<p> Etch pits can be produced in iron whose shape reflects the crystallography of the crystal. It is shown that pit morphology can be adequately predicted from an orientation dependent dissolution theory. The influence of an air-formed surface oxide film on pit nucleation and morphology is demonstrated. </p> / Thesis / Master of Science (MSc)

The road map of the semiconductor industry has followed Moores Law over the past few decades. According to Moores Law the number of transistors in an integrated circuit (IC) will double for a minimum component cost every two years. The features made in an IC are produced by photolithography. Industry is now producing devices at the 65 nm node, however, for every deceasing node size, both the materials and processes used are not only difficult but also expensive to develop. Ultimately, the feature size obtainable via photolithography is dependent on the wavelength used in the process. The limitations of photolithography will eventually make Moores Law unsustainable. Therefore, new methodologies of creating features in the semiconductor substrate are desired. Here we present a new way to make patterns in silicon (Si) and silicon dioxide (SiO2), molecular lithography. Individual molecules and polymers, in a monolayer, serves directly as the etch mask; eliminating the photolighographic size limitation of light at a specific wavelength. The Ohnishi- and Ring parameter suggests that cyclic carbon rich molecules have a high resistance towards the plasma process, used to create the features in the substrate. Therefore highly aromatic molecules were investigated as candidates for molecular lithography. A monolayer of poly cyclic hydrocarbons, fullerene containing polymer, and fullerene molecules were created using the versatile photochemistry of benzophenone as the linker between the substrate and the material. First, a chlorosilane benzophenone derivative was attached to the Si/SiO2 surface. A thin film of the desired material is then created on top of the silane benzophenone layer. Irradiation at ~350 nm excites the benzophenone and reacts with neighboring alkyl chains. After covalent attachment the non-bonded molecules are extracted from the surface using a Soxhlet apparatus. Self-assembly, molecular weight, and wetting properties of the material dictates the features shape and size. These features are then serving as an etchmask in a fluorine plasma. The organic etch resist is then removed either in an oxygen plasma or in a piranha solution. AFM analysis revealed that 3 to 4 nm wide defined structures were obtained using C96 as the etch mask. This is about ten times smaller then industry standards. Also a depth profile of 50 nm, which is the minimum feature depth used in industry, was created using a fullerene containing polymer as the etch mask. Directionality and control over the shape and sizes of the features are naturally critical for implementing this technology in device fabrication. Therefore, alignment of the materials used has also been examined. Monolayers of highly stable molecules has successfully been used as etch masks. Further research and development could implement molecular lithography in device fabrication. Self-assembly among other forces would dictate which materials could be used successfully as a molecular resist.

Made available in DSpace on 2014-06-11T19:24:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-02-27Bitstream added on 2014-06-13T20:51:31Z : No. of bitstreams: 1 freitas_crb_me_arafo.pdf: 1243419 bytes, checksum: 9b17396cab68dbc46f7018d3bc8aec44 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo deste estudo foi avaliar o procedimento de hibridização imediata em restaurações indiretas de resina composta. A hipótese nula foi duplicada: os resultados dos adesivos de condicionamento total e auto-condicionante são similares; e a hibridização imediata produz microinfiltração e resistência adesiva similares à cimentação convencional. Foram selecionados 20 terceiros molares humanos recém extraídos e isentos de cárie, nos quais foram realizados preparos cavitários MOD, padronizados para restaurações indiretas. Os dentes foram divididos aleatoriamente em 4 grupos experimentais: (G1) hibridização com adesivo de condicionamento total (SB, Single Bond, 3M ESPE) imediatamente após o preparo cavitário e antes da cimentação, (G2) hibridização com adesivo de condicionamento total antes da cimentação (SB), (G3) hibridização com adesivo auto-condicionante (AP, Adper Prompt, 3M ESPE) imediatamente após o preparo cavitário e antes da cimentação, (G4) hibridização com adesivo auto-condicionante (AP) antes 157 da cimentação. Os espécimes foram restaurados com inlays de Targis (Ivoclar/Vivadent), cimentados com cimento resinoso Rely X ARC (3M ESPE). Todos produtos foram manipulados de acordo com as instruções do fabricante. Após termociclagem, os espécimes foram imersos em solução de nitrato de prata 50%, seccionados para avaliação da microinfiltração com escores pré-determinados de 0 a 3. Em seguida, os espécimes foram novamente seccionados com 0,8mm x 0,8mm para realização dos testes de microtração. Os resultados obtidos foram submetidos à análise estatística (p<0,05). Os escores da microinfiltração foram submetidos ao teste de Mann-Whitney indicando nenhuma diferença na técnica de hibridização (p>0,05). Os resultados da microtração foram submetidos à análise de variância que revelou... . / An analysis was carried out to determine the behavior of immediate hybridization on indirect composite resin restorations. The null hypothesis was two fold: were whether total etch or self-etch (SEA) adhesives result in similar; and whether immediate hybridization produces similar microleakage and æTBS than conventional cementation. Twenty sound extracted teeth were selected and 20 standardized MOD inlay preparations were made. The prepared teeth were randomly assigned in four experimental groups: (G1) hybridization with total-etch adhesive (SB, Single Bond, 3M ESPE) immediately after preparation and prior cementation, (G2) hybridization with total-etch adhesive prior cementation (SB), (G3) hybridization with SEA (AP, Adper Prompt, 3M ESPE) immediately after preparation and prior cementation; and (G4) hybridization with SEA (AP) prior cementation. The specimens were restored with Targis (Ivoclar/Vivadent) inlays, cemented with composite resin cement (RelyX ARC, 3M ESPE). All products were used according with manufacturer's instructions. The specimens were 160 thermocycled and immersed in 50%w/w silver nitrate. The specimens were sectioned and the microleakage evaluated with predetermined scores (0-3). Then, the specimens were sectioned in 0,8mm x 0,8mm and æTBS tested in a MTS-810 machine. The obtained data were submmited to statistical analysis (p< .05). The microleakage scores were submmited to Mann-Whitney non-parametric test showing no statistical differences among the adhesives and technique (p> .05). The æTBS results submitted to ANOVA parametric test reveled that G1 performed better than G2, and G3 superior to G4. The null hypotheses were partially rejected. None of the adhesives eliminate microleakage. Hybridization immediately after the preparation is done and before cementation improved the bond strengths with... (Complete abstract, click electronic address below).

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This study is focused on the technique for fabrication of high aspect ratio nanostructures by combining both the advantages of maskless patterning of focused ion beam (FIB) and anisotropic etching of inductively coupled plasma etcher (ICP) in CF4 atmosphere. The materials contain p-type (100) single crystal silicon and thermal silicon dioxide. The study details include¡G (1) The reliability of AFM when scanning isotropic and anisotropic nanostructures with high aspect ratio tip in tapping mode. (2) FIB direct writing test. (3) The influences of ICP parameters including ICP power, bias power, content of oxygen, and process pressure. After completion of above-mentioned items, an optimized condition is used to get the anisotropic Si-based high aspect ratio nanostructures of holes array, gratings and cylinder under 100nm. The smallest line width of single crystal silicon gratings is 48nm, and aspect ratio up to 2.36. The smallest line width of silicon dioxide gratings is about 100nm, height is 410nm and aspect ratio up to 2.36 measured by SEM. By combining both advantages of different systems, we can provide another simple and rapid method for nanofabrication.

One of two project reports. Part B can be found at: / Track-etch imaging is investigated as a recording method for neutron radiographic purposes. A theoretical model is formulated and evaluated together with experimental data which is analyzed in an attempt to explore the possibility of maximizing optical contrast. A central converter system with Lithium-6 as the converter and cellulose-nitrate as the recorders is used. It is found that the maximum contrast is achieved by using a clear cellulose-nitrate recorder at least 10 µm thick and a Lithium-6 converter of approximately 140 µm thickness. / Thesis / Master of Engineering (ME)

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In this work, we have developed two different fabrication processes for relaxed Si₁₋xGex-on-insulator (SGOI) substrates: (1) SGOI fabrication by etch-back approach, and (2) by "smart-cut" approach utilizing hydrogen implantation. Etch-back approach produces SGOI substrate with less defects in SiGe film, but the SiGe film uniformity is inferior. "Smart-cut" approach has better control on the SiGe film thickness and uniformity, and is applicable to wider Ge content range of the SiGe film. We have also fabricated strained-Si n-MOSFET’s on SGOI substrates, in which epitaxial regrowth was used to produce the surface strained Si layer on relaxed SGOI substrate, followed by large-area n-MOSFET’s fabrication on this structure. The measured electron mobility shows significant enhancement (1.7 times) over both the universal mobility and that of co-processed bulk-Si MOSFET’s. This SGOI process has a low thermal budget and thus is compatible with a wide range of Ge contents in Si₁₋xGex layer. / Singapore-MIT Alliance (SMA)