Babayode Daniel A, Peterson Stena C, Haber Louis H
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
J Chem Phys. 2024 Aug 28;161(8). doi: 10.1063/5.0217901.
The in situ growth dynamics of colloidal silver-gold core-shell (Ag@Au CS) nanoparticles (NPs) are studied using time-dependent second harmonic generation (SHG) and extinction spectroscopy. Four sequential additions of chloroauric acid, sodium citrate, and hydroquinone are added to a silver nanoparticle solution to form a gold shell around a 45 nm silver core under different reaction conditions, resulting in final sizes ranging from 80 to 125 nm in diameter. In the first addition, a bumpy, urchin-like surface morphology is produced, while the second, third, and fourth additions provide additional nanoparticle growth with the surface morphology becoming more smooth and uniform, as shown using transmission electron microscopy measurements. The in situ extinction spectra increase in intensity for each addition, where blue-shifting and spectral narrowing are observed as the Ag@Au CS NPs grow in size. The extinction spectra are compared to Mie theory simulations, showing general agreement at later stages of the reactions for smooth CS surfaces. The in situ SHG signal is dominated by surface-enhanced plasmonic hotspots at the early stages of the shell growth, followed by gradual decreases in signal as the surface becomes more smooth. Two-photon fluorescence is also monitored during the CS growth, showing complementary information for comparisons to the extinction and SHG results. The holistic study of the synthesis and characterization of Ag@Au CS nanoparticles using in situ SHG spectroscopy, extinction spectroscopy, and Mie theory simulations allows for a comprehensive analysis of the complex growth dynamics occurring at the nanoscale for developing optimized plasmonic nanomaterial properties.
利用时间分辨二次谐波产生（SHG）和消光光谱研究了胶体银金核壳（Ag@Au CS）纳米颗粒（NPs）的原位生长动力学。在不同反应条件下，向银纳米颗粒溶液中依次添加四次氯金酸、柠檬酸钠和对苯二酚，以在45nm的银核周围形成金壳，最终直径范围为80至125nm。第一次添加时，会产生一种表面崎岖不平、类似海胆的形态，而第二次、第三次和第四次添加则使纳米颗粒进一步生长，表面形态变得更加光滑均匀，这通过透射电子显微镜测量得以显示。每次添加后，原位消光光谱的强度都会增加，随着Ag@Au CS NPs尺寸的增大，观察到蓝移和光谱变窄现象。将消光光谱与米氏理论模拟结果进行比较，发现在反应后期，对于光滑的CS表面，二者总体一致。在壳生长的早期阶段，原位SHG信号主要由表面增强等离子体热点主导，随后随着表面变得更加光滑，信号逐渐减弱。在CS生长过程中还监测了双光子荧光，显示出与消光和SHG结果进行比较的补充信息。使用原位SHG光谱、消光光谱和米氏理论模拟对Ag@Au CS纳米颗粒进行合成和表征的整体研究，能够对纳米尺度上发生的复杂生长动力学进行全面分析，以开发优化的等离子体纳米材料特性。
