Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Albert-Einstein Straße 15, 07745 Jena, Germany.
Nanoscale. 2014 May 21;6(10):5200-7. doi: 10.1039/c3nr05685f.
We demonstrate the synthesis as well as the optical characterization of core-shell nanowires. The wires consist of a potassium niobate (KNbO3) core and a gold shell. The nonlinear optical properties of the core are combined with the plasmonic resonance of the shell and offer an enhanced optical signal in the near infrared spectral range. We compare two different functionalization schemes of the core material prior to the shell growth process: silanization and polyelectrolyte. We show that the latter leads to a smoother and complete core-shell nanostructure and an easier-to-use synthesis process. A Mie-theory based theoretical approach is presented to model the enhanced second-harmonic generated (SHG) signal of the core-shell wires, illustrating the influence of the fabrication-induced varying geometrical factors of wire radius and shell thickness. A spectroscopic measurement on a core-shell nanowire shows a strong localized surface plasmon resonance close to 900 nm, which matches with the SHG resonance obtained from nonlinear optical experiments with the same nanowire. According to the simulation, this corresponds to a wire radius of 35 nm and a shell thickness of 7.5 nm. By comparing SHG signals measured from an uncoated nanowire and the coated one, we obtain a 250 times enhancement factor. This is less than the calculated enhancement, which considers a cylindrical nanowire with a perfectly smooth shell. Thus, we explain this discrepancy mainly with the roughness of the synthesized gold shell.
我们展示了核壳纳米线的合成以及光学特性。这些纳米线由铌酸钾（KNbO3）核和金壳组成。核的非线性光学性质与壳的等离子体共振相结合，在近红外光谱范围内提供了增强的光学信号。我们比较了核材料在壳生长过程之前的两种不同功能化方案：硅烷化和聚电解质。我们表明，后者导致更平滑和完整的核壳纳米结构以及更易于使用的合成工艺。提出了一种基于 Mie 理论的理论方法来模拟核壳纳米线的增强二次谐波产生（SHG）信号，说明了制造诱导的半径和壳厚度变化的几何因素的影响。对核壳纳米线的光谱测量显示，在 900nm 附近存在强烈的局域表面等离子体共振，与相同纳米线的非线性光学实验获得的 SHG 共振相匹配。根据模拟，这对应于 35nm 的线半径和 7.5nm 的壳厚度。通过比较未涂层纳米线和涂层纳米线的 SHG 信号，我们获得了 250 倍的增强因子。这小于考虑具有完美平滑壳的圆柱形纳米线的计算增强。因此，我们主要用合成的金壳的粗糙度来解释这种差异。
