Growth and Characterization of Silicon Carbide Thin Films Using a Nontraditional Hollow Cathode Sputtering Technique

Silicon carbide (SiC) is considered a suitable candidate for high-power, high-frequency devices due to its wide bandgap, high breakdown field, and high electron mobility. It also has the unique ability to synthesize graphene on its surface by subliming Si during an annealing stage. The deposition of SiC is most often carried out using chemical vapor deposition (CVD) techniques, but little research has been explored with respect to the sputtering of SiC. Investigations of the thin film depositions of SiC from pulse sputtering a hollow cathode SiC target are presented. Although there are many different polytypes of SiC, techniques are discussed that were used to identify the film polytype on both 4H-SiC substrates and Si substrates. Results are presented about the ability to incorporate Ge into the growing SiC films for the purpose of creating a possible heterojunction device with pure SiC. Efforts to synthesize graphene on these films are introduced and reasons for the inability to create it are discussed. Analysis mainly includes crystallographic and morphological studies about the deposited films and their quality using x-ray diffraction (XRD), reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES) and Raman spectroscopy. Optical and electrical properties are also discussed via ellipsometric modeling and resistivity measurements. The general interpretation of these analytical experiments indicates that the films are not single crystal. However, the majority of the films, which proved to be the 3C-SiC polytype, were grown in a highly ordered and highly textured manner on both (111) and (110) Si substrates.

Preparation of Coated Microtools for Electrochemical Machining Applications

PREPARATION OF COATED MICROTOOLS FOR ELECTROCHEMICAL MACHINING APPLICATIONS Ajaya K. Swain, M.S. University of Nebraska, 2010 Advisor: K.P. Rajurkar Coated tools have improved the performance of both traditional and nontraditional machining processes and have resulted in higher material removal, better surface finish, and increased wear resistance. However, a study on the performance of coated tools in micromachining has not yet been adequately conducted. One possible reason is the difficulties associated with the preparation of coated microtools. Besides the technical requirement, economic and environmental aspects of the material and the coating technique used also play a significant role in coating microtools. This, in fact, restricts the range of coating materials and the type of coating process. Handling is another major issue in case of microtools purely because of their miniature size. This research focuses on the preparation of coated microtools for pulse electrochemical machining by electrodeposition. The motivation of this research is derived from the fact that although there were reports of improved machining by using insulating coatings on ECM tools, particularly in ECM drilling operations, not much literature was found relating to use of metallic coating materials in other ECM process types. An ideal ECM tool should be good thermal and electrical conductor, corrosion resistant, electrochemically stable, and stiff enough to withstand electrolyte pressure. Tungsten has almost all the properties desired in an ECM tool material except being electrochemically unstable. Tungsten can be oxidized during machining resulting in poor machining quality. Electrochemical stability of a tungsten ECM tool can be improved by electroplating it with nickel which has superior electrochemical resistance. Moreover, a tungsten tool can be coated in situ reducing the tool handling and breakage frequency. The tungsten microtool was electroplated with nickel with direct and pulse current. The effect of the various input parameters on the coating characteristics was studied and performance of the coated microtool was evaluated in pulse ECM. The coated tool removed more material (about 28%) than the uncoated tool under similar conditions and was more electrochemical stable. It was concluded that nickel coated tungsten microtool can improve the pulse ECM performance.

Analysis and Transformation of Pipe-like Web Mashups for End User Programmers

Mashups are becoming increasingly popular as end users are able to easily access, manipulate, and compose data from several web sources. To support end users, communities are forming around mashup development environments that facilitate sharing code and knowledge. We have observed, however, that end user mashups tend to suffer from several deficiencies, such as inoperable components or references to invalid data sources, and that those deficiencies are often propagated through the rampant reuse in these end user communities. In this work, we identify and specify ten code smells indicative of deficiencies we observed in a sample of 8,051 pipe-like web mashups developed by thousands of end users in the popular Yahoo! Pipes environment. We show through an empirical study that end users generally prefer pipes that lack those smells, and then present eleven specialized refactorings that we designed to target and remove the smells. Our refactorings reduce the complexity of pipes, increase their abstraction, update broken sources of data and dated components, and standardize pipes to fit the community development patterns. Our assessment on the sample of mashups shows that smells are present in 81% of the pipes, and that the proposed refactorings can reduce that number to 16%, illustrating the potential of refactoring to support thousands of end users developing pipe-like mashups.