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peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 11/02/2021 Summary Ferroelectric materials, and more specifically ferroelectric domain walls (DWs) have become an area of intense research in recent years. Novel physical phenomena have been discovered at these nanoscale topological polarization discontinuities by mapping out the polarization in each atomic unit cell around the DW in a scanning transmission electron microscope (STEM). However, identifying these features requires an understanding of the polarization in the overall domain structure of the TEM sample, which is often a time‐consuming process. Here, a fast method of polarization mapping in the TEM is presented, which can be applied to a range of ferroelectric materials. Due to the coupling of polarization to spontaneous strain, we can isolate different strain states and demonstrate the fast mapping of the domain structure in ferroelectric lead titanate (PTO). The method only requires a high‐resolution TEM or STEM image and is less sensitive to zone axis or local strain effects, which may affect other techniques. Thus, it is easily applicable to in‐situ experiments. The complimentary benefits of Fourier masking with more advanced mapping strategies and its application to other materials are discussed. These results imply that Fourier masked polarization mapping will be a useful tool for electron microscopists in streamlining their analysis of ferroelectric TEM samples. Lay Description This paper addresses a problem that often occurs when looking at a ferroelectric material in the Transmission Electron Microscope (TEM). Ferroelectric samples are interesting because they form tiny areas inside themselves with arrow of charge in each one. The thinner the sample, the smaller these regions, called “domains” become. These arrows of charge point in different directions in each domain of the sample. The boundary where these domains meet have interesting properties to study in a TEM but it's important to figure out which way the arrows point in the domains around the boundary. What causes the arrows in the different domains is tiny shifts of different atoms in unit cell away from their neutral position, usually because they're being squeezed by pressure from the domains nearby. The problem is that these tiny atoms moving are difficult to measure and see where the charged arrow is pointing, often it's hard to know how many different domains are even in the sample and where they begin. This paper discusses a method called “Fourier masking” to quickly see what's going on in the overall TEM sample, where the domains are and roughly where the arrows point. It does this by looking at the spacings of the atoms from a magnification where you can just about see the lines of atoms. In lead titanate the unit cell is a rectangle and the arrow always points in line with the long side of the rectangle. The Fourier masking lets you see which direction the long side of the rectangular unit cell is pointing in different parts of your TEM image. The big advantage is that it takes about two minutes to do and uses software that almost every TEM already has. That lets the TEM user quickly know where the domains are in their TEM samples and roughly which way the arrows of charge are pointing. Then they can choose the most interesting features focus on for higher resolution analysis.

WOS: 000349657600001, There exist many reports on functionalisation of graphene on a non-spatially resolved scale; this report concentrates on reviewing atomic-scale interactions of functionalising agents, i.e. on the electronic behaviour of single atoms, which are introduced as adatoms or lattice site impurities for the purpose of external doping and dosing to achieve bandgap engineering and electrical contacting of graphene; it also reviews the associated defects. Emphasis is put on visualisation of such interactions by advanced imaging in conjunction with localised spectroscopy techniques. Whereas the existing literature describing the development of such techniques in the application to graphene warrants a review in its own right, here the authors focus on observations, with modelling support, of the interaction phenomena themselves and not on the evaluation of measurements by such techniques. Atomic resolution transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS) in imaging and scanning mode, as well as scanning tunnelling microscopy (STM) are the most frequently applied techniques in aid of revealing topography and defect assisted interactions of graphene with foreign atoms and molecules. Electron-probe based investigations additionally lead to electron beam assisted interactions of foreign species with graphene. The graphene metal interaction observed in a transmission electron microscope is a prevalent example of how reactions occurring between metals and graphene can be emphasised and thereby assessed: metal-mediated etching of graphene has proven to be a common phenomenon after metal dosing, e.g. to fabricate electrical contacts. The review reports furthermore on investigations revealing atomic position, bonding and dynamics of non-metal p- and n-dopants as well as on revealing the functionalisation of graphene via molecular self-assembly, intercalation and nano-sculpting. Literature till the end of 2013/begin of 2014 is reviewed., Engineering and Physical Sciences Research Council [EP/I008144/1]

The relationship between structure and properties has been followed for different nanoscale forms of tungsten disulfide (2H-WS2) namely exfoliated monolayer and few-layer nanoplatelets, and nanotubes. The similarities and differences between these nanostructured materials have been examined using a combination of optical microscopy, scanning and high-resolution transmissionelectron microscopy (SEM and HRTEM) and atomic force microscopy (AFM). Photoluminescence (PL) and Raman spectroscopy have also been used to distinguish between monolayer and few-layer material. Strain induced phonon shifts have been followed from the changes in the positions of the A1g and E2g1 Raman bands during uniaxial deformation. This has been modelled for monolayer using density functional theory (DFT) with excellent agreement between the measured and predicted behaviour. It has been found that as the number of WS2 layers increases for few-layer crystals or nanotubes, the A1g mode hardens whereas the E2g1 mode softens. This is believed to be due to theA1g mode, which involves out of plane atomic movements, being constrained by the increasing number of WS2 layers whereas easy sliding reduces stress transfer to the individual layers for the E2g1mode, involving only in-plane vibrations. This finding has enabled the anomalous phonon shift behaviour in earlier pressure measurements on WS2 to be resolved, as well as similar effects in othertransition metal dichalcogenides, such as molybdenum disulfide (MoS2), to be explained.

WOS: 000356554500028, Two-dimensional (2D) layers like graphene are subject to long-wavelength fluctuations that manifest themselves as strong height fluctuations (ripples). In order to control the ripples, their relationship with external strain needs to be established. We therefore perform molecular dynamics (MD) of suspended graphene, by the use of a newly developed force field model (MMP) that we prove to be extremely accurate for both C Diamond and Graphene. The MMP potential successfully reproduces the energy of the a-bonds in both sp(3) and sp(2) configuration. Our MD simulations and experimental electron microscopy analysis reveal that ordered and static ripples form spontaneously as a direct response to external pressure. Furthermore the morphology of graphene and strain response of the crystal bonds differ depending on the particular directions where external pressure is present. Different regions of the strained graphene sheet are then investigated by tight-binding. Localised bandgap opening is reported for specific strain combinations, which also results in particular signatures in the phonon spectrum. Such controllable morphological changes can therefore provide a means to practically control and tune the electronic and transport properties of graphene for applications as optoelectronic and nanoelectromechanical devices. (C) 2015 The Authors. Published by Elsevier Ltd., UK Engineering and Physical Sciences Research Council (EPSRC); Engineering and Physical Sciences Research Council [EP/H01182X/1], We are indebted to Dr. Stephan Birner of nextnano GmbH for his help with the modification needed of the Tight Binding routines in the nextnano source code. We are also grateful to Prof S. Clark of Durham University (UK) and Prof R.J. Young FRS (University of Manchester) for valuable discussions. We like to thank the UK Engineering and Physical Sciences Research Council (EPSRC) for Doctoral Prize Fellowship. We would also like to acknowledge Dr. Brian May CBE, of the band Queen, for kindly granting us permission to use the song Under Pressure (Queen and David Bowie, 1981) as soundtrack for our molecular dynamics video (Video S1). Due to copyright reasons the song was not used.

Silver nanoparticles (AgNPs) are one of the most important nanomaterials for toxicological study due to their extensive use in consumer products and their potential effects on human health, animal health and the environment. There is, however, insufficient information on the impact of silver nanoparticles in the marine environment. We study the effect of AgNPs on sea urchin (Paracentrotus lividus) development by X-ray absorption near edge structure (XANES) and Fourier Transform infrared (FTIR) spectroscopies. Agglomerated AgNPs were observed on sea urchins after exposure to AgNPs at a concentration of 0.3 ppm for 51 h. XANES shows that agglomerated AgNPs contain oxidized Ag species complexed with S and O/N ligands. FTIR results confirm the presence of additional sulphur compounds suggestive of a biological response to the toxicity of AgNPs in the sea urchins. Additionally, it could be concluded from the FTIR results that there is a loss of calcite in the sea urchins exposed to AgNPs

In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C.

Mc 2009. Microscopy Conference, Graz, Austria. 30 August - 4 September 2009. First Joint Meeting Of Dreiländertagung And Multinational Congress On Microscopy.

WOS: 000365464800090, PubMed ID: 26446310, A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations is used to describe the electronic structure modifications incurred by free-standing graphene through two types of single-atom doping. The N K and C K electron energy loss transitions show the presence of pi* bonding states, which are highly localized around the N dopant. In contrast, the B K transition of a single B dopant atom shows an unusual broad asymmetric peak which is the result of delocalized pi* states away from the B dopant. The asymmetry of the B K toward higher energies is attributed to highly localized sigma* antibonding states. These experimental observations are then interpreted as direct fingerprints of the expected p- and n-type behavior of graphene doped in this fashion, through careful comparison with density functional theory calculations., Engineering and Physical Sciences Research Council (EPSRC); Engineering and Physical Sciences Research Council [EP/I008144/1], SuperSTEM is the U.K. National Facility for Aberration-Corrected STEM, supported by the Engineering and Physical Sciences Research Council (EPSRC). T.P.H. would like to thank the EPSRC for the Doctoral Prize Fellowship which funded this research in part. Computational work was undertaken using the advanced research computing (ARC1 and ARC2) HPC facilities at The University of Leeds, which provided access to Accelrys Materials Studio.

WOS: 000341914100007, PubMed ID: 25259987, We demonstrate that 60-keV electron irradiation drives the diffusion of threefold-coordinated Si dopants in graphene by one lattice site at a time. First principles simulations reveal that each step is caused by an electron impact on a C atom next to the dopant. Although the atomic motion happens below our experimental time resolution, stochastic analysis of 38 such lattice jumps reveals a probability for their occurrence in a good agreement with the simulations. Conversions from three- to fourfold coordinated dopant structures and the subsequent reverse process are significantly less likely than the direct bond inversion. Our results thus provide a model of nondestructive and atomically precise structural modification and detection for two-dimensional materials., Vienna Scientific Cluster; CSC Finland Ltd.; Austrian Science Fund (FWF) [M 1497-N19]; Finnish Cultural Foundation; Walter Ahlstrom Foundation; FWF [M 1481-N20, P25721-N20]; University of Helsinki Funds; European Research Council (ERC) [336453-PICOMAT]; Engineering and Physical Sciences Research Council (EPSRC) [EP/I008144/1]; Engineering and Physical Sciences Research Council [EP/I008144/1], We thank the Vienna Scientific Cluster and CSC Finland Ltd. for extensive grants of computational resources, and Ask Hjorth Larsen for help setting up the LCAO calculations. T. S. was supported by the Austrian Science Fund (FWF) through Grant No. M 1497-N19, by the Finnish Cultural Foundation, and by the Walter Ahlstrom Foundation. J. K. was supported by the FWF via Grant No. M 1481-N20, and by the University of Helsinki Funds. J. C. M. and C. M. acknowledge support from the FWF Project No. P25721-N20 and the European Research Council (ERC) Project No. 336453-PICOMAT. SuperSTEM is the UK National Facility for Aberration-Corrected STEM, supported by the Engineering and Physical Sciences Research Council (EPSRC), who also supported R. Z. and U. B. via Grant No. EP/I008144/1.

Since its discovery, the one atom thick material graphene has been at the centre of growing interest in two-dimensional materials. Due to its exceptional properties, graphene is a rich topic to explore by physicists, chemists, engineers and materials scientists. In addition to its use in the fundamental research, graphene is also a promising candidate for future electronics, photonics and energy storage devices.The project presented in this thesis was carried out to explore the structure of suspended graphene in particular in order to probe the metal-graphene interaction via Transmission Electron Microscopy, as most graphene applications require interfacing with metals. As the work was based on free standing graphene, graphene layers obtained by mechanical cleavage or growth on a substrate were transferred onto TEM-grids. Therefore, fabrication, suspended sample preparation and identification of graphene layers were first discussed for a better understanding of how to obtain high quality graphene, as this was essential for the rest of the project.Structural, topographic and chemical analysis of pristine suspended graphene layers were investigated in detail via Transmission Electron Microscopy and Scanning Tunnelling Microscopy. The latter technique was also employed for graphene on a substrate along with establishing annealing conditions for residue free graphene.Metal deposited suspended graphene layers were then investigated in the electron microscopes. Different metal behaviours were observed on the graphene surfaces for the same amount of metal evaporation. Generally, metals interact only weakly with graphene as they are not observed on clean (residue free) parts and are mainly clustered. On the other hand, graphene etching has been observed in the presence of metals. The etching was initiated with graphene vacancy formation as a result of the interaction between metal and carbon atoms on clean graphene. Once a vacancy was created, a hole quickly formed and eventually the graphene layers were destroyed. However, those holes created by metals were healed spontaneously either by non-hexagonal or perfect hexagonal rings. The possible etching and healing mechanisms of the suspended graphene were also discussed.

The research work presented in this thesis comprises an electron microscopy and spectroscopy study of crystal defects that relate to the occurrence of different colours in natural and synthetic diamonds. Two principal lines of investigation have been covered, each with its own objective. The first aims to identify the source of brown colour in natural and synthetic diamond and the second to ascertain the distribution of colour inducing point defects in synthetic diamond. An outline of both areas of research is given below.1) Brown colour in natural and synthetic diamondsColour is a physical property that can be very difficult to characterise in diamond and consequently it receives regular attention from scientists working in the gem industry. In this work, the crystal structures of brown and colourless natural type IIa diamonds are compared along with brown coloured synthetic diamonds manufactured using the chemical vapour deposition (CVD) process. Numerous attempts have been made to trace the origin of brown tints in natural diamond, with the most likely sources, dislocations and nitrogen impurities, ruled out through the application of various analytical techniques. Recently more emphasis has been placed on the study of vacancy related defects in natural diamond and their influence on colour. Differences between the annealing characteristics of brown coloured natural and CVD diamonds suggest that the defect or defects responsible for the brown colour might be different for each type of diamond. The focus of this research work is the analysis of vacancy defects of the order of 1nm in size using aberration corrected scanning transmission electron microscopy (AC-STEM). The sub-nanometre size probe afforded by this technique allows such defect structures to be resolved much more readily than with conventional high resolution transmission electron microscopy (HR-TEM). Small-scale contrast variations are apparent in the lattice images of brown diamonds but not of the colourless variety. These features have been compared to simulated phase contrast images of vacancy clusters in diamond.2) Yellow / Green coloured synthetic diamonds grown using metal solvent catalystSynthetic diamonds for jewellery and industrial applications are routinely manufactured under high pressure-temperature (HPHT) conditions that closely resemble those found during the creation of natural diamonds. Although the manufacturing equipment can vary in design, the HPHT process that occurs inside the reaction vessel remains essentially the same. During processing, the carbon source material is dissolved into a molten metal and then precipitated onto tiny seed diamonds that are added to the reaction chamber. Much time and effort has been expended in refining this process to reduce impurities and defects in the finished diamonds. The presence of remnant transition metal atoms (e.g. nickel) in the crystal structure influences the electronic properties and in particular the colour of the diamonds. The position and configuration of these metallic defects has previously been studied by a variety of analytical techniques, including optical absorption-luminescence spectroscopy and electron paramagnetic resonance spectroscopy (EPR). These studies have proposed a number of optically active nickel centres at both substitutional and interstitial sites. Their association with vacancies and nitrogen atoms has also been highlighted. This work uses electron microscopy and spectroscopy to characterise the nickel defects in synthetic type 1b diamonds.

The thesis presented here entitled “Structural and Compositional Properties of Semiconductor Quantom Dots and Nanocrystals” for the degree of Doctor of Philosophy is submitted to the University of Manchester by Reza Jalilikashtiban in August 2010. The research carried out here employed analytical and imaging transmission electron microscopy and scanning transmission electron microscopy to gain a good understanding of local structure and composition of semiconductor nanocrystals and quantum dots for electronics and optoelectronics applications. One of the world’s most advanced analytical scanning transmission electron microscopes in the field, the Daresbury SuperSTEM, was used to scrutinise the structure and composition of the samples. Three nanostructure systems are investigated in this thesis: 1. Structures consisting of Ge-nanocrystals (NCs) in alumina. Here HRTEM suggests relaxed and twinned smaller NCs grown annealed at lower temperature compared to elongated non-faulty bigger NCs annealed at higher temperature. HRTEM also suggests a polycrystalline structure of the matrix. 2. With regards to the InAs/GaAs quantum dots (QD) the study aims in particular at elucidating QD formation by investigating samples grown with and without growth interrupt (GI). Diffraction contrast TEM shows formation of buried dots in the sample prepared with GI whereas for the sample without GI the immediate growth of GaAs after InAs inhibits diffusion and segregation of In adotoms, and no footprint of buried dots has been observed. HRTEM and HAADF show coherent QDs in the sample with GI and abrupt InAs/GaAs interfaces in the sample without GI. In executing energy electron loss spectroscopy (EELS) and geometric phase analysis (GPA) the distribution of In in InGaAs/GaAs QDs has been obtained in samples grown in the critical thickness regime for quantum dot formation. The highest In percentage achieved in the dots grown with a nominal fraction of 100% was ~70%. EELS shows variations in the In concentration within the QD structure and wetting layer 3. In the case of Er-doped Si-NCs in silica this research tries to provide an understanding of structure, composition and position of excess Si and Er in the silica matrix of materials prepared under different growth conditions and to correlate this information with the PL emission, all with the aim to find preparation routes for optimum optical efficiency for applications of this materials system in silicon photonics. High spatial correlation between Si-NCs, Er and O in the Er and Si co-implanted sample with strong indication of an Er-oxide/Si core-shell structure had been found. The lack of an Er-oxide plasmon indicates, however, that the shell structure and its interface with the SiNCs is highly defective and a likely cause for non-radiative recombination. The sample with similar excess Er and Si concentrations but prepared in a two-stage implantation and annealing process shows a 10 times improvement in the optical emission. Here no spatial correlation between Er and Si-NCs was found in core loss EELS. EELS and HAADF evidenced more highly, near-atomically dispersed Er in the matrix with no formation of a core-shell structure as compared to the co-implanted sample. No footprint of Er-silicide plasmon was observed by low loss valence band EELS investigation in the co-implanted sample.

An Electron Energy Loss Spectroscopy Study of Metallic Nanoparticles of Gold and Silver – A thesis submitted for the degree of PhDThe application of gold and silver nanoparticles to areas such as medical research is based on unique optical properties exhibited by some metals. These properties are a direct consequence of localised excitations occurring at visible frequencies known as Surface Plasmon Resonances (SPRs). The exact frequency of an SPR induced in a nanoparticle can be ‘tuned’ in the optical range by, for example, changing the size of gold and silver nanoparticles, or by varying the relative concentrations of gold and silver within an alloy nanoparticle. Whatever the desired frequency, it is critical that the majority of nanoparticles exhibit the frequency within the resolution limit of the imaging system. The research presented here utilises the high resolution imaging and spectroscopy techniques of (Scanning) Transmission Electron Microscopy ((S)TEM) and Electron Energy Loss Spectroscopy (EELS). It is common practice to analyse the optical properties of alloy nanoparticles using techniques that acquire a single spectrum averaged over multiple particles such as Ultraviolet-Visible (UV-Vis) spectroscopy. However, this technique cannot detect any optical variation between the nanoparticles resulting from compositional change. In this research the author demonstrates through the use of EELS that the SPR can be determined for individual gold/silver alloy nanoparticles, for the purpose of determining the extent of their homogeneity. Importantly, the data presented here suggest dramatic variation in SPR frequency between particles and even within the same particle, indicative of large variations in alloy composition. This puts the assumption that alloying can be scaled down to the nanometre-scale to the test. In order to resolve and extract the SPR in both the pure gold and gold and silver alloy nanoparticles, the author has successfully applied multiple post acquisition techniques such as Richardson-Lucy deconvolution and Principle Component Analysis (PCA) to the EELS Spectrum Imaging (SI) acquisition method. Additionally, the valence band EELS data are supported by complementary electron microscopy techniques; Core loss EELS, Energy Dispersive X-Ray Spectroscopy (EDX) and High Angle Annular Dark Field (HAADF) imaging.