4 research outputs found
Modeling, Fabrication and Characterization of Scalable Electroless Gold Plated Nanostructures for Enhanced Surface Plasmon Resonance
The scientific and industrial demand for controllable thin gold (Au) film and Au nanostructures is increasing in many fields including opto-electronics, photovoltaics, MEMS devices, diagnostics, bio-molecular sensors, spectro-/microscopic surfaces and probes. In this study, a novel continuous flow electroless (CF-EL) Au plating method is developed to fabricate uniform Au thin films in ambient condition. The enhanced local mass transfer rate and continuous deposition resulting from CF-EL plating improved physical uniformity of deposited Au films and thermally transformed nanoparticles (NPs). Au films and NPs exhibited improved optical photoluminescence (PL) and surface plasmon resonance (SPR), respectively, relative to batch immersion EL (BI-EL) plating. Suggested mass transfer models of Au mole deposition are consistent with optical feature of CF-EL and BI-EL films.
The prototype CF-EL plating system is upgraded an automated scalable CF-EL plating system with real-time transmission UV-vis (T-UV) spectroscopy which provides the advantage of CF-EL plating, such as more uniform surface morphology, and overcomes the disadvantages of conventional EL plating, such as no continuous process and low deposition rate, using continuous process and controllable deposition rate. Throughout this work, dynamic morphological and chemical transitions during redox-driven self-assembly of Ag and Au film on silica surfaces under kinetic and equilibrium conditions are distinguished by correlating real-time T-UV spectroscopy with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements. The characterization suggests that four previously unrecognized time-dependent physicochemical regimes occur during consecutive EL deposition of silver (Ag) and Au onto tin-sensitized silica surfaces: self-limiting Ag activation; transitory Ag NP formation; transitional Au-Ag alloy formation during galvanic replacement of Ag by Au; and uniform morphology formation under controlled hydraulic conditions.
A method to achieve the time-resolved optical profile of EL Au plating was devised and provided a new transitional EL Au film growth model which validated mass transfer model prediction of the deposited thickness of ¡Ü100 nm thin films. As a part of the project, validation of mass transfer model, a spectrophotometric method for quantitative analysis of metal ion is developed that improves the limit of detection comparable to conventional instrumental analysis.
The present work suggests that modeling, fabrication and characterization of this novel CF-EL plating method is performed to achieve an ultimate purpose: developing a reliable, inexpensive wet chemical process for controlled metal thin film and nanostructure fabrication
Rate-Limited Electroless Gold Thin Film Growth: A Real-Time Study
Time-resolved,
in situ spectroscopy of electroless (EL) gold (Au)
films combined with electron microscopy showed that the deposition
rate increased up to two-fold on surfaces swept by the bulk flow of
adjacent fluid at Reynolds numbers less than 1.0, compared to batch
immersion. Deposition rates from 5.0 to 9.0 nm/min and thicknesses
of the EL Au film from 20 to 100 nm, respectively, increased predictably
with flow rate at conditions when the deposition was limited primarily
by Fickian diffusion. Time-frames were identified for metal island
nucleation, growth, and subsequent film development during EL Au deposition
by real-time UV–visible spectroscopy of photoluminescence (PL)
and surface plasmon features of nanoscale metal deposits. Film thicknesses
measured by scanning electron microscopy and X-ray photoelectron spectroscopy
paired with real-time optical spectroscopy of kinetic aspects of plasmon
and PL optical features indicated that Au film deposition on surfaces
swept by a steady flow of adjacent fluid can be primarily diffusion
limited