bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanoscale characterization of Co and Co‐B catalytic coatings before and after catalytic tests for the sodium borohydride hydrolysis
Authors: Beltrán Ana M , Paladini M , Godinho V , Arzac G.M. , Jimenez de Haro M.C. , Fernández A 
Published: December 2016

The use of hydrogen as a potential future energy carrier is limited due to the problems of its storage. Hydrolysis of hydrogen storage materials such as sodium borohydride (NaBH
4
, SB) has been one of the most investigated approaches for hydrogen generation. SB is stable in dry air and combines lightweight with high hydrogen content (10.8 wt%).

Although spontaneous, the SB hydrolysis (reaction 1) needs catalysts to occur at appreciable rates. Co has demonstrated to be a good choice because its compromise between activity and cost. However, its major drawback is related to stability: these materials deactivate upon cycling. Despite the great number of works reporting Co and Co‐B based catalysts, the nature of the active phase and deactivation mechanisms are still under intense discussion.
We have recently reported the preparation of supported Co metallic catalysts as thin films by magnetron sputtering for sodium borohydride hydrolysis [1]. Magnetron sputtering is a very versatile technique used in this work to fabricate Co and CoB catalytic coatings under different deposition conditions and supported on different substrates (i.e. silicon and polymeric membranes). In this work we have been able to study by electron microscopy the catalytic coatings as grown on the wires of the polymeric membranes. The structural and compositional characterization by SEM and (S)TEM techniques has been performed before and after the catalytic tests (19 wt% SB in NaOH 4 wt%, 90 min reaction time). Fig. 1 and 2 show the SEM morphology of a Co thin film on the polymeric membrane before and after the catalytic test, respectively, showing the growth of a new layer onto the catalysts upon operation. Further nano‐analysis of the structure and compositional distribution have been performed by (S)TEM techniques coupled to EELS. They also reveal the formation of fiber/nanoflake‐like nanostructures onto the catalytic coatings (Fig. 3 and Fig. 4). Compositional analysis have pointed out the formation of Co‐borates and most likely cobalt oxide/hydroxide nanoflakes (i.e. CoO(OH)) which could be the origin of the leaching and deactivation mechanisms of the Co‐based catalysts for the investigated reaction.
Aberration corrected environmental
STEM
(
AC ESTEM
) for atom‐by‐atom analysis of nanoparticle catalyst activation and deactivation mechanisms
Authors: Boyes Edward , Ward Michael , Martin Thomas , Lari Leonardo , Mitchell Robert , LaGrow Alec , Lloyd David , Wright Ian , Gai Pratibha 
Published: December 2016

The core design for the modern ETEM (1, 2), of which there are now some 20 replicates worldwide, has been modified to support full ESTEM functionality and to be compatible with a different basic instrument, in this case the JEOL 2200, with a series of differentially pumped column sections separated by fixed beamline apertures reconfigured for purpose in size and position. Single atom resolved HAADF imaging and full analytical functionalities, including wide angle electron diffraction, CBDP, EDX and EELS, are enabled under controlled chemical reaction conditions of high temperatures in a continuously flowing gas atmosphere around the supported nanoparticle catalysts samples while retaining sub‐Angstrom resolution and single atom sensitivity for atom‐by‐atom analysis of critical processes. The novel AC ESTEM machine at York provides new insights into the processes of metal nanoparticle catalyst activation, operational state and deactivation (3) which have economic and other societal importance, including for scientifically informed environmental management. At typical 2‐20Pa gas pressures the gas supply covers the sample surface with multiple 1000s of monolayers of gas per second and generally fully adequate to continuously flood the surface with gas molecules. They drive the chemistry under conditions defined in surface science as 'high pressure' (4) and minimise e‐beam driven artefacts. Catalysis is a massive industry with highly leveraged investments in processes and plants. However, in many applications, including automotive emission controls (5), it is still relatively inefficient compared to what might be possible with a better informed knowledge base generating strategies to restrain deactivation processes. The unique to York AC ESTEM supports quantitative atom‐by‐atom analysis of the underlying mechanisms of Ostwald Ripening (OR) through atom detachment, migration and re‐attachment at lower temperatures around constant particle centres of gravity (6,). This is compared with (and sometimes mixed with) higher temperature modes of particle migration and coalscence (PMC), with local nanostructure attributes in the round influencing local outcomes. Neither process is found to be sensitive to gas pressure at 2‐20Pa levels. Both mechanisms have now been studied with new levels of precision using the novel capabilities at York; leading to a better informed understanding of the technical problems and options and helping to specify the enabling developments needed going forward.
In vitro hemocompatibility of thin films materials for direct blood contact
Authors: Major Roman , Trembecka‐Wojciga Klaudia , Lackner Jurgen M , Plutecka Hanna 
Published: December 2016

The main objective of the study was modified surface thin film materials deposited on polymer substrate constituting the microenvironment for the uptake and controlled differentiation of stem cells the controlled share caused by residual stress and optimized stiffness of the surface using the plasma methods.
Plasma surface modification method generating a controlled part of residual stress in the coating affect the formation of the surface topography in the form of a nano‐ wrinkles similar to the niches in the tissue environment where stem cells are stored. Niches like structures can catch stem cells from blood flow and prevent their rapid differentiation. Topography and stiffness of the surface of the coating allow for targeted cellular differentiation. The properly formed full confluence of the endothelial cells effectively inhibits blood clotting processes.
The challenge of the work was to develop the surfaces which would mobilize and activate stem and progenitor cells. The idea was to produce the surface containing the niche like structures, the most appropriate structure for the stem cells. The coatings were developed with controlled residual stresses participation, proper microstructure (Fig. 1) and mechanical properties. Controlled share of residual stress created nano‐wrinkles, similar to the niches where stem cells reside in the natural conditions. The creation of stress generated wrinkles did not lead to delaminating of the coating from the substrate. The coating adhered well to the substrate, and wrinkles provided the cellular microenvironment (Fig. 2). The microstructure and mechanical properties were the key factor that determined the controlled cellular differentiation. The differentiation of stem cells was carried out for endothelial cells formation. The following scientific problems were studied: the anchoring mechanisms of the coating to the polymeric substrate, the effect of ion methods for surface modification towards the microenvironment creation for the stem cells and blood‐ material interaction.
Heterogeneous interfacial chemical nature and bonds in an
Al
matrix composite reinforced with
W
‐coated diamond particles
Authors: Gang Ji , Zhanqiu Tan , Yinggang Lu , Dominique Schryvers , Zhiqiang Li 
Published: December 2016

Over the last decade, a diamond particle reinforced Al matrix, namely diamond/Al, composite has been developed for thermal management applications, mainly in the microelectronic industry. This composite has demonstrated an excellent combination of a Thermal Conductivity (TC) as high as 600 W/mK and a Coefficient of Thermal Expansion (CTE) lower than 10 ppm/K, being compatible with that of electronic components. However, considering the TC (~ 1800 W/mK) of the diamond particles incorporated, it is clear that the overall TC enhancement has not been completely exploited in the composite. One then points at the diamond/Al interface, which should provide good adhesion as well as maximal Interfacial Thermal Conductance (ITC) in order to facilitate thermal exchange across the diamond/Al interface.
Our analytical modelling has recently predicted that introduction of a W interface nanolayer is one of the most efficient ways to achieve high ITC, which provides a practical guide for interface engineering. Accordingly, a cost‐effective sol‐gel process has been tentatively used to deposit the W coating for diamond surface metallization. Compared with the diamond/Al counterpart, TC of the composite with such a W nanolayer improved more than 20 %. In this work, Scanning Transmission Electron Microscopy (STEM)/Energy‐Dispersive X‐ray spectroscopy (EDX) and Precession Electron Diffraction (PED) have been performed in order to investigate interface configurations of a W‐coated diamond/Al composite. The aim is to study the effect of interface formation, reaction and diffusion on the ITC.

The results indicate that the deposited W coating is discontinuous, and consists of nanoparticles with a size in the range 30‐400 nm and homogenously covering the surface of the diamond particle (Figs. 1a and 1b). The average coating thickness is estimated to be around 200 nm (Fig. 1c). A STEM/ADF image in Fig. 1d shows that the formed diamond/Al interface has a heterogeneous configuration at the nanoscale where Al grain contrasts and a particle with high Z contrast are revealed. STEM/EDX mapping in Fig. 2 displays a W and Al rich interfacial particle. Visible O traces can be related to fine microstructural features. Alternatively, a 'clean' diamond/Al interface is tightly‐adhered and is not rich in O (Fig. 3). As shown in Fig. 4, PED zone‐axis patterns recorded from the W and Al rich particles are indexed to be the Al
12
W phase (Cubic,
I2/m‐3,
No. 204). Such different chemical nature of the bonds at the interface can have a pronounced effect on the local ITC [1,2].
Structure and viability of atypical morphological forms of
L
yme disease spirochetes
Authors: Vancová Marie , Rudenko Nataliia , Maryna Golovchenko , Strnad Martin , Bílý Tomáš , Grubhoffer Libor , Nebesářová Jana 
Published: December 2016

Spirochetes Borrelia burgdorferi sensu lato are the causative agents of Lyme disease transmitted by the hard ticks of the genus Ixodes. Spirochetes are motile bacteria with typical flat‐wave morphology. These features are crucial for efficient dissemination and evasion of immune responses. However, several reports described presence of non‐motile atypical morphologies, e.g. rod‐shaped forms, looped/ring shaped forms and spherical/cystic forms called round bodies (RBs). These forms were observed in the cerebral cortex of patient with chronic Lyme neuroborreliosis [1]. Recently, we proved long term survival of Borrelia in patients after extended antibiotic treatment by successful isolation of live spirochetes [2].
Now, we would like to answer questions, (i) whether RBs represent resistant forms of persisting Lyme disease spirochetes and (ii) whether the transformation of flat‐waved spirochetes into RBs forms influences the capability to withstand unfavourable environmental conditions.
For this purpose, we studied morphology and three dimensional arrangements of spirochetes isolated from patients by transmission electron microscopy and electron tomography on serial resin sections and negatively stained spirochetes. Next, using a modification of our novel approach combining cryo‐fluorescence and cryo‐scanning electron microscopy, we interconnect viability assay with visualization of morphology at high resolution [3]. Viability of GFP expressing spirochetes in a response to host sera was assessed using propidium iodide exclusion method. Obtained results confirmed different susceptibility to different host sera, previously described by our colleagues [4]. We confirmed the formation/viability of RB forms under specific conditions.
Investigating lattice strain in Au nanodecahedrons
Authors: Goris Bart , De Beenhouwer Jan , De Backer Annick , Zanaga Daniele , Batenburg Joost , Sanchez‐Iglesias Anna , Liz‐Marzan Luis , Van Aert Sandra , Sijbers Jan , Van Tendeloo Gustaaf , Bals Sara 
Published: December 2016

The three dimensional (3D) structural characterization of nanoparticles is crucial in materials science since many properties heavily depend on size, surface to volume ratio and morphology. In addition, the ability to investigate the crystal structure is just as essential because the presence of defects and surface relaxation will directly affect plasmonic or catalytic properties. A well‐known example of strained nanoparticles are the so‐called “nanodecahedra” or “pentagonal bipyramids”. Such particles consist of five segments bound by {111} twin boundaries, yielding a crystallographic forbidden morphology. Therefore, measuring strain fields in nanodecahedra by transmission electron microscopy (TEM) has been the topic of several studies. However, it is important to note that such studies are based on 2D projections, hereby neglecting the 3D nature of the lattice strain. [1,2] Here, we will quantify the lattice strain in 3D based on high resolution electron tomography reconstructions. [3]
Therefore, a continuous tilt series of 2D projection images was acquired using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) and a dedicated alignment procedure was applied. These projection images are then used as an input for a model based tomography reconstruction algorithm. A major disadvantage of conventional reconstruction techniques is that a continuous volume is reconstructed hampering the extraction of atom coordinates without the use of dedicated post‐processing methods. [4] We could overcome this limitation by assuming that the 3D atomic potential can be modelled by 3D Gaussian functions. This hypothesis significantly simplifies the reconstruction problem to a sparse inverse problem, yielding the coordinates of the individual atoms as a direct outcome of the reconstruction.

Visualizations of the final 3D reconstruction, obtained for a Au nanodecahedron containing more than 90,000 atoms, are presented in Figure 1.a–c along different viewing directions. Since the coordinates of the atoms are a direct outcome of the reconstruction, it becomes straightforward to calculate the 3D displacement map. We computed derivatives of the displacement map in such a manner that 3D volumes were obtained corresponding to ε
xx
and ε
zz
. Slices through the resulting ε
xx
and ε
zz
volumes are presented in Figure 1.d and Figure 1.f. Furthermore, the variation of the lattice parameters was investigated along x and z based on the same slices (Figure 1.e and Figure 1.g). Both along the x and z direction a systematic outward expansion of the lattice can be observed. The expansion along z is limited to a few of the outer atomic layers and shows an asymmetry (Figure 1.f–g) that is likely related to the fact that the decahedron is deposited on a carbon support.
Ten years of
EMCD
: what has been achieved
Authors: Schattschneider Peter , Schachinger Thomas , Löffler Stefan 
Published: December 2016

Energy loss magnetic chiral dichroism (EMCD), established in 2006 [1] celebrates its 10
th
anniversary. EMCD is the TEM equivalent of the X‐ray magnetic circular dichroism (XMCD) technique routinely applied on synchrotron beam lines for the study of magnetic moments. The EMCD signal is detected as an asymmetry in the energy filtered diffraction pattern, or alternatively as a slight difference in the fine structure of energy loss spectra for particular momentum transfers in the inelastic interaction (Fig. 1). The extremely high spatial resolution of modern TEMs makes EMCD interesting for spintronic and micromagnetic applications. In the last decade, the technique has evolved into a reliable tool demonstrating nm‐resolution, site selectivity and separation of spin and orbital moments via sum rules.

One of the consequences of EMCD is that the outgoing inelastically scattered probe electrons have topological charge. Structurally, they are identical with vortex electrons that can be routinely created in the electron microscope [2]. Such vortices are characterized by a spiraling wavefront and a phase singularity at the center, similar to optical vortices that were first described by Nye & Berry [3]. Owing to their short wavelength, these matter waves can be focused to atomic size. Another novel aspect is their magnetic moment, quantized in multiples of the Bohr magneton, independent of the electron spin. These features make electron vortices extremely attractive as a nanoscale probe for magnetic materials.
The discovery of vortex electron beams has spurred efforts to use them for EMCD because of their intrinsic chirality. It became soon clear that atom‐sized vortices are needed to achieve this goal [4], as shown in Fig. 2. At the time of writing, the closest successful approach to such beams is the shaping of the incident wave front with a Cs corrector such that it matches the point group symmetry of the selected atomic column, revealing EMCD signals with atomic resolution [5]. A promising alternative is the use of holographic vortex filters in the outgoing beam to detect spin polarized transitions [6], as sketched in Fig. 3. Other than in the standard EMCD geometry, this approach does not require a precise alignment of the crystal, and would thus allow the study of nanocrystalline and amorphous materials.
3D Mapping of electric potentials and magnetic fields at the nanoscale using Electron Holographic Tomography
Authors: Wolf Daniel , Lubk Axel , Lichte Hannes 
Published: December 2016

Off‐axis electron holography (EH) is a TEM technique that records the phase information of an electron wave transmitted through a thin specimen in an electron hologram. By reconstructing this phase information, it enables electrostatic and magnetic potentials to be mapped quantitatively with high spatial resolution and, when combined with tomography to electron holographic tomography (EHT), in three dimensions (3D) [1,2]. Tomograms obtained by EHT provide the 3D mean inner potential (MIP) distribution of nanoscale materials from which the 3D morphology and the chemical composition can be inferred [3]. Moreover, functional potentials,
e.g
., introduced by doping of impurities in semiconductors, have been successfully revealed in 3D [4]. Recently, we succeeded in the 3D reconstruction of the axial component of the B‐field prevailing in magnetic nanowires [5,6].

EHT as applied on magnetic samples proceeds as follows (see Fig. 1): (1) an electron hologram tilt series (ideally covering a range of 360°) is acquired, (2) the phase image tilt series is reconstructed from the holograms, (3) electric and magnetic phase shifts are separated by computing half of the sum/difference between opposite (180° tilted) projections, and (4) both the electric potential and the B‐field component parallel to the tilt axis are reconstructed with tomographic techniques. Here, we report EHT studies achieved by means of tomography‐dedicated TEM sample holders, in combination with advanced in‐house developed software packages for acquisition, alignment and tomographic reconstruction.
Fig. 2 shows the 3D electric potential reconstruction of a GaAs/AlGaAs core‐multishell nanowire (NW) grown by metalorganic vapour phase epitaxy (MOVPE) using an Au nanoparticle (NP) as catalyst. Such NWs may serve as novel coherent nanoscale light sources (lasers), because they provide an effective gain medium, low‐loss optical waveguiding, and strong optical confinement for axially guided optical modes. The difference in the MIP allows discriminating between GaAs and AlGaAs within the NW. Longitudinal (Fig. 2b) and cross‐sectional (Fig. 2e) 2D slices averaged over a well‐defined thickness reveal not only the GaAs core and the AlGaAs shell, but also a 5nm thin GaAs shell within the AlGaAs, which acts as a quantum well.

Fig. 3 comprises two recent EHT studies revealing the B‐field within a Co nanowire (NW) [5] and a Co
2
FeGa Heusler alloy NW [6] both with spatial resolution higher than 10 nm. The reconstructions of the dominant axial component of the magnetic induction exhibit a small inversion domain at the apex of the Co NW, whereas at the Co
2
FeGa NW, a magnetic dead layer of 10 nm width could be revealed.

The powerful approach presented here is widely applicable to a broad range of 3D electric and magnetic nanostructures and may trigger the progress of novel nanodevices.
Electron beam lithography for the realization of electron beam vortices with large topological charge ( L=1000ħ)
Authors: Mafakheri Erfan , Tavabi Amir , Lu Penghan , Balboni Roberto , Venturi Federico , Menozzi Claudia , Gazzadi Gian Carlo , Frabboni Stefano , Boyd Robert , Dunin‐Borkowski Rafal , Karimi Ebrahim , Grillo Vincenzo 
Published: December 2016

Electron vortex beams (EVBs) are an appealing topic, both in fundamental science and for practical applications in electron microscopy [1, 2]. Some of the most promising applications require beams that have large orbital angular momentum (OAM) [2, 3, 4]. Here, we demonstrate the largest (L=1000 ħ) high quality EVB by using electron beam lithography (EBL) to fabricate a phase hologram. EBL provides superior fabrication quality and a larger number of addressable points when compared with focused ion beam (FIB) milling. We measure the OAM of the generated EVB through propagation after a hard aperture cut [5]. Comparisons with simulations confirm an average OAM of (960±120)ħ , which is consistent with the intended value.
A clear improvement when compared with a FIB‐nanofabricated hologram is demonstrated in terms of 1) the maximum OAM that can be reached; 2) the minimum feature size (33 nm in the present study); 3) the improved uniformity of the frequency response; 4) the better suppression of higher order diffraction due to a nearly perfect rectangular groove profile.
We believe that EBL will be the fabrication technique of choice for most new diffractive optics with electrons in the future, permitting more complex holograms and new applications in material science.