bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron beam lithography for the realization of electron beam vortices with large topological charge ( L=1000ħ)
Authors: Mafakheri Erfan , Tavabi Amir , Lu Penghan , Balboni Roberto , Venturi Federico , Menozzi Claudia , Gazzadi Gian Carlo , Frabboni Stefano , Boyd Robert , Dunin‐Borkowski Rafal , Karimi Ebrahim , Grillo Vincenzo
Published: December 2016

Electron vortex beams (EVBs) are an appealing topic, both in fundamental science and for practical applications in electron microscopy [1, 2]. Some of the most promising applications require beams that have large orbital angular momentum (OAM) [2, 3, 4]. Here, we demonstrate the largest (L=1000 ħ) high quality EVB by using electron beam lithography (EBL) to fabricate a phase hologram. EBL provides superior fabrication quality and a larger number of addressable points when compared with focused ion beam (FIB) milling. We measure the OAM of the generated EVB through propagation after a hard aperture cut [5]. Comparisons with simulations confirm an average OAM of (960±120)ħ , which is consistent with the intended value.

A clear improvement when compared with a FIB‐nanofabricated hologram is demonstrated in terms of 1) the maximum OAM that can be reached; 2) the minimum feature size (33 nm in the present study); 3) the improved uniformity of the frequency response; 4) the better suppression of higher order diffraction due to a nearly perfect rectangular groove profile.

We believe that EBL will be the fabrication technique of choice for most new diffractive optics with electrons in the future, permitting more complex holograms and new applications in material science.
Nanograins in polycrystalline ferroelectric
Hf0.5Zr0.5O2
films on
Si
substrate
Authors: Suvorova Elena , Chernikova Anna , Zarubin Sergei , Zenkevich Andrei , Ricolleau Christian
Published: December 2016

Structure of ultrathin ferroelectric Hf
0.5
Zr
0.5
O
2
films in composites TiN/Hf
0.5
Zr
0.5
O
2
/Si were investigated by TEM, HRTEM, electron diffraction and X‐ray EDS in a FEI Tecnai Osiris microscope (200 kV X‐FEG field emission gun, 1.2 mm spherical aberration, 1.2 mm chromatic aberration, 0.24 nm resolution at Scherzer defocus and 0.14 nm information limit) and a JEOL ARM 200 F Cold FEG (200 kV, CEOS hexapole type aberration corrector, 0.075 nm resolution at Scherzer defocus and 0.046 nm information limit, ‐2 mm spherical aberration). JEMS [1] simulation of HRTEM images, TED patterns and HRTEM diffractograms were performed for the phase analysis of the nanograins in the Hf
0.5
Zr
0.5
O
2
polycrystalline film.

Ultrathin Hf
0.5
Zr
0.5
O
2
films (2.5‐2.7 nm thick) were grown by the Atomic Layer Deposition (ALD) technique on the highly doped n‐type Si (r=0.005 Ohm×cm) substrates and they possess ferroelectric properties [2]. SAED patterns showed that the polycrystalline film contains grains with monoclinic structure (sp.gr. P2
1
/c) and orthorhombic structure (sp.gr. Pbc2
1
). Ferroelectric behavior was assigned to the presence of the grains with the orthorhombic non‐ centrosymmetric space group Pbc2
1
.

HRTEM and HRTEM image simulation was done in order to distinguish monoclinic grains from the orthorhombic non‐centrosymmetric ones and to find possible mutual orientations for better understanding the growth mechanism. The lattice parameters of both phases are very close and the presence of the orthorhombic phase in the mixture can be revealed due to the 111 ring (d
111o
=0.296 nm) in the SAED pattern (Fig.1b) which locates between ‐111 and 111monoclinic reflections (d
‐111m
= 0.316 nm, d
111m
=0.284 nm). High resolution JEOL ARM 200 F Cold FEG microscope with the Cs corrector allowed us to obtain good‐quality HRTEM diffractograms and to find grains with different structures and orientations.

In ultrathin Hf
0.5
Zr
0.5
O
2
films, adjacent grains of 15‐25 nm in size (Fig.1c) with monoclinic and orthorhombic structures are overlapped and nevertheless reveal crystallographic relationships. The monoclinic grain has the zone axis close to [‐11 52] which is parallel to the [112] zone axis of the orthorhombic grain (Fig.2) and the monoclinic (13‐2) plane is parallel to the orthorhombic (‐311) plane creating 6.5 % lattice misfit. The overlapped area of about 5 nm wide is between two grains where two crystals of approximately 1.0 – 1.5 nm thick are superimposed. The HRTEM simulation and structure modeling performed for the conditions used showed good agreement with the experimental HRTEM images (Fig.2).
Structural investigation, corrosion properties and adhesion behavior of magnetron‐sputtered nanocomposite
TiC/a:C
thin film coatings
Authors: Oláh Nikolett , Fogarassy Zsolt , Sulyok Attila , Sáfrán Eszter , Furkó Mónika , Csanádi Tamás , Balázsi Katalin
Published: December 2016

Due to the continuous rise in living standards, the continued growth of the world population and the development of medical science an ever‐increasing need for materials especially suited for bio‐implant applications. In case of an implant material a wide variety of parameter (adhesion, corrosion, structural, biological and mechanical properties) to must be considered. Thus, a TiC / amorphous C (TiC/a:C) nanocomposite thin film as bio‐coating was developed by simultaneously depositing Ti and C on TiAl6V4 and Titanium wafers (blasted and unblasted) using DC magnetron sputtering system at room temperature to improve the aforementioned properties. Furthermore, in order to achieve the higher osseointegration, the TiC/a:C thin film was coated with ~500‐600 nm thick biogenic HAp coating by electrospraying. The relationship between the structural, mechanical, adhesion and corrosion properties of TiC/a:C nanocomposite thin film was investigated. The film's composition and morphology were studied by Transmission Electron Microscopy (TEM), X‐ray Photoelectron Spectroscopy (XPS) and X‐ray Diffraction (XRD). In all cases, combination of columnar TiC nanostructure and thin amorphous carbon was showed
(Fig.1a)
. In the case of Ti content above ~ 18 at%, the presence of the fcc TiC nanocrystals were confirmed by electron diffraction
(Fig. 1b.)
and by XRD
(Fig.2)
. The mechanical characteristics of the thin film were investigated by nanoindentation technique while the simulated body fluid (SBF) was developed initially to evaluate the surface structural changes of the film. The applied pH was 7.25. The potential changes in the surface structure of the thin film were investigated by Scanning Electron Microscope (SEM) which does not show special structure change in the film's surface after the corrosion test and the calcination at 900 °C
(Fig. 3)
. The highest hardness ~ 26 GPa and modulus of elasticity ~ 140 GPa was observed in case of the film prepared at ~ 40 at% Ti content which consisted of ~ 20 nm width TiC columns separated by 2‐3 nm thin a:C layers. Overall, the results demonstrated that the best choice for a protective nanocomposite coating would be the TiC/a:C thin film with ~60 at% a:C and ~40 at% Ti contents which is sufficiently corrosion‐resistant, hydrophobic, nontoxic, biocompatible and mechanically stable.
Electron diffuse scattering in
BNT‐BKT‐BT
ternary compound
Authors: Neagu Alexandra , Tai Cheuk‐Wai
Published: December 2016

Local structure of crystalline materials has been increasingly recognized to play a crucial role in understanding their functional properties. One important example is perovskite ferroelectrics where the structure often involves the presence of chemical short‐range order, correlated atomic displacements and/or oxygen octahedral tilting disorder. In this case electron diffraction can prove to be a suitable technique for probing the local structure. The strong electron‐matter interaction makes it possible to easily record weak superlattice reflections and diffuse scattering with good signal‐to‐noise ratio.

The ternary system
x
Bi
0.5
Na
0.5
TiO
3
–
y
Bi
0.5
K
0.5
TiO
3
–
z
BaTiO
3
(BNT‐BKT‐BT) is a potential candidate for replacing Pb‐based materials in piezoelectric applications
1
. Even though it is one of the most extensively studied lead‐free piezoelectric systems, structural information about local distortions in this material is scarce. In this study Transmission Electron Microscopy (TEM) was employed in order to investigate the long‐ and short‐range structure of this system in both real and reciprocal space. Two and three dimensional electron diffraction data was recorded. The true features of diffuse electron scattering in 3D as well as Bragg reflections were obtained by Rotation Electron Diffraction (RED) method
2
.

A projection of the three‐dimensional reconstructed reciprocal space volume along <001>
pc
, is shown in Fig. 1(a). Superlattice reflections of both
½ooo
and
½ooe
type can be observed indicating the coexistence of two different octahedral tilting systems, anti‐phase

a
‐
a
‐
a
‐

and in‐phase

a
0
a
0
c
+

respectively (in Glazer notation
3
). The anti‐phase

a
‐
a
‐
a
‐

tilting system is consistent with the long‐range order space group, namely
R
3
c
. But, the in‐phase

a
0
a
0
c
+

tilting system is consistent with
P
4
bm
space group indicating local deviations from the average space group. Furthermore two types of diffuse scattering features could be observed: (i)

“asymmetric L‐shaped”

features around Bragg peaks extending along <100>
pc
directions clearly visible for Bragg peaks close to the direct beam, Fig. 1(b) and (ii) linear {
h00
}*, {
0k0
}* and {
00l
}* diffuse scattering

‘rods’

that pass through the superlattice reflections as highlighted in Fig. 1(c). A possible explanation for the observed diffuse features is correlated displacements of the A‐ and B‐cations along <111>
pc
and <100>
pc
chains coupled with disordered (in‐phase/anti‐phase) rotations of the oxygen octahedral
4
.
Micro‐ and nanostructural characterization of melamine‐formaldehyde microcapsule shells using electron microscopy
Authors: Heidari Hamed , Rivero Guadalupe , Idrissi Hosni , Ramachandran Dhanya , Cakir Seda , Egoavil Ricardo , Kurttepeli Mert , Crabbé Amandine , Hauffman Tom , Terryn Herman , Du Prez Filip , Schryvers Nick
Published: December 2016

A systematic study has been carried out to compare the surface morphology, shell thickness, mechanical properties and binding behavior of melamine formaldehyde microcapsules of 5 to 30 μm diameter size with various amounts of core content by using scanning and transmission electron microscopy including electron tomography, in‐situ nanomechanical tensile testing and electron energy‐loss spectroscopy. It is found that porosities are present at the outside surface of the capsule shell but not at the inner surface of the shell. Nano‐mechanical tensile tests on the capsule shells reveal that the Young's modulus of the shell material is higher than that of bulk melamine formaldehyde and that the shells exhibit a larger fracture strain compared to the bulk. Core‐loss elemental analysis of microcapsules embedded in epoxy indicates that during the curing process, the microcapsule‐matrix interface remains uniform and the epoxy matrix penetrates into the surface microporosities of the capsule shells.
Operando electron microscopy in heterogeneous catalysis
Authors: Elkjær Christian F. , Vendelbo Søren , Kooyman Patricia J. , Helveg Stig
Published: December 2016

Visualizing nanoparticles at atomic‐resolution by transmission electron microscopy (TEM) is beneficial for the understanding of their physico‐chemical properties. However, nanoparticles respond dynamically to changes in the surrounding gas or liquid environment, and such changes can have profound impact on their properties. It has therefore remained a long‐standing challenge in heterogeneous catalysis and related chemical fields to functionalize TEM for
operando
studies in which the state and functionality of nanoparticles are simultaneously evaluated at the atomic‐scale under catalytically meaningful reaction conditions [1].

Recent, we have developed a nanoreactor that enables atomic‐resolution TEM of catalysts at ambient pressure conditions and elevated temperatures [2–5]. The nanoreactor is a micro‐electro‐mechanical system (MEMS) device that integrates a micrometer‐sized and unidirectional gas‐flow channel with a micro‐heater and an array of electron‐transparent SiN
x
windows (Fig. 1). This nanoreactor design also allows concurrent mass‐spectrometry, calorimetry and electron energy loss spectroscopy of changes occuring in the gas phase during catalysis. Hereby, the nanoreactor enables
operando
TEM studies in heterogeneous catalysis [6].

Here, we showcase
operando
TEM movies that correlate the atomic‐scale dynamics of Pt nanoparticles with their catalytic activity for the CO oxidation at relevant pressure and temperature conditions (Fig. 2) [6,7]. This reaction has long served as the prototypical example for oscillating chemical reactions. The movies surprisingly show that the catalytically active surface sites undergo periodic and reversible changes that are synchronous with the oscillations in the reaction rate. The atomic‐resolution TEM was performed under low electron dose‐rate conditions to surpress beam‐induced alterations [6,8], and the observations were location‐dependent due to the mass‐ and heat‐distributions across the reaction zone [6,7]. In interplay with density functional theory, microkinetic and mass‐ and heat‐transport calculations, the
operando
TEM observations unveiled a mechanism for the oscillatory behavior based on the difference in CO adsorption energy and oxidation rate on the prevalent Pt surface terminations. Thus,
operando
TEM can extend the description of dynamics and functionality in catalysis with atomic‐scale information that is specific to the surface sites, and bridge simultaneously both the so‐called
materials
and
pressure
gap in catalysis and surface science.
In‐situ atomic scale studies of ammonia synthesis over ruthenium nanocatalysts
Authors: Mitchell Robert , Boyes Edward , Gai Pratibha
Published: December 2016

Ammonia is an important chemical for the production of fertilisers and in chemical synthesis. Catalyst materials are employed to improve the rate of formation of ammonia from diatomic gas precursors. Historically, the industrial catalyst most widely used for this process is based on the magnetite phase of iron oxide, often promoted by alumina and other additives.
1
More recently, graphitic carbon supported ruthenium based catalysts have been developed, which can operate more efficiently and at lower pressures than iron catalysts.
2, 3
In this work, the sintering of Ru/C catalysts under ammonia synthesis conditions was studied by Environmental Scanning Transmission Electron Microscopy (ESTEM).
4

Samples were prepared by incipient wetness impregnation of Ru(NO)(NO
3
)
3
on graphitic carbon. After drying at 150 °C, powdered samples were deposited onto 5 nm amorphous carbon coated MEMS chips supplied by DENS solutions. Additionally, model Ru samples were prepared by direct deposition of Ru precursor onto amorphous carbon MEMS chips. Ru nanoparticles were formed in the microscope by in‐situ reduction in H
2
gas. Suitable regions were identified and treated at 300 – 450 °C in H
2
, N
2
, or a mixed H
2
/N
2
gas atmosphere. Images were taken before and after treatment to study nanoparticle sintering. To limit beam exposure, the beam was blanked between images and during heating steps.

Typical images of the Ru/C samples are shown in Figure 1, showing Ru particles around 1 – 5 nm in size in addition to smaller clusters. After initial reduction, electron diffraction patterns from particles on both supports can be assigned to hexagonal phase Ru metal, space group
P
6
3
/mmc
. An example heating series for Ru on amorphous carbon is shown in Figure 2. Particle migration and coalescence is observed following treatments at both 300 °C for 2 h and 450 °C for 1 h. For this image series the particle size distribution increased from 1.5 ± 0.38 nm before H
2
/N
2
treatment, to 1.57 ± 0.33 nm and 1.64 ± 0.4 nm after 300 °C/450 °C treatments respectively. The sintering behaviour of Ru nanoparticles will be investigated as a function of support, gas atmosphere and temperature.

The authors would like to thank Mr Ian Wright and Dr Leonardo Lari for technical support, and the EPSRC (UK) for the strategic research grant EP/J018058/1.
In situ High Temperature
ESEM
study of carbon nanotubes reactivity under oxidative conditions
Authors: Mehedi Hassan‐Al , Podor Renaud , Ravaux Johann , Michel Thierry , Tahir Said , Yazda Khadija , Odorico Michael , Jourdain Vincent
Published: December 2016

Due to their extraordinary mechanical, electrical, optical, thermal … properties, single wall carbon nanotubes (SWCNTs) have attracted tremendous studies in the last 20 years. However, most of these properties are closely related with the defects present in the carbon layer and with the chirality of the SWNCTs. Two specific studies have been performed in order to better understand the high temperature behavior of SWCNTs, using the high temperature device attached with the environmental scanning electron microscope (HT‐ESEM mode).

SWCNTs imaging (Fig. 1): Isolated SWCNTs cannot be observed directly in the HT‐ESEM due to the relatively poor resolution of this technique. The SWCNTs are deposited on an insulating substrate and low voltage (1‐3kV) charge contrast imaging is used to directly observe the CNTs. While the ESEM is not supposed to operate in such high voltage conditions at high temperature, aligned CNTs images have been recorded under various gas compositions and pressures using the gaseous secondary electron detector. These images have demonstrated the possibility to observe the SWCNTs at high temperature in the ESEM and have opened the path for further in situ experiments in the microscope chamber.

We studied the chemical reactivity of individual single‐walled carbon nanotubes on oxide substrates toward oxygen etching using HT‐ESEM (Fig. 2) coupled with AFM observations. Our in situ observations show that the reactivity of carbon nanotubes on substrates is different from that of free‐standing ones. In particular, semiconducting nanotubes appear as or slightly more reactive than metallic ones, showing that the nanotube type has a secondary influence compared with that of the substrate. In addition, carbon nanotubes are not progressively etched from their ends as frequently assumed but disappear segment by segment. Atomic force microscopy before and after oxidation reveals that nanotube oxidation proceeds first by a local cutting leading to two separate nanotube segments, which is then followed by a rapid etching of the segment that has been electrically disconnected from others. In addition, our study shows that exposure to electron and laser beams can strongly increase the chemical reactivity of single‐walled carbon nanotubes on substrates. These results are rationalized by considering i) the effect of substrate‐trapped charges on the nanotube density of states close to the Fermi level, and ii) the effect of electron and laser beams on the density of these surface charges.
A new method for quantitative
XEDS
tomography of complex hetero‐nanostructures
Authors: Zanaga Daniele , Altantzis Thomas , Polavarapu Lakshminarayana , Liz‐Marzán Luis M. , Freitag Bert , Bals Sara
Published: December 2016

Over the last decades, electron tomography based on HAADF‐STEM has evolved into a standard technique to investigate the morphology and inner structure of nanomaterials. The HAADF‐STEM intensity depends on sample thickness but also scales with the atomic number Z and therefore, chemical compositions can be studied from these three‐dimensional (3D) reconstructions.[1] Nevertheless, it is not straightforward to interpret the gray levels in a 3D HAADF‐STEM reconstruction, when mixing of elements is expected or elements with atomic number Z close to each other are present.

In an increasing number of recent studies, X‐ray Energy Dispersive Spectroscopy (XEDS) has been combined with tomography to understand complex nanostructure morphology and composition in 3D.[2] These studies rely on newly developed XEDS detectors such as the Super‐X detection system, which consists of four individual detectors, symmetrically arranged around the TEM sample.[3] By using the Super‐X detector, one is able to overcome problems that were previously related to extreme shadowing of the XEDS signal caused by the sample‐detector configuration. Although this problem can be largely overcome, some shadowing effects remain, as illustrated in Figure 1. Since such shadowing effects vary for different tilt angles, the XEDS will also depend on the tilt angle and the projection principle for electron tomography is no longer fulfilled. Because of this problem and the low signal‐to‐noise ratio, typical of XEDS mapping, it remains challenging to obtain quantitative information by 3D XEDS and further progress is required.

Here, we propose an alternative approach to optimize the reconstruction of an XEDS tomography series by minimizing the impact of shadowing effects and improving the spatial resolution. The method is based on the synergistic combination of HAADF‐STEM tomography and XEDS quantitative mapping.[4‐5] HAADF‐STEM yields a relatively high signal‐to‐noise ratio, enabling an accurate reconstruction of the morphology. XEDS, on the other hand, yields chemical information, but the limited amount of data that can be usually collected, hampers a good morphological reconstruction. As a proof of principle, we apply our methodology to a nanostructure containing a mix of Au and Ag atoms. It should be mentioned that the approach we propose here enables quantitative 3D chemical characterization of a broad variety of nanostructures.
Sub‐nanosecond electron beam blanking for deep‐subwavelength lifetime probing of nanophotonical devices and nanoparticles
Authors: Moerland Robert , Garming Mathijs , Weppelman Gerward , Kruit Pieter , Hoogenboom Jacob
Published: December 2016

Optical techniques are used to probe carrier or excited energy dynamics down to femtosecond time‐scales, but they lack the resolution to address nanoscopic length scales [1]. Higher spatial resolution can be obtained using pulsed beams of electrons, but this typically requires dedicated microscopes with laser‐triggered electron sources [2]. Here, we use a standard scanning electron microscope equipped with an electrostatic beam blanker operated in conjugate mode (Fig. 1). We show the generation of sub‐nanosecond electron pulses (Fig.2). This system is used to probe nanophotonical devices and nanoparticles using time‐resolved cathodoluminescence (CL). In these devices, optical emitters couple with the nanoscale environment leading to a position‐dependent excited state lifetime. The pulsed electron beam excites the emitters, giving rise to CL. The CL emission is detected using an integrated light microscope [3]. Photon arrival histograms are obtained using time‐correlated single photon counting, synchronized with the input signal of the electron beam blanker, thus measuring spatially resolved CL lifetime.

We demonstrate the ability to identify nanoparticles based on their lifetime as well as their emission wavelength, which provides an additional source of information in nanoparticle‐based biological imaging. Moreover, we conduct a nanoscopic version of the seminal work performed in the 1960s and 1970s by Drexhage, who showed that the lifetime of emitters depends on their distance to a metallic mirror [4]. We locally excite Ce
3+
emitters in YAG, which is partially covered with a thin aluminum film (Fig. 3). We then measure the CL lifetime as a function of distance
d
to the metal, with deep subwavelength (<λ/10) resolution (Fig. 4). Our results firmly establish time‐resolved electron spectroscopy of nanophotonical devices as a powerful characterization tool for nanophotonics.
Cost effective implementation of nanoparticle size measurement for regulation purposes
Authors: Müller Philipp , Wohlleben Wendel , Wieczorek Thorsten , Wagner Thorsten
Published: December 2016

While nano‐scaled intermediate and consumer products are omnipresent in many industries, a huge challenge consists in the development of methods that reliably identify, characterize and quantify nanomaterials both as a substance and in various matrices. For product registration purposes, the European Commission proposed a definition of nanomaterial [1] which requires a quantitative size determination of the primary particles of a sample down to sizes of 1 nm. According to [1] a material is defined as nano if 50% of the primary particles are observed to comprise a smallest dimension <100 nm. The NanoDefine project [5] was set up to develop and validate a robust, readily implementable and cost‐effective measurement approach to obtain a quantitative particle size distribution and to distinguish between nano and non‐nano materials according to the definition [1].

In the present study the mean particle size derived from Brunauer, Emmet, Teller (BET) surface measurement by gas adsorption is systematically compared with the particle size derived from TEM images by manual and automated image evaluation. A correlation between mean particle diameters of 10 different organic pigments is given in figure 1. Automated and manual image evaluation lead to consistent results for the D50 particle size (red and blue bars). Automated TEM image evaluation was accomplished by a software package developed within the NanoDefine project which will soon be available as public ImageJ‐Plugin [2,3]. Samples were carefully selected to represent typical organic pigment particles of different grinding degrees. Figure 2 shows TEM images of such a series of pigment grades. The red ellipses mark the result of the automated particle detection using direct ellipse fitting. The length of the minor axis of each ellipsis was taken as approximation for the particles minimum feret diameter.

In the present study a tiered approach for particle classification is proposed. BET measurements can be used for a coarse classification of the material including a categorization into nano/non‐nano [4]. The presented data help to define the thresholds for this surface‐based classification. Automated evaluation of TEM images improves this classification with reliable results for the number‐based particle distribution within some remaining constraints. The according limitations are elaborated in the present study by comparison with the D50 size values determined by manually evaluation of TEM images.
Behaviour of platinum nanoparticles under reducing and oxidising conditions using
ESTEM
Authors: Ward Michael , Boyes Ed , Gai Pratibha
Published: December 2016

Platinum nanoparticles are well‐known to be catalytically active in a wide variety of important chemical processes including hydrogen fuel cells
1
and diesel oxidation catalysts
2
. Platinum, as well as other nanoparticle catalysts are known to reduce their efficiency over time under operating conditions due to several mechanisms. The first method is via particle migration and coalescence where nanoparticles become mobile, collide and eventually form larger structures. Alternatively, the nanoparticles may undergo Ostwald ripening where large nanoparticles grow at the expense of smaller ones due to diffusion of less stable atoms across the support or in a gaseous phase. In either case, valuable catalytically active sites such as edge, corner and adatom sites may be lost as larger more stable facets take their place. As nanoparticles coalesce, more of the precious metal is locked away beneath the surface of the nanoparticles resulting in loss of active surface area and ultimately wasted metal.

These processes have been studied with the help of atomic resolution transmission electron microscopy where heat combined with gas can be used to replicate real world operating conditions inside the microscope
3,4
. HAADF‐STEM with its Z contrast imaging capability is ideal for studying these nanoparticle growth mechanisms, particularly Ostwald ripening where small clusters/atoms are generally not visible in TEM. To further this important field of research, we investigate the differences in nanoparticle dispersion on two different supports before and after being exposed to a range of gases at different temperatures. We utilised the York JEOL 2200FS featuring double aberration correction and environmental TEM/STEM capability which has previously demonstrated single atom resolution in gas
5
. A MEMs chip holder from DENSsolutions was used for heating.

To produce a simple model system to infer nanoparticle aging mechanisms on more complex industrial catalysts, we deposited platinum via magnetron sputtering onto a SiN
X
MEMs chip upon which graphite had previously been deposited (from ethanol suspension of graphite powder). Figure 1 shows an example of a graphite sheet loaded onto the SiNx MEMs chip. Figure 2 shows an example of the differences in dispersion before and after exposure to O
2
at elevated temperature for 6 hours. The image in Figure 2 is taken near a graphite sheet edge. The nanoparticles on the graphite are slightly larger than those on the SiN
x
on the freshly deposited sample but after the heat treatment in O
2
, the nanoparticles on the graphite are much larger. These results and environmental (S)TEM in general open new avenues into nanoparticle research using electron microscopy and have wide applications in chemical production, exhaust catalyst and future fuel cell design.
Structural characterization of the high thermoelectric performance
PbTe
‐
PbSnS2
system and implications of its structural complexity in low lattice thermal conductivity
Authors: Ioannidou Chrysoula , Lioutas Christos , Frangis Nikolaos , Girard Steven , Kanatzidis Mercouri
Published: December 2016

Thermoelectric materials are promising alternative energy sources, suitable for applications in thermoelectric generators and refrigerators, due to their low cost and environmentally friendly heat‐to‐power generation. Their wide‐scale utilization is limited because of their low efficiency; however, nanoscale inclusions can improve it by suppressing the lattice thermal conductivity.

The high performance PbTe‐SnTe‐PbS thermoelectric system forms a new PbTe ‐ PbSnS
2
composite with high n‐type figure of merit. Electron Diffraction (ED) through tilting and Precession Electron Diffraction (PED) experiments as well as High Resolution Transmission Electron Microscopy (HRTEM) characterization of the thermoelectric composite PbTe + 25% PbSnS
2
reveal that the system is nanostructured in a unique way, with PbSnS
2
nanocrystals in the range of 80 to 500 nm in size. In most of the cases, they are endotaxially grown within the PbTe matrix (Figure 1).

Three independent crystal superstructures were observed for the PbSnS
2
inclusions, originating from the same parent SnS‐type structure. Specifically, the PbSnS
2
inclusions appear with all three known structural modifications within the same matrix and often within the same nanocrystal. HRTEM images were qualitatively improved by Fast Fourier Transform (FFT) and inverse FFT (IFFT) processing, as well as by averaging of selected parts of the images. We then compared the processed images with computer image simulations and a very good resemblance between them was found. Figure 3 depicts a HRTEM image taken with the electron beam parallel to [110]PbSnS
2
direction and is a part of a nanocrystal of about 300 nm in size. Two types of FFT patterns were observed and are shown as insets in Figure 3. Modified structural models for two of the superstructures observed in the PbSnS
2
precipitates are proposed (one of them is presented in Figure 2).

Finally, evidence was also found for the growth process of the nanocrystals. The presence of some PbS nanocrystals implies that the growth process of the minor PbSnS
2
phase starts from PbS crystals where SnS is gradually dissolved to eventually form PbSnS
2
crystals.

Our findings suggest that this nanostructured thermoelectric composite exhibits unique structural complexity, which contributes to the low lattice thermal conductivity reported previously for these nanocomposite materials, by introducing extra scattering mechanisms. Phonon scattering can occur not only at the interfaces between the nanocrystals and the matrix, but also within the nanocrystals, due to their structural heterogeneity.
Localized surface plasmon resonance mapping on aluminium voids with three‐dimensional nanostructures
Authors: Zhu Ye , Nakashima Philip , Funston Alison , Bourgeois Laure , Etheridge Joanne
Published: December 2016

Today's nanotechnology has enabled the fabrication of metallic nanoparticles with a variety of geometries, greatly advancing the research field of plasmonics. The complementary system of the inverted nanostructures such as nano‐voids, however, has so far been limited to either 2D holes or spherical voids, owing to the difficulty in creating voids with well‐defined 3D geometries. Here we present the first localized surface plasmon resonance (LSPR) study, both experimentally and theoretically, on aluminium nano‐voids in the shape of truncated octahedra.

Nano‐voids were made in high‐purity aluminium using an annealing and quenching treatment.
1
To characterize LSPRs of voids, we used electron energy‐loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) – an aberration‐corrected FEI Titan operating at 80 kV. The lower accelerating voltage mitigates irradiation damage on aluminium, which is critical to perform reliable STEM‐EELS mapping on voids. To confirm experimental results, electrodynamic EELS calculations were carried out based on electron‐driven discrete dipole approximation (
e
‐DDA).
2

Our results show that these aluminium nano‐voids exhibit strongly localized field enhancements, with the LSPR energies 10.7 ‐ 13.3 eV (116 ‐ 93 nm), well beyond the conventional LSPR spectrum range. The LSPR tunability was demonstrated by tailoring the shape of nano‐voids using controlled electron irradiation. Furthermore, owing to the simplicity of the nano‐void system which is free of aluminium oxidation and supporting substrates, we demonstrate that the intrinsic LSPR properties of pure Al nanoparticles can be revealed from nano‐voids characterization using the sum rule for the complementary systems. Combined with the low cost and mass producibility of Al, our results indicate that both the Al nano‐voids and nanoparticles can effectively expand the available plasmonic spectrum to the extreme UV region (≤ 124 nm), which opens possibilites for applications such as plasmon‐enhanced UV photoemission spectroscopy and photoionization.
Imaging of deformation of a polypropylene separator due to immersion in electrolyte or due to heating
Authors: takata keiji
Published: December 2016

Pore size of separators is one of the most important factors for Li‐ion batteries. The separator must electrically isolate the anode and the cathode of the battery, but should allow Li ions to pass through easily. Large pores degrade the extent of isolation but small pores degrade the permeability; thus, a balance is needed for optimal performance. The pore size of the separator is determined well before its incorporation into the battery, but the pore size may not be maintained in the electrolyte. We, therefore, observed the structures of the separator before and after immersion in the electrolyte.

Figures 1(a) and 1(b) show atomic force microscopy (AFM) images of a 25‐mm‐thick single‐layer polypropylene separator before and after immersion in the electrolyte, respectively. The figures clearly show the lamellar alignment and the the fibrillae between the lamellae. The spacing between the lamellar layers was around 0.8 mm before immersion, but expanded to 1.4 mm after immersion. The pores expanded like sponge when they immersed in the liquid electrolyte. Expansion of the separator occurs when it is bound tightly inside the battery. Thus, expansion of the pores of the separator must be considered while fabricating good batteries.

One of the most important abilities of the separator is a shutdown ability. When a large current flows between the electrodes, the resultant heating partially melts the separator, and fills the pores. As a result, Li ions cannot pass through the portion of the separator, and the large current is shut down. Thus, shutdown by melting of the separator is an important factor for safety. To investigate melting of the separator, we observed the separator while heating.

AFM images obtained at 398 K show the deformation of the separator. Expansion of the lamellar layers and the filled pores were imaged. The melting band normal to the lamellar layers was extended in the direction of the fibrillae. The melting bands should be formed by fusion of the fibrillae and lamellae, and by conjunction. Partial melting around 390 K is adequate for shutdown. These results prove the good performance of the separator.
On the influence of the elemental addition
Au
on the semi‐coherent interfaces in an
Al‐Cu
alloy
Authors: Chen Yiqiang , Zhang Zezhong , Zhen Chen , Tsalanidis Amalia , Weyland Matthew , Scott Findlay , Les Allen , Li Jiehua , Bourgeois Laure
Published: December 2016

Aluminium light alloys are employed in commercial automotive and aerospace applications due to their high specific strength and corrosion resistance [1]. Precipitation hardening is one of the most important ways to improve the alloy performance. By tailoring precipitate size, aspect ratio, and distribution, the precipitation hardening can be significantly enhanced. The interfacial structure between precipitates and matrix is the critical factor being thought to manipulate the precipitate growth, but the fundamental understanding of these interfaces remains poor due to both limitations in atomic‐resolution compositional characterisation techniques and computational capacity of first principle calculations.

Al‐Cu is a textbook binary alloy having precipitate strengthener θ′ (Al
2
Cu) phase, but recent work showed its semi‐coherent interfaces is not as simple as previously thought [2]. In fact, a complex metastable θ′
t
phase is sandwiched in‐between θ′′ and θ′ precipitates, indicating a non‐intuitive energetically favourable phenomenon. Gold (Au) has strong negative solute formation enthalpy with aluminium and thereby its precipitation is directly linked to η′ and η phases without precursor Guinier–Preston (GP) zone [3]. How such element affects the interfacial structure is still unclear. In this work, we have used atomic‐resolution high angle annular dark‐field (HAADF) via aberration‐corrected scanning transmission electron microscopy (AC‐STEM) for detailed investigations of the influence of Au on the heterophase interfacial structure in an Al‐Cu alloy.

We have experimentally determined the effect of Au and ageing temperature on the complex interfacial structure between solid solution (α) and θ′ (Al
2
Cu). We have observed the sandwiched interfacial structure in Al‐Cu‐Au alloys aged at 200°C (See Fig. 1a) as discovered in Ref. [2], while in comparison some partially direct θ′‐α interface was found (see Fig. 1b) in rare probability. However, Au addition was observed to clearly destabilise the complex interfaces (see fig. 1c) at higher temperature ageing (350°C), whereas the corresponding binary Al‐Cu alloy still somehow displays complex interfacial structures (Fig. 1d). The complex interface was also proved to provide the first solution to the four‐decades‐old mystery where experimental precipitate coarsening rate was found to be hundreds of times that of theoretical predictions based on the direct θ′‐α interface in the Ref. [4].
Direct visualization and quantification of three‐dimensional ferritin crystallization on the nanoscale
Authors: Houben Lothar , Weissman Haim , Wolf Sharon , Rybtchinski Boris
Published: December 2016

We present the proof of concept that a real space tomography approach can be used for the quantification of local ordering in tiny crystals of ferritin. This work is driven by the need for a fundamental understanding of crystal growth of weakly interacting proteins on a molecular level. At present, only tentative ideas exist about interactions in particular in solution and during crystallization. Offering simplicity and controllability the condensation of ferritin molecules from solution was chosen as an ideal system to get insight into the nucleation and crystallisation mechanism that leads to ordered crystals.

The approach involves cryo‐fixation of aging stages of ferritin condensation from solution and subsequent three‐dimensional scanning transmission electron miscoscopy (STEM) tomography (Fig. 1a). Cryo‐STEM tomograms were recorded and analysed to yield the three‐dimensional ferritin particle coordinates for the real‐space refinement of the structure of ferritin agglomerates. 3D pair correlation functions for ordered nanocrystals of a few hundred ferritin particles reproduce well and up to higher coordination shells the crystal structure that was reported from synchrotron experiments on macrocrystals. The local order within ferritin agglomerates is further refined quantitatively by order parameter mapping with the resolution of a single lattice site based on a data‐base correlation technique (Fig. 1b).
UHVEM
observation for the dual structure in spheroidal graphite of cast irons
Authors: Maeda Hidefumi , Inoue Kanako , Sugiyama Akira , Yasuda Hidehiro
Published: December 2016

The phenomenon that spheroidal graphite cast iron was formed by adding magnesium (Mg) was discovered in 1949 [1][2]. Since then, a number of researches have been made on this subject. Due partly to increase in research on the graphite‐spheroidizing, there are various theories such as interfacial energy theory, nuclear theory, bubble theory,,, etc. Among them interfacial energy theory is becoming dominant as of now [3]. However the role of Mg as the graphite‐spheroidizing agent has not been yet identified. And Mg particle is often observed inside of spheroidal graphite experimentally. In order to get the information on the internal structure of spheroidal graphite in cast iron, Ultra‐High Voltage Electron Microscopy (UHVEM) observation was carried out.

The composition of the cast iron in this experiment was FCD450 (Fe:Bal., C:3.645, Si:2.533, Mg:0.0464, Mn:0.368, P:0.018, S:0.0114, Cu:0.176 (wt%), Yodoshi Co.). The position of Mg in spheroidal graphite was predicted from a surface observation result by EPMA. Focused ion beam (FIB) cut out into approximately rectangular parallelepiped shape carbon sample from a spheroidal graphite of FCD450. This sample was observed by UHVEM in Osaka Univ. at 2.0MeV.

Figure 1 shows a bright field image (BFI) of the internal structure of spheroidal graphite. The electron beam in acceleration voltage of 2MeV was transmitted approximately 8μm thickness of graphite (inclination of the incident beam: 30°). Figure 1 indicated that whole area was graphite including the internal structure of spheroidal graphite roughly composed of a core region surrounded by annual rings of a layered intermediate region (central domain) and a layered outer region with some radial factors (covering domain).

Only the covering domain has the radial and superimposed contrast. This radial factor originates from the metal inclusion that grew radially from the central domain. The shape of the external region of the central domain (without superimposed contrast) could be regarded as the almost truth sphere, which might become core for growing graphite crystal spherically. Primary crystal of graphite might be spheroidized by the solidification in liquid state, and crystal growth of graphite reaches the eutectic point at the external region of the central domain. After that, the covering domain formed by the cooperation growth between graphite and austenite.

The spheroidal graphite in cast iron has the dual structure consisting of a spherical central domain and a covering domain. This obtained data using by UHVEM has provided new knowledge of the internal structure of spheroidal graphite in cast iron. And this study might provide important visual data to identify a role of the Mg in the graphite‐spheroidizing of cast iron.
In‐situ thermal measurements with high spatial resolution in the TEM
Authors: Voskanian Norvik , Cumings John , Olsson Eva
Published: December 2016

With the constant miniaturization of electronics, the thermal management issue is becoming the main limiting factor in dictating device performance [1]. Therefore, the study of thermodynamics is of practical interest as well as fundamental scientific interest. However, measuring temperature at these dimensions is difficult due to the increasing influence of the employed measurement tools and therefore new techniques need to be developed. One such technique, Electron Thermal Microscopy (EThM), has been previously used to study heat dissipation in nanowires and carbon nanotubes supported on SiN substrate [3, 4].

EThM is an in‐situ thermal imaging technique using the Transmission Electron Microscope (TEM) and relies on the observation of the solid to liquid phase transition of indium islands and provides a binary temperature map with 50nm spatial resolution[2]. The indium islands, thermally evaporated on the back of the substrate, as seen in the bright‐field TEM image in Figure 1a, melt once heated to 429K. This solid to liquid phase transition is easily observed in the TEM, when operating in the appropriate dark‐field conditions (Figure 1b), at which the molten islands appear bright compared to the solid ones. In addition, the presence of a high melting point thin oxide layer on the indium preserves the structure of the islands and allows the thermometry technique to be used repeatedly over a large experimental range.

Two factors contribute to the observed temperature of the system; the heat source and the efficiency of the heat transfer mechanism to the lower temperature reservoir. Here we present the work on joule heated Pd nanowires supported on SiN substrate and use the EThM technique to evaluate the thermal properties of the device. The measured temperature and the efficiency of the heat transfer mechanism can be quantified in terms of the thermal conductivity of the different materials within the device and their thermal boundary resistances. Conventionally, the thermal transport in dielectrics, such as SiN, is phonon mediated. However, as the dimensions approach the mean free path of the phonons, new modasses of heat dissipation may dominate. Combining our experimental thermal measurements (Figure 1c) with simulations (Figure 1d), based on finite element analysis, we have explored different modes of thermal transport and show that the conventional phonon mediated thermal transport is not sufficient to explain the observed temperature gradient across the SiN, indicating that an additional mode is active.