bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chiral electron sieves for electron vortex beam generation
Authors: Yuan Jun , Yang Yuanjie , Thirunavukkarasu Gnanavel , Babiker Mohamed 
Published: December 2016

The recent discovery of vortex electron beams [1–3] has generated many interests and the new understanding may lead to applications in material characterization [4]. The method of creating vortex electron beams using a forked aperture [2] is popular but has a drawback that electron vortex beams with different orders are produced side‐by‐side in the specimen plane. More recently a method of producing electron vortex using a spiral holographic aperture was demonstrated, with the advantage of being able to select a specific vortex beam in focus on the sample [5,6]. However, the spiral aperture is difficult to reproduce accurately because of many fine features and it is also mechanical fragile and the extra reinforcement bars were added in the mask for mechanical stability[5].
In this study, we propose and experimentally demonstrate a simple and versatile way of generating electron vortex beam carrying orbital angular momentum (OAM), using a chiral electron sieve illuminated by a plane electron wave. Fig. 1 (a) shows an electron sieve mask as viewed using a scanning transmission electron microscope. It consists of a number of spirals (5 in this case), each spiral consists of suitablly arranged holes in such a way that they produce a vortex beam approximate at a near field distance [7]. Fig. 1(b) shows the resultant beam intesnity profile as the designated distance. This shows a characteristic donut shaped beam illumination characteristic of an electron vortex beam. The is confirmed by direct comparison of the intensity profile with the simulated result using Fresnel diffraction theory (Fig. 1(c)). The same simulation shows the phase structure at the center of the donut ring does contains a vortex structure of order 5.
For this particular electron sieve mask, the mask pattern can be compared with the spiral diffractive holographic grating structure produced by interference between the vortex beam and that of a spherical reference waves [5], showing comparable efficiency. However, it has the practical advantage of being much easier to produce and mechanically more robust than the normal binary diffractive grating. We will show that this is a practical example of a much rich set of electron sieves that we can generate to shape electron beams, many of which has no counter part in conventional holographic diffractive grating theory [8].
Atomic‐resolution analysis of the structure and dopants of beam sensitive ordered porous materials
Authors: Mayoral Alvaro , Readman Jennifer , Navarro Marta , Morris Russell E. , Díaz Isabel 
Published: December 2016

With the modern transmission electron microscopes (TEM) sub‐angstrom resolution has become readily achievable overcoming the lateral resolution problem. However, there are many cases where its fully potential cannot be totally exploited due the strong interaction between the high energetic electron beam and the material. Zeolites, zeotypes and metal organic framework (MOFs) suffer from this interaction resulting in an irreversible framework disruption through a radiolytic mechanism[1].
Since the pioneers electron microscopy observations of zeolites in the 70's, its application and image resolution has been always been limited by this high sensitivity making impossible to fully exploit the TEM capabilities. However, in recent years with the introduction of the spherical aberration correctors and paying special attention to the electron dose, images with unprecedented resolution has been able to be obtained, making feasible the truly identification of the atoms conforming the structure.
In here, it will be presented atomic‐column resolution images which will provide new information on guest species[2] within the zeolite cavities, as well as the observation of structural defects[3] providing new information about the ion exchange properties of these solids. Figure 1 displays the data obtained after introducing rare earth metals into ETS‐10.
Furthermore, it will be shown how aberration corrected STEM provide unique information dealing with the analysis of new complex materials[4]; making able the observations of pores linked by single four‐rings, double four‐rings or oxygen linkers.
A multimodal and multiscale approach to investigate the micronsized organisation of a very complex biological material : the wheat grain
Authors: Gaillard Cédric 
Published: December 2016

Nowadays, a large set of microscopy tools are commonly used to investigate the nanostructure of complex biological or synthetic materials with a multiscaled organisation: epi‐fluorescence and laser scanning confocal microscopes (LSCM), scanning and transmission electron microscopes (SEM, TEM), atomic force microscopy (AFM), or Raman imaging. In particular, transmission electron microscopy (TEM) allows observation of the internal structures of natural systems (grains, cells and tissues) with a high spatial resolution. However, such observation requires in parallel dedicated sample preparation steps to prepare the fragile hydrated biological samples with successive steps including chemical or physical fixation, dehydration or vitrification of the water content, resin‐inclusion and contrast‐enhancement staining. Its well‐known these steps may induce artefacts that reduce the image resolution and valuable information, but are often considered as the unique way to access to the ultrastructural information.
We propose here to explore alternative routes for the ultrastructure investigation of the grain tissues, as an example of a very complex biological material, with the main objective to reduce the preparation steps as most as possible while adapting the same preparation to be process with several microscopy tools: TEM, SEM, AFM, Raman imaging, Fluorescence imaging, X‐ray microscopy. Depending on the successfulness of this approach, a set of complementary experiments from the same zone of a native sample can alloy to connect the plant ultrastructure with a high spatial resolution to accurate chemical information.
The multimodal and multiscale approach has been fully tested to study wheat grains tissues. We will show how unique features in the wheat outer layers organisation have been revealed due to both the capacity of keeping the native tissue “true contrast”, free from any chemical artefacts, or the native mechanical stress between the components, exempt from any alteration from resin infiltration. Moreover, taking advantage from the capacity of keeping the wheat tissue in its native shape, the mechanical properties of the native wheat outer layers (intenal and external pericarp, aleurone and sub‐aleurone layers and starchy endosperm) have been characterised by AFM at the nonometer scale, see Figure 1. Additionally, the chemical composition has been acquired by Raman mapping from the different zones of interest, giving in an unique way the capability to understand the natural assemblies of biopolymers and mineral nutrients at the sub‐cellular level in regard to their chemical, physicochemical and structural properties.
A Review on Interface Engineering and Thin Film Nanotechnology for Low‐Cost High Efficient Photovoltaic (
PV
) Solar Cell Devices
Authors: Saad Mohamed , Kim J , Kozlowski P , Ott J , Sadana D , Chen T.C 
Published: December 2016

Currently, the major challenge of the research and development (R&D) in the field of Photovoltaic (PV) renewable energy is to lower the cost per Wp of electricity generation and to improve the conversion efficiency of the solar cell devices.
In comparison with the crystalline silicon technology, silicon (Si) thin film nanotechnology hold the promise of reducing the solar cell cost through lowering the material amounts and energy requirement of the manufacturing process.
In this review, several aspects of the material engineering at interfaces and process optimisation for low‐cost high‐efficient silicon based thin film photovoltaic (PV) solar cells are discussed.
A basic understanding of the thin film growth technique using a plasma enhanced chemical vapour deposition (PECVD) system coupled with analytical nanostructural characterisations of Si thin film solar cells with particular emphasis on hydrogenated amorphous and microcrystalline p‐i‐n single and double (tandem) junction silicon solar cells are presented.
Nanostructural defects including microvoids and cracks at interfaces – as potential extrinsic effects on the hydrogenated microcrystalline (uc‐Si:H) solar cells performance – are studied.
Analytical nanostructures of an ultrathin interfacial buffer amorphous hydrogenated germanium (a‐ Ge:H) layer at the P+‐ type a‐Si:H/Transparent Conducting Oxide (TCO) are investigated using STEM and EDS. It was shown that such an interfacial buffer layer could improve the electrical performance and enhance the efficiency of the a‐Si:H single junction solar cells.
Assessment of doping profiles in semiconductor nanowires by scanning probe microscopy: Study of p‐ type doping in
ZnO
nanowires
Authors: Bremond Georges , Wang Lin , Chauveau Jean‐Michel , Sartel Corine , Sallet Vincent 
Published: December 2016

Methods to measure and quantitatively determine the doping profile in semiconductor nanowires ( NW) are strongly requested for understanding the doping incorporation in such one‐dimensional structures and so for developing technology using them. In the last two decades, scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) based on atomic force microscopy, has emerged as promising tools for two‐dimensional high resolution carrier/dopant profiling. In SCM, the capacitance change providing by an alternating bias applied between the tip/sample system under a DC bias to alternately accumulate and deplete carriers within the semiconductor underneath the local tip is dependent on the local carrier concentration of the semiconductor. In SSRM, the local resistivity is determined via the resistance measurement at the tip/sample system allowing the determination of the doping concentration. These two techniques need of an accurate calibration method for a quantitative doping analysis.
In this communication, we present first a calibration method based on cross‐sectional scanning of multilayers samples with different Ga doping concentration allowing the quantitative measurement of n‐type ZnO doping by SCM and SSRM. Then, to study ZnO NWs, we have developed a methodology of sample preparation, based on dip‐coating filling of NWs field. The dip‐coating parameters as coating solution, removal rate and NW field morphology have been controlled by SEM, ellipsometry and atomic force microscopy topography in order to optimize the filling and polishing process.

One important results has been to be able to measure using SCM and SSRM, the non‐intentionally n‐type doping (nid) of the ZnO nanowires, well estimated at 210
18
cm
−3
, explaining the difficulty to turn these NWs into p‐type during p‐type doping experiments, a crucial problematic in ZnO. Using antimony (Sb) doping in nid ZnO core/ Sb ZnO shell NW structures, we have successfully determined the decrease of carrier concentration with respect to the nid core ZnO, which can be ascribed to the formation of Sb‐related acceptors compensating the native donors. The understanding of this electric compensation mechanism is the clear signature of p‐type Sb doping feasibility in ZnO NW. This important result opens the way to succeed in the p‐type doping in ZnO.

The generalization of this doping profiling methodology to other semiconductors NW could be pointed out.
Structure and dynamics of the endoplasmic reticulum in cultured mammalian cells
Authors: Joensuu Merja , Belevich Ilya , Vihinen Helena , Kumar Darshan , Rämö Olli , Lak Behnam , Jokitalo Eija 
Published: December 2016

The endoplasmic reticulum (ER) is a large, single‐copy, membrane‐bound organelle that comprises an elaborate 3D network of structurally diverse subdomains: highly curved tubules, flat sheets, and parts that form contacts with nearly every other organelle of the cell. The ER is essential for the synthesis, modification, and transport of membrane and secretory proteins; it is also the site of cytosolic calcium level regulation and synthesis and transport of several lipids. To accommodate the vast range of functions, the ER network spreads throughout the cell, and its functions are distributed into structural subdomains according to their specific requirements. Many structural determinants of the network formation and maintenance have been described; however, it is not yet understood e.g. how different functions are distributed to the various subdomains, why the ER is constantly rearranging its architecture, and how the sheet/tubule –balance is maintained.
Proper ER operation requires an intricate balance within and in‐between dynamics, morphology, and functions. While ER structure is in constant flux, it does not move en masse, and the network movement is achieved through dynamics of individual subdomains and through network remodelling, which are accomplished through interactions with the cytoskeleton. Combining live cell imaging, thin section TEM and two 3D‐EM methods, we show that dynamic microtubules and actin filament arrays together contribute to the maintenance of ER sheet‐tubule balance. Perturbations of microtubule or actin cytoskeleton readily shift the balance towards tubules or sheets, which in turn can result in formation of sheet remnants or long and less fenestrated abnormal sheets. We recently identified the unconventional motor protein myosin 1c localizing to and regulating the ER associated actin filament arrays. Manipulation of myo1c levels disturbed the dynamics of actin arrays and affected ER sheet morphology similarly to actin manipulations with drugs. Tubular ER phenotype of myo1c‐depleted cells could be rescued with wild type myo1c, but not with a mutated form lacking the actin binding domain. We propose that ER ‐associated actin filaments have a role in maintaining the ER sheet‐tubule balance and sheet structure by regulating sheet remodeling events, and thus support the maintenance of sheets as a stationary subdomain of the otherwise dynamic ER network.
Knowledge of the mechanisms behind the structural maintenance and dynamics will be the key towards deeper understanding of ER functions and their regulation, and eventually, in unravelling molecular mechanisms behind various ER‐associated diseases.
Optics at the nanoscale with fast electron spectroscopies
Authors: Tizei Luiz 
Published: December 2016

Electron microscopy techniques have been used to probe the optical properties of materials in the subwavelength scale. In particular, it has been shown that using cathodoluminesncence (CL) and electron energy loss spectroscopy (EELS), along with a propitious choice of electron beam energy and target material, resolution below 10 nm is attainable.

In this seminar we will describe recent advances electron spectroscopies in a STEM to probe individual quantum structures. Different experiments attempting to probe their optical properties will be presented (including their lifetimes). Typically, a 1‐nm‐wide 60 keV electron beam was used to excite the sample. Fundamentally, we have measured spectroscopic signals (CL and EELS) and the second order correlation function (g
2
(t)) of the emitted light of different materials using an optical spectrometer, an EEL spectrometer and a Hanbury‐Brown and Twiss interferometer.

We will start by showing how monochromated EELS and CL experiments are well adapted to probe excitonic excitations in different materials. We will show how EELS is specially adapted to probe excitons in 2‐dimensional materials, using MoS
2
and MoSe
2
monolayers as example. For thicker materials, CL is able to more easily produce meaningful information from excitoninc excitations. As examples, we will discuss the luminescence of GaN quantum wells in AlN nanowires (Figure 1) and excitons in hBN flakes.

However, only spectroscopic information does not give a complete picture of the behavior of a specific system. One example are single photon emitters (SPE). To characterize such systems, light intensity interferometry is necessary (a typical experiment in quantum optics). We will demonstrate how a similar experiment using CL is possible, using as example the neutral Nitrogen‐Vacancy center in diamond nanoparticles (Figure 2). Also, we will show how this setup allowed the detection of new SPE in hBN.
Finally, we will discuss how a CL setup with a HBT interferometer in a STEM microscope can be used to measure the lifetime of individual quantum emitters with a high spatial resolution (< 15 nm). We name this technique spatially resolved time‐correlated cathodoluminescence, SRTC‐CL. As an example, we will show that the lifetimes of 8 GaN quantum wells separated by 15 nm in an AlN nanowire can be measured by SRTC‐CL.
Second harmonic imaging of collagen organization in connective tissues
Authors: SCHANNE‐KLEIN Marie‐Claire 
Published: December 2016

Type I collagen is a major structural protein in mammals. This biopolymer is synthesized as a triple helix, which self‐assembles into fibrils (diameter: 10‐300 nm) and further forms various 3D organizations specific to each tissue. In recent years Second Harmonic Generation (SHG) microscopy has emerged as a powerful technique for the
in situ
investigation of the fibrillar collagen structures in matrices or tissues [1]. However, as an optical technique with typically 300 nm lateral resolution, SHG microscopy cannot resolve most of the collagen fibrils. Moreover, in contrast to incoherent fluorescence signals that scale linearly with the chromophore concentration, SHG is a coherent multiphoton signal that scales quadratically with the density of collagen triple helices aligned with the same polarity in the focal volume. Consequently, quantitative SHG measurements have been limited so far to averaged phenomenological parameters [1].

In this study, we correlated SHG and transmission electron microscopies to determine the sensitivity of SHG microscopy and calibrate SHG signals as a function of the diameter of the collagen fibril [2]. To that end, we synthesized in vitro isolated fibrils with various diameters and successfully imaged the very same fibrils with both techniques, down to 30 nm diameter (see figure 1). We observed that SHG signals scale as the fourth power of the fibril diameter, as expected from analytical and numerical calculations. It validated our quantitative bottom‐up approach used to calculate the non‐linear response at the fibrillar scale and demonstrated that the high sensitivity of SHG microscopy originates from the parallel alignment of triple helices within the fibrils and the subsequent constructive interference of SHG radiations. This calibration was then applied to intact rat corneas, where we successfully recovered the diameter of hyperglycemia‐induced fibrils in the Descemet's membrane without having to resolve them [2,3].
Importantly, this calibration only applies to isolated fibrils. Nevertheless, complementary techniques can probe the sub‐micrometer structure of dense distributions of collagen fibrils. In particular, we have shown that polarization‐resolved SHG microscopy can probe the main orientation of collagen fibrils and their orientation disorder within the focal volume [4]. Combination of this modality with traction assays then provides a new method to measure the reorganization of the collagen network upon stretching and to correlate this microscopic response to the biomechanical response at macroscopic scale [4, 5].
In conclusion, our data represent a major step towards quantitative SHG imaging of collagen organization in biomaterials or connective tissues.
Electron interferometry techniques for strain analysis using a multi‐biprism microscope
Authors: Denneulin Thibaud , Röder Falk , Houdellier Florent , Gatel Christophe , Snoeck Etienne , Hÿtch Martin 
Published: December 2016

Electron interferometric techniques have progressed in the last years thanks to the development of multiple biprisms microscopes. Here, we will discuss some recent developments in the field of strain measurement carried out with the I2TEM microscope (In‐situ Interferometry Transmission Electron Microscope) installed in Toulouse in 2012. The I2TEM is a Hitachi HF‐3300 equipped with one pre‐specimen electrostatic biprism, three post‐specimen biprisms, an image corrector (CEOS B‐COR for correcting off‐axial aberrations) and two stages (objective stage and Lorentz stage above the objective lens).

In the dark‐field off‐axis scheme [1], an electron beam diffracted by an epitaxially grown region is interfered with a beam diffracted by the substrate thanks to a post‐specimen biprism (Fig. 1(a)). Fig. 1(b‐d) is an example obtained on a
p
‐MOSFET like transistor with SiGe source/drain. The deformation is recorded as a frequency modulation (FM) in the hologram (Fig. 1(c)) and it can be calculated from the gradient of the reconstructed phase image (Fig 1(d)).

In a recently proposed variant called differential phase contrast dark‐field holography (DPC‐DFEH) [2], a pre‐specimen biprism is used to create two overlapping waves on the sample (Fig. 1(e)). The interference of beams diffracted by slightly distant regions is acquired in a defocused plane. The deformation is recorded as a phase modulation (PM) in the hologram (Fig. 1(f)) and the DPC phase is directly proportional to the deformation (Fig. 1(g)).
Another option is the 4‐wave dark‐field setup where two biprisms oriented perpendicularly are used to interfere three reference waves and one object wave (Fig. 1(h‐j)). The holographic fringes are modulated in amplitude (AM) and each amplitude contour corresponds to a given displacement of the lattice planes [3]. It can provide live information if a sufficient fringe contrast is achieved.
In all cases, strain measurement requires a reference wave diffracted by a region of known lattice parameter (usually the substrate). One solution is the “tilted reference wave” (TRW) where a pre‐specimen biprism and the condenser system are used to create an object‐independent reference wave with an adjustable tilt angle [4]. Fig. 2(a,b) is an example acquired in the vacuum and Fig. 2(c,d) shows the dark‐field configuration for strain measurement.
Finally, a pre‐specimen biprism can also be useful for electron diffraction techniques. For instance, one can create two parallel half cones on the specimen (splitting convergent beam electron diffraction, SCBED) with a controllable distance (Fig. 3(a)) [5]. Each spot in the diffraction pattern contains two lobes related to the regions crossed by the two probes. Fig. 3(b) shows an example of SCBED pattern series where the left and right lobes are related to unstrained and increasingly strained regions respectively.