutting surface remains cylindrical. We confirmed that the areas that do not receive electron dose are not etched. On the other hand, multi‐walled CNTs cannot be cut in a vacuum even after receiving the electron dose much higher to cut in oxygen gas. The scanning areas in multi‐walled CNTs are amorphized. This means that both electron irradiation and oxygen gas are needed for EBIE of multi‐walled CNTs. Oxygen atoms from dissociation of oxygen molecules by electron irradiation [2] react with carbon atoms in multi‐walled CNTs to produce CO and/or CO
2
which desorb from the surface of multi‐walled CNTs. We have succeeded in cutting of multi‐walled CNTs at desired positions at room temperature by EBIE in ETEM.

In the presentation, we will show the dependence of EBIE of multi‐walled CNTs on the pressure of oxygen gas, accelerating voltage of electrons, and gas species. The mechanism of EBIE of multi‐walled CNTs will be discussed.
Diamond‐based
MOSFET
s
: Bandgap interface profiling by
STEM
‐
EELS
Authors: Piñero José , Araújo Daniel , Villar Pilar , Pernot Julien
Published: December 2016

In the view of developing high performance metal‐oxide‐diamond field effect transistor (diamond MOSFET), recent reports presents different approach in the choice of the gate material and, in particular, on the dielectric layer [1‐2]. However, a nanometric analysis of the band levels is necessary to understand the electron dynamic across the MOS stack. Recently, STEM‐EELS have been revealed as reliable technique to estimate the bandgap of SiO
2
dielectric materials. Nevertheless, its applicability has been limited to SiN
x
materials.

To evaluate electron transitions near the bandgap energy in the EELS spectra, researchers have to overcome several experimental difficulties. Here, we evaluate the effect of Čerenkov radiation and volume plasmon‐related peaks in low‐loss range of EELS spectra. In this study, STEM‐EELS techniques are used to analyse the O‐terminated diamond/Al
2
O
3
interface (similarly to previous studies presented in SiO
2
by other authors [3]). Indeed, volume plasmons (VP) and Čerenkov (Ch) radiation contribution are evidenced in Fig.1, which also shows diamond‐related D1‐2 peaks and Al
2
O
3
‐related peak A1 however, in the Al layer, only plasmon‐related peaks are revealed. Probe position of the previously presented EELS spectra are shown in Fig.2, as numbered dots. Figure 2 shows 001‐BF TEM micrography of the diamond/Al
2
O
3
/Al layers. Inset of Fig.2 shows HREM micrography of the diamond/Al
2
O
3
interface, revealing variations in the crystalline quality of the low temperature (100ºC) ALD‐deposited Al
2
O
3
layer.

In this work, we present a methodology to evaluate the influence of the Čerenkov losses and plasmon‐related peaks in the low‐loss EELS spectra. In some cases, such peaks are shown to mask the interband‐related transition. Indeed, in such cases, Čerenkov‐related and plasmon‐related peaks have to be deconvoluted and removed, in order to accurately apply the linear‐fit method [3], which allows calculating the diamond/oxide bandgaps.

The previously described methodology allows determining the bandgap variations in the oxygen‐terminated diamond/oxide interfaces.
Optimisation of the
FIB
induced damage in
TEM
diamond samples
Authors: Rubanov Sergey
Published: December 2016

Due to diamond extreme properties, it is very hard to prepare a TEM sample from diamond using traditional methods of preparation including mechanical thinning, ion milling or chemical etching. At the same time diamond can be relatively easily micro‐machined using focused ion beam (FIB) technique. Using this technique a cross‐sectional TEM sample of diamond can be prepared in a few hours. Also, combination of ion implantation and FIB milling allows device fabrication in diamond at micro and nano scales levels. In the last decade FIB milling became essential tool for TEM sample preparation as well as for nanofabrication in diamond. However, Ga FIB milling has an unavoidable result in formation of the damage layers which can significantly reduce the device working areas and limit the applications of the FIB technique for nanofabrication of diamond. The damage layers in the FIB prepared TEM diamond samples can also significantly aggravate the quality of high‐resolution imaging. So, the knowledge of the extent of damage induced in diamond during FIB milling is critical for nanofabrication as well as for TEM imaging. In this work the damage layers after FIB milling of the synthetic single crystal diamond at different ion beam energies were studied using high‐resolution and analytical electron microscopy.

TEM image of cross‐section of TEM lamella prepared using 30 keV Ga FIB milling is shown in Fig. 1. Amorphous layer with thickness ~ 16 nm are clearly visible on both sides of TEM lamella. EELS measurements of the carbon K‐edge in the amorphous region shows a prominent feature at 285eV, the p
*
peak associated with the presence of sp
2
bonding. This indicates the conversion of diamond sp
3
bonds to sp
2
in the amorphous damage area. Electron energy loss spectrum image was taken in STEM mode from central part of cross‐section of TEM lamella shown in Fig.1. Using Gatan Digital Micrograph software the chemical maps for sp
2
and sp
3
bonded carbon were obtained. Fig.2 shows maps for features of carbon K‐edge at 285 eV (sp
2
) and 290 eV (sp
3
bonding). It is visible from Fig. 1, 2 that TEM lamella prepared from diamond using 30 keV FIB milling contained ~ 20 % of amorphous sp
2
bonded carbon. In case of thinner lamellas (60 nm) prepared using 30 keV FIB milling the fraction of amorphous sp
2
bonded carbon increases to ~50%.

The thickness of damage layers with sp
2
bonded carbon in TEM diamond samples can be reduced by using low voltage FIB milling. Fig.3 and Fig. 4 show the HREM images of damage layers in diamond after 30 keV and 2 keV FIB milling. The thickness of amorphous damage layers reduced from 16 to less than 2 nm. Thus, very thin TEM diamond samples with low fraction of amorphous sp
2
bonded carbon could be prepared by using 2 keV FIB milling at final stage of TEM lamella preparation.
Analytical
STEM
study of sintered polycrystalline c‐
BN
materials for cutting tool applications
Authors: Palmer Jacob , Lattemann Martina , Coronel Ernesto , Meingast Arno , Dues Larry , Shao Rachel , Weinl Gerold
Published: December 2016

Cubic boron nitride (c‐BN) is the second hardest material next to diamond with high thermal conductivity but better chemical stability than diamond, therefore, it is widely used in the form of sintered polycrystalline cubic boron nitride (PCBN) for cutting tools in machining of hardened steel, cast irons and super alloys showing high chemical stability when abraded by ferrous materials at high temperature. Commercial PCBN cutting tools are classified into two types, firstly low c‐BN content composites containing typically 40 ‐70 vol% c‐BN with ceramic binders such as TiN and TiC, and secondly high c‐BN content PCBN containing about 75–95 vol% of c‐BN with Al and other metallic binders in addition. PCBN materials designed for mild to medium interrupted hard part turning (HPT) applications have been produced by using different raw materials and sintering conditions. These PCBN materials have been investigated by SEM and XRD for microstructure and phase information and XRF for the overall chemical composition. It was observed that, for some of the PCBN material, there was a discrepancy between the elements detected as well as their measured quantity by XRF and the phases identified by XRD. Advanced analytical STEM was applied for an in depth characterization of the complex microstructures formed in those PCBN materials with grain size ranging from sub‐micrometer down to a few nanometers. The aim of this study was to increase the understanding of the relationship between raw material selection, processing conditions, and machining performance. The raw material selection, milling and sintering operations play a crucial role in the solid state phase diffusion processes which governs what phases are formed and how these constituents bond to each other and, thus, the mechanical behaviour. To be able to capture the light and heavy elements present in the microstructure, elemental maps were acquired in a C
S
corrected Titan
3
60‐300 kV (FEI Company) equipped with ChemiSTEM and DualEELS capabilities. Figure 1 depicts elemental maps of two PCBN materials produced by different methods of Al processing showing greatly differing microstructures. In Fig. 1a, the Al appears to have flowed well and coated the c‐BN interphases forming a continuous binder phase, mainly consisting of AlN. It appears that almost all of the AlN phase is connected to c‐BN. Whereas in Fig. 1b, the Al phases are much less continuous, but still coat most of the c‐BN. Most of the Al appears to be in discrete aluminium oxide phase. To be able to determine all reaction products and phases present advanced TEM and STEM techniques had to be applied due to the small and overlapping grains. The results presented are of importance to further improve machining performance by tailoring the microstructure by carefully selecting the initial raw material and processing conditions.
Quantitative and non‐destructive defect metrology for beyond Si semiconductors
Authors: Prokhodtseva Anna , Vystavel Tomas , Schulze Andreas , Caymax Matty
Published: December 2016

Electron channeling contrast imaging (ECCI) is a powerful scanning electron microscopy (SEM) technique for the visualization and analysis of crystalline defects like dislocations and stacking faults. Distortion of the crystal lattice of a material due to the presence of such defects causes the variation of the backscattered electron intensity, allowing their visualization. ECCI has been demonstrated to be a fast and robust method for assessing the density and Burgers vector of different defect types in various materials with reliability comparable to that of transmission electron microscopy [1, 2]. However, in contrast to TEM, ECCI can be used for the non‐destructive investigation of large areas.

This fact makes the technique particularly interesting for the semiconductor industry, where defect metrology techniques for the non‐destructive analysis of (Si)Ge and III/V compounds with dislocation densities below 10
5
cm
‐2
, are crucial to support CMOS scaling beyond the 10nm node.

In order to analyze such lowly defective samples, areas exceeding about 200 x 200µm
2
in size need to be examined to ensure proper statistics. For this purpose we acquire a set of tiles that can be stitched into a single image, thereby leading to an image resolution allowing for the detection of single threading dislocations. The FEI software application MAPS, dedicated to the automated acquisition of high resolution images from large areas, is used to record a set of ECC images that are further processed and examined for the presence of defects. It is important to note that for proper ECC imaging (i.e. maximum channeling contrast at a defect site), the sample needs to be oriented close to the Bragg condition. This is facilitated by tilting and rotating the sample according to the electron channeling pattern (Fig. 1) acquired by scanning the sample at low magnification. The investigated area of the tilted specimen is maintained in focus during the acquisition through the interpolation of the settings. Imaging conditions such as accelerating voltage and beam current were fine‐tuned in advance using a sample with higher defect density (Fig. 2). A retractable below‐the‐lens backscatter electron (BSE) detector is used to record the individual ECC images.

Using the above described procedure we analyzed in detail the density and distribution of threading dislocations in blanket SiGe layers of different defect densities. Our results reveal that in case of dedicated strain relaxed buffer layers the surface appears basically defect free over several tens of micrometers, only locally one can observe individual defects and pile‐ups of threadings reaching the layer surface. Results are verified by defect decoration using chemical etching followed by optical etch pit detection.

Our work demonstrates that ECCI in combination with automated image acquisition provides quantitative information on defect density and distribution on systems foreseen for future semiconductor devices.
Correlative microscopy on animal and vegetal samples with In Resin Fluorescence approach
Authors: Petrel Melina , Chambaud Clément , Cordelières Fabrice , Petersen Jennifer , Gontier Etienne , Brocard Lysiane
Published: December 2016

Understanding the biological role of molecules requires to know their precise localization and structural environment. Thanks to fluorescence microscopy and biotechnologies, the localization of proteins of interest has become relatively easy. But in more and more cases, this resolution is not enough and the lack of data on the molecule/cell environment does not allow the characterization of their biological function. Transmission Electron Microscopy (TEM) and immuno‐gold labelling can be used to characterize at the same time the cellular compartments associated with the protein of interest and the ultrastructure of the cellular environment at a high resolution. However, the antigenicity preservation as well as the antibody production are sometimes difficult. Moreover, TEM observations only give access to a static “snapshot” of a fixed, dead sample. For several years, many attempts have been made to correlate Fluorescent and Electron Microscopy in order to combine the advantages of both microscopy techniques on a unique sample. In this way, we develop on the BIC new protocols of sample preparation for animal and vegetal sample (culture cells and tissues), allowing to maintain simultaneously the fluorescence and the overall ultrastructure (Figure 1 and 2), using Quick Freeze Substitution (McDonald KL and Webb RI, J. Microsc, 2011). This technique will allow the correlation of both Light and Electron Microscopy data on the same section (CLEM: Correlative Light Electron Microscopy), works with classical fluorescent tags and improve the antigenicity for gold immunolabelling.
Non‐rigid image registration of low‐dose image series of zeolite materials
Authors: Huang Chen , Berkels Benjamin , Kirkland Angus
Published: December 2016

Zeolites are an important group of materials with a wide range of application in the catalysis industry. Many structural studies of zeolites rely on high resolution electron microscope imaging [1]. However, due to their high sensitivity to electron irradiation, zeolites deteriorate quickly under exposure to the electron beam. Low‐dose imaging techniques use a reduced electron flux to slow the crystal degradation process, which gives more time for adjustment of the microscope configuration and better control over the progression of damage. However the disadvantage of low‐dose imaging is poor signal to noise ratio which is often alleviated by averaging multiple image frames in a time series for improved image quality. Traditional rigid cross‐correlation function (XCF) image registration methods work well for aligning high‐dose time series of radiation‐robust materials which experience little or no deformation during image acquisition. However, the deformation in radiation‐sensitive materials, often manifest by sample shrinkage, means that the single translational shift vector from rigid image registration may not be sufficient for aligning time series and hence a non‐rigid registration scheme is needed.

In this work, a low‐dose time series of ZSM‐5 zeolite consisting 60 image frames were recorded using an aberration‐corrected JEOL2200MCO TEM (Figure 1). Two registration methods, a rigid XCF registration and a new non‐rigid registration, were used to align the series respectively. The non‐rigid registration method [2] is assisted by an IQ factor criterion, which evaluates the quality of the averaged image of the series as the registration proceeds and selects the best averaged image as the reference for future registration iterations.

The results show that the new non‐rigid registration is helpful for alignment of low‐dose TEM image series of radiation‐sensitive materials that experience deformation during imaging, especially when the number of frames is small and when the sample is already damaged (Figure 2). This implies that, for TEM image series, the non‐rigid registration approach is more effective in noise suppression and in avoiding the image components of a damaged sample compromising the final averaged image.

For further comparison, a low‐dose STEM time series of zeolite Y, was registered by both rigid and non‐rigid methods. A comparative analysis of IQ factor was carried out on the averaged images and showed that the non‐rigid registration consistently outperforms the rigid XCF registration (Figure 3). The reason for this advantage is attributed to the fact that the STEM images often suffer from additional scan noise due to the pixel‐by‐pixel acquisition in STEM imaging.
SI
ev: Implementation of an anisotropic binning strategy to optimize the chemical analysis of heterogeneous interfaces
Authors: Afonso Carlos F. , Carbó‐Argibay Enrique , Claro Marcel S. , Stroppa Daniel G.
Published: December 2016

Outstanding properties emerge at the interfaces of heterogeneous materials, so that their engineering offers promising prospects for achieving novel functional structures. The design and realization of highly‐controlled interfaces require reliable characterization techniques with high spatial resolution and chemical sensitivity, and X‐rays Energy Dispersive Spectroscopy Spectrum Imaging (XEDS‐SI) has been used qualitatively for this purpose with ample success. However, the extraction of quantitative features from XEDS‐SI by the overall signal integration around the X‐rays peaks location tends to be inaccurate for high spatial resolution analysis due to their typically reduced signal to noise ratio.

This work presents a strategy for an improved and quantitative chemical analysis at the interface of heterostructures based on the processing of XEDS‐SI datasets obtained by aberration‐corrected Scanning Transmission Electron Microscopy (STEM). The successive XEDS‐SI dataset breakdown with decreasing binning sizes is implemented in the SIev software tool, and its application results in the improved detection of X‐rays peaks and estimation of local noise levels. This approach supports the actual chemical signal extraction from XEDS‐SI with the maximum spatial resolution with respect to signal to noise ratio (SNR) significance limit.

Results of anisotropic XEDS‐SI dataset breakdown obtained with aid of SIev software indicate that sub‐nm precision, considering a 2σ confidence level, can be routinely attained on the determination of a projected intermixing layer at the interface of heterogeneous materials. Given that the SIev data processing is significantly faster than a high‐SNR XEDS‐SI dataset acquisition by the use of currently available high efficiency X‐rays detectors, the perspective of an accurate and real‐time profile across the interfaces of heterogeneous materials via chemical mapping is foreseen.