Nano-thick-dielectric encapsulation effects on the refractive index sensitivities of Ag plane-nanosphere-cluster sensors

Abstract

The nano-thick-dielectric encapsulation effects on the bulk and local refractive index sensitivity behaviors of Ag plane-nanosphere-cluster sensors (including nanosphere monomers, dimers, trimer chains and trimer equilateral triangles, four kinds of normally encountered nanoparticles in experiments) have been numerically investigated by finite element method (FEM). The encapsulation is revealed to decrease the quadratic magnitude of the refractive index responses of their peak wavelengths of localized surface plasmon resonances (LSPR), while it does not violate such quadratic response natures. Its effect on their capabilities of surface enhanced Raman scattering (SERS) behaviors is discussed too. It is demonstrated to provide an efficient type of SERS substrate for plasmonic sensing and detections, which improves the stability of the concerned nanoparticles, and not diminish their SERS signals, in agreement well with experiments under the same nanostructure parameters. This work holds great promise for further designing SERS-based sensing/detecting substrates and sensors/detectors.

New hybridization coupling mechanism and enhanced sensitivity in a Cu2−xS@Au nanoparticle dimer

“…Therefore, based on the sharp line shape profile profile (Mode C), both the Cu 2−x S@Au CSNDs with a gap of 4 nm, a shell thickness of 2 nm, an FoM of 7.360 and an RIS of 541.082 nm per RIU and the Cu 2−x S@Au CSNDs with a gap of 2 nm, a shell thickness of 2 nm, an FoM of 5.932 and an RIU of 591.966 nm per RIU appear to be optimal, which means that the Cu 2−x S@Au CSNDs exhibit greater tunability in the RIU by changing the gap and t according to the experimental requirements. Compared with other nanoparticle sensors, such as Ag core/Au shell nanospheres (109.5 nm RIU −1 ) [11], dielectric encapsulation Ag nanospheres cluster sensors (193 nm RIU −1 ) [25], Ag nanosphere cluster sensors (200 nm RIU −1 ) [48], dielectric core/metal shell nanoparticles dimer sensor (220 nm RIU −1 ) [24], hollow gold nanoshells (400 nm RIU −1 ) [26], hollow overlapping gold shells (474 nm RIU −1 ) [11] and gold nanoparticles trimer (546 nm RIU −1 , FoM ∼ 3.2) [30], the RIS and FoM sensitivity of the Cu 2−x S@Au CSNDs are larger than those of other nanoparticle dimers. The reason is that the electric charge intensity is enhance with the decreasing the gap and shell thickness t, resulting in the increased multipole moments for the Cu 2−x S@Au dimer, as shown in figures 5 and 6.…”

“…Compared to other plasmonic nanostructure-based sensors, in the visible and nearinfrared regions, the coupled plasmon resonance can be tuned with different short separation distances and the ratio of the shell thickness to the core radius. The interparticle hybridization plasmon coupled resonances with a sharp line shape profile exhibit high sensitivity in terms of the LSPR wavelength shift per unit refractive index (RIU) and a high figure of merit (FoM), with values that are higher than those previously reported for nanoparticle dimer plasmonic sensors [11,[24][25][26][27][28][29][30].…”

“…This results in that the coupling mechanism of the semiconductor-metal coreshell nanoparticle is different from that of metal/dielectric [22] nanoparticle and bimetal core-shell nanoparticle [23], which results in improving its sensitivity [20]. Therefore, it also means that the coupling mechanism and sensing performance of semiconductor-metal dimer are also different from that of metal/dielectric dimer [10,24,25] and nanoshell dimer [26]. On the other hand, considing the good biological effect of Au nanoparitles, the nanoshell is made of gold.…”