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An (e,2e) electron scattering spectrometer has been constructed and used for the first time to investigate the spectral momentum density of the valence bands of a solid target. This technique provides fundamental information about the electronic structure of both crystalline and amorphous solids. The three fundamental quantities, the band structure, electron density of states, and electron momentum distribution can be simultaneously derived from the measured (e,2e) cross section. A review of single electron and (e,2e) scattering theory is given with an emphasis on scattering from solids. The effects of multiple scattering are discussed and a method of deconvoluting those effects from the measured (e,2e) cross section is developed. There is a detailed description of the spectrometer design and operation with particular attention given to the electron optics and voltage distribution. The algorithms and software for computer aided data acquisition and analysis are also outlined, as is error analysis. The techniques employed in the preparation and characterization of extremely thin film samples of a-C and single crystal graphite are described. An analysis of the data taken for a-C samples is given. The data are compared with the results of complementary experiments and theory for graphite, diamond, and a-C which are given in a review of the literature. The existence of a definite dispersion relation ε(q) in amorphous carbon is demonstrated. The a-C band structure appears to be more similar to that of graphite than to that of diamond, however it differs significantly from both in some respects. The measured spectral momentum density seems compatible with a model of a-C based on small, randomly-oriented islands of quasi-2D graphite-like continuous random network structures. However, no definitive interpretations can be made until higher resolution experiments are performed on both a-C and single crystal graphite. / Ph. D.

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<p>In this dissertation core level electron spectroscopy has been employed to study various aspects of metal oxide films grown under ultra-high vacuum conditions. </p><p>Studies on <i>in situ</i> ion insertion of lithium into thin TiO₂ systems were performed. The electronic and geometric properties are investigated in detail, along with an estimation of charge transfer from Li to Ti. </p><p>A detailed study of chemical vapour deposition of ZrO₂ on Si(100)-(2x1) was performed. ZrO₂ is found to be an insulator, i.e. its electronic levels are decoupled from the substrate and the Zr levels are best referenced to the local vacuum level. The alignment of the valence and conduction band has been determined. </p><p>Combinatorial chemical vapour deposition of TiO₂ and ZrO₂ on Si(100)-(2x1) was realized. A film with graded stoichiometry consisting of pure TiO₂ and ZrO₂ on the opposing ends and mixed composition of both oxides in the middle was obtained. A detailed study of the electronic levels revealed that ZrO₂ remains an insulator in the monolayer regime and that modification of ZrO₂ with a small amount of TiO₂ leads to a more symmetric alignment of the bands relative to Si. </p><p>The influence of a core hole on the O 1s x-ray absorption spectrum in TiO₂ and ZrO₂ is elucidated. Supported by O 1s photoemission measurements and <i>ab initio</i> calculations it is concluded that the static final state picture as well as dynamical threshold effects must be considered in order to determine the location of the conduction band minimum within the XAS framework. </p><p>Finally a Co modified Co:ZnO film was shown to display ferromagnetic properties. It could be evidenced that Co with oxygen as nearest neighbours was responsible for the magnetism and not metallic Co.</p>

For an electronic device well-designed interfaces are critical for the performance. Studies of interfaces down to an atomic level are thus highly motivated both from a fundamental and technological point of view. In this thesis, a surface science approach has been employed to study the formation of interfaces in systems relevant for transistor and solar cell applications. Surface science methodology entails ultra high vacuum environment, single crystalline surfaces, submonolayer control of deposited material, surface sensitive spectroscopy and atomic resolution microscopy. The primary experimental method for characterization is electron spectroscopy. This is a family of very powerful experimental techniques capable of giving information on the atomic level. Additionally, studies have been performed using scanning tunnelling microscopy. Combined these two methods can provide an atomic level characterisation of the geometric and electronic properties of the surface. The emphasis of this work is placed on ultra thin TiO2 and ZrO2 films grown on silicon substrates by means of ultra-high vacuum metal-organic chemical vapour deposition. ZrO2 has also been grown on SiC and FeCrAl. Deposition has been performed with different process parameters. The interface region of each film has been characterised. The band alignment, a most important issue with regard to the development of new transistor devices, for the ZrO2/Si(100) system has been explored. Decomposition pathways of the metal organic precursors have been studied in detail. Changing process parameters is shown to alter both the precursor decomposition pathway and the nature of the interface region, thus opening the possibility to tailor the material function. The titanium dioxide films grown in situ have shown to be excellent models of nanostructured electrode materials. In this spirit, interfaces of model systems for the solid-state dye-sensitized solar cell have been studied. Links between device performance and interface structure have been elucidated.

The dye-sensitized solar cell is a promising solar cell technology. In these systems the key process for light to electricity conversion is molecular in nature and is initiated in dye molecules adsorbed at a semiconducting surface. This thesis focuses on the electronic and molecular surface structure of the dye/TiO2 interface, and the experimental results were obtained from surface sensitive X-ray based electron spectroscopic methods. Two families of dyes, triarylamine based organic dyes and ruthenium based inorganic dyes, were investigated. The effect of dye structural modications on the interfacial properties was studied, such as the surface concentrations, dye molecular surface orientation, molecular interactions, and energy level matching. Also, the impact of additional parameters such as the incorporation of coadsorbents and the solvents used for dye sensitization were studied and complementary photoelectrochemical characterization was used to demonstrate functional properties corresponding to changes in the molecular layers. The experiments provided information on how specic structural modications change the frontier electronic structure. The results also showed that the adsorption of the organic dye leads to submolecular electronic changes, and that the dye surface orientations in general favor effcient energy conversion. Moreover, effects of solvents and coadsorbents, on both energy level matching between the dye and the TiO2 substrate and the surfacemolecular structure were quantied.

In this dissertation core level electron spectroscopy has been employed to study various aspects of metal oxide films grown under ultra-high vacuum conditions. Studies on in situ ion insertion of lithium into thin TiO2 systems were performed. The electronic and geometric properties are investigated in detail, along with an estimation of charge transfer from Li to Ti. A detailed study of chemical vapour deposition of ZrO2 on Si(100)-(2x1) was performed. ZrO2 is found to be an insulator, i.e. its electronic levels are decoupled from the substrate and the Zr levels are best referenced to the local vacuum level. The alignment of the valence and conduction band has been determined. Combinatorial chemical vapour deposition of TiO2 and ZrO2 on Si(100)-(2x1) was realized. A film with graded stoichiometry consisting of pure TiO2 and ZrO2 on the opposing ends and mixed composition of both oxides in the middle was obtained. A detailed study of the electronic levels revealed that ZrO2 remains an insulator in the monolayer regime and that modification of ZrO2 with a small amount of TiO2 leads to a more symmetric alignment of the bands relative to Si. The influence of a core hole on the O 1s x-ray absorption spectrum in TiO2 and ZrO2 is elucidated. Supported by O 1s photoemission measurements and ab initio calculations it is concluded that the static final state picture as well as dynamical threshold effects must be considered in order to determine the location of the conduction band minimum within the XAS framework. Finally a Co modified Co:ZnO film was shown to display ferromagnetic properties. It could be evidenced that Co with oxygen as nearest neighbours was responsible for the magnetism and not metallic Co.

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.

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Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-28T14:15:00Z No. of bitstreams: 1 rafaelfelipecoelhoneves.pdf: 2969229 bytes, checksum: cff09b57af6263220760e29c729a1382 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-07T21:09:40Z (GMT) No. of bitstreams: 1 rafaelfelipecoelhoneves.pdf: 2969229 bytes, checksum: cff09b57af6263220760e29c729a1382 (MD5) / Made available in DSpace on 2017-08-07T21:09:40Z (GMT). No. of bitstreams: 1 rafaelfelipecoelhoneves.pdf: 2969229 bytes, checksum: cff09b57af6263220760e29c729a1382 (MD5) Previous issue date: 2011-07-22 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Em uma variedade de técnicas espectroscópicas de impacto de elétrons em amostras gasosas, é fundamental utilizar feixes de elétrons de baixas energias focalizados, colimados e monocromatizados. Sua intensidade deve ser tal que seja possível realizar a aquisição de dados em um tempo mínimo, apresentando boa estatística. O requisito da monocromatização é o que garante obter o máximo de informações espectroscópicas de dado espectro. É na região de baixas energias do elétron incidente que ocorrem importantes processos, tais como distorções na nuvem eletrônica do alvo, efeitos de polarização, efeitos de troca, captura eletrônica. Entretanto, é justamente nesta faixa de energia onde se observa maior dificuldade experimental de se trabalhar devido a alta sensibilidade do feixe eletrônico tanto incidente, como espalhado. Neste trabalho, desenvolvemos pela primeira vez no país um canhão de elétrons de baixas energias, produzindo feixes de elétrons monocromatizados. O canhão foi cuidadosamente caracterizado em termos da intensidade do feixe eletrônico incidente e sua monocromatização, atingindo-se valores de energia de 0,105 eV e intensidades de até 280 nA para feixes de 170 eV. / In a variety of spectroscopic techniques of electron impact on gaseous samples, it is essential to use electron beams of low energy focused, collimated and monochromatized. The electron beam intensity should be such that it is possible to perform data acquisition in minimal period time, with good statistics. The requirement of electron beam monochromatization ensures to get as much information of a spectrum. It is in the low-energy electron incident that important processes occur, such as distortions in the electron cloud of the target, polarization effects, exchange effects and electron capture. However, it is precisely in this energy range where the experiments are more difficult to run due to the high sensitivity of the incident and scattered electron beam. In this work, we developed first in this country an electron gun for low energies, producing monochromatized electron beams. The electron gun has been carefully characterized in terms of intensity of the incident electron beam and its capacity of monochromatization, reaching values of energy of 0.105 eV and beam intensities up to 280 nA of 170 eV.