Bio-Assisted Cobalt Nanoparticles Assembly of Device Architectures

The main focus of this dissertation is to assemble discrete, nanoscale magnetic particles for logic and memory device applications. In this study, we use tubulin biological templates to provide a non-lithographic method for assembling magnetic nanoparticles (NPs). Alternative bottom-up methods are being investigated for building nanoscale architectures including the use of bio-supramolecular structures as templates. This approach bypasses the limitations of conventional top-down lithographic processes as our goal is to assemble NPs at dimensional scales less than 100 nm.;In this dissertation, a facile synthetic route for preparing magnetic NPs and nanowires using tubulin biotemplates has been developed. Tubulin, a protein isolated from eukaryotic cells, can be polymerized in vitro into different conformations, such as nanoscale rings and nanotubes (microtubules), and used as a template for fabricating magnetic nanostructures. The different tubulin conformations are preserved during a two step electroless cobalt plating process, enabling NP assembly to occur. We also investigated the use of various chelating agents to control the morphology of cobalt NPs and the spacing between the NPs on the microtubule.;The magnetic characteristics of Co NPs assembled on the different templates were determined using SQUID measurements and magnetic-atomic force microscopy (MFM). The magnetic measurements indicate that one-dimensional (1-D) cobalt nanowires exhibit ferromagnetic behavior with a small coercivity, ∼ 30 Oe. The strong magnetic interactions between magnetic domains along the 1-D tubulin biotemplates enable us to fabricate ferromagnetic nanowires with diameters of < 50 nm for device applications. The assembly of cobalt NPs onto ring-shaped tubulins leads to the formation of 100 nm Co spheres which exhibit paramagnetic behavior with a much larger coercivity, ∼ 400 Oe. These very different magnetic responses underscore the importance of morphology in using bio-templated assemblies of nanostructures.;In addition, the microtubule-templated cobalt NPs are electrically conducting and individual nanowires display conductance switching effects that consist of bistable states with an on/off ratio larger than two orders of magnitude. Non-volatile memory device and granular type of magneto-resistance device were constructed using microtubule-templated Co NPs. These results demonstrate that biotemplating can be used to form nanoarchitectures whose multifunctional properties can be exploited in magnetic and electronic devices.