bluuebunny/crossref_metadata_2025_split huggingface dataset:
Can quantum wave filters outperform image processing?
Authors: Clark Laura , Verbeeck Jo 
Published: December 2016

As electron microscopists, we are often limited by both low contrast, and high‐noise levels for beam‐sensitive materials. The contrast is a function of the imaging technique, and the sample under study. The noise level of the image is a fundamental property of the finite electron dose, which must remain limited, to avoid damaging the sample.
As a result of these, one route to improving microscopy images lies in developments of novel imaging techniques. Image post processing techniques are commonly used for example, to remove noise in images or increase the contrast of specific features of interest. These methods perform well in specific cases, but one can wonder whether this post processing approach is the most optimal in terms of electron dose efficiency.
The primary source of noise in electron micrographs is Poisson noise due to the electron counting process occurring at the point of detection.
However, if we can manipulate the coherent electron wave prior to its detection, implementing a specific operator acting on the wave, noise will occur on the detected processed image rather than prior to the processing.
Such a setup can be obtained by using phase plates in the diffraction plane. Ideally, these phase plates affect the phase of the passing electron wave without invoking a detection process, effectively acting as a quantum filter.
We discuss and compare three primary examples of such quantum wave filtering, and the results they have on the noise behaviour of the resulting images: vortex filtering as an edge enhancement filter [1], wave background removal [2], and tuneable wave background reduction. We find each method improves the image signal‐to‐noise ratio compared to image post processing implementing a similar filter. We show that each quantum wave filter has different advantages which may be used to enhance certain image features of interest.
Removal of the background in the wave decreases noise specifically in image regions of low intensity, reducing the variance of the noise in the image, allowing more precise measurements. Reduction rather than removal of the background however, enables a noise decrease, while avoiding contrast reversals due to sign changes in the wave, improving direct interpretability. The vortex‐ filtering method provides robust directional, or isotropic edge detection, with high contrast possible.
We demonstrate each of these options on a selection of different model samples, and discuss their noise properties, required dose levels and their possible implementation.
Impact of high energy electrons on nitrides for nanocathodoluminescence
Authors: Griffiths James , Zhang Siyuan , Lhuillier Jeremy , Zhu Dandan , Wallis David , Howkins Ashley , Boyd Ian , Stowe David , Humphreys Colin , Oliver Rachel 
Published: December 2016

Nitride quantum well (QW) light emitting diodes (LEDs) exhibit high efficiencies relative to traditional lighting sources. The quantum wells serve to confine carriers and lead to higher device efficiencies. To achieve the highest device efficiencies requires optimisation of the active quantum wells and hence experimental observations of the structural and optical characteristics. Recently, by imaging the cathodoluminescence (CL) in a scanning transmission electron microscope (STEM), the structural and optical properties were correlated with a spatial resolution of a few nanometres [1], an approach referred to as nanoCL. NanoCL has also been used to reveal quantum confinement in high brightness LEDs [2], and optimise the device structure to achieve the highest device efficiency.
Whilst the improved spatial resolution associated with nanoCL can reveal optical characteristics on the nanoscale, the higher electron energies can lead to structural damage. Here we investigate the effect of high energy electrons on the luminescent intensity. An exponential decline in the luminescent intensity is observed over time with exposure to the electron probe. Spectral time profiles are performed over a range of accelerating voltages from 80 to 200 keV to study the variation in the luminescence with the electron energy. We observe that the luminescent intensity is substantially more stable at lower accelerating voltages and predict a threshold for damage below which there is no damage. NanoCL can thus potentially provide a reliable approach to the study of functional optoelectronic devices.
Compressed sensing for beam sensitive materials imaging in
S
canning
T
ransmission
E
lectron
M
icroscopy
Authors: Béché Armand , Goris Bart , Freitag Bert , Verbeeck Jo 
Published: December 2016

Transmission electron microscopy (TEM) is a very powerful technique to investigate materials down to their atomic components. Its versatility allows quantifying samples from their shape to the nature of their constituents and surroundings. However, the strong interaction of the electron beam with matter potentially induces damages in samples under investigation, especially for those composed of soft matter such as zeolites, metal organic frameworks (MOFs) and most life science samples. Current workarounds involve the reduction of the beam intensity, such as in the so‐called low dose imaging, or increase of the detector performances as provided e.g. by direct electron detectors.
Recently, improvement in signal processing lead to the development of compressed sensing [1, 2], a numerical algorithm based on the assumption that real life images are sparse in some particular well‐chosen basis. Images can then be expressed with much less components than what required by the Nyquist sampling theorem. By extension, not all pixels in a given image are necessary and only a random selection of them is sufficient to retrieve the original image with fidelity. By definition, compressed sensing is a very dose efficient technique as only parts of the sample need to be exposed to the electron beam to reconstruct a faithful image. So far, only theoretical implementations of compressed sensing were investigated in the TEM community, focused mostly on the case of tomographic reconstructions [3].

Very recently, we demonstrated the first physical implementation of compressed sensing in a Scanning TEM (STEM) based on the use of a solenoid as a fast beam blanker [4]. The solenoid is placed in the condenser plane of a STEM in a specially designed condenser aperture holder with feedthrough electrical contacts. By synchronizing the STEM signal with the current source driving the solenoid, we successfully acquired compressed images by shifting the beam away from the region of interest on blanked pixels. The case of both medium scale imaging (Fig.1) and high resolution imaging (Fig. 2) was investigated and reconstructed using the SPGL1 algorithm [5] with a signal compression of 80%. The present setup, although still quite far from low dose imaging conditions, has lead to successful imaging of a cross grating and a SrTiO
3
sample. Latest results revealed that a checkerboard pattern, the most demanding pattern for the fast beam blanker, could be acquired with a dwell time of 40 µs and a beam deflection of 225 nm, as shown in Fig. 3.

By further improving the experimental setup, we expect reducing the acquisition dwell time to values within the µs range. Such improvements will offer possibilities for realizing improved images and tomography experiments of electron beam sensitive materials.
Characterization of the microstructure of composite
Ti6Al4V
‐
AA
2519 obtained by explosive welding
Authors: Bazarnik Piotr , Cantoni Marco , Śnieżek Lucian , Lewandowska Małgorzata 
Published: December 2016

A composite which combines good thermal resistance and high mechanical properties of titanium alloys with good plasticity and low density of aluminium alloys seems to be a promising materials for airspace applications. However, welding of titanium and aluminium is difficult because they are extremely chemically reactive with oxygen and nitrogen at high temperatures. In this concept, the explosive welding (EXW) is one of most promising solid‐state welding methods because it gives an opportunity to form the bonding on over the entire junction surface. In order to understand the phenomena taking place at joined surfaces, the detailed microstructural analysis is required, which was a prime goal of the present work.
Ti6Al4V and AA2519 plates 5 mm in thickness were joined via EXW with a detonation speed of 2000 m/s. The samples for scanning electron microscopy (SEM) observations were prepared by using HITACHI IM‐4000 ion milling system, which is a damage‐less polishing process and allows to see the structure on SEM through the channelling contrast. SEM observation was carried out in a HITACHI SU‐70 field emission Schottky scanning electron microscope at 10 kV accelerating voltage with the in‐lens back‐scatter electron (BSE) mode at 7mm working distance to get as much as possible surface contrast and resolution. Careful observations of selected areas were carried out on CS‐corrected dedicated scanning transmission electron microscope (STEM) Hitachi HD‐2700 operating at the accelerating voltage of 200 kV. The STEM thin foilswere prepared via in‐situ lift‐out in Hitachi NB 5000 focused ion beam. Precise EDX analysis were carried out on FEI Tecnai Osiris 200 kV microscope using Super‐X EDX detectors.

Figure 1a shows an overview of a Ti‐Al interface. EXW caused a high grain refinement in aluminium plate. The interface zone can be divided into two sections. The first one is 5 µm thickness zone consisted of nano‐sized grains of three intermetallic phases: TiAl
3
, TiAl
2
and TiAl which were identified by X‐ray analysis and electron diffraction. The second zone consist of a small aluminium grains and a white (BSE) Cu rich net around them (Figure 1b). These intermetallic inclusions were often accompanied by nano‐cracks (Figure 1b). Figure 2a shows the magnified structure of this interfacial area in High‐Angle Annular Dark‐Field (HAADF)‐STEM mode. The high resolution imaging (Figure 2b) shows that the copper net region have a crystalline structure. EDX mapping presented on Figure 3 shows the distribution of Ti, Al and Cu in the matrix and a gradient distribution of these alloying compounds in the structure. Copper net phenomenon was explained by the breaking or dissolving of big rich in copper equilibrium particles during explosive welding. Supersaturated solid solution of aluminium cannot contain all dissolved copper, so its excess was secondarily separated in the grain boundaries.
Concepts for an electrostatic phase shifting device
Authors: Wagner Tolga , Niermann Tore , Berger Dirk , Lehmann Michael 
Published: December 2016

The advantage of providing amplitude and phase information of an object exit‐wave makes off‐axis electron holography a powerful tool for analyzing field and potential distributions up to an atomic scale. The ability to selectively manipulate the phase of the incoming electron wave additionally opens doors to new possibilities and microscopic methods, such as the direct interferometric measurement of the coherence length of an electron wave packet [1, 2] or energy‐loss magnetic chiral dichroism (EMCD) based investigations [3].
In principle, a selective phase shifting device is realized by directing one of two coherent electron beams through an electrostatic potential surrounded by a grounded electrode to shield stray fields, while the other beam propagates undisturbed in the vacuum. We present two different concepts to create such a device.
The first one is a variation of an experiment G. Moellenstedt suggested in 1980 [1] and was first realized in 1985 by H. Schmid [2]. Instead of using two concentric tubes, we realized a setup with two separated and electrically isolated 1 mm long micro tubes on an especially developed modular carrier chip (M1) to electrify them (figure 1).
The second concept includes two perforated metallic plates (20 µm X 20 µm X 3 µm) in a distance of 3 µm to each other. The micro device shown in figure 2 was produced with focussed ion beam (FIB) allowing both a selective phase shift as well as the investigation of influences of stray fields.
We performed first in‐situ biasing TEM experiments with the phase shifting micro tubes. A big and necessary achievement was the enlargement of the hologram width from 2 µm to more than 25 µm. This was realized by using solely the TL22 lens of the image Cs corrector as objective lens of the FEI Titan 80‐300 Berlin Holography Special TEM. However, the micrographs in figure 3 show strong artefacts which we attribute to beam tilting due to charging effects of the tube surfaces. These artefacts manifest in a bending‐like projection of a biprism beneath the micro tubes.
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.
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.
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.