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O objetivo do presente trabalho foi a fabricação de micro e nanotubos de silício através de métodos eletroquímicos, utilizando como material de partida o silício poroso. Os resultados obtidos durante o desenvolvimento deste trabalho apresentam contribuições significativas nos campo da micro e nanotecnologia, bem como no campo da eletroquímica do silício. Esses resultados mostraram que a formação dos microtubos é sensível às variações do pH, tipo e concentração dos oxidantes, tempo de corrosão, espessura das camadas porosas e tratamento prévio da superfície polida das amostras com alumínio e posterior recozimento térmico. A análise estrutural, via microscopia eletrônica de varredura (MEV), mostra que os microtubos de silício (MTS) podem ser formados em valores de pH entre 5,5 a 7,5, dependendo do tipo e concentração dos oxidantes. A análise da composição química dos MTS, realizada mediante a espectroscopia por dispersão de energia (EDS). Os resultados da espectroscopia Raman indicaram que as estruturas são tubos de Silício, cuja estequiometria é a mesma que a do cristal de Silício. Foi demonstrada a possibilidade de formação de microtubos metálicos através do controle das condições químicas e eletroquímicas da solução, utilizadas na formação das estruturas tubulares de silício. A condição da solução eletroquímica com nível de pH 6,5 permitiu formar microtubos de níquel, enquanto que estruturas tubulares de manganês foram obtidas em soluções com nível de pH 7,5. Em ambos os casos, foram utilizados agentes oxidantes originados de sais de níquel e manganês, respectivamente. Os resultados indicam que o processo de formação destas estruturas acontece por efeito do deslocamento galvânico. Os resultados apresentados neste trabalho são completamente inéditos e mostram-se vantajosos em relação àqueles reportados na literatura, já que estes últimos são obtidos mediante processos de alto custo que requerem sofisticados equipamentos, enquanto os microtubos de silício obtidos mediante técnicas eletroquímicas, aqui usadas, são de baixo custo e fácil montagem. / The aim of this work was to fabricate micro and nanotubes of silicon, through electrochemical methods and using the porous silicon as starting material. The results achieved during the development of this work present significant contributions into the micro and nanotechnology field, as well as in the silicon electrochemistry field. The obtained results have shown that the formation of the microtubes is sensitive to variations of pH, type and concentration of the oxidants, time of corrosion, thickness of the porous layers, and previous treatment of the polished silicon surface with aluminum and subsequent thermal annealing. The results of the structural analysis by scanning electron microscopy (SEM) show that the silicon microtubes can be formed at pH values ranging between 5,5 and 7,5, depending on the type and concentration of the oxidants. The chemical analysis upon the composition of these silicon tubular structures was carried out by Energy Dispersion Spectroscopy (EDS). Raman spectroscopy results indicated that the tubular structures are silicon tubes, whose stoichiometric structure is similar to the silicon crystal. The possibility of formation of metallic microtubes, just by controlling the chemical and electrochemical conditions of the etching solution used to form the silicon tubular structures was shown. The electrochemical condition of the solution with level of pH 6,5 allowed the formation of nickel microtubes structures, and the formation of manganese tubular structures was obtained in solutions with pH of 7,5. In both cases there have been used oxidants agents originated from nickel and manganese salts, respectively. The results indicate that the formation process of these metallic structures happens by a galvanic displacement process. The results presented in this work are completely unpublished and reveal advantageous in relation to those reported in literature because these last ones are obtained by using high cost processes which require sophisticated equipment, while the silicon microtubes obtained by electrochemical techniques used in the present work are of low cost and of easy assembly.

No description available.

Chow Chi Fai. / Thesis submitted in: August 2005. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract / Abstract (Chinese) / A cknowledgements / Table of Contents / List of Figures / List of Tables / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- The need for light emission from silicon --- p.1-1 / Chapter 1.2 --- Silicon-based light emitting material 1 - --- p.2 / Chapter 1.3 --- Literature overview --- p.1-4 / Chapter 1.4 --- Project goal --- p.1-10 / Reference --- p.1-11 / Chapter Chapter 2 --- Experimental details / Chapter 2.1 --- Introduction --- p.2-1 / Chapter 2.2 --- Sample preparation techniques --- p.2-1 / Chapter 2.2.1 --- MEVVA ion implantation --- p.2-1 / Chapter 2.2.2 --- PL samples preparation conditions --- p.2-3 / Chapter 2.2.3 --- EL samples preparation conditions --- p.2-4 / Chapter 2.3 --- Characterization techniques --- p.2-7 / Chapter 2.3.1 --- Photoluminescence spectroscopy (PL) --- p.2-7 / Chapter 2.3.2 --- Electroluminescence spectroscopy (EL) --- p.2-9 / Chapter 2.3.3 --- Rutherford backscattering spectroscopy (RBS) --- p.2-10 / Chapter 2.3.4 --- X-ray diffraction (XRD) --- p.2-12 / Chapter 2.3.5 --- Transmission electron microscopy (TEM) --- p.2-13 / Reference --- p.2-15 / Chapter Chapter 3 --- Resutls and Discussions / Chapter 3.1 --- RBS results --- p.3-1 / Chapter 3.2 --- XRD results --- p.3-8 / Chapter 3.3 --- TEM results --- p.3-12 / Chapter 3.3.1 --- Effects of the implantation energy on the microstructure of samples --- p.3-13 / Chapter 3.3.2 --- Effects of the implantation dose on the microstructure of samples --- p.3-16 / Chapter 3.4 --- Photoluminescence results --- p.3-19 / Chapter 3.4.1 --- Effect of implantation energy on the PL --- p.3-19 / Chapter 3.4.2 --- Effect of FA temperature on the PL --- p.3-24 / Chapter 3.4.3 --- Effect of FA duration on the PL --- p.3-26 / Chapter 3.4.4 --- Effect ofRTA duration on the PL --- p.3-28 / Chapter 3.4.5 --- Effect ofRTA temperature on the PL --- p.3-30 / Chapter 3.4.6 --- Effect of implantation dose on the PL --- p.3-32 / Chapter 3.4.7 --- Si band edge enhancement --- p.3-34 / Chapter 3.4.8 --- Photoluminescence spectra as a function of excitation power density --- p.3-37 / Chapter 3.4.9 --- Photoluminescence spectra as a function of measurement temperature --- p.3-45 / Chapter 3.5 --- Electroluminescence results --- p.3-52 / Chapter 3.5.1 --- EL quantum efficiency --- p.3-60 / Reference --- p.3-61 / Chapter Chapter 4 --- Conclusion and future works / Chapter 4.1 --- Conclusion --- p.4-1 / Chapter 4.2 --- Future works --- p.4-2 / Appendix I / Appendix II

O objetivo do presente trabalho foi a fabricação de micro e nanotubos de silício através de métodos eletroquímicos, utilizando como material de partida o silício poroso. Os resultados obtidos durante o desenvolvimento deste trabalho apresentam contribuições significativas nos campo da micro e nanotecnologia, bem como no campo da eletroquímica do silício. Esses resultados mostraram que a formação dos microtubos é sensível às variações do pH, tipo e concentração dos oxidantes, tempo de corrosão, espessura das camadas porosas e tratamento prévio da superfície polida das amostras com alumínio e posterior recozimento térmico. A análise estrutural, via microscopia eletrônica de varredura (MEV), mostra que os microtubos de silício (MTS) podem ser formados em valores de pH entre 5,5 a 7,5, dependendo do tipo e concentração dos oxidantes. A análise da composição química dos MTS, realizada mediante a espectroscopia por dispersão de energia (EDS). Os resultados da espectroscopia Raman indicaram que as estruturas são tubos de Silício, cuja estequiometria é a mesma que a do cristal de Silício. Foi demonstrada a possibilidade de formação de microtubos metálicos através do controle das condições químicas e eletroquímicas da solução, utilizadas na formação das estruturas tubulares de silício. A condição da solução eletroquímica com nível de pH 6,5 permitiu formar microtubos de níquel, enquanto que estruturas tubulares de manganês foram obtidas em soluções com nível de pH 7,5. Em ambos os casos, foram utilizados agentes oxidantes originados de sais de níquel e manganês, respectivamente. Os resultados indicam que o processo de formação destas estruturas acontece por efeito do deslocamento galvânico. Os resultados apresentados neste trabalho são completamente inéditos e mostram-se vantajosos em relação àqueles reportados na literatura, já que estes últimos são obtidos mediante processos de alto custo que requerem sofisticados equipamentos, enquanto os microtubos de silício obtidos mediante técnicas eletroquímicas, aqui usadas, são de baixo custo e fácil montagem. / The aim of this work was to fabricate micro and nanotubes of silicon, through electrochemical methods and using the porous silicon as starting material. The results achieved during the development of this work present significant contributions into the micro and nanotechnology field, as well as in the silicon electrochemistry field. The obtained results have shown that the formation of the microtubes is sensitive to variations of pH, type and concentration of the oxidants, time of corrosion, thickness of the porous layers, and previous treatment of the polished silicon surface with aluminum and subsequent thermal annealing. The results of the structural analysis by scanning electron microscopy (SEM) show that the silicon microtubes can be formed at pH values ranging between 5,5 and 7,5, depending on the type and concentration of the oxidants. The chemical analysis upon the composition of these silicon tubular structures was carried out by Energy Dispersion Spectroscopy (EDS). Raman spectroscopy results indicated that the tubular structures are silicon tubes, whose stoichiometric structure is similar to the silicon crystal. The possibility of formation of metallic microtubes, just by controlling the chemical and electrochemical conditions of the etching solution used to form the silicon tubular structures was shown. The electrochemical condition of the solution with level of pH 6,5 allowed the formation of nickel microtubes structures, and the formation of manganese tubular structures was obtained in solutions with pH of 7,5. In both cases there have been used oxidants agents originated from nickel and manganese salts, respectively. The results indicate that the formation process of these metallic structures happens by a galvanic displacement process. The results presented in this work are completely unpublished and reveal advantageous in relation to those reported in literature because these last ones are obtained by using high cost processes which require sophisticated equipment, while the silicon microtubes obtained by electrochemical techniques used in the present work are of low cost and of easy assembly.

High performance inductors are playing an increasing role in modern communication systems. Despite the superior performance offered by discrete components, parasitic capacitances from bond pads, board traces and packaging leads reduce the high frequency performance and contribute to the urgency of an integrated solution. Embedded inductors have the potential for significant increase in reliability and performance of the IC. Due to the driving force of CMOS integration and low costs of silicon-based IC fabrication, these inductors lie on a low resistivity silicon substrate, which is a major source of energy loss and limits the frequency response. Therefore, the quality factor of inductors fabricated on silicon continues to be low. The research presented in this thesis investigates amorphous Si and porous Si to improve the resistivity of Si substrates and explores amorphous Si as a structural material for low temperature MEMS fabrication. Planar inductors are built-on undoped amorphous Si in a novel application and a 56% increase in quality factor was measured. Planar inductors are also built-on a porous Si and amorphous Si bilayer and showed 47% improvement. Amorphous Si is also proposed as a low temperature alternative to polysilicon for MEMS devices. Tunable RF MEMS inductors and transformers are fabricated based on an amorphous Si and aluminum bimorph coil that is suspended and warps in a controllable manner. The 3-D displacement is accurately predicted by thermomechanical simulations. The tuning of the devices is achieved by applying a DC voltage and due to joule heating the air gap can be adjusted. A tunable inductor with a 32% tuning range from 5.6 to 8.2 nH and a peak Q of 15 was measured. A transformer with a suspended coil demonstrated a 24% tuning range of the mutual coupling between two stacked windings. The main limitation posed by post-CMOS integration is a strict thermal budget which cannot exceed a critical temperature where impurities can diffuse and materials properties can change. The research carried out in this work accommodates this temperature restriction by limiting the RF fabrication processes to 150°C to facilitate system integration on silicon.

High performance inductors are playing an increasing role in modern communication systems. Despite the superior performance offered by discrete components, parasitic capacitances from bond pads, board traces and packaging leads reduce the high frequency performance and contribute to the urgency of an integrated solution. Embedded inductors have the potential for significant increase in reliability and performance of the IC. Due to the driving force of CMOS integration and low costs of silicon-based IC fabrication, these inductors lie on a low resistivity silicon substrate, which is a major source of energy loss and limits the frequency response. Therefore, the quality factor of inductors fabricated on silicon continues to be low. The research presented in this thesis investigates amorphous Si and porous Si to improve the resistivity of Si substrates and explores amorphous Si as a structural material for low temperature MEMS fabrication. Planar inductors are built-on undoped amorphous Si in a novel application and a 56% increase in quality factor was measured. Planar inductors are also built-on a porous Si and amorphous Si bilayer and showed 47% improvement. Amorphous Si is also proposed as a low temperature alternative to polysilicon for MEMS devices. Tunable RF MEMS inductors and transformers are fabricated based on an amorphous Si and aluminum bimorph coil that is suspended and warps in a controllable manner. The 3-D displacement is accurately predicted by thermomechanical simulations. The tuning of the devices is achieved by applying a DC voltage and due to joule heating the air gap can be adjusted. A tunable inductor with a 32% tuning range from 5.6 to 8.2 nH and a peak Q of 15 was measured. A transformer with a suspended coil demonstrated a 24% tuning range of the mutual coupling between two stacked windings. The main limitation posed by post-CMOS integration is a strict thermal budget which cannot exceed a critical temperature where impurities can diffuse and materials properties can change. The research carried out in this work accommodates this temperature restriction by limiting the RF fabrication processes to 150°C to facilitate system integration on silicon.

In this thesis, silicon oxide thin films fabricated on silicon substrates by reactive radio frequency (rf) magnetron sputtering and supercritical CO2 (SCCO2) treatment at room temperature were investigated. The electrical properties including I-V and C-V of the films prepared at different processing conditions were discussed. Using the Transmission Electron Microscope (TEM), the thickness of silicon oxide thin films were measured. The results suggested that the film quality can be significantly improved by the SCCO2 treatment after reactive sputtering. The leakage current of the films at an electrical field of 1 MV/cm is 1¡Ñ10-8A/cm2 with a hysteresis voltage of 0.01V. The silicon oxide thin films can be used as a barrier layer for Al/SiO2/Si silicon solar cells. The energy conversion efficiency of a single crystal silicon solae cell is 10.2% under AM1.5 (965W/m2) radiation. After rapid thermal annealing(RTA) at 500¢J, the measured short-circuit current, open- circuit voltage, fill factor are 53mA, 0.54V and 0.53, respectively.

Electrochemical reductions of porous SiO2 pellets and bulk SiO2 plate were investigated in molten CaCl2 and/or CaCl2-NaCl salt mixture. The study focused on effects of temperature, particle size of the starting material, electrolyte composition and cathode design on the reduction rate. The behavior of the cathode contacting materials was also examined. Moreover, cyclic voltammetry study was conducted to investigate the mechanism of the electrochemical reaction. Mainly, XRD analysis and SEM examinations were used for characterizations. The rates of electrochemical reduction were interpreted from the variations of current and accumulative electrical charge that passed through the cell as a function of time under different conditions. The results showed that reduction rate of SiO2 increased slightly with increasing temperature or decreasing the particle size of SiO2 powder. Higher reduction rate was obtained when porous pellet was replaced by bulk SiO2 plate. Use of Kanthal wire mesh around the SiO2 cathode increased but addition of NaCl to the electrolyte decreased the reduction rate. X-ray diffraction results confirmed the reduction of SiO2 to Si in both CaCl2 salt and CaCl2-NaCl salt mixture. However, silicon produced at the cathode was contaminated by the nickel and stainless steel plates which were used as the cathode contacting materials. Microstructures and compositions of the reduced pellets were used to infer that electrochemical reduction of SiO2 in molten salts may become a method to produce solar grade silicon (SOG-Si). In addition, overall reduction potential of SiO2 pellet against the graphite anode and the potential of the cathode reaction at 750&deg / C in molten CaCl2-NaCl salt mixture were determined as 2.3 V (at 1.19 A current) and 0.47 V, respectively by cyclic voltammetry.

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references (p.139-151).