bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
Time resolvedHREMofAl crystal surface
Authors: Lereah Yossi , Biskupek Johannes , Kaiser Ute 
Published: December 2016

The crystallization of Ge:Al amorphous films was studied by time resolve TEM intensively in previous years and reported[1]. These studies included the geometry and the dynamics of Al‐amorphous interface with time resolution of 40 milliseconds by conventional bright‐field (BF) and dark‐field (DF) TEM imaging of films of 50 nm thickness and by conventional high resolution (HR) TEM of films of 25nm thickness. The propagation of the Al interface is diffusion controlled, i.e. the velocity is temperature dependent [1]. The Al‐amorphous interface was found to be rough with a fractal dimension of 1.2 for the projected image [2]. However, the quantitative analysis of the interface propagation indicates a long range interaction in the Al‐amorphous phase interface [3]. These interactions were attributed to existence of ramified clusters of Al in the Ge:Al amorphous phase [4].Here we will report on quantitative measurements that were obtained with 5 nm thick films heated locally by the electron beam resulting in the modification of the surface. The quantitative measurements will be based on observations that include aberration corrected HRTEM with low time resolution (1 sec) and by conventional HRTEM with high time resolution (few milliseconds). The later will be used also for evaluating the stability of the interface toward its 3D construction.