bluuebunny/crossref_metadata_2025 huggingface dataset:
In‐situ propagation ofAlin germanium nanowires observed by transmission electron microscopy
Authors: El Hajraoui Khalil , Robin Eric , Lopez‐Haro Miguel , Zeiner Clemens , Brunbauer Florian , Kral Sébastian , Lugstein Alois , Rouvière Jean‐Luc , Hertog Martien Den
Published: December 2016

Semiconductor nanowires (NWs) are promising candidates for many device applications ranging from electronics and optoelectronics to energy conversion and spintronics. However, typical NW devices are fabricated using electron beam lithography and therefore source, drain and channel length still depend on the spatial resolution of the lithography. In this work we show fabrication of NW devices in a transmission electron microscope (TEM) where we can obtain atomic resolution on the channel length using in‐situ propagation of a metallic phase in the semiconducting NW. The corresponding channel length is independent on the lithography resolution. We show results on semiconducting NW devices fabricated on two different electron transparent Si3N4membranes: a calibrated heater chip from DENs solution [1] and homemade membranes where the NW‐metal contact is locally heated by Joule heating [2]. We demonstrate a real‐time observation of the metal diffusion in the semiconducting NW. First we present results on in‐situ propagation of aluminum metal in Ge NWs while monitoring the system temperature [3] and by Joule heating while measuring the current through the device. We study the kinetics and rate limiting step by monitoring the position of the reaction front as a function of time. Second we will show characterization of the formed phase at atomic length scales with different (S)TEM techniques (energy dispersive X‐ray spectroscopy, HR(S)TEM) to understand how the metal atoms diffuse and incorporate into the Ge NW at the reaction front and how these parameters relate to the electrical properties of the same interface.

Using EDX analysis and comparing with 3D NW model calculations we show that the reacted NW part is pure Al, with a shell of Al2O3with a low Ge content on both sides of the Al2O3shell see Fig.2. EDX analysis show that both Al and Ge are diffusing in opposite directions.
Nanostructure and luminescence of
Ga
and Fe‐doped
IZO
's
Authors: García‐Fernández Javier , Torres‐Pardo Almudena , Ramirez‐Castellanos Julio , Cremades Ana , Piqueras Javier , González‐Calbet Jose M
Published: December 2016

The study of transparent semiconducting oxides (TCO) constitutes a large field of research due to its applications as transparent electrodes in transistors, flat panel displays, solar cells, sensors, etc. [1, 2]. Most of the interest is aimed to optimize both conductivity and transparency in the visible region of commercial indium tin oxide (ITO), with lower production costs. In this sense, the In
2
Zn
k
O
3+k
system seems to be one of the best candidates. Moriga
et al
[3] reported the discovery of nine members in this system. The physical properties of these phases are a function of the k value. Likewise these phases allow doping with other elements, which provides greater flexibility when designing materials [4, 5].

In this work, In
2‐x
M
x
Zn
7
O
10
(
M
= Ga and Fe, and 0≤x≤0.5) materials have been prepared by the ceramic method. The k=7 term crystallizes in the space group R‐3m, the introduction of dopant decreasing the lattice parameter without changing the crystalline structure. HRTEM images show these materials formed by ordered layers of InO octahedra sharing edges with layers of (InZn
k
)O
k+1
+
composition along c‐axis, in such a way that the (001) plane of the ZnO structure and the (111) In
2
O
3
plane are epitaxially equivalent to the (001) plane of Zn
k
In
2
O
k+3
. The existence of extended defects such as twins, dislocations and disordered intergrowths were observed.

Cathodoluminescence (CL) measurements show the existence of two emission bands, one associated to defects whose intensity and width vary depending on the chemical composition of the material. The second issue is the band edge of the material, which is present in the undoped sample, and it disappears and reappears depending on dopant concentrations. EDS spectroscopy confirms the presence of Ga and Fe dopants. A deeper study by means of atomic resolved microscopy has been performed in order to stablish the structure‐properties relationship.
Topotactic reduction in
SrMnO3
‐δ nanoparticles followed by atomically‐resolved microscopy
Authors: Torres‐Pardo Almudena , González‐Jiménez Irma Noemí , Varela Aurea , Parras Marina , González‐Calbet Jose M.
Published: December 2016

The current technological demand of new devices requires the continuous stabilization of new compounds with nanometric scale for novel applications. The huge diversity of functional properties of the perovskite related mixed oxides make them ideal candidates to study the effect of the particle size reduction [1]. Particular attention has been paid to Mn related perovskites since Mn can be stabilized in different oxidation states leading to a series of functional materials. Here, we present the study of SrMnO
3
nanoparticles obtained from a novel [SrMn(edta)(H
2
O)
5
]·3/2H
2
O heterometallic precursor and we evidence the different reactivity of the SrMnO
3
material in nanometric size [2].

Atomically‐resolved high angle annular dark field (HAADF) images, acquired in a JEOL JEMARM200cF microscope, reveals 40‐60 nm size SrMnO
3
nanoparticles with 4H hexagonal related‐perovskite structure (Figure 1). Oxygen deficient samples were obtained from SrMnO
3.0
nanoparticles by reducing the oxygen content in a controlled way. The 4H‐related structure is kept in the SrMnO
2.82
sample confirming a topotactic reduction of the nanoparticles when the oxygen content decreases down to δ=0.2. This fact makes a difference with respect to the bulk material, where the stabilization of a cubic‐related perovskite structure is observed for the same oxygen content [3]

The structural study performed on SrMnO
3.0
reveals the presence of dislocations at the origin of the structural disorder in the 4H‐perovskite structure, while more complex arrangement of cubic and hexagonal layers seems to be responsible for structural defects in SrMnO
2.82
sample (Figure 2a). Additionally, electron energy loss spectra (EELS) were acquired to access the local oxidation state of manganese. The coexistence of Mn
3+
and Mn
4+
is observed in SrMnO
2.82
but differences in the Mn‐L
2,3
line position suggests a higher presence of Mn
3+
associated to the structural defect areas (Figure 2b).
Quasi in‐situ catalytic studies using a
TEM
grid microreactor
Authors: Masliuk Liudmyla , Willinger Marc G. , Dunphy Darren , Schlögl Robert , Lunkenbein Thomas
Published: December 2016

Conventionally, catalysts are analyzed in the transmission electron microscope (TEM) under static conditions in the vacuum. However, catalysts surfaces dynamically response to the reaction conditions. In addition, comparing TEM images before and after the catalytic reaction may give conclusions that are difficult to verify, because of the inhomogeneous conditions along the catalyst in normal fixed bed reactors [1]. For obtaining relevant information it is advisable to study the material under catalytic relevant conditions (gas composition, pressure, temperature) which also includes the monitoring of conversion. Therefore,
in‐situ
TEM approaches, such as environmental TEM (ETEM) or microelectromechanical systems (MEMS)‐based gas cell TEM holders, were developed. They allow the direct observation of the dynamic changes of a catalyst during the prevailing time of a reaction [2]. However, drawbacks regarding the reaction pressure and fast dynamics give rise to pressure gaps and may limit the resolution, respectively.

To overcome these limitations we have developed a TEM grid microreactor that allows a decoupling of the catalytic reaction and the imaging process. This
quasi in‐situ
method combines relevant and well‐controlled conditions for all catalyst particles at ambient pressure with high resolution imaging of exactly the same particles. In order to avoid the exposure to ambient air, a secure transfer of the catalyst to and from the TEM can be guaranteed via the glovebox and vacuum transfer holders. Furthermore, the catalytic conversion can be followed by using an ultra‐sensitive proton‐transfer reaction mass spectrometer (PTR‐MS).

Here, we present the utilization of this microreactor in the CO oxidation over metal catalysts. For instance, identical location imaging of active Pt nanoparticles (proven by PTR‐MS measurements) reveals structural changes, which are induced by the catalytic process (Figure 1).

In conclusion, the microreactor complements the state of the art
in‐situ
imaging, where one can study the structural dynamics, by delivering catalytic relevant kinetic information, which can be coupled to changes on the atomic scale.
Direct Observation of
CVD
Graphene Growth and Related Surface Dynamics of Active Metal Catalysts by In‐situ Scanning Electron Microscopy
Authors: Wang Zhu‐Jun , Weinberg Gisela , Schlögl Rober , Willinger Marc Georg
Published: December 2016

During the last three years, we have modified the set‐up of a conventional scanning electron microscope in order to enable the observation of catalyst surface dynamics under controlled atmosphere and temperature. Using this instrument, we investigate chemical vapor deposition (CVD) growth of graphene on different metal catalysts. Since the experiments are performed in the chamber of a microscope, it is possible to observe a complete CVD process from substrate annealing through graphene nucleation and growth and, finally, substrate cooling in real time at nanometer‐scale resolution without the need of sample transfer. The nucleation and growth of single layer graphene can be investigated at temperatures of up to 1000°C, while at the same time, surface dynamics of the active metal catalyst can be imaged and directly related to the catalytic activity (Figure 1).[1] Due to the high sensitivity of the secondary electron signal to changes in the work function and charge transfer at the surface, we are able to visualize different degrees of graphene‐substrate coupling [2] as well as the stacking sequence of few layer graphene. The
in situ
SEM image in Figure 2a and the plot in Figure 2b illustrate the step‐wise variation of the contrast that allows identification of up to 9 individual graphene layers on platinum substrates, starting with the brightest first layer in contact with the substrate. In addition, the
in situ
SEM images of edge misalignment between mutual layers and individual sheets provide real‐time information on the evolution of the rotation angle between growing layers and formation of the stacking order. The growth behavior of graphene on nickel, copper and platinum substrates shows characteristic differences that are related to the catalytic activity and carbon solubility of the respective catalysts (Figure 3).

In the case of Cu and Pt substrates, we observe grain orientation dependent growth dynamics. Real‐time imaging during growth thus allows us to directly visualize and study the catalytic activity of differently oriented surfaces.

ESEM observations during graphene growth highlight the dynamic nature of catalysts and reveal the sensitive response of the surface to changes in the chemical potential of the gas phase.
In situ
scanning electron microscopy furthermore covers the spatial resolution of complementary
in situ
techniques that provide spectroscopic information, such as ambient pressure X‐ray and Raman spectroscopy. It completes the spectroscopic data with visual information and spatially resolved chemical dynamics.
Alteration mechanisms of limestone used in built cultural heritage : use of isotoping labelling to determine the water penetration and reaction sitesIn France 52% of the historical monuments are made out of limestone; the preservation of this material is
Authors: Drici Adam , Saheb Mandana , Mertz Jean‐Didier , Verney‐Carron Aurélie , Sessegolo Loryelle , Remusat Laurent , Gonzalez‐Cano Adriana
Published: December 2016

In France 52% of the historical monuments are made out of limestone; the preservation of this material is therefore an economic, scientific and cultural challenge. In urban area, limestones used in the façade of the buildings are exposed to a polluted environment and their degradation is already well documented. Several alteration processes are expected to occur such as phases precipitation and dissolution. In such environment, the most common alteration secondary phase is gypsum (CaSO
4
, 2H
2
O) formed from the reaction between calcareous stones, environmental water and sulfuric acid from the atmosphere.

Whatever the alteration process, water as rainfall (wet deposition) or as vapor state (dry deposition) is the alteration agent, so that it is the main parameter to focus on .Thus in order to better understand the stone/water interaction and to propose solutions for preserving the built cultural heritage, we developed an original methodology based on water isotopic tracers (D and
18
O). Deuterium was used to localize water penetration front in the material, while
18
O enabled to determine secondary phase reaction sites, mainly composed of gypsum.

Pristine samples from quarry and samples from Parisian monuments were selected to compare different alteration stages. Firstly, their main chemical and physical properties linked to the alteration were studied based on a multiscale characterization.(Saheb
et al.
, 2015)
.
Then, samples were altered in laboratory by realistic and controlled conditions of dry deposition during 2 months using isotopically labeled water. The reaction zones were analyzed by nano‐SIMS. This experimentation enabled determining that water entirely penetrated in samples from quarry and from monuments, what highlights that the alteration layer does not seem to have a protection effect. In surface or deeper inside the sample,
18
O enrichment highlights preferential reaction sites, localized in micro‐cracks inside the gypsum zones and along grains of calcite (Figures 1 and 2).

This innovative methodology is a first step to understand the alteration mechanism formation on limestone used in the façade of the buildings. Understanding the mechanisms and especially the role of the alteration layer will contribute to improve the knowledge of stone chemical alteration processes to develop appropriate conservation strategies for the buildings.
Laboratory diffraction contrast tomography ‐ applications and future directions
Authors: Lavery Leah , Holzner Christian , Bale Hrishikesh , Merkle Arno , McDonald Samuel , Withers Philip , Zhang Yubin , Jensen Dorte Juul , Reischig Peter , Lauridsen Erik
Published: December 2016

Determining crystallographic microstructure of a given material in 2D can be challenging. Further extending such an investigation to 3D on meaningful volumes (and without sample sectioning) can be even more so. Yet reaching this insight holds tremendous value for 3D materials science since the properties and performance of materials are intricately linked to microstructural morphology including crystal orientation. Achieving direct visualization of 3D crystallographic structure is possible by diffraction contrast tomography (DCT), albeit only available at a limited number of synchrotron X‐ray facilities around the world. Recent developments, however, have made DCT possible on an X‐ray microscope with a laboratory source.

The introduction of diffraction contrast tomography as an additional imaging modality on the ZEISS Xradia 520 Versa laboratory X‐ray microscope has opened up a whole new range of possibilities for studies of the effect of 3D crystallography on materials performance. The capability to link directly the crystallographic and grain microstructure information with that obtained via conventional absorption or phase contrast imaging, non‐destructively in three‐dimensions and all in the laboratory, creates a powerful and easy to access tool. [1] Using a polychromatic X‐ray source, laboratory diffraction contrast tomography technique (LabDCT) takes advantage of the Laue focusing effect, improving diffraction signal detection and allows handling of many and closely spaced reflections. Additionally, LabDCT opens the way for routine, non‐destructive and time‐evolution studies of grain structure to complement destructive electron backscatter diffraction (EBSD) end‐point characterization. Combination of grain information with microstructural features such as cracks, porosity, and inclusions all derived non‐destructively in 3D presents new insights for materials characterization of damage, deformation and growth mechanisms. Furthermore, 3D grain orientation data is a valuable input into multi‐scale, multi‐layered modeling platforms that can virtually evaluate mechanical properties to produce high fidelity simulation results. Here, we introduce the LabDCT technique and demonstrate its unique capability through a selection of application examples for materials science as well as discuss innovative methods to extend the current capabilities of the technology for a better understanding of materials structure evolution in 3D.
Precision top‐down delayering of microelectronics devices using broad‐beam argon ion milling
Authors: Nowakowski Pawel , Olexa Kristin , Ray Mary , Fischione Paul
Published: December 2016

The semiconductor industry is a dynamic, rapidly growing manufacturing sector. In 2015, global sales of semiconductor products increased 9.9% and reached a record US $335.8 billion [1]. Constantly evolving microelectronic device designs continue to grow more complex, more compact, and smaller. For example, three‐dimensional (3D) NAND flash memory cells are layered vertically in three‐dimensional stacks, which provides much greater cell density and increases memory capacity [2]. Such design complexity makes maintaining manufacturing quality standards a consistent challenge for the industry and failure analysis plays a critical role in meeting that challenge. Failure analysis can determine the root cause of a defective device; it enables failure identification and characterization, as well as provides feedback for product and process improvement. Many failure analysis techniques, both nondestructive and destructive, have been developed in the past five decades [3, 4]:

· nondestructive techniques: electrical measurement and testing, infrared and X‐ray examination, and optical or electron microscopy evaluation

· destructive techniques: chemical etching, mechanical polishing, plasma etching, and delayering

Many techniques are untenable for multilayer devices. For example, Samsung found that etching agents are too aggressive and the company enumerated several major structural failures that can occur in NAND flash memory related to etching or particle contamination. Delayering is a popular choice because it allows top‐down, whole chip characterization. However, delayering 3D devices with multiple layers is difficult. The main challenge presented by a vertical stack is looking through a stack of many dissimilar layers. Instrumentation that employs low energy, broad beam, argon ion milling using a top‐down delayering technique can help to expose a defect region for further analysis [5]. The work presented is a new development in semiconductor device delayering for failure analysis using low energy, broad‐beam argon ion milling.
Microscopic study of
TiO2
nanostructures formed by electrochemical method
Authors: Irena Kereković , Milivoj Plodinec , Krunoslav Juraić , Vilko Mandić , Krešimir Salamon , Daniel Meljanac , Vesna Janicki , Davor Gracin , Andreja Gajović
Published: December 2016

TiO
2
as the material exhibits properties that allow its use in various applications such as photocatalysts, solar cells, gas sensors, and biomedical applications. The typical organic solar cells are produced on transparent conductive layers covered with nanostructured TiO
2
. The surface roughness is one of the key parameters for high efficiency. In that sense the nanotube arrays offer numerous advantages.

The initial Ti films were deposited by evaporation (Fig 1) or magnetron sputtering. By variation of deposition conditions, different crystal sizes, orientation and grain sizes were obtained. TiO
2
nanostructures were formed by anodic oxidation on Ti substrates in ethylene glycol based electrolytes. Anodization parameters (anodization time, applied voltage, amount of added water and ammonium fluoride), were varied during preparation of TiO
2
nanostructures. As‐prepared TiO
2
films were amorphous, while polycrystalline TiO
2
anatase phase was obtained after heat treatment. The film structure and crystallinity, before and after annealing, were studied by Raman spectroscopy and grazing incidence X‐ray diffraction. Scanning electron microscopy was used to determine the morphologies of prepared anodic films.

The diameter, shape and density of the nanostructures were correlated with the processes parameters. The results indicate that geometric characteristics and morphology of prepared TiO
2
critically depend on initial Ti crystal grains sizes as well as anodization conditions (Fig 2).
Degradation of
(La,Sr)(Co,Fe)O3‐δ
SOFC
Cathodes at the Nanometre Scale and Below
Authors: Na Ni , Samuel Cooper , Stephen Skinner
Published: December 2016

For developing solid oxide fuel cells (SOFCs) operating at intermediate temperatures, metallic materials have become a preferential choice for the interconnect due to their low cost and excellent physical and chemical properties. However the presence of chromium in all commonly used metallic alloys has been found to cause poisoning of the cathode leading to rapid electrochemical performance degradation of the cathodes including one of the most promising (La,Sr)(Co,Fe)O
3‐δ
(LSCF) perovskite oxides [1‐3]. Despite the extensive research on the chromium deposition and poisoning processes, careful microstructural studies, especially at the nanoscale, are rare, which can provide valuable information for the fundamental understanding of the Cr poisoning mechanisms required for developing Cr tolerant cathode materials.

In this paper, we examine the Cr poisoning mechanisms in LSCF materials by correlating the bulk electrochemical properties of the cell with their structural and chemical change at multi‐scales down to the nanometer level. Cells with LSCF cathodes were prepared, and the effect of Cr poisoning on the electrochemical behavior of the cell was assessed by impedance spectroscopy. The change in nano/microstructure and chemistry due to poisoning were studied in parallel by a combination of several advanced electron microscopy techniques including focus ion beam (FIB) tomography, high resolution (scanning) transmission electron microscopy ((s)TEM) and analytical STEM. Our results show that Cr poisoned samples exhibit multiscale changes especially at the nanoscle including formation of nanometer size Cr rich phases (Figure 1), Cr segregation at LSCF grain boundaries (Figure 2), alternation of local LSCF stoichiometry and structure (Figure 3), and change of valence state of the B site elements. These observed nanoscale changes are consistent with the impedance data measured from the same samples that shows the reduction of both oxygen surface reaction rate and oxygen diffusion by 1‐2 orders of magnitude after Cr poisoning. The work revealed critical degradation mechanisms effective at the nano to atomic scale and provide new insight for the development of future poisoning resistant electrode materials not only for SOFCs but also for other devices such as solid oxide electrolysis cells.
Heterogeneity in nanoparticle size determination using several biophysical and microscopy methods
Authors: Pellequer Jean‐Luc , Cambedouzou Julien , Gerdil Adèle , Godon Christian , Habert Aurélie , Herlin‐Boime Nathalie , Podor Renaud , Ravaux Johann , Teulon Jean‐Marie
Published: December 2016

Nanoparticles belong to the class of nanomaterial that are natural, incidental, or manufactured materials containing elementary particles where at least one external dimension is in the range of 1 nm to 100 nm for 50% or more of the particles in the number size distribution. Therefore, size criteria is a key control parameter for defining nanoparticles. Moreover, nanoparticles have the property of assembling, agglomerating, or aggregating elementary particles into larger entities. But, the definition clearly refers to elementary particle and thus fine methodology must be used to obtain the critical size of nanoparticles. Besides, nanotoxicology which is the field of study of toxicological effect of nanoparticle in health aims to relate putative toxicological effect to the size of nanoparticles as the current dogma in the field suggest a greatest impact/reactivity with smaller particles than larger ones. Thus, obtaining accurate size measurements of nanoparticles is of great scientific significance.

In this work, we have combined several biophysical and microscopic methods to characterize the size of several nanoparticles of main interest in toxicological studies. Although we have worked on more than 50 different metallic nanoparticles, we only focused our interest on two families: Silver (Ag) and titane oxide (TiO
2
). We have used atomic force microscopy, wet scanning transmission electron microscopy, dynamic light scattering, small‐angle X‐ray scattering. First, controls on well‐behaved nanosize samples were performed and maximum dispersion between low‐bound and high‐bound sizes was about 30%. The striking results of this work is the relatively large dispersion of results obtained on Ag and TiO
2
(several hundreds of percent) depending on the method used. Several hypotheses can explain these results: nanoparticle solutions are highly heterogeneous and some methods may capture different forms, measurement methods are biased toward a certain size, methodologies used to extract sizes are inaccurate. All these hypotheses are plausible and will be discussed in this work.
Synthesis and Characterization of
Ag2Se
‐Based Hybrid and Ternary Semiconductor Nanocrystals with potential termoelectric applications
Authors: Besa Pau Torruella , Dalmases Mariona , Fernàndez‐Altable Víctor , Cabot Andreu , Ibáñez Maria , Llorca Jordi , López‐Conesa Lluís , Martín Gemma , Estradé Sónia , Peiró Francesca
Published: December 2016

Ag
2
Se is a heavy‐metal free, low band gap semiconductor that is currently attracting much attention in several fields. Remarkably, its high Seebeck coefficient and its low thermal conductivity have made of Ag
2
Se a definitely promising thermoelectric material. Considering that material nanostructuration often entails a significant increase of the ZT figure of merit with respect to the bulk, the synthesis and study of Ag
2
Se nanocrystals and of its nanostructured derivatives seems exciting and definitely deserves an effort.

With regard to the synthesis of metal‐Ag
2
Se hybrid nanocrystals, very few examples are currently available in the literature and none of them has addressed their potential applications.

The aim of this work is studying the ternary Au‐Ag‐Se system at the nanoscale in order to figure out appropriate synthetic protocols for the controlled growth of hybrid and compositionally‐controlled Ag2Se‐based nanocrystals and perform an in‐depth structural characterization of the materials obtained while also studying the thermoelectric potential of this new ternary nanosystem.
Random scanning mode for the spectroscopy of sensitive materials
Authors: Tararan Anna , Tencé Marcel , Brun Nathalie , Kociak Mathieu , Zobelli Alberto
Published: December 2016

Electron Energy Loss Spectroscopy (EELS) and Cathodoluminescence (CL) in a STEM microscope allow to characterize chemical composition and optical properties down to a subatomic scale. Nevertheless, a high electron dose is conveyed onto limited regions of the specimen and generates strong radiation damages in fragile materials. Spectroscopy of individual molecular systems remains therefore still highly challenging. Here we demonstrate how this traditional limit can be largely overcome by acquiring hyperspectral images through a non‐standard random scanning mode. This is achieved by considering the pixels in the scanning array as a list that is shuffled and loaded into a dedicated scan generator. At the end of spectrum acquisition a signal from the detector triggers the next beam position.

The luminescence of high efficiency molecular dyes has been investigated through an original CL set up integrated within a STEM microscope, which allows a nanometric spatial resolution. Illumination damages have been reduced thanks to a liquid nitrogen cooling system at the sample stage and a 60 keV electron beam.

The dyes have been deposited at a very low concentration on hexagonal boron nitride (h‐BN) flakes. This one represents the ideal substrate for luminescence, being chemically inert and displaying a wide energy band gap. Furthermore, it can actively participate in the luminescence processes: electron induced excitations in the h‐BN substrate may recombine at the molecular sites. The luminescence of the molecules should appear therefore in CL‐hyperspectral images as isotropic emission spots some tens of nanometres wide, corresponding to the excitation diffusion length in h‐BN.

We show that a traditional sequential line‐by‐line scan leads to a rapid bleaching of the molecules, whose luminescence appears only in a short line of pixels. On the contrary, by using a random scan routine we were able to obtain the expected isotropic emission spots. Unlikely a sequential scan, in a random survey the energy deposited in an illuminated area can be evacuated before an adjacent pixel is illuminated. Even when the bleaching of the molecule cannot be avoided, this acquisition mode allows to collect a signal from a higher number of pixels with respect to the sequential scan.

Beside CL, EELS investigations could in principle derive great advantage from this random acquisition. More precisely, core EELS studies of fragile materials could benefit from a higher spatial resolution of the hyperspectra. Finally, the random scan opens also new perspectives in terms of compressed sensing techniques.
IR
Nano‐spectro‐imaging: Characterization of polymeric nanoparticles and in vitro study of their interaction with cells
Authors: Mathurin Jérémie , Pancani Elisabetta , Deniset‐Besseau Ariane , Gref Ruxandra , Dazzi Alexandre
Published: December 2016

Recently near‐field techniques play a fundamental role in Nanoscience microscopy. Two different ways exist to make infrared studies with near‐field techniques: optical techniques measuring the transmitted signal coming from the nano‐object or photothermal approachs using thermometer to link temperature to absorption measurements. Considering the limitations of the optical techniques, we have developed in our team an innovative photothermal technique called AFM‐IR
1
. The AFM‐IR technique is a user‐friendly benchtop technique that enables infrared spectroscopy with a spatial resolution well below conventional optical diffraction limits. It acquires IR absorption imaging spectrally resolved with lateral resolution of tens of nanometer
2
.

First we will present the experimental set‐up and some of the critical technical sides and then illustrate technological advances. Then we will show the result obtained on biodegradable polymeric nanoparticles. This work has been done in collaboration with the Institut of molecular science (ISMO). We have used this technique to characterize the composition of the nanoparticles (drug encapsulation, presence of lignad) and to localize them inside fixed macrophages at the subcellular scale.
Chemical tomography of nested‐network nanoporous gold
Authors: Krekeler Tobias , Wang Ke , Wang Lida , Ritter Martin
Published: December 2016

Nanoporous gold (NPG) is the paradigm of the novel class of nanostructured metals consisting of a randomly interconnected solid and void structure. Due to the high surface area of these materials, there are numerous promising fields of application in catalysis, sensors or electronics. The most common synthesis method of NPG is electrochemical dealloying of Ag‐Au alloys [1].

To enlarge the surface area of NPG even further, a two‐step dealloying process on a Pt‐doped Ag‐Au master alloy has been developed [2]. In the first step of the dealloying process, a fair amount of silver is removed by electrochemical corrosion, leading to a porous structure with very small ligaments of about 20 nm diameter. After gentle annealing, resulting in a porous structure with a feature size of about 100 nm (NPG), a second dealloying process is performed. The residual silver is removed, generating a porous structure (ligament size smaller than 10 nm) inside the initial formed ligaments of the porous structure, forming a nested‐network nanoporous gold (N
3
PG) (Figure 1).

The retention of silver in the first dealloying step is presumed to be the result of a passivation of the master‐alloy surface during dealloying by successive accumulation of platinum on the electrolyte‐solid interface during the electrochemical removal of silver. During the subsequent annealing, the platinum diffuses from the surface into the Ag/Au Ligaments, which is consistent with thermodynamic calculations [3] and spectroscopic measurements [4], exposing a fresh surface of Ag/Au for the second dealloying step, resulting in the hierarchical structure of N
3
PG. The proposed accumulation of Pt is plausible because of the lower mobility of platinum compared to silver and gold and has been proven by cyclic voltammetry [5]. However, cyclic voltammetry and other spectroscopic methods only give an averaged analysis of the surface. To further investigate this theory, localized information of the surface composition of the NPG ligaments is needed.

In this work, we present the electron microscopic examination of NPG by the means of electron tomography in combination with EDX. The complex material structure with a high void fraction, high element numbers, and low concentration of minor constituents (Ag, Pt), however, aggravates the specimen preparation and data collection. To obtain reasonably thin, artifact‐free specimen of NPG, the voids have to be filled with epoxy and then cut by ultramicrotomy. The image and elemental maps (Figure 2) collection is performed on a modern TEM optimized for electron tomography, equipped with four EDX‐Detectors covering a large solid angle and a high brightness gun for high probe currents. For data analysis HyperSpy [6] is used.
Fusion to a symmetric scaffold allows cryo‐
EM
analysis of a small monomeric protein
Authors: Coscia Francesca , Estrozi Leandro , Hans Fabienne , Malet Hélène , Noirclerc‐Savoye Marjolaine , Schoehn Guy , Petosa Carlo
Published: December 2016

Single particle cryo‐electron microscopy (cryoEM) is a powerful method for determining the structures of large macromolecules and their complexes. Recent technical advances in direct electron detectors, phase plates and computational procedures for image processing have revolutionized the field, allowing 3D reconstructions to be obtained at near‐atomic resolution (<4 Å). However, most monomeric proteins of biomedical interest remain too small (<100 kDa) for cryo‐EM analysis. In this work we propose a new method to overcome this size limitation by fusing a monomeric protein (target) to a homo‐oligomeric scaffold protein, whose large size and symmetry facilitates cryoEM analysis. As proof‐of‐principle, we fused maltose‐binding protein (MBP), a 40 kDa monomer, to glutamine synthetase (GS), a dodecamer formed by two hexameric rings.

We designed an initial MBP‐GS construct with a linker sufficiently long to allow the fused moieties to fold properly without mutual steric hindrance. The junction was optimized by progressively deleting linker and/or flanking residues to reduce the spatial separation between the two fusion partners, thereby restricting the relative mobility of the target subunits (Figure A). We bacterially expressed 18 MBP‐GS constructs and used biophysical analysis (native poly‐acrylamide gel electrophoresis, size exclusion chromatography, dynamic light scattering and differential scanning fluorimetry) to screen for particle compactness and homogeneity. Negative stain EM analysis confirmed the trend observed by the biophysical assays, and both approaches identified the same construct as the most compact and conformationally homogeneous.

Cryo‐EM analysis of the most promising construct led to a reconstruction with an overall resolution of 4.2 Å (FSC=0.143 criterion) and a local resolution that varied from ~4 Å within the GS subunit to between 6 and 10 Å within the MBP subunit. Fitting the GS crystal structure into this map revealed an excellent fit, allowing all secondary structure elements and certain large side chains to be visualized. A good fit was also observed for MBP: the N‐ and C‐terminal lobes enclosing the active site were clearly defined, several helical elements were well resolved, and the bound maltose ligand was partly visible (Figure B). These findings illustrate the feasibility of using homo‐oligomeric scaffolds to enable cryo‐EM analysis of monomeric proteins, raising the prospect of applying this strategy to more challenging structures resistant to crystallographic and NMR analysis.
Structure‐function insights reveal the human ribosome as a cancer target for antibiotics
Authors: Myasnikov Alexander , Natchiar Kundhavai , Nebout Marielle , Hazemann Isabelle Isabelle , Imbert Véronique , Khatter Heena , Peyron Jean‐François , Klaholz Bruno
Published: December 2016

Abstract

Many antibiotics in clinical use target the bacterial ribosome by interfering with several mechanistic steps of the protein synthesis machinery. However, targeting the human ribosome in the case of protein synthesis deregulations such as in highly proliferating cancer cells has not been much considered up to now. Here we report the first structure of the human 80S ribosome with a eukaryote‐specific antibiotic and show its anti‐proliferative effect on cancer cell lines. Structural sorting of the cryo electron microscopy data shows that the cycloheximide ligand induces an equilibrium shift of ribosome subpopulations in different states, revealing that the mechanism of action relies on an active release of the tRNA from the exit site. The structure provides unprecedented insights into the detailed interactions in a ligand‐binding pocket of the human ribosome that are required for structure‐assisted drug design. Furthermore, anti‐proliferative dose response in leukemic cells and interference with synthesis of c‐myc and mcl‐1 short‐lived protein markers reveals specificity of a series of antibiotics towards cytosolic rather than mitochondrial ribosomes, establishing the human ribosome as a promising cancer target. In addition, we present a protocol that primarily uses the crystallographic tools for atomic model building and refinement into cryo‐EM maps, as exemplified by our recent human ribosome structure.
Order/disorder mechanisms in complex (
CaFe2O4
)(
FeO
)n ferrites (n=1,3)
Authors: Delacotte Charléne , Monnier Laurine , Bréard Yohann , Hébert Sylvie , Pelloquin Denis
Published: December 2016

Numerous studies are always devoted to mixed valence state iron oxides in materials research due to their complex magneto transport properties like the famous Verwey transition [1]. Among these oxides, a special attention is focused on the orthoferrites LnFeO
3
(Ln= rare earth) related to the distorted GdFeO
3
‐type perovskite structure which can exhibit some possible spin reorientation transitions versus temperature and the nature of Ln [2]. Recently, iron based oxides like LnFe
2
O
4
have also focused a large attention due to their ability to exhibit some multiferroic properties [3]. In these systems, both kinds of Fe species (Fe
2+
and Fe
3+
) localize magnetic moments leading to a ferrimagnetic ordering associated to ferroelectric properties. An exciting challenge is to evidence similar properties in other iron based systems. The Ca‐Fe‐O system offers several interesting candidates like the CaFe
5
O
7
and CaFe
3
O
5
phases in regard to the richness of its phase diagram.

CaFe
5
O
7
oxide exhibits a complex structure which can be described as an intergrowth between one CaFe
2
O
4
unit and n=3 slices of FeO Wustite‐type structures [4]. A recent structural study performed by transmission electron microscopy (TEM) observations has revealed a supercell with a lower monoclinic symmetry [5]. From the intensity extraction and
hkl
conditions deduced from the precession electron diffraction (PED) study, a structural model considering to this supercell and the centrosymmetric P2
1
/m setting can be proposed. The fine structural analysis combining Rietveld refinements from neutron and X‐ray data evidence six independent iron sites and two specific oxygen environments with coordination 6 and 5+1 respectively. According to the chemical formula CaFe
5
O
7
, the iron species average state valence is +2.4 and implies the coexistence of Fe
+3
and Fe
2+
. The magnetic dependence versus temperature has been studied and susceptibility measurements have revealed discontinuity around 360K [6]. The structural evolution of CaFe
5
O
7
depending on temperature has been also tuned from diffraction techniques. A clear reversible transition (monoclinic to orthorhombic) has been detected in the same temperature range with the disappearing of the supercell [6]. A complementary STEM‐HAADF study has allowed to highlight the impact of this superstructure at atomic scale (Fig.1) : ordered contrasts at the level of calcium rows can be observed. A second ferrite, CaFe
3
O
5
related to the n=1 member of the generic (CaFe
2
O
4
)(FeO)n series, has also been analysed by TEM techniques. Thus a superstructure is revealed but the first STEM‐HAADF highlight a complex nanostructural feature related to the coexistence of two polymorphs (Fig.2)
Probing the radiative and full electromagnetic local densities of states with electron energy loss spectroscopy and cathodoluminescence spectroscopy
Authors: Losquin Arthur , Kociak Mathieu
Published: December 2016

Electron Energy Loss Spectroscopy (EELS) and CathodoLuminescence spectroscopy (CL) map the surface plasmon modes of metallic nanoparticles at the nanometer scale [1]. Although they yield similar results, EELS and CL differ by nature. EELS measures the energy lost by fast electrons interacting with a sample whereas CL measures the energy of the light emitted from this interaction [2]. However, the consequence of this different nature has remained unexplored because combining EELS and CL on single nanoobjects could not be achieved.

We combined EELS and CL on single nanoobjects using a Scanning Transmission Electron Microscope (STEM) [3]. In a STEM, an electron beam is focused onto a nanometric probe that is scanned over the sample. At each point of the sample, the transmitted electrons are collected for EELS, while the emitted light is collected for CL; both a full EELS spectrum and a full CL spectrum are recorded. We studied small gold triangular nanoprisms as a model system (Fig. 1a). The combination of EELS and CL allows us to map the same surface plasmon modes using both techniques (Fig. 1b and c).

We showed that CL only probes the dipolar mode, contrary to EELS that probes both the dipolar and quadrupolar modes. Furthermore, the dipolar mode resonates at shifted resonances in EELS and CL for prisms with edge lengths larger than 100 nm relying on carbon substrate (Fig. 2a). The magnitude of the shift relates to the mode damping.

Having demonstrated that EELS and CL signals differ, we showed that the full and radiative ElectroMagnetic Local Densities Of States (EMLDOS) differ similarly (Fig. 2b) [4]. Whereas EELS measures a quantity close to the full EMLDOS projected along the electron direction [5], CL measures a quantity close to the radiative EMLDOS projected along the electron direction [4]. Contrary to EELS, CL probes only the radiative modes, which are not necessarily dipolar for object sizes beyond the quasistatic limit. The ratio of the CL resonance to the EELS resonance quantifies the radiative weight of the mode damping. If the modes are damped and induce interfering radiation, CL resonant line shapes are shifted and asymmetric compared to EELS.

This work demonstrates the great interest of combining EELS and CL for plasmonics [3, 4].

The research leading to these results has received funding from the European Union Seventh Framework Programme [No. FP7/2007‐2013] under Grant Agreement No. n312483 (ESTEEM2). We gratefully aknowledge the following collaborators who significantly contributed to this work : Luiz F. Zagonel, Viktor Myroshnychenko, Benito Rodríguez‐González, Marcel Tencé, Leonardo Scarabelli, Jens Förstner, Luis M. Liz‐Marzán, F. Javier García de Abajo and Odile Stéphan.
Heterointerfaces
TEM
characterization of buffer layers in
KF
treated
CIGS
solar cells. Towards a new buffer layer?
Authors: Gautron Eric , Lepetit Thomas , Harel Sylvie , Arzel Ludovic , Assmann Lionel , Frelon Agathe , Andrade R‐Ribeiro , Sadewasser Sascha , Douillard Thierry , Epicier Thierry , Barreau Nicolas
Published: December 2016

Cu(In,Ga)Se
2
–based (CIGS) solar cells are thin film devices achieving nowadays the highest conversion efficiency (22.3% at the laboratory scale [1]), surpassing any other thin‐film or multi‐crystalline silicon technology. A heterojunction is obtained in these solar cells by depositing a cadmium sulfide (CdS) buffer layer (n‐type semiconductor) on the CIGS absorber layer (p‐type semiconductor). The strong conversion efficiency increase over the past three years is due to the introduction of a potassium fluoride treatment (KF evaporation) between the CIGS coevaporation stage and the CdS chemical bath deposition stage [2]. The understanding of the KF deposition stage on the solar cell performance is still under debate, due at least partly to the lack of material characterization at the nanometer scale.

We first present the characterization of two samples with the same CIGS absorber, with and without KF treatment. Transmission electron microscopy (TEM) conducted on cross section lamellae prepared by focused ion beam (FIB) allowed us to evidence several material changes induced by the KF treatment: compared to the untreated sample, the KF‐treated sample shows a depletion of Cu, Ga, and Se and a segregation of K and O at grain boundaries close to the CIGS/CdS interface (figure 1). Without KF the CdS/CIGS interface is abrupt and homogenous in the longitudinal direction. The KF treated sample exhibits a 5 nm‐thick layer containing mainly Cd, S, In, Se and O at the CdS/CIGS interface, as well as few 50 nm large CdSe particles (figure 2). This ultra‐thin interface layer could result in p‐CIGS/n
+
‐CdIn
2
(S,Se)
4
type/n‐CdS heterojunction, explaining the possibility to reduce the CdS thickness without loss of performance, as already reported in [2].

To go deeper in the understanding of the benefit of such a layer, two other samples were synthesized: both with the same CIGS layer but either with a CdS or a CdIn
2
S
4
buffer layer. The CdS layer was obtained by chemical bath deposition while the CdIn
2
S
4
layer was deposited by physical vapor deposition (PVD). TEM results concerning the sulfur diffusion in CIGS and the crystalline structure of CdIn
2
S
4
layer will be presented [3].