Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 189-197).

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 156-167).

En els darrers anys, el desenvolupament de nous mètodes per a la fabricació de xarxes ordenades de nanoestructures magnètiques (litografia magnètica) ha esdevingut un camp de recerca de gran interès. Això es deu tant per l'ampli ventall d'aplicacions tecnològiques que se'n deriven de les estructures magnètiques de grandària submicromètrica (biomedicina, gravació magnètica, ...), com per raons de caire més fonamental, ja que sovint el comportament magnètic d'aquests materials a escala nanomètrica és diferent del corresponent als materials massissos. Els aliatges de Fe60Al40 (percentatge atòmic) i els acers inoxidables austenítics posseeixen una combinació de propietats estructurals i magnètiques que els converteix en materials amb cert potencial per a ser litografiats magnèticament. Des d'un punt de vista magnètic, mentre que els aliatges de Fe60Al40 ordenats atòmicament són paramagnètics a temperatura ambient, els aliatges de Fe60Al40 desordenats a nivell atòmic presenten un comportament ferromagnètic. Pel que fa als acers inoxidables austenítics, a partir de deformació mecànica, es pot induir la transformació en estat sòlid de la fase austenita (paramagnètica) a la fase martensita (ferromagnètica) en aquests aliatges ferris. A més, els processos de nitruració a temperatura moderada en acers inoxidables austenítics permeten transformar parcialment la fase austenita en la fase "austenita expandida", que és una solució sòlida sobresaturada de nitrogen que presenta un comportament ferromagnètic. Aquesta Tesi està basada en la generació de xarxes ordenades d'entitats ferromagnètiques a escala micro/nanomètrica, dins d'una matriu paramagnètica, en la superfície d'aliatges de Fe60Al40 i acers inoxidables austenítics. Aquest propòsit s'assoleix aprofitant les transicions magnètiques que tenen lloc en aquests materials després de sotmetre'ls a processos de deformació plàstica local (nanoindentació) i irradiació controlada amb ions (αs de feixos d'ions focalitzats i irradiació amb ions de gasos nobles a través de màscares en el cas del Fe60Al40 i processos de nitruració a través de màscares d'irradiació en els acers inoxidables austenítics). Cal esmentar que també s'ha dut a terme un estudi detallat de les modificacions a nivell estructural, mecànic i magnètic que ocorren en aquests materials una vegada s'han deformat mecànicament o irradiat amb ions. / In recent years, intense research is being pursued in the development of novel methods for the fabrication of arrays of ordered magnetic nanostructures. This is motivated, in part, by the technological applications of sub-micron magnetic structures, ranging from biomedicine to recording media, but it is also due to fundamental scientific reasons, since the behavior of magnetic materials at this length scale is often significantly different from that in the bulk. Fe60Al40 (at. %) alloys and austenitic stainless steels show an interesting combination of magnetic and structural properties, which makes them turn into potential candidates to be magnetically patterned. Namely, from the magnetic point of view, whereas atomically ordered Fe60Al40 (at. %) is paramagnetic at room temperature, disordered Fe60Al40 becomes ferromagnetic. Concerning austenitic stainless steels, due to mechanical deformation, a phase transformation from the paramagnetic austenite phase to the ferromagnetic martensite phase can occur in these ferrous alloys. In addition, nitriding of austenitic stainless steels at moderate temperatures is able to partially transform the austenite phase into the supersaturated nitrogen solid solution, often called in the literature "expanded austenite" phase, which shows ferromagnetic behavior. This Thesis is mainly focused on the generation of ordered arrays of micro/nanoscaled ferromagnetic entities (i.e., magnetic patterning), embedded in a paramagnetic matrix, at the surface of either Fe60Al40 (at. %) alloys or austenitic stainless steels. This is accomplished by taking advantage of the magnetic transitions which occur in these alloys upon local plastic deformation (nanoindentation) and controlled ion irradiation (focused ion beam and broad beam noble gas ion irradiation through shadow masks in FeAl alloys and ion beam nitriding through shadow masks in austenitic stainless steels). Furthermore, a detailed study of the structural, mechanical and magnetic changes which take place in these materials upon either mechanical deformation or ion irradiation is presented.

Lighting is a big business, lighting consumes considerable amount of the electricity. These facts motivate for the search of new illumination technologies that are efficient. Semiconductor light emitting diodes (LEDs) have huge potential to replace the traditional primary incandescent lighting sources. They are two basic types of semiconductor LEDs being explored: inorganic and organic semiconductor light emitting diodes. While electroluminescence from p-n junctions was discovered more than a century ago, it is only from the 1960s that their development has accelerated as indicated by an exponential increase of their efficiency and light output, with a doubling occurring about every 36 months, in a similar way to Moore's law in electronics. These advances are generally attributed to the parallel development of semiconductor technologies, optics and material science. Organic light emitting diodes (OLEDs) have rapidly matured during the last 30 years driven by the possibility to create large area light-emitting diodes and displays. Another driving force to specifically use semiconducting polymers is the possibility to build the OLED on conventional flexible substrates via low-cost manufacturing techniques such as printing techniques, which open the way for large area productions. This thesis deals with the demonstration and investigation of heterojunction LEDs based on p-organic semiconductor and n-ZnO nanostructures. The ZnOorganic heterojunctions are fabricated using low cost and simple solution process without the need for sophisticated vacuum equipments. Both ZnO-nanostructures and the organic materials were grown on variety of substrates (i.e. silicon, glass and plastic substrates) using low temperature methods. The growth mechanism of the ZnO nanostructures has been systematically investigated with major focus in ZnO nanorods/nanowires. Different organic semiconductor materials and device configurations are explored starting with single polymer emissive layer ending up with separate emissive and blocking layers, or even blends. Interestingly, the photoluminescence and electroluminescence spectra of the hybrid LEDs provided a broad emission band covering entirely the visible spectrum [∼400-∼800nm]. The hybrid light emitting diode has a white emission attributed to ZnO intrinsic defects and impurities in combination with the electroluminescence from the conjugated polymers. The ZnO nanostructures in contact with a high workfunction electrode constitute an air stable electron injecting contact for the organic semiconductor. Hence, we have shown that a white light emission can be achieved in a ZnO-organic hybrid light emitting diode using cheap and low temperature growth techniques for both organic and inorganic materials. / The series number "1504" is incorrect and is changed in the electronic version to the correct number "1405".

A systematic investigation into the growth of one-dimensional nanostructures of select II-VI compounds with the wurtzite crystal structure. Two process parameters are systematically altered to observe how each affects deposition. The results of which give a further understanding into the formation of one nanostructure over another, as well as experimental parameters for optimizing the growth of particular CdSe nanomaterials. A statistical analysis is conducted on the experimental data to quantitatively determine the variability and robustness of the experimental setup and process. The information complied from this extensive study will yield a more complete understanding of the experimental setup and how improvements can be made to reduce variability, increase yield, and gain insight into the mechanisms controlling this class of materials.

Reducing fabrication and operation costs while maintaining high performance is a major consideration for the design of a new generation of solid-state ionic devices such as fuel cells, batteries, and sensors. The objective of this research is to fabricate nanostructured materials for energy storage and conversion, particularly porous electrodes with nanostructured features for solid oxide fuel cells (SOFCs) and high surface area films for gas sensing using a combustion CVD process. This research started with the evaluation of the most important deposition parameters: deposition temperature, deposition time, precursor concentration, and substrate. With the optimum deposition parameters, highly porous and nanostructured electrodes for low-temperature SOFCs have been then fabricated. Further, nanostructured and functionally graded La0.8Sr0.2MnO2-La0.8SrCoO3-Gd0.1Ce0.9O2 composite cathodes were fabricated on YSZ electrolyte supports. Extremely low interfacial polarization resistances (i.e. 0.43 Wcm2 at 700¡ãC) and high power densities (i.e. 481 mW/cm2 at 800¡ãC) were generated at operating temperature range of 600¡ãC-850¡ãC. The original combustion CVD process is modified to directly employ solid ceramic powder instead of clear solution for fabrication of porous electrodes for solid oxide fuel cells. Solid particles of SOFC electrode materials suspended in an organic solvent were burned in a combustion flame, depositing a porous cathode on an anode supported electrolyte. Combustion CVD was also employed to fabricate highly porous and nanostructured SnO2 thin film gas sensors with Pt interdigitated electrodes. The as-prepared SnO2 gas sensors were tested for ethanol vapor sensing behavior in the temperature range of 200-500¡ãC and showed excellent sensitivity, selectivity, and speed of response. Moreover, several novel nanostructures were synthesized using a combustion CVD process, including SnO2 nanotubes with square-shaped or rectangular cross sections, well-aligned ZnO nanorods, and two-dimensional ZnO flakes. Solid-state gas sensors based on single piece of these nanostructures demonstrated superior gas sensing performances. These size-tunable nanostructures could be the building blocks of or a template for fabrication of functional devices. In summary, this research has developed new ways for fabrication of high-performance solid-state ionic devices and has helped generating fundamental understanding of the correlation between processing conditions, microstructure, and properties of the synthesized structures.

This research focuses on developing comprehensive frameworks for developing robust parameter design methodology for dynamic systems with automatic control and for synthesis of nanostructures. In many automatically controlled dynamic processes, the optimal feedback control law depends on the parameter design solution and vice versa and therefore an integrated approach is necessary. A parameter design methodology in the presence of feedback control is developed for processes of long duration under the assumption that experimental noise factors are uncorrelated over time. Systems that follow a pure-gain dynamic model are considered and the best proportional-integral and minimum mean squared error control strategies are developed by using robust parameter design. The proposed method is illustrated using a simulated example and a case study in a urea packing plant. This idea is also extended to cases with on-line noise factors. The possibility of integrating feedforward control with a minimum mean squared error feedback control scheme is explored. To meet the needs of large scale synthesis of nanostructures, it is critical to systematically find experimental conditions under which the desired nanostructures are synthesized reproducibly, at large quantity and with controlled morphology. The first part of the research in this area focuses on modeling and optimization of existing experimental data. Through a rigorous statistical analysis of experimental data, models linking the probabilities of obtaining specific morphologies to the process variables are developed. A new iterative algorithm for fitting a Multinomial GLM is proposed and used. The optimum process conditions, which maximize the above probabilities and make the synthesis process less sensitive to variations of process variables around set values, are derived from the fitted models using Monte-Carlo simulations. The second part of the research deals with development of an experimental design methodology, tailor-made to address the unique phenomena associated with nanostructure synthesis. A sequential space filling design called Sequential Minimum Energy Design (SMED) for exploring best process conditions for synthesis of nanowires. The SMED is a novel approach to generate sequential designs that are model independent, can quickly "carve out" regions with no observable nanostructure morphology, and allow for the exploration of complex response surfaces.

Nanostructures are nanometer scale structures (characteristic length less than 100 nm) such as nanowires, ultra-small junctions, etc. Since nanostructures are less stable, their characteristic volume is much smaller compared to defect sizes and their characteristic length is close to acoustical phonon wavelength. Moreover, because nanostructures include significantly fewer charge carriers than microscale structures, electronic noise in nanostructures is enhanced compared to microscale structures. Additionally, in microprocessors, due to the small gate capacitance and reduced noise margin (due to reduced supply voltage to keep the electrical field at a reasonable level), the electronic noise results in bit errors. On the other hand, the enhanced noise is useful for advanced sensing applications which are called fluctuation-enhanced sensing. In this dissertation, we first survey our earlier results about the limitation of noise posed on specific nano processors. Here, single electron logic is considered for voltage controlled logic with thermal excitations and generic shot noise is considered for current-controlled logic. Secondly, we discuss our recent results on the electronic noise in nanoscale sensors for SEnsing of Phage-Triggered Ion Cascade (SEPTIC, for instant bacterial detection) and for silicon nanowires for viral sensing. In the sensing of the phage-triggered ion cascade sensor, bacteriophage-infected bacteria release potassium ions and move randomly at the same time; therefore, electronic noise (i.e., stochastic signals) are generated. As an advanced model, the electrophoretic effect in the SEPTIC sensor is discussed. In the viral sensor, since the combination of the analyte and a specific receptor located at the surface of the silicon nanowire occurs randomly in space and time, a stochastic signal is obtained. A mathematical model for a pH silicon nanowire nanosensor is developed and the size quantization effect in the nanosensor is also discussed. The calculation results are in excellent agreement with the experimental results in the literature.

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.

This thesis presents the development of a novel atomic force microscope (AFM) based nanofabrication technique termed as thermochemical nanolithography (TCNL). TCNL uses a resistively heated AFM cantilever to thermally activate chemical reactions on a surface with nanometer resolution. This technique can be used for fabrication of functional nanostructures that are appealing for various applications in nanofluidics, nanoelectronics, nanophotonics, and biosensing devices. This thesis research is focused on three main objectives. The first objective is to study the fundamentals of TCNL writing aspects. We have conducted a systematic study of the heat transfer mechanism using finite element analysis modeling, Raman spectroscopy, and local glass transition measurement. In addition, based on thermal kinetics analysis, we have identified several key factors to achieve high resolution fabrication of nanostructures during the TCNL writing process. The second objective is to demonstrate the use of TCNL on a variety of systems and thermochemical reactions. We show that TCNL can be employed to (1) modify the wettability of a polymer surface at the nanoscale, (2) fabricate nanoscale templates on polymer films for assembling nano-objects, such as proteins and DNA, (3) fabricate conjugated polymer semiconducting nanowires, and (4) reduce graphene oxide with nanometer resolution. The last objective is to characterize the TCNL nanostructures using AFM based methods, such as friction force microscopy, phase imaging, electric force microscopy, and conductive AFM. We show that they are useful for in situ characterization of nanostructures, which is particularly challenging for conventional macroscopic analytical tools, such as Raman spectroscopy, IR spectroscopy, and fluorescence microscopy.