Technological breakthroughs to support societal needs, such as solar energy harvesters and improved data storage strategies, require disruptive advances in new materials with novel functionalities. To that end, this project employs the tools of nanotechnology to fabricate, characterize and tailor the response of titanium-iron-oxide-based nanotube arrays with simultaneous functionality employing electronic charge, magnetic spin and optical response. Properly engineered, these materials hold promise for potential application in devices to efficiently absorb and transfer solar energy and/or to process data with increased speed, precision and accuracy. The research is carried out by an interdisciplinary team of researchers from science and engineering and includes the involvement of students, teachers and junior scientists at all levels of experience. Unique features of the educational experience of this proposal are the opportunities to introduce students to research at large scientific facilities such as the National Synchrotron Light Source at Brookhaven National Laboratory and the fact that the proposal is led by a majority female PI team, providing diversity models to both students and colleagues.
TECHNICAL DETAILS: Iron-doped titania nanotubes are fabricated by electrochemical means and studied using a variety of probes (structural, magnetic and optical, including synchrotron-based spectroscopies) to obtain a fundamental understanding of their magnetic, spintronic, optical and magnetocatalytic properties as functions of composition and structural attributes. As pure titania is a large-bandgap semiconductor, Fe additions not only perturb the band structure but also serve as sensitive probes of the lattice modification by virtue of the large Fe magnetic moment. Further, nanostructured titania is anticipated to exhibit enhanced functional responses due to its large surface area. In this manner it is desired to develop novel multifunctional nanostructures for combined spintronic, optical and photocatalytic properties, at room temperature, in one material. Eventual device applications in sensing, catalysis and spintronics to enable advances in alternative energy and data processing technologies are envisioned.
TiO2 nanotube arrays are promising candidates for applications such as photocatalysis and for potential employment in spin-electronic (spintronic) devices. The functionality of TiO2-based nanotubes are highly dependent on their structure (microstructure and crystallographic symmetry) and magnetic properties. Unified understanding of the influence of these factors on the electronic structure of TiO2 is of paramount importance towards engineering these materials. The goal of this work was to investigate, understand and predict correlations among crystallinity, crystal structure, electronic structure and magnetic properties of TiO2 nanotubes, with potential relevance to their functionality. In this work, self-ordered arrays of amorphous TiO2 nanotubes (pure and Fe-doped with cationic concentration of ~2.1 at%) were synthesized by the electrochemical anodization technique, followed by subjecting them to thermal treatments up to 450 °C to crystallize these nanostructures. A variety of probes – morphological, structural, magnetic and spectroscopic – were used to characterize the properties of these nanostructures as functions of their processing conditions and the dopant content. Structure-functionality relationships in these nanostructures were verified by examining the photodegradation rate of methyl orange (a model water pollutant) in presence of TiO2 nanotubes under UV-Visible light irradiation. Results from this research demonstrated that post-synthesis processing conditions – specifically, nature of the annealing environment, as well as the presence of an external dopant can alter the crystal structure and local electronic environment in TiO2 nanotubes, with subsequent effects on the magnetic properties of these nanostructures. The fundamental knowledge obtained in this research, on the interrelations of structural-magnetic properties and their potential influence on the functionality of TiO2-based nanotubes, can be extended to the metal oxide semiconducting systems in general and is anticipated to provide avenues toward novel materials with enhanced functionality that originates from such tailored structural and magnetic characteristics. This research has produced or contributed to 2 Ph.D. dissertations and has involved 5 undergraduate students and 2 post-doctoral scholars in the research. It has produced 4 peer-reviewed publications, with 3 more either in preparation or in submission, and 18 presentations.
