Nanovoids embedded in FIB-fabricated Au/Ag nanorod arrays for ultrasensitive SERS-active substrate

Abstract

A focused ion beam (FIB) was employed to fabricate Au/Ag nanorod (NR) arrays (fibAu/Ag_NR). After an annealing process, the fibAu/Ag_NR exhibited a Au/Ag diffused structure or nanovoids (NVs) embedded in NRs preferentially at the Au/Ag interface. With crystal violet (CV) used as the probe molecule, NV_Au/Ag_NRs were found to show an increase in the effect of surface-enhanced Raman scattering. An enhancement of 7 orders of magnitude was obtained at low concentrations of CV. It is most likely that the embedded NVs increase the effective surface area for the interactions between CV molecules and laser light. A strong electromagnetic field effect is presumably generated inside NVs and around NRs.

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“…These values were higher than the corresponding values for Au NCsfibAu_NR samples G_1fibAu_NR, G_2fibAu_NR, and G_3fibAu_NR (13-21 nm). Notably, the EM effect, and thus the SERS effect, is significantly increased by surfaces with a relatively high R a (Costa et al, 2009;Kleinman et al, 2013;Rycenga et al, 2009;Shao et al, 2014;Sivashanmugan et al, 2014Sivashanmugan et al, , 2015Sivashanmugan et al, , 2013aSivashanmugan et al, , 2013bYamamoto Fig. 2(a $ c-i) and S3(a $ c-i) show HR-FETEM images of Ag or Au NCsfibAu_NR.…”

“…The most intense Raman shift from the characteristic peaks of CV usually appears at 1618 cm À 1 (CV peak ), which is assigned to the ring C-C stretching modes. The other Raman band shifts are listed in Table S3 (Sivashanmugan et al 2015(Sivashanmugan et al , 2013a(Sivashanmugan et al , 2013b. Based on Eq.…”

“…In our previous work, SERS-active substrates with well-ordered Au or Au/Ag multilayered NR arrays were fabricated using FIB technology (Sivashanmugan et al, 2015(Sivashanmugan et al, , 2013a(Sivashanmugan et al, , 2013b. It is hypothesized that a high EM effect due to the availability of multiple edges and a small curvature induced in the substrate (Costa et al, 2009;Shao et al, 2014;Sivashanmugan et al, 2014Sivashanmugan et al, , 2015Sivashanmugan et al, , 2013a.…”

“…It is hypothesized that a high EM effect due to the availability of multiple edges and a small curvature induced in the substrate (Costa et al, 2009;Shao et al, 2014;Sivashanmugan et al, 2014Sivashanmugan et al, , 2015Sivashanmugan et al, , 2013a. In addition, the localized surface plasmon resonance (LSPR) effect strongly depends on NR shape and the spacing between NRs.…”

“…Nanofabrication methods create highly precise and regular patterns that have a high enhancement factor (EF). SERS-active substrates have been used to detect nucleoproteins, oligonucleotides, and viruses due to the strong light scattering in the vicinity of nanogaps and NSs Sivashanmugan et al, 2015Sivashanmugan et al, , 2013a.…”