Growth of Au nanoparticle films and the effect of nanoparticle shape on plasmon peak wavelength

Abstract

Metal nanoparticles (NPs) exhibit localized surface plasmon resonance (LSPR) and thus have potential for use in a wide range of applications. A facile technique for the preparation of NP films using an electron-cyclotron-resonance plasma sputtering method without a dewetting process is described. Field emission scanning electron microscopy (FE-SEM) observations revealed that the Au NPs grew independently as island-like particles during the first stage of sputtering and then coalesced with one another as sputtering time increased to ultimately form a continuous film. A plasmon absorption peak was observed via optical measurement of absorption efficiency. The LSPR peak shifted toward longer wavelengths (red shift) with an increase in sputtering time. The cause of this plasmon peak shift was theoretically investigated using the finite-difference timedomain calculation method. A realistic statistical distribution of the particle shapes based on FE-SEM observations was applied for the analysis, which has not been previously reported. It was determined that the change in the shape of the NPs from spheroidal to oval or slender due to coalescence with neighbouring NPs caused the LSPR peak shift. These results may enable the design of LSPR devices by controlling the characteristics of the nanoparticles, such as their size, shape, number density, and coverage. V C 2014 AIP Publishing LLC.

Surface-Enhanced Absorption Spectroscopy for Optical Fiber Sensing

“…Across all samples, the peak absorption wavelength increased with increasing film thickness. A possible explanation for the red-shift seen in the resonance wavelength with increasing film thickness is that the resonance wavelength is influenced by the structure on the side of the fiber, which resembles a bi-continuous structure reported in a previous LSPR study [32]. When transitioning from separated nano-particles to islands and nano-films for gold and silver, a similar trend to the results presented in Figure 4b appears [32,33].…”