This thesis is focused on adsorption of phthalocyanines on tin and indium passivated silicon Si(111) surfaces with the √3 × √3 reconstruction at room temperature. Scanning tunneling microscopy was used for obtaining atomically resolved surface images. Molecules on these surfaces predominantly adsorb on Si-substitutional defects. Local density of states (LDOS) of strongly adsorbed molecules was obtained by scanning tunneling spectroscopy. The origin of fuzzy imaging of molecules sitting on Si-substitutional double defects was probed. Voltage dependence of mean lifetime of two observed states, between which the "fuzzy" molecule is switching, was measured by analysis of tunneling current fluctuations. We discussed the influence of external parameters on the switching between the two states. We attribute the fuzzy behaviour of the molecule and resulting tunneling current fluctuations to the motion of the molecule in a double-well potential and propose two most likely kinds of the motion which most closely agree with the obtained data.

>Magister Scientiae - MSc / Tin dioxide (SnO2) thin films are a worthy candidate for an electron transport layer (ETL) in perovskite solar cells, due to its suitable energy level, high electron mobility of 240 cm2 v-1 s- 1, desirable band gap of 3.6 - 4.0 eV, and ultimately proves to be suited for a low temperature thermal oxidation technique for ETL production. A variety of methods are available to prepare SnO2 thin films such as spin and dip coating and chemical bath deposition. However, the customary solid-state method, which incorporates thermal decomposition and oxidation of a metallic Sn precursor compound in an oxygen abundant atmosphere prevails to be low in cost, is repeatable and allows for large-scale processing.

Ce travail porte sur l’élaboration de matériaux nanostructurés et le contrôle de la formation de nanocristaux d’oxyde d’étain dans une matrice de silice amorphe obtenue par voie sol-gel. Préalablement à l’étude structurale et microstructurale des xérogels, une première partie de ces travaux de thèse concerne le procédé sol-gel. Le lavage des gels par des solutions hydro-alcooliques permet d’extraire une quantité importante d’acide chlorhydrique après gélification. Ainsi si les solutions de lavage sont renouvelées, 50 % de l’acide introduit peut être retiré. Ce lavage, associé avec un séchage contrôlé, a également permis de réduire significativement la durée du séchage et d’obtenir des xérogels centimétriques non fissurés.La seconde partie de ce travail a porté sur l’étude structurale et microstructurale des xérogels réalisée au travers de mesures de diffraction des rayons X ex situ ou de diffusion centrale et diffraction des rayons X couplée in situ en fonction de la température sur des lignes de lumière situées autour de sources synchrotrons. Nous avons montré que dans des xérogels contenant 10 % d’étain, la quantité de cristaux nanométriques d'oxyde d'étain peut augmenter continuellement sans que leur taille moyenne ne s’accroisse. La taille moyenne la plus faible est obtenue après un prétraitement thermique de séparation de phases préalable à celui de cristallisation et plus ce traitement est long plus la taille des cristaux est faible. Cette étude a été complétée par des traitements thermiques effectués in situ afin de suivre simultanément la séparation de phases et la cristallisation. Ces mesures ont permis d’observer le phénomène de séparation de phases dans les xérogels contenant 10 % d’étain et dont la quantité cristallisée obtenue lors d’un traitement thermique à 350 °C est la plus importante au regard des autres températures de traitement thermique et des concentrations en étain. / This PhD work deals with the development of nanostructured oxide materials and the control of the formation of tin oxide nanocrystals in an amorphous silica matrix obtained by sol-gel process. Prior to the structural and microstructural study of xerogels, a first part of this work concerns the sol-gel process. Washing the gels with hydroalcoholic solutions allows to extract a significant quantity of hydrochloric acid after gelation. Thus, if the washing solutions are renewed, 50% of the acid introduced can be removed. This washing, combined with improvement of the drying process, allowed to reduce the drying duration and finally to obtain bulk xerogels exhibiting a centimetric size.The second part of this work focuses on the structural and microstructural evolution of xerogels through thermal treatments. The results of this second part are obtained through ex situ measurements of X-ray diffraction or coupled small angle X-ray scattering and X-ray diffraction experiments realized in situ as a function of temperature. In both cases the measurements have been performed on synchrotron beamlines. We show that in xerogels containing 10% tin, the amount of nanosized tin oxide crystals can continuously increases without increasing the average size of these crystals. The lowest average size is obtained after a phase separation thermal pretreatment before crystallization and the longer this treatment is, the smaller the size of the crystals. This study is completed by heat treatments carried out in situ in order to simultaneously evidence phase separation and crystallization. These measurements allow to observe the phenomenon of phase separation by small angle X-ray scattering in xerogels containing 10% tin and whose crystallized quantity obtained during a thermal treatment at 350 °C is the highest compared to other heat treatment temperatures and tin concentrations.

Abstract Organic derivatives of tin, lead, mercury are the most widely distributed organometallic ecotoxicants in the environment. While some of these organometallic compounds exist in the environment as a result of direct discharge, anthropogenic emissions alone cannot explain the ubiquity, for example, of the organomercury and organolead compounds in marine and fresh waters, sediments and biota. It is known that some organometallic compounds are formed via a bioconversion from the inorganic contaminants. Depending on the source, they can enter the environment in varied forms inorganic species of different stability. These can be bio-converted further by environmental biota; for instance metals such as tin and lead can be discharged into the environment in the form of organometallic species which can undergo further transformation. Determination of organometallics in environmental and biological samples is difficult due to matrix effect and their low concentrations. Separation and preconcentration is necessary to enhance final determination. Speciation studies are even more complicated. Speciation is an important aspect and gives information about bioavailability of the metal thus their toxicity. This work focused on the development of a method for speciation of organospecies of tin, lead and mercury. A new derivatisation agent has been synthesised and used successfully. SLM probe extraction has been exposed to a new matrix. Different environmental samples have been analysed for organo-species of tin and lead and their pathways predicted. The SLM probe extraction gives the advantage of carrying out several extractions, reduction of the amount of solvent used and avoidance of emulsion problems. A simple system has been developed and applied successfully on organotin and organolead extraction from aqueous environmental sample. For reproducibility of the results, pH, salinity, stirring rate and extraction time were optimized. An analytical method for simultaneous in situ ethylation, using new derivatisation agent bromomagnesium tetraethylborate (Et4BMgBr), of organotin and organomercury compounds in sediment samples was developed. The determination of mercury and tin compounds is achieved by species-specific isotope dilution, derivatisation and gas chromatography – inductively coupled plasma mass spectrometry (GC-ICP-MS). In derivatisation, pH and the amount of derivatisation agent were studied. Percentage recovery and accuracy of the method was confirmed by comparison of experimental results with sediment and plant certified reference material (IAEA 405 for sediment and CRM 279 for plant). Although organolead compounds as a gasoline additive are banned in most countries, in some regions, lead is still added to gasoline in varying proportions of different tetraalkyllead compounds and contamination by organolead compounds is still present at different places, e.g.: lead alkyl manufactures The use of both tetraalkyllead and butyltin is banned (tetraalkyllead as gasoline additive and butyltin in antifouling pints and PVC materials). This work focussed on their conversion in water and soil. This should provide an insight into their presence in the environment and an understanding of their degradation in the environment. A method for full speciation and determination of alkyl lead and inorganic lead (II) after the tetramethyllead degradation in aqueous samples has been developed. This was accomplished by in situ derivatisation with sodium tetraphenyllead borate NaB(Ph)4 derivative. The derivatisation was carried out directly in the aqueous sample and the derivatives were extracted using the supported liquid membrane probe extraction (SLMPE). The extracted analytes were then transferred to a GC/MS for separation and detection. This study focused on the transformation of tetramethyllead in aqueous media, at different concentration of major elements, K+,Na+,Ca++, Mg++,Cl-,SO4 --. Adsorption / desorption on soil of ionic organolead and organotin were also studied. As South Africa is one of the world’s major producers of coal, mercury should be monitored as it is a side product in coal combustion. The trend of inorganic mercury and methylmercury in sediment found in this work indicated a possible methylation of inorganic mercury to methylmercury in Klipriver sediments.

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In this thesis, in investigation of various diffusion couple designs is discussed with the aim of enhancing the interaction between the three diffusive flow. Experimental investigation of the theoretical predictions his been carried out for infinite and finite couple boundary conditions. The four independent diffusion coefficients in the copper-rich copper-zinc-tin system have been measured it two temperatures for the dilute composition range. / Thesis / Master of Science (MS)

Metal artifacts from the pirate Blackbeard's flagship, Queen Anne's Revenge (1718), were studied and a preliminary assessment of the corrosion products that have formed on them is presented. Artifacts made of iron, lead, tin, copper, mercury, gold, and silver were recovered from the site with only those made of precious metals displaying no corrosion products. Detailed analysis was conducted of the surfaces of pewter artifacts, made from a tin-rich alloy, revealing corrosion products composed of romarchite (SnO), hydroromarchite (5SnO.2H2O), and abhurite (Sn3O(OH)2Cl2). For comparison, corroded pewter artifacts originating from five other archaeological sites submerged in seawater, dating to between ~1550 and 1733, were analyzed. All of these samples also exhibit abhurite, romarchite, and hydroromarchite, however, some of the artifacts also display cassiterite (SnO2). Textural analysis indicates that abhurite is the first alteration product to arise, followed by romarchite and hydroromarchite and, in some cases, ending with the formation of cassiterite. The absence of cassiterite on many samples demonstrates that, while appearing to be stable under the conditions that were present, the phase has not yet had time to form. Because of the very limited stability field for romarchite, its presence on these artifacts seems to be the result of a kinetic effect, while its universal appearance suggests that it is a required step in the oxidation of pure tin to the final most stable phase of cassiterite. Knowledge of the stability of pewter corrosion products and their effectiveness as agents of passivation can provide insight into the processes of tin corrosion. / Master of Science

The first chapter consists of an overview of the southern plantation as it survives in cultural imagination, especially in William Faulkner’s Absalom, Absalom! and Margaret Mitchell’s Gone With the Wind. The second chapter discusses A Streetcar Named Desire and how Williams reimagines the plantation in an urban setting through the New Orleans Marigny neighborhood. The third chapter examinesWilliams’s reinvention of the rural plantation in Cat on a Hot Tin Roof. The conclusion explores how Williams’s work is used as a blueprint in representing the plantation in postsouthern literature and culture.

<p> The de Haas-van Alphen effect has been used to measure the Fermi surface areas, cyclotron masses and Dingle temperatures in antimony and its alloys containing less than 0.3 percent tin. The Fermi surface of each alloy was similar to the pure antimony surface. However the hole surface increased in size and the electron surface shrunk since tin removes electrons from the alloy. The cyclotron masses increased and decreased for holes and electrons respectively, giving a definite indication of nonparabolic conduction and valence bands. The cyclotron masses were found from the temperature dependence of the dHvA amplitude after interfering dHvA frequency components were removed by a Fourier analysis technique. The Dingle temperature increased roughly linearily with tin concentration.</p> <p> A comparison of the hole and electron Fermi surface volumes with the number of tin atoms added to the alloys shows that one tin atom removes one electron from the alloy as expected from the unit valence difference between antimony and tin. This value is higher than that found by other workers using different techniques.</p> <p> The shapes of the energy bands along with the cyclotron masses have been compared with several band models. An ellipsoidal band provides a rough overall description of both holes and electrons while an ellipsoidal nonparabolic band describes the mass behaviour on alloying more accurately. A pseudopotential band calculated using the method and potential of Falicov and Lin (1967) was also compared with the data.</p> <p> The observed relative frequency changes were used to compare the data with the rigid band model of alloying. The bands are rigid for low concentrations. At higher concentrations there are deviations apparently caused by the cyclotron mass change and an axial ratio change in the hole Fermi surface.</p> / Thesis / Doctor of Philosophy (PhD)