Surface plasmon resonance

About: Surface plasmon resonance is a research topic. Over the lifetime, 24909 publications have been published within this topic receiving 810976 citations. The topic is also known as: Surface plasmon resonance & SPR (technology).

Reversing the size-dependence of surface plasmon resonances

Abstract: The size-dependence of surface plasmon resonances (SPRs) is poorly understood in the small particle limit due to complex physical/chemical effects and uncertainties in experimental samples. In this article, we report an approach for synthesizing an ideal class of colloidal Ag nanoparticles with highly uniform morphologies and narrow size distributions. Optical measurements and theoretical analyses for particle diameters in the d ≈ 2–20 nm range are presented. The SPR absorption band exhibits an exceptional behavior: As size decreases from d ≈ 20 nm it blue-shifts but then turns over near d ≈ 12 nm and strongly red-shifts. A multilayer Mie theory model agrees well with the observations, indicating that lowered electron conductivity in the outermost atomic layer, due to chemical interactions, is the cause of the red-shift. We corroborate this picture by experimentally demonstrating precise chemical control of the SPR peak positions via ligand exchange.

The Optimal Aspect Ratio of Gold Nanorods for Plasmonic Bio-sensing

Abstract: The plasmon resonance of metal nanoparticles shifts upon refractive index changes of the surrounding medium through the binding of analytes. The use of this principle allows one to build ultra-small plasmon sensors that can detect analytes (e.g., biomolecules) in volumes down to attoliters. We use simulations based on the boundary element method to determine the sensitivity of gold nanorods of various aspect ratios for plasmonic sensors and find values between 3 and 4 to be optimal. Experiments on single particles confirm these theoretical results. We are able to explain the optimum by showing a corresponding maximum for the quality factor of the plasmon resonance.

Influence of Plasmonic Au Nanoparticles on the Photoactivity of Fe2O3 Electrodes for Water Splitting

Abstract: An experimental study of the influence of gold nanoparticles on α-Fe2O3 photoanodes for photoelectrochemical water splitting is described. A relative enhancement in the water splitting efficiency at photon frequencies corresponding to the plasmon resonance in gold was observed. This relative enhancement was observed only for electrode geometries with metal particles that were localized at the semiconductor-electrolyte interface, consistent with the observation that minority carrier transport to the electrolyte is the most significant impediment to achieving high efficiencies in this system.

Silver Nanodisk Growth by Surface Plasmon Enhanced Photoreduction of

Abstract: The photoreduction of silver ions by citrate, catalyzed on silver seeds, is used to synthesize disk-shaped silver nanoparticles in solution. The reaction is characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), optical absorption spectroscopy, and by measuring the silver ion concentration during the reaction. The irradiation wavelength determines the final shape of these particles due to the shape dependence of the Ag plasmon spectrum. The quantum yield of this reaction has been calculated, and a growth mechanism is outlined. Introduction. Silver particles provide an ideal system for study of size and shape effects in the surface plasmon resonance; indeed, this sensitivity is a tool to monitor the shape of the particles during their synthesis via the optical extinction spectrum. Plasmon resonances concentrate an incident electromagnetic field via near-field enhancement; this antenna effect is the source of surface enhanced Raman scattering (SERS). The intense Ag resonance allows single molecule observation in SERS, 1-5 enables coupled Ag particles to form a subwavelength waveguide, 6 and enables sensitive colorimetric DNA screening. 7,8 Henglein 9,10 has shown that the physical and chemical properties of finely divided, nm-sized Ag particles are strongly modified by the adsorption of nucleophilic species and that Ag particles catalyze thermal and optical electro- chemical reactions. For example, core/shell metallic particles can be grown. 11 Indeed, adsorption of chemical species modifies the Fermi level of both the metal and the reactant, like a polarized nanoelectrode. Combining these effects, we now report controlled pho- tochemical Ag particle growth from adsorbed Ag silver ions in the presence of citrate. If different shapes and sizes are present in a seed colloid, the particle with the largest plasmon absorption cross-section at the laser wavelength initially grows fastest. The reaction accelerates for those shapes whose plasmons move into resonance with the photochemical wavelength as growth occurs. This effect allows control of shape in the dominant photoproduct by choice of photo- chemical wavelength. There have been previous observations of reduced silver formation by irradiation of citrate and Ag ion, however, without control of shape or size. 12,13