Type of Document	Dissertation
Author	Chen, Kan-Sheng
Author's Email Address	kc05h@fsu.edu
URN	etd-06282011-155224
Title	Characterization, Fabrication, and Application of Molecularly Modified Semiconductor Nano-devices
Degree	Doctor of Philosophy
Department	Physics, Department of
Advisory Committee	Advisor Name Title Peng Xiong Committee Chair Irinel Chiorescu Committee Member Nicholas Bonesteel Committee Member Volker Crede Committee Member Albert Stiegman University Representative
Keywords	Carbon nanotubes Self-assembled Monolayer Schottky barrier Biosensor electrochemical biosensor superparamagnetic beads
Date of Defense	2011-05-12
Availability	unrestricted
Abstract The integration of soft (organic, biological) and hard (semiconducting, metallic) materials is of central importance in a host of emerging areas in materials research and nanoscience. Micro- and nano-scale hybrid soft/hard condensed matter structures are necessary components for such diverse applications as molecular electronics, biological and chemical sensing, directed assembly of functional nanostructures, and controlled solution-chemistry synthesis of nanomaterials. Organic molecules have been employed not only as pathways for molecular recognition (e.g., in biosensing and directed assembly), but also as means to produce novel electronic functionality and even as active electronic components (e.g., in molecular junctions and single molecule transistors). In recent years, the scientific and engineering community has expended unprecedented effort on fundamental research in this area of nanotechnology, in hope of finding new paradigms of nanoelectronics and biomedical sensors. Inspired by this concept, this dissertation research explores the fabrication and characterization of several diverse types of solid-state/molecular hybrid nanostructures. The objectives of the research are two-fold: 1) to investigate directed self-assembly of semiconductor nano devices using molecular templates and examine molecular modification of the electronic characteristics of such devices, and 2) to study molecular functionalization of semiconductor micro/nano devices and the utilization of the functionalized devices for biomolecular sensing. Carbon nanotubes are a class of quasi-one-dimensional nanomaterials which have received extensive interest. Single-walled carbon nanotubes (SWNTs) exhibit excellent electrical properties suitable for high performance nanoelectronics. Individual SWNT field-effect transistors (FETs) have been shown to outperform state-of-the-art silicon counterparts. However, the integration of the SWNT devices into high-density architectures remains a challenge. Through the bottom-up approach, utilizing directed assembly of solvent suspended SWNTs onto a molecular template, we demonstrated the fabrication of high performance SWNT-FETs. Furthermore, selective functionalization of the metal electrodes with various polar molecules patterned by dip-pen nanolithography (DPN) gave rise to molecularly modified SWNT-FETs comprising of s-SWNT/molecule/Au heterojunction and resulted in pronounced modification to the key electrical characteristics of the SWNT-FETs, including subthreshold swing, ON/OFF ratio, and threshold voltage. By replacing the semiconducting SWNT to a metallic one, the same strategy produced m-SWNT/molecule/Au heterojunction, where the m-SWNT serves a metallic nanoprobe to study the tunneling properties of electrical current through the molecular SAM. The extraordinary precision and high spatial registry of DPN were also used to selectively functionalize active regions of micro-Hall magnetometers fabricated from an InAs quantum well heterostructures, as a necessary step towards using the -Hall devices for biomolecular sensing. To demonstrate detection of protein binding, the submicron molecular SAM functionalized region was subsequently attached with biotin molecules. The streptavidin coated superparamagnetic nanobeads were specifically assembled onto the biotinylated region of μ-Hall device through the biotin-streptavidin linkage and detected by the ac-phase sensitive Hall magnetometry at room temperature. The same sensing scheme was employed for label-free discrimination of a 35 base pair (bp) single strand (ss) DNA target, as a demonstration for point of care (POC) pathogenic DNA detection. An independent study of fluorescence microscopy based on arrays of mimic μ-Hall crosses showed that the platform is feasible for discriminating target DNA at a concentration of 36 pM and < 10 ppm in the presence of extraneous DNA. Binary oxide nanobelts, synthesized through a catalyst-free physical vapor deposition growth method, have emerged as a class of useful quasi-one-dimensional nanomaterials with unique “belt” like morphology. We have fabricated high-performance channel-limited SnO2 nanobelt FETs and utilized them as high sensitivity electrochemical transducers to detect various biomolecules by molecularly modifying the surface of the nanobelt with specific molecular receptors. We first demonstrated the efficacy of the sensing scheme and platform via detection of streptavidin protein using biotinylated SnO2 nanobelt FETs. The same platform was then modified to detect cardiac troponin I (cTnI) antigen, a biomedically significant marker that has been widely considered to be an effective indicator of cardiac damage upon trauma to the heart. A systematic effort was placed on optimizing and extending the capabilities of the platform. The procedures for functionalizing the oxide surface of nanobelts were modified to improve the contact transparency between the molecularly functionalized nanobelt channel and the metal electrodes to increase the yield in obtaining channel-limited SnO2 FETs for sensing applications. The versatility of the sensing scheme was finally extended by the successful attachment of DNA aptamer to the surface of the oxide nanobelts, which provides a potential general pathway to the binding of a broad variety of biomolecules, such as small molecules, proteins, nucleic acids, and even cells, tissues, and organisms. With the DNA aptamer functionalized SnO2 nanobelt FET devices, we successfully demonstrated the detection of thrombin molecules.
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