Nuño Zachary, Hessler Brandon, Ochoa Jerry, Shon Young-Seok, Bonney Codi, Abate Yohannes
Department of Physics and Astronomy, California State University Long Beach, CA 90840, USA.
Opt Express. 2011 Oct 10;19(21):20865-75. doi: 10.1364/OE.19.020865.
We report on high resolution subsurface and material specific differentiation of silica, Au and silica-capped Au nanoparticles using scattering-type scanning near-field optical microscopy (s-SNOM) in the visible (λ=633 nm) and mid-infrared (λ=10.7 μm) frequencies. Strong optical contrast is observed in the visible wavelength, mainly because of the dipolar plasmon resonance of the embedded Au nanoparticles which is absent in the infrared. We show that the use of small tapping amplitude improves the apparent image contrast in nanoparticles by causing increased tip-particle and reduced tip-substrate interactions. Experimental results are in excellent agreement with extended dipole model calculations modified to include the capping layer characterized by its refractive index.
我们报道了利用散射型扫描近场光学显微镜（s-SNOM）在可见光（λ = 633 nm）和中红外（λ = 10.7 μm）频率下对二氧化硅、金以及二氧化硅包覆的金纳米颗粒进行高分辨率的地下和材料特异性区分。在可见光波长下观察到强烈的光学对比度，主要是由于嵌入的金纳米颗粒的偶极等离子体共振，而在红外区域不存在这种共振。我们表明，使用小的轻敲振幅通过增加针尖 - 颗粒相互作用并减少针尖 - 基底相互作用，改善了纳米颗粒的表观图像对比度。实验结果与经过修正以包含由其折射率表征的包覆层的扩展偶极模型计算结果非常吻合。
