A hybrid bearing designed for use in a next generation turbo-pump is evaluated for the performance of initial lift-off, referred to as start-transient. The radial test rig features a high-speed spindle motor capable of 20,000 rpm that drives a 718 Inconel rotor attached via a high-speed coupling. The drive end is supported by ceramic ball bearings, while the hybrid bearing supports the opposite end. A magnetic bearing delivers the applied loading along the mid-span of the rotor. Many parameters, including ramp rate [rpm/s] (drive torque), supply pressure at 15,000 rpm, magnitude of the applied load, and load orientation, are varied to simulate different start-transient scenarios. The data are recorded in .dat files for future evaluation of transient predictions. Analysis of the data includes an evaluation of hydrodynamic and hydrostatic liftoff, an assessment of rub from passing through a lightly damped critical speed, and observation of pneumatic hammer instability. Hydrodynamic lift-off occurs when the hydrodynamic pressure, resulting from the relative motion of two surfaces, overcomes the forces acting on the rotor; no indication of hydrodynamic lift-off is provided. Hydrostatic lift-off results from the external supply pressure (which for this test rig is speed dependent) overcoming the forces acting on the rotor as determined from rotor centerline plots. With 0.263 bar applied unit load in the vertical direction, hydrostatic lift-off occurs at 0 rpm and 2.08 bar supply pressure. With a much higher load of 1.53 bar, hydrostatic lift-off is at 12,337 rpm and 10.7 bar supply pressure. The required supply pressure for hydrostatic lift-off is approximately a linear function of the applied unit load. In a turbopump, hydrostatic lift-off depends on the speed because the supply pressure is proportional to the speed squared. With the load in the horizontal direction, hydrostatic lift-off occurs at lower speeds and pressures. The ramp rate did not affect the required supply pressure for hydrostatic lift-off. A lower supply pressure at 15,000 rpm lowered the required supply pressure for hydrostatic liftoff as well as the natural frequencies creating a rub. The hydrostatic lift-off speed should be minimized to avoid damage to the rotor/bearing surfaces due to contact.

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Aluminum nitride (AlN) thin films were deposited on Z-cut LiNbO3 substrates using the reactive RF magnetron sputtering in this thesis. By means of the analyses of XRD, SEM and AFM, the optimal deposition conditions of highly C-axis oriented AlN films were sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power of 165W and substrate temperature of 400¢J. The piezoelectric bi-layers structure of SAW devices was then fabricated. The interdigital transducers (IDTs) were fabricated on bi-layers structure. The AlN thin film thickness of piezoelectric bi-layers structure was varied in order to discuss its effects on SAW devices. From the experimental results, it reveals that the center frequency of SAW filters increases with the increased AlN thin films thickness. It means that the SAW velocity increases as the AlN thin films thickness increases. The effects of bi-layers structure on SAW devices can be discussed in detail by measuring the parameters of SAW devices like insertion loss (IL), electromechanical coupling coefficient (K2) and the temperature coefficient of delay (TCD).

abstract: The rationale of this thesis is to provide a thorough understanding of spalling for semiconductor materials and develop a low temperature spalling technology that reduces the surface roughness of the spalled wafers for Photovoltaics applications. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

Dans les biotechnologies, les particules magnétiques sont de plus en plus utilisées dans diverses applications, de thérapies ou de diagnostics : « Drug delivery », traitements de cancers, IRM, etc. Inscrit dans le démarrage d'un nouvel axe de recherche du laboratoire SPINTEC, le travail de thèse a mis en œuvre des particules élaborées par une approche de type «top-down». Les matériaux utilisés sont antiferromagnétiques synthétiques (SAF). L'intérêt des nanoparticules magnétiques dans les domaines biomédicaux a été présenté en introduction. L'étude réalisée à SPINTEC a tout d'abord consisté à caractériser et modéliser différents matériaux SAF, et développer les procédés technologiques permettant la fabrication des particules. Ensuite le travail a été consacré à l'observation et la modélisation du comportement des particules en suspension dans un champ magnétique appliqué. Un modèle des phénomènes d'autopolarisation et d'agglomération des particules SAF a permis de déterminer une susceptibilité seuil en dessous de laquelle les particules restent dispersées en solution, évitant les phénomènes d'agglomération. / In the biotechnologies, the magnetic particles are more and more used in different applications, therapy or diagnostics such as: drug-delivery, cancer treatments, MRI …This thesis, which marks the beginnings of a new research area at SPINTEC laboratory, implemented particles made by an approach top-down. The used materials are synthetic antiferromagnetic (SAF). The interest for the magnetic nanoparticles was shown in the introduction. The study made at SPINTEC was first of all the characterization and modeling of different SAF materials, and the development of the technological processes for making the particles. Then the work was devoted to observation and modeling of the behavior of the particles in suspension in the applied magnetic field. A model of self-bias and agglomeration of SAF particles allowed to determine a susceptibility threshold below which the particles remain dispersed in solution, avoiding the agglomeration phenomena.

There are numerous numerical and experimental studies to find correlations of octane rating with fuel properties. This thesis was based on the hypothesis that quenching characteristics at ignition locations impact the flame development. Conversely, determination of quenching characteristics might serve as an effective measure to determine the fuel mixture octane number. This hypothesis was tested with premixed flame experiments using primary reference fuels (iso-octane and n-heptane) and commercial grade gasoline. Premixed flame experiments were conducted on a flat flame burner. Primary reference fuels of different ratios were taken and correlated to their respective thermal quenching condition by introducing co-flowing inert gasses at room temperature with fuel-air mixture. The inert gasses that were used in the experiment are nitrogen and helium and the results are analyzed using a camera and an imaging spectrometer. The experimental results support the hypothesis that flame quenching can be correlated to fuel mixture octane number, and holds potential as an alternative method to determine the octane number.

Abstract Negative index structures could be implemented through surface Plasmon polariton waves generated by nanostructures. We are interested in PMMA grating structure on curved metal surface. In order to fabricate this kind of samples, a series process parameters have been tested and also the lift-off process has been developed. Our results show superlens effect under optical microscope(OM). The sub-wavelength grating image is reconstructed in the non-grating region where the PMMA dielectric layer is not uniform. Surface Plasmon(SPP) waves generated in the grating region propagate to the non-grating region and are scattered out through the non-uniform PMMA layer. The grating information is not resolvable under OM but clear in the reconstructed region. It shows that SPP waves can show super resolution and a simple batch process should be developed in the future.

Three flexure pivot pad bearings (FPBs) with different preloads are evaluated for use in high performance applications by comparing them to a hybrid hydrostatic bearing (HHB). One application of these bearings is in turbopumps for liquid rocket engines. To evaluate bearing performance, the lift-off speed of the shaft from the bearing surface is experimentally determined. Experimental data of lift-off are collected using a circuit running through the shaft and the designed bearing. Other methods for measuring liftoff speeds were attempted but did not yield consistent results. Water is used as a lubricant to simulate a low viscosity medium. In comparison to load-capacity-based predictions for FPBs, the experimental results showed lower lift-off speeds, higher load capacities, higher eccentricity ratios, and lower attitude angles. The bearings’ predicted load capacity determined lift-off speed predictions, but the experimental results show no clear trend relating lift-off speed to load capacity. This was for a range of running speeds, with the design speed defined as the final speed in a particular test case. At 0.689 bar supply pressure and for a design speed of 3000 rpm, the HHB showed greater load capacities and lower eccentricities than the FPBs, but the FPBs had lower lift-off speeds and attitude angles. In fact, the FPBs in the load-between-pad orientation outperformed the HHB in the load-on-pocket orientation with lower lift-off speeds for the shaft weight-only case. An increased supply pressure lowered the lift-off speeds in the HHB tests. If the load in the bearing application remains relatively small, a FPB could be substituted for an HHB.

Transparent thin film transistors fabricated at room temperature by radio frequency magnetron sputtering using indium oxide material system were proposed. The electrodes of the transparent thin film transistors were obtained by depositing indium oxide with 10% tim doping. Resistivity as low as 4¡Ñ10-4£[-cm at room temperature was achieved. The channel layers of the transparent thin film transistors were fabricated using pure indium oxide target in an Argon and oxygen environment. Resistivity larger than 10-5£[-cm was obtained with 60% oxygen partial pressure. Silicon nitride prepared by room temperature radio frequency sputtering were used for the gate dielectric layer with low leakage current. Environmental-safe lift-off processes were used to fabricated the electrodes, the isolation layer, and the channel layer. The transistor characteristics were obtained by standard I-V measurement. The on-off ratio of the 30£gm ¡Ñ 150£gm transparent thin film transistor is 100.

Aluminum nitride (AlN) thin films were deposited on SiO2/Si substrates using the reactive RF magnetron sputtering in this thesis. By means of the analysis of XRD, SEM, TEM and AFM, the optimal deposition conditions of highly C-axis oriented AlN films were obtained with RF power of 190W, sputtering pressure of 3mTorr, nitrogen concentration (N2/N2+Ar) of 30%, and substrate temperature of 400¢J. The characteristics of films annealed at temperature range from 600¢J to 1150¢J with N2 flow for 2 hours has been studied. Experimental results reveal that the films retain the high quality up to 800¢J. But when the temperature above 1000¢J, AlN films will be oxided to AlO:N. In addition, the interdigital transducers (IDTs) were fabricated on the films annealed at 800¢J for 2 hours to study the characteristics of SAW devices. The results show that the central frequency, insertion loss and phase velocity of SAW were 182.25 MHz, -12.95 dB and 5824 m/sec, respectively. At the same time, we try to match the impedence of devices and improve the frequency response by using a simulation program. After the impedence was matched, the insertion are not strongly improved but the frequency response and closed-in sidelobe rejection exhibit better. The effects of temperature on the SAW devices show that the central frequency almost does not shift when the temperature increases. But the insertion loss slightly increases with the temperature increased, the variation is about -0.02 dB/¢J.