bluuebunny/crossref_metadata_2025_split huggingface dataset:
Examination of semiconducting properties of oxides in the vicinity of metal‐oxide interfaces for selected alloys
Authors: Vanta Radovan , Abolhassani Sousan , Dadras M 
Published: December 2016

Radovan Vanta
1
,

Sousan Abolhassani
1
, Shiv Ashish Kumar
2
,

Massoud Dadras
2
, Adrienn Baris
1
, Guillaume Boetsch
3
,

Harry Brandenberger
4
,

Andreas Rummel
5

1

Laboratory for Materials Behaviour, Paul Scherrer Institut, 5232 Villigen‐PSI, Switzerland,

2

Service of Microscopy and Nanoscopy, IMT, University of Neuchâtel, Neuchâtel, Switzerland,

3

Imina Technologies SA, EPFL Innovation Park, Bâtiment E, 1015 Lausanne, Switzerland,

4

Gloor Instruments AG, Schaffhauserstrasse 121, 8301 Kloten, Switzerland,

5

Kleindiek Nanotechnik GmbH, Aspenhaustr. 25, 72770 Reutlingen, Germany,

This paper provides a brief overview of the studies performed on semi‐conducting properties of oxides and the change of these properties, for specific materials. A direct method is developed to measure the properties of the oxide by means of micromanipulators, in the SEM.
The interest of this method is to evaluate the role of such change of properties in the vicinity of interface of metal‐oxides and to correlate the properties to the oxidation behavior and also to the hydrogen uptake of the alloy.
In a previous study the properties of a material has been measured by means of micromanipulators, outside of the microscope. This study has been performed in the SEM. The present study reports the properties of two families of alloys. It shows that an alloy with a sub‐stoichiometric oxide in the vicinity of the interface has a lower resistivity. The method consists of using a fine micromanipulator installed in the SEM; a surface is created by FIB micromachining and the measurements are made by means of the micromanipulators inside the SEM, in this manner an accurate positioning is possible.
As it can be observed in Figure 1, the oxide in alloy Zr2.5%Nb is sub‐stoichiometric near the metal oxide interface [1]. Figure 2 presents the results of measurements of the Zr2.5%Nb and low‐tin Zircaloy‐4. The results of measurements and the comparison of the two alloys show that the second alloy having a stoichiometric oxide does not show such variation in resistivity in the vicinity of the metal‐oxide interface. The results will be discussed to confirm the role of the different properties of the oxide, on the oxidation behavior.
Electron energy loss spectroscopy (
EELS
) fingerprints of p‐ and n‐type doping in graphene
Authors: Kepaptsoglou Demie , Hardcastle Trevor , Seabourne Che , Bangert Ursel , Zan Recep , Amani Julian , Hofsäss Hans , Nicholls Rebecca , Brydson Rik , Scott Andrew , Ramasse Quentin 
Published: December 2016

Doping is a great way to make nanomaterials suitable for use in nanoscale devices and electronics. Dopant atoms supply mobile charge carriers in the form of electrons (n‐type) or holes (p‐type) whilst leaving the material neutral, and the physical interface between p‐ and n‐type materials ‐ the pn junction diode ‐ is a fundamental building block of electronic circuits. There is a general consensus that moving beyond the (mainly) Si‐, Ge‐ and GaAs‐based technology of the last seventy years is highly desirable, so there is currently lots of interest in finding superior replacements for next‐generation electronics. Graphene's discovery [1] lies at the root of this renewed interest, and it now seems likely that graphene, or nanomaterials inspired by graphene, will find their way into consumer and industrial electronics in some significant form quite soon.
To make progress, we need information about the electronic structure of the material of interest, and how doping affects that electronic structure. Atomic‐resolution electron energy loss spectroscopy (EELS) is a great way to achieve this because it can reveal the bonding around an individual dopant atom. This insight can then be directly compared with theoretical electronic structure calculations in the form of density functional theory (DFT) to yield a detailed understanding of the electronic structure and the potential implications for use in nanoscale devices.

In this talk I shall present atomic‐resolution
K
‐edge EEL spectra for the case of substitutional B and N dopants in graphene synthesised using low‐energy ion implantation, and I shall explain how a careful comparison with theoretical DFT calculations indicates that the EELS data is in fact the first direct experimental evidence of p‐ and n‐type doping in graphene. [2] This approach demonstrates how potentially very lucrative information can be extracted from joint studies of experimental and theoretical EELS, and it could be readily extended to other nanomaterials.
Dynamics of magnetic domain walls and skyrmions studied by high resolution
XMCD
‐
PEEM
microscopy
Authors: Pizzini Stefania , Vogel Jan , Rougemaille Nicolas , Sirotti Fausto , Cesar Julio , Chaves Dayane , Mentes Onur , Foester Michael , Aballe Lucia , Locatelli Andrea , Boulle Olivier 
Published: December 2016

Photoemission electron microscopy combined with x‐ray magnetic circular dichroism (XMCD‐PEEM) is a powerful synchrotron radiation technique that can be used to observe magnetic configurations of nano‐objects with high spatial resolution. Combined with time resolution, using stroboscopic detection, the magnetisation dynamics of such objects can be studied with sub‐nanosecond resolution.
We will describe the study of domain wall (DW) dynamics and magnetic skyrmions in multilayers of composition Pt/Co/MOx (M=Al, Mg), characterised by a large perpendicular magnetic anisotropy (PMA) and anti‐symmetric exchange interaction (Dzyaloshinskii‐Moriya interaction, DMI). Such interaction favours non‐collinear magnetic textures such as chiral Néel walls and magnetic skyrmions.

In systems with large DMI, such as Pt/Co/AlOx with ultrathin Co, domain walls acquire a Néel chiral structure and move at large speeds when driven by current pulses. Most microscopic studies of domain wall dynamics have been performed using quasi‐static measurements, where the DW position and structure are imaged before and after the excitation pulse. In order to better understand the details of the interaction between current and DW magnetisation, we have observed DWs
during
the application of the current pulses, by synchronising the current pulses with the x‐ray pulses, in stroboscopic mode. The measurements reveal that the DWs move without inertia, showing a practically vanishing mass. The negligible inertial effects can be explained taking into account the narrow domain wall width induced by the large PMA, the large damping parameter and the stabilising effect of the longitudinal field associated to the Dzyaloshinskii‐Moriya interaction.

Magnetic skyrmions are nanometer scale whirling spin configurations, predicted in the 80's but only recently observed with high resolution magnetic microscopies. Their small size, topological protection and the fact that they can be moved by very small current densities call for applications to novel memory and logic devices where skyrmions are the information carriers. Here we report on the experimental observation of magnetic skyrmions in Pt/Co/MgO sputtered ultrathin magnetic nanostructures, stable at room temperature without applied magnetic field. XMCD‐PEEM measurements allowed us to observe such skyrmions and to demonstrate their chiral Néel structure. The skyrmion sizes are typically of the order of 120 nm. Our experimental observations are well reproduced by micromagnetic simulations and numerical modelling. This allows the identification of the physical mechanisms governing the size and stability of the skyrmions, which are keys for the design of devices based on their manipulation.
Cathodoluminescence and
EBIC
study of widegap semiconductors and devices
Authors: Sekiguchi Takashi 
Published: December 2016

Cathodoluminescence (CL) and electron‐beam‐induced current (EBIC) are versatile techniques to characterize semiconductor materials and devices. In this talk, we review our achievement on the study of widegap semiconductors, GaN and SiC.

The major defects in GaN are dislocations. GaN wafers on sapphire include dislocations of 10
9
to 10
7
cm
−2
due to lattice mismatch. Fig. 1 shows the secondary electron (SE) and CL images of GaN wafer with different thickness. Such dislocations may agglomerate and form the hexagonal pits of micrometer size. These defects are detrimental for the device performance. Homoepitaxial GaN wafer take over the dislocations of 10
6
cm
−2
from the seeds. We have performed CL study to distinguish dislocation characters and to clarify the effect of dislocations.

The major defects in SiC are threading screw dislocations (TSD) and stacking faults (SF). TSD act as the killer defects due to the surface roughness at the dislocation core region. SF may be generated and expanded due to e‐beam irradiation. EBIC is very effective to characterize these defects in SiC. The e‐beam enhanced defect generation of SF (Fig.2) will be reviewed.
At the end, we demonstrate 3D spectra imaging of CL, which is very promising to analyze the details of extended defects.
This work was supported from “GaN project”, Study of Future Semiconductors for Sustainable Society in MEXT, Japan.
Extreme Nanowires: The Smallest Crystals in the Smallest Nanotubes
Authors: Sloan Jeremy , Kashtiban Reza , Marks Sam , Beanland Richard , Sanchez Ana , Brown Sam , Vasylenko Andrij , Brommer Peter , Morawiec Krzysztof , Kret Slawomir , Medeiros Paulo , Wynn James , Spencer Joe , Smith David , Ramasse Quentin , Liu Zheng , Suenaga Kazu , Morris Andrew , Quigley David , Faulques Eric 
Published: December 2016

A logical extension to fabrication of monolayer 2D materials such as graphene is creation of ‘Extreme Nanowires’ (i.e. Fig. 1), down to a single atom column in width.[1,2] In this limit, crystals have fundamentally different physical characteristics and properties.[3‐5] We and others have created atomically regulated nanowires by confining them within the smallest diameter carbon nanotubes (i.e. either single walled carbon nanotubes (SWNTs) or double walled carbon nanotubes (DWNTs)), and are investigating their structural and electronic properties. These materials also provide an ultimate benchmark for testing the most sensitive characterisation methodologies which, when corroborated with suitable theory, will provide new data on physics at the most fundamental length scale accessible to nanomaterials fabrication. The most powerful investigative tools for structural investigation are aberraton‐corrected Transmission Electron Microscopy (ac‐TEM) and Scanning Transmission Electron Microscopy (ac‐STEM) and, here, we describe the application of these methods to a variety of Extreme Nanowire systems.
One of the most crucial aspects of the role of electron microscopy in our investigation is the 2D and 3D elucidation of the structure of quasi‐ or true 1D nanowires formed in SWNTs as these form the primary source of information for density functional theory (DFT) and other ab initio theoretical approaches to both structure and properties elucidation. When combined with real physical measurements, this combined approach becomes even more powerful as we can start to piece together how the fundamental physics of a crystalline nanowire changes once we constrain its width down to one or two atoms in cross section. For example we recently record Raman Spectra from 2x2 atom thick HgTe nanowires embedded within 1.2‐1.4 nm SWNTs[4] and found that we are able to model the Raman‐measured lattice phonons of this system based on a simple structural model previously determined from two pairs of Exit Wave Reconstruction images which we also used to make DFT predictions about the altered electronic structure of this system which is predicted to change from a ‐0.3 eV semi‐metal to a ~1.2 eV band gap semiconductor.[3] Following on from the exciting recent work of Senga et al.[2] who imaged the first true 1D crystals of CsI in DWNTs we are now modeling single atomic chain coils of tellurium formed within narrow SWNTs (Fig. 2).[6]
From core and valence excitations to orbital mapping: a theorist's perspective
Authors: Draxl Claudia 
Published: December 2016

Ab initio
spectroscopy is a powerful combination of quantum‐based theories and computer simulations, covering a wide range of theoretical and computational methods that incorporate many‐body effects and interactions showing up in the excited state. This framework, combining density‐functional theory (DFT) with many‐body perturbation theory, not only allows for analyzing data obtained by experimental probes, but also for shining light onto the underlying physics. I will demonstrate this with a series of selected materials and excitation processes:

Oxygen K‐edge spectra from the wide‐gap semiconductor Ga
2
O
3
will reveal how signals from atoms located in a particular environment can be selectively enhanced or quenched by adjusting the crystal orientation [1]. These results suggests ELNES, combined with
ab initio
many‐body theory, to be a very powerful technique to characterize complex systems, with sensitivity to individual atomic species and their local environment.

With the example of self‐assembled phases of functionalized azo‐benzene it will be shown, how excitonic effects in core and valence excitations can be tuned by molecular packing [2], and how this may affect the switching functionality of the molecules.
Finally, I will discuss how transmission electron microscopy can be used for mapping atomic orbitals, exploring its capabilities by a first principles approach [3]. For defected graphene, exhibiting either an isolated vacancy or a substitutional nitrogen atom, different kinds of images are to be expected, depending on the orbital character (see Figure 1).
Combining advanced
TEM
techniques for full characterization of extended defects in creep‐deformed single crystal superalloys
Authors: Spiecker Erdmann , Müller Julian , Eggeler Yolita M. , Lenz Malte 
Published: December 2016

Single crystal superalloys are used for turbine blades in the hottest parts of gas engines, where they have to withstand high stresses at temperatures exceeding 1000°C. This is only possible because of the well‐known γ/γ′‐microstructure of these alloys, forming the basis for excellent creep properties [1]. One of the research objectives is to gain a microscopic understanding of the elementary deformation mechanisms and defect processes that govern high‐temperature creep and to use this knowledge for further improvement of single crystal superalloys. Beside Ni‐base superalloys which are well established in applications new Co‐base superalloys have attracted a lot of research interest since the discovery of stable γ/γ′‐microstructure in these alloys in 2006 [2]. Research on Co‐base superalloys is still in its infancy, meaning that there is strong need for fundamental studies on elementary deformation mechanisms and defect processes.
In this contribution we give an overview of our recent research on extended defects that form upon high‐temperature creep in Ni‐ and Co‐base superalloys. We demonstrate that the combination of advanced transmission electron microscopy (TEM) techniques, employing dedicated diffraction, high‐resolution and analytical methods, is generally required for full characterization of such extended defects and for obtaining a complete picture of their role in elementary creep processes.
Figure 1 illustrates an example of full characterization of superdislocations in a Ni‐base superalloy. First, large‐angle convergent beam electron diffraction (LACBED) is employed for reliable determination of the Burgers vector [3], overcoming the well‐known problems of conventional Burgers vector analysis of such dislocations. Secondly, using a new FIB cross‐sectioning technique [4], the core structure of the same dislocation is studied by high‐resolution scanning TEM (HRSTEM). This approach enables scale‐bridging characterization of complex superdislocations on the micrometer and atomic scale.
Figures 2 and 3 summarize advanced TEM studies on extended faults that form upon creep of Ni‐containing Co‐base (CoNi) superalloys [5]. Inside of γ′ precipitates a characteristic defect configuration is observed in which superintrinsic stacking fault (SISF) loops are fully embedded in antiphase boundaries (APB). LACBED is used to determine the full Burgers vector (including sign and magnitude!) of the partial dislocation loop [5]. Pronounced segregation of alloying elements at SISF and APB is revealed by HRSTEM and energy‐dispersive X‐ray spectroscopy (EDXS). Based on these and other results, an elementary creep mechanism is proposed which is characterized by ½<112> slip involving a SISF→APB transformation [5]. Atomic diffusion at creep temperature appears to be a rate limiting step by gradually changing the fault energies which control the kinetics of the transformation.
Unique Reactivity of α‐Substituted Electron‐Deficient Allenes using Sulfinate Salts as Lewis Base Organocatalysts
Authors: Martzel Thomas , Lohier Jean‐François , Gaumont Annie‐Claude , Brière Jean‐François , Perrio Stéphane 
Published: December 2016

AbstractThe efficient sulfinate‐catalyzed intermolecular addition reaction of α‐substituted allenyl sulfones and allenoates with Michael acceptors is highlighted. The sequence proceeds under mild conditions to provide a scalable and efficient access to versatile functionalized alkynes, displaying a quaternary stereocentre at the propargylic position. This work enriches the diversity of Lewis base organocatalysts in the field of allene chemistry, in addition to the well‐established phosphine and amine catalysts.magnified image
Tertiary Amine‐Catalyzed Difluoromethylthiolation of Morita–Baylis–Hillman Carbonates of Isatins with Zard's Trifluoromethylthiolation Reagent
Authors: Fan Xing , Yang Haibin , Shi Min 
Published: December 2016

AbstractIn this paper, we report that a novel tertiary amine‐catalyzed [3+2] annulation between Morita–Baylis–Hillman (MBH) carbonates derived from isatins with thiocarbonyl fluoride (F2C=S) in situ generated from Zard's reagent proceeds smoothly under mild conditions, affording difluoromethylthiolated spirocyclic oxindoles in good to excellent yields. Moreover, the asymmetric variant could be realized with a modified Cinchona alkaloid, giving the desired cyclic adducts in good to excellent yields with good enantioselectivities.magnified image
Diastereoselective Intramolecular Aldol‐Type Trapping of Zwitterionic Intermediates by Ketones for the Synthesis of Spiro[chroman‐4,3′‐oxindole] Derivatives
Authors: Jia Shikun , Lei Yubing , Song Longlong , Krishna Reddy A. Gopi , Xing Dong , Hu Wenhao 
Published: December 2016

AbstractA simple, mild and efficient rhodium‐catalyzed aromatic C–H functionalization of α‐phenoxy ketones by 3‐diazooxindoles for the synthesis of the spiro[chroman‐4,3′‐oxindole] ring system is described. A series of functionalized spiro[chroman‐4,3′‐oxindole] derivatives bearing two adjacent quaternary carbon centers have been attained in a highly diastereoselective manner with very good yields. Control experiments suggested the possibility of an intramolecular aldol‐type trapping of zwitterionic intermediates after the C–H functionalization. Furthermore, the applicability of this method has been tested by a gram‐scale synthesis. A facile treatment with base enabled the access to both syn‐ and anti‐diastereomers via isomerization.magnified image
Connecting the quantum and classical worlds
Authors: Drossel Barbara 
Published: December 2016

By considering (non‐relativistic) quantum mechanics as it is done in practice in particular in condensed‐matter physics, it is argued that a deterministic, unitary time evolution within a chosen Hilbert space always has a limited scope, leaving a lot of room for embedding the quantum‐classical transition into our current theories without recurring to difficult‐to‐accept interpretations of quantum mechanics. Nonunitary projections to initial and final states, the breaking of time‐reversal symmetry, a change of Hilbert space, and the introduction of classical concepts such as external potentials or localized atomic nuclei are widespread in quantum mechanical calculations. Furthermore, quantum systems require classical environments that enable the symmetry breaking that is necessary for creating the atomic configurations of molecules and crystals. This paper argues that such classical environments are provided by finite‐temperature macroscopic systems in which the range of quantum correlations and entanglement is limited. This leads to classical behavior on larger scales, and to collapse‐like events in all dynamical processes that become coupled to the thermalized degrees of freedom.
image
One‐Step Annulative π‐Extension of Alkynes with Dibenzosiloles or Dibenzogermoles by Palladium/o‐chloranil Catalysis
Authors: Ozaki Kyohei , Murai Keiichiro , Matsuoka Wataru , Kawasumi Katsuaki , Ito Hideto , Itami Kenichiro 
Published: December 2016

AbstractReliable and short synthetic routes to polycyclic aromatic hydrocarbons and nanographenes are important in materials science. Herein, we report an efficient one‐step annulative π‐extension reaction of alkynes that provides access to diarylphenanthrenes and related nanographene precursors. In the presence of a cationic palladium/o‐chloranil catalyst system and dibenzosiloles or dibenzogermoles as π‐extending agents, a variety of diarylacetylenes are transformed successfully into 9,10‐diarylphenanthrenes in a single step with good functional‐group tolerance. Furthermore, double π‐extension reactions of 1,4‐bis(phenylethynyl)benzene and diphenyl‐1,3‐butadiyne are demonstrated, affording oligoarylene products, which show potential for application in the synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.
Ribonucleotides and RNA Promote Peptide Chain Growth
Authors: Griesser Helmut , Tremmel Peter , Kervio Eric , Pfeffer Camilla , Steiner Ulrich E. , Richert Clemens 
Published: December 2016

AbstractAll known forms of life use RNA‐mediated polypeptide synthesis to produce the proteins encoded in their genes. Because the principal parts of the translational machinery consist of RNA, it is likely that peptide synthesis was achieved early in the prebiotic evolution of an RNA‐dominated molecular world. How RNA attracted amino acids and then induced peptide formation in the absence of enzymes has been unclear. Herein, we show that covalent capture of an amino acid as a phosphoramidate favors peptide formation. Peptide coupling is a robust process that occurs with different condensation agents. Kinetics show that covalent capture can accelerate chain growth over oligomerization of the free amino acid by at least one order of magnitude, so that there is no need for enzymatic catalysis for peptide synthesis to begin. Peptide chain growth was also observed on phosphate‐terminated RNA strands. Peptide coupling promoted by ribonucleotides or ribonucleotide residues may have been an important transitional form of peptide synthesis that set in when amino acids were first captured by RNA.