bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of the platelet structure in natural diamond by
ADF
‐
STEM
Authors: Korneychuk Svetlana , Turner Stuart , Abakumov Artem , Verbeeck Johan 
Published: December 2016

Electron microscopy is well known for its capability of determining the structure of many materials down to the atomic scale. A heavily studied material is natural diamond, but its rather small interatomic distance has made it a challenging material for TEM investigation. In this work we will demonstrate how novel TEM techniques can give fresh insights to this heavily studied material. Imperfections in natural diamond range from point lattice defects to dislocations and platelets. Platelet defects were first observed by means of TEM in the 1960s [1, 2] and nitrogen was detected making use of EELS in the 1980s [3]. Nevertheless, the exact crystalline structure of the platelets in natural diamond remains, perhaps surprisingly, still unclear.
In this work, we demonstrate our approach to determine the structure of platelet defects making use of annular dark field scanning transmission electron microscopy (ADF‐STEM) combined with advanced image processing. Combining experimental data with image simulations we are able to offer a consistent crystallographic model of the defect. Furthermore, using monochromated energy loss spectroscopy technique we suggest the type of nitrogen embedding into the defect plane.
TEM samples were prepared by a focused ion beam lift out procedure from natural type Ia diamond. ADF‐STEM and EELS experiments were carried out on FEI Titan microscope equipped with probe aberration corrector. We studied more than 50 platelets from different parts of the sample. In order to reduce scan distortions and damage to the defect plane a series of images with fast dwell time was obtained. The images were treated in the Smart Align software [4] to reduce the scan noise, correct the sample drift and a final summed image was obtained. Improved signal to noise ratio in this image allowed us to estimate the atomic positions and create a model of the platelet. Based on this model STEM image simulations were carried out. They are found to be in the good agreement with the experimental data. Using STEM‐EELS we prove the presence of nitrogen exactly in the platelet plane. Comparing DFT calculations of different nitrogen centres in diamond and the experimental spectra extracted from the defect plane we suggest the model for the nitrogen coordination in the platelet. Using this detailed information on the platelet defect, we will discuss the possible mechanisms of platelet formation.
The use of Correlation Coefficient maps to enhance visibility of internal structure for nanocrystalline thin foils
Authors: RAUCH Edgar , KISS Akos , LABAR Janos 
Published: December 2016

Orientation and phase are routinely determined with the automated ACOM tool developed for Transmission Electron Microscopes [1]. With this attachment, the beam is scanned over the area of interest and all the diffraction patterns are collected and kept in memory for further off‐line analysis. The present work concerns a novel approach that makes use of the memorized data to compute a structural image of the sample through a straightforward post‐processing algorithm that consists in weighting the similarities between the neighbor diffraction patterns [2].
The successive diffraction patterns acquired within a given crystal are anticipated to be nearly identical, while an abrupt change is expected when the beam is crossing a grain or a phase boundary. Plotting the value of a correlation coefficient that compares the intensities of every pixels of the neighbor diffraction patterns produces a contrasted picture in which all structural features that modify the local diffracting conditions are highlighted.
Fig. 1 gives a typical example where grain boundaries for a polycrystalline sample are retrieved. Of particular interest is the fact that the grain boundary contrasts are directly related to the boundary inclination. Indeed, the sharp changes in diffraction patterns expected for boundaries parallel to the electron beam are associated to a strong contrast. A weak and extended contrast indicates qualitatively a gradual modification of the diffracting signal as expected for inclined boundaries. Quantitative evaluation needs different processing [3].
The correlation coefficient is sensitive to any structural component that modifies the diffracting conditions. This is valid for dislocations, too. Two of them appear in the upper grain in figure 1.
Moreover, the correlation coefficient is less sensitive to non‐visibility conditions. This is because it is constructed on the difference between the intensities of all reflections including the faint ones. In particular, if the sample is in a so‐called two beam condition, the main reflection g remains unchanged when the beam is crossing a dislocation line whose Burgers vector is normal to g. This reflection will be dominant in the bright field image and the dislocation will not be visible. Being constant, g will not contribute to the correlation coefficient. By contrast faint reflections that always exist in the diffraction pattern ‐ even in two beam conditions ‐ will be affected by the distortion around the defect line. Figure 2 compares the virtual bright‐field image and the correlation coefficient map for a deformed ferritic steel sample. The thin foil is slightly bended (less than 2°, mainly from left to right) so that the contrast conditions are not homogeneous in the micrograph and part of the structural information is missing. The correlation coefficient is less sensitive to the exact illumination conditions and consequently additional dislocations appear in the map.
Detection of magnetic circular dichroism in amorphous materials utilizing a single‐crystalline overlayer
Authors: Zhong Xiaoyan , Lin Jie , Cheng Song , Rusz Jan , Xin Huolin , Cui Bing , Vancho Kocevski , Han Lili , Zhu Jing 
Published: December 2016

Electron energy‐loss magnetic chiral dichroism (EMCD) in a transmission electron microscope allows the quantification of the magnetic structure of crystalline materials down to the nanometer scale
[
1‐3]
. However, restricted by a confined diffraction geometry applied in EMCD experiments
[4]
, no experiments or theories have yet been performed to obtain EMCD signals for amorphous materials, due to their lack of long range ordering.

In this work, we for the first time demonstrate it is possible to detect element‐specific magnetic signals in amorphous materials utilizing a single‐crystalline overlayer as an EMCD beam splitter. The approach is applied to a bilayer sample where a very thin amorphous magnetic FeO
x
layer is grown on a single‐crystalline Yttrium‐stabilized ZrO
2
substrate. We found that both experimental results and theoretical calculations lead to unprecedented EMCD signals. The quantitative orbital to spin magnetic moment ratio of Fe in amorphous FeO
x
layer has been acheived.

Our approach allows us to break through the constraint of crystal formats in EMCD spectra measurements, providing new prospects of detecting EMCD signals from amorphous and ultrathin materials at the nanometer scale. This approach might also be extended to the magnetic quantitative analysis of other heterogeneous materials at high spatial resolution.
This work may open a door to meet the challenge of exploring magnetic states and behaviors of amorphous films, and have important consequences for revealing the magnetic structures of magnetic materials in various crystal forms at the nanoscale using transmission electron microscopy.
Transmission
K
ikuchi Diffraction: effective nano‐scale analysis using conventional
EBSD
hardware
Authors: Goulden Jenny , Mansour Haithem , Bewick Angus 
Published: December 2016

SEM‐based Transmission Kikuchi Diffraction (SEM‐TKD) [1,2] is an extension to the conventional technique of reflection EBSD (using bulk samples) to transmision EBSD using thin samples. The main advantage of SEM‐TKD over the conventional method is a large improvement in spatial resolution of point‐analysis from small particles and of mapping data from thin films.
This improvement is primarily a consequence of examining thin, electron‐transparent TEM samples in transmission, which reduces the effective diffraction and escape volume, as well as the use of zero‐ to low sample tilts which reduces anisotropic beam‐spreading effects. The technique is used to produce 2D datasets from flat, thin sample areas. This data is then used for microstructural analysis including crystallographic orientation, grain size, phase distribution, and grain boundary character and distribution. It is especially useful in characterizing highly‐strained materials and materials with grain sizes under 50nm.
A significant attraction of TKD is that these improvements can be realised using conventional EBSD hardware, in its conventional position on the SEM, without any modification. However, for TKD the sample position, pattern centre (high up or above the detector screen) and sample tilt (close to horizontal) are very different to those required for conventional EBSD (just above the screen centre line, and 70° respectively). Thus the TKD‐mode imposes a more extreme case of the gnomonic projection which is already inherent to the capture of conventional electron backscatter patterns.
The most notable effects of the TKD projection geometry are that horizontal bands near to the bottom of the screen are imaged wider than normal, and that the non‐symmetric intensity across these bands is highlighted (as illustrated in Figure 1).
Here we discuss how these distortions affect analysis using a conventional EBSP solving engine and some new technology developed to improve performance.
The effect of spark plasma sintering on structure and phase stability in half‐Heusler thermoelectric alloys
Authors: Tofan Raluca , Echevarria‐Bonet Cristina , Berland Kristian , Schrade Matthias , Sørby Magnus , Hauback Bjørn Christian , Persson Clas , Prytz Øystein , Hansen Vidar , Gunnæs Anette Eleonora 
Published: December 2016

Thermoelectric (TE) materials have the capability to directly convert a temperature difference into an electric voltage across the material and vice versa. Half‐Heusler (HH) compounds are a promising group of TE materials. They are ternary intermetallic compounds, with the general formula XYZ – X and Y transition metals (e.g., X=Ti, Zr, Hf and Y=Ni, Co) and Z a metal or metalloid (e.g., Sn, Sb). The electronic structure and charge carrier concentration can be manipulated by atomic substitution on each crystallographic site to enhance the TE properties. However, further increase of efficiency of the alloys is limited by the relatively high thermal conductivity. Nanostructuring is reported to reduce the thermal conductivity as a result of an enhancement of the phonon scattering, thus increasing the efficiency of the TE materials [1].
Spark plasma sintering (SPS) is reported to give rapid densification of powders into bulk specimens and retain nanostructures (grain boundaries) from the starting powders. In the current study, n‐type XNiSn alloys with different (Ti, Zr, Hf) compositions on the X‐site were prepared by ball‐milling of arc‐melted and thermally annealed ingots, followed by SPS for 10 minutes, with temperatures between 850 and 1100 °C and applied pressures between 65 and 80 MPa. The SPS prepared alloys were investigated with a combination of X‐ray diffraction (XRD) and scanning and transmission electron microscopy (SEM and TEM) techniques, supported by density functional theory (DFT) thermodynamic calculations.

In all SPS samples, graphite is present in the surface regions. At the interface between the graphite and the XNiSn alloys, carbides are present as illustrated in figure 1 for the HfNiSn alloy – sintered at 1100 °C and 80 MPa. In agreement with previous reports on HH studies, single phase HH does not form in any of the alloy systems [2]. Secondary phases are distributed along compositional HH boundaries as illustrated in figure 2 from the TiNiSn alloy, sintered at 900 °C and 80 MPa. Phase separation of HH phases, with different composition X
i
and HH lattice parameter, is generally evident by splitting of the HH reflections in the XRD diffractograms. In the case of the TiNiSn alloy, such splitting of the HH reflection is not observed; however, we find compositional variations of the HH phase from the nominal composition – consistent with the variations in the shades of grey seen in the HH regions in figure 2. In addition to the HH and secondary phases seen in the figure, grains of full‐Heusler TiNi
2
Sn exist in the alloy.
Direct determination of calibration factors for quantitative
DPC
measurements
Authors: Schwarzhuber Felix , Wild Johannes , Zweck Josef 
Published: December 2016

Differential phase contrast microscopy (DPC) is a measurement technique which is utilized in a scanning transmission electron microscope (STEM) equipped with a special direction sensitive detector [1,2]. It is based on the deflection of the electron beam by an angle α due to either Lorentz or Coulomb force, when the electron probe is scanned over an area with intrinsic magnetic or electric fields. This deflection causes a shift of the diffraction disk (DD) in the detector plane of the microscope, which is proportional to strength and direction of the field within the specimen. By measuring this shift with a direction sensitive segmented ring detector one obtains information about the intrinsic fields.
In this work we present an approach to determine calibration factors relating the qualitative DPC signals to absolute magnetic and electric field strengths or deflection angles just by measuring the size of the DD on the DPC detector. For this we derived a formula for the calibration factor by considering geometrical properties of the annular DPC detector and the DD. With this we can for example describe the absolute electric field strength E(x,y) at a certain specimen position (x,y) by:

E(x,y)[V/m] = ( S
DPC
(x,y) / S
sum
(x,y) ) · ( κ
el
[V] / t(x,y)[m] ) (1)

S
DPC
(x,y) being the DPC signal normalized with the sum signal S
sum
(x,y) of all four detector segments, the specimen thickness t(x,y) and the calibration factor κ
el
for electric fields. The latter can be described by:

κ
el
= [ (R
2
‐ r
2
) / (R · C) ] · [ (m
rel
· v
rel
2
) / e ] (2)

with R and r being the radii of the DD in the detector plane and the detector hole (see fig. 1) and C the used camera length of the microscope. The second term describes the energy of the accelerated electrons with their relativistic mass m
rel
, velocity v
rel
and elemental charge e.

Equation 2 shows us two important things. Firstly that the calibration factor is highly dependent on the radius R of the DD (see fig. 2 and 3). This means that even a small change of the DD radius due to beam broadening caused by the specimen can lead to significant different field values when they are quantified with a calibration factor determined for the same set of microscope parameters but with a slightly smaller disk radius.

The other one is, that it is possible to calculate κ
el
just by the measurement of R, because all the other variables in eq. 2 are well known parameters of the DPC measurement. The disk size itself can be easily determined e.g. with a CCD camera. This is a convenient way to calibrate a DPC system for quantitative measurements. Further it is possible to obtain individual calibration factors for each DPC measurement performed. The latter allows to minimize the error of the quantification due to disk broadening.

In addition to the theoretical approach we will also present our first experimental results showing the validity of the statements made above.
Comparison of different
EM
methods for observation of lipidic structures in the cell nucleus
Authors: Schrenkova Jana , Sobol Margarita , Philimonenko Vlada , Hozak Pavel 
Published: December 2016

Permanent progress in electron microscopy (EM) techniques enables us to reveal the finest ultrastructural details of the cell nucleus. Our recent work is focused on the previously unrecognized nucleoplasmic structures composed of phosphatidylinositol 4,5‐bisphosphate, so called PIP2 islets. The super‐resolution light microscopy enabled us to localize PIP2 islets inside the cell nucleus and reveal their colocalization with several components of Pol II transcription machinery and chromatin. However, only EM provides sufficient resolution to reveal the PIP2 islets ultrastructure and composition via immunostaining.
The usage of appropriate method for EM sample preparation is a crucial step in the whole procedure as PIP2 islets are lipidic structures which are predisposed to extraction or translocations. Here we compare different EM sample preparation techniques which we have optimized for the best ultrastructural preservation and antigenicity retention of PIP2 islets. We have analyzed several chemical fixation and cryoimmobilization approaches followed by various embedding media including both acrylic and epoxy resins. Moreover, different immunolabeling techniques were used such as pre‐embedding, on‐section labeling, and Tokuyasu method. With all these approaches we were able to observe roundish PIP2 islets (40‐100 nm) recognized by anti‐PIP2 antibodies. Preliminary results demonstrate that PIP2 islets are stable nuclear structures resistant to aldehyde fixation and extraction during preparation and cutting procedures. Based on the upcoming statistical analysis, the best approach for immunological studies of PIP2 islets will be selected.
Characterisation of theMedipix3detector for electron imaging
Authors: Mir Jamil , Mir Jamil , Clough Robert , MacInnes Ruaraidh , Gough Christopher , Plackett Richard , Sawada Hide , MacLaren Ian , Maneuski Dima , O'Shea Val , McGrouther Damien , Kirkland Angus 
Published: December 2016

AbstractHybrid pixel sensors, originally developed for particle physics, incorporate advanced analogue processing and digital conversion circuitry at the individual pixel level. Medipix3 [1] is an example of such a sensor and we have investigated its performance as an imaging detector for transmission electron microscopy (TEM). Measurements were performed with electron beam energies in the range, 60–200 keV on a JEOLARM200cF TEM/STEM [2] utilising a 256x256 pixel Medipix3 detector with 300 µm thick Si sensor layer.In order to characterise the Modulation Transfer Function (MTF) and the Detective Quantum Efficiency (DQE) performance, 32 repeated datasets were acquired containing images of free space and a knife‐edge for known beam current conditions at each energy across the full range of relevant Medipix3 energy threshold values. Data was acquired in Single Pixel Mode (SPM) and in Charge Summing Mode (CSM) [3], where, in the latter mode, effects from charge spreading in individual electron events are corrected for on the detector. We have also measured DQE(0) using the methods described in [4].At high lower threshold (THL) DAC values the MTF for this counting detector in single pixel mode is better than the theoretical maximum due to the reduction in the effective pixel size [4] as shown in Figure 1. However, the DQE at such high THL DAC values in single pixel mode is significantly reduced as seen in Figure 2, seeing as many real electron events are now not counted as the charge is deposited in more than one pixel and therefore falls below the threshold for detection. Consequently, there is a balance to be made between optimizing DQE and MTF, depending on the exact requirements in the given application.As is shown in Figure 3, the use of the CSM allows the achievement of a much higher MTF whilst retaining high DQE by using a lower threshold DAC value. This therefore offers additional benefits over the more conventional SPM, thus allowing very high efficiency imaging whilst preserving maximal detail in the images, which is particularly beneficial for minimizing the required electron dose to the sample required to produce interpretable data, with obvious applications in beam sensitive materials.
Structural characterisation of nanomaterials incorporated into bioengineered samples: An electron microscopy approach
Authors: Hobbs Christopher , Metel Sonia , Nicolosi Valeria 
Published: December 2016

This study analyses the properties of nanohydroxyapatite (nHA) and layered double hydroxide (LDH) materials that can be used as non‐viral gene delivery vectors. The former is a biocompatible, non‐toxic calcium phosphate mineral which makes it a suitable candidate as a delivery platform
1
. On the other hand, LDHs are composed of brucite‐like layers with a charge compensating anionic interlayer
2
.

(Scanning) Transmission electron microscopy ((S)TEM) and Energy Dispersive X‐ray Spectroscopy (EDX) methods were utilised to characterize LDH and nHA nanomaterials and their respective interactions with plasmid DNA structures (pDNA). The current work also characterizes the ultrastructure of mesenchymal stem cells (MSCs), as well as investigating the uptake and localisation of the LDH gene delivery vectors at the nanoscale.
Fig. 1(a) and Fig. 1(b) present the TEM images of the nHA and LDH particles respectively. The nHA particles are found to have a spherical structure of diameter ~50nm, indicating that nHA is a good candidate for cellular transfection. LDHs present a well‐defined hexagonal platelet‐like structure of ~100nm, providing promising results towards their application as a gene delivery vector.
The interaction of nHA and LDH particles with pDNA was also investigated using STEM. Morphological variations are clearly evident in both the pDNA‐nHA and pDNA‐LDH composites. An annular‐like structure is presented in the case of pDNA‐nHA, whereas the DNA structures absorb to the surface of the LDH particles, displayed in Fig. 2(a) and Fig. 2(b) respectively.
The application of STEM to MSCs highlight intracellular features such as membranes and nuclei, as shown in Fig. 3. The complimentary EDX techniques portray evidence of the LDH gene delivery vectors within the cell due to a presence of an Mg, Al and P peak, hence confirming uptake and localisation at the molecular level. The enhanced resolution provided by electron microscopy techniques allows for the study and understanding of cellular biological processes, such as that of pDNA‐nanoparticle delivery.