Song Yujun, Nallathamby Prakash D, Huang Tao, Elsayed-Ali Hani E, Xu Xiao-Hong Nancy
Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529.
J Phys Chem C Nanomater Interfaces. 2010 Jan 14;114(1):74-81. doi: 10.1021/jp9083019.
We have developed a new and effective methodology to correlate optical and AFM images of single Ag nanoparticles (NPs), allowing us to study 3D-morphological dependent localized surface plasmon resonance (LSPR) spectra of individual Ag NPs. We fabricated arrays of distinctive microwindows on glass coverslips using photo-lithography method, and created well-isolated individual Ag NPs with a wide variety of shapes and morphologies on the glass coverslips using a modified nanosphere lithography method (NSL). Using distinctive geometries of microwindows, we located individual Ag NPs of interest in their optical and AFM images, enabling us to correlate and characterize the LSPR spectra and 3D morphologies of the same single NPs using dark-field optical microscopy and spectroscopy (DFOMS) and AFM, respectively. We found that LSPR spectra of single Ag NPs, with nearly equal volume [(8.6 ± 0.4) × 10(3) nm(3)], cross-section [(2.2 ± 0.2) × 10(2) nm(3)], and height (39.6 ± 3.6 nm), highly depend on their shapes, showing the red shift of peak wavelength to 629 nm (quasi trapezoidal cylindrical NP) from that of 506 nm (quasi circular cylindrical NP). LSPR spectra of single Ag NPs simulated using discrete dipole approximation (DDA) agree well with those measured experimentally when their shapes and morphologies can be accuractely described in both methods, but differ when they are not. Furthermore, we found location-dependent LSPR spectra on and around a single NP, offering a unique opportunity to characterize multi-mode plasmonic NPs at nanometer resolution for better understanding their plasmonic optical properties and for rational design of single NP optics.
我们开发了一种全新且有效的方法，用于关联单个银纳米颗粒（NP）的光学图像和原子力显微镜（AFM）图像，从而能够研究单个银纳米颗粒的三维形态相关的局域表面等离子体共振（LSPR）光谱。我们使用光刻法在玻璃盖玻片上制作了独特的微窗口阵列，并采用改进的纳米球光刻法（NSL）在玻璃盖玻片上制备了具有各种形状和形态的、相互良好隔离的单个银纳米颗粒。利用微窗口的独特几何形状，我们在光学图像和AFM图像中定位出感兴趣的单个银纳米颗粒，进而能够分别使用暗场光学显微镜和光谱学（DFOMS）以及AFM来关联和表征同一单个纳米颗粒的LSPR光谱和三维形态。我们发现，体积几乎相等[（8.6±0.4）×10³ nm³]、横截面[（2.2±0.2）×10² nm³]以及高度（39.6±3.6 nm）的单个银纳米颗粒的LSPR光谱高度依赖于其形状，峰值波长从506 nm（准圆柱形纳米颗粒）红移至629 nm（准梯形圆柱形纳米颗粒）。当使用离散偶极近似（DDA）模拟的单个银纳米颗粒的形状和形态在两种方法中都能被准确描述时，其LSPR光谱与实验测量结果吻合良好，但当描述不准确时则会有所不同。此外，我们发现单个纳米颗粒及其周围存在位置依赖的LSPR光谱，这为在纳米分辨率下表征多模等离子体纳米颗粒提供了独特的机会，有助于更好地理解其等离子体光学性质以及合理设计单个纳米颗粒光学器件。
