bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural analysis of
GaSb/GaAs
quantum rings for Solar Cells
Authors: Khan Atif Alam , Herrera Miriam , Fernández‐Delgado Natalia , Montesdeoca Denise , Carrington Peter , Fujita Hiromi , Asirvathan Juanita Saroj James , Wagener Magnus , Botha Reinhardt , Marshall Andrew , Krier Anthony , Molina Sergio
Published: December 2016

A type‐II GaSb/GaAs quantum dot (QD)/quantum ring (QR) solar cell (SC) achieves higher photo‐response than its type‐I counterpart [1], as it supports an enhanced carrier recombination rate due to a larger separation between the electron and hole confinements [2]. This behavior leads to greater valence band offset [2] and, eventually, the solar cell is also able to function well into the near infrared (NIR) regions [3]. The stacking of several GaSb/GaAs QDs layers within the SC is essential to increase the photon absorption, however these heterostructures face a large lattice mismatch (7.8%) that causes a high local strain [4]. Because of this, sometimes QDs tend to relax by diffusing Sb from its center, followed by As/Sb exchange, giving place to nanostructures in the form of quantum rings (QR). [5].

In this communication, we analyze a GaSb/GaAs structure grown at 480ºC by molecular beam epitaxy (MBE) on a GaAs substrate. The GaSb layers (2.1 ML) are capped by two consecutive GaAs layers (10nm at 480ºC and 30nm at 580ºC), and this whole segment is repeated 10 times. The structural properties of this sample have been analyzed by diffraction contrast Transmission Electron Microscopy (TEM) in a JEOL 2100 LaB
6
microscope, working at 200 kV. 220 bright field (BF) images of the GaSb layers have shown that no dislocations or other type of defects appear in the structure, and only some strain contrasts due to the lattice mismatch are observed. Fig. 1 shows a 002 dark field (DF) image of the sample that clearly shows two‐lobe shaped nanostructures corresponding to the presence of QR. We have found that the average diameter of the QR is 14 ± 5 nm, with average diameter of the individual lobes of 4±2 nm and an average height of 3±2 nm. Also, it is worth highlighting that a vertical stacking of the QR is not observed which is a consequence of a reduced propagation of the strain to the subsequent QR layers because of the large thickness of the GaAs barrier layers. High angle annular dark field (HAADF) analyses using an aberration corrected electron microscope are in progress in order to obtain more detailed information about the composition and the strain in these heterostructures.
Analysis of semipolarInxGa1‐xN/GaNheterostructures byWBDFandHRTEMimaging
Authors: Chen Xiaodan , Qi Haoyuan , Li Yueliang , Meisch Tobias , Scholz Ferdinand , Kaiser Ute
Published: December 2016

GaN‐based optoelectronic structures have been successfully applied in the fabrication of blue light emitting diodes (LEDs) and laser diodes [1]. The fabrication of high‐efficient green LEDs remains challenging which is referred to as the “green gap”. In GaN‐based green LEDs, the active region consists of InxGa1‐xN quantum wells (QWs) and GaN barrier layers (BLs) where the emitting wavelength is controlled by theIncontent (x). However,Inincorporation often results in inferior crystal quality due to the miscibility gap and lattice mismatch when theIncontent is increased [2]. Although conventionalc‐plane InxGa1‐xN /GaN QWs have demonstrated the highest crystal quality, the quantum efficiency remains low as a result of the polarization field along thec‐axis which tilts the conduction and valence bands thus reducing the recombination probability (i.e., quantum confined Stark effect, QCSE). Semipolar InxGa1‐xN/GaN structures, on the other hand, offer a good compromise between reduced QCSE and acceptable crystal quality [3].

In this study, we investigated the crystal quality of two sets of InxGa1‐xN/GaN structures grown on (11‐22) and (10‐11)‐semipolar planes. The samples were grown on sapphire by using metalorganic vapor phase epitaxy (MOVPE). The weak‐beam dark‐field technique (WBDF) was applied to investigate the distribution of the threading dislocations (TDs). Figure 1 shows the WBDF images of a (11‐22)‐semipolar sample. The GaN growth starts on thec‐plane‐like facets by MOVPE, forming triangular shaped stripes. The stripes subsequently coalesce forming a closed {11‐22}‐semipolar surface. TDs originate from the inclined c‐plane‐like GaN/sapphire interface and propagate inc‐direction and then bend 90° to thea‐directions. Most of the dislocations accumulate around the coalescence area and penetrate the QWs. The bending phenomenon is related to the triangular shape of the original GaN stripes and the SiNxinterlayers deposited during the growth of GaN.

By using high‐resolution TEM, we characterized the local structures of the QWs. Figure 2 shows the experimental HRTEM images of a (10‐11)‐semipolar sample acquired from the active region. Structural factors, such as the thickness of the QWs, the interfacial sharpness between the QWs and the BLs and the stacking faults formed with in the active region, can be analyzed with atomic resolution. Stacking faults are observed and confirmed to be the I2intrinsic type. [4]
FIB
characterisation of cell/device interface
Authors: Panaitov Gregory , Neumann Elmar , Offenhäusser Andreas
Published: December 2016

Cryo‐preparation of biological samples for electron microscopy has many advantages against the chemical fixation. Cryo‐fixation is extremely rapid which can inhibit, within milliseconds, the intracellular movements of macromolecules and other substances. Due to its rapidity, it may even allow the detection of the processes of contacting between the vesicles and the membrane in the cells. One can try to capture the processes at synapse contact, which would be impossible with much slower chemical fixation.

The problems may arrive if the biological sample is contacting to the solids for example at the interface of biological sensor. Due to different thermal expansion coefficient of the solid and biological materials, it may lead to unwonted artefacts at the interface area.

We will present the information about the interface between our structurally modified biosensors and biological cells of different preparation techniques. We have used cryo‐fixation, standard chemical fixation with critical point drying and epoxy embedding. For characterisation of the interface, we apply SEM and FIB (FEI Helios NanoLab DualBeam) sectioning at cryo‐ and room temperatures.
Tracking Atoms, Vacancies and Electrons via Aberration‐corrected Microscopy and First‐Principles Theory
Authors: Pennycook Stephen , Varela Maria , Gazquez Jaume , Biškup Nevan , Salafranca Juan , Pennycook Timothy , Zhang Yuyang , Wu Haijun , Feng Tian , Masahito Nagahata , Pantelides Sokrates , Venkatesan Thirumalai
Published: December 2016

The aberration‐corrected scanning transmission electron microscope (STEM) can provide real space imaging and spectroscopy at atomic resolution with a new level of sensitivity to structure, bonding, elemental valence and even spin state [1]. Coupled with first‐principles theory, this represents an unprecedented opportunity to probe the functionality of complex nanoscale systems. Two case studies will be presented utilizing the Nion UltraSTEM: first, determining the origin of the unexpected ferromagnetism in ultrathin, insulating LaCoO
3‐x
(LCO) films, which is induced by the spontaneous
ordering
of oxygen vacancies to relieve misfit strain (see Fig. 1) [2]. Second, the origin of the colossal ionic conductivity in Y‐stabilized ZrO
2
/SrTiO
3
superlattices [3], which is due to spontaneous
disordering
of the oxygen sublattice in response to biaxial strain coupled with the incompatibility of the oxygen sublattices at the interfaces (see Fig. 2) [4‐6].

A JEOL ARM 200F has recently been installed in the National University of Singapore, equipped with UHR pole piece, ASCOR hexapole aberration corrector, Gatan Quantum ER and OneView camera and Oxford Aztec EDS system. It is installed within a JEOL isolated room with thermal radiation panels, vibration and magnetic field isolation systems. Fig. 3 shows a Ronchigram at 200 kV with near 70 mrad half angle flat phase region, and initial results from Si [110] show good splitting of the dumbbells with information transfer to sub‐Angstrom levels, see Fig. 4. Results on oxides will be presented at the meeting [7].
Optical quantitative phase imaging by focal series reconstruction with partially coherent illumination
Authors: Mueller Johannes , Blessing Katharina , Koch Christoph
Published: December 2016

Optical phase imaging has many applications, it allows to image transparent objects like cells without staining, which is a huge benefit in biology, and also allows to measure the phase from reflecting objects to determine their topography. Furthermore, there are many applications in life science, material science, healthcare and industry for optical phase imaging.

There exist different methods to image phases, phase contrast microscopy converts the phase information into amplitude contrast, but is difficult to interpret quantitatively, quantitative phase microscopy (QPM) on the other hand tries to determine the phase information quantitatively. Several full‐field QPM methods exist, they can be divided in off‐axis approaches and inline approaches. Off‐axis approaches need a special microscope due to the reference beam and suffer from the high coherence of the illumination resulting in phase noise. Inline approaches could be divided in phase‐shifting methods, common‐path methods, digital inline holography, ptychography, Shack–Hartmann wave front sensors and focal series reconstruction, e.g. from the transport of intensity equation (TIE). Some of these approaches need special equipment, like laser illumination, gratings or spatial light modulators, which makes them expensive or introduces artefacts from the experimental setup or from the reconstruction algorithm.

Focal series reconstruction has the advantage, that it only needs a standard optical microscope plus a computer and no additional equipment, this makes quantitative phase imaging from focal series reconstruction both an easy and a low‐cost method.

Figs. 1 & 2 present results obtained by our current approach to optical quantitative phase imaging, where we use focal series reconstruction with partially coherent illumination (a green LED source). The images were aquired using a Zeiss Axiovert 200M microscope and a pco edge sCMOS camera by varying the object height (z = 0µm is the focal plane). We apply our flux‐preserving iterative reconstruction algorithm [1] and combine it with a TIE‐like approach [2]. It aligns the images during reconstruction and applies gradient‐flipping regularization [3]. This full‐resolution inline holography (FRIH) algorithm [2] was originally developed for electron microscopy, but here we apply it to optical microscopy. We will discuss the validity of the reconstruction, especially with respect to artefacts and present the algorithm and the results in more detail.
Spectroscopy on Black Phosphorus exfoliated down to the monolayer
Authors: Gaufrès Etienne , Favron Alexandre , Fossard Frédéric , Lévesque Pierre , Phaneuf‐L'Heureux Anne‐Laurence , Francoeur Sébastien , Martel Richard , Loiseau Annick
Published: December 2016

Black Phosphorus (P(black)) is a 2D semiconductor characterized by a direct band gap associated to high carriers mobility. The crystal is composed by tetravalent P atoms stacked by weak van der Waals interactions that can be exfoliated down to the monolayer using similar procedures than for graphene. Studying pristine thin layers of P(black) is however challenging due to its strong degradation upon exposure to visible light in air.

In this study, we have investigated the chemistry of degradation using
in‐situ
Raman spectroscopy, Transmission Electron Microscopy imaging and Electron Energy core‐Loss spectroscopy (EELS) of mechanically exfoliated layers prepared in their pristine state in a glove box. The results highlight a thickness dependent photo‐assisted oxidation reaction by adsorbed oxygen in water [1]. Using EELS, we have inspected the O K‐edge and P L2,3 edge which gets shifted from 130.2 eV in pristine phosphorus to 136 eV in oxidized phosphorus. As shown in Fig.1, the thickness dependence to oxidation has been clearly revealed by comparing layers of different thicknesses before and after a 30s exposure to ambient air and light. On the basis of such experiments, we have proposed an oxidation mechanism involving electron transfer processes based on quantum confinement and found appropriate manipulation procedures opening a route to first Raman measurements on 1 to 5 pristine layers of P(black)[1].

We use also low‐loss‐EELS spectroscopy to investigate the angular dependence in the Brillouin zone of the dielectric response of exfoliated P(black) in the range [2‐40 eV], taking advantages of the TEM‐STEM Libra 200 machine at LEM. This machine is equipped with an electrostatic monochromator operating at 80 kV and makes possible the investigation of the angular dependence of the dielectric function at a nm scale and with an energy resolution below 100 meV. To this aim we applied the technique developed in [2] and fully adapted to the machine. Using this technique we have studied the onset of electronic excitations and the dispersion of the plasmons as a function of the q momentum for different crystallographic in plane orientations in mechanically exfoliated P(black) down to 2‐3 layers. An example of w ‐ q mapping recorded along the [002] q‐direction is displayed in Fig.2 and reveals a large dispersion of the plasmon peak occurring at 19 eV at q= 0. The quantification of this dispersion is obtained by extracting the q dependence of this plasmon peak from the map as shown in Fig.3. Q dependences along two different in plane directions of the layers, namely [200] and [002], are compared in Fig.4 and clearly reveal high anisotropy effects, which will be discussed with the help of suitable ab initio calaculations.
3‐D areal functional parameters extracted from
AFM
data of polished dental tooth‐restorative nanocomposites
Authors: Lainović Tijana , Ţălu Ştefan , Stach Sebastian , Vilotić Marko , Blažić Larisa
Published: December 2016

The analysis of contemporary areal functional surface parameters of functional parts in any system of elements, that are in contact with each other, is essential for the understanding of their frictional behaviour. Oral environment is a specific tribological system where a tooth or a tooth‐restoration is exposed to the cyclic mechanical, thermal, and pH changes. 3‐D areal texture parameters of tooth replacing materials are of a great importance for prediction and understanding of the materials' tribological properties during their functional use.

The aim of this study was to conduct a detailed AFM morphological analysis of contemporary dental nanocomposites and to calculate specific 3‐D surface texture parameters, after four dental polishing protocols.

Two representative materials were chosen for testing: nanohybrid (Filtek Z550, 3M ESPE ‐ FZ550) and nanofilled (Filtek Ultimate Body, 3M ESPE ‐ FUB). The polymerized composite samples were polished by four different dental polishing procedures: multi‐step (MSP), single‐step (SSP), multi‐step followed by diamond paste (MSP+D), and single‐step followed by diamond paste (SSP+D). For the texture analysis the atomic force microscopy was used (Veeco di CP‐II). Using the software packages: Mountains Map
®
7 (Digital Surf, Besançon, France, available from:
http://www.digitalsurf.fr
) and Gwyddion 2.28 (available from:
http://gwyddion.net/
), the depth histograms, volume surface parameters, peak count histograms, watershed segmentation algorithms, average power spectral density were calculated to describe the 3‐D surface properties of tested specimens.

These parameters offered the possibility of a more profound understanding of the structure‐related functional properties of the surfaces of tested materials. The MSP created a more favourable surface texture on both tested materials. It had narrower height distribution and volume surface parameters which indicated the lower wear probability of materials polished by MSP than the SSP. The number of motifs after the watershed segmentation was the highest on the samples polished by MSP, due to the presence of fine surface irregularities. SSP created lower number of motifs, by cutting the surface details and creating deep and wide grooves, plane aspects of dales or hills. MSP or MSP+D mostly created more isotropic surface texture, which indicates that the MSP can be considered as a reliable method for dental composites polishing in comparison with the SSP or SSP+D.
Recognition and measurements of nanoparticles in
TEM
/
STEM
images by fitting the model grayscale distribution to the real one: new approach for automated statistical analysis
Authors: Shvedchenko Dmitry , Suvorova Elena
Published: December 2016

The main challenge to manufacture nanoparticles for applications in catalysis, medicine and pharmaceuticals is a mass production of stable nanoparticles with a narrow size distribution to target and control specific effects. Therefore reliable and fast statistical analysis of (nano)particles is of great interest especially for the particle size less than 10 nm due to strong chemical and biological activity associated with high penetrating capabilities through cell membranes. We would like to see these particles, to know their structure and composition, and to measure sizes. The intelligent, fast and reliable program can be a very useful tool for image analysis of “small” nanoparticles in TEM/STEM images.

In our work, we show that fitting of the calculated grayscale distribution to the real distribution in (S)TEM images is able to provide the maximum accuracy in measurements of the particle diameters in opposite to algorithms based on image binarization.

We apply such fitting to the truth in the vicinity of a nanoparticle image revealing the mass‐thickness, diffraction, and Z‐contrast. In order to describe the dependence of grayscale from thickness of nanoparticles the polynomial g(t) = g
0
+g
1
t+g
2
t
2
+… with sufficiently high power (≥2) and uncertain coefficients was chosen. The high‐degree polynomial is required to take into account the possible non‐monotonic dependence of the grayscale from particle thickness due to the presence of diffraction contrast (in opposite to pure mass‐thickness contrast). Monotonic dependence of the grayscales from specimen thickness is the characteristic of mass‐thickness contrast of particles (amorphous or crystalline particles positioned out of Bragg conditions) in TEM images and Z‐contrast in STEM images. The transfer function of CCD cameras determined the grayscale in the given point of the micrograph through the intensity of the incident wave has also monotonic character. Only the presence of diffraction contrast in the images breaks the monotonic dependence. Thickness of the spherical nanoparticle in a point having (x,y)‐coordinates can be expressed as t(x,y)=((d/2)
2
‐(x‐x
c
)
2
‐(y‐y
c
)
2
)^(1/2). During fitting, the uncertain coefficients g
i
, coordinates of the particle center (x
c
,y
c
), and the particle diameter d are computing. Our algorithm for particle recognition and measuring sizes is proposed and realized in the program ANN (Automatic Nanoparticle Numerator).

Our algorithm for particle recognition and measuring sizes out of thresholding approach is proposed and realized in the program ANN (Automatic Nanoparticle Numerator). The comparative study of distributions of silver nanoparticle synthesized in different polymer‐water solutions determined manually (about 1000 particles), using ImageJ and ANN was performed (Fig.1 and Fig.2). It shoved a good agreement between results obtained manually and with ANN.
Understanding the use of scattering cross‐sections in quantitative
ADF STEM
Authors: Martinez Gerardo T , van den Bos Karel H.W. , Alania Marcos , Nellist Peter D , Aert Sandra Van
Published: December 2016

Quantitative scanning transmission electron microscopy (STEM) using an annular dark field (ADF) detector has become a widely used technique for the characterization of materials at the atomic level. The quantification process involves the comparison of experimental data with image simulations, the use of statistical tools in a parameter estimation framework or a combination of both [1]. These methods have been developed using different measures for comparison, like peak intensities at the atom column position [2], image contrast variations [3] or so‐called scattering cross‐sections [4, 5]. The latter correspond to the total scattered intensity integrated over the atom column area. They have been shown to be very sensitive to the number of atoms in a column and its composition [1, 4, 6, 7]. Figure 1a shows the increase in peak intensity (green axis) and cross‐section (black axis) versus increase in number of atoms for a Pt column in [110] zone axis. As it can be observed, the peak intensity saturates after around 8 atoms meanwhile the cross‐section monotonically increases. In this work, we perform an analysis of how the electron wave propagates inside the crystal for the probe positions that conform the scattering cross‐section. With this, we analyse how the signal is generated for different detector collection angle regimes. Then, the analysis allows to identify the origin of the scattered signal and why scattering cross‐sections are more sensitive for composition and number of atoms as compared to peak intensities. In Figure 1b, we show a simulated image of a unit cell of a Pt crystal in [110] zone axis with a color‐edited version indicating the labels of the probe positions that form the scattering cross‐section and their respective distance to the atom column position. Figure 2 shows the probability amplitude of the electron wave as it propagates through the crystal for probe position r0 (a), which corresponds to the peak intensity, and for the sum of all the probe positions that conform the scattering cross‐section (b). From this, we observe that the atom column is excited deeper in the column when analyzing the cross‐sections. The off‐column probe positions carry more rich information about the scattering process for different thickness and collection regimes, which explains the increased sensitivity of this measure to the number of atoms and its composition. We then discuss the contribution to the scattered intensity for different detector collection angle regimes, such as LAADF, MAADF and HAADF.
Including the effects of atomic bonding inTEMandSTEMimage simulations
Authors: Naginey Timothy , Nellist Peter , Nicholls Rebecca , Yates Jonathan
Published: December 2016

Most of the software used to simulate TEM/STEM images completely neglects interatomic interactions in the sample and thus leaves out the effects of charge transfer and chemical bonding. The effect of these interactions on the image is generally small compared to the total charge density, but essential to understanding many important properties of materials. These interactions are especially important for fully quantitative interpretations of TEM/STEM images of certain sample types such as bulk oxides because of the strong ionic bonds, and 2D materials composed of light elements since most of the electrons are involved in bonding. In order to accurately simulate TEM/STEM phase images of these and other such materials, we have employed the CASTEP [1] code to generate accurate projected potentials which take into account both intra‐ and interatomic electron interactions. CASTEP uses density functional theory (DFT) to calculate electron densities, which are directly related to the electrostatic potential via Poisson's equation. These potentials are then used to calculate the projected potentials for use in multislice algorithms to simulate TEM/STEM images. We have added to the functionality of CASTEP so that these projected potentials can be obtained directly from the software, thus allowing us easy and accurate simulation of images with bonding effects included which enables accurate interpretation of experimental images of materials, such as h‐BN. Although a similar approach has been used by Kurasch et al. who obtained projected potentials by post‐processing output from the WIEN2k software [2], no one, to our knowledge, has done this with a code which benefits from the use of pseudopotentials such as CASTEP.
He‐filled bi‐dimensional defects in Ti3SiC2
MAX
Phases
Authors: Nicolai Julien , Beaufort Marie‐France , Barbot Jean‐François , Warot‐Fonrose Bénédicte
Published: December 2016

Ti
3
SiC
2
is a member of the family of layered ternary compounds well known as the M

n

+1
AX

n

phases (
n
= 1 – 3, or ‘MAX phases’) where M is a transition‐metal, A is an A‐group element and X is either carbon or nitrogen. These compounds have attracted increasing attention since they possess a unique combination of metallic and ceramic properties. They are elastically stiff, electrically and thermally conductive, relatively soft, damage tolerant and resistant to thermal shock. Therefore, Ti
3
SiC
2
have been proposed to be used in the generation IV nuclear reactors and several works were devoted to studying radiation damage by high energy heavy ions. Ti
3
SiC
2
is mainly synthesised by powder metallurgy. Nevertheless, it was recently shown that monocrystalline Ti
3
SiC
2
thin films onto 4H‐SiC can be formed by magnetron sputtering using Al and Ti co‐deposition on SiC at room temperature following by an annealing [1]. Ti
3
SiC
2
formation is based on interdiffusion processes between the substrate and the deposited layer. A layered hexagonal structure is obtained which consists of alternate near‐close‐packed layers of Ti
6
C octahedral interleafed with layers of Si atoms. Thin‐film of Ti
3
SiC
2
could become suitable for many applications such as electrical contacts, wear protective coatings and to produce the new 2D materials labelled MXène. It is then crucial to progress in the knowledge of the physical properties of Ti
3
SiC
2
thin‐film especially their behaviour under ion implantation. Light ion implantation (He, H) is commonly used to produce two dimensional defects in Si which are considered to be the precursors of cracks that are particularly interesting for the thin layer transfer technique well‐known as the smart‐cut process. The purpose of this work is to study the defects induced by light ion implantation (He, H) in Ti
3
SiC
2
thin‐film in order to create He/H‐platelets. The microstructural analysis of the implant Ti
3
SiC
2
thin films and their evolution under subsequent annealing will be performed by XRD and XTEM. First XTEM results (Fig. 1) show a high density of He‐platelets after low energy He implantation at medium fluence and subsequent annealing. Works are in progress for studying in more detailed the MAX phase and the He‐platelets. Results will be compared to a theoretical work who predicts that He atoms prefers staying near Si atoms [2].

The authors wish to acknowledge P. Guerin for his help during the film deposition and M. Marteau for He implantation experiments.
The Effect of Modified University of Wisconsin Solution on Kidney Preservation Time
Authors: Coskun Abdurrahman , Yegen Cumhur , Arbak Serap , Attaallah Wafi , Gunal Omer , Seckin Ismail , Cetiner Banu , Yildirim Zeynep , Erdemgil Yigit , Elmas Merve Acikel , Demirci Sibel , Can Ozge , Serteser Mustafa , Ozpınar Aysel , Basdemir Gulcin , Belce Ahmet , Unsal Ibrahim
Published: December 2016

Protection of organ function is important factor for the success of organ transplantation. Protection activity and also protection time period are dependent on a large scale of pre‐transplant preservation solutions. Therefore, donor organs are being preserved in special preservation solutions such as University of Wisconsin (UW), Histidin‐Triptophan‐Ketogluterate (HTK) and Celcior solution. For that aim, UW is the most preferred solution, even so, this solution could not preserve the organs over 36 hours. In this study, the ingredients of the UW solution were changed to extend the preservation time and also to provide more effective protection. Rat model is used for investigation of time related morphological changes between UW (group I) and Modified UW (Mod UW) (group II) solutions during preservation time. Rat kidneys were perfused with respective solutions. Totally perfused kidneys were removed and placed either in UW or Mod UW solutions and also kept during 2, 10, 24 and 72 h at 4° C. Kidney tissue samples were taken at given time intervals and fixed with 10% formaldehyde, and then these samples were prepared for paraffin sections. These tissue samples were also taken at 72nd hour, they were fixed in 2.5% glutaraldehyde and processed for epoxy resin embedding. For light microscopical evaluation, renal injury, based on tubular and glomerular degeneration, inflammatory cell infiltration, and vasocongestion has been scored with using a scale ranging from 0 to 3 (0: none; 1: mild; 2: moderate; and 3:severe) for each criterion. Liquid samples were also taken 2, 10, 24 and 72 h at 4° C from the storage media and investigated for LDH activity which was measured using standard chemistry method (Siemens ADVIA 1800 chemistry System). Microscopical examinations showed that Mod UW solution provided good preservation for all time intervals than UW solution. These results are consistent with lactate dehydrogenase (LDH) levels. Vacuolated tubular cells, as well as decreased renal tubules and glomerular degeneration described a prominent tissue injury revealed at 72nd h of UW group. Podocyte degeneration, formation of hump with GBM thickening revealed in 72nd h of UW group at transmission electron microscopical level. These degeneration parameters were observed less than in 72nd h of Mod UW group. It was concluded that Mod UW solution at low temperature is very effective and suitable for preservation up to 72 h.
Experiment design for quantitative dark field imaging and spectroscopy of catalyst nanoparticles using Scanning Transmission Electron Microscopy (
STEM
)
Authors: Varambhia Aakash , Jones Lewys , De Backer Annick , Fauske Vidar , Van Aert Sandra , Ozkaya Dogan , Lozano‐Perez Sergio , Nellist Peter
Published: December 2016

The performance of catalyst nanoparticles is generally dependent on their size, shape, strain, composition and support. However, the relationship between these parameters and the catalyst performance is not well understood. In most instances, the catalyst design process involves several design and testing iterations until the desired performance is attained, and identifying the structure‐property relationships would enable rational catalyst design. In order to relate the nanoparticle properties to catalytic activity, it is necessary to characterise them at atomic resolution.

With aberration corrected STEM it is now possible to image and perform spectroscopy on nanocatalysts at high resolution to obtain detailed structural and compositional information. Here we show how experiment design including detailed calibration of imaging and spectroscopy parameters can reveal the required information, using Ru, Pt and alloyed Pt‐Co catalyst nanoparticles as examples.

As a first example, structural studies of Ru nanoparticles, using methods recently developed
[1]–[3]
, indicated the formation of thin Ru rafts (Figure 1). The formation of Ru rafts has been controversial since their hypothesis
[4]
. These results demonstrate how quantitative ADF imaging can be used to resolve this question.

Using a new detector mapping technique developed at Oxford University, a range of Pt nanoparticles were characterised for their three dimensional structure (Figure 2). The models, created using an energy minimisation approach previously described in ref [3], indicate a Wulff‐like structure. We will show how these models can be used as input for density functional theory simulations, thus unlocking the possibility to study the electronic structure of experimental catalyst nanoparticles.

It is important to increase analysis throughput by software automation
[3]
in order to gain statistically meaningful results. In Figure 3 a rapid particle size measuring algorithm was used to measure the size distribution of Pt and Pt‐alloy nanoparticle systems. The size distribution can then be used as a guide for the microscopist to selectively choose nanoparticles which represent the particle ensemble.

Finally, experiment design and preliminary EDX and EELS results at high resolution will be presented. This approach aims to decouple composition and thickness effects in order to obtain structural information of alloyed nanoparticles.
The inverse problem of quantitative emission electron microscopy with account of distribution of the electron energy
Authors: Nepijko Sergej , Schönhense Gerd
Published: December 2016

In emission electron microscope (EEM) energy distribution of emitted electrons can significantly affect the image contrast of microfields. This influence is the more the less energy of emitted electrons in volts differs from the residual of potentials of effective microfields. As usual it is accomplished in threshold photoelectron emission. Analytically this objective was solved for cases of contrast formation in EEM with using aperture or without that one. Determined from the obtained formulas and measurements built‐in potential between Ag particles (thickness 30 nm, lateral size 20×20 µm
2
) and Si(100) substrate is 0.7 eV. Calculation shows that this value is two times higher without accounting of photoelectrons energy distribution (high pressure mercury lamp was used for excitation).

Remarkable that the expression for correction that appeared in energy distribution of electrons emitted from the sample coincides with contrast defocus formula. It means that some initial energy of emitted electrons is equivalent to image defocus and thus can be compensated by some refocusing of images.
Nanocathodoluminescence reveals the mitigation of the Stark shift in InGaN quantum wells by silicon doping
Authors: Griffiths James , Zhang Siyuan , Rouet‐Leduc Bertrand , Fu Wai Yuen , Zhu Dandan , Wallis David , Howkins Ashley , Boyd Ian , Stowe David , Humphreys Colin , Oliver Rachel
Published: December 2016

InGaN quantum wells (QWs) show high internal quantum efficiencies over the ultraviolet to green spectrum and in white light emitting diodes (LEDs). However a persistent challenge to the development of higher efficiency devices is the strong polarisation field across the across the QWs along the polar axis. The polarisation induced internal electric fields cause the spatial separation of the electron and hole wavefunctions in the QWs, known as the quantum confined Stark effect (QCSE). It has been proposed that the internal electric field can be suppressed by silicon doping the quantum barriers (QBs) [1]. Moreover, Kim
et al
. have theoretically shown that the device efficiency may be improved by variations in the silicon dopant concentration through the QWs [2]. To confirm the simulated properties though, it is crucial to resolve the spectral properties of individual QWs.

In this study, nano‐cathodoluminescence (nanoCL) reveals for the first time the spectral properties of individual InGaN QWs in high efficiency LEDs and the influence of silicon doping on the emission properties [3]. A silicon doped layer at 5×10
18
cm
‐3
is included immediately prior to the growth of the 1
st
QW and the QBs between the QWs are subsequently doped to 1×10
18
cm
‐3
(sample A). Two further multiple QW InGaN/GaN structures were also grown for reference with QB doping levels of 1×10
18
cm
‐3
(sample B) and 1×10
17
cm
‐3
or less (sample C). NanoCL reveals variations in the emission wavelength that directly correlate with individual QWs. With QB doping greater than 1×10
18
cm
‐3
, there is a continuous blue shift in the emission wavelength of each of the subsequently grown QWs. The inclusion of a higher doped layer immediately prior to the growth of the 1
st
QW in the LED structure leads to a blue shift unique to the 1
st
QW.

The experimental variations in the emission wavelengths were reproduced by Schrödinger‐Poisson simulations. The blue shift in emission wavelength through the QWs due to QB doping is found to be caused by screening of the internal electric fields. The reduction in the emission wavelength of the first grown QW due to the higher doped layer is also found to be the result of screening of the internal electric field. The mitigation of the QCSE and consequently stronger overlap of the electron and hole wavefunction, thus should result in an increase in the radiative recombination. NanoCL thus may serve as an experimental approach to study and refine the design of future optoelectronic nanostructures, including the effects from doping and lead to improvements in device efficiency and functionality.
Characterization of
CoO@MnFe2O4
Magnetic Hollow Nanoparticles
Authors: Benito Rodríguez‐González J. , Mariño‐Fernández Rosalía , Ramos‐Docampo Miguel A. , Salgueiriño Verónica
Published: December 2016

Magnetic core@shell nanoparticles are interesting candidates for applications in areas such as drug delivery, medical imaging, hyperthermia, sensing and biodetection. In many of these applications the availability of particles, being at the same time hollow and magnetic is a great technological advantage ahead of a realistic implementation. In this work we show the characterization of CoO@MnFe2O4 magnetic hollow nanoparticles obtained using octahedron‐shaped CoO nanoparticles as templates. A 3 nm magnetite (Fe
3
O
4
) layer was first deposited over the CoO octahedrons. In a second steep, a solid‐state reaction transforms the Fe
3
O
4
into MnFe
2
O
4
, and the former solid octahedrons into CoO@MnFe
2
O
4
hollow and pierced nanoparticles. Characterization showed the octahedron shape was maintained along the process, electron diffraction and FT also confirmed an almost perfect epitaxial growth of the shell. Finally, EELS showed a higher Fe content in the shell.
Microscopic approach to reveal nanoparticles effects in fish
Authors: Perrier Fanny , Mesmer‐Dudons Nathalie , Mornet Stéphane , Baudrimont Magalie , Simon Olivier , Feurtet‐Mazel Agnès
Published: December 2016

According to the US National Nanotechnology Initiative, nanoparticles are a set of solid particles with a diameter ranged from 1 to 100 nm. Numerous domains employ nanoparticles (such as industry, cosmetic, construction, medicine…) due to their specific properties.

The significant arise of nanomaterials application leads to a boost of environmental discharges and especially in aquatic systems which represent an important pollutants receptacles. Nevertheless, the lack of knowledge about the toxicity of nanomaterials can be detrimental for the aquatic ecosystems sustainability. Trophic transfer is often referred as an important pathway of nanoparticles contamination in aquatic systems being reportedly the main exposure route to organisms. Among their great variety of nature and characteristics, gold nanoparticles (AuNPs, PEG coating, diameter 10nm) have been chosen as model contaminant due to their high stability in solution.

This work aims to characterize: (i) AuNPs transfer within food chain and (ii) a histological study of AuNPs damages in fish. Thereby natural river biofilms contaminated in laboratory for 48h at environmental AuNPs' concentrations were grazed by the fish
Hypostomus plecostomus
during a 21‐days laboratory experiment. Gold analyses (by atomic absorption spectroscopy) revealed that biofilms presented a high AuNPs retention capacity. Secondly, results point out that AuNPs were effectively transferred from natural biofilms to the grazer fish showing their ability to enter the food chain. Regarding AuNP fish distribution, organs involved in metabolism and excretion (
i.e
. liver and kidney) presented a significant bioaccumulation. Moreover, transmission electron microscopy observations showed tissue alterations indicating inflammatory responses for all organs studied. AuNPs appeared to be: (a) distributed by the circulatory system into fish organs without entering the erythrocytes and (b) not degraded once internalized by the fish.
Nanostructure of
Mo2BC
thin films and the effect on mechanical properties
Authors: Gleich Stephan , Djaziri Soundes , Bolvardi Hamid , Schneider Jochen M. , Dehm Gerhard , Scheu Christina
Published: December 2016

The demand for materials in structural and functional applications requires nowadays more and more combined properties like high stiffness and simultaneously good ductility. The investigation and understanding of these unique properties is very important regarding a continuing optimizing of the materials and finally taking benefit from the outstanding properties in the future. Mo
2
BC is a promising candidate in this field as it combines properties preventing crack formation and also ensuring long lifetime. Density functional theory calculations predicated a high stiffness and a moderate ductility for Mo
2
BC by determining the electronic structure and the mechanical properties.[1, 2] A possible application of this material is the use as a hard coating for cutting tools protection.

In our work, we investigated Mo
2
BC thin films on silicon substrates which were synthesized by high‐power pulsed magnetron sputtering deposition technique.[3] Transmission electron microscopy (TEM) methods (bright‐field, high‐resolution TEM, selected area diffraction, electron energy loss spectroscopy) were used to compare the nanostructure of several Mo
2
BC films which were deposited at different substrate temperatures ranging from 380 °C to 630 °C. TEM samples were prepared conventionally using grinding and Ar
+
ion beam milling as well as by focused ion beam fabrication of thin lamellae extracted from the Mo
2
BC films. TEM investigations were performed at 300 kV using a FEI Titan Themis 60‐300. In Figure 1, TEM cross‐sectional micrographs of the Mo
2
BC film synthesized at the highest substrate temperature are shown exemplarily. The coating is fully crystalline and exhibits nanocrystalline columnar grains with a diameter of 10‐20 nm.[4]

Furthermore, X‐ray diffraction experiments and micromechanical tests were performed in order to correlate the mechanical properties of the films with their nanostructure. We detected an increasing crystallinity and hardness but a decreasing fracture toughness with increasing substrate temperature.
Calculation of phase contrast in
Cc/Cs
‐corrected
STEM
Authors: Lee Zhongbo , Kaiser Ute , Rose Harald
Published: December 2016

For STEM imaging, the pattern on the detector is a result of interference between elastically scattered wave and the incident wave. By recording the constructive interference and destructive interference with separate detectors, as well as by subtracting the two parts of intensity from each other, one can remove the background intensity as well as nonlinear information. As result, the remaining signal is enhanced phase contrast [1]. A recent experimental demonstration of differential contrast in STEM achieved by matching the detector geometry and the physical phase plates in STEM mode has been reported in [2].

On an aberration‐corrected STEM, an optimized differential phase contrast can be obtained by well designing the PCTF of the objective lens, and detector geometry accordant with the designed phase plate. The integrated spatial frequencies corresponding to positive contrast transfer is equal to those corresponding to negative contrast transfer. This ensures that nonlinear information cancels when the two parts of detector signals subtract each other.

Our calculation in Fig. 1 for Cc/Cs‐corrected STEM without damping factors illustrates the advantage of differential contrast compared with the conventional bright‐field imaging in STEM. The differential contrasts of single‐layer graphene are dominantly stronger than the contrasts achieved in STEM‐BF mode equipped with the same corrector. The differential contrast can reach 12, 18 and 26 times of the bright‐field contrast at 20kV, 50kV and 80kV, respectively! This demonstrates that in STEM mode equipped with an aberration corrector and a detector, matching the geometry of the phase plate, phase objects can be imaged with descent contrast.

With further improvement of the corrected state of the microscope, our calculation show that phase contrast imaging in STEM offers even more exciting possibilities. When the 5th‐order spherical aberration is corrected, the illumination angle dependent on the largest usable aperture, also increases, resulting in a shallow depth of field. This allows accurate focus at certain thickness of the sample, as shown in Fig. 2. At the 8
th
layer of a total 16‐layer (28nm) thick sample of Si, one silicon atom is replaced by a Germanium atom. A focal series through the sample shows that the layer marked by a substituted Ge atom is in focus at △f=‐12Å.

As a summary, the method of obtaining differential contrast in an aberration‐corrected STEM can be powerful for investigating weak scattering objects. Under a further improved corrected state of the Cc/Cs corrector, the differential contrast realized with this technique is extremely thickness‐sensitive, and focussing through atomic planes may come into reach.
Joint plasmon and core‐loss fitting for electron energy loss spectroscopy of
InGaN
Authors: Wang Xiaoyi , Walther Thomas
Published: December 2016

We demonstrate a method to fit electron energy‐loss spectra (EELS) of InGaN thin film samples by fitting both plasmon and core losses over the energy range of 13‐30eV. The main plasmon peak is relatively strong and broad. In our previous research, we have suppressed noise by using Lorentz fitting for the plasmon peaks of InGaN. Pure core‐loss spectra of Ga (Ga 3d transitions yield M
4,5
peaks at 23.8 and 28.5eV) and In (In 4d transitions yield N
4,5
peaks at 20.0 and 25.9eV) can be artificially constructed from EELS of binary compounds by subtracting the GaN plasmon peak (19.35eV) or the InN plasmon peak (15.5eV), see figure 1. Then the Ga 3d and In 4d reference spectra can be obtained by further smoothing the core‐loss spectra. Multiple linear regression is applied to experimental GaN and InN spectra of different relative thicknesses (t/λ), and the fitting quality is defined by adjusted R
2
, which lies higher than 0.998. In order to fit spectra from InGaN with different indium concentrations, InGaN core‐loss reference spectra were constructed by using artificial InN and GaN core‐loss spectra with linear compositional weightings, simultaneously, the chemical shift and broadening of the plasmon loss is considered in the MLLS fitting. For plasmon peak shifts we have applied our previous research results on the relationship between indium concentration and plasmon peak position [1]. The core‐loss chemical shift was assumed to follow the plasmon loss chemical shift, as depicted in figure 2. Finally, the MLLS regression can be performed to fit experimental spectra from InGaN as weighted superpositions of reference plasmon and core‐loss spectra corresponding to GaN, InN and a specific ternary InGaN alloy.

InGaN samples grown at high temperatures as typically applied in metal organic chemical vapour phase deposition are prone to phase separation, which was first predicted by Ho and Stringfellow [2]. The experimental spectra were recorded in TEM mode with a conventional Schottky field‐emission transmission electron microscope (FEG‐TEM). By using the joint plasmon and core‐loss spectra fitting of GaN, InN and InGaN, we have studied InGaN spectra with nominal indium concentrations of x=0.54 and x=0.62, where energy dispersive x‐ray spectroscopy suggests the indium concentrations are close to x=0.59 and x=0.68 respectively. The fitted spectrum in figure 3 indicates a strong evidence of phase separation in the nominal x=0.62 InGaN sample.