bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of the climates of the Medieval Climate Anomaly, Little Ice Age, and Current Warm Period reconstructed using coral records from the northern South China Sea
Authors: Deng Wenfeng , Liu Xi , Chen Xuefei , Wei Gangjian , Zeng Ti , Xie Luhua , Zhao Jian‐xin
Published: December 2016

For the global oceans, the characteristics of high‐resolution climate changes during the last millennium remain uncertain because of the limited availability of proxy data. This study reconstructs climate conditions using annually resolved coral records from the South China Sea (SCS) to provide new insights into climate change over the last millennium. The results indicate that the climate of the Medieval Climate Anomaly (MCA, AD 900–1300) was similar to that of the Current Warm Period (CWP, AD 1850‐present), which contradicts previous studies. The similar warmth levels for the MCA and CWP have also been recorded in the Makassar Strait of Indonesia, which suggests that the MCA was not warmer than the CWP in the western Pacific and that this may not have been a globally uniform change. Hydrological conditions were drier/saltier during the MCA and similar to those of the CWP. The drier/saltier MCA and CWP in the western Pacific may be associated with the reduced precipitation caused by variations in the Pacific Walker Circulation. As for the Little Ice Age (LIA, AD 1550–1850), the results from this study, together with previous data from the Makassar Strait, indicate a cold and wet period compared with the CWP and the MCA in the western Pacific. The cold LIA period agrees with the timing of the Maunder sunspot minimum and is therefore associated with low solar activity. The fresher/wetter LIA in the western Pacific may have been caused by the synchronized retreat of both the East Asian Summer Monsoon and the Australian Monsoon.
Synoptic analysis and urban signatures of a heavy rainfall on 7 August 2015 in Beijing
Authors: Yu Miao , Miao Shiguang , Li Qingchun
Published: December 2016

A heavy rainfall event that occurred in Beijing on 7 August 2015 was investigated by means of several nonconventional observational data and the Beijing Rapid Update Cycle Model (v3.0). A cold front guided by an upper trough and the wind shear line are main factors influencing this rainfall event. The two factors combined were enhanced after passing the Beijing downtown area. A Nourban land use scenario was employed to analyze the impact of urbanization on this rainfall event. The results show that the urban land use type, which induces the wind shear line, is indispensable in forecasting the rainstorm. The urban land use type leads to gradients of the sensible heat flux, temperature, and wind increasing in the suburban area, which may allow the synoptic systems to merge and enhance. Urbanization caused the precipitation to increase in the downstream suburban area and the spatial distribution of precipitation to become more concentrated. Ensemble tests of different parameterization schemes confirm that the results are reliable.
Assessing crop yield simulations driven by the NARCCAP regional climate models in the southeast United States
Authors: Shin D. W. , Baigorria Guillermo A. , Romero Consuelo C. , Cocke Steve , Oh Ji‐Hyun , Kim Baek‐Min
Published: December 2016

A set of the North American Regional Climate Change Assessment Program (NARCCAP) regional climate models is used in crop modeling systems to assess economically valuable agricultural production in the southeast United States, where weather/climate exerts strong impact on agriculture. The maize/peanut/cotton yield amounts for the period of 1981–2003 are obtained in a regularly gridded (~20 km) southeast U.S. using (a) observed, (b) a reanalysis, and (c) the NARCCAP Phase I multimodel data set. It is shown that the regional‐climate model‐driven crop yield amounts are better simulated than the reanalysis‐driven ones. Multimodel ensemble methods are then adopted to examine their usefulness in improving the simulation of regional crop yield amounts and are compared to each other. The bias‐corrected or weighted composite methods combine the crop yield ensemble members better than the simple composite method. In general, the weighted ensemble crop yield simulations match marginally better with the observed‐weather‐driven yields compared to those of the other ensemble methods.
Premammalian origin of the sperm‐specific Slo3 channel
Authors: Vicens Alberto , Andrade‐López Karla , Cortez Diego , Gutiérrez Rosa María , Treviño Claudia L.
Published: December 2016

Slo3 is a sperm‐specific potassium (K+) channel essential for male fertility. Slo3 channels have so far been considered to be specific to mammals. Through exploratory genomics, we identified the Slo3 gene in the genome of terrestrial (birds and reptiles) and aquatic (fish) vertebrates. In the case of fish, Slo3 has undergone several episodes of gene loss. Transcriptomic analysis showed that vertebrate Slo3 transcript orthologues are predominantly expressed in testis, in concordance with the mammalian Slo3. We conclude that the Slo3 gene arose during the radiation of early vertebrates, much earlier than previously thought. Our findings add to the growing evidence indicating that the phylogenetic profiles of sperm‐specific channels are intermittent throughout metazoan evolution, which probably reflects the adaptation of sperm to different ionic milieus and fertilization environments.
Mass Spectrometry of Biological Molecules
Authors: Fuchs Beate , Schiller Jürgen
Published: December 2016

Mass spectrometric methods may serve as powerful analytical methods in life sciences and medicine. Mass spectrometry (MS) is comparable in sensitivity to techniques based on chromatography or electrophoresis but has superior resolution. Although there are a number of suitable ionization methods, allowing the analysis of biological molecules that are of high molecular weight and low volatility, there are mainly two ‘soft‐ionization’ techniques that confer only a minimum of degradation of the analyte: MALDI (matrix‐assisted laser desorption/ionization) and ESI (electrospray ionization). The following article provides a short overview on the advantages and drawbacks of MALDI analysis of biological samples. While most applications of MALDI are in the field of protein analysis, the analyses of carbohydrates and lipids are also comprehensively discussed. It is shown that MALDI is a useful tool especially in the field of lipid analysis, whereas with carbohydrate analysis, still a number of problems have to be solved. MALDI is a rapid and very sensitive (from the low picomolar to the attomolar range) tool that tolerates high amounts of impurities (in contrast to ESI), which are typically present in biological samples. A further advantage is that mainly singly charged ions are formed; this enables MALDI to be applied even to the analysis of crude mixtures although ion yields may differ significantly in dependence on the molecules of interest. In comparison with ESI, MALDI detects compounds of higher molecular weights more sensitively, whereas ESI is more suitable for labile compounds. Therefore, the combination of both methods is, in many cases, the ideal solution for a number of analytical problems.
Multidimensional Nuclear Magnetic Resonance of Biomolecules
Authors: Craik David J. , Horne James , Scanlon Martin J. , Nichols Scott R. , Frueh Dominique P.
Published: December 2016

Nuclear magnetic resonance (NMR) is associated with transitions, induced by radiofrequency (RF) irradiation, between energy levels of nuclei with nonzero spin quantum numbers in a magnetic field. Traditional ‘one‐dimensional’ (1D) NMR spectra are presented as a plot of signal intensity versus applied frequency and provide information about the chemical environment of magnetically active nuclei. This is used to deduce information about the chemical structure and dynamics of molecules containing the magnetically active nuclei (most often protons). The frequencies of individual nuclei are referred to as their chemical shifts. Multidimensional NMR encompasses a range of related techniques, based on the application of a variety of precisely timed RF pulses to the sample, which extends traditional 1D NMR into two‐, three‐, or four‐frequency dimensions. In multidimensional NMR of biomolecules, the most common frequencies correspond to1H in the directly detected dimension and one or more of1H,13C, or15N in the additional dimensions. Peaks in such spectra are defined by their intensity and frequency coordinates in two, three, or four dimensions obtained by extrapolation back to the respective frequency axes, which are in turn determined by the nature of the applied RF pulse sequences. The intensity and chemical shifts of such peaks provide information about the chemical environment, molecular connectivity, or spatial proximity of the participating nuclei. Multidimensional NMR has major advantages over 1D NMR: reduction of peak overlap and provision of information on connectivity (either through bonds or through space). Multidimensional NMR spectroscopy of biomolecules is usually done for samples in solution at millimolar concentration. Where experiments require the use of13C or15N frequencies, it is usually necessary to isotopically enrich the macromolecule with these nuclei to >90%. This is readily achieved with modern molecular biology techniques and does not present a major limitation. As molecular weight increases, spectra exhibit severe overlap and suffer from sensitivity losses. Despite this limitation, it is becoming commonplace to study biological macromolecules up to 50 kDa and molecular assemblies reaching megadaltons.
Understanding the enhanced ductility of TiAl alloys using a hybrid study of in‐situ TEM experiment and molecular dynamics
Authors: Kim Seong‐Woong , Ryu Seung‐Hwa , Na Young‐sang , Kim Seung‐Eon
Published: December 2016

An in‐situ transmission electron microscopy study was conducted at room temperature in order to understand an underlying mechanism on room temperature ductility of TiAl alloys. Also, melecular dynamics simulation was conducted to calculate the stacking fault energy of TiAl alloys and to show which deformation mode is dominant. From in‐situ straining transmission electron microscopy experiments, it was revealed that the crack path and deformation mode is different between the TiAl alloys with/without room temperature ductility. The crack in TiAl alloys having room temperature ductility interacted with lamellae by forming bridging ligaments between the two α2 lamellae and the γ lamellae. In contrast, the cracks in TiAl alloys without room temperature ductility propagated along grain (colony) boundaries showing brittle intergranular fracture. From the quantitative in‐situ TEM experiements, it was found that the γ lamellar of TiAl alloys having room temperature ductility was deformed by slip (Fig. 1). However, the γ lamellar of TiAl alloys without room temperature ductility was deformed by deformation twin (Fig. 2). The difference in deformation mode was explained by stacking fault energy of the TiAl alloys which was calculated by molecular dynamics. The TiAl alloy with low stacking fault energy was deformed by deformation twin (Fig. 2) whereas the TiAl alloy with high stacking fault energy was deformed by dislocation slip (Fig. 1). Furthermore, the role of lamellar orientation of tensile direction on deformation behavior was examined using Schmid factor of each orientation.

Finally, we proposed the important microstructural factors to have room temperature ductility of TiAl alloys.
The Nanoworkbench: Automated Nanorobotic system inside of Scanning Electron or Focused Ion Beam Microscopes
Authors: Burkart Ivo , Burkart Eva , Klocke Volker , Peters David
Published: December 2016

The Nanoworkbench is the first system substituting eye‐hand coordination effectively with nano‐precision in a SEM/FIB‐system. It can be imagined how technology could evolve, when tools within a SEM/FIB can be used as easily as tools used under optical microscopes.

Many every day developments would not exist today without preparation, handling and assembly of materials under optical microscopes. There would be no wristwatch, no in vitro fertilization, no mini‐gearbox, just to mention a few. These products depend on using toolsets like tweezers, knives, hooks, probes and several different measurement tools in combination with optical microscopes. But material properties and functionalities also depend on structure dimensions that are smaller than the wavelength of light.

The operators of SEM, FIB or Dual Beam systems generally work without toolsets. One reason for this is the disconnected closed loop operation between human eyes and hands that enable complex operations under optical microscopes without even thinking about it

The two main aspects of the new Nanoworkbech by Klocke Nanotechnik GmbH, the development of its Nanorobotics technology and the applications enabled by it, are described in this paper.

Aspect 1, development of the technology: In general the success of in‐SEM/FIB Nanorobotics depends on the co‐operation of several important modules in one global system. The main developments include:

Nanomanipulators in automation, for movement of end‐effectors and sample handling,

Different end‐effectors for nano‐ probing, cutting, cleaning, force distance or wear measurements, gripping, sorting or material preparation and processing,

Automatic in‐situ tip cleaning process

Automatic 3D position detection of all tools and SEM/FIB

A control of all tool and SEM/FIB sample stage positions in a common global coordinate system,

SEM picture assisted haptic interface by “Live Image Positioning”,

Modular design for fast configuration & teaching of nano‐analytical or nano‐handling processes.

With instantiating these technical demands the Nanoworkbench enables secure and easy usage of toolsets within SEM/FIB systems, for manual operation, for non‐professional users and in high level of automation, e.g. for high throughput industrial processes, even as job‐shop [1].

Aspect 2, development of a series of new applications in one system: Expanding the SEM/FIB to a material processing system and a nano‐analytical workbench opens the door to many applications in all fields of research and development up to industrial production [5]. Several examples of these new interdisciplinary research and development fields will be described during the presentation.

A few examples of Nanoworkbench applications are highlighted in Figure 1. Although these examples may raise the impression of a review about different machines and their usage, this is not the case. Described is the development of the Nanoworkbench.
Electron microscopy characterization of yttrium‐doped barium zirconate electrolytes prepared with Ni additive: Influence of hydrogen treatment
Authors: Haghi‐Ashtiani Paul , Hassine Mohamed BEN , Ciria Desiree , Jimenez‐Melendo Manuel , Aubin Veronique , Dezanneau Guilhem
Published: December 2016

Proton‐conducting Fuel or Electrolysis Cells (PCFCs) are thought to be a promising alternative to Solid Oxide Fuel/Electrolysis Cells [1‐2]. The most interesting proton conducting materials for electrolytes include doped barium zirconate, doped barium cerate or their solid solution. Recently, an innovative approach was proposed which allowed obtaining dense ceramics with grain size of typically 2‐4 µm. This new process is based on the reactive sintering of all oxide precursors with the use of NiO as sintering aid [2‐4]. Besides being dense, the samples obtained, such as yttrium‐doped barium zirconate (BZY), show a very high proton conduction with little influence of Ni‐species on conduction properties.

We tested the mechanical properties of this BZY material for application as PCFCs electrolyte and we showed that materials made from this process present a fast degradation of mechanical properties when put in hydrogen‐rich conditions.

The objective of the present work was thus to understand the atomic‐scale origin of this fast degradation. For this purpose, different electron microscopy techniques have used such as Scanning Transmission Electron Microscopy (STEM‐HAADF), Energy dispersive spectroscopy (EDS), Electron Energy Loss spectroscopy (EELS). Structural and chemical microscopy analysis show that the sample failure is due to the reduction of NiO nanoparticles at grain boundaries (Figure 1, 2).
Correlative Microscopy:
R
aman Imaging Meets
AFM, SNOM
, and
SEM
Authors: Schmidt Ute , Tchaya Maxime , Ayasse Philippe , Hollricher Olaf
Published: December 2016

The characterization of low‐dimensional materials such as graphene or transition metal dichalogenides (TMDCs) often requires more than one technique to obtain a thorough understanding of their attributes for specific applications. Graphene and TMDCs both have layered structures and properties that vary significantly with thickness as compared to single layer conformations, making them very interesting for electronics design [1, 2]. Electronic device performance optimization can benefit greatly from knowledge of their crystalline structure and exciton dynamics. The aim of the following analysis is to show how several spectroscopy (Raman/Photoluminescence) and microscopy techniques (AFM/SEM) can, in correlation, provide a more detailed depiction of low‐dimensional materials than the constituent measurements could offer in isolation.

Raman spectroscopy, and Raman imaging in particular, has proved to be of great value in differentiating spectra obtained from single, double and multi‐layered low‐dimensional materials. Raman imaging was also used to evaluate strain, doping, chirality and disorder in graphene and TMDCs [3, 4]. The information acquired with Raman spectroscopy and imaging can be complemented by data from highest resolution microscopy techniques such as Atomic Force Microscopy (AFM), Scanning Near‐Field Microscopy (SNOM), or Scanning Electron Microscopy (SEM).

Fig. 1a shows a correlative Raman‐SEM image of exfoliated graphene deposited on a non‐conductive glass coverslip. The SEM image was acquired in the low vacuum mode using a BSE detector. Different graphene sheets can be clearly visualized. In the center of the SEM image a confocal Raman image was acquired, showing the presence of different number of graphene layers, from one (green) to ten (yellow). The high resolution confocal Raman image (Fig. 1b), acquired from the area marked in Fig. 1a shows the intensity distribution of the G band as a function of layers in the graphene sheet as indicated with 1, 2 and M (multy‐) layers. By evaluating the intensity of the D‐band, the chirality of the graphene crystal could be determined as highlighted in red color in Fig. 1b. The SNOM image from the same area (Fig. 1c) shows that the transparency of the graphene decreases with increase of number of layers providing direct access to the fine structure of graphene.

In a second example a high resolution SEM image of CVD grown MoS2 is pesented (Fig. 2a). The Raman‐SEM image (RISE image) presented in Fig. 2b shows a correlation of changes in the Raman spectrum at the defects of the crystals.
Atom‐Probe Tomography and Nanosciences
Authors: Blavette Didier , Mouton Isabelle , Duguay Sébastien
Published: December 2016

The design of Atom probe tomography (APT) at Oxford and Rouen universities 25 years ago has been an outstanding breakthrough in the microscopy world. APT is the only analytical microscope able to provide 3D images of a material at the atomic scale [1]. Because of its ultimate spatial resolution (0.1 nm in depth, a few tenths of a nm at the sample surface), combined with its quantitativity in composition measurements, APT has played a major role for the investigation of the segregation of impurities to crystal defects or of the early stages of phase separation in solids. APT was the first to show Cottrell atmospheres (tiny clouds of impurity atoms around dislocations in crystals) at the atomic‐scale in the dimensions of space [2].

A new breakthrough has been achieved ten years ago with the implementation of ultrafast pulsed laser (duration < 1ps) to atom probe tomography [3]. This new generation of instrument, designed in our lab and abroad, has made it possible the analysis of semi‐conductors (figure 1) and oxides that are key materials in micro‐electronics and nanosciences [4]. This major innovation with the use of FIB ion milling (focused ion beam) to prepare samples in the region of interest opened a new insight in many fields of nanoscience related to nano‐wires [5], nanostructured magnetic thin films [6], heavily‐doped ultra‐shallow junctions in microelectronics [7]. One of the biggest challenge being the atomic‐scale reconstruction of MOSFET transistors [8,9]. Unique capabilities of atom probe tomography in nanoscience and salient findings will be highlighted on the basis of some selected illustrations. 3D APT reconstructions related to phase separation in GeMn self‐organised thin films (figure 2) will be confronted to atomistic Kinetic Monte Carlo simulations conducted on rigid lattice [6].
HREM
observation and elucidation of edge‐bonding
MoS2
on {101}‐facet exposing surface of anatase
TiO2
support
Authors: Guo Changyou , Shen Zhiqi , Wang Shaojun , Ling Fengxiang
Published: December 2016

An urgent demand for clean fraction oil makes a great pressure on the hydrotreating (HDT) technology due to progressively stringent environmental regulations. Conventional HDT catalysts supported g‐Al2O3 has been used for near 100 years. An alternative of taking anatase‐type TiO2 (A‐TiO2) as support other than g‐Al2O3 could greatly improve the performance of the catalyst. The superior performance of Mo/TiO2 originates from the increasing of type II active sites numbers because of the presence of new MoS2‐TiO2 interaction in an edge‐bondingway3. However, the interaction was never reported from specific crystallography. The sulfidation process of Mo/TiO2 catalyst could be partly regarded as epitaxial growth of MoS2 on TiO2 support. And thus, the crystallographic orientation relationship (OR) between MoS2 and TiO2 is very important for understanding the active sites of the catalyst.

The TiO2 support was obtained by pressing anatase TiO2 powder, synthesized by hydrothermal method, into disc under 5 MPa pressure and breaking up into 20˜40 mesh grains. Mo/TiO2 (10wt%) was synthesized by impregnating ammonium molybdate solution onto TiO2 support followed by dryness and calcination. Sulfiding experiments were carried out on a fixed‐bed micro‐reactor at 350°C under 10%H2S/H2 atmosphere. The catalysts were observed by HREM on a JEOL 2200FS microscope operated at 200kV.

HREM image in Figure 1A shows the interface relationship between MoS2 and TiO2 in sulfided Mo/TiO2 catalyst. MoS2 slab is anchored on (101) facet‐exposing surface of A‐TiO2 in edge‐bonding way. The angle between (001)MoS2 and (101) A‐TiO2 is 66°. The interface relationship could be elucidated by Coincidence Reciprocal Lattice Points (CRLP)4 theory, expressed by a scheme in Figure 2. The intersecting volume function of reciprocal lattice points of two crystals (hexagonal MoS2 and tetrahedral TiO2 shown in Figure 3A) could be computed from home‐made program. The OR of two crystals at the initial orientation is (001)MoS2//(001)A‐TiO2 and [100]MoS2//[100] A‐TiO2 (Figure 3B).The intersecting volume function V(a,b) is computed and plotted versus a and b angle. Figure 3C shows the corresponding 3D drawing. The same peak value presents at (0,15), (0,45) and (0,75) points, which reflects optimum OR presents at the orientations. At initial orientation, the deduced angle between (001)MoS2 and (101) A‐TiO2 is 68 degree. At (0,15), (0,45) and (0,75) orientation, the values are 83°, 66°and 36°, respectively. The 66° angle between (001)MoS2 and (101) A‐TiO2 at (0, 45) is highly consistent with that value observed by HREM. As a result, the conclusion could be drawn that CRLP theory could well predict interface relationship in MoS2/TiO2 HDT catalyst.
Influence of Hydrogenation on Microstructure of
T
i3
A
l Alloy
Authors: Wang Qing , Zhao Qiongyang , Sun Yueqi , Sun Dongli
Published: December 2016

The hydrogenation technology with different parameters of Ti3Al alloy was studied in this paper, and the effect of hydrogen on microstructure of Ti3Al alloy was analyzied. The results showed that the higher the hydrogenation temperature and the larger specific surface area of sample, the hydrogen content of Ti3Al alloy increased. With hydrogen content increasing, the proportion of α2 phase diminishes greatly and disappears finally, B2 phase laths become narrow and the O phase laths become wider. When the hydrogen content reached 0.3wt%, the plate‐like hydrides, ε phase, precipitated from O phase, and with increasing hydrogen content the plate‐like hydrides grew and the dislocation density inreased. The orientation relationship between ε phase and O phase possibly exists as following : [111][212]Oε,(101)(223)Oε. The results of hot compression test showed that the reduction of peak stress of Ti3Al alloy could be attributed to the hydrogen. In addition, the hydrogen may accelerate the dynamic recrystallization and dynamic recovery process of Ti3Al alloy during the deformation.
The study on interface structure of
SiC/Ti
joint diffusion bonded under pulse electric field
Authors: Sun Dongli
Published: December 2016

The pulse electric field applied during the diffusion bonding process can impact the diffusion of the atoms and defects in materials and improve the structure and properties. The diffusion bonding process, interface structure and mechanical properties of SiC/Ti joint bonded under pulse electric field have been studied. The results show that the interface reaction layer thickness increases with increasing the pulse amplitude and the duty ratio, whereas it is effected barely by the pulse frequency. The shear strength of SiC/Ti joint increases firstly and then decreases with increasing the pulse amplitude, duty ratio, pulse frequency, that is, there is an optimum value of shear strength. At low pulse frequency, a small amount of TiC phase formed can reduce the residual stress at the interface between SiC and Ti. When the pulse frequency or amplitude is too high, some large TiC particles were produced near the interface, and they induced the micro‐cracks at the interface, so the joint performance was deteriorative. The TEM analysis of SiC/Ti diffusion bonding interface reveals that from SiC to Ti side, the interface structure is SiC/fine grain region(phase structure unknown)/ (TiC + Ti5Si3) / TiC / Ti.
Ferromagnetic Nanocrystalline Coatings over Steel trough Laser Cladding of Fe and Ni‐based Glass Former Alloys
Authors: Moreira Afonso Conrado Ramos , de Carvalho Marcos Fernandes , Catto Fausto Lopes , Botta Filho Walter José , Kiminami Claudio Shyinti
Published: December 2016

Fe‐based bulk glassy alloy properties indicates that coatings can represent good applications opportunities for metallic glasses. The Fe72Nb4Si10B14 (at%) bulk metallic glassy (BMG) alloy in order to produce coatings over AISI 1020 mild steel substrate using spray forming and laser cladding processing routes. For the spray forming process an additional Ni brazing alloy was applied on the substrate before the deposition to improve adhesion. For the laser cladding process, different laser parameters, power (W) and scanning speed (mm/s), were tested, using a Yb fiber laser (up to 2kW), to verified the best condition for to obtained the coatings [1]. The coatings was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DCS). The Fe72Nb4Si10B14 and Ni59Nb35Sn6 (at%) coatings obtained by spray forming presented high fraction of amorphous phase when produced with thickness up to 1 mm), some porosity and low oxidation level. XRD analysis showed Fe‐α, Fe23B6 and halo of amorphous phase, depending on thickness. In addition, these coatings presenting partial or complete glassy structure with high hardness around 1150 HV. The amorphous overspray powder of the BMG alloy obtained by spray forming, grain size < 45 µm, was used in order to produce coatings on AISI 1020 mild steel substrate by laser cladding of the pre‐placed powder. SEM micrographs of the clad tracks showed that at 200 W and 100 mm/s, no crystalline phases were observed, indicating maintenance of glassy phase due to high glass forming ability (GFA) of this alloy. XRD analysis showed only halo of amorphous phases in this condition. Moreover, for higher powers and same scanning speed, the diffractograms showed halo of amorphous phases and the Fe‐α and FeNbB crystalline phases. The coatings showed hardness ranging from 340‐1180HV, depending on laser parameters. These results suggesting that processing routes are promising to fabricate coatings for industrial applications.
Tomography of particle plasmon fields by electron energy‐loss spectroscopy
Authors: Haberfehlner Georg , Hörl Anton , Schmidt Franz P. , Trügler Andreas , Hohenester Ulrich , Kothleitner Gerald
Published: December 2016

Tailoring shape of metallic nanoparticles and alignment of nanoparticle assemblies allows controlling the properties of localized surface plasmon resonances, such as peak positions or near field‐coupling and enhancement [1]. Electron beam lithography is a versatile tool for nanoparticle manufacturing, but the technique usually suffers from imperfections, surface roughness, and limited spatial resolution, which leads to particle shapes that deviate from design objectives. Similar limitations apply to chemical synthesis, which leads to nanoparticle assemblies with size dispersion and geometry variations. Therefore, to exploit the full potential of plasmonics, full 3D characterization and simulation taking into account the imperfections of real structures become mandatory. Here we present two different tomography‐based approaches to understanding complex plasmonic nanoparticles created by electron beam lithography.

In our first approach the precise 3D geometry of a particle dimer fabricated by means of electron beam lithography was reconstructed through electron tomography. This full 3D morphological information was used as an input for simulations of energy‐loss spectra and plasmon resonance maps (Figure 1). Here excellent agreement between measured EELS data and theory was found, bringing the comparison between EELS imaging and simulations to a quantitative and correlative level [2].

In our second approach we directly reconstruct particle plasmon fields from a tomographic tilt series of EELS spectrum images. While first approaches and demonstrations of plasmon field tomography were limited to very small particles [3–5] – small enough to neglect retardation – we lift this limitation with our approach making plasmon field tomography generally applicable to nanoparticles of all sizes [6]. Formulation EELS tomography as an inverse problem allows reconstructing the complete dyadic Green tensor for plasmonic particles, which is linked to the photonic local density of states (LDOS). Using this approach we are able to reconstruct the full 3D LDOS for a silver metallic nanoparticle (Figure 2).

This work overcomes the need for geometrical assumptions or symmetry restrictions of the sample in simulations and generalizes plasmon field tomography to particles of all sizes, paving the way for detailed investigations of realistic and complex plasmonic nanostructures.
Microstructural evolution and thermal stability of nitride‐based metal/semiconductor superlattices for thermoelectric and hard‐coating applications
Authors: Garbrecht Magnus , Schroeder Jeremy L. , Hultman Lars , Birch Jens , Sands Timothy D. , Saha Bivas
Published: December 2016

A detailed analysis on the quality and microstructure of various metal/semiconductor superlattices employing HR(S)/TEM (high‐resolution (scanning)/transmission electron microscopy) imaging and energy dispersive x‐ray spectroscopy (EDX) mapping on as‐deposited and annealed samples is presented.

Epitaxial metal/semiconductor superlattices are known to be promising candidates for compounds in electronic, photonic, and plasmonic devices, but are also of interest for applications as hard coatings, and in thermoelectric materials [1]. The crystalline quality of the superlattices, in terms of their defect density, phase purity, interface roughness, and stoichiometry of the individual layers, plays a crucial role with respect to the physical properties and thus the applicability of such superlattice stacks. It was recently shown that metal/semiconductor superlattices based on (Al,Sc)N as the semiconductor component can be grown epitaxially with low‐defect densities by magnetron sputtering on [001]MgO substrates [2].

Phase formation and thermal stability studies of as‐deposited and long‐time annealed cubic TiN/(Al,Sc)N superlattices employing a combination of HR(S)/TEM and EDX mapping revealed intermixing of the TiN and (Al,Sc)N layers by interdiffusion of the metal atoms with increased annealing time [3].

Improved (Ti,W)N/(Al,Sc)N [4] and (Hf,Zr)N/ScN [5] superlattices were grown by magnetron sputtering and analyzed with various TEM methods, and their microstructural evolution as well as thermal stability becomes presented here. An example is show in Figure 1, which shows an overview of an improved cubic (Ti,W)N/(Al,Sc)N superlattice stack in cross‐section STEM (a), and a typical HRTEM micrograph of the metal/semiconductor interface region, demonstrating the high epitaxial quality of the growth [4].

Figure 2 demonstrates the superior thermal stability of the (Zr,Hf)N‐ based systems as compared to previous TiN‐ based superlattices. EDX mapping at high‐resolution before and after annealing at 950 °C for 120 hours reveals diffusion of the metal atoms in the TiN/AlScN system (b), while the Hf0.5Zr0.5N/ScN superlattice stays intact (d).

All experiments were conducted at Linköping's image‐ and probe‐corrected and monochromated FEI Titan3 60‐300 microscope equipped with a Gatan Quantum ERS GIF, high‐brightness XFEG source, and Super‐X EDX detector, operated at 300 kV [6].
Formation of bimetallic clusters in superfluid helium nanodroplets analysed by atomic resolution electron tomography
Authors: Haberfehlner Georg , Thaler Philipp , Knez Daniel , Volk Alexander , Hofer Ferdinand , Ernst Wolfgang E. , Kothleitner Gerald
Published: December 2016

Metallic nanoparticles consisting of a few thousand atoms are of large interest for potential applications in different fields such as optics, catalysis or magnetism. Structure, shape and composition are the basic parameters responsible for their properties. To reveal these parameters in three dimensions at the nanoscale, electron tomography is a powerful tool. Advancing electron tomography to atomic resolution in an aberration‐corrected transmission electron microscope is challenging though [1–3], and the ultimate goal of resolving position and type of each single atom inside a material remains elusive.

Here we demonstrate atomic resolution electron tomography on silver/gold core/shell nanoclusters grown in superfluid helium nanodroplets [4,5] (Figure 1a). Superfluid helium droplets represent a versatile, novel tool for designing such nanoparticles, allowing fine‐tuned synthesis of pure or composite clusters for a wide range of materials. Using ultra‐high vacuum conditions and getting on without solvents or additives compared with chemical synthesis, the method delivers high purity materials, which can be well controlled in terms of size and composition.

Analytical TEM investigations reveal smaller clusters mainly consisting of a single silver core, surrounded by a gold shell, whereas larger clusters contain two or more silver grains embedded in a gold matrix [6] (Figure 1b&c). The measured transition between single‐ and double‐core growth appears at a cluster size of about 5000 atoms and similar values are found when cluster agglomeration inside the He‐droplet is simulated for the used process parameters [7] (Figure 1d).

One cluster with two silver cores was analysed three‐dimensionally for its atomic structure, shape and composition [6] (Figure 2). We identify gold‐ and silver‐rich regions in three dimensions and we are able to estimate atomic positions inside the nanocluster. Two silver cores are visible as darker regions, separated by gold with a minimal thickness of 2–3 atomic layers. The cluster appears in a highly symmetric multiply twinned structure, shaped roughly as an icosahedron, which is structurally modified due to binding of the cluster to the surface.

This work demonstrates estimation of atomic positions within nanoparticles in 3D without any prior information, while at the same time information about the local elemental composition is retrieved at near‐atomic resolution. Our results give insight into the growth and deposition process of composite nanoclusters created in superfluid helium droplets. This understanding will allow fine‐tuning of process parameters for optimizing nanoparticle properties.
Design and realization of an ultrafast cold field emission source operating under high voltage
Authors: Houdellier Florent , Caruso Giuseppe Mario , Abeilhou Pierre , Arbouet Arnaud
Published: December 2016

Investigation of nanostructures physics requires atomic spatial resolution, meV spectral resolution and femto to nanosecond time‐resolution. Accessing all these informations simultaneously would be a breakthrough in nanophysics.

Ultrafast Transmission Electron Microscopes (UTEM) combining subpicosecond temporal resolution and nanometer spatial resolution have recently emerged as unique tools for investigations at both ultimate spatial and temporal resolutions [1]. However, the performances of state‐of‐the‐art UTEM are, in practice, brightness limited by their ultrafast electron source. These sources are commonly based either on photocathode excited by an ultrafast laser beam [2] or, very recently, on Schottky type assembly [3].

The FemtoTEM project aims at developing an alternative Ultrafast Transmission Electron Microscope based on a high brightness laser‐driven cold field emission electron source working under 200kV acceleration voltage. The latter consists of a metallic nanotip in tungsten illuminated by femtosecond laser pulses [4]. This development has been achieved by bringing together a commercial femtosecond laser source and a customized 200kV cold‐field emission Transmission Electron Microscope Hitachi HF2000.

The main difficulty was to develop the ultrafast cold field emission source modifying the old HF2000 design, well known in CEMES [5]. Indeed, to perform a proper laser assisted field emission, the femtosecond laser beam need to be injected in the ultra high vacuum and high voltage area of the gun, where the tip is located, then focused and aligned in three dimensions on the fine apex of the FE W tip. The new design has been thought to allow such complex operation while keeping the possibility of cold field emitting electrons in continuous operation, as for the standard source. This new design has been finally produced and patented [6].

To build this new source, deep modifications, compared to the original Hitachi design, have been implemented, from the high voltage gun housing and cable to the inner structure of the gun assembly. With the help of finite element modeling, and ray tracing software, the influence of the new design on the electric field, and electrons trajectories, brightness, … has been investigated and compared to experimental results (see Figure). Last results will be also presented highlighting the potentiality of this new source for ultrafast electron holography application, for which a good brightness is mandatory.
Comparison of energy filtered
TEM
spectra image and automated crystal orientation mapping in
LiFePO4/FePO4
phase mapping
Authors: Mu Xiaoke , Kobler Aaron , Wang Di , Kiran Chakravadhanula Venkata Sai , Schlabach Sabine , Szabo Dorothee‐Vinga , Norby Paul , Kübel Christian
Published: December 2016

Lithium iron phosphate (LiFePO
4
, LFP) is one of the most promising cathode materials for the next generation of Li ion batteries and attracts great attentions. Experimental mapping the lithiated (LFP) and delithiated phase (FePO
4
, FP) at nanoscale resolution provides knowledge on the microscopic mechanism of the reaction processes during electrical cycling, which is crucial to improve the limits of this material. Versatile scanning / transmission electron microscopy (S/TEM) techniques, due to the advantage of intrinsic imaging ability by the electron optics, have attracted extreme interest in high resolution phase mapping. The methods are generally sorted into two kinds: one is based on electron energy loss spectroscopy (EELS), such as energy filtered TEM (EFTEM) [1], relying on the chemical information in the energy spectra; the other is automated crystal orientation mapping (ACOM) [2], originally designed for orientation analysis of nanocrystalline materials [3], relying on the crystallographic information recorded in diffraction patterns. However, so far, there is no strongly convincing evidence indicating the consistency between the chemical and the crystallographic information in the phase map, because of lacking comparison of the results between the two kind methods.

In this work, we applied both EFTEM and ACOM methods to the same part of a sample (half lithiated) for comparison. Maps obtained by ACOM and EFTEM of Fe‐L
3,2
(figure 1 a, b) show excellent agreements with each other. It proves the reliability of both methods, i.e. the consistence of the chemical and crystallographic information for the LFP/FP system. Furthermore, we demonstrate that the properties of the LFP/FP interfaces can be further characterized from the crystallographic data obtained by ACOM: on average 1.4 ° misorientation was observed at all interfaces (figure 1 d, e), and these interfaces have a preferred orientation with the normal close to the a‐axis (100), but slightly deviated towards the c‐axis (001) (figure 1 f, g) in agreement with [4]. Further attention is drawn to the low energy loss regime for EFTEM analysis. Figure 2 a, c and e respectively shows a map measured from the Li‐K & Fe‐M edges (figure 2 b), and mapping of the dielectric function (figure 2 d) and the volume plasmon center (figure 2 f). Finally, a comprehensive comparison of all methods is given in terms of information contents, dose level, acquisition time and signal quality. The latter three are crucial for the design of in‐situ experiments [5].
Observation of thermal behavior of black phosphorus as a
2D
material
Authors: Yoo Seung Jo , Lee Ji‐Hyun , Lee Sang‐Gil , Kim Jin‐Gyu
Published: December 2016

Recent works have focused on a black phosphorus (black P) joined as a family of 2D materials, because of its tunable band gap depended on a thickness from 0.3eV in a bulk to more than 1.0eV in a few layers black P. Very recently, the successful fabrication of a single layer black P from the bulk has been reported. Additionally, unique properties of atomic layers of black P have been demonstrated such as high mobility, large on‐off rations, and anisotropic properties and so on. With these results, the black P as a 2D material is extremely attractive in electronic and optoelectronic applications. However, there is a lack of characterization of the few layers black P and the reported properties are still in theory. Especially, the basic parameters concerned with the thermal stability are not determined, though the most thermodynamically stable phosphorus allotrope is the black P. Therefore, it is important to investigate the thermal phenomena of the black P in a various temperature condition within an atomic scale. In this study, we studied the reaction behavior of a single crystal black P under in situ heating conditions. In addition, the microstructure of black P at different temperatures was analyzed using high‐resolution TEM (HRTEM).
Determination of the three particle structure factor from experimental images
Authors: Vrana Semir , Kohl Helmut
Published: December 2016

The structure of amorphous materials can be described by their correlation functions gn(r
1
,…,r
n
) where g
n
(r
1
,…,r
n
) d
3
r
1
···d
3
r
n
gives the probability of finding particle i in the volume d
3
r
i
and so on [1]. The pair correlation function g
2
(r
1
, r
2
) is well known experimentally from scattering experiments. However, it describes only the distribution of atomic distances. Information about bond angles is lost. This would be accessible if the triple correlation function g
3
(r
1
,r
2
,r
3
) could be measured.

The Fourier transform of the correlation functions are the so‐called structure factors. These can be directly obtained from experimental images [2]. Previous attempts to implement this approach, however, have failed [3, 4].

A few years ago Huang et al. [5] made incredibly well defined images of a layer of amorphous silica where the resolution was high enough to resolve atomic spacings. As the atomic positions are directly visible in these images, we used them to obtain the three particle structure factor.

In a first approximation we assumed ideal imaging and determined the structure factor S
(1)
simply as the Fourier transform of the measured intensity. The two particle structure factor S
(2)
is then calculated as the square of its absolute value and finally the three particle structure factor is obtained as S
(3)
(q
1
,q
2
) = S
(1)
(q
1
) S
(1)
(q
2
) S
(1)
(−q
1
−q
2
) where q
1
, q
2
are spatial frequencies in two dimensions [2].

Figure 1 shows the two particle structure factor of amorphous silica. There are two peaks. The first one at q ≈ 0.3 Å
‐1
is broader and we expect it to represent the atomic distances in the specimen. The second peak at q ≈ 0.5 Å
‐1
is sharper and due to the graphene substrate. Since amorphous matter is expected to be isotropic we average over one spatial angle and consider S
(3)
as a function of only three variables |q
1
|, |q
2
| and the angle φ between q
1
and q
2
. To reduce the number of degrees of freedom even more, we took q
1
= q
2
=: q and chose q to be at the first peak in S
(2)
(q) and only varied φ. A first result is shown in figure 2.

In a crystal one has well‐defined binding angles and thus expects S
(3)
(φ) to have sharp peaks at those angles. In our case we find peaks around 60° and 120° stemming from the approximate 6‐fold symmetry of silica but compared to the case of crystals they are smeared out. For the first time we have been able to determine the three particle structure factor from TEM images. We are now undertaking a systematic study to obtain further insights into the amorphous structure of two‐dimensional glasses.