Electron crystallography is powerful for determination of complex structures. The newly-developed 3D electron diffraction (ED) methods make structure determination from nano- and micron-sized crystals much easier than using other methods, for example X-ray diffraction. Almost complete 3D ED data can be collected easily and fast from crystals at any arbitrary orientations. Dynamical effects are largely reduced compared to zonal ED patterns. 3D ED is powerful for phase identification and structure solution from individual nano- and micron-sized crystals, while powder X-ray diffraction (PXRD) provides information from all phases present in the samples. 3D ED methods and PXRD are complementary and their combinations are promising for studying multiphasic samples and complicated crystal structures. In this thesis, the feasibility and capability of 3D ED methods, specifically rotation electron diffraction (RED), in phase identification and structure determination of different kinds of crystalline materials with nano- or submicrometer-sized crystals are investigated. Experimental conditions for RED data collection and data processing in relation to data quality, as well as the challenges in the applications of RED are discussed. RED was combined with PXRD to identify phases from as-synthesized samples and to characterize atomic structures of eleven crystalline compounds. It was shown to be possible to identify as many as four distinct compounds within one sample containing submicron-sized crystals in a Ni-Se-O-Cl system. RED was also used to determine unit cell and symmetry of isoreticular metal-organic frameworks (SUMOF-7) and solve five zeolite structures with new frameworks, ITQ-51, ITQ-53, ITQ-54, EMM-23 and EMM-25 and that of a metal-organic framework (MOF), SUMOF-7I. The structure of an open-framework germanate SU-77 was solved by combining RED with PXRD. The structures of the zeolites and SU-77 were confirmed by Rietveld refinement against PXRD. High-resolution transmission electron microscopy was used to confirm the structure models of ITQ-51, EMM-25 and SUMOF-7I. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Accepted. Paper 6: Manuscript. Paper 7: Epub ahead of print. Paper 9: Manuscript. Paper 11: Manuscript.</p>

Thesis (doctoral)--Helsinki University of Technology, 2007. / Includes bibliographical references. Also available on the World Wide Web.

Abstract Experimental synchrotron radiation induced electron- and ion spectroscopies together with electron-ion and ion-ion coincidence techniques as well as electron energy loss spectroscopy have been used to study the electronic properties of several vapor phase samples. In this thesis studies of the electronic structure and fragmentation of Sb4 clusters, photo- and Auger electron spectroscopy of atomic Si and Pb as well as ultra high resolution VUV absorption of vapor phase KF molecules have been performed. The instrumentation and techniques used in the studies, especially the electron energy loss apparatus and the newly built ultra high resolution FINEST beamline branch, are presented.

The four pillars of material science and engineering namely structure, processing, properties and performance form the so-called material paradigm. At the heart of the material paradigm is materials characterization, which is used to measure and identify the relationships. Materials Characterization typically reconstructing the conditions giving rise to a measurement, a classic inverse problem. The solutions of these inverse problems are under or over determined and not unique. The solutions of these inverse problems can be greatly improved if accurate forward models exist for these characterization experiments. In this thesis, we will be focusing of developing forward models for electron diffraction modalities. Specifically, four different forward models for electron diffraction, namely the Electron Backscatter Diffraction, Electron Channeling Patterns, Precession Electron Diffraction and Transmission kikuchi Diffraction modalities are presented. Further, these forward models are applied to important materials characterization problems, including diffraction pattern indexing using the dictionary approach and forward model based orientation refinement. Finally, a novel pole figure inversion algorithm using the cubochoric representation and model based iterative reconstruction is also presented.

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Electron Ptychography is a technique to retrieve the phase information of the medium through which the electron wave travels in a Transmission Electron Microscope (TEM). Phase calculation is carried out by acquiring an oversampled dataset of diffraction patterns from the sample and execution of a Fourier-based mathematical solution or algorithm using the collected dataset of intensity patterns. The phase of the electron wave contains valuable information about the structure of the material under study. In this contribution, we provide a scientific background necessary for understanding the phase calculation method, examine the capabilities and limitations of the Electron Ptychography in experimental setup and introduce two novel methods to increase the signal to noise ratio by using the same dose budget used in a classic Ptychography experiment. / Thesis / Master of Applied Science (MASc)

Cette thèse expérimentale traite de l'électroluminescence de contacts atomiques en or. Les contacts métalliques ponctuels sont formés et pilotés à l'aide d'un dispositif de jonction brisée contrôlée mécaniquement. Les contacts sont formés à partir d'un fil d'or et sont étudiés à la température ambiante.L'électroluminescence est observée dans le visible au travers d'un microscope optique. Le détecteur est une caméra sensible en silicium. Pour l'analyse du spectre émis, un dispositif dispersif en ligne a été spécifiquement développé. Pour l'infrarouge, le détecteur photovoltaïque monocanal est en InAsSb.Nos mesures électriques et optiques simultanées permettent de sonder la physique des interactions entre électrons et photons à l'échelle nanométrique. L'électroluminescence est attribuée à l'émission spontanée d'un nanogaz à haute température d'électrons chauds, conséquence des fortes densités de courant. Cette haute température électronique est fonction des conditions opératoires. Pour ces nanojonctions d'or, nos expériences nous permettent d’en proposer une expression analytique simple.Ces travaux complètent des expériences similaires menées depuis le début des années 2000. Ils sont discutés dans le cadre d'un modèle développé pour expliquer l'émission d'électrons chauds à partir de films métalliques granulaires. Nous discutons de la physique d’échauffement du gaz d’électron en rapprochant nos résultats d'expériences pompe/sonde femtoseconde interrogeant la dynamique des électrons hors équilibre dans des nanobilles d'or ainsi que d'expériences de transport en physique mésoscopique menées à très basse température. / This experimental thesis deals with electroluminescence from gold atomic point contacts. Metallic point contacts are formed and driven with a home-made mechanically controlled break junction device. The nanojunctions are made from gold wires. Experiments are performed at room temperature and in air.Electroluminescence is observed in the visible range with an infinity corrected inverted optical microscope. The detector is a high sensitivity silicon camera. To perform spectral analysis, a dispersive on-line device has been developed to be inserted directly within the microscope. A reflective objective collects infrared photons and focuses them onto an InAsSb photovoltaic cooled detector.Our simultaneous electrical and optical measurements allow us to investigate the physics of electrons and photons interactions at the nanometric scale. Electroluminescence is explained by the spontaneous emission of a hot electron nano-gas favoured by huge current densities. This high electron temperature depends on operating conditions. For gold ballistic nanojunctions, our results lead us to propose a simple expression of this temperature. This work extends similar electroluminescence studies performed since the early 2000’s. The results are discussed in this context and in the framework of a model first introduced to account for hot electron emission from thin granular metallic films. Moreover, we discuss the physics leading to the hot electron gaz with the support of pump/probe femtosecond experiments probing the nonequilibrium electron dynamics in gold nanosphere and with the support of low temperature mesoscopic transport experiments.

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This work investigates the electronic properties of very small gold and semiconductor particles using Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and Ballistic Electron Emission Spectroscopy (BEES). Complementary theoretical works were also performed. The first theoretical work was to calculate the quantized states in the CdS/HgS/CdS quantum-well-quantum-dot nanocrystals. An eight-band envelope function method was applied to this system. This method treats exactly the coupling between the conduction bands, the light-hole bands, the heavy-hole bands, and the spin-orbit split bands. The contributions of all other bands were taken into account using second order perturbation theory. Gold nanocrystals with diameters of 1.5 nm have discrete energy levels with energy spacings of about 0.2 eV. These values are comparable to the single electron charging energy, which was about 0.5 eV in our experimental configuration. Since bulk gold doesnt have an energy gap, we expect the electron levels both below and above the Fermi level should be involved in the tunneling. Measured spectroscopy data have rich features. In order to understand and relate these features to the electronic properties of the nanocrystals, we developed a tunneling model. This model includes the effect of excited states that have electron-hole pairs. The relaxation between discrete electron energy levels can also be included in this model. We also considered how the nanocrystals affect the BEES current. In this work an ultra-high vacuum and low-temperature STM was re-designed and rebuilt. The BEEM/BEES capabilities were incorporated into the STM. We used this STM to image gold nanocrystals and semiconductor nanocrystals. STS and BEES spectra of gold nanocrystals were collected and compared with calculations.