Person:

Phillips, Katherine

This thesis explores the production, characterization, and water oxidation efficiency of wide bandgap semiconductors made through femtosecond-laser irradiation of various materials. Our investigation focuses on three main aspects: 1) producing titanium dioxide (TiO2) from titanium metal, 2) using our laser-made materials in a photoelectrochemical cell for water oxidation, and 3) utilizing the femtosecond laser to create a variety of other mixed metal oxides for further water oxidation studies and biological applications.

We first discuss producing TiO2 and titanium nitride. We report that there is chemical selectivity at play in the femtosecond laser doping process so not all dopants in the surrounding atmosphere will necessarily be incorporated. We then show that the material made from laser-irradiation of titanium metal, when annealed, has a three-fold enhancement in overall water oxidation when irradiated with UV light. We attribute this enhancement through various material characterization methods to the creation of a more pure form of rutile TiO2 with less defects. We then present a variety of studies done with doping both TiO2 and other oxides with broadband photoelectrochemistry and offer that the dopant incorporation hurts the overall water oxidation rate. Lastly, we use the laser-treated titanium to test cell adhesion and viability. Our results demonstrate an ability to femtosecond-laser process semiconductors to produce materials that no one has made previously and study their properties using collaborations across chemistry and biology, yielding true interdisciplinary research.

Nature evolved a variety of hierarchical structures that produce sophisticated functions. Inspired by these natural materials, colloidal self-assembly provides a convenient way to produce structures from simple building blocks with a variety of complex functions beyond those found in nature. In particular, colloid-based porous materials (CBPM) can be made from a wide variety of materials. The internal structure of CBPM also has several key attributes, namely porosity on a sub-micrometer length scale, interconnectivity of these pores, and a controllable degree of order. The combination of structure and composition allow CBPM to attain properties important for modern applications such as photonic inks, colorimetric sensors, self-cleaning surfaces, water purification systems, or batteries. This review summarizes recent developments in the field of CBPM, including principles for their design, fabrication, and applications, with a particular focus on structural features and materials’ properties that enable these applications. We begin with a short introduction to the wide variety of patterns that can be generated by colloidal self-assembly and templating processes. We then discuss different applications of such structures, focusing on optics, wetting, sensing, catalysis, and electrodes. Different fields of applications require different properties, yet the modularity of the assembly process of CBPM provides a high degree of tunability and tailorability in composition and structure. We examine the significance of properties such as structure, composition, and degree of order on the materials’ functions and use, as well as trends in and future directions for the development of CBPM.