Physics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2800
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Item Creating Localized Amyloid Nucleation of Silk-Elastin-Like Peptide Polymer Using Atomic Force Microscopy(2015) Stock, Brian; Seog, Joonil; Biophysics (BIPH); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research into amyloids was initially motivated by pathogenic amyloids involved in disease states such as Alzheimer's; however, new research implicates small oliogmeric species and not the mature fibers. This lack of toxicity has allowed for the development of amyloid-based biomaterials for use as nanowires, biosensors, and tissue regeneration. The directed self-assembly of peptides into amyloid-like fibers for use as biomaterials requires the ability to control both the nucleation location and growth direction of the fiber. We have used Atomic Force Microscopy to repeatedly stretch Silk-Elastin-Like Peptide Polymer (SELP) in the normal direction using continuous pulling in a force acquisition mode which has the ability to create nanodots of SELP at a specified location which are capable of nucleating SELP nanofibers. This work, if generalized to other amyloidogenic systems, may aid in the mechanistic understanding of the assembly process of both pathogenic and functional amyloids.Item Electronic transport in low dimensions: carbon nanotubes and mesoscopic silver wires(2008-12-08) Ghanem, Tarek Khairy; Fuhrer, Michael S.; Williams, Ellen D.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis explores the physics of low-dimensional electronic conductors using two materials systems, carbon nanotubes (CNTs) and lithographically-defined silver nanowires. In order to understand the intrinsic electronic properties of CNTs, it is important to eliminate the contact effects from the measurements. Here, this is accomplished by using a conductive-tip atomic force microscope cantilever as a local electrode in order to obtain length dependent transport properties. The CNT-movable electrode contact is fully characterized, and is largely independent of voltage bias conditions, and independent of the contact force beyond a certain threshold. The contact is affected by the fine positioning of the cantilever relative to the CNT due to parasitic lateral motion of the cantilever during the loading cycle, which, if not controlled, can lead to non-monotonic behavior of contact resistance vs. force. Length dependent transport measurements are reported for several metallic and semiconducting CNTs. The resistance versus length R(L) of semiconducting CNTs is linear in the on state. For the depleted state R(L) is linear for long channel lengths, but non-linear for short channel lengths due to the long depletion lengths in one-dimensional semiconductors. Transport remains diffusive under all depletion conditions, due to both low disorder and high temperature. The study of quantum corrections to classical conductivity in mesoscopic conductors is an essential tool for understanding phase coherence in these systems. A long standing discrepancy between theory and experiment regards the phase coherence time, which is expected theoretically to grow as a power law at low temperatures, but is experimentally found to saturate. The origins of this saturation have been debated for the last decade, with the main contenders being intrinsic decoherence by zero-point fluctuations of the electrons, and decoherence by dilute magnetic impurities. Here, the phase coherence time in quasi-one-dimensional silver wires is measured. The phase coherence times obtained from the weak localization correction to the conductivity at low magnetic field show saturation, while those obtained from universal conductance fluctuations at high field do not. This indicates that, for these samples, the origin of phase coherence time saturation obtained from weak localization is extrinsic, due to the presence of dilute magnetic impurities.