Growth Engineering of Plasmonic Nanostructures with ALD

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Solar energy is a critical component of the national strategy to transition our economy away from fossil fuels to combat carbon dioxide emissions and climate change. Sunlight is composed of different wavelengths of electromagnetic energy that primarily range from ultraviolet to infrared, with visible light in between. Current photovoltaic (PV) solar cell technologies based on silicon and other semiconductors capture only a portion of the electromagnetic energy from the sun due to their intrinsic electrical properties. The partial collection and use of sunlight limits their efficiency and the amount of power that can be generated from a given solar cell area, e.g., the most common silicon PV cell has an absolute upper efficiency limit of 32%. Light has properties of both photons and electromagnetic waves and there are advantages to harvesting sunlight’s electromagnetic waves with new types of solar cells made with antennas. Nanoscale antennas are more flexible than PV materials and may be useful to collect the portion of the solar spectrum that current semiconductor PV cells are incapable of converting to electrical current. In this research project, the properties of nanoscale antenna arrays, together with nanofabrication techniques capable of atomistic levels of control, will be studied to advance understanding of how new materials may help harvest solar energy. The project also will support the recruitment and education of a diverse STEM workforce. Both undergraduate and graduate engineering students will participate in the research activities.An experimental research program is proposed to investigate process engineering of plasmonic nanostructures for energy applications. Plasmonic materials have a growing number of applications in photocatalysis, chemical sensors, electro-optics, and energy generation. Plasmonic nanostructures are especially interesting for collecting solar energy due to strongly enhanced light-matter interactions that excite localized surface plasmon resonances (LSPR). Nanostructures can be engineered so that plasmon resonances directly overlap the solar spectrum, including the UV, visible, and near-infrared (NIR) regions, which makes them highly suitable for solar energy harvesting, overcoming the band-gap-limited nature of semiconductor PV cells. One of the new applications for plasmonics is collecting light with optical frequency antennas. Plasmonic antennas are nanostructures that convert electromagnetic (EM) energy into electrical currents and voltages. They can enhance solar energy technology by collecting unused NIR regions of the solar spectrum to enhance overall efficiency. To collect sunlight efficiently, the plasmonic antennas must have nanoscale features (tunnel junctions) that are impossible to generate with current nanofabrication methods. Therefore, it is proposed that area-selective atomic layer deposition (AS-ALD) will be combined with nanofabrication to create the interconnected arrays of antenna junctions. Methods to reduce the temperature and the exposure times of current metal AS-ALD processes will be investigated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.