Browsing by Subject "Lift-off"
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Item Three dimensional conductivity modulation in biocompatibly functionalized nano-engineered structures(Texas Tech University, 2006-05) Nallabolu, Madhuri LataThe objective of this work is to fabricate a biosensor consisting of a boron doped silicon nanopillar array whose surface when modified with biotin exhibits a three dimensional modulation in conductivity upon the addition of streptavidin. For this purpose, direct write e-beam lithography technique is used to print a dot array on 950k PMMA C7 resist and the nickel dots obtained after lift-off are used as an etch mask to etch into silicon to realize the nanopillar array. A number of experiments are conducted to optimize the exposure dose for the dot array pattern and understand the effect of various parameters of the beam substrate and pattern on the dose required. A 25 X 25 silicon pillar array consisting of pillars with diameters 150-200nm and a spacing 1µm between the pillars is fabricated. Surface modification experiments are done to immobilize streptavidin on biotinylated silicon surface. An approach to the fabrication of the top electrode has been suggested. A theoretical model is developed to explain the conductivity modulation.Item Transient Lift-off Test Results for an Experimental Hybrid Bearing in Air(2011-02-22) Klooster, DavidA 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.