Continuous flow electroless plating enhances optical features of au films and nanoparticles

A novel continuous flow (CF) electroless (EL) plating method deposits gold (Au) films which exhibit increased continuity and uniformity relative to batch immersion as measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Transmission UV-vis (T-UV) spectra exhibit lower peak heights (PH) and narrower full-width-half-maxima (fwhm), consistent with microscopy measures. Nanoparticles (NPs) obtained by thermal transformation of CF-EL Au film are larger and monodisperse relative to I-EL NPs. Their extinction spectra exhibit higher PH due to enhanced localized surface plasmon resonance (LSPR) and narrower fwhm than NP from I-EL films. Au deposition during CF-EL plating is calculated to be 78.3% higher than during I-EL plating for each 30-s interval. Optical features of T-UV [PH, fwhm, and resonant extinction maxima (λ_max)] increase in proportion to time-integrated mass transport coefficient and suggest that increased mass transfer rate and steady higher average local Au concentration during CF improve continuity, uniformity, and overall smoothness of CF plated films.