Center for Nanophotonics, FOM Institute AMOLF , Science Park Amsterdam 104, 1098 XG Amsterdam, The Netherlands.
ACS Nano. 2015 Feb 24;9(2):2049-60. doi: 10.1021/nn5072254. Epub 2015 Feb 6.
Gallium has recently been demonstrated as a phase-change plasmonic material offering UV tunability, facile synthesis, and a remarkable stability due to its thin, self-terminating native oxide. However, the dense irregular nanoparticle (NP) ensembles fabricated by molecular-beam epitaxy make optical measurements of individual particles challenging. Here we employ hyperspectral cathodoluminescence (CL) microscopy to characterize the response of single Ga NPs of various sizes within an irregular ensemble by spatially and spectrally resolving both in-plane and out-of-plane plasmonic modes. These modes, which include hybridized dipolar and higher-order terms due to phase retardation and substrate interactions, are correlated with finite difference time domain (FDTD) electrodynamics calculations that consider the Ga NP contact angle, substrate, and native Ga/Si surface oxidation. This study experimentally confirms previous theoretical predictions of plasmonic size-tunability in single Ga NPs and demonstrates that the plasmonic modes of interacting Ga nanoparticles can hybridize to produce strong hot spots in the ultraviolet. The controlled, robust UV plasmonic resonances of gallium nanoparticles are applicable to energy- and phase-specific applications such as optical memory, environmental remediation, and simultaneous fluorescence and surface-enhanced Raman spectroscopies.
镓最近被证明是一种具有相变等离子体特性的材料，具有紫外可调性、易于合成以及由于其薄的自终止天然氧化物而具有的显著稳定性。然而，分子束外延法制备的密集不规则纳米颗粒（NP）集合体使得对单个颗粒的光学测量变得具有挑战性。在这里，我们采用高光谱共焦阴极发光（CL）显微镜通过空间和光谱分辨平面内和平面外等离子体模式来表征不规则集合体中各种尺寸的单个 Ga NPs 的响应。这些模式包括由于相位延迟和基底相互作用引起的混合偶极子和更高阶项，与考虑 Ga NP 接触角、基底和天然 Ga/Si 表面氧化的有限差分时间域（FDTD）电动力学计算相关。该研究通过实验证实了先前关于单个 Ga NPs 中等离子体尺寸可调性的理论预测，并表明相互作用的 Ga 纳米颗粒的等离子体模式可以发生杂交，从而在紫外光中产生强热点。镓纳米颗粒可控且稳健的紫外等离子体共振适用于特定能量和相位的应用，如光学存储、环境修复以及荧光和表面增强拉曼光谱学的同时应用。
