bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transmission electron microscopy of deformed Laves phase
NbFe2
Authors: Šlapáková Michaela , Voss Simon , Kumar Sharvan , Liebscher Christian , Stein Frank 
Published: December 2016

Laves phases are the largest class of intermetallic phases, showing very high strength up to temperatures above 1000 °C, but being very brittle at room temperature. The mechanical behavior and the deformation mechanism of these phases is very much different from that of pure metals and is still not well understood [1, 2].

The unit layer of a Laves phase AB
2
does not consist of only one plane but a slab of four planes, each of which is composed of either only A‐ or B‐atoms. This package of four atomic planes can be sub‐divided in one single B‐atom layer and a triple layer of successive A‐, B‐ and A‐atom planes [3].

The present work summarizes results obtained from transmission electron microscopy on single‐phase NbFe
2
before and after compression tests at high temperatures. The material was produced by levitation melting and has hexagonal
C
14‐type structure (
hP
12,
P
6
3
mmc
). The compressive stress‐strain curves are characterized by a pronounced stress peak in the stress‐strain curves at lower temperatures (up to 1200 °C) and by steady state flow at higher temperatures (above 1200 °C) [4].

Undeformed NbFe
2
is almost free of dislocations. It is assumed that the lack of dislocations in the as‐cast condition leads to the pronounced yield stress maximum observed during compression testing at lower deformation temperatures.

After deformation at 1200 °C new dislocations are introduced into the material. Widely‐extended stacking faults on the basal plane dominate the microstructure. They are bounded either by partial dislocations or terminate at low angle grain boundaries (Fig. 1).
Material deformed at 1300 °C shows a high density of dislocations, which are split into pairs of partial dislocations that bound stacking faults on the basal plane (Fig. 2). The observation that most dislocations are split up into Shockley partial dislocations could indicate deformation by the synchroshear process [5], as the occurrence of such partial dislocations is essential for this mechanism. Synchroshear is based on the idea of a synchronous shear motion of two adjacent planes within the triple layer.
Dislocation networks (Fig. 3 and 4) indicate the activation of dislocation climb. The improvement of dislocation mobility at higher deformation temperatures leads to the absence of a pronounced stress maximum in the stress‐strain curves.

The observed perfect dislocations are of (0001) 1/3<11‐20> type, the dissociated Shockley partials are (0001) 1/3<10‐10> type. The main deformation mechanism in the NbFe
2
C
14 Laves phase is basal slip.
A Variable‐Temperature Continuous‐Flow Liquid‐Helium Cryostat Inside a (Scanning) Transmission Electron Microscope
Authors: Börrnert Felix , Horst Alexander , Krzyzowski Michael A. , Büchner Bernd 
Published: December 2016

The progress in (scanning) transmission electron microscopy development had led to an unprecedented knowledge of the microscopic structure of functional materials at the atomic level. Additionally, although not widely used yet, electron holography is capable to map the electric and magnetic potential distributions at the sub‐nanometer scale. This opens a route to investigate the phase structures of electronic and magnetic phenomena in condensed matter at a microscopic level. Many of the most interesting solid state phenomena occur at low temperatures only. Nevertheless, low temperature studies inside a (scanning) transmission electron microscope ((S)TEM) are extremely challenging because of the much restricted size and accessibility of the sample space. Up to date, there are no cryo‐(S)TEMs or special sample holders that are capable to cool a sample controllably to any but its base temperature below room temperature.
Recently, we introduced a concept for a dedicated in‐situ (S)TEM for flexible multi‐stimuli experimental setups with the capabilities of holographic recording and scanning electron microscopy type imaging. A central part was a large sample chamber with multiple ports. With a prototype instrument, we demonstrated a maximum resolving power of about 1 nm in conventional imaging mode and substantially better than 5 nm in scanning mode while providing an effectively usable pole piece gap of 70 mm [1].
Here, we report about the state of the first major plug‐in fitted into the prototype in‐situ (S)TEM: A variable‐temperature liquid‐helium continuous‐flow cryostat for nanometer resolved imaging and diffraction at controlled temperatures between 10 K and 300 K. Arbitrary temperatures in the offered range can be installed and held stable by a heating in the sample mount with the help of a PID controller. The cryostat has two operation modes, one with two cooled radiation shields for temperatures below 10 K and one without the shields for free sample access from outside the cryostat at temperatures down to 20 K. Sample drift due to negative thermal expansion is reduced by a circular cooled sample mount and a flexible copper strand to the cold finger. The design of a continuous flow cryostat with a low consumption rate offers a long working time at low temperature while sucking helium from a 100 l vessel. Additionally, the cryostat offers four cooled terminals for fixed electrical contacts and is prepared for a future incorporation of two mobile electrical probes.
Examples of experiments now possible with this new setup are the mapping of the phase structure of different electronic and magnetic phenomena, like charge density waves and Skyrmions.
The measurement of off‐plane magnetic field through electron vortex beams
Authors: Grillo Vincenzo , Harvey Tyler , Pierce Jordan , Venturi Federico , Balboni Roberto , Gazzadi Gian Carlo , Frabboni Stefano , McMorran Benjamin , Boyd Robert , Karimi Ebrahim 
Published: December 2016

It is well known that a magnetic field produces a phase change proportional to the in plane magnetic field B [1]. Alas the out of plane magnetic field is more elusive. The only measurement that so far seems to produce any out of plane information is the magnetic dichroism [2] as it actually measures the out of plane magnetization.Unfortunately magnetic dichroism experiment is still a complicated experiment that requires a considerable control of the condition and of the material; moreover the measures of the magnetization , often with the objective on, is not directly a measure of the magnetic field itself.However while a plane wave along the optical axis has no significant interaction with a magnetic field along z , vortex beams with winding number l do feel such field through a Larmor phase effect.We will demonstrate here that through the use of large vortex beams [3][4][5] we are able, for the first time, to measure the out of plane magnetic field generated by a magnetic pillar of Co [6].We placed the vortex around the pillar ensuring as much as possible an axial symmetry and observed the phase effect. The result is in good agreement with the typical magnetization expected for the pillar with an average field at surface of about 2T.Fig 1 illustrates the A and B field produced by a magnetic pillar. The actual magnetic pillar fabricated by EBID deposition is illustrated in fig 1b. Fig 2 depicts the vortex beam density with L=200 as imaged in its focal plane. Thanks to an interferometric approach we were able to measure the magnetic phase contribution and bind it to the magnetic field in proximity of the sample. The magnetic phase is visible in the inset of fig 2 showing approximate axial symmetry.The technique has been carried on in Low Mag mode with the main objective lens off but there are no principle limitation to the application in conventional (S) TEM mode.Moreover this promises to be one of the best recognition of the importance of vortex beams in microscopy for material science.
Radial distribution function imaging by STEM diffraction: a method development in resolving the mysteries of amorphous materials
Authors: Mu Xiaoke , Wang Di , Feng Tao , Kübel Christian 
Published: December 2016

Interpreting atomic structure of amorphous materials have attracted attentions for a century and, in recent years, especially heterogeneous nanoglasses have fueled the interest because of their unusual structure and properties [1]. However, only few experimental means offer a way to characterize the disordered structures. Atomic radial distribution function (RDF) is one of the important tools for the goal, which was first obtained from X‐ray diffraction data of organic solids [2], and afterward extended to electron diffraction for metallic glasses [3]. RDF describes the probability to find certain atomic pairs as a function of the pair separation and consequently, provides structural information in the short‐ and medium‐range. However, the traditional diffraction experiments only average large sample areas and lack spatial resolution especially at nanometer scale. Plenty information is hidden in the averaged signal.
In this work, we demonstrate a newly developed method, RDF‐imaging, combining diffraction imaging in scanning transmission electron microscopy (STEM) mode [4] with RDF analysis and spectral‐imaging analysis (e.g. multiple linear least square (MLLS) fitting) to achieve structural mapping of heterogeneous amorphous materials with 1 nm resolution. Figure 1 schematically shows the procedure for data acquisition and RDF calculation: a 4‐dimensional (D) diffraction‐image is acquired by recording diffraction patterns in STEM mode with quasi parallel nano‐beam configuration (0.8 mrad convergence angle) and 1 nm spot size. RDFs are calculated from the diffraction patterns according to description in [3][5]. A 3D data cube of RDFs (RDF‐cube) is constructed by relating pixel positions of the initial diffraction‐image to the calculated RDFs. The RDF‐cube can then be analyzed by MLLS fitting of reference spectra taking experimentally from pure phase or numerically from matrix decomposition by multivariate statistical analysis.

The method is extremely sensitive to atomic packing variation. Figure 2 shows an application to amorphous ZrO
2
(a‐ZrO
2
) and a‐ZrFe multilayers. Not surprisingly, both the a‐ZrO
2
and the a‐ZrFe phases are unambiguously distinguished by RDF‐image (figure 2d,e), but also an interface layer between ZrO
2
and ZrFe (figure 2c) is detected, which could not be identified in STEM‐EELS and EDX maps. The atomic structure (figure 2a, red dashed‐line) of the interfacial layers possesses the same atomic packing as that of the a‐ZrO
2
phase (figure 2a, blue line) but with a 0.04 Å shrinkage of the average bonding distance. The shift in bonding distance could be introduced by Fe replacing Zr atoms in the ZrO
2
clusters due to diffusion of Fe atoms from the a‐ZrFe into the ZrO
2
layers.
In situ
TEM
study of nanoalloys in solution
Authors: De Clercq Astrid , Margeat Olivier , Henry Claude R , Giorgio Suzanne 
Published: December 2016

1. Introduction
Different Pt‐Pd nanoalloys were prepared from organic precursors in solution. Their nucleation and growth in the liquid was in situ studied in a graphene oxide liquid cell by the direct reduction in the electron beam [1‐3].
Then, the morphological evolution of the nanoalloys under gas pressure was in situ studied in an environmental sample holder [4] by standard TEM.

2. Pt@Pd core shell NPs
Increasing amounts of Pt could be deposited on Pd nanocubes cubes by sequential reduction, with a resulting concave shape as seen in fig. 1.

Fig.2 is a set of images during the Pt growth around the same Pd cube, during 20 mn. The operating conditions (magnification 800 K, electron density 3. 10
5
A/m
2
) corresponds to an increasing electron dose. During this time, the variation of liquid quantity in the drop was not visible. From the set of images, it seems that the Pt layer has an homogeneous thickness during the growth, so that the final concave shape results from other steps in the preparation process.

Then, the morphology of Pt@Pd nanocubes was in situ observed during oxido reduction cycles in a few mbar of pure O
2
and H
2
.

Fig. 3 clearly shows that the Pd@Pt nanocubes have concave shapes in pure H
2
. In pure O
2,
they are much rounded at the corners and the (110) facets are extended compared to the same samples in H
2
, as the anisotropy ratio between the surface free energies of (001) and (110) faces, increases from 0.7 in H
2
to 0.8 in O
2
.

3. Properties
A maximal reactivity in gas has been found for an equivalent thickness of 0.4 atomic Pt layers on the Pd nanocubes. For this thickness the core‐shell particles are more active than pure Pd cubes or similar Pt cubes reported in literature. This behavior is explained by a decrease of the adsorption energy of molecules, due a compressive strain, induced by the misfit between the two metal bulk lattices and by a ligand effect due to the modification of the electronic structure of Pt atoms in contact with Pd atoms. A similar qualitative evolution as a function of thickness of the Pt layer was already observed in electrocatalysis and was also explained by the decrease of the strength of adsorbed species.
Correlative nonlinear optical microscopy and infrared nanoscopy reveals collagen degradation in altered parchments
Authors: Latour Gael , Robinet Laurianne , Dazzi Alexandre , Portier François , Deniset‐Besseau Ariane , Schanne‐Klein Marie‐Claire 
Published: December 2016

Non‐invasive investigation techniques are strongly needed to avoid sampling during the examination of heritage artefacts. This study aims at developing specific and non‐destructive mapping of the degradation of parchment, which is mainly composed of dermal fibrillar collagen. The main issue is to characterize gelatinization, its ultimate and irreversible alteration corresponding to collagen denaturation to gelatin, both from the morphological and chemical point of view. To that end, we implement correlative imaging of parchment using nonlinear optical (NLO) microscopy and nanoscale infrared spectroscopy (nanoIR).
NLO microscopy, also called multiphoton microscopy, advantageously provides non‐invasive three‐dimensional (3D) multimodal imaging of scattering samples with micrometer‐scale resolution [1]. Among the collected signals, SHG signals are specific for dense non‐centrosymmetric materials. These signals therefore provide a unique structural probe of fibrillar collagen at the micrometer scale since the small signals from the collagen triple helices at molecular scale are amplified by constructive interferences at macromolecular scale due to the tight alignment of the collagen molecules to form collagen fibrils [2]. Nanoscale infrared spectroscopy is carried out thanks to an Atomic Force Microscope (AFM) coupled with an IR pulsed tunable laser [3]. This IR nanoscopy allows acquiring chemical mapping and local IR spectra to characterize and image samples at nanoscale.
Using this multiscale approach, key information about collagen and gelatin signatures is obtained in parchments and assessed by characterizing the denaturation of pure collagen reference samples. A new absorbing band is observed near the amide I band in the IR spectra, colocalized with the onset of fluorescence signals in NLO images. Meanwhile, a strong decrease is observed in Second Harmonic signals (see figure 1).
NLO microscopy therefore appears as a powerful tool to reveal collagen degradation in a non‐invasive way. It should provide a relevant method to assess or monitor the condition of collagen‐based materials in museum and archival collections and opens avenues for a broad range of applications regarding this widespread biological material.
Ultrafast nano‐fabrication and analysis using Xe plasma‐
FIB
‐
SEM
microscope and its applications for Cu milling using the Rocking‐stage
Authors: Benkouider Abdelmalek , Sharang Sharang , Hrnčíř Tomaš , Oboňa Jozef Vincenc , Jiruše Jaroslav , Principe Edward 
Published: December 2016

Conventional Ga FIB has a reasonable resolution (typically up to 2.5 nm). However, these instruments present some limitations, including Ga ion implantation and contamination, and slow sputtering rate. New liquid metal alloy ion sources (LMAIS) have been developed to overcome these limits[1]. However, none of the proposed LMAIS sources is suitable for rapid milling because they can only deliver probe current up to few tens of nA. Contrary, emerging Xe plasma FIB systems promise faster removal rates[2],[3].
Homogenous copper FIB milling arises from the need to perform various circuit edit operations below the dielectric layer following the copper layer. If the layer beneath the dielectric is affected by inhomogeneous milling, it can lead to short‐circuit and eventual device breakdown. Failure analysis on an integrated circuit was performed using rocking stage with 6‐axes piezo movement capabilities together with the novel approach of the combined Xe‐plasma ion source FIB and SEM system (XEIA). The new Xe plasma FIB offers sputtering speed up to 50 times faster than the most powerful Ga FIBs. Compared to conventional Ga ion sources, the Xe plasma ion source reduces dramatically the time for cross‐sectioning from tens of hours or even days to a matter of hours[4],[5].

Site‐specific milling of copper with different milling strategies were tested to optimize time and homogeneity of the milling across the target surface and to overcome the channeling effect posed by polycrystalline copper. Only during the last few nanometers of copper layer the water vapor is used to protect the dielectric layer. The complete removal of copper was followed with XeF
2
assisted milling of the dielectric layer to observe the unharmed circuitry. Channeling effect was reduced by regulating the sputtering rates across different grains keeping the underlying dielectric layer safe. Ultra‐high‐resolution scanning electron microscopy (UHR‐SEM) imaging was used for constant monitoring of the removed material to help modulate the process for highest throughput in the least possible amount of time[6].
Direct mapping of Li‐enabled octahedral tilt ordering and associated strain in nanostructured perovskites
Authors: Zhu Ye , Withers Ray , Bourgeois Laure , Dwyer Christian , Etheridge Joanne 
Published: December 2016

Self‐assembled nanostructures are promising for creating 2D and 3D superlattices with exceptional functionalities. Understanding the mechanisms driving the superlattice formation demands the underlying structural information. However, nanoscale structural modulations intrinsic to these superlattices are difficult to be characterized by conventional diffraction‐based structure determination. A real‐space, direct imaging method is necessary to probe the local structure characteristics, providing essential information for theoretical understanding and subsequent design of structure‐property correlations.
Using the aberration‐corrected scanning transmission electron microscopy (STEM), we developed an optimized atomic‐level bright‐field (BF) condition to image the oxygen octahedra in perovskite oxides. We used multislice calculations to determine detector collection angles that allow oxygen octahedra to be imaged sensitively and robustly over large specimen thicknesses. These calculations also provided a calibration by which the octahedral‐tilt angle can be measured quantitatively from the image of each octahedron.

Applying this real‐space octahedral‐tilt mapping on Li

0.5–3
x

Nd

0.5+
x

TiO
3
, a promising solid electrolyte in Li‐ion batteries, we directly revealed an unconventional superlattices with 2D modulated octahedral tilting. A mathematical description of the octahedral‐tilt modulation was derived based on the quantitative tilt maps, which explicitly identified the high‐order harmonic character of the modulation. Using simultaneous annular‐dark‐field (ADF) imaging, we also mapped the lattice parameters unit‐cell by unit‐cell, uncovering highly‐localized strain associated with the tilt modulation. Furthermore, we demonstrate the tunability of the tilt modulation by changing Li stoichiometry. Fascinatingly, we observe a reversible annihilation/reconstruction of the tilt modulation correlated with delithiation/lithiation process, suggesting the structural transformation that is associated with Li‐ion conduction in this promising Li‐ion conductor.
1

The above observations are largely inaccessible from conventional diffraction analysis,
2
and lead to an unprecedented mechanically‐coupled tilting competition model to explain the superlattice formation.
1
Our real‐space approach to quantify local octahedral structure and correlate it with strain can be applied to other advanced oxide systems.
Quantitative
STEM
analysis of multiscale
CNT
assemblies
Authors: Gnanasekaran Karthikeyan , de With Gijsbertus , Friedrich Heiner 
Published: December 2016

Carbon nanotubes (CNTs) and their macroscopic assemblies have shown their potential as advanced conductors. The assembly of individual CNT's into hierarchical structures is determined either by their interactions (bottom‐up self‐assembly) or during the fabrication process (top‐down strategy). Hence, to tailor the macroscopic functional properties (e.g. electrical conductivity or porosity) of assemblies, a detailed understanding on how interactions create multiscale morphologies and finally function is required. STEM is widely employed for the nanoscale analysis of (in)organic materials. However, (S)TEM imaging of hierarchical CNT assemblies has several limitations. For instance, CNT/polymer composites are only composed of light elements which results in low contrast between the phases. Moreover, they are beam sensitive. We have optimized the contrast between the CNT's and the polymer phase combining experiments and simulations at limited electron dose [1]. In addition, a hierarchical morphology extends across several length scales, hence, depending on the area of imaging, interpretations could vary, questioning the representativeness of the analysis. Our approach to imaging of representative volumes of hierarchical materials included the development of a toolbox to acquire large‐areas at high‐resolution, which in essence brings STEM closer to a bulk characterization technique [2].
With these technical developments and relevant image analysis tools, the processing‐structure‐property relationship of porous CNT assemblies and CNT/polymer composites (PNCs) have been studied on a scale that was previously impossible. We will illustrate the potential of the methodology on examples of: 1) CNT compacts where the final structure and electrical conductivity can be controlled by the polydispersity and aspect ratio of the CNT population (Figure 1) [3]; 2) CNT/polymer composites where residual CNT‐CNT interactions during compounding lead to inhomogeneous but highly conducting CNT networks [4]; and 3) CNT alignment can be induced by spin‐coating of polymer latex‐CNT mixture which exhibit directionally varying electrical conductivity (Figure 2) [5]. In above investigations it has becomes clear that CNT‐CNT contacts play a crucial role in the formation of least resistance pathway. At present we are investigation such contacts in details employing electron tomography combined with template matching to deduce the contact number and contact area per unit volume. In summary, we are developing (S)TEM towards bulk characterization tool for the analysis of beam sensitive hierarchical materials over multiple length scale which are materials of scientific and technological importance.