The Sensitivity of the Distance Dependent Plasmonic Coupling between Two Nanocubes to their Orientation: Edge-to-Edge versus Face-to-Face

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• 作者：Nasrin Hooshmand ; Justin A. Bordley ; Mostafa A. El-Sayed
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：March 3, 2016
• 年：2016
• 卷：120
• 期：8
• 页码：4564-4570
• 全文大小：385K
• ISSN：1932-7455

文摘

Using DDA calculations, the electromagnetic field distribution and polarization vector plots were calculated as functions of the separation distance between a pair of 42-nm Ag nanocube dimers oriented in either an edge-to-edge or face-to-face configuration. We found that, as the separation distance of the nanocube dimer is decreased, the orientation of the dimer dramatically affects its near-field coupling behavior. The expected dipole–dipole exponential coupling behavior between the surfaces of the two nanocubes was found to fail at a separation distance of 6 nm for the face–to-face configuration and 14 nm for the edge-to-edge arrangement. The failure of the dipole–dipole coupling mechanism results from an increased contribution from the higher-order multipoles (e.g., quadrupole–dipole). Because this failure occurs at a larger separation distance for the edge-to-edge orientation, the relative ratio of the multipole to the dipole moment generated by the edge-to-edge dimer must be larger than the ratio for the face-to-face orientation. To form a multipole, two or more oscillating dipoles are required; thus, one would expect that an increase in the ratio of the multipole to the dipole moment would suggest a higher density of oscillating dipoles for the edge-to-edge dimer. This increased density is supported by the larger calculated maximum electromagnetic field for the edge-to-edge orientation (∼7000) compared to the calculated field for the face-to-face orientation (∼5000).