bluuebunny/crossref_metadata_2025 huggingface dataset:
Focused ion beam based highly resistive and reproducible sub‐5nm nanogaps in thin gold wire
Authors: Jafri Syed Hassan Mujtaba , Li Hu , Wani Ishtiaq Hassan , Leifer Klaus
Published: December 2016

The measurements of physical properties such as electrical characterization of single or few nano‐objects like nanoparticles, nanoclusters and single molecules require the fabrication of nanoscale gaps between electrodes [1]. It is difficult to fabricate electrical contacts at this scale with standard lithography techniques but focused ion beam (FIB) can fabricate nanogaps by milling thin metallic wires on the insulation substrate. It is a not only a mask less technique but also enables to fabricate large numbers of nanogaps with reproducible properties at the room temperature [2]. The FIB milled nanogaps are employed to determine single or few nano‐entities such as nanoparticles and molecules [3]. Due to limitation of ion beam diameter and profile, the size of FIB milled nanogap is more than 10 nm thus not applicable to measure single less than 10nm object. We have developed two strategies to create sub‐5nm gaps 1) by a control and precise dosage of ions during milling 2) by electrodeposition of gold in 30nm FIB cut gaps

1)
A series of nanogaps are milled with size range from sub‐5 to 30nm in thin gold wires, through precise control of the applied ion dosages with a range between 4.6 and 9.2 x 10
10
ions/cm using focused gallium ion beam at 30KV. As shown in figure 1a, the nanogap is not fully milled with the ion dosage of 4.6×10
10
ions/cm, whereas the large nanogaps are milled with high ion dosage of 9.2 x 10
10
ions/cm having resistances in 100‐1000TΩ range (figure 1b). With ion dosage of 5×10
10
ions/cm the nanogap begin to show up in gold nanowire (figure 2), which is verified by the current‐voltage (I‐V) characteristic demonstrating the resistance up to 12 TΩ. The Fowler‐Nordheim tunneling effect is also observed in the sub‐5 nm. The application of Simmon's model to the milled nanogaps and the electrical analysis indicates that the minimum effective nanogap size approaches to 2.3 nm

2)
The 30nm FIB cut nanogaps (figure 1b) are connected to a potentiostat controlled by GPES software. A 10 µL drop of diluted gold chloride is added on top of a FIB cut gap. In one of the configuration when working electrode (WE) is connected to to one side of nanoelectrode setup, other side of setup is connected to reference electrode (RE) and counter electrode(CE) is placed inside the drop on silsicon dioxide as shown in figure 3, well defined and well‐shaped reduction of gap size has occurred with the growth on both electrodes from deposition of gold atoms (figure 4). The calculated growth rate in the nanogap is in the order of 1 nm/s and growth rates depend directly on the deposition time. The current‐voltage characteristics have demonstrated the open gap resistance of 5nm nanogap in the order of 300TΩ. The FIB templating also improves the shape of electrochemically grown nanogaps.

These two strategies allow us to create large number of nanogaps thus enabling to measure physical properties of a sub 5nm single nano‐object.
3D
mapping of subcellular structures with super‐resolution array tomography
Authors: Markert Sebastian , Britz Sebastian , Proppert Sven , Lang Marietta , Witvliet Daniel , Mulcahy Ben , Sauer Markus , Zhen Mei , Bessereau Jean‐Louis , Stigloher Christian
Published: December 2016

The combination of fluorescence light microscopy (FLM) and electron microscopy (EM) makes it possible to put molecular identity in its full ultrastructural context. With array tomography (AT) long ribbons of serial ultrathin sections are labelled via immunohistochemistry (IHC). After FLM imaging the same sections are processed for scanning electron microscopy (SEM) and re‐analyzed. The resulting images are correlated and superimposed. Due to the serial nature of this approach it is possible to obtain large volumes of correlated multi‐channel light and electron microscopic data. One drawback of this method is the large discrepancy of resolution between light and electron microscopy. To alleviate this we advanced AT for two super‐resolution light microscopy techniques, Structured Illumination Microscopy (SIM) and direct Stochastic Optical Reconstruction Microscopy (
d
STORM). We also devised a method for easy, precise, and unbiased correlation of EM images and super‐resolution imaging data using endogenous cellular landmarks and freely available image processing software. Together, these advances make it possible to map even small subcellular structures with high precision and confidence. We applied our super‐resolution AT approach in
C. elegans
to address an important problem in connectomics research: the mapping of gap junctions at connectomes.
The analysis of
Mo5SiB2
in the
SEM
with the use of
EDS
and
WDS
Authors: Dijkstra Hans , Kellner Peter , Reichstein Werner , Glatzel Uwe
Published: December 2016

Refractory metals and their alloys show potential for high temperature applications due to their increased melting point and creep resistance. Mo‐Si‐B ternary alloys consisting of the phases Mo
ss
(molybdenum‐based solid solution)‐Mo
3
Si (A15)‐Mo
5
SiB
2
(T2), with melting points over 2000 °C, are particularly favorable for new high‐temperature materials. However these alloys show a lack of oxidation resistance in the intermediate temperature range, 650‐750 °C, and possess a relatively high density (9.6 g/cm
3
) compared to Nickel‐Based Superalloys.

The characterization of the Mo
5
SiB
2
phase with an SEM with X‐ray microanalysis analytical capabilities presents a real challenge. The B‐Kα X‐ray has an energy of 183.3 eV, but might shift slightly due to its bonding with Mo. This X‐ray line energy is very close to the Mo‐Mζ line which is at 192.6 eV. In addition, the K‐shell absorption edge of boron is at 192 eV, just below the Mo‐Mζ line. Finally the absorption coefficient of B‐Kα in Mo is very high, and is even more extreme in Si.

As a result, EDS microanalysis proved to be insufficient. The EDS spectrum of the Mo
5
SiB
2
phase shows a very small peak at the B‐Kα position, but without any separation from the Mo‐Mζ line. The elemental distribution maps even showed a strong artifact: due to the higher Mo content in the Mo
ss
phase and the absence of a boron absorption edge the Mo‐Mζ peak is considerably higher in that phase, resulting in an incorrect increase of intensity of boron in the Mo
ss
phase. See figure 1.

Alternatively, WDS spectrometers have a much better energy resolution and are capable of separating to a large extend the B‐Kα and Mo‐Mζ peaks. Modern parallel‐beam WDS spectromers are also very sensitive to the low‐energy part of the spectrum, and can detect small amounts of boron with very high efficiency. A careful energy scan over the B‐Kα and Mo‐Mζ peaks can be seen in figure 2. And of course creating an element distribution image for boron now indeed showed the correct boron distribution, as can be seen in figure 3.

The final challenge lies with the quantitative analysis: what exactly is the weight percentage of boron in the supposed Mo
5
SiB
2
phase? The B‐Kα and Mo‐Mζ peaks still partially overlap even with WDS, and one has to be very careful in the selection of the background support points to correctly subtract the background X‐ray intensity. Using a stoichiometric Mo
5
SiB
2
standard this can still be done, and an accurate quantification can be performed.

This case shows how vital it can be for certain applications to widen the range of available microanalysis tools with a parallel‐beam WDS spectrometer to perform analyses beyond the performance limit of EDS.
Novel spectroscopy with atomic‐size aberrated electron probes in stem
Authors: Idrobo Juan Carlos , Rusz Ján , Spiegelberg Jakob , McGuire Michael A. , Symons Christopher T. , Vatsavai Ranga Raju , Cantoni Claudia , Lupini Andrew R
Published: December 2016

it has been theoretically argued that atomic‐size electron probes with customized phase distributions can detect electron magnetic circular dichroism (EMCD) [1]. Based on this prediction we have recently shown that deliberately aberrated electron probes in scanning transmission electron microscopy (STEM) can be utilized to obtain chiral dichroic signals in materials via electron energy‐loss spectroscopy (EELS) with high spatial resolution [2].

The experiments were performed in an aberration‐corrected Nion UltraSTEM
TM
100, equipped with a cold field emission electron source and a corrector of third and fifth order aberrations, operating at an accelerating voltage of 100kV [3]. EEL spectra were collected using a Gatan Enfina spectrometer, with 0.3 eV/channel dispersion, giving an energy resolution of 0.9 eV. The convergence semi‐angle for the incident probe and the EELS collection semi‐angle were 30 mrad and 48 mrad, respectively.

Figure 1 shows two examples of drift (affine)‐corrected Z‐contrast images and denoised EEL spectra that were acquired simultaneously from the room temperature C‐type antiferromagnet LaMnAsO. The data were acquired with the beam along the
c
‐axis using a corrected electron probe (Fig. 1a to 1c) and the C
34
= 15 μm aberrated probe (Figs. 1d to 1f) [2].

A clear EMCD signature in the EEL spectra, defined as (Mn↑ ‐ Mn↓) presenting a change of sign in its integrated intensity between the L
3
and L
2
peaks, is only visible for the Mn L‐edge acquired using the C
34
aberrated probe. In Figs. 1e and 1f, this signal, shown in green, is positive at the L
3
peak and negative at the L
2
peak. For comparison, the Mn signal in 1b and 1c, shown in grey, does not display this distinctive signature, with both positive and negative components on both peaks.

We will discuss the experimental conditions necessary to reveal the magnetic ordering of individual atomic columns and atomic‐size defects in materials [4].
Super‐resolution fluorescence microscopy of cryo‐immobilized samples
Authors: Kaufmann Rainer , Hagen Christoph , Grünewald Kay
Published: December 2016

Correlative light and electron microscopy (CLEM) benefits greatly from the development of super‐resolution fluorescence microscopy. With a resolution down to the 10 nm range it enables to bridge the large resolution gap between the two different microscopy techniques. However, equally important as the achievable resolution of the imaging system is the preservation of the biological structures during the sample preparation process. Imaging undisturbed structures in living cells remains very challenging for super‐resolution fluorescence microscopy with its relatively long acquisition times. Typically, chemical fixation is used to immobilize the sample for achieving best technical results, but unfortunately this is associated with structural changes in the sample, especially at a level below the diffraction limit of light [1,2].

Cryo‐immobilization offers a preferable alternative. Here, fast freezing techniques enable vitrification of the sample and preserve the structures in a near‐native state. Although cryo‐immobilization has been established as a routine technique in the fields of electron and X‐ray microscopy, it was long unclear whether super‐resolution fluorescence microscopy could be performed under cryo‐conditions to image vitrified samples [3].

Recently, we demonstrated on the single molecule level that photo‐switching of fluorescent proteins is possible under cryo‐conditions and suitable for the super‐resolution method of single molecule localization microscopy (SMLM) [4]. Chang et al. and Liu et al. have shown the correlation of cryo‐SMLM with electron cryo‐microscopy [5,6]. Here, we present cryo‐SMLM of vitrified biological samples and its prospects for cryo‐CLEM. We demonstrate that a resolution improvement of up to 5x compared to conventional fluorescence cryo‐microscopy is possible.

Super‐resolution fluorescence cryo‐microscopy offers the possibility to image fluorescently labelled biological samples with diffraction‐unlimited resolution, immobilized, but with structural preservation in a near‐native state. This is not only helping to bridge the large resolution gap in cryo‐CLEM, but might also offer an alternative to the dilemma in conventional super‐resolution imaging, where one has to choose between the limited temporal resolution in case of living cells or the disadvantages of chemical fixation.
Chiral electron sieves for electron vortex beam generation
Authors: Yuan Jun , Yang Yuanjie , Thirunavukkarasu Gnanavel , Babiker Mohamed
Published: December 2016

The recent discovery of vortex electron beams [1–3] has generated many interests and the new understanding may lead to applications in material characterization [4]. The method of creating vortex electron beams using a forked aperture [2] is popular but has a drawback that electron vortex beams with different orders are produced side‐by‐side in the specimen plane. More recently a method of producing electron vortex using a spiral holographic aperture was demonstrated, with the advantage of being able to select a specific vortex beam in focus on the sample [5,6]. However, the spiral aperture is difficult to reproduce accurately because of many fine features and it is also mechanical fragile and the extra reinforcement bars were added in the mask for mechanical stability[5].

In this study, we propose and experimentally demonstrate a simple and versatile way of generating electron vortex beam carrying orbital angular momentum (OAM), using a chiral electron sieve illuminated by a plane electron wave. Fig. 1 (a) shows an electron sieve mask as viewed using a scanning transmission electron microscope. It consists of a number of spirals (5 in this case), each spiral consists of suitablly arranged holes in such a way that they produce a vortex beam approximate at a near field distance [7]. Fig. 1(b) shows the resultant beam intesnity profile as the designated distance. This shows a characteristic donut shaped beam illumination characteristic of an electron vortex beam. The is confirmed by direct comparison of the intensity profile with the simulated result using Fresnel diffraction theory (Fig. 1(c)). The same simulation shows the phase structure at the center of the donut ring does contains a vortex structure of order 5.

For this particular electron sieve mask, the mask pattern can be compared with the spiral diffractive holographic grating structure produced by interference between the vortex beam and that of a spherical reference waves [5], showing comparable efficiency. However, it has the practical advantage of being much easier to produce and mechanically more robust than the normal binary diffractive grating. We will show that this is a practical example of a much rich set of electron sieves that we can generate to shape electron beams, many of which has no counter part in conventional holographic diffractive grating theory [8].
Texture, microstructure and mechanical anisotropy in
SLM
processed superalloys
Authors: Kunze Karsten , Etter Thomas , Geiger Fabian , Cloots Michael
Published: December 2016

Samples of Nickel‐based (IN738LC and Hastelloy X) and Cobalt‐based (Mar‐M509) alloys were built by selective laser melting (SLM). To evaluate the anisotropy in the mechanical behavior of the material due to layer‐wise build up, specimens were built with their cylinder axis (loading direction) oriented either parallel to the building direction, or perpendicular to the building direction. After building up the specimens by SLM, they were investigated either under the “as‐built” condition or after heat treatment. The analysis of microstructural anisotropy in SLM made specimens was done by using EBSD, EDX and X‐ray texture analysis methods, and then correlated with anisotropic material behavior observed during tensile and creep testing at room temperature and 850°C. All Ni‐based samples possess the same general texture, with the majority of grains forming one single component of a cube texture with one of the cubic axes parallel to the building direction, and another cubic axis parallel to the laser scanning direction. The Young's modulus determined during tensile testing is lowest parallel to the building direction and parallel to the laser scanning direction. By applying suitable laser scanning strategies, the possibility to switch from transverse anisotropic to transverse isotropic properties and reverse is demonstrated for triple layered tensile samples. While the Ni‐based alloys exhibit coarse and elongated grains with a sharp texture and thus a pronounced mechanical anisotropy, the Co‐based alloy shows smaller grains with only moderate structural and mechanical anisotropy. These differences are discussed with respect to different recovery and recrystallization behavior of the two groups. Furthermore, recrystallisation heat treatment leads to a weakening of the texture and a reduction in mechanical anisotropy. The anisotropy of Young's modulus was modeled based on the single crystal elastic tensor and the measured crystallographic preferred orientations, and compares well with the data from tensile tests.
Decoupling of valence and coordination number contributions at perovskite surfaces
Authors: Tileli Vasiliki , Ahmad Ehsan , Webster Ross , Mallia Giuseppe , Duchamp Martial , Stoerzinger Kelsey , Shao‐Horn Yang , Dunin‐Borkowski Rafal , Harrison Nicholas
Published: December 2016

Perovskite oxide nanostructures are on the forefront of technology due to the wide spectrum of possible applications pertinent to renewable energy sources, such as water‐splitting, solar cells, fuel cells, batteries, and catalysis. In particular, the exceptional properties for the oxygen reduction reaction in catalysis have been detailed recently in a volcano plot and the results reveal that orthorhombic, Jahn‐Teller distorted LaMnO
3
perovskite nanoparticles are the leading, non‐noble metal candidate for enhanced catalytic activity on the cathode electrode of fuel cells [1]. Since the functional properties of these nanoparticles lie on their active surfaces, our approach involves a detailed structural and chemical evaluation of the surfaces on the atomic scale to determine what/where the reaction centres are. Subsequently, the morphology of the particles can be optimised to maximise the number of these reaction centres, allowing us to attain the highest possible performance of perovskite catalysts.

From structural transmission electron microscopy (TEM) data it was determined that polar facets exist on crystallites, which lead to assumptions on possible surface reconstruction/relaxation. However, high resolution TEM indicated that the atomic terminations of several surfaces remained defect‐free up to the very surface with no visible reconstruction taking place [2], as shown in Figure 1. Next, the surface and subsurface of the working perovskite catalyst was probed by high spatial and temporal resolution electron energy‐loss spectroscopy (EELS) in scanning TEM mode. The results revealed that the surface shows different character than the bulk. Tan
et al.
has previously shown that different oxidation states of Mn can be probed at neighbouring sites in the same compound [3] but it was also theoretically predicted that such a change can be attributed to coordination number differences as well [4]. Indeed, the extracted experimental information by EELS for the pristine LaMnO
3
powder was analysed utilising density functional theory calculations under the optic matrix elements approximation, as shown for the Mn L
3
peak in Figure 2, and the shift to lower energies of the Mn L
3,2
edge was found to be a convolution of both changes in oxidation state and in the number of nearest neighbours (coordination).
Real‐time observation of the transformation of silver nanoparticles during carbon gasification
Authors: Aires Francisco José Cadete Santos , Aouine Mimoun , Li Shiwen , Tuel Alain , Farrusseng David , Epicier Thierry
Published: December 2016

Gasification of carbon can be achieved, in the presence of metal catalysts supported on solid carbon materials, at high temperature in oxidative environments. Indeed, oxygen adsorbs and dissociates on the metal surface then interacts with the carbon at the interface with the metal leading to the formation of carbon dioxide; concurrently carbon is consumed and the metallic nanoparticle maintains the interface with the carbon and thus advances, forming in this way a trench on the surface of the carbon. On structured materials such as graphite or graphene these trenches tend to be rather 2D [1,2] at the surface of the material (hereafter named “pacman effect”). In this work we have studied the gasification of a non‐structured material (amorphous carbon) by silver‐based nanoparticles (NPs) in presence of oxygen and at variable temperatures. We were particularly interested on the dynamic structural evolution of the silver NPs observed in real‐time within an environmental TEM and at atomic resolution as permitted by the imaging Cs‐corrector.

The studies were performed in the Ly‐EtTEM (Lyon Environmental and tomographic Transmission Electron Microscope), a 80–300 kV TITAN objective lens Cs‐corrected Environmental TEM from FEI equipped with a GATAN high resolution Imaging Filter (GIF) [3]. Samples were prepared according to a synthesis method described in [4]; the silver based NPs stand on the supporting carbon film and gasification of this film is observed between 400 and 500°C under variable oxygen partial pressures (between 10
−1
and 5 mbar).

We were able to follow in real‐time the dynamics of carbon gasification and catalyst evolution by high resolution imaging (Figure 1) unlike previous studies.
In situ
EELS yields complementary information necessary to fully interpret the observed phenomena (structural changes, shrinking and coating of the catalyst, …). The mechanism deduced from our in situ study is schematically summarized in Figure 2 : (i) at the beginning of the gasification experiment the NP have surprisingly an hexagonal structure consistent with previously identified hexagonal forms of silver, either metallic or containing diluted oxygen (Figure 2a‐c); (ii) at a given moment during gasification the NP transforms to fcc‐Ag, gasification slows down, the particle begins to shrink (surface oxide formation that decomposes) while a coating forms around it (Figure 2d); (iii) once the particle is completely coated gasification stops and the NP shrinking stops (Figure 2e).

Gasification of amorphous carbon by Ag NPs was studied in situ (P oxygen, T variable) in an ETEM. Gasification rate slows when the Ag NPs transform from initial hexagonal structure to fcc; concurrently the Ag NPs shrink rapidly. The dynamic real‐time high resolution images associated with local EELS measurements allowed to propose a mechanism for the observed phenomena.
Electron microscopy of novel technical superconducting materials
Authors: Vasiliev Alexander , Karateev Igor , Kovalchuk Mikhail , Presnyakov Mikhail
Published: December 2016

The improvement of characteristics of modern superconducting devices could be achieved by changing technologies or utilization of new materials. The electron microscopy (EM), electron diffraction (ED) and microanalysis (MA) investigations of Nb‐Sn based superconducting wires used for ITER project demonstrated the severities to form A15 Nb
3
Sn structure over all volume of superconducting wires. Similar wires might be used for upgraded Large Hadron Collider (LHC) and Very Large Hadron Collider (VLHC). The Sn content in the large part of the superconducting wires could be less then 20 at% which could lead to the deviation of crystal structure of wires from A15 and consequent drop of electrophysical properties. The superconducting wires were formed by bronze method [1] and Nb
3
Sn phase was grown during solid phase reaction of Sn solved in the bronze with Nb inserts. One possible reason of Sn depletion is the diffusion barrier appeared on the Nb/bronze interface at the early stages of superconducting wires formation. It was found that this barrier is simply uniform and slowly growing layer of Nb
3
Sn adopted A15 crystal structure. The EDX elemental mapping with the help of SuperX detector (Bruker, US) in Osiris (FEI, US) STEM (Fig.1) unambiguously demonstrated the absence of Sn diffusion along Nb grain boundaries. After A15 Nb
3
Sn reached critical thickness the Nb‐Sn grains with Sn content less than 18 at% began to form. HAADF STEM study of these Sn depleted grains in C
s
probe corrected TITAN 80‐300 TEM/STEM (FEI, US) at 300 kV (Fig.2) indicated that these grains contained high density of antisite defects start to form and it was Nb substituted for Sn atoms. That conclusion was made by the estimation of intensities of atomic columns as it was done in [2] and comparison with simulated images (P.Stadelmann's JEMS software was used for image simulations). To increase Sn content in the grains, the changes of technology were proposed. Another possibility is the utilization of new materials and possible candidates are FeTeX (where X‐ Se or S) superconductors. The X‐ray crystal structural analysis, TEM, HAADF STEM, electron diffraction and microanalysis (TITAN 80‐300 TEM/STEM) were applied to the study of FeTeX based single crystals and thin films on different substrates. One of HRSTEM images is presented in Fig.3. It was found that there are uncertainties in Fe1 and Fe2 position in FeTeX compounds and ordering of S atoms. The misfit between the FeTeX films and substrates were released through misfit dislocation or an intermediate layer at the film/substrate interface. Thus the FeTeX films were stress free and critical temperature Tc should not change due to structural modifications.
Atomic‐resolution analysis of the structure and dopants of beam sensitive ordered porous materials
Authors: Mayoral Alvaro , Readman Jennifer , Navarro Marta , Morris Russell E. , Díaz Isabel
Published: December 2016

With the modern transmission electron microscopes (TEM) sub‐angstrom resolution has become readily achievable overcoming the lateral resolution problem. However, there are many cases where its fully potential cannot be totally exploited due the strong interaction between the high energetic electron beam and the material. Zeolites, zeotypes and metal organic framework (MOFs) suffer from this interaction resulting in an irreversible framework disruption through a radiolytic mechanism[1].

Since the pioneers electron microscopy observations of zeolites in the 70's, its application and image resolution has been always been limited by this high sensitivity making impossible to fully exploit the TEM capabilities. However, in recent years with the introduction of the spherical aberration correctors and paying special attention to the electron dose, images with unprecedented resolution has been able to be obtained, making feasible the truly identification of the atoms conforming the structure.

In here, it will be presented atomic‐column resolution images which will provide new information on guest species[2] within the zeolite cavities, as well as the observation of structural defects[3] providing new information about the ion exchange properties of these solids. Figure 1 displays the data obtained after introducing rare earth metals into ETS‐10.

Furthermore, it will be shown how aberration corrected STEM provide unique information dealing with the analysis of new complex materials[4]; making able the observations of pores linked by single four‐rings, double four‐rings or oxygen linkers.
A multimodal and multiscale approach to investigate the micronsized organisation of a very complex biological material : the wheat grain
Authors: Gaillard Cédric
Published: December 2016

Nowadays, a large set of microscopy tools are commonly used to investigate the nanostructure of complex biological or synthetic materials with a multiscaled organisation: epi‐fluorescence and laser scanning confocal microscopes (LSCM), scanning and transmission electron microscopes (SEM, TEM), atomic force microscopy (AFM), or Raman imaging. In particular, transmission electron microscopy (TEM) allows observation of the internal structures of natural systems (grains, cells and tissues) with a high spatial resolution. However, such observation requires in parallel dedicated sample preparation steps to prepare the fragile hydrated biological samples with successive steps including chemical or physical fixation, dehydration or vitrification of the water content, resin‐inclusion and contrast‐enhancement staining. Its well‐known these steps may induce artefacts that reduce the image resolution and valuable information, but are often considered as the unique way to access to the ultrastructural information.

We propose here to explore alternative routes for the ultrastructure investigation of the grain tissues, as an example of a very complex biological material, with the main objective to reduce the preparation steps as most as possible while adapting the same preparation to be process with several microscopy tools: TEM, SEM, AFM, Raman imaging, Fluorescence imaging, X‐ray microscopy. Depending on the successfulness of this approach, a set of complementary experiments from the same zone of a native sample can alloy to connect the plant ultrastructure with a high spatial resolution to accurate chemical information.

The multimodal and multiscale approach has been fully tested to study wheat grains tissues. We will show how unique features in the wheat outer layers organisation have been revealed due to both the capacity of keeping the native tissue “true contrast”, free from any chemical artefacts, or the native mechanical stress between the components, exempt from any alteration from resin infiltration. Moreover, taking advantage from the capacity of keeping the wheat tissue in its native shape, the mechanical properties of the native wheat outer layers (intenal and external pericarp, aleurone and sub‐aleurone layers and starchy endosperm) have been characterised by AFM at the nonometer scale, see Figure 1. Additionally, the chemical composition has been acquired by Raman mapping from the different zones of interest, giving in an unique way the capability to understand the natural assemblies of biopolymers and mineral nutrients at the sub‐cellular level in regard to their chemical, physicochemical and structural properties.
A Review on Interface Engineering and Thin Film Nanotechnology for Low‐Cost High Efficient Photovoltaic (
PV
) Solar Cell Devices
Authors: Saad Mohamed , Kim J , Kozlowski P , Ott J , Sadana D , Chen T.C
Published: December 2016

Currently, the major challenge of the research and development (R&D) in the field of Photovoltaic (PV) renewable energy is to lower the cost per Wp of electricity generation and to improve the conversion efficiency of the solar cell devices.

In comparison with the crystalline silicon technology, silicon (Si) thin film nanotechnology hold the promise of reducing the solar cell cost through lowering the material amounts and energy requirement of the manufacturing process.

In this review, several aspects of the material engineering at interfaces and process optimisation for low‐cost high‐efficient silicon based thin film photovoltaic (PV) solar cells are discussed.

A basic understanding of the thin film growth technique using a plasma enhanced chemical vapour deposition (PECVD) system coupled with analytical nanostructural characterisations of Si thin film solar cells with particular emphasis on hydrogenated amorphous and microcrystalline p‐i‐n single and double (tandem) junction silicon solar cells are presented.

Nanostructural defects including microvoids and cracks at interfaces – as potential extrinsic effects on the hydrogenated microcrystalline (uc‐Si:H) solar cells performance – are studied.

Analytical nanostructures of an ultrathin interfacial buffer amorphous hydrogenated germanium (a‐ Ge:H) layer at the P+‐ type a‐Si:H/Transparent Conducting Oxide (TCO) are investigated using STEM and EDS. It was shown that such an interfacial buffer layer could improve the electrical performance and enhance the efficiency of the a‐Si:H single junction solar cells.
3D
investigation of a
PS
/
ABS
polymer using different microscopy techniques
Authors: Jaurand X. , Errazuriz E. , Reynaud S. , Douillard Th. , Dalmas F. , Descartes S. , Simonet F. , Mondon M. , Anselme‐Bertrand I.
Published: December 2016

This study is developed in the framework of RéCaMiA, a French regional (Rhône‐Alpes / Auvergne) microscopy network, which offers facilities through a panel of microscopes such as SEM, TEM, FIB, AFM, Confocal.

The objective of the study is to compare results obtained with different microscopy techniques currently employed in three‐dimensional imaging, but it focuses more specifically on polymers [1‐3]. For the purpose a blend of polystyrene / acrylonitrile butadiene styrene (PS/ABS) is chosen. This material allows to obtain good contrast in SEM or TEM; microstructural features exist at the submicronic and nano scales; and its glass transition temperature T
g
is above 50°C. Two samples are stained by contact with a 4% osmium tetraoxide (OsO
4
) water solution to reveal contrasts. 2 FIB–SEM (FEI Helios600, Zeiss NVisio40 dual beam), 2 TEM (JEOL JEM 1400, JEOL 2100F), 2 SEM (FEI ESEM XL30, FEI Quanta250) are used to study the 3D structure of the polymer. This study develops a multiscale approach. The tools used require 2 different procedures to get a 3D image: (a) to acquire a stack of individual imaging planes and to transform it into the corresponding 3D data volume or (b) to perform electron tomography. In the first case individual images are obtained through a slice and view approach in FIB, or through individual observations, in SEM or TEM, of several thin foils prepared by ultramicrotomy method at room temperature (serial sectioning). Backscattered electron images are collected. The 3D reconstructions of the polymer obtained by the different tools are compared each other. Whatever the approach used, the morphology “salami” shape is observed in the structure of the polymer. Structure parameters, such as size distribution of the nodules and the anisotropy coefficient, are extracted and compared. Different test parameters effects are investigated, the preparation of the sample (compression of the microstructure more or less), the voltage, the spacing between the individual imaging planes, etc. The balance between the reconstructed volume size, the voxel resolution, the total time to get the 3D data volume, the advantages and limitations of the methods used in this multiscale approach will also be discussed.
Assessment of doping profiles in semiconductor nanowires by scanning probe microscopy: Study of p‐ type doping in
ZnO
nanowires
Authors: Bremond Georges , Wang Lin , Chauveau Jean‐Michel , Sartel Corine , Sallet Vincent
Published: December 2016

Methods to measure and quantitatively determine the doping profile in semiconductor nanowires ( NW) are strongly requested for understanding the doping incorporation in such one‐dimensional structures and so for developing technology using them. In the last two decades, scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) based on atomic force microscopy, has emerged as promising tools for two‐dimensional high resolution carrier/dopant profiling. In SCM, the capacitance change providing by an alternating bias applied between the tip/sample system under a DC bias to alternately accumulate and deplete carriers within the semiconductor underneath the local tip is dependent on the local carrier concentration of the semiconductor. In SSRM, the local resistivity is determined via the resistance measurement at the tip/sample system allowing the determination of the doping concentration. These two techniques need of an accurate calibration method for a quantitative doping analysis.

In this communication, we present first a calibration method based on cross‐sectional scanning of multilayers samples with different Ga doping concentration allowing the quantitative measurement of n‐type ZnO doping by SCM and SSRM. Then, to study ZnO NWs, we have developed a methodology of sample preparation, based on dip‐coating filling of NWs field. The dip‐coating parameters as coating solution, removal rate and NW field morphology have been controlled by SEM, ellipsometry and atomic force microscopy topography in order to optimize the filling and polishing process.

One important results has been to be able to measure using SCM and SSRM, the non‐intentionally n‐type doping (nid) of the ZnO nanowires, well estimated at 210
18
cm
−3
, explaining the difficulty to turn these NWs into p‐type during p‐type doping experiments, a crucial problematic in ZnO. Using antimony (Sb) doping in nid ZnO core/ Sb ZnO shell NW structures, we have successfully determined the decrease of carrier concentration with respect to the nid core ZnO, which can be ascribed to the formation of Sb‐related acceptors compensating the native donors. The understanding of this electric compensation mechanism is the clear signature of p‐type Sb doping feasibility in ZnO NW. This important result opens the way to succeed in the p‐type doping in ZnO.

The generalization of this doping profiling methodology to other semiconductors NW could be pointed out.
Tracking tumor metastasis in vivo at high‐resolution
Authors: GOETZ Jacky
Published: December 2016

Three reasons explain why most of the critical events driving normal and pathological scenarios had been less investigated: they occur rarely in space and time, they are highly dynamic, they differ when studied
in situ
in an entire living organism. Metastasis is the primary cause for cancer‐related mortality, but its mechanisms remain to be elucidated. Intravital imaging has opened the door to
in vivo
functional imaging in animal models of cancer, however it is limited in resolution. Ultrastructural analysis of tumor metastasis
in vivo
has so far been hindered by the limited field of view of the electron microscope, making it difficult to retrieve volumes of interest in complex tissues. We recently developed a multimodal correlative approach allowing us to rapidly and accurately combine functional in vivo imaging with high‐resolution ultrastructural analysis of tumor cells in a relevant pathological context. The multimodal correlative approach that we propose here combines two‐photon excitation microscopy (2PEM), microscopic X‐ray computed tomography (microCT) and three‐dimensional electron microscopy (3DEM). It enables a rapid and accurate correlation of functional imaging to high‐resolution ultrastructural analysis of tumor cells in a relevant pathological context. As an example, we are now capable of providing high‐ and isotropic (8nm) resolution imaging of single metastasizing tumor cells previously imaged in the process of extravasation in the living mouse brain. This reliable and versatile workflow offers access to ultrastructural details of metastatic cells with an unprecedented throughput opening to crucial and unparalleled insights into the mechanisms of tumor invasion, extravasation and metastasis in vivo.
Structure and dynamics of the endoplasmic reticulum in cultured mammalian cells
Authors: Joensuu Merja , Belevich Ilya , Vihinen Helena , Kumar Darshan , Rämö Olli , Lak Behnam , Jokitalo Eija
Published: December 2016

The endoplasmic reticulum (ER) is a large, single‐copy, membrane‐bound organelle that comprises an elaborate 3D network of structurally diverse subdomains: highly curved tubules, flat sheets, and parts that form contacts with nearly every other organelle of the cell. The ER is essential for the synthesis, modification, and transport of membrane and secretory proteins; it is also the site of cytosolic calcium level regulation and synthesis and transport of several lipids. To accommodate the vast range of functions, the ER network spreads throughout the cell, and its functions are distributed into structural subdomains according to their specific requirements. Many structural determinants of the network formation and maintenance have been described; however, it is not yet understood e.g. how different functions are distributed to the various subdomains, why the ER is constantly rearranging its architecture, and how the sheet/tubule –balance is maintained.

Proper ER operation requires an intricate balance within and in‐between dynamics, morphology, and functions. While ER structure is in constant flux, it does not move en masse, and the network movement is achieved through dynamics of individual subdomains and through network remodelling, which are accomplished through interactions with the cytoskeleton. Combining live cell imaging, thin section TEM and two 3D‐EM methods, we show that dynamic microtubules and actin filament arrays together contribute to the maintenance of ER sheet‐tubule balance. Perturbations of microtubule or actin cytoskeleton readily shift the balance towards tubules or sheets, which in turn can result in formation of sheet remnants or long and less fenestrated abnormal sheets. We recently identified the unconventional motor protein myosin 1c localizing to and regulating the ER associated actin filament arrays. Manipulation of myo1c levels disturbed the dynamics of actin arrays and affected ER sheet morphology similarly to actin manipulations with drugs. Tubular ER phenotype of myo1c‐depleted cells could be rescued with wild type myo1c, but not with a mutated form lacking the actin binding domain. We propose that ER ‐associated actin filaments have a role in maintaining the ER sheet‐tubule balance and sheet structure by regulating sheet remodeling events, and thus support the maintenance of sheets as a stationary subdomain of the otherwise dynamic ER network.

Knowledge of the mechanisms behind the structural maintenance and dynamics will be the key towards deeper understanding of ER functions and their regulation, and eventually, in unravelling molecular mechanisms behind various ER‐associated diseases.
Optics at the nanoscale with fast electron spectroscopies
Authors: Tizei Luiz
Published: December 2016

Electron microscopy techniques have been used to probe the optical properties of materials in the subwavelength scale. In particular, it has been shown that using cathodoluminesncence (CL) and electron energy loss spectroscopy (EELS), along with a propitious choice of electron beam energy and target material, resolution below 10 nm is attainable.

In this seminar we will describe recent advances electron spectroscopies in a STEM to probe individual quantum structures. Different experiments attempting to probe their optical properties will be presented (including their lifetimes). Typically, a 1‐nm‐wide 60 keV electron beam was used to excite the sample. Fundamentally, we have measured spectroscopic signals (CL and EELS) and the second order correlation function (g
2
(t)) of the emitted light of different materials using an optical spectrometer, an EEL spectrometer and a Hanbury‐Brown and Twiss interferometer.

We will start by showing how monochromated EELS and CL experiments are well adapted to probe excitonic excitations in different materials. We will show how EELS is specially adapted to probe excitons in 2‐dimensional materials, using MoS
2
and MoSe
2
monolayers as example. For thicker materials, CL is able to more easily produce meaningful information from excitoninc excitations. As examples, we will discuss the luminescence of GaN quantum wells in AlN nanowires (Figure 1) and excitons in hBN flakes.

However, only spectroscopic information does not give a complete picture of the behavior of a specific system. One example are single photon emitters (SPE). To characterize such systems, light intensity interferometry is necessary (a typical experiment in quantum optics). We will demonstrate how a similar experiment using CL is possible, using as example the neutral Nitrogen‐Vacancy center in diamond nanoparticles (Figure 2). Also, we will show how this setup allowed the detection of new SPE in hBN.

Finally, we will discuss how a CL setup with a HBT interferometer in a STEM microscope can be used to measure the lifetime of individual quantum emitters with a high spatial resolution (< 15 nm). We name this technique spatially resolved time‐correlated cathodoluminescence, SRTC‐CL. As an example, we will show that the lifetimes of 8 GaN quantum wells separated by 15 nm in an AlN nanowire can be measured by SRTC‐CL.
Studying membrane proteins in intact cells using nanoparticle labels and liquid‐phase electron microscopy
Authors: de Jonge Niels , Peckys Diana
Published: December 2016

Cells have receptor proteins in their plasma membranes ‘listening’ to chemical signals from the outside world. These signals consist of ligands, small molecules that bind specifically to a receptor. But how those signals are interpreted and lead to decisions is incompletely understood mainly on account of limitations of present analytical methods. It is typically extremely difficult to directly see how endogenously expressed individual proteins respond to ligand binding in the intact cell, which can lead, for example, to the formation of protein complexes triggering signaling processes. Much knowledge about cellular function has been obtained via biochemical methods but these analyze pooled material from many thousands of cells and the knowledge is thus based on population averages. But we need to look at the individual cell in order to understand the fundamentals of how a cell interprets a signal. Studying membrane proteins at the nanoscale in intact eukaryotic cells is now possible using liquid‐phase scanning transmission electron microscopy (STEM) [1, 2]. The key step is to specifically label the proteins of interest in a one‐to‐one ratio with small probes combined with nanoparticles, for example, gold nanoparticles or quantum dots. Cells in liquid are then placed in a microfluidic chamber enclosing the sample in the vacuum of the electron microscope, and are imaged with STEM. It is not always necessary to enclose the cells in the microfluidic chamber. For some studies, it is sufficient to obtain information from the thin outer regions of the cells, and those can be imaged with high resolution using environmental scanning electron microscopy (ESEM) with STEM detector [3]. Liquid‐phase STEM was used to explore the formation of the epidermal growth factor HER2 at the single‐molecule level in intact SKBR3 breast cancer cells in liquid state [4]. HER2 is a membrane protein and plays an important role in breast cancer aggressiveness and progression. Data analysis based on calculating the pair correlation function from individual HER2 positions revealed remarkable differences in functionality between different cellular regions, and between cells with possible relevance for studying cancer metastasis and drug response.