bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomic resolution
HR
(S)
TEM
and
EDXS
analyses of
GaInAs/GaSb
and
GaInP/GaSb
bond interfaces for high‐efficiency solar cells
Authors: Kovács András , Duchamp Martial , Predan Felix , Dimroth Frank , Dunin‐Borkowski Rafal , Jäger Wolfgang 
Published: December 2016

The use of direct wafer bonding to combine semiconductor materials that have a large lattice mismatch is especially beneficial for high efficiency multi‐junction solar cells. Multi‐junction solar cells that have been fabricated by wafer bonding are of particular interest since efficiencies of up to 46% have been obtained [1] and efficiencies of up to 50% are within reach for concentrator solar cells based on III‐V compound semiconductors. Fast atom beam activation is used as a pre‐treatment to remove oxides and contamination before bonding [2]. Aberration‐corrected transmission electron microsocpy (TEM) analyses of GaAs/Si interfaces have previously been applied successfully to support the implementation of bonding concepts for the development of high‐efficiency solar cells [3].

Here, we investigate cross‐sectional specimens of GaInAs/GaSb and GaInP/GaSb bond interfaces in wafer‐bonded multi‐junction solar cells, in order to obtain an improved understanding of their interface structures and thermal stability, by combining aberration‐corrected high‐resolution TEM (HRTEM), high‐angle annular dark‐field scanning TEM (HAADF STEM), energy‐dispersive X‐ray spectroscopy (EDXS) in the STEM and
in situ
TEM heating experiments.

Figures 1a‐e shows results obtained from the GaInP/GaSb bond interface. Fig.1a shows the interface at low magnification. Figure 1b shows an HRTEM image, which reveals an amorphous interface layer (~1 nm thick). Figure 1c shows an atomic resolution HAADF STEM image of the bond interface structure and a digital diffractogram (inset), revealing a nearly perfect structural orientation relationship between the two crystalline layers. When correctly positioned with respect to the HAADF image, elemental maps extracted from EDXS spectrum images (Figs 1d and 1e) reveal that a high level of Ga is present at the interface. The Ga can be attributed to the pre‐treatment procedure and bonding conditions.
I situ
thermal treatment of this interface results in pronounced interdiffusion for temperatures above 225°C (not shown here).

Figures 2a‐c show the GaInAs/GaSb bond interface, which is decorated by pores and cavities that extend along the interface by more than 10 nm. As a result of the use of misoriented wafers for bonding, the crystal lattices are rotated with respect to each other by a few degrees (Figs 2b and 2c).
Our results confirm that the advanced imaging and spectroscopic methods of aberration‐corrected (S)TEM are advantageous for characterizing the morphology, elemental distribution and structure of layers and bond interfaces for the monitoring, control and optimization of different concepts used for fabricating high‐efficiency solar cells. Out results are also of interest for assessing electrical conductivity phenomena at these interfaces.
Mycobacterial protein weaponry studied by cryo‐correlative microscopy
Authors: Notelaers Kristof , Berger Casper , Iakobachvili Nino , Chen Delei , Siroy Axel , Furusho Hirotoshi , Ravelli Raimond , López‐Iglesias Carmen , Peters Peter 
Published: December 2016

In correlative light and electron microscopy, the discerning power of fluorescence microscopy (FM) is combined with the ultra‐high resolution of electron microscopy (EM). We fluorescently label protein complexes in cells, with the purpose of facilitating their identification in transmission electron tomograms. Our imaging strategy is to perform cryogenic selected volume tomography, continuously keeping the specimen in a vitreous state. To this end, we are developing a cryogenic workflow in collaboration with FEI, consisting of three microscopes: CorrSight light microscope (LM), Scios Dualbeam scanning electron microscope (SEM) with a focused ion beam (FIB) and Tecnai Arctica cryo–transmission electron microscope (TEM). The focus of my presentation is on the integration of the CorrSight light microscope into the workflow (1). This translates to performing cryogenic light microscopy and correlating the images with EM for guided ion beam milling and tomography (2).The data we collected from cryogenic fluorescence microscopy of mammalian and bacterial cells on TEM grids shows great promise for complementing EM (Fig. 1). This is substantiated by alignment of LM and SEM images utilizing FEI MAPS software, allowing for fluorescence based navigation during SEM imaging (Fig. 2). My future efforts will focus on improving localization precision and correlation accuracy, to guide FIB‐milling of sub‐cellular structures in the SEM. FIB‐milling is used to fabricate thin lamellae in cells, making them suitable for cryo‐TEM. Our results indicate that tomograms can be recorded from lamellae using a 200kV cryo‐TEM, but vitrification of the specimen is essential. The ultimate goal of our workflow is to obtain structural insight of the Type 7 Secretion System (T7SS), formed by the ESX‐1 machinery. To this end, we will perform tomography of mycobacterial membranes inside professional antigen‐presenting cells. The T7SS is an important part of the mycobacterial protein weaponry, as it mediates virulence and phagosomal escape (4, 5).
Investigation of structural changes of
ZnO:Ti
thin films prepared by
RF
sputtering
Authors: Medlín Rostislav , Sutta Pavol , Netrvalova Marie , Novak Petr 
Published: December 2016

ZnO is a wide used ferroelectric material with a variety of applications. This study investigates ZnO thin films doped by Ti as showing structure change from ZnO wurtzite up to ZnTiO
3
perovskite.

ZnO:Ti thin films were prepared by RF reactive magnetron co‐sputtering in Ar/O
2
atmosphere from pure Zinc and Titanium targets (99.99%). Changes of amount of Ti in films were documented by EDS and EELS measurements, structure changes were measured by electron diffraction from thin film cross section (XTEM ED) and two geometries of XRD together with measurement of material optical properties.

Pure ZnO wurtzite structure show with increasing amount of Ti texture change from 8 degrees for 2.4 at % Ti to the 39 degrees for 8.7 at % Ti as it can be seen on electron diffraction patterns on figure 1a together with figure 1b. Structure measured by XRD appear to be more amorphous with Ti increasing as intensity of diffraction lines decreases and interatomic distances change from wurtzite to perovskite ZnTiO
3
structure (fig. 2).

Diffraction measurement is by the Voight function method also capable to measure from single diffraction line size and lattice distortions of the diffracted particles. In our case results for 2.4 at % Ti ZnO line 002 is 52 nm and for 7.8 at % Ti ZnTiO
3
line 104 is 19 nm, both with dualism indicates two regions of low and highly distorted part of particles. This correspond to relaxed core and distorted surface of the grains as it can be seen on figure 1c and d for Ti content 2.4 at % Ti or 8.7 at % Ti respectively.

Electron diffraction pattern from cross section is also capable to show and compare information from XRD measurements in two different geometries; situation is illustrated on figure 3. Circle integration of ED by ProcessDiffraction program [1] is capable to compare JCPDS diffraction database with electron diffraction pattern, however, this procedure do not take into consideration texture of investigated materials. Different geometries of XRD measurement takes in case of textured material different places indicated on XTEM electron diffraction pattern on Fig.3. Comparing of both results have to be carefully considered.
Direct comparation of measured interplanar distances is illustrated in Fig.4.
Synthesis and characterization of bimetallic nanorods
Authors: van der Hoeven Jessi , Albrecht Wiebke , Deng Tiansong , de Jongh Petra , van Blaaderen Alfons 
Published: December 2016

Anisotropic metal nanoparticles (NPs), and especially nanorods (NRs) exhibit interesting optical properties, which arise from their localized surface plasmon. Unlike nanospheres, gold NRs have a longitudinal surface plasmon resonance (LSPR) in the visible or near‐infrared range of the spectrum. By altering e.g. the shape or the dimensions (aspect ratio) of the NRs, the LSPR can be tuned, which makes them interesting materials for a broad range of light based applications, such as photocatalysis [1], data storage [2] and photothermal applications. The optical properties of gold nanoparticles can be extended even further by introducing a second metal. However, synthesizing bimetallic NRs with a good control over the metal composition and distribution while retaining the rod shape is challenging.
In this study we present bimetallic systems composed of gold‐based NRs coated with a protective mesoporous silica layer. We show that it is possible to synthesize bimetallic core‐shell nanorods within a mesoporous silica shell, by etching away part of the gold and overgrowing the remaining Au‐core with a second metal while precisely controlling the core‐size, metal‐shell thickness and thus the metal‐to‐metal ratio [3]. Depending on the choice of metal, different growth behavior was observed. Overgrowth with Ag resulted in a smooth shell whereas the Pt and Pd metal shells had a rough morphology (Figure 1). The different types of bimetallic NRs were characterized in detail with advanced electron microscopy techniques such as Energy‐dispersive X‐ray spectroscopy (EDX), high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and electron tomography. Subsequently, we used these silica coated bimetallic core‐shell structured rods as a starting material to make fully alloyed NRs, whereby the two metals were mixed via thermal treatment without loss of anisotropy [4]. The alloying process was followed in detail with in‐situ HAADF‐STEM heating and EDX measurements by making use of a special heating holder (Figure 2).
Three dimensional confocal imaging using coherent elastically scattered electrons
Authors: Zheng Changlin , Zhu Ye , Lazar Sorin , Etheridge Joanne 
Published: December 2016

To fully understand structure‐property relationships in nanostructured materials, it is important to reveal the three dimensional (3D) structure at the nanometre scale.Scanning electron confocal microscopy (SCEM) was introduced as an alternative approach to 3D imaging in 20031. The confocal method was originally developed in optical microscopy to image the 3D structure of biological samples2. The incident beam is focused at a certain depth in a thick sample, and the excited fluorescence signal is imaged onto the detector plane through the imaging system. A small pin hole before the detector only allows the signal from the confocal plane to reach the detector and blocks the out‐of‐focus signal. Critically, by using a fluorescent signal, the incident and outgoing waves lose their phase relationship and an incoherent 3D point spread function can be achieved.The optical setup in SCEM is analogous to fluorescence confocal microscopy and also requires an incoherent signal to achieve the incoherent 3D point spread function. Several groups have developed different approaches to using inelastically scattered electrons to achieve an incoherent confocal condition in the TEM3,4,5, however, difficulties remain. Core‐loss electrons have a suitably limited coherence length, however, the excitation probability is extremely low which leads to a poor signal to noise ratio (SNR). Low loss electrons give a much better SNR but still have a significant coherence length due to the collective nature of the excitation.In this work, we introduce a different approach to achieve 3D imaging in a confocal mode by using the elastically scattered, coherent electrons. This method exploits the depth sensitivity of electrons that have suffered a specific momentum change, rather than an intensity change. According to Fourier optics, when a thin object is inserted at a distance z above the confocal plane, the new wave function at the confocal plane will be the original probe convoluted with the Fourier transform of the object function, together with a scale factor related to z (defined in fig.1). For crystalline specimens, the Fourier transform of the object function is a set of delta functions, so a diffraction‐like pattern will be generated at the confocal plane. Importantly, the separation between the diffraction spots is proportional to the distance z (see fig.1), so that the resulting diffraction contrast is very sensitive to depth. This strong depth sensitivity is combined with the very strong SNR due to the use of the elastically scattered signal. Applications to the imaging of 3D engineered nanostructures are demonstrated (fig. 2 and 3).
Vibrational Spectroscopy in the Electron Microscope
Authors: Krivanek Ondrej , Aoki Toshihiro , Batson Philip , Crozier Peter , Dellby Niklas , Egerton Raymond , Lovejoy Tracy , Rez Peter 
Published: December 2016

Vibrational spectroscopy in the scanning transmission electron microscope (STEM) was introduced two years ago [1, 2], and it has made much progress since. It has opened a new window on the world of materials, in which nothing is quite like it was before.The main vibrational modes occur at energies of 0‐500 meV, and exploring them requires a monochromated STEM‐EELS system with an energy resolutionThe energy of vibrational modes is given byΔE = ħ √(k/m), wherekis the force constant of the atomic bond andmthe effective mass of the vibrating nucleus. Strongly bonded light atoms give the highest vibrational energies, starting with hydrogen, an element that is nearly invisible in traditional electron microscopy. Fig. 1(a) shows a vibrational spectrum of Ca(OH)2[3], in which the peak at 452 meV is due to O‐H stretch, and Fig. 1(b) shows the particle from which the spectrum was recorded. Fig. 1(c) shows how the strength of the vibrational peak varied with the distance from the particle: the signal decayed only gradually outside the particle, and was still 50% strong 35 nm away.Fig. 2 shows an EEL spectrum of guanine compared to an IR spectrum from the same specimen [4]. The agreement between the two types of spectra is very good. EELS has worse energy resolution (~10 meV), but much better spatial resolution than regular IR. As is typical of vibrational spectroscopies, the different peaks can be assigned to different types of bonds and vibration modes (see the inset in Fig. 1).In order to minimize radiation damage, both the OH and guanine spectra were acquired in an “aloof” mode, with the electron beam parked just outside the sample [1, 3‐5]. Aloof spectroscopy makes it possible to select the maximum energy of the beam‐sample interaction, simply by adjusting the beam‐sample distance [4,5]. Its great import to vibrational EELS is that the vibrational signal can be excited even when the interaction energy is limited so that ionization damage of the sample cannot occur. It may even be possible to spatially map the vibrational features of a beam‐sensitive sample by “coarse step (leapfrog) scanning”: scanning with a discrete pixel increment of 10‐100 nm, so that even though the area that the beam traverses in each new position is essentially destroyed, large parts of the sample are not touched by the beam and remain in a pristine state [6].
Grain size determination in nanocrystalline materials using the
TKD
technique
Authors: Guitton Antoine , Guyon Julien , Zhang Yudong , Bouzy Emmanuel 
Published: December 2016

Nanocrystalline (nc) materials,
i.e
. polycrystalline structures with grain sizes below 100 nm exhibit extraordinary properties strength. As a first assumption, such property derives from the short paradigm “smaller is stronger”. For grain sizes below 50 nm deformation mechanisms usually involve a quasi‐stationary balance between dislocation slip and grain boundary mediated mechanisms. But there is still an ongoing debate, which one of these mechanisms governs the deformation behavior of nc metals [1,2].

Therefore determination of grain size, analysis of the local texture and characterization of grain boundaries in nanocrystalline materials are crucial. Different techniques have been tested, such as automated crystal orientation mapping in Transmission Electron Microscopes (TEM) [3]. But they suffer a lack of accuracy due to the nanocrystalline nature of tested specimen. Grain overlapping, for instance, trends to observe smaller grains. By x‐ray diffraction, it is also possible to determine grain size, but measurements provide size of coherent domains only that we consider equal to grains.
In this framework, a new technique based of Transmission Kikuchi Diffraction (TKD) has been been recently introduced as a Scanning Electron Microscope (SEM) based method capable of giving orientation maps as the EBSD method but with a spatial resolution improved by up to one order of magnitude [4]. The technique requires a specimen thin enough to be transparent to the electron beam. In the current configuration, it uses hardware and software developed for the EBSD technique. We proposed a new configuration of the TKD where the detector is disposed horizontally on the axis of the microscope instead of being vertically positioned as in the conventional configuration (see Figure). This achieves better spatial resolution and angular resolution than the ones of the current TKD configuration [5]. Moreover, acquisition times are shorter than in the conventional technique, because the intensity of the forward scattered electrons is much higher than that of the large angle scattered electrons.
Firstly, technological challenges such as technique design will be presented. Secondly first results on electrodeposited nanocrystalline nickel will be discussed and they clearly show the full potentialities of this original characterization set‐up.
Optical and structural properties of facetted boron nitrides nanotubes
Authors: Pierret Aurélie , Schué Léonard , Fossard Frédéric , Barjon Julien , Ersen Ovidiu , Moldovan Simona , Ducastelle François , Loiseau Annick 
Published: December 2016

Luminescent devices operating at sub‐250nm wavelength present a strong commercial interest. Applications such as antibacterial properties, high density optical storage or nanofabrication possibilies require reliable, portable and efficient devices. Actual Deep UltraViolet (DUV) sources are based on gaz active regions which are difficult to integrate in mobile devices, exhibit poor efficiencies and are harmful for environment. Thus, the development of solid state based DUV emitters is getting more and more relevant.
Hexagonal boron nitride is a wide band gap semiconductor (~ 6.5 eV), which meets a growing interest for DUV applications. In contrast to carbon nanotubes, Boron Nitride Nanotubes (BNNTs) are all semiconductors whatever their diameter and chirality and their luminescence emission occurs between 200 nm and 250 nm and is governed by strong excitonic effects. Until recently, the optical properties were poorly known due to both the scarcity of samples and suitable investigation tools. This situation has changed thanks to the development of dedicated photoluminescence (PL) and cathodoluminescence (CL) experiments running at 4K and adapted to the detection in the far UV range [1, 2, 3].
These previous studies on boron nitride nanotubes have mainly dealt with multi‐wall BNNTs with a large number of walls (20‐120 walls). These tubes luminesce between 226 and 234nm and this spectral range has been assigned, in hBN, to transitions involving defects. A critical point to further study the confinement effect on the excitonic transitions is therefore to elucidate the luminescence origin of these multiwalls. Furthermore it is important to investigate the luminescence of small diameter BNNTs (with a reduced number of walls), which actually appears to be very challenging.
Cathodoluminescence from a single BNNT with a large number of walls have been measured with a spatial resolution of about ten nanometers, thanks to an UV dedicated SEM system. Different areas along the tube were investigated, from which luminescence is detected at few wavelengths. From 224 to 228 nm, monochromatic cathodoluminescence images exhibit features, which can be linked to defects in the crystallographic structure, separately observed by Transmission Electron Microscopy (TEM) on the same tube.HRTEM observations and tomography experiments revealed that the BNNTs exhibit a peculiar shape. The section of the tube is polygonal with a number of facets between 6 and 9 (Fig 1). These facets forms an helix along the axis of the nanotube. An important consequence of this facetting is the formation of a large number of dislocations along the tube.
We will discuss the relations between these structural properties and the luminescence as shown on fig 2.
Crystalline nanoplatelets of a
PCL
‐fructose block copolymer
Authors: Förster Beate , Ganda Sylvia , Stenzel Martina 
Published: December 2016

Nanosheets have in recent years received considerable attention because of their unique electronic and mechanical properties. They can be prepared by exfoliation of layered materials, but can also be formed via self‐assembly which offers a much larger variability in size and chemical functionality. Self‐assembly of amphiphilic molecules and polymers though usually leads to the formation of spherical, cylindrical and vesicular structures. The generation of nanosheets requires one to adjust the molecular structure such that planar bilayers sheets are formed with large bending constant to prevent closure into vesicles.
We report the formation of nanosheets or nanoplatelets from an amphiphilic block copolymer consisting of a poly(caprolactone) (PCL) and a fructose‐functionalized poly(acrylate) (PFA) block (Scheme 1), prepared by RAFT‐polymerization, in water. The nanoplatelets have a core/shell‐structure, consisting of an inner core‐sheet of the water‐insoluble PCL‐blocks and an outer sheet of the water‐soluble PFA‐blocks. The nanoplatelets are stabilized by the crystallization of the poly(caprolactone) block providing a sufficiently large bending constant. We use transmission electron microscopy (TEM) with phosphotungstic acid (PTA) negative staining to determine the thickness and lateral dimension of the nanoplatelets (Fig. 1). Using selected area electron diffraction (SAED) we prove the crystallinity of the poly(caprolactone) core‐sheet (Fig. 2). The fructose‐functionalized nanoplatelets have a thickness of 8 nm and lateral dimensions of 50 – 200 nm and are potential vectors for targeted drug delivery, where the planar geometry allows for large‐area cooperative binding to cell surface receptors.