Abstract: A new approach to generate differential phase contrast (DPC) images for the visualization and quantification of local magnetic fields in a wide range of modern nano materials is reported. In contrast to conventional DPC methods our technique utilizes the idea of a unitary detector under bright field conditions, making it immediately usable by a majority of modern transmission electron microscopes. The approach is put on test to characterize the local magnetization of cylindrical nanowires and their 3D ordered arrays, revealing high sensitivity of our method in a combination with nanometer-scale spatial resolution.

Abstract: Knowledge about the synthesis, growth mechanisms, and physical properties of colloidal nanoparticles has been limited by technical impediments. We introduce a method for determining three-dimensional (3D) structures of individual nanoparticles in solution. We combine a graphene liquid cell, high-resolution transmission electron microscopy, a direct electron detector, and an algorithm for single-particle 3D reconstruction originally developed for analysis of biological molecules. This method yielded two 3D structures of individual platinum nanocrystals at near-atomic resolution. Because our method derives the 3D structure from images of individual nanoparticles rotating freely in solution, it enables the analysis of heterogeneous populations of potentially unordered nanoparticles that are synthesized in solution, thereby providing a means to understand the structure and stability of defects at the nanoscale.

Abstract: Quantitative annular dark field scanning transmission electron microscopy (ADF STEM) has become a powerful technique to characterise nano-particles on an atomic scale. Because of their limited size and beam sensitivity, the atomic structure of such particles may become extremely challenging to determine. Therefore keeping the incoming electron dose to a minimum is important. However, this may reduce the reliability of quantitative ADF STEM which will here be demonstrated for nano-particle atom-counting. Based on experimental ADF STEM images of a real industrial catalyst, we discuss the limits for counting the number of atoms in a projected atomic column with single atom sensitivity. We diagnose these limits by combining a thorough statistical method and detailed image simulations.

Abstract: Vertical stacking of two-dimensional (2D) crystals has recently attracted substantial interest due to unique properties and potential applications they can introduce. However, little is known about their microstructure because fabrication of the 2D heterostructures on a rigid substrate limits one's ability to directly study their atomic and chemical structures using electron microscopy. This study demonstrates a unique approach to create atomically thin freestanding van der Waals heterostructures-WSe2/graphene and MoS2/graphene-as ideal model systems to investigate the nucleation and growth mechanisms in heterostructures. In this study, we use transmission electron microscopy (TEM) imaging and diffraction to show epitaxial growth of the freestanding WSe2/graphene heterostructure, while no epitaxy is maintained in the MoS2/graphene heterostructure. Ultra-high-resolution aberration-corrected scanning transmission electron microscopy (STEM) shows growth of monolayer WSe2 and MoS2 triangles on graphene membranes and reveals their edge morphology and crystallinity. Photoluminescence measurements indicate a significant quenching of the photoluminescence response for the transition metal dichalcogenides on freestanding graphene, compared to those on a rigid substrate, such as sapphire and epitaxial graphene. Using a combination of (S)TEM imaging and electron diffraction analysis, this study also reveals the significant role of defects on the heterostructure growth. The direct growth technique applied here enables us to investigate the heterostructure nucleation and growth mechanisms at the atomic level without sample handling and transfer. Importantly, this approach can be utilized to study a wide spectrum of van der Waals heterostructures.

Abstract: Using aberration corrected scanning transmission electron microscopy combined with advanced imaging methods, we directly observe atom column specific, picometer-scale displacements induced by local chemistry in a complex oxide solid solution. Displacements predicted from density functional theory were found to correlate with the observed experimental trends. Further analysis of bonding and charge distribution was used to clarify the mechanisms responsible for the detected structural behavior. By extending the experimental electron microscopy measurements to previously inaccessible length scales, we identified correlated atomic displacements linked to bond differences within the complex oxide structure.

Abstract: By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmission electron microscopy (STEM) is currently crossing the border to probing subatomic details. A major challenge is the measurement of atomic electric fields using differential phase contrast (DPC) microscopy, traditionally exploiting the concept of a field-induced shift of diffraction patterns. Here we present a simplified quantum theoretical interpretation of DPC. This enables us to calculate the momentum transferred to the STEM probe from diffracted intensities recorded on a pixel array instead of conventional segmented bright-field detectors. The methodical development yielding atomic electric field, charge and electron density is performed using simulations for binary GaN as an ideal model system. We then present a detailed experimental study of SrTiO3 yielding atomic electric fields, validated by comprehensive simulations. With this interpretation and upgraded instrumentation, STEM is capable of quantifying atomic electric fields and high-contrast imaging of light atoms.

Abstract: Although the overall atomic structure of a nanoscale crystal is in principle accessible by modern transmission electron microscopy, the precise determination of its surface structure is an intricate problem. Here, we show that aberration-corrected transmission electron microscopy, combined with dedicated numerical evaluation procedures, allows the three-dimensional shape of a thin MgO crystal to be determined from only one single high-resolution image. The sensitivity of the reconstruction procedure is not only sufficient to reveal the surface morphology of the crystal with atomic resolution, but also to detect the presence of adsorbed impurity atoms. The single-image approach that we introduce offers important advantages for three-dimensional studies of radiation-sensitive crystals.

Abstract: Surface in and ex situ analysis have shown that in the course of cathodic oxygen reduction (ORR), all along the reversible potential range (the low slope Tafel plots, about 30 mVs/dec), nanostructured Pt electrocatalyst is covered by the interfering primary (Pt-OH) and surface (Pt═O) oxide mixture, while the higher polarization (120 mVs/dec) characterizes electrocatalytic surface deprived from these oxides and, consequently, the reaction mechanism of direct electron exchange on clean electrode surface. The substantial difference between the standard RHE (reversible hydrogen electrode) and ROE (reversible oxygen electrode), is that the former implies spontaneous hydrogen adsorption, fast H-adatoms (Pt-H) effusion and reversible electrode behavior (Pt(H2)/Pt-H/H3O+), while the latter features the strong irreversible Pt═O adsorptive strength, and which is more significant, missing the Pt-OH spillover within the critical potential range between the primary oxide adsorption/desorption peaks position and oxygen evolving limits in both potentiodynamic scan directions (or the imposed polarization energy barrier of about 600 mVs). Since the Pt-OH presence and spillover are unavoidable decisive and indispensable for establishing the ROE properties, and thermodynamic electrode equilibrium (Pt(O2)/Pt-OH/Pt═O/OH-), within the pronounced high polarization broad potential range, such spillover species has the same meaning and significance for the ROE as Pt-H plays for the RHE. Thence, to fill such a high polarization gap, the guiding concept implies homogeneous nanostructured distribution and selective grafting while interactive hypo-hyper-d-d-interelectronic bonding of Pt nanoclusters upon various mixed valence hypo-d-oxide supports, primarily Nb2O5,TiO2 (or Ta2O5,TiO2), because of their much thermally advanced electronic conductivity and extra high stability. In such a constellation, nanoparticles of Pt and solid oxides establish the so-called SMSIs (strong metal-support interactions), the strongest ones in all of chemistry, together with advanced electron conductive transfer, while the exposed surface of the latter undergoes spontaneous dissociative adsorption of water molecules (Nb2O5 → 2 Nb(OH)5), and thereby becomes, along with continuous further water vapor supply, the undisturbed and almost unlimited, (alike electrons in metals) renewable latent storage and spillover source of the Pt-OH all along the potential axis between oxygen and hydrogen evolving limits, with inexhaustible abilities of further optimizations. The reversible alterpolar changes instantaneously result by the spillover of H-adatoms with corresponding bronze type (Pt/HxNbO5, x ≈ 0.3) electrocatalysts under cathodic, and/or its hydrated state (Pt/Nb(OH)5), responsible for Pt-OH effusion, under anodic polarization. This way there establishes the reversibly revertible alterpolar bronze features (Pt/HxNbO5 ↔ Pt/Nb(OH)5), as the thermodynamic equilibrium, and thereby substantially advanced electrocatalytic properties of these composite interactive electrocatalysts for both oxygen and hydrogen electrode reactions, in particular unique and superior for the revertible (proton exchange membrane fuel cell (PEMFC) versus water electrolysis (WE)) cells.

Abstract: The realization of superconductivity at the interface between a topological insulator and an iron-chalcogenide compound is highly attractive for exploring several recent theoretical predictions involving these two new classes of materials. Here we report transport measurements on a Bi2Te3/FeTe heterostructure fabricated via van der Waals epitaxy, which demonstrate superconductivity at the interface, which is induced by the Bi2Te3 epilayer with thickness even down to one quintuple layer, though there is no clear-cut evidence that the observed superconductivity is induced by the topological surface states. The two-dimensional nature of the observed superconductivity with the highest transition temperature around 12 K was verified by the existence of a Berezinsky-Kosterlitz-Thouless transition and the diverging ratio of in-plane to out-plane upper critical field on approaching the superconducting transition temperature. With the combination of interface superconductivity and Dirac surface states of Bi2Te3, the heterostructure studied in this work provides a novel platform for realizing Majorana fermions.

Abstract: Dimensionality has a significant impact on the optical properties of solid-state nanostructures. For example, dimensionality-dependent carrier confinement in semiconductors leads to the formation of quantum wells, quantum wires and quantum dots. While semiconductor properties are governed by excitonic effects, the optical response of metal nanostructures is dominated by surface plasmons. Here we find that, in contrast to excitonic systems, the mode dispersions in plasmonic structures of different dimensionality are related by simple scaling rules. Employing electron energy loss spectroscopy, we show that the modes of silver nanodisks can be scaled to the surface and edge modes of extended silver thin films. We thereby introduce a general and intuitive ordering scheme for plasmonic excitations with edge and surface modes as the elementary building blocks.

Abstract: Metallic nanoparticles exhibit plasmon resonances, which are collective, coherent oscillations of their conduction electrons that can couple very efficiently to light. Originally a subfield of condensed-matter physics, the past decade has seen tremendous growth of plasmonics as an interdisciplinary field spanning chemistry, materials science, and biology. On page 1496 of this issue, Tan  et al.  ( 1 ) discuss an experiment that will almost certainly further fuel this growth-the coupling of plasmon excitations to molecular conduction. The merging of plasmonics with molecular electronics promises both novel fundamental discoveries and new applications.

Abstract: Quantum tunneling between two plasmonic resonators links nonlinear quantum optics with terahertz nanoelectronics. We describe the direct observation of and control over quantum plasmon resonances at length scales in the range 0.4 to 1.3 nanometers across molecular tunnel junctions made of two plasmonic resonators bridged by self-assembled monolayers (SAMs). The tunnel barrier width and height are controlled by the properties of the molecules. Using electron energy-loss spectroscopy, we directly observe a plasmon mode, the tunneling charge transfer plasmon, whose frequency (ranging from 140 to 245 terahertz) is dependent on the molecules bridging the gaps.

Abstract: Elemental mapping using energy-dispersive x-ray spectroscopy in scanning transmission electron microscopy, a well-established technique for precision elemental concentration analysis at submicron resolution, was first demonstrated at atomic resolution in 2010. However, to date atomic resolution elemental maps have only been interpreted qualitatively because the elastic and thermal scattering of the electron probe confounds quantitative analysis. Accounting for this scattering, we present absolute scale quantitative comparisons between experiment and quantum mechanical calculations for both energy dispersive x-ray and electron energy-loss spectroscopy using off-axis reference measurements. The relative merits of removing the scattering effects from the experimental data against comparison with direct simulations are explored.

Abstract: Fabricating stable functional devices at the atomic scale is an ultimate goal of nanotechnology. In biological processes, such high-precision operations are accomplished by enzymes. A counterpart molecular catalyst that binds to a solid-state substrate would be highly desirable. Here, we report the direct observation of single Si adatoms catalyzing the dissociation of carbon atoms from graphene in an aberration-corrected high-resolution transmission electron microscope (HRTEM). The single Si atom provides a catalytic wedge for energetic electrons to chisel off the graphene lattice, atom by atom, while the Si atom itself is not consumed. The products of the chiseling process are atomic-scale features including graphene pores and clean edges. Our experimental observations and first-principles calculations demonstrated the dynamics, stability, and selectivity of such a single-atom chisel, which opens up the possibility of fabricating certain stable molecular devices by precise modification of materials at the atomic scale.

Abstract: The controlled patterning of anisotropic gold nanoparticles is of crucial importance for many applications related to their optical properties. In this paper, we report that gold nanorods prepared by a seed-mediated synthesis protocol (without any further functionalization) can be selectively deposited on hydrophilic parts of hydrophobic-hydrophilic contrast patterned substrates. We have seen that, when nanorods with lengths much smaller than the width of the hydrophilic stripe are used, they disperse on these stripes with random orientation and tunable uniform particle separation. However, for nanorods having lengths comparable to the width of the hydrophilic stripes, confinement-induced alignment occurs. We observe that different interactions governing the assembly forces can be modulated by controlling the concentration of assembling nanorods and the width of the hydrophilic stripes, leading to markedly different degrees of alignment. Our strategy can be replicated for other anisotropic nanoparticles to produce well-controlled patterning of these nanoentities on surfaces.

Abstract: A great variety of single- and multi-component nanocrystals (NCs) can now be synthesized and integrated into nanocrystal superlattices. However, the thermal and temporal stability of these superstructures and their components can be a limiting factor for their application as functional devices. On the other hand, temperature induced reconstructions can also reveal opportunities to manipulate properties and access new types of nanostructures. In situ atomically resolved monitoring of nanomaterials provides insight into the temperature induced evolution of the individual NC constituents within these superstructures at the atomic level. Here, we investigate the effect of temperature annealing on 2D square and hexagonal arrays of FexO/CoFe2O4 core/shell NCs by in situ heating in a transmission electron microscope (TEM). Both cubic and spherical NCs undergo a core-shell reconfiguration at a temperature of approximately 300 ° C, whereby the FexO core material segregates at the exterior of the CoFe2O4 shell, forming asymmetric dumbbells ('snowman-type' particles) with a small FexO domain attached to a larger CoFe2O4 domain. Upon continued annealing, the segregated FexO domains form bridges between the CoFe2O4 domains, followed by coalescence of all domains, resulting in loss of ordering in the 2D arrays.

Abstract: Accumulation of carbonaceous deposits (also known industrially as "coke") on catalytic active sites derived from process conditions has been a long-standing problem in industrial catalysis. Over accumulation of the deposits ultimately lead to deactivation; thus, characterization of coke evolution becomes critical toward developing catalytic materials with improved stability. This study focuses on extending an understanding of how and where coke forms on Pt−Re/γ-Al2O3, an industrial catalyst used in reforming processes. With the use of spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) and enhanced energy dispersive X-ray spectroscopy (EDX), we characterize the Pt−Re metal sites and show, to our knowledge, the first examples of chemically imaged subnanometer particles and also the first to use chemical maps to identify coke location on a catalyst. A two-step mechanism is reported based on the results whereby coke appears to stream from the metal function of the catalyst resulting in heterogeneous coverage.

Abstract: A fast method for determination of the Co-valence state by electron energy loss spectroscopy in a transmission electron microscope is presented. We suggest the distance between the Co-L3 and Co-L2 white-lines as a reliable property for the determination of Co-valence states between 2+ and 3+. The determination of the Co-L2,3 white-line distance can be automated and is therefore well suited for the evaluation of large data sets that are collected for line scans and mappings. Data with a low signal-to-noise due to short acquisition times can be processed by applying principal component analysis. The new technique was applied to study the Co-valence state of Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF), which is hampered by the superposition of the Ba-M4,5 white-lines on the Co-L2,3 white-lines. The Co-valence state of the cubic BSCF phase was determined to be 2.2+ (±0.2) after annealing for 100 h at 650°C, compared to an increased valence state of 2.8+ (±0.2) for the hexagonal phase. These results support models that correlate the instability of the cubic BSCF phase with an increased Co-valence state at temperatures below 840°C.

Abstract: Accumulation of carbonaceous deposits (also known industrially as "coke") on catalytic active sites derived from process conditions has been a long-standing problem in industrial catalysis. Over accumulation of the deposits ultimately lead to deactivation; thus, characterization of coke evolution becomes critical toward developing catalytic materials with improved stability. This study focuses on extending an understanding of how and where coke forms on Pt-Re/γ-Al2O3, an industrial catalyst used in reforming processes. With the use of spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) and enhanced energy dispersive X-ray spectroscopy (EDX), we characterize the Pt-Re metal sites and show, to our knowledge, the first examples of chemically imaged subnanometer particles and also the first to use chemical maps to identify coke location on a catalyst. A two-step mechanism is reported based on the results whereby coke appears to stream from the metal function of the catalyst resulting in heterogeneous coverage.

Abstract: The experimental search for magnetic monopole particles  has, so far, been in vain. Nevertheless, these elusive particles of magnetic charge have fuelled a rich field of theoretical study . Here, we created an approximation of a magnetic monopole in free space at the end of a long, nanoscopically thin magnetic needle . We experimentally demonstrate that the interaction of this approximate magnetic monopole field with a beam of electrons produces an electron vortex state, as theoretically predicted for a true magnetic monopole. This fundamental quantum mechanical scattering experiment is independent of the speed of the electrons and has consequences for all situations where electrons meet such monopole magnetic fields, as, for example, in solids. The set-up not only shows an attractive way to produce electron vortex states but also provides a unique insight into monopole fields and shows that electron vortices might well occur in unexplored solid-state physics situations.

Abstract: Theoretical studies exist to compute the atomic arrangement in gold nanowires and the influence on their electronic behavior with decreasing diameter. Experimental studies,  e.g. , by transmission electron microscopy, on chemically synthesized ultrafine wires are however lacking owing to the unavailability of suitable protocols for sample preparation and the stability of the wires under electron beam irradiation. In this work, we present an atomic scale structural investigation on quantum single crystalline gold nanowires of 2 nm diameter, chemically prepared on a carbon film grid. Using low dose aberration-corrected high resolution (S)TEM, we observe an inhomogeneous strain distribution in the crystal, largely concentrated at the twin boundaries and the surface along with the presence of facets and surface steps leading to a noncircular cross section of the wires. These structural aspects are critical inputs needed to determine their unique electronic character and their potential as a suitable catalyst material. Furthermore, electron-beam-induced structural changes at the atomic scale, having implications on their mechanical behavior and their suitability as interconnects, are discussed.

Abstract: The atomic structure and interfaces of CdS/Cu 2 S heterostructured nanorods are investigated with the aberration-corrected TEAM 0.5 electron microscope operated at 80 kV and 300 kV applying in-line holography and complementary techniques. Cu 2 S exhibits a low-chalcocite structure in pristine CdS/Cu2S nanorods. Under electron beam irradiation the Cu 2 S phase transforms into a high-chalcocite phase while the CdS phase maintains its wurtzite structure. Time-resolved experiments reveal that Cu + -Cd2 2+  cation exchange at the CdS/Cu 2 S interfaces is stimulated by the electron beam and proceeds within an undisturbed and coherent sulfur sub-lattice. A variation of the electron beam current provides an efficient way to control and exploit such irreversible solid-state chemical processes that provide unique information about system dynamics at the atomic scale. Specifically, we show that the electron beam-induced copper-cadmium exchange is site specific and anisotropic. A resulting displacement of the CdS/Cu 2 S interfaces caused by beam-induced cation interdiffusion equals within a factor of 3-10 previously reported Cu diffusion length measurements in heterostructured CdS/Cu 2 S thin film solar cells with an activation energy of 0.96 eV.

Abstract: Stimulus-responsive shape-memory materials have attracted tremendous research interests recently, with much effort focused on improving their mechanical actuation. Driven by the needs of nanoelectromechanical devices, materials with large mechanical strain, particularly at nanoscale level, are therefore desired. Here we report on the discovery of a large shape-memory effect in bismuth ferrite at the nanoscale. A maximum strain of up to ~14% and a large volumetric work density of ~600±90 J cm −3  can be achieved in association with a martensitic-like phase transformation. With a single step, control of the phase transformation by thermal activation or electric field has been reversibly achieved without the assistance of external recovery stress. Although aspects such as hysteresis, microcracking and so on have to be taken into consideration for real devices, the large shape-memory effect in this oxide surpasses most alloys and, therefore, demonstrates itself as an extraordinary material for potential use in state-of-art nanosystems.

Abstract: We present a tomography technique which couples scanning transmission electron microscopy (STEM) and X-ray energy dispersive spectrometry (XEDS) to resolve 3D distribution of elements in nanoscale materials. STEM imaging when combined with XEDS mapping using a symmetrically arranged XEDS detector design around the specimen overcomes many of the obstacles in 3D chemical imaging of nanoscale materials and successfully elucidates the 3D chemical information in a large field of view of the transmission electron microscopy (TEM) sample. We employed this technique to investigate 3D distribution of Nickel (Ni), Manganese (Mn) and Oxygen (O) in a Li 1.2 Ni 0.2 Mn 0.6 O 2  (LNMO) nanoparticle used as a cathode material in Lithium (Li) ion batteries. For this purpose, 2D elemental maps were acquired for a range of tilt angles and reconstructed to obtain 3D elemental distribution in an isolated LNMO nanoparticle. The results highlight the strength of this technique in 3D chemical analysis of nanoscale materials by successfully resolving Ni, Mn and O elemental distributions in 3D and discovering the new phenomenon of Ni surface segregation in this material. Furthermore, the comparison of simultaneously acquired high angle annular dark field (HAADF) STEM and XEDS STEM tomography results shows that XEDS STEM tomography provides additional 3D chemical information of the material especially when there is low atomic number ( Z ) contrast in the material of interest.

Abstract: Dislocations, one of the key entities in materials science, govern the properties of any crystalline material. Thus, understanding their life cycle, from creation to annihilation via motion and interaction with other dislocations, point defects and surfaces, is of fundamental importance. Unfortunately, atomic-scale investigations of dislocation evolution in a bulk object are well beyond the spatial and temporal resolution limits of current characterization techniques. Here we overcome the experimental limits by investigating the two-dimensional graphene in an aberration-corrected transmission electron microscope, exploiting the impinging energetic electrons both to image and stimulate atomic-scale morphological changes in the material. The resulting transformations are followed  in situ , atom-by-atom, showing the full life cycle of a dislocation from birth to annihilation. Our experiments, combined with atomistic simulations, reveal the evolution of dislocations in two-dimensional systems to be governed by markedly long-ranging out-of-plane buckling.

Abstract: Developments in semiconductor technology are propelling the dimensions of devices down to 10 nm, but facing great challenges in manufacture at the sub-10 nm scale. Nanotechnology can fabricate nanoribbons from two-dimensional atomic crystals, such as graphene, with widths below the 10 nm threshold, but their geometries and properties have been hard to control at this scale. Here we find that robust ultrafine molybdenum-sulfide ribbons with a uniform width of 0.35 nm can be widely formed between holes created in a MoS2 sheet under electron irradiation.  In situ  high-resolution transmission electron microscope characterization, combined with first-principles calculations, identifies the sub-1 nm ribbon as a Mo5S4 crystal derived from MoS2, through a spontaneous phase transition. Further first-principles investigations show that the Mo5S4 ribbon has a band gap of 0.77 eV, a Young's modulus of 300GPa and can demonstrate 9% tensile strain before fracture. The results show a novel top-down route for controllable fabrication of functional building blocks for sub-nanometre electronics.

Abstract: A new STEM XEDS tomography technique is proposed thanks to the implementation of multi EDX SDD detectors in analytical TEMs. The technique flow is presented and the first results obtained on a 28 nm FDSOI transistor are detailed. The latter are compared with 2D XEDS analysis to demonstrate the interest of the slice extraction in all directions from a large analyzed volume without any 3D overlap effect issues.

Abstract: Scanning-Transmission and Transmission Electron Microscopy techniques (STEM and TEM) have been applied to the characterization of nanostructured gadolinium oxides doped with europium synthesized by spray pyrolysis. The High Angle Annular Dark Field (HAADF) - Scanning Transmission Electron Microscopy (STEM) tools have been used to perform a tomographic study to identify morphological characteristics of nanostructured particles, and to differentiate them according to the heat treatments to which these have been subjected. With these techniques it has been possible to confirm the hollowness and porous nature of samples subjected to low temperature annealing (900 °C). Moreover, the beginning of the densification and sintering processes in samples subjected to thermal treatment at higher temperature (1100 °C) have been evaluated. Chemical analysis by electron energy loss spectroscopy (EELS) and X ray energy dispersive spectroscopy (EDS) carried out in STEM mode have allowed to confirm the high uniformity and the expected chemical composition. The high resolution tools either allowed to confirm the presence of a cubic (Ia3 symmetry) and the monoclinic (c2/m symmetry) phases in the nanostructured particles.

Abstract: Dislocations and their interactions strongly influence many material properties, ranging from the strength of metals and alloys to the efficiency of light-emitting diodes and laser diodes.  Several experimental methods can be used to visualize dislocations. Transmission electron microscopy (TEM) has long been used to image dislocations in materials , and high-resolution electron microscopy can reveal dislocation core structures in high detail , particularly in annular dark-field mode . A TEM image, however, represents a two-dimensional projection of a three-dimensional (3D) object (although stereo TEM provides limited information about 3D dislocations ). X-ray topography can image dislocations in three dimensions, but with reduced resolution . Using weak-beam dark-field TEM and scanning TEM , electron tomography has been used to image 3D dislocations at a resolution of about five nanometres . Atom probe tomography can offer higher-resolution 3D characterization of dislocations, but requires needle-shaped samples and can detect only about 60 per cent of the atoms in a sample . Here we report 3D imaging of dislocations in materials at atomic resolution by electron tomography. By applying 3D Fourier filtering together with equal-slope tomographic reconstruction, we observe nearly all the atoms in a multiply twinned platinum nanoparticle. We observed atomic steps at 3D twin boundaries and imaged the 3D core structure of edge and screw dislocations at atomic resolution. These dislocations and the atomic steps at the twin boundaries, which appear to be stress-relief mechanisms, are not visible in conventional two-dimensional projections. The ability to image 3D disordered structures such as dislocations at atomic resolution is expected to find applications in materials science, nanoscience, solid-state physics and chemistry.

Abstract: The celebrated electronic properties of graphene have opened the way for materials just one atom thick to be used in the post-silicon electronic era . An important milestone was the creation of heterostructures based on graphene and other two-dimensional crystals, which can be assembled into three-dimensional stacks with atomic layer precision . Such layered structures have already demonstrated a range of fascinating physical phenomena , and have also been used in demonstrating a prototype field-effect tunnelling transistor , which is regarded to be a candidate for post-CMOS (complementary metal-oxide semiconductor) technology. The range of possible materials that could be incorporated into such stacks is very large. Indeed, there are many other materials with layers linked by weak van der Waals forces that can be exfoliated and combined together to create novel highly tailored heterostructures. Here, we describe a new generation of field-effect vertical tunnelling transistors where two-dimensional tungsten disulphide serves as an atomically thin barrier between two layers of either mechanically exfoliated or chemical vapour deposition-grown graphene. The combination of tunnelling (under the barrier) and thermionic (over the barrier) transport allows for unprecedented current modulation exceeding 1 × 10 6  at room temperature and very high ON current. These devices can also operate on transparent and flexible substrates.

Abstract: The crystal structure of SrCo 0.7 Fe 0.2 Nb 0.1 O 2.72 was determined using a combination of precession electron diffraction (PED), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and spa-tially resolved electron energy loss spectroscopy (STEM-EELS). The structure has a tetragonal P4/mmm symmetry with cell parameters a ¼ b ¼ a p , c ¼ 2a p (a p being the cell parameter of the perovskite parent structure). Octahedral BO 2 layers alternate with the anion-deficient BO 1.4 layers, the dif-ferent B cations are randomly distributed over both layers. The specific feature of the SrCo 0.7 Fe 0.2 Nb 0.1 O 2.72 microstruc-ture is a presence of extensive nanoscale twinning resulting in domains with alignment of the tetragonal c-axis along all three cubic direction of the perovskite subcell.

Abstract: We report the observation of an unusual phase assembly behavior during the growth of hexagonal LuFeO3thin films which resulted in the formation of epitaxial Fe3O4 nanolayers. The magnetite layers were up to 5 nm thick and grew under the conditions at which Fe2O3 is thermodynamically stable. These Fe3O4nanolayers act as buffer layers promoting a highly epitaxial growth of the hexagonal LuFeO3 thin film up to 150 nm thick. Using scanning transmission electron microscopy, we show that the interface between (001) LuFeO3 and (111) Fe3O4 can be reconstructed in two ways depending on the sequence in which these compounds grow on each other. We suggest the polarity of the interface is the reason behind the observed interface reconstruction and epitaxial stabilization of magnetite.

Abstract: We present a detailed investigation on the nature of the interfacial layer (IL) in ultra-thin TiN/LaLuO3 (LLO) gate stacks, which is of importance to facilitate CMOS scaling. The molecular beam deposited LaLuO3films are found to be amorphous by high-resolution transmission electron microscopy. A ∼9 Å thick LaLuO3/interlayer transition observed by medium energy ion scattering correlates with the presence of a dual silicate/SiO2-like interfacial layer derived from the analysis of photoelectron line positions and electron energy loss spectra. A theoretical model is used for the dielectric transition in a bi-layer LaLuO3/IL structure, linking physical and electrical characterization data. The obtained leakage current of 10−3 A/cm2 at 1.5 V and equivalent oxide thickness of 0.75 nm for TiN/LaLuO3 gate stacks are adequate for scaling in the 14-12 nm node. 

Abstract: We assess the imaging performance of a transmission electron microscopy (TEM) system operated at a relatively low acceleration voltage using the three-dimensional (3D) Fourier transform of through-focus images. Although a single diffractogram and the Thon diagram cannot distinguish between the linear and non-linear TEM imaging terms, the 3D Fourier transform allows us to evaluate linear imaging terms, resulting in a conclusive assessment of TEM performance. Using this method, information transfer up to 98 pm is demonstrated for an 80 kV TEM system equipped with a spherical aberration corrector and a monochromator. We also revisit the Young fringe method in the light of the 3D Fourier transform, and have found a considerable amount of non-linear terms in Young fringes at 80 kV even from a typical standard specimen, such as an amorphous Ge thin film.

Abstract: The structure of an epitaxial thin film of cobalt-doped hexagonal LuFeO 3  was studied by aberration-corrected high-resolution scanning transmission electron microscopy. The distribution maps of the chemical elements in the film were obtained using atomically resolved energy-dispersive X-ray spectroscopy. The study showed that cobalt ions have a strong tendency towards forming double layers of (Fe/Co)O 2.5  between the Lu-O layers in a hexagonal structure. A significantly smaller amount of cobalt is found in single layers of FeO 1.5 , suggesting the presence of a trigonal-bipyramidal coordination of cobalt. The hexagonal LuFeO 3  structure contains numerous reconstructed stacking faults that represent intergrown structural fragments of LuFe 2 − x Co x O 4 . Magnetization measurements revealed a decrease in the magnetic transition temperature of the LuFe 0.7 Co 0.3 O 3  thin film compared to those of the parent hexagonal LuFeO 3 and LuFe 2 − x Co x O 4  forms. 

Abstract: A method for measuring and correcting the row displacement errors in lattice images acquired using scanning based methods is presented. This type of distortion is apparent in lattice-resolved images acquired using scanning-based techniques such as scanning transmission electron microscopy (STEM) and translates to vertical streaks convolving every feature in Fourier space. This paper presents a method to measure and correct the distortion based on the phase analysis of the streaks in Fourier space. The validity and the precision of the method is demonstrated using a model image and two experimental STEM images of Si <110> thin film and a 5 nm CoPt disordered nanocrystal. The algorithm is implemented in a freely available Digital Micrograph™ script.

Abstract: Aberration corrected scanning transmission electron microscopy (STEM) with high angle annular dark field (HAADF) imaging and the newly developed annular bright field (ABF) imaging are used to define a new guideline for the polarity determination of semiconductor nanowires (NWs) from binary compounds in two extreme cases: (i) when the dumbbell is formed with atoms of similar mass (GaAs) and (ii) in the case where one of the atoms is extremely light (N or O: ZnO and GaN/AlN). The theoretical fundaments of these procedures allow us to overcome the main challenge in the identification of dumbbell polarity. It resides in the separation and identification of the constituent atoms in the dumbbells. The proposed experimental via opens new routes for the fine characterization of nanostructures, e.g., in electronic and optoelectronic fields, where the polarity is crucial for the understanding of their physical properties (optical and electronic) as well as their growth mechanisms.

Abstract: We have imaged, with electron energy loss spectroscopy, the plasmonic response of straight and bent silver nanowires for their potential use in nanophotonic circuits. The guided surface plasmon polaritons appear unaffected by the presence of sharp kinks and corners in the nanowires studied, shown by direct imaging of excited Fabry-Perot-type resonances. Nanoscale detection is extended down to 0.17 eV, enabling detailed measurements of the spatial extent and dispersion of guided surface plasmon polaritons at low wave numbers. The experimental measurements are in excellent agreement with calculations, and the results are relevant in the design of integrated nanophotonic circuits and devices.

Abstract: This work presents a theoretical analysis of image formation in a scanning transmission electron microscope equipped with electron detectors in a plane conjugate to the specimen. This optical geometry encompasses both the three-dimensional imaging technique of scanning confocal electron microscopy (SCEM) and a recently developed atomic resolution imaging technique coined real-space scanning transmission electron microscopy (R-STEM). Image formation in this geometry is considered from the viewpoints of both wave optics and geometric optics, and the validity of the latter is analysed by means of Wigner distributions. Relevant conditions for the validity of a geometric interpretation of image formation are provided. For R-STEM, where a large detector is used, it is demonstrated that a geometric optics description of image formation provides an accurate approximation to wave optics, and that this description offers distinct advantages for interpretation and numerical implementation. The resulting description of R-STEM is also demonstrated to be in good agreement with experiment. For SCEM, it is emphasized that a geometric optics description of image formation is valid provided that higher-order aberrations can be ignored and the detector size is large enough to average out diffraction from the angle-limiting aperture.

Abstract: This paper provides further insights into the degradation mechanisms of nanometer-sized Pt 3 Co/C particles under various proton-exchange membrane fuel cell (PEMFC) operating conditions. We confirm that Co atoms are continuously depleted from the mother Pt 3 Co/C electrocatalyst because they can diffuse from the bulk to the surface of the material. The structure of the Pt-Co/C nanoparticles in the long-term is determined by a balance between Co surface segregation and formation of oxygenated species from water splitting. When the PEMFC is operated at high current density (low cathode potential, below the onset of surface oxide formation from water), a steady-state is reached between the rate of Co dissolution at the surface and Co surface segregation. Consequently, Co and Pt atoms remain homogeneously distributed within the Pt-Co/C particles and the thickness of the Pt-shell is maintained to a small value not detectable by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. When the PEMFC is operated at low current density (high cathode potential), the formation of surface oxides from water and the resulting "place-exchange" mechanism enhance the rate of diffusion of Co atoms to the surface. Consequently, the fresh Pt 3 Co/C particles form core/shell particles with thick Pt-shells and Co content < 5 at% and, ultimately, "hollow" Pt nanoparticles (Kirkendall effect). To the best of our knowledge, this is the first report on the formation of "hollow" Pt particles in a PEMFC.

Abstract: Via flame spray pyrolysis (FSP), SnO 2  gas sensing layers have been doped with 0.01-4 wt% Sb as well as 0.01 wt% Pd in combination with 1 wt% Sb. Characterization of these materials through X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis, and transmission electron microscopy (TEM) revealed particle grain sizes and crystallinity unchanged by the presence of Sb and/or Pd. The addition of Sb to SnO 2 resulted in the significant decrease in baseline resistance; up to two orders of magnitude in dry air at 300 °C and three orders of magnitude in humid air at 300 °C, which is significant for FSP-prepared gas sensors with high porosity and low particle coordination number since they typically suffer from high baseline resistance. While the baseline resistance was improved with Sb-doping, the sensor signal ( R0 / Rgas ) remained constant over all concentrations explored. Moreover, regarding the surface functionalization of SnO 2  with Pd in combination with Sb-doping, the reduction of baseline resistance was preserved without influencing sensor signal.

Abstract: A novel PtRu catalyst consisting of a Ru-rich core and a Pt-rich shell was synthesized using a two-step microwave irradiation technique. The synthesized PtRu/C catalysts were characterized by X-ray diffraction (XRD), extended X-ray absorption finestructure (EXAFS), transmission electron microscopy (TEM) as well as energy dispersive X-ray spectrometry (EDXS). The produced PtRu/C catalysts showed identical crystalline structure and diffraction peaks to Pt itself, but with negligible higher 2 shift degrees, indicating the formation of a specific composite structure rather than alloy formation. This novel structure of PtRu/C catalyst was also further verified via X-ray absorption spectroscopy. The particle size of PtRu catalysts identified by TEM was less than 5 nm. In order to investigate the CO tolerance in the hydrogen oxidation reaction (HOR), H 2 streams with six different concentrations of CO (0, 10, 50, 100, 300, and 500 ppm) were used. The electrocatalytic activity thus obtained was not only better than that of Pt/C catalyst in HOR, but also showed a better CO tolerance in various CO concentrations.

Abstract: This article describes a novel software tool, the KSpaceNavigator, which combines sample stage and crystallographic coordinates in a control sphere. It also provides simulated kinematic diffraction spot patterns, Kikuchi line patterns and a unit cell view in real time, thus allowing intuitive and transparent navigation in reciprocal space. By the overlay of experimental data with the simulations and some interactive alignment algorithms, zone axis orientations of the sample can be accessed quickly and with great ease. The software can be configured to work with any double-tilt or tilt-rotation stage and overcomes nonlinearities in existing goniometers by lookup tables. A subroutine for matching the polyhedral shape of a nanoparticle assists with 3D analysis and modeling. The new possibilities are demonstrated with the case of a faceted BaTiO 3  nanoparticle, which is tilted into three low-index zone axes using the piezo-controlled TEAM stage, and with a multiply twinned tetrahedral Ge precipitate in Al, which is tilted into four equivalent zone axes using a conventional double-tilt stage. Applications to other experimental scenarios are also outlined.

Abstract: Tool degradation may be significantly different depending on small variations in chemical compositions of the workpiece material. The present study is an in-depth microstructure investigation of worn low content polycrystalline cubic boron nitride tool materials after dry hard turning of steels with low and high sulphur contents. The results illustrate the important role of sulphur content on the degradation of the crater zone. Sulphides tend to adhere on the wear surface and form layers that protect the tool from workpiece ingress. In the absence of sulphides in the workpiece material, no protective layer can form and iron compounds make their way into the tool microstructure already at lower cutting speeds (150 m/min) and preferably attack cBN grains compared to Ti(C,N) grains.

Abstract: Focused ion beam (FIB) induced damage in nanocrystalline Al thin films has been characterized using advanced transmission electron microscopy techniques. Electron tomography was used to analyze the three-dimensional distribution of point defect clusters induced by FIB milling, as well as their interaction with preexisting dislocations generated by internal stresses in the Al films. The atomic structure of interstitial Frank loops induced by irradiation, as well as the core structure of Frank dislocations, has been resolved with aberration-corrected high-resolution annular dark-field scanning TEM. The combination of both techniques constitutes a powerful tool for the study of the intrinsic structural properties of point defect clusters as well as the interaction of these defects with preexisting or deformation dislocations in irradiated bulk or nanostructured materials.

Abstract: The evolution of microtwins during high temperature creep deformation in a strengthened Ni-base superalloy has been investigated through a combination of creep testing, TEM characterization, theoretical modeling and computer simulation. Experimentally, microtwin nucleation sources were identified and their evolution was tracked by characterizing the deformation substructure at different stages of the creep deformation. Initially, deformation is highly localized around stress concentrators such as carbides, borides and serrated grain boundaries, which act as sources of a/2<110> matrix type dislocations. Due to microstructural effects such as fine channels between particles and low matrix stacking fault energies, the a/2<110> matrix dislocations dissociate into a/6<112> Shockley partials, which were commonly observed to be decorrelated from one another, creating extended intrinsic stacking faults in the matrix. As deformation progress further, microtwins form via partial dislocations cooperatively shearing both and phases on adjacent {111} glide planes. The TEM observations lead directly to an analysis of dislocation-precipitate interactions. Through phase field simulations and theoretical analysis based on Orowan looping, the important processes of dislocation dissociation and decorrelation are modeled in detail, providing comprehensive insight into the microstructural features and applied stress conditions that favor the microtwinning deformation mode in strengthened Ni-based superalloys.

Abstract: This paper demonstrates the use of Sidewall Lateral Epitaxial Overgrowth (S-LEO) on a-plane GaN thick films on r-plane sapphire by hydride vapor phase epitaxy (HVPE). Comprehensive study of the extended defect microstructure of the a-plane GaN films was carried out using cross-sectional and plan-view transmission electron microscopy (TEM). A very low density of primary threading dislocations and a heterogeneous microstructure can be found in the GaN films. In the window region and N-face wing region, the extended defects included type I 1  and type I 2  basal stacking faults (BSFs), as well as prismatic stacking faults (PSFs) on a-planes. The density of type I 1  BSFs was in the order of ∼2×10 5  cm −1 , type I 2  BSFs in the order of ∼10 4  cm −1 , and corresponding localized partial dislocation density less than 1.5×10 9  cm −2 . PSFs on a-planes were connected to two neighboring type I 1  BSFs with an estimated density of 3×10 2  cm −1  in the plan-view images. In the Ga-face overgrowth regions, the density of BSFs was lower than 10 4  cm −1 . However, inversion domains bounded by (1 1̄ 0 2), (1 1̄ 0 2̄), and (1 1̄ 0 0) planes were found in the Ga-face wing regions. The nature of inversion domain boundaries (IDB) on m-planes can be explained by the Auserman-Gehamn model using high-angle annular dark-field TEM images.

Abstract: Mesoporous CdS spheres with large surface areas and ordered pore size distribution were synthesized through a facile solution processes. Their potential application in integrated hybrid (poly[2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/CdS) photovoltaic cells has been demonstrated. The MEH-PPV-CdSMS electrode shows improved photoelectrochemical properties with the maximum conversion efficiency (Eff) of 2.39% with a short circuit current (Jsc) of −4.26mA/cm2, an open-circuit voltage (Voc) of 0.824V, and a fill factor (FF) of 68.6%. The good performance, low cost and straightforward fabrication method made the mesoporous CdS materials promising for the development of effective photoelectrochemical cells and a powerful tool for a wide range of applications in modern photoelectronics.

Abstract: In this work, multiwall carbon nanotubes (CNT) were functionalized by acid treatment and characterized using Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Polystyrene/CNT composites of both the untreated and acid treated carbon nanotubes were prepared by thermal bulk polymerization without any initiator at different loadings of CNT. The tensile tests showed that the addition of 0.5 wt.% of acid treated CNT results in 22% increase in Young's modulus. The DSC measurements showed a decrease in glass transition temperature ( T g ) of PS in the composites. The rheological studies at 190 °C showed that the addition of untreated CNT increases the viscoelastic behavior of the PS matrix, while the acid treated CNT acts as plasticizer. Thermogravimetric analysis indicated that the incorporation of CNT into PS enhanced the thermal properties of the matrix polymer.

Abstract: Sr 0.5 Ba 0.5 Si 2 O 2 N 2 :Eu 2+  is a promising new phosphor for white light phosphor converted (pc)-LEDs. The material shows broad-band emission due to parity allowed 4f 6 ( 7 F)5d → 4f 7 ( 8 S 7/2 ) transition in the yellow spectral range ( λem  ≈ 560 nm) while excited with UV to blue radiation. The X-ray powder diffraction pattern shows noticeable intensity maxima indicative for diffuse scattering from planar defects and also "missing" reflections compared to SrSi 2 O 2 N 2 :Eu 2+ . Rietveld refinement reveals an average structure of Sr 0.5 Ba 0.5 Si 2 O 2 N 2 :Eu 2+  which is isotypic to that of SrSi 2 O 2 N 2 :Eu 2+ , with the latter representing a twinned layered oxonitridosilicate with disordered metal atoms. The average structure of Sr 0.5 Ba 0.5 Si 2 O 2 N 2 :Eu 2+  was refined in space group  P 1 (no. 1) resulting in lattice parameters  a  = 7.2059(2),  b  = 7.3887(3),  c  = 7.3340(2) Å, α  = 88.524(4),  β  = 84.454(3),  γ  = 75.980(4)° and V = 377.07(2) Å 3 . Based on the crystallographic results and considering lattice relaxation behavior as a consequence of lattice expansion, the observed unexpectedly large Stokes shift (as compared to SrSi 2 O 2 N 2 :Eu 2+ ; 3573 vs. 3285 cm −1 ) can be explained using a least square fit of the emission spectra. With almost identical chromaticity coordinates with respect to the most frequently used commercial LED phosphor YAG:Ce 3+  but significantly higher luminous efficacy (LE = 495 lm/W), Sr 0.5 Ba 0.5 Si 2 O 2 N 2 :Eu 2+  is a promising material for outdoor lighting, e.g. in cool-white pc-LEDs. To elucidate the real structure, powder XRD simulations have been recorded compiling a disorder model taking into account all permutations of metal ion sets and silicate layer orientations. Experimental diffraction data were well reproduced including the diffuse intensities observed in powder XRD and also in SAED patterns. These simulations show that crystallites of Sr 0.5 Ba 0.5 Si 2 O 2 N 2 :Eu 2+  are built up of small anti-phase domains within larger twin domains.

Abstract: Using a combination of high-angle annular dark-field scanning transmission electron microscopy and atomically resolved electron energy-loss spectroscopy in an aberration-corrected transmission electron microscope we demonstrate the possibility of 2D atom by atom valence mapping in the mixed valence compound  Mn 3 O 4 . The Mn  L 2,3  energy-loss near-edge structures from  Mn 2+  and  Mn 3+  cation sites are similar to those of MnO and  Mn 2 O 3  references. Comparison with simulations shows that even though a local interpretation is valid here, intermixing of the inelastic signal plays a significant role. This type of experiment should be applicable to challenging topics in materials science, such as the investigation of charge ordering or single atom column oxidation states in, e.g., dislocations.

Abstract: The precipitation mechanism of ordered phases in metallic solid solutions has been a long-standing controversy due to the competing roles of chemical clustering (or phase separation) and chemical ordering. In the present study, this controversy has been resolved through the coupled use of aberration-corrected high-resolution scanning transmission electron microscopy and atom probe tomography. The experimental results, obtained at atomic resolution, can only be interpreted satisfactorily on the basis of phase separation via spinodal decomposition followed by chemical ordering.

Abstract: This paper presents results on the synthesis of Cu-Pd alloy thin films on Ti substrates by co-electrodeposition of Pd and Cu from nitrate-base electrolytic baths. The deposition rates of Cu and Pd were determined by Electrochemical Quartz Crystal Microbalance as a function of the electrode potential and Cu +2  and Pd +2  concentrations. It is shown that electrodeposition of copper and palladium occurs simultaneously at −0.50 V  vs.  SCE and that Cu-Pd thin films over the entire composition range were obtained by changing the composition of the solution. X-ray diffraction analyses indicated that these films have a nanocrystalline single-phase face-centered cubic structure and scanning electron microscopy analyses showed that potentiostatically deposited films are rough and porous, which is appropriate for electrocatalysis applications. In an attempt to get denser deposits as required for H 2  purification applications, pulsed potential co-electrodeposition was performed and the effect of the deposition conditions on the roughness of the films was assessed by double layer capacitance measurements. It was shown that smooth Cu-Pd films (with  Rf  value as low as 8, as opposed to more than 120 for films prepared in the potentiostatic mode) could be obtained with a proper choice on the deposition conditions.

Abstract: The effect of adding 0.1 wt% Nb to low interstitial (N 0.01 wt%, C 0.01 wt%) 13Cr super martensitic stainless steel (SMSS) on solid phase transformation and microstructures achieved by normalizing and tempering was investigated using dilatometer, electron backscattered diffraction (EBSD), transmission electron microscope (TEM), X-ray diffraction (XRD), and its consequence on mechanical properties was examined to clarify the role of Nb in low interstitial martensitic stainless steel. Nb was found to retard kinetics of reversed austenite formation during tempering and to suppress the occurrence of Cr rich precipitates. The measurement of mechanical properties shows that while the strength properties were significantly increased by nano-scale precipitates enriched in Nb in the steel with 0.10 wt% Nb, the ductility and toughness properties were restored by optimum volume fraction of retained austenite. Excellent strength and adequate toughness properties were obtained by tempering the steel with 0.10 wt% Nb and low interstitial (N 0.01 wt%, C 0.01 wt%) steel at 600 °C.

Abstract: Although the outer surface of single-walled carbon nanotubes (atomically thin cylinders of carbon) can be involved in a wide range of chemical reactions, it is generally thought that the interior surface of nanotubes is unreactive. In this study, we show that in the presence of catalytically active atoms of rhenium inserted into nanotubes, the nanotube sidewall can be engaged in chemical reactions from the inside. Aberration-corrected high-resolution transmission electron microscopy operated at 80 keV allows visualization of the formation of nanometre-sized hollow protrusions on the nanotube sidewall at the atomic level in real time at ambient temperature. Our direct observations and theoretical modelling demonstrate that the nanoprotrusions are formed in three stages: (i) metal-assisted deformation and rupture of the nanotube sidewall, (ii) the fast formation of a metastable asymmetric nanoprotrusion with an open edge and (iii) a slow symmetrization process that leads to a stable closed nanoprotrusion.

Abstract: La 0.6 Sr 0.4 Co x Fe 1−x O 3−δ  (LSCF), La 0.6 Sr 0.4 Cu 0.2 Fe 0.8 O 3−δ , Ba 0.5 Sr 0.4 Co 0.8 Fe 0.2 O 3−δ and LaFeO 3−δ  nanoparticles were synthesized by a reverse micelle procedure. Controlling the size of the micelles through the water:oil phase ratio enabled synthesis of phase pure perovskite particles with average sizes from 14 nm to 50 nm. Small amounts of an impurity phase, likely cobalt oxide, were detected in the XRD spectrum of high cobalt content samples of LSCF (x = 0.8). La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ  nanoparticles were utilized to coat the surface of a dense thin-film La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ  solid oxide fuel cell cathode. The polarization resistance of the nanoparticle coated electrode, measured at open circuit in air at 973 K, was 20% lower than an equivalent un-coated electrode.

Abstract: The ability to tune the properties of graphene nanoribbons (GNRs) through modification of the nanoribbon's width and edge structure 1 ,  2 ,  3  widens the potential applications of graphene in electronic devices 4 ,  5 ,  6 . Although assembly of GNRs has been recently possible, current methods suffer from limited control of their atomic structure 7 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13 , or require the careful organization of precursors on atomically flat surfaces under ultra-high vacuum conditions 14 . Here we demonstrate that a GNR can self-assemble from a random mixture of molecular precursors within a single-walled carbon nanotube, which ensures propagation of the nanoribbon in one dimension and determines its width. The sulphur-terminated dangling bonds of the GNR make these otherwise unstable nanoribbons thermodynamically viable over other forms of carbon. Electron microscopy reveals elliptical distortion of the nanotube, as well as helical twist and screw-like motion of the nanoribbon. These effects suggest novel ways of controlling the properties of these nanomaterials, such as the electronic band gap and the concentration of charge carriers.

Abstract: Understanding the effect of radiation damage and noble gas accommodation in potential ceramic hosts for plutonium disposition is necessary to evaluate their long-term behaviour during geological disposal. Polycrystalline samples of Nd-doped zirconolite and Nd-doped perovskite were irradiated  ex situ  with 2 MeV Kr +  at a dose of 5 × 10 15 ions cm −2  to simulate recoil of Pu nuclei during alpha decay. The feasibility of thin section preparation of both pristine and irradiated samples by Focused Ion Beam sectioning was demonstrated. After irradiation, the Nd-doped zirconolite revealed a well defined amorphous region separated from the pristine material by a thin (40-60 nm) damaged interface. The zirconolite lattice was lost in the damaged interface, but the fluorite sublattice was retained. The Nd-doped perovskite contained a defined irradiated layer composed of an amorphous region surrounded by damaged but still crystalline layers. The structural evolution of the damaged regions is consistent with a change from orthorhombic to cubic symmetry. In addition in Nd-doped perovskite, the amorphisation dose depended on crystallographic orientation and possibly sample configuration (thin section or bulk). Electron Energy Loss Spectroscopy revealed Ti remained in the 4+ oxidation state but there was a change in Ti coordination in both Nd-doped perovskite and Nd-doped zirconolite associated with the crystalline to amorphous transition.

Abstract: The resolution of electron energy loss spectroscopy (EELS) is limited by delocalization of inelastic electron scattering rather than probe size in an aberration corrected scanning transmission electron microscope (STEM). In this study, we present an experimental quantification of EELS spatial resolution using chemically modulated 2 × (LaMnO 3 )/2 × (SrTiO 3 ) and 2 × (SrVO 3 )/2 × (SrTiO 3 ) superlattices by measuring the full width at half maxima (FWHM) of integrated Ti M 2,3 , Ti L 2,3 , V L 2,3 , Mn L 2,3 , La N 4,5 , La N 2,3  La M 4,5  and Sr L 3  edges over the superlattices. The EELS signals recorded using large collection angles are peaked at atomic columns. The FWHM of the EELS profile, obtained by curve-fitting, reveals a systematic trend with the energy loss for the Ti, V, and Mn edges. However, the experimental FWHM of the Sr and La edges deviates significantly from the observed experimental tendency.

Abstract: Single plane platelets of niobium nitride have been observed to form in a Fe-Nb-N alloy during ageing at 600 °C, using High Resolution Electron Microscopy, Field Ion Microscopy and Atom Probe Tomography. Small-angle neutron scattering has been used to investigate the kinetics of formation of these platelets. They are shown to nucleate in less than 5 min at this ageing temperature, and subsequently to grow in-plane to a size of about 10 nm without experiencing any change in thickness.

Abstract: For high-voltage cycling of rechargeable Li batteries, a nano-scale amorphous Li-ion conductor, lithium phosphorus oxynitride (Lipon), has been coated on surfaces of LiCoO 2 particles by combining a RF-magnetron sputtering technique and mechanical agitation of LiCoO 2  powders. LiCoO 2  particles coated with 0.36 wt% (∼1 nm thick) of the amorphous Lipon, retain 90% of their original capacity compared to non-coated cathode materials that retain only 65% of their original capacity after more than 40 cycles in the 3.0-4.4 V range with a standard carbonate electrolyte. The reason for the better high-voltage cycling behavior is attributed to reduction in the side reactions that cause increase of the cell resistance during cycling. Further, Lipon coated particles are not damaged, whereas uncoated particles are badly cracked after cycling. Extending the charge of Lipon-coated LiCoO 2  to higher voltage enhances the specific capacity, but more importantly the Lipon-coated material is also more stable and tolerant of high voltage excursions. A drawback of Lipon coating, particularly as thicker films are applied to cathode powders, is the increased electronic resistance that reduces the power performance.

Abstract: Current approaches to initial corrosion rate reduction of biodegradable magnesium alloys include alloying with rare earth elements, mechanical processing, coatings and the use of metallic glasses. The latter has limited ductility needed for implant adaptively to various surgery procedures. Furthermore, slow corroding magnesium alloys, coatings or metallic glasses have not proved to be fully dissolvable in vivo. With this in mind, we have developed a new class of biocompatible, biodegradable ductile magnesium alloys with 40% elongation at room temperature. The alloys are based on the Mg-Bi system and undergo a series of production routes, which include rapid solidification (RS) and various extrusion processes. The Mg-Bi-Si (B-BS) system exhibited a high corrosion rates in vitro and was excluded from in vivo screening. In preliminary experiments of Mg-Bi-Ca (B-BX) in rabbit femur bones, the alloy corroded rapidly without any clinically visible gas formation. Only 30% of the B-BX implant remained uncorroded after 4 weeks of implantation. After using low iron Mg for implant preparation the corrosion rate of HP-B-BX was reduced in bone leaving 70% of the implant uncorroded after 4 weeks, while the corrosion in intramuscular and subcutaneous sites were still high leaving only 40% and 10% uncorroded after 4 weeks. The foreign body reaction was very mild and enhanced bone formation could be observed in the vicinity of the corroding implant. Thus, these new magnesium alloys are potentially promising biomaterials, although more detailed in vivo studies need to be performed in actual implant situations.

Abstract: This paper studies the photocatalytic degradation of phenol using zirconia-doped TiO(2) nanoparticles. ZrO(2) was chosen due to its promising results during preliminary studies. Particles smaller than 10nm were synthesised and doped with quantities of ZrO(2) ranging from 0.5 to 4% (molar metal content). Particles were calcined at different temperatures to alter the TiO(2) structure, from anatase to rutile, in order to provide an ideal ratio of the two phases. Powder X-ray diffraction (PXRD) analysis was used to examine the transformation between anatase and rutile. Degradation of phenol was carried out using a 40 W UV bulb at 365 nm and results were measured by UV-vis spectrometry. TEM images were obtained and show the particles exhibit a highly ordered structure. TiO(2) doped with 1% ZrO(2) (molar metal content) calcined at 700 °C proved to be the most efficient catalyst. This is due to an ideal anatase:rutlie ratio of 80:20, a large surface area and the existence of stable electron-hole pairs. ZrO(2) doping above the optimum loading acted as an electron-hole recombination centre for electron-hole pairs and reduced photocatalytic degradation. Synthesised photocatalysts compared favourably to the commercially available photocatalyst P25. The materials also demonstrated the ability to be recycled with similar results to those achieved on fresh material after 5 uses.

Abstract: In this work we investigate methods of statistical processing and background fitting of atomic resolution electron energy loss spectrum image (SI) data. Application of principal component analysis to SI data has been analyzed in terms of the spectral signal-to-noise ratio (SNR) and was found to improve both the spectral SNR and its standard deviation over the SI, though only the latter was found to improve significantly and consistently across all data sets analyzed. The influence of the number of principal components used in the reconstructed data set on the SNR and resultant elemental maps has been analyzed and the experimental results are compared to theoretical calculations.

Abstract: The precipitates present in an Al-0.59Mg-0.71Ge (at.%) alloy have been studied using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. Two types of needle-shaped precipitates growing along 〈0 0 1〉 Al  were found: a phase isostructural to the trigonal U1 phase found in Al-Mg-Si alloys, and finer precipitates with a hexagonal arrangement of Ge columns. The study revealed the presence of a complex interface structure surrounding the U1-like precipitates, and an explanation based on interatomic distances is proposed.

Abstract: We compare the near edge structure (NES) of cubic boron nitride (cBN) measured using both electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) with that calculated using three commonly used theoretical approaches. The boron and nitrogen K-edges collected using EELS and XAS from cBN powder were found to be nearly identical. These experimental edges were compared to calculations obtained using an all-electron density functional theory code (WIEN2k), a pseudopotential density functional theory code (CASTEP) and a multiple scattering code (FEFF). All three codes were found to reproduce the major features in the NES for both ionisation edges when a core-hole was included in the calculations. A partial core hole (1/2 of a 1s electron) was found to be essential for correctly reproducing features near the edge threshold in the nitrogen K-edge and to correctly obtain the positions of all main peaks. CASTEP and WIEN2k were found to give almost identical results. These codes were also found to produce NES which most closely matched experiment based on  χ2 calculations used to qualitatively compare theory and experiment. This work demonstrated that a combined experimental and theoretical approach to the study of NES is a powerful way of investigating bonding and electronic structure in boron nitride and related materials.

Abstract: Preparation of fine grained, hard and ductile pure tungsten for future fusion reactor applications was tested using the bottom-up approach via powder consolidation by spark plasma sintering (SPS) at different temperature (1300-1800 °C) and pressure (90-266 MPa) conditions. Pure tungsten powders with an average particle size of about 1 μm were sintered to high density (about 94%) with almost no grain growth at a temperature below 1400 °C and an applied pressure up to 266 MPa. These samples had a multi-modal grain size distribution (resembling the size distribution of the initial powder) and a very high Vickers hardness (up to 530 kg/mm 2 ). Above 1500 °C fast grain growth occurred and resulted in a drop in hardness. XRD on the surface of bulk samples showed a small amount of tungsten oxides; however, XPS and EDS indicated that these oxides were only surface contaminants and suggested a high purity for the bulk samples. The results demonstrate that SPS can lead to ultrafine and nanocrystalline tungsten if used to consolidate pure nano tungsten powders.

Abstract: We have explored experimentally the effects of the TEM sample thickness, zero-loss energy filtering, and probe coherence on fluctuation electron microscopy (FEM) experiments implemented using nanodiffraction. FEM measures the variance  V  of spatial fluctuations in nanodiffraction. We find that  V  is inversely proportional to the sample thickness, as predicted by earlier models. Energy filtering increases  V  at all thicknesses we measured.  V  increases as the coherence of the probe increases. All of these factors must be carefully controlled to obtain quantitatively reliable FEM data.

Abstract: Two new methods for the measurement of transverse spatial coherence in a transmission electron microscope (TEM) are developed and applied to measure the spatial coherence in a field emission gun TEM. Measurements are made under different illumination and operating conditions, illustrating the effect of these conditions on the spatial coherence. The relative merits and limitations of these methods are discussed and compared, together with the previously described "Ronchigram" method.