Acoustic Vibrations of Al Nanocrystals: Size, Shape, and Crystallinity Revealed by Single-Particle Transient Extinction Spectroscopy
Acoustic Vibrations of Al Nanocrystals: Size, Shape, and Crystallinity Revealed by Single-Particle Transient Extinction Spectroscopy
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DOI：
10.1021/acs.jpca.0c01190
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发表时间：
2020-05-14
影响因子：
2.9
通讯作者：
Link, Stephan
中科院分区：
文献类型：
--
作者：
Ostovar, Behnaz;Su, Man-Nung;Link, Stephan
通过全光学手段监测的等离子体纳米颗粒中的声振动引起了越来越多的兴趣，因为它们为这些金属纳米结构的机械性能提供了独特的见解。铝纳米结构是最近新兴的贵金属纳米粒子的替代品，因为它们的宽波长可调性和高自然丰度使其成为许多潜在应用的理想选择。在这里，我们结合电子显微镜和单粒子瞬态消光光谱研究了单个铝纳米晶体的声振动，这通过低脉冲能量、高灵敏度和探头波长可调的单粒子瞬态消光显微镜成为可能。对于化学合成的多面铝纳米晶体，观察到的振动频率与颗粒直径成反比。相比之下，三角形的铝纳米晶体支持两种不同的频率，对应于它们的面内和面外呼吸模式。与测量平均属性的系综测量不同，测量单个粒子的声振动的阻尼时间使我们能够研究粒子间品质因数的变化。令人惊讶的是，我们发现即使对于尺寸和形状相似的纳米晶体，品质因数也存在很大差异。这种观察到的异质性似乎是由纳米粒子结晶度的显着变化造成的，即使对于化学合成的纳米晶体也是如此。
Acoustic vibrations in plasmonic nanoparticles, monitored by an all-optical means, have attracted significant increasing interest because they provide unique insight into the mechanical properties of these metallic nanostructures. Al nanostructures are a recently emerging alternative to noble metal nanoparticles, because their broad wavelength tunability and high natural abundance make them ideal for many potential applications. Here, we investigate the acoustic vibrations of individual Al nanocrystals using a combination of electron microscopy and single-particle transient extinction spectroscopy, made possible with a low-pulse energy, high sensitivity, and probe-wavelength-tunable, single-particle transient extinction microscope. For chemically synthesized, faceted Al nanocrystals, the observed vibration frequency scales with the inverse particle diameter. In contrast, triangularly shaped Al nanocrystals support two distinct frequencies, corresponding to their inand out-of-plane breathing modes. Unlike ensemble measurements, which measure average properties, measuring the damping time of the acoustic vibrations for individual particles enables us to investigate variations of the quality factor on the particle-to-particle level. Surprisingly, we find a large variation in quality factors even for nanocrystals of similar size and shape. This observed heterogeneity appears to result from substantially varying degrees of nanoparticle crystallinity even for chemically synthesized nanocrystals.