The College of William and Mary, Department of Physics, Williamsburg, VA, 23187, USA.
Helmholtz Zentrum Dresden-Rossendorf, Institute for Radiation Physics, Dresden, 01324, Germany.
Sci Rep. 2017 Mar 14;7:44335. doi: 10.1038/srep44335.
Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD) and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes.
金属光栅在受到电磁辐射照射时可以支持法诺共振，其特征反射率与入射角的线形状可以受到周围介电环境和光栅几何形状的极大影响。通过使用共形斜入射薄膜沉积到光学光栅基底上，可以由于阴影效应增加光栅的幅度，从而能够调整法诺共振的阻尼过程和电磁场耦合，从而优化相关的局域电场强度。为了研究这些效应，我们比较了在通过斜角沉积（OAD）和在相同图案化表面上进行的正常沉积（ND）制备的样品中在共振激发下的光学反射率。我们观察到，通过应用 OAD 方法，与在 ND 下获得的相比，样品在共振处表现出更深和更窄的反射率下降。这可以根据斜入射样品中法诺共振的阻尼降低来解释，这导致了更强的局域电场。这种方法为应用开辟了一条途径，通过调整法诺共振引起的电磁场可以提高特定器件特性的品质因数，例如基于光栅的金属光电阴极的量子效率（QE）。
