(24d) High Quality Tunable Plasmonic Nanostructures By Atomic Layer Deposition

Nanostructures made of Cu, Ag, and Au exhibit localized plasmon resonances that are tunable through visible and infrared wavelengths. Plasmonic effects enhance the interaction of light and matter, and nanostructures can act as tiny antenna to collect light and focus it at the nanoscale. The broad spectral tuning range and overlap with the solar spectrum have stimulated applications in energy harvesting, photocatalysis, photodetection, spectroscopy, and novel molecular scale devices. Many of these applications benefit from intense local electric fields generated by plasmons at resonance. These enhanced fields influence molecular transitions and may generate highly energetic carriers as well as localized heating. Field enhancements are most intense in nanoscale junctions between neighboring particles, and there has been much effort to fabricate nanoscale junctions between plasmonic particles. Modern nanofabrication methods are generally limited to minimum feature sizes of 10 nm, which makes it difficult to achieve the highest field enhancements that occur for smaller nanojunctions. Atomic layer deposition (ALD) is a proven tool for highly precise thin film growth rates and thickness control, and it can be applied to arbitrary sizes and shapes of nanostructures, including lithographically fabricated nanostructures for nanodevices. In this paper, we present work on area selective ALD of Cu metal to create new types of plasmonic nanostructures, including nanostructures with electrical interconnects. We investigate several strategies to integrate Cu ALD with Pd and Au materials for achieving nanoscale junctions with plasmonic properties, and compare experimental measurements with finite difference time domain simulations. We demonstrate how ALD can achieve sub-10 nm nanojunctions and study their optical properties and plasmonic characteristics. We demonstrate single nanometer size nanojunctions with high quality plasmonic resonances. Our studies indicate that thermal effects and alloying strongly affect plasmonic properties, and we identify areas for improvement. The findings are promising for new devices that combine plasmon resonances with electrical functions.