The Growth and Characterization of Alkylphosphonic Acid Self-Assembled Nanofibers

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Title: The Growth and Characterization of Alkylphosphonic Acid Self-Assembled Nanofibers
Author: Salmon, Michael Edward
Advisors: Phillip Russell, Committee Chair
Dieter Griffis, Committee Member
John Mackenzie, Committee Member
Richard Spontak, Committee Member
Abstract: The focus of this research was to investigate the formation and properties of novel Self-Assembled Nanofibers (SANs) created by the treatment of Al with solutions of short chain-length alkylphosphonic acids (APAs) in ethanol. A special emphasis was placed on the creation of APA SANs isolated from the immersed Al source and development of analysis techniques for artifact reduced characterization of as-grown individual SANs. Novel immersion growth techniques were devised for the reproducible creation of supported and unsupported isolated methylphosphonic acid (C1), propylphosphonic acid (C3), and pentylphosphonic acid (C5) SANs on Si3N4 and Al coated ProtoChipsTM DuraSiNTM Si3N4 meshes respectively. Additionally, a novel biased immersion growth technique was developed, increasing growth rates as well as allowing for APA SAN deposition onto a variety of substrates including Au microelectrodes. A combination of complimentary analysis techniques including: Atomic force microscopy (AFM), Scanning Transmission Electron Microscopy (STEM), Energy Dispersive Spectrometry (EDS), X-Ray Photoelectron Spectroscopy (XPS), and Electron Energy Loss Spectroscopy (EELS) were utilized to characterize the morphology, composition and chemistry of isolated individual APA SANs. STEM and AFM revealed individual APA SANs are actually composed of layered fibril bundles. Qualitative compositional analysis showed APA SANs were primarily composed of O, C, P, and Al with P:Al ratios determined to be between 1.5 and 4.2. Quantitative XPS and EELS analysis provided further evidence that the detected Al was non-metallic and likely oxidized. STEM with EELS was utilized to definitively correlate the presence of Al, P, O, and C to a 5 nm region of several overlapping unsupported C1 SANs. Thermal analysis of APA SANs on Al as well as isolated on Si3N4 revealed a nearly 5X increase in thermal stability as compared to the ˜ 100C-120C melting points of pure APAs. AFM nanoindentation and nanoscratching were utilized to investigate the mechanical response of individual APA SANs. Evidence of cracking and layering were observed in good agreement with the STEM fibril observations. The reduced elastic modulus, E*, or stiffness, was estimated utilizing a Hertzian mechanics analysis of AFM nanoindentation data and determined to range from ˜ 10GPa to 1 GPa varying inversely with chain-length. Electric Force Microscopy (EFM) of C1 SANs revealed no evidence of conductivity as compared to a control sample consisting of Focused Ion Beam (FIB) deposited Pt nanowires on Si3N4. Additionally, Current-Voltage (IV) measurements were made on individual APA SANs deposited on Au microelectrodes again with no evidence of conductivity.
Date: 2006-12-06
Degree: PhD
Discipline: Materials Science and Engineering

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