Design and fabrication of nanostructures for thermal conductivity measurements and picosecond acoustics
This thesis describes three fabrication processes for measurement in three different phonon applications. First, fabrication of sub-10nm fluorocarbon films is presented for thin film thermal conductivity measurement. Thermal conductivity of this ultra-thin polymer film is especially interested in phonon study due to its atomic confinement in one dimension. Using plasma polymerization technique, sub-10 nm polymer film can be easily deposited by reactive ion etching system (RIE) with 80 sccm of CHF3 flow rate, 80W of RF power, and 150 mTorr of pressure. Bonding components of these polymers are also analyzed by x-ray photo-electron spectroscopy (XPS). Second, fabrication of MEMS platform for thermal conductivity measurement in single nanowire is presented. Thermal conductivity of single nanowire is interested especially for Si nanowire with rough surface for efficient thermoelectric device. This MEMS platform is design to have capability of measuring not only thermal conductivity but also Seebeck coefficient and electrical conductivity. E-beam lithography and optical lithography with oxygen plasma etching are used to pattern sub-micron patterning and TMAH wet etching and XeF2 etching are used to release the structures to free standing. Last, fabrication of metallic gratings is presented for picosecond acoustics. Generating and detecting picosecond acoustics are interested especially for terahertz regime. We have fabricated aluminum gratings with 300nm and 400nm period with different duty cycle (η=w/p, where w is width of gratings and p is period of gratings). We have verified that generating surface acoustic frequency was determined by its period and higher duty cycle leads higher attenuation of the signal.
Fabrication, Plasma polymerization, Single nanowire, Thermal conductivity, Surface acoustic wave
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign