Dr. Tansel Karabacak’s research group has specialized in the applications of nanostructured materials in renewable energy technologies including fuel cells, solar cells, batteries, and hydrogen storage. These alternative energy systems have attracted the interest of many researchers and industries due to serious concerns regarding the world’s energy resources. However, current state-of-the-art systems are still far behind the conventional energy sources especially in power efficiency and/or cost. Dr. Karabacak’s Thin Films and Nanostructures Laboratory (http://ualr.edu/txkarabacak/) utilizes a novel glancing angle deposition (GLAD) method, which uses a “shadowing effect”, to fabricate nanostructured materials of various kinds including metals, alloys, oxides, and semiconductors in a simple and cost-effective way (Fig. 1). Dr. Karabacak’s group demonstrated that GLAD nanostructures can be implemented as advanced electrode/active/functional materials for several alternative energy technologies due to their superior properties such as enhanced light trapping and charge carrier collection (for solar cells), higher catalyst activity (fuel cell electrodes), faster ion insertion/de-insertion kinetics (Li-ion batteries), and enhanced gas adsorption/desorption (hydrogen storage). GLAD nanostructures provide a high surface area coating due to increased surface/volume ratio at smaller scales. It is expected that the large surface area and roughness of the nanostructured photosensitive materials will dramatically enhance internal scattering, trapping, and absorption of incident light. This can lead to photoconductive and photovoltaic devices such as photodetectors and solar cells that are energy efficient and extremely sensitive to small number of photons that would be otherwise below the noise limit in conventional planar films. Another advantage is the capability of coating these nanostructures with very small weight loadings, which will reduce the cost of the electrode manufacturing. In addition, these nanostructures can be assembled on almost any surface and the drawbacks of conventional support materials (e.g. oxidation, chemical byproducts, and poor adhesion of carbon supports in fuel cells) become irrelevant. Therefore, nanostructured electrodes with large effective surface area, small weight loadings, and simpler material compositions will significantly improve the performance and power efficiency of these energy devices, while at the same time the manufacturing costs are greatly lowered.
In addition, Dr. Karabacak recently developed a new small angle deposition (SAD) that allows the conformal coating of nanostructured arrays using a physical vapor deposition system such as sputtering or thermal evaporation. Through the combination of SAD and GLAD approaches, his group demonstrated that it is possible to produce core-shell nanorod arrays in a simple way. Core-shell geometry can further enhance the properties of nanostructures in applications such as fuel cells, where a catalyst shell coated on non-precious metal core can greatly improve the utilization of expensive catalyst material and therefore lower the cost. Core-shell SAD-GLAD nanorods made of semiconducting materials can also enhance charge carrier collection due to the smaller distances involved in the radial-junction geometry, which allows the use of lower quality and therefore low-cost materials towards high-efficiency solar cells.
More recently, Dr. Karabacak has been exploring the fabrication of density modulated thin films using a high working gas pressure (HIWOGAP) sputter deposition technique that produces nanostructured thin films by introducing shadowing effect in a much simpler way compared to GLAD. This can lead to the fabrication of low density nanostructured films of a wide variety of materials using industrial scale deposition systems. Dr. Karabacak’s group successfully demonstrated the use of HIWOGAP silicon films as high specific capacity durable anodes in Li-ion batteries.
Furthermore, Dr. Karabacak’s group has invented a facile method of producing nanostructured metal and metal oxide layers by simply treating metals with hot or boiling water. By combining this new technique with a mechanical sanding process, his team fabricated hierarchical surfaces that incorporate both micro- and nano-scale features. Such a simple and low cost sanding & boiling method can produce micro-nano-structured semiconducting metal oxide surfaces that can be used in several applications including solar cells, hydrogen production by water splitting, and water generation from air. Along with energy shortage, access to clean water resources has become one of the most challenging scientific, social, economic, and political issues of today world.
In addition to his expertise in experimental material processing and fabrication, Dr. Karabacak’s team has pioneered in computational modelling work using Monte Carlo simulation and finite difference time domain (FDTD) methods, which provided guidance in design of materials and also helped understanding the fundamental morphological and optical properties of the structures produced. Moreover, through several interdisciplinary collaborations he developed expertise in detailed material characterization including physical, mechanical, optical, electrical, chemical, and electrochemical properties.