Optical Properties and Optoelectronic Applications of Nano-size Metallic Films and Metamaterials
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Future optical and optoelectronic devices are desired to have compact sizes, high efficiencies, robust performance, and low manufacturing costs. All these advances call for developments both in their constituent materials and design concepts. This PhD thesis presents some of the recent developments of the above aspects.
Silver (Ag) is one of the most widely used materials for optoelectronic devices and metamaterials, due to its low optical loss in the visible and near infrared (NIR) range, as well as good electrical conductivity. However, Ag is well known to have several issues, including difficulty to form high-quality thin films, poor stability in an ambient environment and under elevated temperatures, and inferior adhesion with substrates. These issues constrain Ag's applications in various devices. In light of this, a new kind of silver: doped silver is developed. With the aid of small amount of doping elements during the Ag deposition, ultra-thin, smooth, and low-loss Ag films are obtained. Compared to pure Ag films, doped Ag films have a significantly improved long-term and thermal stability, as well as good adhesion to various substrates. Doped Ag films have facilitated diverse high-performance optical and optoelectronic devices, such as organic solar cells, organic light emitting diodes, optical metamaterials, and plasmonic devices.
Metamaterials are artificially designed materials with extraordinary optical properties, and have the potential to replace conventional bulky optical systems. Nano-size metamaterials (metasurfaces) are demonstrated for polarization and direction control of light. In addition, a large-area, printed metasurface is designed and fabricated. It is made of lossless dielectric materials and offers the functionality of converting a linearly polarized incident light into a radially polarized light in transmission.
These optical and optoelectronic devices also provide valuable solutions to problems in other fields, such as acoustic wave detection. It is shown that optical resonating structures provide a unique approach for acoustic wave detection. Nanoimprinted polymer microring resonators are investigated as high-performance ultrasound detectors. They have good detection sensitivity, broad response bandwidth, and immunity to electromagnetic interferences. These advantages have facilitated their various applications in photoacoustic imaging and real-time terahertz (THz) pulse detection. To further reduce the detector size, polymer filled metasurfaces on the fiber tips are also designed.