| Summary: | 博士 === 國立清華大學 === 物理系 === 103 === Plasmonic nanostructures and metamaterials offer unique possibilities for manipulating and amplifying linear and nonlinear optical processes at subwavelength scales. At optical frequencies, silver (Ag) is the best plasmonic material in optical property owing to its lowest intrinsic loss among all metals. However, additional scattering losses originated from grain boundaries and surface roughness limit the performance of polycrystalline Ag plasmonic structures prepared by conventional techniques. Therefore, the development of ultrasmooth, macroscopic-sized Ag crystals exhibiting reduced scattering losses is critical to fully understand the ultimate performance of Ag as a plasmonic material and can also lead to cascaded and integrated plasmonic devices with reproducible characteristics. Here, we demonstrate the growth of single-crystalline Ag plates with millimeter lateral size—the largest colloidal Ag crystals ever reported—for low-loss linear and nonlinear plasmonic applications. Using these Ag crystals, we have achieved record-breaking surface plasmon polariton propagation lengths beyond 100 m in the red wavelength region. These lengths even exceed the predicted propagation lengths using the Johnson-Christy optical constants. Furthermore, these crystals allow the fabrication of highly tunable and reproducible plasmonic nanostructures by focused-ion-beam milling. We have designed and fabricated novel double resonant nanogroove arrays using these crystals for spatially uniform and spectrally tunable second-harmonic generation (SHG). In contrast to “hot”-spot-based nonlinear optical processes such as surface-enhanced Raman scattering (SERS) and SHG using either randomly roughened films or top-down fabricated plasmonic nanoantenna arrays, our approach can achieve nonlinear signal generation over a larger sample area with dramatically improved uniformity and controllability.
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