Graduate Thesis Or Dissertation
 

Characterization and Investigations of Thin-Film Materials with X-ray Photoelectron Spectroscopy

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  • Surface characterization of materials is widely utilized over a range of disciplines and essential to the development of new materials, technology, or processes. Metal oxide nanoclusters have shown promise as potential new generation photoresist materials for extreme ultraviolet (EUV) nanolithography. Organotin clusters have been proposed as potential candidates for resist materials due to a high photoabsorption cross section in the EUV energy range. Before industrial implementation, these new materials must undergo rigorous analysis through the use of numerous characterization techniques to verify effectiveness and satisfactory performance. In addition to characterization, not much information is known about the radiation induced mechanism that causes a solubility transition; a key component for acting as a photoresist. The use of near ambient pressure X-ray photoelectron spectroscopy (NAPXPS) provides the ability to study chemical changes in organotin nanocluster thin films during radiation exposure in a range of ambient environments. NAPXPS using synchrotron X-rays determined that impinging photon energy can play a role in the solubility transition mechanism since the total electron yield is dependent on the photon energy. The presence of ambient oxygen was also shown to enhance resist sensitivity. NAPXPS with a monochromated Al Kα X-rays were used to measure a contrast curve, further highlighting oxygen’s ability to enhance resist sensitivity, while also showing a decrease in sensitivity for ambients of nitrogen, water, and methanol. Thermal NAPXPS studies following the solubility transition in the resist determined a significant amount of carbon remains in the film even though carbon removal was hypothesized to be a primary step during solubility transition. This led to the conclusion that a metal oxide polymer is formed following sufficient X-ray exposure and annealing. Metal oxide materials have also shown promise as oxidation catalysts. The conversion of volatile organic compounds to non-toxic molecules like CO2 is important for pollution control. Interactions of near ambient pressures of 2-propanol (IPA) with a well ordered SnO2 surface has yet to be studied from a mechanistic standpoint. For these studies, a SnO2 single crystal was prepared with a stoichiometric oxidized surface and characterized with low energy electron diffraction (LEED) and valence band spectra. NAPXPS was used to track chemical changes in the Sn surface oxidation state and adsorbate reactions during exposure to up to 3 mbar of IPA and mixtures of IPA and oxygen at 400, 500, and 600 K. The reaction products were measured using mass spectrometry to compliment the NAPXPS results. Oxygen was found to be required for the complete conversion of IPA to CO2 to prevent the surface reduction of the Sn, which otherwise would yield the intermediate product acetone. Ultimately, surface characterization is imperative towards forming foundational chemical knowledge of materials, which can lead to new and improved technology.
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  • This research was funded by the Semiconductor Research Corp. (SRC) Contract Number 2013-OJ-2438 and the Center for Sustainable Materials Chemistry (CSMC) supported by the U.S. National Science Foundation under grant number CHE-1606982. This work was performed, in part, at the Northwest Nanotechnology Infrastructure, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation under grant number NNCI-1542101. Acquisition of the Ambient-Pressure X-ray Photoelectron Spectroscopy/Ambient-Pressure Scanning Tunneling Microscopy system was supported by the National Science Foundation-Major Research Instrumentation program (grant DMR-1429765), the M. J. Murdock Charitable Trust, Oregon BEST, Oregon Nanoscience and Microtechnologies Institute, and Oregon State University.
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  • Pending Publication
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  • 2019-09-07 to 2021-10-07

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