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Bi2Se3 is a three-dimensional topological insulator which has been extensively studied because it has a single Dirac cone on the surface, inside a relatively large bulk band gap. However, the effect of two-dimensional topological insulator Bi bilayers on the properties of Bi2Se3 and vice versa, has not been explored much. Bi bilayers are often present between the quintuple layers of Bi2Se3, since (Bi2)n(Bi2Se3)m form stable ground-state structures. Moreover, Bi2Se3 is a good substrate for growing ultrathin Bi bilayers. By first-principles techniques, we first show that there is no preferable surface termination by either Bi or Se. Next, we investigate the electronic structure of Bi bilayers on top of, or inside a Bi2Se3 slab. If the Bi bilayers are on top, we observe a charge transfer to the quintuple layers that increases the binding energy of the surface Dirac cones. The extra states, originating from the Bi bilayers, were declared to form a topological Dirac cone, but here we show that these are ordinary Rashba-split states. This result, together with the appearance of a new Dirac cone that is localized slightly deeper, might necessitate the reinterpretation of several experimental results. When the Bi bilayers are located inside the Bi2Se3 slab, they tend to split the slab into two topological insulators with clear surface states. Interface states can also be observed, but an energy gap persists because of strong coupling between the neighboring quintuple layers and the Bi bilayers.

Aberration-corrected transmission electron microscopy, electron energy-loss spectroscopy, and density functional theory (DFT) calculations are used to solve several key questions about the surface structure, the particle morphology, and the distribution and nature of nitrogen impurities in detonation nanodiamond (DND) cleaned by a recently developed ozone treatment. All microscopy and spectroscopy measurements are performed at a lowered acceleration voltage (80/120kV), allowing prolonged and detailed experiments to be carried out while minimizing the risk of knock-on damage or surface graphitization of the nanodiamond. High-resolution TEM (HRTEM) demonstrates the stability of even the smallest nanodiamonds under electron illumination at low voltage and is used to image the surface structure of pristine DND. High resolution electron energy-loss spectroscopy (EELS) measurements on the fine structure of the carbon K-edge of nanodiamond demonstrate that the typical * pre-peak in fact consists of three sub-peaks that arise from the presence of, amongst others, minimal fullerene-like reconstructions at the nanoparticle surfaces and deviations from perfect sp(3) coordination at defects in the nanodiamonds. Spatially resolved EELS experiments evidence the presence of nitrogen within the core of DND particles. The nitrogen is present throughout the whole diamond core, and can be enriched at defect regions. By comparing the fine structure of the experimental nitrogen K-edge with calculated energy-loss near-edge structure (ELNES) spectra from DFT, the embedded nitrogen is most likely related to small amounts of single substitutional and/or A-center nitrogen, combined with larger nitrogen clusters.

Electron-energy-loss spectroscopy (EELS) is used to investigate single layers of LaAlO3 grown on SrTiO3 having an n-type interface as well as multilayers of LaAlO3 and SrTiO3 in which both n- and p-type interfaces occur. Only minor changes in Ti valence at the n-type interface are observed. This finding seems to contradict earlier experiments for other SrTiO3/LaAlO3 systems where large deviations in Ti valency were assumed to be responsible for the conductivity of these interfaces. Ab initio calculations have been carried out in order to interpret our EELS results. Using the concept of Bader charges, it is demonstrated that the so-called polar discontinuity is mainly resolved by lattice distortions and to a far lesser extent by changes in valency for both single layer and multilayer geometries.

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

The effect of the size of the GaAs barrier and the Ga1−xInxAs well on the structural properties of a Ga1−xInxAs/GaAs multiple quantum well structure is investigated using the Metropolis Monte Carlo approach based on a well-parametrized Tersoff potential. It is found that within the well the Ga-As and In-As bond lengths undergo contractions whose magnitude increases with increasing In content in sharp contrast with bond-length variations in the bulk Ga1−xInxAs systems. For fixed barrier size and In content, the contraction of the bonds is also found to increase with increasing size of the well. Using the local atomic structure of the heterostructures, a more local analysis of the strain state of the systems is given and comparison with the prediction of macroscopic continuum elasticity theory shows deviations from the latter.

This work provides values of electron scattering 002 structure factors for InxGa1-xAs as a function of the In concentration x=0 to 1. These results allow accurate compositional analysis of pseudomorphically grown InxGa1-xAs/GaAs layers by transmission electron microscopy methods relying on the chemical sensitivity of the (002) beam. The calculations go beyond the limits of the isolated atom approximation, because they take into account charge redistribution effects between atomic sites in the crystal, strain, and static atomic displacements. The computations were performed by the full potential linearized augmented plane-wave method using a generalized gradient approximation for the exchange and correlation part of the potential. The calculations of strained InxGa1-xAs correspond to the strain state in specimens with large, small, and intermediate thickness in the electron beam direction. Additionally, the effect of static atomic displacements is taken into account. All results are listed in a parameterized form. The calculated 002 structure factor vanishes at an In concentration of 16.4%. This value is in a good agreement with previously reported experimental measurements. Hence, our results are a significant improvement with respect to the isolated atom approximation which is conventionally applied in transmission electron microscopy simulations, and which predicts a value of 22.5%.

A microscopic theory for the coupling of molecular orientations with acoustic lattice displacements is proposed. The relevant interaction is quadratic in the orientational-order-parameter variables and linear in longitudinal strains. The coupling is evaluated for a complex molecular structure. The intermolecular potential is obtained from interaction centers placed at nuclei and at the centers of interatomic bonds. The free energy is derived and the experimental consequences of the theory are studied. The Clausius-Clapeyron equation for orientational melting is obtained. The theory explains the decrease of the lattice constant at the first-order phase transition and the increase of the transition temperature with applied pressure.

Topological insulators, a new class of fascinating materials, are ideally bulk insulating and surface conducting. They are intensely studied due to their special physics and possible future applications, such as in spintronics. Adding defects (point-, line-, planar- and 3D defects), modulating the structure or interfacing the material with another material is a common practice to obtain the desired properties for applications. In this thesis, different kinds of adaptations of topological insulators and structurally related materials were studied. The atomic structure of the materials was determined, because this will affect the properties of the material. Different transmission electron microscopy techniques, complemented with first-principles calculations using the VASP code, were used to characterize the structures. The first part of the thesis concerns the characterization of the bulk structure of topological insulators. Bi2Se3 and (Bi1-xInx)2Se3 showed atomic mobility around and across the van der Waals gap between the quintuple layers. The topological insulator-normal insulator Sb2(Te1-xSex)3 showed a different substitution order than reported in literature. Some members of the GemBi2nTe(m+3n) series were trigonal layered structures with l-layered (l=7,9,11,5-7) building blocks instead of the five-layered building blocks for Bi2Se3 and others were rock salt structures with planar defects. The second part of the thesis reveals the structure and chemical composition of the oxidized layers and sublayers of Bi2Te3, Sb2Te3, (Sb0.55Bi0.45)2Te3 and GemBi2nTe(m+3n) and oxidation mechanisms were proposed. Also the structure and chemical composition of the interface between the (approximately) 20 nm thick Fe layer and Bi2Te3 is shown, unfolding the intermediate 3.5 nm amorphous FeTe interface layer, where excessive Bi migrates to the shallow bulk forming septuple layers of Bi3Te4. In the last part of the thesis, the bulk structures of two structurally related materials, α-GeTe and Fe2Ge3, were solved: α-GeTe, showed a planar defect structure, while Fe2Ge3 was incommensurately modulated.

Chemical tankers transport a wide variety of chemical products over sea. On the modern parcel tankers, up to 50 different cargoes can be transported on the same voyage and request special attention towards compatibility and segregation of the products. But the characteristics of the various products might also be a danger for the ship and its crew, related to flammability and toxicity. Prevention of contamination of the cargo is another major concern of a ship’s officer. It is very unusual that the same cargo is loaded consecutively in the same tank, this in contrast to the transportation of crude oil. Considering the number of tanks and parcels on board modern chemical tankers, tank cleaning and gas-freeing operations are frequently occurring events, both in port and at sea. It is common for several cargo operations to happen at the same time. The discharging of product A is going on while the loading of product B is underway and also the cleaning of another tank that previously contained product C, not forgetting possible ballast operations and sampling of tanks with surveyors. IMO circular 1095§11 [1], which refers to possible danger for the crew, was the prime motive for this thesis. This circular states verbatim that during cargo loading, tank cleaning and gas-freeing operations on board a tanker carrying liquid bulk containing benzene, the crew is exposed to the largest risk of exposure to vapours from the products carried, both whilst in the accommodation and on open deck. IMO circular 1220 [2] discusses the same cargo operations, stating “Experience has shown that it has proven impossible to keep the measured vapour concentrations below acceptable levels”. The presence of cargo vapours in the accommodation gives particular cause for concern and is something we investigated in more detail. To date, Marpol Annex VI [3], regulation 15, is the only regulation related to the emission by ships of volatile organic compounds. This regulation requires only for the loading of the vessel a vapour emission collecting system. There are no regulations for the other cargo operations. At first we performed an on-board measurement program where we quantitatively analysed the presence of 7 aromatic hydrocarbons, namely Benzene, Toluene, Ethylbenzene, m+p-xylene, o-xylene (BTEX), 1,3,5 trimethylbenzene (1,3,5-TMB) and 1,2,4 trimethylbenzene (1,2,4-TMB) . With the use of the Radi¨ello® passive samplers we analysed the presence of cargo vapours on board 3 sister ships during their multi-stop journeys and normal cargo operations. At every port of call, cargo was loaded and/or discharged. The following voyages were studied: (1) ship A handling BTEX related cargo, (2) ship B with cargo that was not BTEX related, (3) ship C with the focus on transport of benzene, and (4) ship C where BTEX pollutant sources other than the cargo sources were identified. From these various journeys we found confirmation of the IMO statement related to the tank cleaning and gas-freeing operations of tanks with liquids in bulk containing benzene. We compared our results with the European Union threshold-limit values, time-weighted vi average. Only for benzene we exceeded this threshold during tank cleaning and tank ventilating. We compared the position of the accommodation ventilation inlet with the engine room ventilation inlet regarding possible pollution with cargo vapours. Our results further indicated that the difference in absolute concentration between the cargo area and the non-cargo area is less pronounced than expected. Furthermore, the pollutant concentrations inside the engine room were relatively high during all 4 investigations. This might be an indication of insufficient or inefficient ventilation or the fact that other pollution sources being present in the engine room. Further research is needed to identify the exact cause for the increased concentrations. Secondly, we performed wind tunnel simulations in order to obtain a complete picture of the pollution gradients around the ship and their evolution for different wind orientations and wind velocities. In the first wind tunnel experiment we used the method of smoke visualization to ascertain the streamlines around the vessel. Via the cargo tank outlet we released an amount of smoke that was visualized by means of a laser plane and recorded with a CCD camera. Here we developed our own method of image treatment in order to make even the smallest smoke concentrations visible. In the second wind tunnel experiment we used a tracer gas in order to calculate K-values as a measure for dispersion. The tracer gas was released from the tank manhole and the tank high velocity pressurevacuum valve (PV-valve). One of the goals of this experiment was to compare both outlets regarding the resulting concentration of cargo vapours inside the accommodation and engine room. The PV-valve gave the best results for all different wind conditions, except for the situations with a wind direction from the bow. This situation must be avoided and therefore the ship’s course and/or speed must be changed to obtain a different relative wind direction when the PV-valve is in use. Finally we set up a CFD simulation of the situation where for different wind velocities headwind situations were analysed. In the resulting images we focused on the streamlines of the cargo vapours when using the PV-valve compared to the use of the manhole. These images were a confirmation of previous results, namely that (1) for a wind direction near the bow, the use of the PV-valve as tank outlet will significantly increase the cargo vapour concentrations in and around the accommodation and (2) the position of the ventilation inlet of the accommodation is the best option. Thanks to its elevation it proves a far better position than the engine room ventilation inlet.

Thin films of heavily B-doped nanocrystalline diamond (B:NCD) have been investigated by a combination of high resolution annular dark field scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy performed on a state-of-the-art aberration corrected instrument to determine the B concentration, distribution and the local B environment. Concentrations of [similar]1 to 3 at.% of boron are found to be embedded within individual grains. Even though most NCD grains are surrounded by a thin amorphous shell, elemental mapping of the B and C signal shows no preferential embedding of B in these amorphous shells or in grain boundaries between the NCD grains, in contrast with earlier work on more macroscopic superconducting polycrystalline B-doped diamond films. Detailed inspection of the fine structure of the boron K-edge and comparison with density functional theory calculated fine structure energy-loss near-edge structure signatures confirms that the B atoms present in the diamond grains are substitutional atoms embedded tetrahedrally into the diamond lattice.