Sun Muhua, Li Ying, Zhang Bo, Argyropoulos Christos, Sutter Peter, Sutter Eli
Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States.
Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States.
Langmuir. 2020 Mar 3;36(8):2044-2051. doi: 10.1021/acs.langmuir.9b03765. Epub 2020 Feb 21.
The light-stimulated transformation of ensembles of spherical nanoparticles into anisotropic metal nanostructures mediated by localized surface plasmon resonance (LSPR) excitation is an elegant way of synthesizing triangular silver nanoprisms with extraordinary control over size and shape. Generally, the transformation occurs in oxidizing environments along a pathway that involves the oxidative etching of small preexisting Ag seeds, followed by plasmon-mediated reduction of the resulting Ag ions and Ag incorporation into the anisotropic nanocrystals. Here, we investigate pathways toward Ag nanoprisms from initially homogeneous AgNO solutions held under reducing conditions. Observations using in situ electron microscopy show that reducing environments and high Ag precursor concentrations in the presence of sodium citrate favor two alternative transformation routes of initial spherical nuclei into anisotropic nanoprisms: (i) the aggregation of spherical nanoparticles and plasmon-mediated conversion of small clusters into triangular prisms; (ii) shape fluctuations of individual small nanoparticles. Simulated field distributions confirm that the coupling of the LSPR excitation between closely spaced nanoparticles causes significant field enhancements near the local plasmonic hot spots, which facilitates accelerated Ag incorporation and thus supports the transformation into nanoprisms.
由局部表面等离子体共振（LSPR）激发介导的球形纳米粒子集合体向各向异性金属纳米结构的光刺激转变，是一种合成具有尺寸和形状非凡控制能力的三角形银纳米棱镜的精妙方法。一般来说，这种转变发生在氧化环境中，其路径包括对预先存在的小银种子进行氧化蚀刻，随后通过等离子体介导还原生成的银离子，并将银掺入各向异性纳米晶体中。在此，我们研究了在还原条件下，由初始均匀的硝酸银溶液生成银纳米棱镜的路径。原位电子显微镜观察表明，在柠檬酸钠存在的情况下，还原环境和高银前驱体浓度有利于初始球形核向各向异性纳米棱镜的两种替代转变途径：（i）球形纳米粒子的聚集以及小团簇通过等离子体介导转化为三角形棱镜；（ii）单个小纳米粒子的形状波动。模拟场分布证实，紧密间隔的纳米粒子之间的LSPR激发耦合会在局部等离子体热点附近引起显著的场增强，这有利于加速银的掺入，从而支持向纳米棱镜的转变。
