Dillon Alva D, Gieseking Rebecca L M
Department of Chemistry, Brandeis University, 415 South Street, Waltham, Massachusetts 02453, USA.
J Chem Phys. 2022 Feb 21;156(7):074301. doi: 10.1063/5.0080839.
Silver nanowires and nanorods are useful prototypical systems to study the emergence of plasmons within a quantum mechanical context because their high aspect ratios enable plasmons to emerge in smaller systems than for roughly spherical nanoclusters. Here, we quantify the plasmon-like character of the excited states of silver nanorods and nanowires based on three nearly orthogonal criteria: (1) collectivity, (2) dipole additivity, and (3) superatomic character. Based on these three criteria, we classify the excited states as plasmon-like, collective, single-particle, interband, or as intermediate between these categories. We show that linear nanowires have a longitudinal absorption peak that has single-particle character and a transverse absorption peak that evolves from a single-particle to plasmon-like to a mix of plasmon-like and interband with increasing length. Increasing the width tends to increase the plasmon-like character of the longitudinal excited state. In contrast, increasing the nanorod width tends to decrease the length at which interband transitions start mixing significantly into the transverse plasmon-like excited states.
银纳米线和纳米棒是研究量子力学背景下等离子体激元出现的有用原型系统，因为它们的高纵横比使得等离子体激元能够在比大致球形纳米团簇更小的系统中出现。在此，我们基于三个近乎正交的标准对银纳米棒和纳米线的激发态的类等离子体激元特性进行量化：（1）集体性，（2）偶极可加性，以及（3）超原子特性。基于这三个标准，我们将激发态分类为类等离子体激元、集体性、单粒子、带间跃迁或这些类别之间的中间状态。我们表明，线性纳米线具有单粒子特性的纵向吸收峰和横向吸收峰，横向吸收峰随着长度增加从单粒子态演变为类等离子体激元态，再到类等离子体激元与带间跃迁混合态。增加宽度往往会增加纵向激发态的类等离子体激元特性。相反，增加纳米棒宽度往往会缩短带间跃迁开始显著混入横向类等离子体激元激发态的长度。
