Journal
ACS APPLIED NANO MATERIALS
Volume 3, Issue 5, Pages 4477-4485Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsanm.0c00569
Keywords
surface-enhanced raman scattering; multipolar resonances; hot spots; anodic aluminum oxide; signal-to-background ratio
Funding
- Ministry of Science and Technology of Taiwan [MOST 107-2112-M-003-013-MY3, MOST 108-2112-M-002-010-MY3, MOST 108-2639-M-001-003-ASP]
- National Center for Theoretical Sciences
- NEMS Research Center of National Taiwan University
- National Center for High-Performance Computing in Taiwan
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Hot spots generated through the electrodynamic coupling of the local plasmons in metallic nanoparticles play an important role in enhancing surface-enhanced Raman spectroscopy (SERS) signal. However, the accompanied increasing penetration field inside the nanoparticles is known to be one of the mechanisms contributing to the continuum background. Here, we systematically explored the multipolar resonances for SERS substrates comprised of Ag-nanoparticle (Ag-NP) arrays grown in anodic aluminum oxide nanochannels and their roles in affecting the signal amplification and the background noise at three typical wavelengths for Raman spectroscopy (532, 633, and 785 nm). By varying the diameters of the Ag-NP arrays, different orders of electric-quadrupole (EQ) modes are excited at each studied wavelength. Compared to the dipolar resonance, the second-order EQ mode was found to exhibit stronger hot spot intensity confined at the exposed side of the nanogaps, which are beneficial to serve as active sites interacting with analyte molecules. More importantly, a significant suppressed SERS background was achieved for these higher-order modes due to their small penetration depth inside the particles. The enhanced signal-to-background ratio for the second EQmode was validated among the three Raman wavelengths, which provide promising design guideline for SERS-active substrates with higher sensitivity.
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