bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards Conductivity Measurements in Battery Materials Using Scanning Electron Microscopy
Authors: Sturn Sebastian , Golla‐Schindler Ute , Bernhard Jörg , Rapp Manfred , Wachtler Mario , Kaiser Ute
Published: December 2016

There are several ways of determining the conductivity of bulk materials, especially known in the field of solid state physics [1]. The most commonly used procedure is a four‐point‐probe measurement. By applying voltage on two of the probes, a current can be measured with the remaining two probes.

We introduce a new method for determining the conductivity of battery electrode materials such as graphite using an SEM. A constant current of electrons is injected into a specimen by the electron beam. A Pt pad which is sputtered on the specimen surface is contacted with a micromanipulator. (cf. fig. 1). The specimen itself serves as a current divider (cf. fig. 2). The beam current is diminished by the secondary and backscattered electron current and is thus

I
in
= I
0
‐ I
SE
‐ I
BSE
(1)

The absorbed current, measured with a picoammeter via the micromanipulator, and the transmitted current, measured with a second picoammeter, sum up to the total effective injected current

I
in
= I
abs
+ I
trans
(2)

To spatially resolve the electrical conductivity [2] of the battery electrodes, the electron beam is scanned parallel to the rectangular Pt pad in various distances. The specimen itself is of constant thickness which allows us to assume the resistance

R
2

along the height axis of the specimen to be constant (cf. fig. 3). The absorbed current I
abs
can be expressed in dependence of the distance
d
between the electron probe and the Pt pad as

I
trans
(d) = I
in
R
2
*((ρd/A) + R
2
)
‐1
(3)

By varying the distance
d
we extrapolate the resistivity
ρ
and therefore the conductivity of the material.
A
is the contact area between the Pt pad and the specimen surface. It can either be measured directly or also extrapolated from eq. 3.

In a first step, it is necessary to measure the effective electron beam current remaining in the sample (cf. eq. 1). Therefore it is crucial to quantitatively determine the secondary electron and backscattered electron current. The secondary electron yield is highly dependent of the sample topography. Thus, one of the preconditions is to observe samples with identical topography and measure experimentally the absorbed current. To obtain identical sample topographies, a Focused Ion Beam (FIB) system is used. This makes it possible to polish the sample surface and get plane topographies. The experimental results of I
SE
and I
BSE
can be cross‐checked using Monte‐Carlo simulations.

The use of a Gas Injection System (GIS) allows for sputtering platinum contacts on top of the specimen. We use these platinum pads as contact areas [3] for micromanipulators to read out absorbed currents.

We introduce the basic principle of measuring currents in an SEM using this new technique and show first results for state‐of‐the‐art Li‐Ion battery electrodes.
HAADF
HRSTEM
of one dimensional
CuI
crystals inside
SWCNT
s
Authors: Kumskov Andrey , Zhigalina Victoria , Kiselev Nikolay , Eliseev Andrey , Verbitskiy Nikolay , Vasiliev Alexander
Published: December 2016

Reduced coordination in 1D crystals is obviously a consequence of the sterically confined space in which the encapsulated crystals have to grow. It was interesting to investigate the differences of the one dimensional crystals in comparison with their three‐dimensional unit cell.

In our previous investigations of 1DCuI@SWCNT HRTEM revealed hexagonal, monoclinic [1] and cubic [2] modifications of copper iodide. In cases of HRTEM investigations in order to obtain the 1D crystal structure it was necessary to get sets of micrographs (about hundreds) while HAADF HRSTEM method allows to determine 1D crystal structure with a help of a few micrographs, owing to an ability to designate various atoms according to their atomic numbers. Within a framework of this study the perspectives of HRSTEM method combined with local EELS for determination of atomic and electron structure of individual nanocrystals are shown. These analytical electron microscopy methods applied together have allowed to reveal a new type of 1DCuI@SWCNT nanocomposite structure and to identify a space group of 1D CuI unit cell in the nanotube channel which appeared to be
Pmmm
. The results of our investigation bear evidence of the necessity of using HRSTEM in both bright field and dark field modes simultaneously (Fig. 1). A formation of chemical bond between Cu3d and C2dz orbitals of the intercalated nanocrystal and the nanotube wall is accompanied by electron density transfer of ~ 0.09 e/atom towards C. Electron microscopy is performed in JEOL ARM 200F at 80 kV in HAADF HRSTEM mode.
VEELS
investigation of perovskite manganite interfaces
Authors: Wallisch Wolfgang , Stöger‐Pollach Michael , Navickas Edvinas , Steiger‐Thirsfeld Andreas , Bernardi Johannes
Published: December 2016

As promising candidates for magnetic storage and magnetic field sensing applications at room temperature Sr‐doped LaMnO
3
(LSM) perovskite manganites show a very large negative magnetoresistance [1]. These materials exhibit a colossal magnetoresistance (CMR) which is very sensitive to the behaviour of the interface, due to the lattice misfit between substrate and thin film, and hence to the induced strain.

The investigated LSM thin film synthesised from La
0.8
Sr
0.2
MnO
3
powder was prepared by pulsed laser deposition (PLD). The 140 nm thick LSM layer was epitaxially grown on a single crystalline LaAlO
3
(LAO) (100) substrate. The preparation of a cross section specimen for TEM analysis was done by focused ion beam (FIB) followed by subsequently Ar
+
ion polishing. The analytical TEM investigations were performed by using a FEI TECNAI G20 TEM equipped with a Gatan GIF 2001 energy filter and a field‐emission FEI TECNAI F20 TEM equipped with a Gatan GIF Tridiem energy filter. In this work, we will present a study of the microstructure as well as the optical and electronic properties of LaSrMnO
3
‐LaAlO
3
interfaces at different temperatures and operating voltages. High‐resolution (HR) TEM, high‐angle annular dark field (HAADF) STEM and analytical methods, such as valence electron energy loss spectrometry (VEELS) and electron magnetic chiral dichroism (EMCD) were applied.

The bright field (Fig. 1B) and the dark field (Fig. 1C) image convey the impression of a non‐uniform distribution in the LSM layer. This fact is confirmed by means of the HAADF image in Fig. 1A. A columnar structure is distinguished in the thin film. In addition, spot splitting perpendicular to the interface occurs from the lattice mismatch as shown in the Fourier transform (FT) (Fig. 1D) of the HRTEM image (Fig. 1E) recorded at the interface. It was observed that the columnar growth mechanism starts directly at the interface within a heavily strained region as reported in [2].

The EELS investigations of the LaSrMnO
3
‐LaAlO
3
interface are shown in Fig. 2. In the case of determining optical properties, high beam energy alters the valence EELS (VEELS) spectrum by exciting retardation losses and therefore, we reduced the operation voltage in order to eliminate these effects [3]. The Cerenkov contribution is observed at 200 keV in LAO and LSM in Fig. 2, while these losses are vanished at lower beam energy. The EELS spectrum after zero‐loss peak (ZLP) removal is shown for LAO in Fig. 2A and for LSM in Fig. 2B at 40 keV and 200 keV, respectively. A pre‐measured zero‐loss peak was used for the ZLP removal of the VEELS signal. However, some artefacts at the bandgap can be seen in the insertion above in Fig. 2A. The VEELS spectrum image in Fig. 2C exhibits the bandgap transition at the LaSrMnO
3
‐LaAlO
3
interface with a beam energy at 60 keV.
Colloidal Rods in Irregular Spatial Confinement
Authors: Moghimian Pouya , Harnau Ludger , Srot Vesna , de la Peña Francisco , Bafi Nima Farahmand , Facey Sandra J. , van Aken Peter A.
Published: December 2016

Spontaneous assembly of anisometric colloidal particles, such as rod‐like particles, in two‐dimensions (2D) can be carried out via incubation of colloid‐containing suspensions on solid surfaces [1]. Rod‐like particles having a high aspect ratio (e.g. very long inoviruses) show liquid crystal (LC) behavior in suspensions. An ordered medium of liquid crystals often possesses a variety of defects, at which the director
n(r)
of the liquid crystal undergoes an abrupt change. Experimental research on these effects has remained challenging and has not been performed, to our knowledge, on confined rod‐like colloidal particles on irregularly structured substrates. Therefore, we studied semi‐flexible M13 phages in contact with irregular stranded webs of thin amorphous carbon (a‐C) films (Figure 1a,b) using transmission electron microscopy (TEM) and theoretical considerations. In this work, we show that on the structureless and wide amorphous carbon (a‐C) surface areas, far from the surface edges, the phages exhibited random orientations (Figure 1c). However, close to the surface edges the orientation of M13 phages in two‐dimensional nematic films was controlled by the orientation and curvature of the edges. When constrained to surface strands, the M13 phages adopted a configuration that matched the confining boundary conditions (Figure 2). An annulus sector was superimposed on these oriented phage bundles that allowed us to derive analytic expressions for the bending energy of such oriented bundles. Our theoretical approach provides an explanation for the different number of phages orienting close to the surface edges with different local curvatures. By comparing the self‐assembly on differently shaped carbon substrates, it was demonstrated that the alignment of the phages can be controlled by choosing appropriate substrate shapes [2]. This offers a convenient means to fabricate designed structures of orientationally ordered M13 phages. The understanding of such systems opens up new possibilities for defect engineering of liquid crystals, which can be beneficial for applications of liquid crystals in the presence of microscopic surface pores and irregularities.
Faster than 10 ns scintillator material based on
YAP
:
P
r
Authors: Pokorný Martin , Horodyský Petr , Nikl Martin , Houžvička Jindřich
Published: December 2016

YAP:Pr (praseodymium‐doped YAlO
3
) is a promising scintillation material with fast response time around 10 ns and a photon yield up to 20 000 photons/MeV (depending on the preparation method) [1], about half of that of widely‐used YAG:Ce (which has decay time about 70 ns). Nowadays, there is a growing demand on a scintillation materials with such a fast response times for use in high‐speed electron microscopes.

The luminescence spectra of YAP:Pr has two‐peak band in the UV range (230‐300 nm), and a few more peaks in the green region (500‐600 nm) [2]. Pr
3+
radiative transitions from 5d
1
orbitals are responsible for the fast, former ones. Appropriate colour filter can easily separate the fast and the slow components. Moreover, a modified growth method using co‐dopants (patent pending) which we used, led to a decrease of the decay time by one third of the former value. The fastest sample we have obtained up to now has an exponential decay with main decay time 6 ns.

Since the transport of the emitted light can be ensured by a quartz lightguide and the photomultipliers are also available for this wavelength region, the main challenge for the use of YAP:Pr as a scintillator in the electron microscopes for secondary electrons or back‐scattered electrons detectors is therefore improvement of light yield of the fast component and inhibition or even full suppression of the afterglow luminescence.
Dynamic spectro‐microscopy of nanoparticle growth and corrosion
Authors: Goode Angela , Koronfel Mohamed , Weker Johanna Nelson , Tay Stephen , Cruickshank Amy , Heutz Sandrine , Hart Alister , Porter Alexandra , Toney Michael , Ryan Mary
Published: December 2016

X‐ray spectro‐microscopy provides quantitative chemical information similar to electron energy‐loss spectroscopy (EELS), but at different spatial and spectral resolutions and penetration length into the sample. The relaxed thickness constraint of X‐ray microscopy also offers exciting opportunities for spectro‐microscopy of samples in liquids. Here we present X‐ray microscopy (XM) studies of
in situ
nanoparticle growth and corrosion. Dynamic X‐ray experiments are correlated with electron microscopy analysis of
ex situ
samples to provide structural and/or chemical information at higher spatial resolution.

Figure 1 shows a custom‐built electrochemical cell which has been developed to allow real‐time imaging of the growth of ZnO nanostructures [1]. This method allows us to directly observe transient events which occur during electrodeposition such as instantaneous versus delayed nucleation, providing insights into the growth mechanisms of electrodeposited ZnO. The X‐ray microscope provides information with ~30 nm spatial resolution; this data is then correlated to subsequent
ex situ
morphological analysis in the scanning electron microscope.

These techniques have then been applied to the corrosion of nanoscale wear debris from cobalt‐chromium‐molybdenum metal‐on‐metal (MOM) hip prostheses. The wear debris has been implicated in the eventual failure of MOM hips. EELS and XM analysis of explanted tissue from patients with failed hip prostheses reveals debris that is rich in octahedrally coordinated Cr
3+
and Co‐deficient. However, the mechanism for cobalt loss is not understood. Using adapted electrochemical cells to simulate oxidative biological environments, the response of CoCrMo nanoparticles is investigated by
in situ
XM, revealing the conditions under which Co is leached from the wear debris.
Valence states of new Mn coordination sites at the ferromagnetic domain walls of
TbMnO3
thin films
Authors: Guzman Roger , Iñiguez Jorge , Farokhipoor Saeedeeh , Noheda Beatriz , Magén César
Published: December 2016

Bulk TbMnO
3
is a classic multiferroic material that combines antiferromagnetic ordering below 42 K and, below 27 K, a spin spiral transition with inversion symmetry breaking below 27 K that causes ferroelectricity [1]. However, it was recently demonstrated that strained TbMnO
3
thin films grown on SrTiO
3
(001) display an induced ferromagnetic behavior absent in the bulk material. This net magnetic moment arises from a two‐dimensional ferromagnetic phase synthesized at the ferroelastic (orthorhombic) domain walls (DW), which nucleate to accommodate the huge epitaxial strain induced by the substrate, and thus, scales with the DW density [2]. These ferromagnetic DWs are characterized by a spatially‐ordered substitution of alternate Tb sites by Mn atoms along the pseudocubic [100] growth direction, inducing magnetic frustration and a spin canted ferromagnetic ground state. First‐principle calculations point to two different types of Mn atoms occurring at the boundary planes, Mn(I) and Mn(II), with different magnetic moments and crystal environments, i.e. tetrahedral and a quasi‐square‐planar O coordinations, respectively [see Fig.1(a)].

This work presents the detailed aberration‐corrected Scanning Transmission Electron Microscopy (STEM) study of the different structural environments and electronic properties of Mn cations located at the Tb sites of the DW structure. For this purpose, atomically resolved High Angle Annular Dark Field (HAADF), Annular Bright Field (ABF) imaging and fine structure Electron‐Energy Loss Spectroscopy (EELS) in plane view and cross sectional configurations have been combined. ABF imaging evidences that the two first neighbor O coordinations for Mn(I) and Mn(II) sites predicted theoretically are present in plane‐view specimens, see Fig. 1(b). Furthermore, the analysis of the O K edge fine structure has allowed us to map the nominal Mn oxidation state [3] using atomic‐resolution STEM‐EELS, see Figure 2. This experiment has confirmed the decrease of the overall Mn valence at the domain wall previously reported and a fine modulation of the electronic state between the tetrahedrally‐coordinated Mn(I) and the square‐planar‐coordinated Mn(II) replacing Tb cations, as predicted by DFT calculations.
Mapping electrostatic potentials across the p‐n junction in
GaAs
nanowires by off‐axis electron holography
Authors: Fiordaliso Elisabetta Maria , Balogh Zoltan Imre , Kasama Takeshi , LaPierre Ray , Aagesen Martin
Published: December 2016

The development of III−V materials on Si platforms, with the aim of reducing production costs while achieving high conversion efficiency, has been a continuing area of photovoltaic research in the last decades [1,2]. This process is challenging due to large lattice mismatches, the polar non‐polar interfaces and the differences in thermal expansion coefficients. The use of III–V nanowires (NWs) provides a novel method of integrating III‐V materials with Si, which avoids dislocations [3]. However the control of other parameters, such as vertical yield in a patterned array, crystal phase, dopant concentrations and electrostatic potential distribution, become challenging.

The electrical performance of a semiconductor device relies strongly on how precisely the electrostatic potentials are distributed across the active region. An accurate measurement of this potential distribution is of vital interest to the semiconductor industry. The technique of off‐axis electron holography in the transmission electron microscope (TEM) is a powerful tool for fulfilling the required accuracy in mapping electrostatic potentials [4]. Here, we present electron holography measurements from single GaAs core‐shell nanowires with a p‐n junction, grown on a Si (1 1 1) substrate.

The Ga‐assisted vapor–liquid–solid (VLS) growth mechanism on a silicon substrate was used for the formation of a patterned array of radial p‐i‐n GaAs NWs encapsulated in AlInP passivation. A cross‐sectional specimen for off‐axis electron holography was prepared perpendicular to the growth direction of the NW using focused ion beam milling (FIB) and the
in‐situ lift‐out
technique in an FEI Helios Dualbeam FIB/SEM, equipped with a micromanipulator. Holograms were acquired at 120 kV using an FEI Titan 80‐300ST TEM, equipped with a rotatable Möllenstedt biprism. The thickness of the specimen was measured to be around 280 nm by convergent beam electron diffraction (CBED).

Fig. 1 shows the reconstructed phase and amplitude from the hologram of the cross‐sectional specimen. A core‐shell structure is observed, with the core being p‐type and the shell being n‐type. The phase shift across the p‐n junction is close to 1 radian, corresponding to a built‐in potential of 0.4 V, as shown in Fig.2. The potential variation measured by holography is used to quantify the actual doping densities in the n‐type layer and p‐type layer of the NW. This holography measurement indicates that the active dopant concentrations are lower than nominal values, causing a low built‐in potential. A greater control on the dopant concentration and distribution is required in order to achieve a higher efficiency of the NW solar cells.
Advanced Electron Tomography of Assemblies of Nanoparticles
Authors: Bals Sara , Altantzis Thomas , Zanaga Daniele , Goris Bart , Claes Nathalie , Tendeloo Gustaaf Van
Published: December 2016

Nano assemblies are two‐ or three‐dimensional (3D) collections of nanoparticles. The properties of the assemblies are determined by the number of particles, their position, shape and chemical nature as well as the bonding between them. If we are able to determine these parameters in 3D, we will be able to provide the necessary input for predicting the properties and we can guide the synthesis and development of new assemblies or superstructures. A detailed structural characterization is therefore of utmost importance.

Electron tomography is a versatile and powerful tool that has been increasingly used in the field of materials science. Also for the investigation of nanoassemblies, electron tomography has been of high value as illustrated in Figure 1 [1‐3]. However, to extract quantitative information, optimization of the electron tomography experiment is required, especially for large assemblies or assemblies consisting of more than one type of nanoparticle. Here, we will show how advanced electron microscopy, in combination with novel reconstruction algorithms, enables us to determine the number of particles, their stacking, interparticle distances and outer morphology. This will be illustrated for very large assemblies consisting of spherical nanoparticles [4], assemblies that contain anisotropic particles (Figure 2) and binary assemblies (Figure 3) consisting of particles with different sizes or different compositions [5,6].

Going a step further is the investigation of self assembly and oriented attachment at the atomic scale. Using annular bright field scanning transmission electron microscopy, the possible effect of polarity can be investigated, whereas high angle annular dark field scanning transmission electron microscopy in combination with advanced computational techniques enables the investigation of the interfacial planes in two‐dimensional superlattices from nanocrystals [7]. Finally, we will discuss the use of exit wave reconstructions to investigate the effect of surface ligands on self assembly.
Structure solution of the complex λ‐
La6W2O15
Authors: Kodjikian Stéphanie , Lepoittevin Christophe , Klein Holger , Schönenberger Thomas , Lebedev Oleg , Leynaud Olivier , Chambrier Marie‐Hélène , Goutenoire François
Published: December 2016

Oxides in the Ln
2
O
3
‐MO
3
(M = Mo and W) system are of significant technological interest for their laser applications [1], ionic conduction [2], catalytic [3] and ferroelectric [4] properties. The La
2
O
3
‐WO
3
phase diagram has been studied by a number of groups [5–7], but little detailed crystallographic information was reported due to the lack of good single crystals. Some of the reported compositions have not been appropriately characterized. Recently, the structures of La
2
WO
6
, La
18
W
10
O
57
and La
10
W
2
O
21
were solved using X‐ray powder diffraction (XRPD) [8–10].

For the La
6
W
2
O
15
compound phase transitions at 630 and 930 °C have been reported [1–3]. The structure of the high temperature phase α‐La
6
W
2
O
15
was determined ab‐initio by XRPD [11]. The lower‐temperature forms β and γ, however, couldn't be determined due to the large number of reflections in the X‐ray powder diffraction pattern and the relatively low symmetry of the system. The existing literature on γ‐La
6
W
2
O
15
only relates two sets of unit cell parameters [5–6], that almost match the XRPD pattern of γ‐La
6
W
2
O
15
, but some weak peaks remain without indexation and can't be explained by the presence of any impurity.

Here we present the structure solution using transmission electron microscopy of the complex structure of γ‐La
6
W
2
O
15
. From zone axis precession electron diffraction the unit cell was determined to be monoclinic with cell parameters
a=1.57 nm, b=1.21 nm, c=1.57 nm, β=110°
. As an example, the [100] zone axis is presented on figure 1. Due to the low symmetry of the crystal system and the large unit cell, a huge number of reflections needed to be acquired, so that electron diffraction tomography was used to record the intensities. The cation positions were obtained but the distribution of the cations on the sites was not evident. Z‐contrast imaging showed that disorder on some cationic sites has to be considered (fig.2).
Characterization of nanodispersed graphite in mesoporous carbon for supercapacitor applications
Authors: Lari Leonardo , Nedelkoski Zlatko , Shuttleworth Peter , Ellis Gary , Budarin Vitaliy , Clark James , Lazarov Vlado
Published: December 2016

Starbon®, a family of mesoporous carbonaceous materials, was recently developed at the University of York from polysaccharides (e.g. starch) [1,2]. The novelty and the advantages of these materials include cheap, green and renewable sources, low temperature carbonization processing, avoidance of harmful chemicals, and a tunability of the surface functionality from hydrophilic to hydrophobic. These properties make Starbon® an ideal candidate for applications in catalysis and material absorption [3]. Recently the tunability of the properties of these materials has been successfully extended to their functional properties by ballmixing it with graphite before the carbonization process. This resulted in an enhanced nanocomposite material (see picture) that adds to the porosity of the mesoporous carbon the conductivity of the graphite nanoflakes. This material shows promising characteristics as electrode material in electrochemical double layer capacitors (EDLC or supercapacitor). Here we present an Electron Microscopy study of this enhanced composite material, by combining Electron Diffraction, Electron Energy Loss Spectroscopy and Aberration Corrected TEM/STEM Imaging in correlation with the physical and transport properties exhibited by the materials as electrodes for supercapacitors including I‐V curves, Galvanostatic charge‐discharge curves and charge retention measurements.
GENESIS
Rouen : An open platform for the study and nano analysis (Atom probe,
SEM
Cross beam station and
TEM
(in situ straining, temperature, tomography) of irradiation effects in radioactive materials for nuclear application
Authors: ETIENNE Auriane , PAREIGE Philippe , RADIGUET Bertrand , PAREIGE Cristelle , CUVILLY Fabien , CADEL Emmanuel
Published: December 2016

Nuclear materials undergo degradations due to neutron/matter interaction. The degradation initially occurs at atomic scale. The French GENESIS platform, divided among three sites in France: GPM Rouen, CIMAP Caen and CEA Saclay, gathers experimental nanoanalysis tools devoted to irradiated and radioactive materials. Results allow understanding, modelling, and finally simulation of the long time behaviour of the nuclear materials.

In GPM Rouen, this platform will give access to tomographic atom probe, transmission electron microscopy with in‐situ experiments (heating, in‐situ straining tests, tomography) and a dual beam station for sample preparation in active materials irradiated in nuclear power plants. The samples may reach an activity of 200 MBq. These characterizations will allow the extraction of reliable data necessary to develop and validate the multi‐scale numerical simulation of metal, oxide, ceramic or glass materials.

Facilities in GPM Rouen are open since March 2016. The study of irradiated and radioactive materials will begin in September 2016.

Characteristics of the techniques will be described with some results that may be achieved as well as the protocol access.
Towards atomic magnetic measurements with single electron vortex beams on nanocubes
Authors: Pohl Darius , Rusz Jan , Spiegelberg Jakob , Schneider Sebastian , Tiemeijer Peter , Nielsch Kornelius , Rellinghaus Bernd
Published: December 2016

X‐ray magnetic circular dichroism is a well‐established method to study element specific magnetic properties of a material, while electron energy‐loss magnetic chiral dichroism (EMCD), which is the electron wave analogue to XMCD, is scarcely used today. Recently discovered electron vortex beams, which carry quantized orbital angular momenta (OAM) L, promise to also reveal magnetic signals [1]. Since electron beams can be easily focused down to sub‐nanometer diameters, this novel technique provides the possibility to quantitatively determine local magnetic properties with unrivalled lateral resolution. In order to generate the spiralling wave front of an electron vortex beam with an azimuthally growing phase shift of up to 2p and a phase singularity in its axial centre, specially designed apertures are needed [2,3]. Dichroic signals on the L
2
and L
3
edge are expected to be of the order of 5% [4,5].

The generation of EVBs in the double aberration‐corrected FEI Titan
3
80‐300 transmission electron microscope (TEM) is achieved by the implementation of a dislocation‐type apertures into the condenser lens system. The setup allows for scanning TEM investigations (STEM) with vortex beams, whose OAM is selected by means of an additional discriminator aperture. New FIB cutting strategies facilitate the production for 50 µm wide and 1 µm thick high quality vortex apertures (see fig. 1a). However, in the case of a fork‐type aperture, the EVB are dispersed in the x‐y plane resulting in mixed probe that interacts with the magnetic sample.

We have recently devised an escape route to this problem by blocking any partial beams that carry other but the desired OAM prior to the interaction of the beam with the ferromagnetic sample. This is achieved by using a special condensor aperture in combination with a fork‐type aperture to select a single partial beam with the chosen OAM (s. fig 1b). This approach allows to generate atom‐sized EVB with angstrom‐sized probes and a well‐defined OAM by which atomic resolution HR‐STEM is achieved (see. fig 2). Although this discretization results in an increased signal‐to‐noise ratio, this novel technique is capable of atomic resolution EELS measurements which is the prerequisite for atomic EMCD measurements. First experiments using this new optical setup show very promising EMCD results on ferromagnetic FePt nanoparticles.
Enamel evolution: Back in time by a molecular manipulation
Authors: Wald Tomas , Spoutil Frantisek , Osickova Adriana , Prochazkova Michaela , Benada Oldrich , Kasparek Petr , Bumba Ladislav , Klein Ophir , Sedlacek Radislav , Sebo Peter , Prochazka Jan , Osicka Radim
Published: December 2016

Biomineralization is one of the key processes during vertebrate evolution that incorporates calcium and phosphate ions into soft matrices in the form of hydroxyapatite. Occurrence of mineralized tissues have offered the basis for various adaptive phenotypes such as endoskeleton for locomotion (bone), body armor for protection and teeth (enamel, dentin) for predation. Enamel is unique among the mineralized tissues, as it is formed on specific network of enamel matrix proteins (EMPs) secreted by epithelial ameloblasts. The two key structural proteins of enamel, amelogenin (AMEL) and ameloblastin (AMBN), self‐assemble into higher‐ordered structures from monomeric intrinsically disordered subunits as does the type I collagen (COL1), the predominant matrix protein in bone and dentine. While COL1 undergoes self‐assembly via consecutive Gly‐X‐Y motif, the mechanism of self‐assembly of EMPs and their subsequent role in formation of organized layer of hydroxyapatite crystals remains poorly understood.

We report here a novel evolutionary conserved self‐assembly motif common to the key structural enamel matrix proteins AMBN and AMEL. The presence of this motif is essential for self‐assembly of AMBN and AMEL into higher‐ordered structures. These structures are essential for proper enamel formation. Transgenic mice that were unable to produce supramolecular structures of AMBN due to point substitutions within the identified self‐assembly motif then produced severely affected enamel with simplified organization. Despite the normal cellular organization, EMPs secretion and Ca and P levels within the growing enamel of transgenic mouse, the affected enamel lacked organized prismatic structures and showed only radial organization without visible Hunter‐Schreger bands. Moreover, enamel of mutant mice contained an enormous portion of interprismatic matrix with hypomineralized, yet well recognizable, crystallites, while no formation of oriented crystallites was observed within the compromised prisms.

This is the first
in vivo
evidence that the formation of supramolecular structures of enamel matrix proteins was essential for evolution of highly structured enamel in mammals.
Where does the FIB sputtered matter accumulate in the
SEM
chamber ?
Authors: CADEL Emmanuel , CUVILLY Fabien , VAUDOLON Charly , ETIENNE Auriane
Published: December 2016

Scanning electron microscopes (SEM) equipped with focused ion beam (FIB) column are nowadays dual platform instruments commonly used in various micro sample preparation processes. While the mainstream of FIB usage remains within the semiconductor industry, it has expanded to a wide range of materials in metallurgical research. In particular, FIB milling capabilities are today used in the area of advanced materials for nuclear applications, involving in most cases the manipulation of activated samples. Sputtering of radioactive materials is far from trivial and numerous questions remain still open to guarantee the user safety even if small volumes of matter are generated by FIB milling [1]. For instance, where does the FIB sputtered matter accumulate in the SEM chamber?

Angular distributions of FIB sputtered atoms have been investigated for 0°, 30° and 54° ion beam incidence. FIB patterns have been milled on a nanocrystalline Nickel alloy using a 30 keV Ga
+
ion bombardment in a scanning electron microscope (Fig 1a). Sputtered matter is collected on a silicon planar collector. The thickness of the deposit on the collector is measured by means of Z‐contrast imaging and two dimensional spatially resolved thickness maps are drawn (Fig 1b and Fig 1c). Angular distributions of sputtered atoms, in a plane containing the primary ion beam, are deduced from the maps (Fig 3). Our experimental data show that, at oblique incidence, sputtering matter is emitted in two main emission directions, normal to the target surface and towards the FIB column. For normal incidence, all the sputtered matter is projected towards the FIB column. The microstructure of the deposit, at normal incidence, has been studied by Transmission Electron Microscopy and Atom Probe Tomography (Fig 2).
Tailoring the wave function of electron probes for the selective detection of plasmonic modes
Authors: Guzzinati Giulio , Lourenço‐Martins Hugo , Béché Armand , Kociak Mathieu , Martin Jerôme , Verbeeck Jo
Published: December 2016

Electronic spectroscopies are important in the study of localised surface plasmon resonances of metallic nanostructures, allowing to detect and image the strong spatial variations in the electrical field of the induced resonances of a single nanoparticle [1].

These techniques do however present some drawback when compared to their optical counterparts. While optical spectroscopies can make use of polarisation to directionally probe the response of a nanoparticle, an electronic beam can't discriminate between energy‐degenerate eigenmodes and is also blind to optical activity and dichroism.

Here we present a way to expand the applicability of EELS to the characterisation of plasmonic resonances by exploiting the recently developed methods of electron beam shaping through phase manipulation [3].

This radically new approach is based on the idea of tailoring the electronic probe to fit the properties under investigation that can then be selectively detected, allowing to perform new measurements that were previously impossible [3].

In particular, we first show how the phase in the electron beam's complex wave function couples to the electric potential of the plasmonic excitation (see fig1), allowing to selectively detect localised plasmonic excitations that possess the same symmetry as the electron probe [4].

While this concept is entirely general and potentially applicable to any plasmonic resonance, we decide to focus a first experimental demonstration on detecting the dipolar mode of a nanorod.

The ideal probe for this purpose is formed by two intensity lobes opposite in phase as shown in figure 1a, which we successfully generate in the TEM by applying state of the art phase manipulation techniques.

Finally, we show experimental proof of the method's effectiveness on purposefully made test sample, demonstrating the viability of this new approach and opening to a new generation of plasmon oriented TEM experiments, that will expand in parallel with the availability of wave manipulation methods.
Generation of nondiffracting beams: beam shaping beyond holographic reconstruction
Authors: Guzzinati Giulio , Béché Armand , Verbeeck Jo
Published: December 2016

The last few years have seen a rapid acceleration in the field of beam manipulation [5].

Central to this expansion is the idea that the purposeful design of the beam's wavefunction can imbue the electron with new properties that potentially enable new measurements previously impossible.

Examples of this are the orbital angular momentum possessed by electron vortex beams [1], or the reduced diffraction of Airy and Bessel beams [2–4].

In these studies, holographic reconstruction remains the most widely used method to generate new wave types due to its generality and flexibility but presents several shortcomings, chiefly the production of multiple diffracted beams [1–3,5].

Here we showcase different approaches to the production of reduced diffraction beams.

We generate Airy waves by a careful tuning of the aberration function of an aberration corrected TEM, and produce a Bessel beam by limiting the angular spread of the electrons with an annular aperture.

We study the beam propagation to prove the limited diffraction, and give experimental proof of extended depth of focus in imaging with Bessel beams.
Surface‐sensitive investigation of semiconductor devices with a signal‐selective SEM detection system
Authors: Jiruše Jaroslav , Kološová Jolana , Mareš Petr , Váňa Rostislav
Published: December 2016

The detection system of a scanning electron microscope (SEM) is just as important for image quality as the design of its electron optics [1]. Recent studies [2, 3] emphasize the importance of angle‐ and energy‐filtering of backscattered electrons signal (BSE) to reveal details not usually observable in the integral BSE signal.

Here we introduce a novel detection system tested on a recently developed ultra‐high resolution electron optical column [4, 5] that comprises three BSE detectors capable of angle‐ and energy‐filtering. The system can be switched between a “high‐signal” mode where no bias is applied to the filtering grid and an “energy‐selective” mode where the filtering voltage can be tuned to achieve various degrees of signal separation.

High‐pass energy filtering enables detection of BSEs which have undergone minimal energy loss. Their escape depth is limited and the resulting micrograph becomes surface sensitive. This is beneficial for samples with complex surface and sub‐surface structure. Clear visualization of the topmost layer of the sample is critical e.g. for failure analysis of 3D semiconductor devices, given the continuously decreasing dimensions of the local structures in such devices.

Figure 1 shows a SEM micrograph of a semiconductor memory device cross‐section acquired at 3 keV primary beam energy and 265 pA probe current. Contrast of the images decreases continuously with increasing bias of the filtering grid. With no bias applied the material contrast is highest, yet it contains information about both surface and subsurface area of the specimen. With increasing filtering bias only the electrons backscattered from the very surface of the sample are detected. This is in agreement with theoretical simulations for 3 keV primary beam in silicon that show an escape depth of 80 nm for the integral BSE signal and only 2 nm for the low‐loss BSE signal.
Atomic structure and segregation phenomena at copper grain boundaries
Authors: Meiners Thorsten , Liebscher Christian H. , Dehm Gerhard
Published: December 2016

The segregation of impurity atoms to grain boundaries can have significant influence on the cohesive properties, atomic arrangements and the mechanical properties of such interfaces. Therefore, it strongly impacts the macroscopic behavior of materials and understanding the atomic structure and related segregation behavior at grain boundaries is crucial to tailor materials with optimized physical properties
[1]
. Copper (Cu) is an attractive material for electronic applications, because of its good electrical and thermal conductivity. The effect of Sulphur on grain boundaries in Cu is of particular interest since it is improving the electromigration resistance but can also lead to grain boundary embrittlement
[2]
.

In this study the atomic structure and chemistry of grain boundaries in polycrystalline Cu with variable Sulphur content (7 – 4000 ppm) are analyzed. In order to determine the distribution, size and orientation of the grains, Electron Backscatter Diffraction (EBSD) measurements were performed, as shown in Figure 1. The measurement reveals a grain size of 1‐4 mm and an orientation of the grain normal close to the [001] direction. Transmission electron microscopy (TEM) specimens are prepared conventionally by grinding, electro polishing and Ar
+
ion beam milling at specific regions from the EBSD scan in order to select special grain boundaries. This is shown exemplarily by the black circle in Figure 1.

TEM methods (bright‐field imaging, selected area diffraction and high resolution TEM) are used to investigate the structure of selected grain boundaries. A preliminary example represented in Figure 2 reveals a high angle grain boundary. The specimen is tilted so that the upper grain is oriented in [001] zone axis while the resulting orientation of the lower grain is close to the [013] zone axis. The tilt component between both grains was determined to by measuring the misorientation between the (200) reflexes of both grains which is in good agreement with the EBSD measurement. The twist component of this random grain boundary is not yet fully determined and is part of current investigations.

The atomic structure and segregation of Sulphur are characterized by aberration‐corrected scanning transmission electron microscopy (STEM) in combination with analytical techniques including energy‐dispersive X‐ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). Hence, information on the atomic arrangement of impurity atoms (interstitial and substitutional), the respective bonding and possible grain boundary precipitates will be obtained with sub‐nanometer resolution.
Reflection profile and angular resolution with Precession Electron Diffraction
Authors: Rauch Edgar , Renou Gilles , Veron Muriel
Published: December 2016

Template matching has proved to be an efficient numerical approach to identify orientation and/or phase signatures in electron diffraction patterns [1]. With this technic, all patterns for all orientations and all phases considered are pre‐calculated and compared to the experimental data by cross‐correlation. The capacity of the approach to recognize the diffracting signal is substantially improved with precession electron diffraction (PED). This is because dynamic effects are partly swept out of the experimental signal. Of interest is the fact that, up to now, templates were always computed without including precession. In particular the specific reflection profile resulting from the beam rotation was never considered properly. The present work is an attempt to enhance the degree of matching by adapting the templates to precession in particular for large precession angles.

First, the Bragg spot profile is determined for Si single crystal by tilting progressively the sample. The pattern collection procedure is similar to the fast diffraction tomography setup of Gemmi et
al
[2]. The precession angle was monitored with the Nanomegas Digistar P1000 attachment to a JEOL 2100F TEM and set up to 0.3, 0.6 and 1.2°. The crystal orientation evolution is followed with the ASTAR system through template matching and compared to the quasi linear trend expected from the constant angular speed of 1°/min imposed by the TEM goniometer.

The change in reflection profile with increasing precession angle is illustrated in figure 1. The profile exhibits two maximums separated by twice the precession angle. This shape, systematically recorded, is modeled and introduced in the template generation routine. The improvement in angular resolution is characterized by comparing the misorientation measurements with respect to the expected linear trend (Fig 2).

The templates computed with the recorded PED profile, differ significantly from the standard ones (Fig 3). The resulting set of templates being closer to the diffraction patterns acquired with precession, the crystal orientation is determined with an increased accuracy (Fig. 2.b), at least at large precession angles. The standard deviation obtained without and with precession adaptation is nearly identical and equal to 0.17° for precession angles lower or equal to 0.6°. By contrast, this value degrades down to 0.5° at the largest precession angle if no precession correction are included (Fig. 2) but remains equal to 0.17° with adapted templates.

Besides, the orientation resolution may be further refined by using the interpolating algorithm presented elsewhere [3]. With adapted templates and interpolation the standard deviation decreases down to 0.13°, for the largest precession angle. A non‐intuitive conclusion of the present work is that the angular resolution of the orientation determination is not bounded by the precession angle.
Mapping electrostatic potentials and deformation in semiconductor devices by off‐axis electron holography and other techniques
Authors: Boureau Victor , Cooper David , Bernier Nicolas , Rouviere Jean‐Luc
Published: December 2016

Off‐axis electron holography can be used to measure the electrostatic and magnetic potentials in semiconductor devices with high‐sensitivity and nm‐scale resolution [1]. In this presentation we will show experimental results that have been obtained using combinations of electron holography, precession diffraction and differential phase contrast (DPC) on a range of different semiconductor devices.

Deformation maps have been acquired using dark field electron holography on a variety of different device structures and these results have been compared to those obtained by precession electron diffraction (NPED). Figure 1 shows STEM images and results obtained by dark holography and NPED on a Si specimen containing 10‐nm‐thick SiGe layers with different Ge concentrations and also a recessed source and drain SiGe device. The deformation maps obtained by dark holography and shown here have a spatial resolution of 6 nm and a precision of 0.05 %. The maps obtained by precession electron diffraction have a spatial resolution of 2 nm and a precision of 0.02 %. In this presentation we will show the advantages and difficulties associated with the use of the different techniques [2].

We will also compare electron holography and DPC for dopant profiling on fully processed and electrically tested devices. Figure 2(a) and (b) shows STEM images that have been acquired from two different pMOS devices with different spacer widths. The spacers are used to prevent dopants from diffusing under the gate during the activation anneals. Figure 2(c) shows how the specimen is rotated to remove the top metal layers in the device, backside milling is then used to provide a high quality TEM specimen. Figures 2(d) and (e) show maps of the electrostatic potential in the devices that have been acquired using off‐axis electron holography. The spatial resolution in these maps is 5 nm and the difference in the potential distribution under the gate can be clearly seen. Potential profiles have been obtained from across the device and the parameters such as the electrical gate width can be measured. From the analysis of these real devices, the advantages and problems that are associated with electron holography and DPC can be discussed.