Este trabalho trata do estudo teórico atomístico das conformações da molécula de estireno sobre a superfície de Si(100)(2xl):H. Estudamos a molécula fisissorvida e quimissorvida sobre esta superfície. Os cálculos foram realizados através de Dinâmica Molecular Clássica. Nós reparametrizamos o Universal Force Field (UFF) com base em cálculos ab initio para sistemas modelo, e comparação a dados experimentais. Nossos resultados indicam que no processo de fississorção a região de vale da superfície é preferencial, e ocorre formação de agregados de moléculas antes do contato com a superfície. Quando passamos à análise da quimissorção de uma molécula, a região de vale permanece sendo o sítio preferencial para a posição do grupo vinil. Para as conformações de linhas de estireno, a estrutura mais estável tem todas as moléculas dispostas sobre a região de vale (ordenamento tipo \"pilha-1r\"); identificamos também outra estrutura, quase degenerada em energia, na qual o grupo vinileno se dispõe em conformação tipo \"espinha de peixe\", alternando entre a região de vale e sobre o dímero. / In this work we present a theoretical study of ,the conformation of styrene molecules on the Si(100)(2xl):H surface. We studied the conformations for styrene molecules physisorbed and chemisorbed on this surface. The study was conducted by Classical Molecular Dynamics. We performed a re-parametrization of the Universal Force Field (UFF), based on ab initio calculations for model structures, and comparison to experimental data. Our results show that for the physisorbed situations, the styrene molecules preferentially interact with the surface valley. We also identified that the molecules aggregate in clusters before reaching the surface. The valley is again the region of lowest energy for the vinylene position, for chemisorption of a single styrene molecule on the monohydride surface. For systems where we have a styrene layer chemisorbed on the dimer row, the most stable structure has ali the molecules arranged on the valley region o f the surface ( 1r -stack); we find another structure, almost degenerate in energy, in which molecules arrange in a herringbone- like configuration, with the vinylene group alternating between the valley and dimer regions.

Since 1982, the Si (111)-(7x7) surface has been extensively studied both theoretically and experimentally with the modern powerful tools of STM and Scanning Tunneling Spectroscopy (STS). In this work, a simple atomic orbital model for the Si (111)-(7x7) surface is developed to simulate the experimental results of STM and STS. Based on Tersoff-Hamann’s theory for the tunneling current, simulations of clean Si (111)-(7x7) constant-current images are presented. The direct, real-space simulated topographic images of the surface are compared to experimental results qualitatively and quantitatively. The simulation of spectroscopic imaging and normalized conductance spectra are also included. The adsorption of atomic hydrogen atoms onto the Si (111)-(7x7) surface is also simulated. / xiv, 146 leaves ; 29 cm.

Dissociation of trichloroethylene (TCE) molecules on the Si(111)-7x7 and the Si(100)-2x1 surfaces was studied using STM. Though molecular adsorption may also be observed on the Si(111)-7x7 surface, dissociation is the dominant process. From the STM images acquired, products of dissociation were identified, namely chlorine atoms and dichlorovinyl groups. Dissociation of chlorine from the TCE molecule was confirmed by studying not just appearance in STM images but also from studies of tip-induced diffusion. Different binding configurations were proposed for the vinyl group on the Si (111)-7x7 and the Si(100)-2x1 surfaces. Site preference for each product of dissociation is reported on the Si(111)-7x7 surface. Dissociation of molecules such as ammonia, dimethylamine and methyl chloride on the Si(111)-7x7 and Si(100)-2x1 surfaces is reviewed. The field emission process is explained in detail. The usefulness of making field emission measurements is in evaluating the sharpness of STM tips. / xviii, 175 leaves : ill. (some col.) ; 29 cm

Este trabalho trata do estudo teórico atomístico das conformações da molécula de estireno sobre a superfície de Si(100)(2xl):H. Estudamos a molécula fisissorvida e quimissorvida sobre esta superfície. Os cálculos foram realizados através de Dinâmica Molecular Clássica. Nós reparametrizamos o Universal Force Field (UFF) com base em cálculos ab initio para sistemas modelo, e comparação a dados experimentais. Nossos resultados indicam que no processo de fississorção a região de vale da superfície é preferencial, e ocorre formação de agregados de moléculas antes do contato com a superfície. Quando passamos à análise da quimissorção de uma molécula, a região de vale permanece sendo o sítio preferencial para a posição do grupo vinil. Para as conformações de linhas de estireno, a estrutura mais estável tem todas as moléculas dispostas sobre a região de vale (ordenamento tipo \"pilha-1r\"); identificamos também outra estrutura, quase degenerada em energia, na qual o grupo vinileno se dispõe em conformação tipo \"espinha de peixe\", alternando entre a região de vale e sobre o dímero. / In this work we present a theoretical study of ,the conformation of styrene molecules on the Si(100)(2xl):H surface. We studied the conformations for styrene molecules physisorbed and chemisorbed on this surface. The study was conducted by Classical Molecular Dynamics. We performed a re-parametrization of the Universal Force Field (UFF), based on ab initio calculations for model structures, and comparison to experimental data. Our results show that for the physisorbed situations, the styrene molecules preferentially interact with the surface valley. We also identified that the molecules aggregate in clusters before reaching the surface. The valley is again the region of lowest energy for the vinylene position, for chemisorption of a single styrene molecule on the monohydride surface. For systems where we have a styrene layer chemisorbed on the dimer row, the most stable structure has ali the molecules arranged on the valley region o f the surface ( 1r -stack); we find another structure, almost degenerate in energy, in which molecules arrange in a herringbone- like configuration, with the vinylene group alternating between the valley and dimer regions.

La conception de surfaces "intelligentes" sensibles aux stimuli externes (lumière, champ électromagnétique, environnement chimique ...) attire un intérêt considérable en raison de leur potentiel pour une large gamme d'applications. Dans ce contexte, nous étudions les propriétés de transfert de photos d'une monocouche de photochromes organiques immobilisés sur des surfaces de silicium.Les groupes Fulgimide sont ancrés par liaison covalente au-dessus de monocouches alkyliques fonctionnalisées greffées sur des surfaces Si (111) exemptes d'oxyde. La composition des monocouches dans les états stationnaires photo EPS-UV et EPS-Vis est déterminée à partir de l'analyse quantitative de l'intensité de la bande infrarouge caractéristique des isomères ouverts (E, Z) et fermés (C). La photocommutation de surface UV-Vis est surveillée par des mesures infrarouge à transformée de Fourier in situ en temps réel lors de l'éclairage UV-Vis. Les études de dépendance temporelle de la photocommutation montrent une diminution de l'efficacité quantique pendant la commutation. Cette diminution de l'efficacité quantique dépend faiblement de la densité de fulgimide et n'est pas observée en solution. Cependant, les mesures de PC en fonction du flux de photons ont permis de déterminer une section efficace de la PC (σ) de la majorité des molécules commutables. Les études de photocommutation dépendantes de la polarisation montrent une forte dépendance de σ par rapport au champ électrique local de la lumière excitante d'isomérisation.Les modèles analytiques et les simulations de Monte Carlo basées sur les interactions des voisins les plus proches sont effectuées pour obtenir une meilleure compréhension des observations expérimentales. Ces simulations expliquent qualitativement la dépendance à la température de la cinétique de commutation, diminuant l'efficacité quantique et la faible densité de surface de la photocommutation.Il a été montré dans cette thèse que σ dépend du champ électrique local. À l'instar de la spectroscopie Raman améliorée en surface, le champ électrique local sur les surfaces augmente en raison du plasmon des nanoparticules d'or. Le plasmon de la monocouche de nanoparticules d'or et ainsi l'amélioration du champ électrique dépend de la longueur d'onde de l'irradiation externe. L'exploitation de cet effet améliore significativement la cinétique de la commutation en fonction de la longueur d'onde de l'irradiation. Cette amplification dépendant de la longueur d'onde de la cinétique de la commutation s'explique par la même amplification dépendante de la longueur d'onde du champ électrique. / The design of “smart” surfaces responsive to external stimuli (light, electromagnetic field, chemical environment…) is attracting considerable interest because of their potential for a wide range of applications. Within this context we are studying the photoswitching properties of a monolayer of organic photochromes immobilized onto silicon surfaces.Fulgimide groups are anchored through covalent linkage atop of functionalized alkyl monolayers grafted on oxide free Si(111) surfaces. The monolayers composition at the photo stationary states PSS-UV and PSS-Vis is determined from quantitative analysis of the infrared band intensity characteristic of open (E,Z) and closed (C) isomers. The UV-Vis surface photocommutation is monitored by in-situ real time FTIR measurements during UV-Vis illumination. Time dependence studies of photocommutation evidence decreasing quantum efficiency during the commutation. This decrease in quantum efficiency only weakly depends on fulgimide density and is not observed in solution. However, PC measurements as a function of photon flux enabled determining a PC cross section (σ) of the majority of switching molecules. Polarization dependent photocommutation studies show the strong dependence of σ with respect to the local electric field of the isomerization-exciting light.Analytical models and Monte Carlo simulations based on nearest neighbor interactions are performed to gain deeper insight in the experimental observations. These simulations qualitatively explain the temperature dependence of the commutation kinetics, decreasing quantum efficiency and weak surface density dependence of the photocommutation.It has been shown in this thesis that σ depends on the local electric field. Similar to the Surface Enhanced Raman Spectroscopy the local electric field at surfaces is increased due to the plasmon of gold nanoparticles. The plasmon of the gold nanoparticle monolayer and thereby the enhancement of the electric field depends on the wavelength of the external irradiation. Exploitation of this effect improves the photo switching kinetics significantly depending on the wavelength of the irradiation. This wavelength dependent amplification of the switching kinetics is explained by the same wavelength dependent enhancement of the electric field.

Extending electronic devices beyond the limitations of current micro-electronics manufacturing will require detailed knowledge of how to make contacts to semiconductor surfaces. In this work, we investigated several methods by which such connections to silicon surfaces could be achieved. Scanning tunneling microscopy (STM) was our main experimental tool, allowing direct imaging of the surfaces at the atomic level. First, the growth of self-forming linear nanostructures of organic molecules on silicon surfaces offers a possibility of creating devices with hybrid organic-silicon functionality. We have studied the growth of many different molecules on a variety of hydrogen-terminated silicon surfaces: H-Si(100)-2x1, H-Si(100)-3x1, and H-Si(111)-1x1. We found molecular growth patterns affected by steric crowding, by sample doping level, or by exposure to ion-pump created radicals. We formed the first contiguous "L-shaped" molecular lines, and used an external electric field to direct molecular growth. We attempted to study a novel method for nanoscale information transfer along molecular lines based on excitation energy transfer. The second part of the work focuses on the development and use of a new multiple-probe STM instrument. The design and the custom STM control software written for it are described. Connections to Si surfaces were achieved with a combination of lithographically defined metal contacts and STM tips. Two-dimensional surface conductivity of the Si(111)-7x7 surface was measured, and the effect of modifying the surface with organic molecules was investigated. A novel method, scanning tunneling fractional current imaging (STFCI), was developed to further study surface conductance. This method allowed us to determine, for the first time, that the resistance of steps on the Si(111)-7x7 surface is significantly higher than that of the surface alone.

No description available.

To investigate conditions of silver electroless deposition on silicon (100), optical microscope, atomic force microscope (AFM) and attenuated total reflection infrared spectroscopy (ATR-FTIR) spectroscopy were used. Twenty second dipping in 0.8mM AgNO3/4.9% solution coats a silicon (100) wafer with a thin film of silver nanoparticles very well. According to AFM results, the diameter of silver particles is from 50 to 100nm. After deposition, arithmetic average of absolute values roughness (Ra) increased from ~0.7nm to ~1.2nm and the root mean square roughness (Rq) is from ~0.8nm to ~1.5nm. SCN- ions were applied to detect the existence of silver on silicon surface by ATR-FTIR spectroscopy and IR spectra demonstrate SCN- is a good adsorbent for silver metal. Patina is the general name of copper basic salts which forms green-blue film on the surface of ancient bronze architectures. Patina formation has been found on the surface of platinum or ruthenium after several scans of cyclic voltammetry in 2mM CuSO4/0.1M K2SO4, pH5 solution. Evidence implies that oxygen reduction reaction (ORR) triggers the patina formation. ORR is an important step of fuel cell process and only few sorts of noble metals like platinum can be worked as the catalyst of ORR. Mechanisms of patination involving ORR were investigated by cyclic voltammetry, optical microscope, AFM, rotating disk electrode and other experimental methods: the occurrence of ORR cause the increase of local pH on electrode, and Cu2+ ions prefer to form Cu2O by reduction. Patina forms while Cu2O is oxidizing back to Cu2+.

Fabrication of surfaces with versatile functional groups is an important research area. Hence, it is essential to control and tune the surface properties in a reliable manner. Vinyl-terminated self-assembled monolayers (SAMs) offer significant flexibility for further chemical modification and can serve as a versatile starting point for tailoring of surface properties. Here a synthetic route for the preparation of vinyl-terminated trichlorosilane self-assembling molecules: 9-decenyltrichlorosilane (CH₂=CH-(CH₂)₈-SiCl₃), 10-undecenyltrichlorosilane (CH₂=CH-(CH₂)₉-SiCl₃), and 14-pentadecenyltrichlorosilane (CH₂=CH-(CH₂)₁₃-SiCl₃) is presented. These molecules were used for the preparation of SAMs in either liquid or vapour phase processes. Commercially available methyl-terminated self-assembling molecules: decyltrichlorosilane (CH₃-(CH₂)₉-SiCl₃) and octadecanetrichlorosilane (CH₃-(CH₂)₁₇-SiCl₃) were used as controls. The resultant films were characterised by X-ray photoelectron spectroscopy (XPS), contact angle analysis, ellipsometry, and atomic force microscopy (AFM). Well defined, vinyl-terminated SAMs were further chemically modified with carbenes (:CCl₂, :CBr₂, :CF₂) and hexafluoroacetone azine (HFAA). The reactions were performed in the liquid or the vapour phase. The resulting SAMs were characterised using the same methods as for the vinyl-terminated monolayers. Successful modification was confirmed by the appearance of new signals in the XPS spectrum, with simultaneous changes in water contact angle values and unchanged thickness values. Methyl-terminated SAMs were also exposed to carbenes and HFAA as a control system. These are the first examples of C-C bond formation on SAMs in the vapour phase.

To form Cu interconnects, dual-damascene techniques like chemical mechanical planarization (CMP) and post-CMP became inevitable for removing the "overburden" Cu and for planarizing the wafer surface. During the CMP processing, Cu interconnects and barrier metal layers experience different electrochemical interactions depending on the slurry composition, pH, and ohmic contact with adjacent metal layers that would set corrosion process. Ruthenium as a replacement of existing diffusion barrier layer will require extensive investigation to eliminate or control the corrosion process during CMP and post CMP. Bimetallic corrosion process was investigated in the ammonium citrate (a complexing agent of Cu in CMP solutions) using micro test patterns and potentiodynamic measurements. The enhanced bimetallic corrosion of copper observed is due to noble behavior of the ruthenium metal. Cu formed Cu(II)-amine and Cu(II)-citrate complexes in alkaline and acidic solutions and a corrosion mechanism has been proposed. The currently used metallization process (PVD, CVD and ALD) require ultra-high vacuum and are expensive. A novel method of Si surface metallization process is discussed that can be achieved at room temperature and does not require ultra-high vacuum. Ruthenation of Si surface through strong Si-Ru covalent bond formation is demonstrated using different ruthenium carbonyl compounds. RBS analysis accounted for monolayer to sub-monolayer coverage of Si surface. Interaction of other metal carbonyl (like Fe, Re, and Rh) is also discussed. The silicon (111) surface modifications with vinyl terminated organic compounds were investigated to form self-assembled monolayers (SAMs) and there after these surfaces were further functionalized. Acrylonitrile and vinylbenzophenone were employed for these studies. Ketone group of vinylbenzophenone anchored to Si surface demonstrated reactivity with reducing and oxidizing agents.