Spectral Response of Plasmonic Gold Nanoparticles to Capacitive Charging: Morphology Effects

Abstract

We report a study of the shape-dependent spectral response of the gold nanoparticle surface plasmon resonance at various electron densities to provide mechanistic insight into the role of capacitive charging, a topic of some debate. We demonstrate a morphology-dependent spectral response for gold nanoparticles due to capacitive charging using single-particle spectroscopy in an inert electrochemical environment. A decrease in plasmon energy and increase in spectral width for gold nanospheres and nanorods was observed as the electron density was tuned through a potential window of -0.3 to 0.1 V. The combined observations could not be explained by existing theories. A new quantum theory for charging based on the random phase approximation was developed. Additionally, the redox reaction of gold oxide formation was probed using single-particle plasmon voltammetry to reproduce the reduction peak from the bulk cyclic voltammetry. These results deepen our understanding of the relationship between optical and electronic properties in plasmonic nanoparticles and provide insight toward their potential applications in directed electrocatalysis.

Electrochemical impedance spectroscopy of single Au nanorods

“… 28 – 34 For instance, existing studies have shown that the LSPR band of AuNRs immobilized on the ITO substrate is subject to a blue-shift when applying a negative potential, which is due to the increase in the electron density of AuNRs under the electrochemical charging. 35 – 38 We accordingly recorded the corresponding scattering spectrum of a single AuNR at different potentials as shown in Fig. 1a .…”

“…The results are nicely consistent with literature reports. 35 , 37 , 38 To date, maximal scattering wavelength ( λ max ) is the major optical parameter that reflects the electron density of AuNRs. Because it usually takes several seconds or even longer time to acquire a scattering spectrum, it is impossible to determine the λ max when applying an alternating potential as high as tens of kilohertz.…”

Review of Experimental Setups for Plasmonic Photocatalytic Reactions

“…Plasmonic responses can be easily observed in dark-field imaging. Therefore, combining electrochemical measurements with dark-field microscopy [96][97][98], particularly hyperspectral dark-field imaging is valuable [99]. The charge carrier density can be precisely controlled by altering the applied potential and allowing for real-time optical monitoring of the affected LSP resonance responses [97,98,100].…”

“…Therefore, combining electrochemical measurements with dark-field microscopy [96][97][98], particularly hyperspectral dark-field imaging is valuable [99]. The charge carrier density can be precisely controlled by altering the applied potential and allowing for real-time optical monitoring of the affected LSP resonance responses [97,98,100]. Using hyperspectral dark-field imaging, Byers et al [99] demonstrated that upon electrochemical tuning, a population of nanoparticles can undergo several processes ranging from nanoparticle charging to electrochemical reactions, such as chloride ion oxidation and hydrogen evolution reaction.…”

Active control of plasmonic colors: emerging display technologies

“…The spectral changes due to applied electrochemical potentials have mainly but not always 49 been attributed to two effects occurring inside the particles rather than in the surrounding electrolyte: 50 The first is capacitive charging, which alters the electron density in the metal and thus the effective plasma frequency. 47,51 The second is specific ion adsorption, which creates a lossy optical surface layer.…”