No description available.

No description available.

Nesta tese foram utilizadas as espectroscopias de espalhamento Raman intensificado pela superficie(Surface-EnhancedRaman Scattering- SERS) e Raman ressonante para monitorar a adsorção e o comportamento faradáico do ácido esquárico e seus derivados, além de um sal de transferência de carga de esquarato e tetratiofulvaleno e dois copolímeros de esquarato e pirróis. Outro tema desenvolvido neste estudo foi a construção de substratos SERS-ativos de elevado desempenho. A técnica SERS tem sido campo de grande interesse desde a detecção do espectro aman de uma única molécula, em 1997.O desenvolvimento de substratos SERS-ativos de elevado desempenho depende da apropriada manipulação de superficies metálicas nanoestruturadas, o que nos levou a adquirir conhecimento na síntese destes substratos. Colóides e filmes de Ag e Au foram preparados e seu desempenho SERS comparado com a superficie de eletrodos ativados por ciclos de oxidação-redução. A intensificação obtida para esses filmes foi comparávelà observada em eletrodos. O ânion esquarato, produto da dupla desprotonação do ácido esquárico, apresenta substancial delocalização de carga, sendo amplamente usado na síntese de materiais orgânicos condutores. Foram realizadas as caracterizações vibracionais do ácido esquárico, hidrogeno-esquarato e esquarato, além de seu radical, através da técnica SERS. Baseado nos resultados experimentais, um mecanismo de adsorção destas espécies sobre eletrodos de Au e filmes de ilhas de Ag ou Au foi proposto. Os resultados SERS também mostram que o ácido esquárico adsorvido sobre Au é decomposto em um processo catalisado pela superficie metálica, emboraestas espécies sejam muito estáveis em solução. Baseado nos resultados SERS do tetratiofulvaleno e de suas espécies oxidadas, foi eletroquimicamente, e formado pelo radical-cátion tetratiofulvaleno e o radical-ânion esquarato. Os elevados fatores de intensificação de Raman ressonante e SERS do tetratiofulvaleno impediram a detecção do esquarato no sal de transferência de carga. Duas poliesquaraínas polí(1-metilpirrol-co-ácido esquárico) e poli(1-dodecilpirrol-coácido esquárico) foram sintetizadas e caracterizadas pelas espectroscopias Raman ressonante, SERS e ressonância paramagnética de spin (EPR). Estes resultados nos levaram a propor uma estrutura polimérica diferente da apresentada pela literatura. Nossos resultados mostraram a presença de um radical orgânico delocalizado, do ânion esquarato protonadoe de dicátions similares aos presentes no polipirrol. / In this Thesis Surface-Enhanced Raman Scattering (SERS) and resonance Raman spectroscopy were used for monitoring the adsorption and faradaic behavior of squaric acid and its derived species. In addition, the charge transfer salt of squarate and tetrathiofulvalene and the copolymers of squarate and pyrroles were also studied. Another theme developed in this study was the manufacturing of. high performance SERS-active substrates. SERS technique has been a field of great interest since the detection of a single molecule Raman spectrum in 1997. The development of high perforrnance SERS-active substrates depends on the proper manipulation of nanostructured metal surfaces, and order to acquire know-how in the synthesis of such substrates. Ag and Au island films as well as colloid substrates were prepared and compared with electrode surfaces SERS activated by oxidation-reduction cycles. The enhancement factor obtained for such films is comparable to those observed in electrodes. The squarate anion, product of the double deprotonation of squaric acid, shows substantial charge delocalization, being largely used in the synthesis of conducting organic materiaIs. The vibrational characterization of squaric acid, hydrogen-squarate, squarate as well as its radical was carried out from the SERS data. Based on the experimental data an adsorption mechanism of such species on Au electrodes and Au or Ag islands was proposed. SERS results also show that squaric acid adsorbed on Au is decomposed in a process catalyzed by the metal surface, although in solution it proves to be a very stable specles. The vibrational characterization of an electrochemically forrned charge transfer salt between tetrathiofulvalene radical-cation and squarate radical-anion was done based on the SERS data of tetrathiofulvalene and its oxidation species. The large resonance Raman and SERS enhancement factors of tetrathiofulvalene preclude the detection of the squarate species in the charge transfer salt. Two polysquaraines: poly(1-methylpyrrole-co-squaric acid) and poly(1-dodecylpyrrole-co-squaric acid) were synthesized and characterized by resonance Raman, SERS and Electron Paramagnetic Resonance Spectroscopy (EPR) techniques. The results lead us to propose a polymeric structure different from that present in the literature. Our data showed a delocalized organic radical in the polymeric matrices together with dications similar to those present in polypirrole and protonated squarate anion.

When an electronic system is confined in one or more dimensions to a length scale comparable to the de Broglie wavelength, quantum confinement occurs. In metallic quantum thin films grown on semiconductor substrates, such confinement occurs between the vacuum-solid and the solid-solid interfaces, which results in the formation of distinctive quantum well states (QWS). Due to this confinement, many physical phenomena occurring in the thin metal system are totally different from the bulk system, which makes the study of quantum thin films interesting and important. In this thesis, quantum thin film studies, mainly based on the Pb/Si(111) system, were performed utilizing low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) with a focus on three main aspects: phase relationship, surface reactivity, and coherent coupling. The Pb/Si(111) system is chosen due to its unique phase matching between the Fermi wavelength and the lattice spacing along [111], leading to a bi-layer quantum oscillation in many physical properties, including the surface energy and the work function. Surprisingly, STM/STS measurement revealed that quantum oscillations of work function and surface energy have identical phase, in contrast to a theoretically predicted 1/4 wavelength phase shift in the phase relationship. Here, a new solution to this puzzle is provided. Furthermore, it is found out that the oxidation rate of Pb/Si(111) system is greatly enhanced in the presence of atomic scale catalyst -- Cs substitutional atoms, while the reactivity to CO is saturated after the initial enhanced nucleation. Finally, by inserting thin Ag layers in between Pb/Si(111) system, the coherent coupling of double quantum wells (a Pb quantum well and a Ag quantum well) are probed, where combined QWS features are observed by STS measurement. The growth mechanism of these heterostructures -- Pb/Ag/Si(111) -- is also investigated. / text

Nesta tese foram utilizadas as espectroscopias de espalhamento Raman intensificado pela superficie(Surface-EnhancedRaman Scattering- SERS) e Raman ressonante para monitorar a adsorção e o comportamento faradáico do ácido esquárico e seus derivados, além de um sal de transferência de carga de esquarato e tetratiofulvaleno e dois copolímeros de esquarato e pirróis. Outro tema desenvolvido neste estudo foi a construção de substratos SERS-ativos de elevado desempenho. A técnica SERS tem sido campo de grande interesse desde a detecção do espectro aman de uma única molécula, em 1997.O desenvolvimento de substratos SERS-ativos de elevado desempenho depende da apropriada manipulação de superficies metálicas nanoestruturadas, o que nos levou a adquirir conhecimento na síntese destes substratos. Colóides e filmes de Ag e Au foram preparados e seu desempenho SERS comparado com a superficie de eletrodos ativados por ciclos de oxidação-redução. A intensificação obtida para esses filmes foi comparávelà observada em eletrodos. O ânion esquarato, produto da dupla desprotonação do ácido esquárico, apresenta substancial delocalização de carga, sendo amplamente usado na síntese de materiais orgânicos condutores. Foram realizadas as caracterizações vibracionais do ácido esquárico, hidrogeno-esquarato e esquarato, além de seu radical, através da técnica SERS. Baseado nos resultados experimentais, um mecanismo de adsorção destas espécies sobre eletrodos de Au e filmes de ilhas de Ag ou Au foi proposto. Os resultados SERS também mostram que o ácido esquárico adsorvido sobre Au é decomposto em um processo catalisado pela superficie metálica, emboraestas espécies sejam muito estáveis em solução. Baseado nos resultados SERS do tetratiofulvaleno e de suas espécies oxidadas, foi eletroquimicamente, e formado pelo radical-cátion tetratiofulvaleno e o radical-ânion esquarato. Os elevados fatores de intensificação de Raman ressonante e SERS do tetratiofulvaleno impediram a detecção do esquarato no sal de transferência de carga. Duas poliesquaraínas polí(1-metilpirrol-co-ácido esquárico) e poli(1-dodecilpirrol-coácido esquárico) foram sintetizadas e caracterizadas pelas espectroscopias Raman ressonante, SERS e ressonância paramagnética de spin (EPR). Estes resultados nos levaram a propor uma estrutura polimérica diferente da apresentada pela literatura. Nossos resultados mostraram a presença de um radical orgânico delocalizado, do ânion esquarato protonadoe de dicátions similares aos presentes no polipirrol. / In this Thesis Surface-Enhanced Raman Scattering (SERS) and resonance Raman spectroscopy were used for monitoring the adsorption and faradaic behavior of squaric acid and its derived species. In addition, the charge transfer salt of squarate and tetrathiofulvalene and the copolymers of squarate and pyrroles were also studied. Another theme developed in this study was the manufacturing of. high performance SERS-active substrates. SERS technique has been a field of great interest since the detection of a single molecule Raman spectrum in 1997. The development of high perforrnance SERS-active substrates depends on the proper manipulation of nanostructured metal surfaces, and order to acquire know-how in the synthesis of such substrates. Ag and Au island films as well as colloid substrates were prepared and compared with electrode surfaces SERS activated by oxidation-reduction cycles. The enhancement factor obtained for such films is comparable to those observed in electrodes. The squarate anion, product of the double deprotonation of squaric acid, shows substantial charge delocalization, being largely used in the synthesis of conducting organic materiaIs. The vibrational characterization of squaric acid, hydrogen-squarate, squarate as well as its radical was carried out from the SERS data. Based on the experimental data an adsorption mechanism of such species on Au electrodes and Au or Ag islands was proposed. SERS results also show that squaric acid adsorbed on Au is decomposed in a process catalyzed by the metal surface, although in solution it proves to be a very stable specles. The vibrational characterization of an electrochemically forrned charge transfer salt between tetrathiofulvalene radical-cation and squarate radical-anion was done based on the SERS data of tetrathiofulvalene and its oxidation species. The large resonance Raman and SERS enhancement factors of tetrathiofulvalene preclude the detection of the squarate species in the charge transfer salt. Two polysquaraines: poly(1-methylpyrrole-co-squaric acid) and poly(1-dodecylpyrrole-co-squaric acid) were synthesized and characterized by resonance Raman, SERS and Electron Paramagnetic Resonance Spectroscopy (EPR) techniques. The results lead us to propose a polymeric structure different from that present in the literature. Our data showed a delocalized organic radical in the polymeric matrices together with dications similar to those present in polypirrole and protonated squarate anion.

The present work represents a systematical study of the growth of columnar, metallic thin films deposited under highly oblique vapor incidence on planar substrates. Oblique angle deposition is a physical vapor deposition technique that is based on the self-shadowing effect. This enables the fabrication of highly porous thin films that are composed of three-dimensionally separated, micro-, and nano-sized columns. For this study, metals that cover a wide range of melting points and crystal structures have been chosen, and the observed growth characteristics are compared with each other to gain information about the growth of obliquely deposited metallic thin films in general. Among the various parameters that have an influence on the growth of columnar thin films, in the focus of this work are the angle of the incoming particle flux, substrate rotation frequency, and substrate temperature as well as the influence of the residual gas atmosphere. The first part deals with a morphological analysis of the columnar, metallic thin films by scanning electron microscopy (SEM). The columnar shape, the columnar tilt angle, and the thin film porosity are investigated depending on the incidence flux direction as well as substrate temperature and rotation. It is examined how a reduction of the substrate temperature down to 77 K - realized by a liquid nitrogen cooled sample holder - influences the growth of the columnar thin films. Further, it is analyzed how substrate rotation influences the local deposition geometry and accordingly the growth behavior of tilted columns, spirals, screws, and upright columns. Based on geometrical considerations, a theoretical model is proposed and compared with the made observations. The second part focusses on the high-resolution local structure analysis of individual columns via (scanning) transmission electron microscopy (TEM). On the one hand, the columnar structure is analyzed depending on the substrate temperature and substrate rotation via high resolution TEM. On the other hand, the crystallinity of individual columns is studied along the entire column by nanobeam electron diffraction. This technique is also applied to gain information about the orientation of the crystallites at the substrates surface and to investigate the selection processes of crystalline orientations during the growth. Moreover, the presented studies reveal under which conditions single crystalline columns are forming. In the final part, the texture of the columnar, metallic thin films is analyzed depending on the film thickness, the angle of the incoming particle flux as well as on the substrate temperature. X-ray diffraction (XRD) measurements, such as pole figures, are applied to determine the orientation of the lattice planes in the columns depending on the incident flux direction and on the substrate temperature. The observations are backed by reflection high-energy electron diffraction (RHEED) investigations. A model is developed that enables to explain why the tilt of the lattice directions in the columns is not equal to the tilt angle of the columns. A further theoretical model is introduced that enables to roughly estimate the tilt angle of the lattice direction that ensures the fastest vertical columnar growth.:1 MOTIVATION 7 2 BASICS OF OBLIQUE ANGLE DEPOSITION 9 2.1 Thin film growth by oblique deposition 9 2.1.1 Physical vapor deposition 9 2.1.2 Nucleation 10 2.1.3 Shadowing 11 2.1.4 Structure of individual columns 12 2.2 Sculpturing thin films on the nanometer scale 13 2.2.1 Angle of the incoming particle flux 13 2.2.2 Substrate rotation 16 2.2.3 Substrate temperature 17 2.3 Application areas for metallic nanostructured thin films 20 3 EXPERIMENTAL DETAILS 23 3.1 Sample fabrication 23 3.1.1 General deposition system setup and evaporation process 23 3.1.2 Crucibles, substrates, and sample holders 25 3.1.3 Controlling substrate movement and temperature 26 3.1.4 Controlling film thickness and deposition rate 29 3.2 Sample characterization 30 3.2.1 Scanning electron microscope (SEM) 30 3.2.2 Transmission electron microscopy (TEM) 31 3.2.3 X-Ray Diffraction (XRD) and In-Plane Pole Figure measurements (IPPF) 33 3.2.4 Reflection high-energy electron diffraction (RHEED) 36 3.2.5 Raman scattering spectroscopy 36 4 MORPHOLOGICAL ANALYSIS OF COLUMNAR THIN FILMS 39 4.1 Oblique angle deposition 40 4.1.1 Deposition at room temperature 40 4.1.2 Deposition at different temperatures 43 4.2 Glancing angle deposition 61 4.2.1 Continuous substrate rotation 61 4.2.2 Discrete substrate rotation 66 4.3 Summary of results 69 5 STRUCTURAL ANALYSIS OF INDIVIDUAL COLUMNS 71 5.1 Oblique angle deposition 71 5.1.1 Tilted columns grown at room temperature 71 5.1.2 Tilted columns grown at different substrate temperatures 78 5.2 Glancing angle deposition 82 5.2.1 Vertical columns grown by continuous substrate rotation 82 5.2.2 Zigzag columns grown by discrete substrate rotation 85 5.3 Discussion 87 5.4 Summary of results 89 6 TEXTURE ANALYSIS OF COLUMNAR THIN FILMS 91 6.1 Influence of the film thickness 91 6.2 Influence of the incoming flux direction 99 6.3 Influence of the substrate temperature 110 6.4 Summary of results 116 7 SUMMARY AND CONCLUSIONS 119 8 LIST OF LITERATURE 123 9 LIST OF ABBREVIATIONS 134 10 LIST OF VARIABLES AND CONSTANTS 136 11 ACKNOWLEDGEMENTS 139 PUBLICATION LIST 140 SELBSTSTÄNDIGKEITSERKLÄRUNG 143

No description available.

Metallic thin films consisting of separated nanostructures are fabricated by evaporative glancing angle deposition at room temperature. The columnar microstructure of the Ti and Cr columns is investigated by high resolution transmission electron microscopy and selective area electron diffraction. The morphology of the sculptured metallic films is studied by scanning electron microscopy. It is found that tilted Ti and Cr columns grow with a single crystalline morphology, while upright Cr columns are polycrystalline. Further, the influence of continuous substrate rotation on the shaping of Al, Ti, Cr and Mo nanostructures is studied with view to surface diffusion and the shadowing effect. It is observed that sculptured metallic thin films deposited without substrate rotation grow faster compared to those grown with continuous substrate rotation. A theoretical model is provided to describe this effect