†Department of Electronics Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan.
‡Department of Chemistry, and §Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30010, Taiwan.
ACS Nano. 2015 Apr 28;9(4):3875-86. doi: 10.1021/nn5070887. Epub 2015 Apr 7.
Aluminum, as a metallic material for plasmonics, is of great interest because it extends the applications of surface plasmon resonance into the ultraviolet (UV) region and is superior to noble metals in natural abundance, cost, and compatibility with modern semiconductor fabrication processes. Ultrasmooth single-crystalline metallic films are beneficial for the fabrication of high-definition plasmonic nanostructures, especially complex integrated nanocircuits. The absence of surface corrugation and crystal boundaries also guarantees superior optical properties and applications in nanolasers. Here, we present UV to near-infrared plasmonic resonance of single-crystalline aluminum nanoslits and nanoholes. The high-definition nanostructures are fabricated with focused ion-beam milling into an ultrasmooth single-crystalline aluminum film grown on a semiconducting GaAs substrate with a molecular beam epitaxy method. The single-crystalline aluminum film shows improved reflectivity and reduced two-photon photoluminescence (TPPL) due to the ultrasmooth surface. Both linear scattering and nonlinear TPPL are studied in detail. The nanoslit arrays show clear Fano-like resonance, and the nanoholes are found to support both photonic modes and localized surface plasmon resonance. We also found that TPPL generation is more efficient when the excitation polarization is parallel rather than perpendicular to the edge of the aluminum film. Such a counterintuitive phenomenon is attributed to the high refractive index of the GaAs substrate. We show that the polarization of TPPL from aluminum preserves the excitation polarization and is independent of the crystal orientation of the film or substrate. Our study gains insight into the optical property of aluminum nanostructures on a high-index semiconducting GaAs substrate and illustrates a practical route to implement plasmonic devices onto semiconductors for future hybrid nanodevices.
铝作为一种用于等离子体学的金属材料，具有很大的吸引力，因为它将表面等离子体共振的应用扩展到了紫外（UV）区域，并且在丰度、成本和与现代半导体制造工艺的兼容性方面优于贵金属。超光滑单晶金属膜有利于制造高清晰度的等离子体纳米结构，尤其是复杂的集成纳米电路。没有表面波纹和晶界也保证了优越的光学性能和在纳米激光器中的应用。在这里，我们展示了单晶铝纳米缝和纳米孔的紫外到近红外等离子体共振。这些高清晰度的纳米结构是通过聚焦离子束铣削到一个在半导体制备 GaAs 衬底上用分子束外延法生长的超光滑单晶铝膜上而制成的。由于表面超光滑，单晶铝膜表现出提高的反射率和减少的双光子光致发光（TPPL）。线性散射和非线性 TPPL 都被详细研究。纳米缝阵列显示出明显的类 Fano 共振，而纳米孔被发现既支持光子模式又支持局域表面等离子体共振。我们还发现，当激发偏振与铝膜边缘平行而不是垂直时，TPPL 的产生效率更高。这种违反直觉的现象归因于 GaAs 衬底的高折射率。我们表明，从铝中产生的 TPPL 的偏振保持激发偏振，并且与膜或衬底的晶体取向无关。我们的研究深入了解了在高折射率半导体 GaAs 衬底上的铝纳米结构的光学性质，并说明了在未来的混合纳米器件中在半导体上实现等离子体器件的实际途径。
