bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural investigation of
Fe‐Mn‐B‐Nb
glassy ribbons
Authors: Whitmore Lawrence , Ababei Gabriel , Budeanu Luiza , Lupu Nicoleta , Chiriac Horia
Published: December 2016

The microstructure of Fe
79.7‐x
Mn
x
B
20
Nb
0.3
glassy ribbons has been investigated using transmission electron microscopy (TEM) and energy dispersive X‐ray spectroscopy (EDX), for manganese concentrations of x=12, 16 and 20. For each manganese concentration the ribbon is found to consist of nanocrystalline inclusions in an amorphous matrix. Through detailed analysis of electron diffraction patterns and in conjunction with JEMS simulation, the crystalline phase is shown to be manganese diboride (MnB
2
), and high resolution TEM investigation confirms this. Using dark‐field TEM, the mean size of the nanocrystalline inclusions as well as their phase fraction are measured and found to increase with manganese concentration. EDX mapping shows the tendency for manganese to form nano‐scale clusters in agreement with the dark‐field investigation.

This research was supported by the European Commission FP7‐REGPOT‐2012‐2013‐1, Grant Agreement no. 316194 NANOSENS.
Picometre‐precision atomic structure of inversion domain boundaries in
GaN
Authors: Haas Benedikt , McLeod Robert A. , Auzelle Thomas , Daudin Bruno , Eymery Joël , Lançon Frédéric , Zuo Jian‐Min , Rouvière Jean‐Luc
Published: December 2016

Here, we report on the precise analysis of the atomic structure of inversion domain boundaries (IDBs) in GaN by scanning transmission electron microscopy. IDBs are a common defect in GaN that traps carriers and leads to a slightly modified luminescence wavelength [1,2].

Our analysis of IDBs in MOCVD grown nanowires confirms recent coherent Bragg imaging (CBI) results [3] stating that the atomic structure of this IDB is different or slightly different from the one determined in 1996 by first‐principle calculations (IDB*) [4]. CBI experiments measured a 8 pm shift of the c‐planes of the two domains [3], whereas first‐principle calculations predicted no shift. A previous study by STEM [5] found a shift of “ca. 0.6 Å” (60pm), corresponding roughly to the switch of the Ga and N positions without any additional shift. Here in addition to a shift along c, we show that the interface configuration corresponds qualitatively to the IDB* model (cf. Fig. 1) and that there is a 10 pm dilatation perpendicular to the interface (shown in Fig. 3) in agreement with this model, while CBI did not find a dilatation.

To facilitate the measurement of atom positions across the IDB with picometre‐precision, we use HAADF‐STEM to avoid coherent effects leading to artefacts. Scanning and drift artefacts are being suppressed by acquiring series of rapid STEM images and aligning them using the newly developed Zorro code. This algorithm is based on calculating estimated drift positions by correlating every frame to multiple frames and minimizing the error of the overdetermined system to obtain a best estimate for the frame positions relative to each other. The sub‐pixel aligned frames are then averaged and the peak positions are determined via TeMA (template‐matching algorithm).

Our quantitative analysis of experimental and simulated STEM images shows that when atomic columns are very close to each other the measured distance can be slightly different from the real value. For instance, when the distance between atomic columns becomes smaller than 0.1 nm, the difference between the measured and real values can account for several picometres. This effect can be well observed when an IDB kinks perpendicular to the observation direction leading to closely projected columns in the overlap region of the two domains as seen in Fig. 2. Electron scattering simulations show that the apparently wider distance between atoms is a channeling effect.

These results have provided elements to revisit previous theoretical models of IDBs in GaN.
Dispersion, dose and stability of semiconductor quantum dot biomarkers
Authors: Brown Andy , Harvie Andrew , Critchley Kevin , Chantry Ruth , Kepaptsoglou Demie , Ramasse Quentin , Rees Paul , Brown M Rowan , Summers Huw , Brydson Rik , Hondow Nicole
Published: December 2016

Photoluminescent semiconductor nanoparticles or quantum dots have significant potential for medical imaging. For optimum performance however, the dispersion of the nanoparticulate material when suspended in delivery or incubation media, any transformation of the particles in the media, plus the nature and degree of uptake of the nanoparticles by a particular cell or organism all need to be understood. Analytical electron microscopy can play a vital role in assessing this complex inter‐relationship, and we discuss here specific methods developed for this type of analysis.

First, we will review the in vitro cellular uptake of commercially available CdSe/ZnS quantum dot nanoparticles with a coating specifically targeted for endocytic uptake (Invitrogen QTracker 705), dispersed in cell culture media and exposed to human osteosarcoma (U‐2 OS) cells. We have examined these nanoparticles as‐dispersed in cell culture media (t = 0 h), after 1 hour exposure to cells and after a round of cell division (t = 24 h). Transmission electron microscopy (TEM) has been used to assess the dispersion state of the nanoparticles in media after rapidly freezing suspensions to avoid drying artefacts [1], and in exposed cells which have been fixed and resin embedded [2]. The resin‐embedded cells have been further examined using serial block face scanning electron microscopy (SBF‐SEM), which enables quantification of nanoparticle loaded organelles in whole cell volumes for quantitative correlation to imaging flow cell cytometry [2]. From this we have measured probability densities for the number of quantum dots per agglomerate when in cell culture media and following uptake by cells in vitro [3, 4 and Figure 1 a‐d]. Thus, we will discuss the agglomeration processes that occur both in suspension and during endocytosis.

Second and looking forward, most commercially available semiconductor quantum dots currently contain cadmium although its health and environmental risks may limit exploitation. Thus, copper indium sulfide (CIS) quantum dots have been investigated as a potential replacement [5]. Aberration corrected STEM‐EELS has identified some elemental separation of Cu and In within individual quantum dots [Figure 1 e‐h], which may be the origin of an In‐Cu anti‐site defect state known to act as a donor in the radiative recombination pathway for chalcopyrite CIS quantum dots. We will report here on further analysis using a FEI Titan cubed Themis 300 G2 S/TEM to assess elemental distribution by STEM‐EDX. Such analysis will enable additional characterisation of core‐shell coatings (e.g. CIS/ZnS/ZnS:Al) designed to improve photo luminescent quantum yield while enhancing environmental stability of the particles.
Grain boundaries in nanoparticles made of self‐assembled amphiphilic β‐cyclodextrins
Authors: Putaux Jean‐Luc , Lancelon‐Pin Christine , Choisnard Luc , Gèze Annabelle , Wouessidjewe Denis
Published: December 2016

One major challenge of nanomedicine is to design nanocarriers that deliver active compounds to a target site, at a sufficient concentration and without premature degradation, in order to maximize the efficiency of the substance while limiting secondary effects. In this context, we have developed colloidal nanovectors based on cyclodextrin (CD) amphiphilic derivatives obtained by an enzymatically‐catalyzed transesterification by thermolysin. We have shown that after dissolution in acetone, depending on the length of the grafted alkyl chains, the derivatives had the ability to self‐organize in water, forming nanoparticles with various shapes and ultrastructures [Gèze et al.,
Mater. Sci. Eng
. C29 (2009), 458]. The knowledge of the morphology and ultrastructure of these nanovectors is crucial in order to optimize their formulation and lyoavailability.

The present communication focuses on the βCD‐C
14
derivative,
i.e
. βCDs (made of 7 glucosyl units) acylated on their secondary face with C14 chains. The resulting nanoparticle suspensions were quench‐frozen and observed by cryo‐transmission electron microscopy (cryo‐TEM). The βCD‐C
14
particles exhibited tortuous multidomain shapes (Figure 1a) and the corresponding small‐angle X‐ray scattering (SAXS) pattern collected from a concentrated suspension contained peaks whose distribution was consistent with a columnar hexagonal structure (Figure 1c). Depending on the orientation of the particles in the embedding film of vitreous ice, the cryo‐TEM images revealed that some particles consisted of misoriented domains separated by sharp interfaces (Figure 1b). A direct view of the hexagonal organization was obtained when the incident beam was parallel to the columns and grain boundaries with various tilt angles were observed. The analysis of the structure of the grain boundaries was based on the concepts of coincidence site lattice (CSL) and structural units (SUs) frequently used to describe the atomic structure of interfaces in metallic alloy and semiconductor polycrystals [Thibault et al.,
Mat. Sci. Eng. A
164 (1993), 93‐100]. An example of stepped tilt boundary is shown in Figure 2b. Assuming that the repeating motif in each grain corresponds to the projection of hollow columns made of βCD‐C
14
molecules (Figure 2a), the boundary was described with a series of SUs differing by the number of neighboring columns (5, 6 or 7), each of them exhibiting a distinct contrast (Figure 2c) To our knowledge, it is the first time that such grain boundaries are observed in nanoparticles of self‐organized amphiphilic molecules and described at the nanometric scale.
Morphologies of a solvent cast polystyrene‐polybutadiene‐polystyrene (S‐B‐S) triblock copolymer characterised by
TEM
,
AFM
and Energy Filtered
SEM
Authors: Zhou Zhaoxia , Doak Scott S , Grandy Dave B , Abrams Kerry J , Rodenburg Cornelia , Weston Nicole , Hourston Douglas J
Published: December 2016

The most common method of characterisation of the morphologies of block copolymers is transmission electron microscopy (TEM) of ultrathin sections because of the nanoscale of the domains in the morphologies of this block copolymer[1]. The contrast of polymer phases is often enhanced by heavy metal element staining using, typically, OsO
4
. TEM provides imaging at high resolution at the cost of time‐consuming and challenging specimen preparation by cryo‐ultramicrotoming and the negative staining which is not only toxic but also introduces artifacts[2]. Furthermore, the 2D projection by TEM imaging makes direct interpretation of a nanoscale complex material difficult when the specimen sections thickness (~100nm) is considered. Atomic force microscopy (AFM) can characterise a multiphase material by detecting localised variation in mechanical properties, e.g. friction, adhesion and modulus, and has been used to identify the morphology in block copolymers in some recent studies without staining [3]. Combined AFM and TEM characterisation of multiphase copolymers has been developed to characterise the complex microstructures of block polymers in a complementary way [3,4]. Novel holders were designed to facilitate sample preparation for both techniques and to direct correlation of the topographical information provided by the AFM better to interpret the two‐dimensional images provided by TEM. However, the lateral resolution of AFM is significantly worse than TEM limited by the scanning tip although the depth resolution is super. An alternative approach is to use the recent energy‐filtered scanning electron microscopy (EFSEM) technique, which is based upon the energy spectroscopy of detected secondary electrons (SE)[5]. In this work, the S‐B‐S triblock copolymer cast from toluene, cyclohexane and ethyl acetate was characterised in order to understand the effect of casting solvent on the solid state morphology of this triblock copolymer. The morphology varies from continuous to spherical and lamella structures ranging from a few nm to ~100nm. Preliminary results have shown complementary morphologies provided by AFM and TEM, as shown in Figures 1 and 2. The contrast mechanisms from the three methods and consequences for the morphology determination will be discussed, as well as the sample preparation methods.
Revealing the symmetry breaking, growth and surface properties of gold nanorods
Authors: Etheridge Joanne , Walsh Michael J. , Katz‐Boon Hadas , Tong Wenming , Dwyer Christian , Funston Alison, M.
Published: December 2016

The unique properties of nanoparticle structures are directly determined by particle composition, size, shape and surface faceting; each offering a tuneable parameter with which one can tailor properties to a given application. Advances in wet‐chemistry techniques now enable the synthesis of nanoparticles with shape anisotropy and novel surface faceting that exhibit exciting optical and catalytic properties. Here, we develop and apply quantitative scanning transmission electron microscopy methods to observe key structural changes that enable anisotropic growth; characterise the nanorod faceting in three dimensions; and probe the relative surface “energies” of both high and low index facets.

Gold nanorods are an archetypal system with which to study anisotropic nanoparticle growth. Yet despite intense research it remains unclear how or why a single crystal seed particle, with a cubic lattice, grows preferentially in two of six nominally symmetry‐equivalent directions. Observations at various stages of gold nanorod growth reveal the onset of asymmetry occurs only in single crystal seed particles that have reached diameters between 4 and 6 nm. In this size range only, small, asymmetric truncating surfaces with an open atomic structure become apparent, and in the presence of Ag
+
ions are stabilised, becoming side facets in the embryonic nanorod structure [1,2]. These results provide the first direct observation of the structural changes that break the symmetry of the seed particle and provide key insights into the mechanism of anisotropic growth.

The various facets exhibited by the nanoparticle [3] and their relative surface energies are a crucial driver of shape control whilst also directly determining how the resulting particle will interact with its environment. We apply a quantitative STEM technique [4] to count the number of atoms in each atomic column as identified in STEM images of a single crystal gold nanorod orientated in two different zone axes. Using this method we are able to determine the morphology and facet crystallography of the nanorod, finding it is comprised of both high {0 1 1+√2} and low {110}, {100} index side‐facets, each of comparable size and shape. Furthermore, by applying this method at successive time intervals and comparing the images it is possible to quantify atomic movement on the surface and therefore determine the relative stability of different crystallographic facets and the overall stability of the nanoparticle shape [5]. These results provide important information on the effect of surfactants on the relative surface energies of high and low index facets, and shed new light on the growth kinetics of Au nanorods.
Characterization and Preparation of Carvacrol Loaded Solid Lipid Nanoparticles and Imaging with Scanning Electron Microscopy (
SEM
)
Authors: Dikmen Gokhan , Dag Ilknur , Gursu Bukay Yenice
Published: December 2016

Characterization and Preparation of Carvacrol Loaded Solid Lipid Nanoparticles and Imaging with Scanning Electron Microscopy (SEM)

Gökhan DIKMEN
1*
, Ilknur DAG
2
, Bukay YENICE GURSU
3

1,2,3

Eskisehir Osmangazi University, Central Research Laboratory Application and Research Center (ARUM), Odunpazarı, 26480, Eskisehir‐Turkey

gokhandikmen1@gmail.com

Backgrounds:
Drug carrier systems such as nano lipid particles, polymeric micelles, dendrimers and solid lipid nanoparticles (SLNs) provide controlled release of the drug both in the desired time and in specific region. A lot of anti cancerogen and anti microbial drugs such as carvacrol exhibit various side effects due to especially high dosage. These side effects can be eliminated using drug delivery systems such as SLNs and NLPs.

Material and methods:
SLN formulations were prepared using hot homogenization method after then these formulations were characterized by Zeta Sizer, FT‐IR, NMR and SEM. In order to image of SLN formulations, formulations were coated with Au‐Pd complex and than imaged by SEM.

Results:
Carvacrol loaded SLNs formulations were proven good stability (‐34.4 mV) and small size (almost 190 nm). SLN formulations were compared with the freshly prepared formulations of carvacrol and tween 80 by FT‐IR spectroscopy. In FT‐IR spectra, any chemical shift or deformation in the bands and any stability problems were not observed. Moreover, SEM images were taken and measured the particle size of these formulations.

Conclusions:
Particle size of Carvacrol was decreased using solid lipid nanoparticles and this formulation may be suitable as a nano drug carrier system for cancer and microbial treatment.

Keywords:
Carvacrol, SLNs, SEM, Caharcterization, Spectroscopy
Studies of the structure of spray pyrolysed bioactive glasses using electron diffraction and
DFT
simulations
Authors: Chou Yu‐Jen , Borisenko Konstantin , Shih Shao‐Ju , Kirkland Angus
Published: December 2016

Bioactive glasses have received considerable attention during the past few decades. Recently, Shih et al. demonstrated that Si‐Ca‐P based glasses prepared by spray pyrolysis can have better bioactivity than glasses prepared by other methods [1]. To understand the reason behind these improved properties we have studied the structure of several Si‐Ca‐P glasses with different compositions.

In this study structural information from bioactive glass samples was obtained using electron diffraction. Compared to X‐ray and neutron diffraction electrons can be easily focused on specific nano volumes and used to probe nanoscale variations in structure. Using reduced density function (RDF) analysis local structural parameters of the materials can be extracted from experimental diffraction patterns with high precision [2]. However, experimental diffraction data alone is not sufficient to build reliable atomic models. Therefore, we used DFT molecular dynamics simulations of liquid‐quench to obtain atomic models of the materials, which serve as initial models for further structure refinements.

All experimental data presented here was collected using a JEOL JEM2100 transmission electron microscope (TEM) operating at 200kV. Electron diffraction patterns were recorded on a Gatan Orius CCD that eliminates charge overflow to the neighbouring pixels, even when saturated. Using a camera length of ~180mm and the central beam positioned at the edge of the detector, the usable range of scattering vectors,
q
extends to 18Å
‐1
, comparable with X‐ray experiments. Figure 1 (a‐d) shows typical TEM images and diffraction patterns of two specimens, with the corresponding RDF curves shown in Figure 1 (e).

DFT simulations were carried out on ARC supercomputer facilities at the University of Oxford. The CASTEP software [3] was used to perform molecular dynamics simulations of liquid quench from 3000K to 300K, with cooling rate of 2·10
14
K/s. Energy optimizations with a 300eV pseudo potential cut‐off were performed after quenching. Figure 2 (a) shows a model of 60%SiO
2
‐35%CaO‐5%P
2
O
5
glass simulated by Reverse Monte Carlo using only experimental diffraction data and the model after DFT simulation is presented in Figure 2 (b), indicating considerable structural changes. This model already demonstrates a good agreement with the experimental RDF curve (Figure 2 (c) and has been used for further RMC refinements.

We will discuss correlations between bioactivity and structural data in these materials.

Financial support from the European Union under the Seventh Framework Program under a contract for an Integrated Infrastructure Initiative (Ref 312483‐ESTEEM2) is gratefully acknowledged.
Nitride layers grown on patterned graphene/
S
i
C
Authors: Pecz Bela , Kovacs Andras , Dunin‐Borkowski Rafal E , Yakimova Rositza , Heuken Michael
Published: December 2016

Self‐heating of high power GaN devices during their operation is a major drawback that limits the performance. Integration of sheets with very high thermal conductivity material could help in this matter. After some unsuccessful GaN growth experiments carried out directly on graphene, we succeeded to grow nitride layers on patterned graphene/6H‐SiC by Metalorganic Chemical Vapour Deposition (MOCVD). The growth is similar to the well‐known Epitaxial Lateral Overgrowth method in which the graphene buried stripes are overgrown laterally from the window regions, where AlN could grow on bare SiC with epitaxy. An AlN buffer layer was first deposited on patterned graphene/6H‐SiC surface followed by a deposition of ~ 300 nm thick Al
0.2
Ga
0.8
N and ~ 1.5 µm thick GaN layer. The AlN buffer deposited onto the graphene stripe was grown in a 3D way (Fig.1a). The heterostructure was studied using aberration‐corrected transmission electron microscopy (TEM) methods in combination of electron energy‐loss X‐ray spectroscopy (EDXS) and electron energy‐loss spectroscopy (EELS). TEM specimens were prepared using both conventional and focused ion beam methods.

The most surprising details of this study is the appearance of the AlN/GaN superlattices, which were formed in a self‐organised way over the buffer layer. Instead the ternary AlGaN we have superlattice (Fig. 1.b and c) in which the thickness of the AlN/GaN is determined by the available elements from the Al
0.2
Ga
0.8
N which we wanted to grow. The control sample (without graphene) showed a much more flat AlN buffer and a ternary Al
0.2
Ga
0.8
N on that without any phase separation. EDXS mapping and also superlattice reflections show however, clearly the complete phase separation in the case the nitride layers are grown on graphene. We suppose, that some excess carbon induced the phase separation.

The detailed TEM studies revealed the AlN nucleation directly on SiC and lateral overgrowth of graphene island as shown in Fig.2a. The high resolution image in Fig.2.b shows three layers of graphene and the AlN that is in epitaxy with SiC. Both interfaces are sharp and no interdiffusion of the elements are observed according to the Si, C (not shown) and Al maps in Fig. 2c The results show that high quality GaN layer over graphene/SiC can be grown with MOCVD that can serve as templates for high power GaN devices.
Imaging Dynamic Processes in Liquids: Application for Batteries
Authors: Mehdi B. Layla , Stevens Andrew , Hufschmid Ryan , Park Chiwoo , Muller Karl , Browning Nigel
Published: December 2016

The development of
in‐situ
liquid stages for the (S)TEM presents many opportunities to study dynamic processes important for next generation energy storage, transport and conversion systems. However, to use the microscope to study these systems we must be aware of the effect of the electron beam in controlling/altering the experiment. Fortunately, the effect of the beam current can be calibrated and understood in terms of its effect on the nucleation and growth of nanoparticles from solution. Here, we demonstrate the beam effect by analyzing the degradation mechanisms in Li battery electrolytes. Figure 1 shows the degradation mechanisms for lithium hexafluoroarsenate (LiAsF
6
) in 1,3‐dioxolane, DOL (Figure 1a) and dimethyl carbonate, DMC (Figure 1b). There are different mechanisms of breakdown in each case – the size, shape and morphology of the precipitates is different. These results demonstrate that the electron beam has the potential to mimic electrochemical reduction, and therefore must be taken into account during
in‐situ
electrochemical measurements to ensure results are free from artifacts.

Having calibrated the electron dose for the particular electrolyte, we can now use an
operando
electrochemical cell to investigate the role and mechanism of electrolyte additives during Li deposition/stripping. We prepared two electrolytes, LiPF
6
in propylene carbonate (PC) with different trace‐amounts of water. Figure 2A shows a comparison of the cyclic voltammograms for the two electrolytes and Figure 2B shows the corresponding amount of Li deposited/stripped during these cycles (Figure 2C and D shows representative STEM images of the process). The higher concentration of water, leads to an increased concentration of highly conducting LiF in the SEI layer, leading to a larger grain size through increased diffusion of Li ions during battery cycling. SEM images show Li deposited on a Cu electrode surface in the presence of 10 ppm (Figure 2E) and 50 ppm (Figure 2F) of water at a current density of 1mA/cm
2
for 15 h. The Li deposits in the electrolyte containing 10 ppm shows a typical dendritic microstructure. However, the electrolyte with 50 ppm of water forms smooth, thin and dense dendritic layer. This result provides crucial insides into the performance of Li metal anodes and their successful incorporation into the next generation battery system.
Crystal structure solution of K6.4(Nb,Ta)36.3O94 compound, by using advanced
TEM
Authors: Paria Sena Robert , Babaryk Artem A. , Khainakov Sergiy , Garcia‐Granda Santiago , Slobodyanik Nikolay S. , Tendeloo Gustaaf Van , Abakumov Artem M , Hadermann Joke
Published: December 2016

We determined the crystal structure of the K
6.4
Nb
28.2
Ta
8.1
O
94
pseudo‐tetragonal tungsten bronze‐type material using advanced transmission electron microscopy techniques with an aberration corrected microscope. [1] The crystal structure solution obtained with TEM was afterwards refined using X‐ray and neutron powder diffraction data. The crystal structure consists of a framework containing trigonal, tetragonal and pentagonal tunnels, all built from (Nb,Ta)O
6
octahedra. Using ABF‐STEM and atomic resolution EDX we found that the tetragonal tunnels are occupied by K and Nb atoms, not observed before in the K
2
Nb
8
O
21
counterpart, whereas part of the trigonal tunnels are occupied with K. The occupation of the trigonal tunnels was not reported before for any of the compounds with similar structure type.
Deformation mapping in a
TEM
: Dark Field Electron Holography, Nanobeam Electron Diffraction, Precession Electron Diffraction and GPA compared
Authors: Cooper David , Bernier Nicolas , Rouviere Jean‐Luc
Published: December 2016

The properties of nanoscaled materials can be changed by applying strain and as such there is an interest in the accurate measurement of deformation with nm‐scale resolution. This was until recently considered as a difficult problem. However, the last ten years has seen a great deal of development in techniques that can be used to measure deformation with the required resolution [1,2]. Today there are many different approaches which can be used to recover valuable information about the deformation. Each of these techniques has strengths and weaknesses and requires different set ups in the electron microscope [2]. In this presentation we will present dark field electron holography, nanobeam electron diffraction (NBED), precession diffraction (NPED) and the geometrical phase analysis (GPA) of TEM and high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images. We will then discuss which technique is most suitable for different types of materials problems and benchmark their performance with respect to the accuracy of the measurements, precision and spatial resolution.

Figure 1(a) shows a HAADF STEM image of a 100‐nm‐thick Si test specimen containing 10‐nm‐thick SiGe layers with different Ge concentrations. As the specimen has been grown epitaxially we expect no deformation to be measured in the ex direction. However, due to the expanded lattice parameter of the SiGe layers relative to the Si reference, tensile deformation is expected in the ez direction. Figure 1 shows deformation maps that have been acquired by (b) GPA of HAADF images (c) dark holography and (d) precession diffraction. These are compared to finite element simulations that are shown in Figure 1(e). These results reveal that all of the different techniques provide accurate measurements of the deformation. Figure 2(a) shows a HAADF STEM image of a SiGe test device structure with a gate length of 35 nm. Finite element simulations showing the expected deformation in the struture is shown in Figures 2(b) and (c). Deformation maps are shown in Figure 2(d) and (e) for precession diffraction, (f) and (g) for dark holography and (h) and (i) for GPA of HAADF STEM images [4]. Again, accurate measurements of the deformation are made, but the precision and spatial resolution depends on the experimental technique that has been used. As well as presenting state of the art results from a range of strained materials we will highlight improvements that are required for all of the different techniques in order to optimise their performance and provide the best possible measurements of deformation.

Acknowledgements : These experiments have been performed on the platform nanocharacterisation (PFNC) at Minatec. The work has been funded by the ERC Starting Grant 306365 « Holoview ».
Vectorial field tomography from single projection for cylindrically symmetric nanostructures
Authors: Phatak Charudatta , Knoop Ludvig De , Houdellier Florent , Hytch Martin , Masseboeuf Aurélien
Published: December 2016

One‐dimensional (1D) nanostructures have been regarded as the most promising building blocks for nanoelectronics and nanocomposite material systems as well as for alternative energy applications [1]. Magnetic nanowires with circular cross‐section, are of utmost importance from theoretical and technological aspects [2]. 1D carbon‐based nanostructures such as carbon nanotubes are amongst the best candidates for field emission displays and new high‐brightness electron sources [3]. The confinement effects in 1D nanostructures can alter their properties and subsequently their behavior significantly. Hence it is necessary to understand the strong effect of their size on their three‐dimensional (3D) properties such as the magnetic and electric fields associated with nanowires and nanotubes completely before they can be used in applications. There are currently very few methods, which have the capability to visualize the complete 3D fields associated with nanowires. In this work, we show that using a combination of symmetry arguments and electron‐optical phase shift data obtained using TEM, it is possible to recover the entire 3D magnetic or electric field in and around nanowires and nanotubes from a single image.

The phase change φe+φm of an electron wave traveling through a thin foil can be expressed in terms of tomographic quantities [4]. The phase shift can be recovered experimentally using various techniques such as transport‐of‐intensity based methods or off‐axis electron holography. Nominally, determining the 3D magnetic field or 3D elestrostatic potential requires recording a series of phase shift images as the sample is tilted about its axis. However, in a 1D nanostructure such as a nanocylinder that is uniformly magnetized along its long axis, the magnetic field possesses cylindrical symmetry with respect to the long axis. Similarly, carbon nanotubes under applied bias exhibit a cylindrically symmetric potential and electric field. Exploiting these conditions of cylindrical symmetry, we can reconstruct the full 3D magnetic or electric field associated with a nanowire from a single phase image using the inverse Abel transform. Simulations were performed for a uniformly magnetized sphere, which also possesses cylindrical symmetry to analyze the fidelty of the reconstruction algorithm. Fig. 1(a) shows the magnetic phase shift of such a uniformly magnetized sphere, (b) shows the derivative with respective to the horizontal axis (∂φm/∂x) showing the cylindrical symmetry, and (c) the 3D reconstructed magnetic induction using the single image method developed in this work. Experiments were performed on nickel nanowires that were uniformly magnetized to reconstruct the 3D magnetic induction. Similarly the 3D electric field was reconstructed from in‐situ biased carbon cone nanotips under varying applied bias.
Probing the directionality of local electronic states in
SrTiO3
by momentum‐selected
STEM‐EELS
Authors: Yamaguchi Atsushi , Haruta Mitsutaka , Nemoto Takashi , Kurata Hiroki
Published: December 2016

Electron energy‐loss spectroscopy in the scanning transmission electron microscope (STEM‐EELS) enable to investigate the local electronic states at the specific atomic column selected by an incident electron probe. Even though the same elements, crystallographically non‐equivalent atoms give the different energy‐loss near‐edge structure (ELNES) [1]. Although SrTiO
3
has a single oxygen atom in the unit cell, the chemical bonds between Ti and O have directionality as shown in Fig. 1(a), depicting the ligand field orbital with e
g
symmetry formed by Ti‐d
x
2
−y
2
and O‐p orbital. If the oxygen K‐edge ELNES is acquired with an off‐axis collection aperture to select a specific direction of momentum transfer, the intensity related to the transition to the unoccupied e
g
state should vary with O1 and O2 sites as predicted previously [2]. In this study, we show that the directionality of local electronic states at different oxygen sites can be detected by momentum‐selected STEM‐EELS.

STEM‐EELS measurements were performed using Cs‐corrected STEM (JEM‐9980TKP1 equipped with a cold‐FEG and an omega filter) operated at 200 kV. Fig. 1(b) shows the setup of experiment. An electron probe with a convergence semi‐angle (α) of 23 mrad incidents along the c‐axis of SrTiO
3
and EEL spectra are recorded with the spectrum collection aperture (β = 10 mrad) placed at the edge of the transmitted beam disc along θ
y
direction. In order to simulate the experimental results, the electronic structure of SrTiO
3
was calculated by WIEN2k [3] based on the density functional theory, and the O‐K edge ELNESs were calculated by TELNES3 code incorporated in WIEN2k.

Fig. 2(b) shows the experimental O‐K edge ELNES obtained by scanning electrons along two different O‐TiO‐O lines shown in Fig. 2(a). It is found that the intensity of peak b which can be assigned to the transition to the e
g
state is different between the two spectra. Since these spectra are acquired with a collection aperture shifted in the θ
y
direction, the partial density of state of O‐p
y
hybridized with Ti‐d
x
2
‐y
2
state should predominantly contribute to the spectrum. Actually, the spectrum acquiring from the oxygen atoms aligned in the y‐direction has an enhanced peak b, which is indicated that the present method can detect the directionality of Ti‐O bonding at a specific oxygen site.

Fig. 3(b) shows the O‐K edge ELNES calculated by adding the contribution from the two oxygen sites shown in Fig. 3(a). The features in the calculated spectra are in good agreement with that of the experimental one, which verifies the reliability of the experimental finding.
Mapping
2D
strain components from
STEM
moiré fringes
Authors: Hytch Martin , Gatel Christophe , Ishizuka Akimitsu , Ishizuka Kazuo
Published: December 2016

Artificial moirés are created in a STEM by deliberately choosing a low magnification where the scan step is close to the crystalline periodicity (see Figure 1a) [1]. A moiré contrast then results from the interference between the scan and the crystal lattice. The technique has been developed to analyse strain [2], and has been applied to the study of strained‐silicon devices [3].

In reciprocal space, STEM moiré fringes can be understood as the convolution of the lattice created by the scan, characterized by the scan‐step, s in real‐space, or s
*
in reciprocal space, and the reciprocal lattice of the crystalline lattice, characterized by d
*
(Figure 1b). Interference between neighbouring periodicities gives rise to moiré fringes of periodicity
q
M
. In general, only a few moiré fringe periodicities will be present in the image as the scan reciprocal lattice is in reality multiplied by the MTF of the probe: the size of the probe limits the possible interference terms (indicated by the yellow area in Figure 1b). The moiré peridocity
q
M
is related vectorially to
s
*
, which is usually 1 or 2 pixel
−1
, and the
d
*
(or g‐vector) for a particular set of lattice fringes (Figure 1c).

Here we show how the strain information can be extracted using the concept of geometric phase, previously used for the analysis of high‐resolution TEM images [4]. The advantage of this formulation is that the moiré fringes do not need to be aligned exactly with the crystalline lattice, thus freeing up the experimental work. The periodicity of the moiré fringes (Figure 2a) is identified from the power spectrum of the image and the corresponding geometric phase determined (Figure 2b). The strain is in turn calculated from the geometric phase (Figure 2c). It is not necessary to know the exact calibration of the original image providing a reference region of known crystal parameter is present, as the vectorial relationship (Figure 1c) provides a strong constraint.

We have also developed a procedure to determine maps of the 2D strain tensor from two differently oriented SMFs [5] (Figure 3). The results from two separate moiré fringe images need to be aligned (Figure 3b) and combined to determine the full 2D in‐plane strain tensor. Whilst the examples here are simulated, we anticipate presenting experimental results from devices and piezo‐electric materials.
New approach for low dose electron diffraction tomography
Authors: Ghadimi Reza , Tietz Hans , Olyenikov Peter
Published: December 2016

Due to strong interaction of electrons with matter, 3D electron diffraction tomography has been proven to be a reliable method to solve structures of very small crystals, compared to X‐ray diffraction; even for small protein crystals [1].

Several procedures for automated acquisition of tomographic diffraction data sets have been described [2, 3], using precession technique or discrete beam tilt perpendicular to the goniometer tilt axis. However, those mentioned methods are mainly used for less beam sensitive materials and are not suitable for low dose applications.

Shi et al. [4–7] refined the collection of 3D data sets under low dose condition (less than 10 e
−
/Å
2
). Here, the camera system is continuously acquiring diffraction data during a continuous tilt of the goniometer. This allows to completely scan the Fourier space. It turned out that the stability of the goniometer tilt speed and the limited flexibility of the tilt acquisition parameters are problematic.

Here, we present a newly developed automatic data acquisition system, combining real‐time direct control of the TEM‐deflection systems, the goniometer tilt and the acquisition of high‐resolution diffraction patterns with a synchronized CMOS camera. This can be realized by the TVIPS
U
niversal
S
can
G
enerator (USG), controlling eight TEM deflection coils, i. e. four beam deflection coils and four image deflection coils.

For a static goniometer alpha, the total beam tilt range (±3° to ±5°, depending on the TEM) can be fragmented by a defined beam tilt range, e.g. 0.5° (see Fig. 1). During the camera exposure time the beam is continuously tilted for this defined range (e.g. 0.5°). The continuous beam sweep during exposure time ensures the complete sampling of the Fourier space.

Several crystal structures (Carbamazepin: C
15
H
12
N
2
O, bismuth oxychloride: BiOCl, Mayenite: Ca
12
Al
14
O
33
) have been successfully solved by this method. The total acquisition time for 190 high resolution (1Å resolution) diffraction patterns is about 15 minutes, with a total electron dose of about 10 e
−
/Å
2
. The collected 3D electron diffraction data sets were processed using the EDT‐PROCESS software [8].
Electrical transport‐induced transformations in filled carbon nanotubes imaged in situ by scanning‐transmission electron microscopy
Authors: Lozano Juan G , Aslam Zabeada , Nicholls Rebecca J , Koos Antal A , Dillon Frank , Sarahan Michael , Nellist Peter D , Grobert Nicole
Published: December 2016

Fe‐filled CNTs have been proposed as perfect candidates for a large and varied number of applications, ranging from the biological to optoelectronics or memory storage devices1. For any of these applications, it seems crucial to understand the interactions, possible phase changes or reactions that can take place as a consequence of exposure to their real working conditions.

Conventional bright‐field transmission electron microscopy (BF‐TEM) has been the tool traditionally employed to observein‐situthe dynamical effects that take place when individual CNTs are exposed to high electrical currents and Joule heating. Despite being a much more powerful technique, scanning TEM‐annular dark field (STEM‐ADF) imaging has been scarcely for this purpose2. One of the main advantages of STEM‐ADF over BF‐TEM is that the intensity in the images is highly dependent on the atomic number of the species which are present and therefore the images show compositional in addition to structural information. This gives a much better understanding of current‐induced migration effects, formation of intermediate phases or alloying, or phase separation phenomena, something that using BF‐TEM alone would miss. In the STEM‐ADF configuration it is also possible to perform complementary analytical spectroscopy simultaneously with imaging and with comparable spatial resolution.

Here we show the significant advantages of combiningin‐situexperiments with STEM‐ADF and related analytical techniques to gain new insights into the electrical transport induced transformations in P, N doped Fe‐filled carbon nanotubes. It has been possible to monitor in real time a multistage process (Figure 1) in which the Fe filling reacts with nitrogen to form an intermediate alloy phase, which then decomposes into smaller particles. The presence of N2gas within the inner channel of the tube is found to be crucial to this process.
Morphology, structure and composition of TiO2‐based nanocomposites fabricated by dealloying
Authors: Wang Wu , Wang Di , Mu Xiaoke , Kübel Christian
Published: December 2016

Abstract:

Nanostructured TiO
2
and many titanates are of tremendous fundamental and technological interests for a wide range of applications not only in areas such as catalysis, but also for energy or hydrogen storage because of their unique structure and large surface area [1–3]. TiO
2
and titanates in form of nanotubes, nanowires or nanobelts can be fabricated by reaction of raw TiO
2
and NaOH [4,5]. Nanostructured TiO
2
can also be directly fabricated by dealloying Al‐Ti ribbon using a simple and highly efficient corrosion process [6], where the reaction solution is one of the key factors for the morphology and structure of the final product.

In the present work, several TEM techniques are employed to study the morphology, crystal structure and composition of products from Al
85at.%
‐Ti
15at.%
ribbons dealloyed in NaOH, KOH and HCl solutions. Figure 1, 2 and Table 1 show the analytic results for the dealloyed product in NaOH solution. A polycrystalline layered structure with ~0.75 nm lattice distance is observed (Fig.1). Around 8 at.% Na were identified by EDX analysis of different areas (Table 1). In order to further study the structure of this phase, a radial distribution function (RDF) was calculated based on electron diffraction to provide the distribution of atomic distances and compared to a simulated RDF for crystalline Na
2
Ti
6
O
13
structure, which shows good agreement (Fig.2a). The determined structure is supported by XRD result in Fig.2b, which shows that this product consists of two compositions, Na
2
Ti
6
O
13
phase and some anatase TiO
2
. Multivariate statistical analysis of 2500 EDX spectra of an area of 100 nm
×
100 nm is used to image the Na
2
Ti
6
O
13
/TiO
2
distribution and electron tomography is used to provide three dimensional (3D) information of the morphology. Comparing the structures fabricated by different dealloying solutions will lead to understand the formation mechanism and to better control nanostructures TiO
2
‐based compounds.

Keywords:
TiO
2
‐based nanocomposites, Dealloying, Layer structure.
Microstructural characterization of Delaminated
2D
Cobaltites
Authors: Lafarga Alberto Azor , Ruiz María Luisa , Portehault David , Sanchez Clemént , González‐Calbet José María
Published: December 2016

The lamellar cobaltites Na
x
CoO
2
have awakened the interest of scientific community because of their superconductive phases [1], thermoelectric [2] and photocatalytic properties [3], and their possible use as cathodes in sodium batteries [4]. Their basic structure can be described on the basis of infinite [CoO
6
] octahedral edge‐sharing layers with Na cations at the interlayer space. Depending on the Na content different polymorphs have been described [5]. The synthesis of these species at the nanoscale could be a key factor for their technological exploitation. Furthermore, recent researches have proved that the inclusion of certain transition metals as dopants in the original structure could improve some of these properties [6].

Here we present an electron microscopy study of delaminated 2D cobaltites in the Na
y
Co
1‐x
M
x
O
2
, (M = Mn, Ni, Cu) system obtained through a new synthesis strategy based on a co‐precipitation reaction in a basic medium. After purification by centrifugation, a soft thermal treatment is performed before a selective sedimentation process in order to select the smallest flakes. Transmission electron microscopy proves the success of the delamination process. Low magnification TEM (figure 1a) shows the presence of two remarkable features: i) an apparently very thin matrix and ii) elongated particles in between 5 and 30 nm. The corresponding HREM (figure 1b) study reveals that both matrix and particles are crystalline with periodicities that can be interpreted in terms of [001] and [100] projections of the monoclinic cell of Na
0.6
CoO
2
[5]. To get information about the atoms distribution and oxidation states a study in a probe aberration corrected microscope JEOL JEM ARM200 cFEG has been performed. Preliminary HAADF and ABF (figure 2) studies evidenced a lamellar structure similar to the Na
0.6
CoO
2
with the alkali metal interlaying the Co
1‐x
M
x
O
2
sheets. EELS study confirms the presence of all Na, Co, Ni and O (figure 2c) suggesting an intermediate oxidation state of cobalt cations between 3 and 4 in good agreement with the sodium content stablished by ICP.