Tuning of Spectral and Angular Distribution of Scattering from Single Gold Nanoparticles by Subwavelength Interference Layers

Abstract

Localized surface plasmon resonance (LSPR) as the resonant oscillation of conduction electrons in metal nanostructures upon light irradiation is widely used for sensing as well as nanoscale manipulation. The spectral resonance band position can be controlled mainly by nanoparticle composition, size, and geometry and is slightly influenced by the local refractive index of the near-field environment. Here we introduce another approach for tuning, based on interference modulation of the light scattered by the nanostructure. Thereby, the incoming electric field is wavelength-dependent modulated in strength and direction by interference due to a subwavelength spacer layer between nanoparticle and a gold film. Hence, the wavelength of the scattering maximum is tuned with respect to the original nanoparticle LSPR. The scattering wavelength can be adjusted by a metallic mirror layer located 100-200 nm away from the nanoparticle, in contrast to near-field gap mode techniques that work at distances up to 50 nm in the nanoparticle environment. Thereby we demonstrate, for the first time at the single nanoparticle level, that dependent on the interference spacer layer thickness, different distributions of the scattered signal can be observed, such as bell-shaped or doughnut-shaped point spread functions (PSF). The tuning effect by interference is furthermore applied to anisotropic particles (dimers), which exhibit more than one resonance peak, and to particles which are moved from air into the polymeric spacer layer to study the influence of the distance to the gold film in combination with a change of the surrounding refractive index.

Efficient Plasmonic Gas Sensing Based on Cavity-Coupled Metallic Nanoparticles

“…1d) exhibits green doughnut-shaped patterns, rather than the dots pattern as shown in AuNPs supported by other substrates. As revealed by Ref [24] and our previous study [25], these substrate-induced AuNPs' optical properties are the result of resonance coupling between LSPs and optical cavity modes.…”

“…photoemission enhancement [15], surface enhanced Raman scattering [16][17][18], bio-or chemical sensing [12,[19][20][21][22] and temperature sensing [23]. Recently Wirth et al discovered that tuning the position of individual NPs with respect to the mirror can effectively alter the cavity-NP coupling states, leading to the spectral and directional reshaping of nanoparticle scattering [24]; while we found that this position tuning can also induce a large modification of single NP scattering intensity [25].…”

Enhanced Plasmonic Resonance Characteristics of AgNRs–Gold Film Hybrid System

“…Taking Figure 1A (II) as an example to explain the interaction process between light and nanostructure, it can be divided into three consecutive steps (Wirth et al, 2014): (1) when the light wave irradiates on the dielectric layers (PE/gold film), thereby forming a specific electromagnetic field in the space layer; (2) the generated electromagnetic field interacts with nanorods and induces the light scattering; and (3) the scattered light from nanorods interfere with the reflected light from the space layer. In the gold film, the transmission light can be ignored because the thickness of the gold film is 45 nm, which is larger than the penetration depth of the light beam in the gold layer (about 25-30 nm) (Groeblacher et al, 2007).…”

An Au@Ag nanocube based plasmonic nano-sensor for rapid detection of sulfide ions with high sensitivity

“…25 LSPR characters strongly depend on the shape, size and compositions of nanoparticles and the surrounding dielectric environment. 30,31 Compared to those used in uorescent sensing, plasmonic nanomaterials used in LSPR biosensing are more sensitive, non-toxic, and do not suffer from background suppression. The LSPR scattering spectroscopy of a single plasmonic nanoparticle (PNP) could be easily performed by dark-eld microscopy and a microspectral analyzer, and the notable spectral shis indicate the refractive index of the microenvironment surrounding an individual nanoparticle.…”