The control of the surface morphology of a metal deposit plays an important role in (i) tuning the signal in surface-enhanced Raman scattering studies,¹ (ii) assembly of patchy particles, and (iii) catalysis. Recently, we developed a novel templating procedure to manufacture surface-anisotropic, silver-modified polystyrene spheres via electroless silver deposition.² Our data indicated that the silver deposition process might be diffusion-controlled due to the observed dependence of the amount of silver deposited on the stirring rate. Here we report on the effect of reaction conditions on the morphology of the silver deposit. In our experiments, we use 2.4, 0.99, and 0.51 µm polystyrene (PS) spheres partially embedded in polydimethylsiloxane. The templated PS spheres are modified using electroless deposition of silver. The deposition is initiated by addition of a reducing agent, i.e., formaldehyde, to a silver acetate solution in the presence of a complexing agent, i.e., ammonia. In order to determine the function of each component of the electroless bath, we expose the templated PS spheres to changing reaction conditions, namely stirring rate, exposure time, and reactant concentrations/ratios. Variation of the stirring rate and exposure time are efficient and easy to perform experiments to determine the influence of diffusion on the deposition process and the deposit morphology. Stirring rates between 0 and 270 rpm are explored as well as exposure times between 5 and 30 min. In addition, silver salt, formaldehyde, and ammonia concentrations are varied to study the effect on the morphology of the deposit. Silver nanoparticle size and quantity are counted from SEM images. High magnification images are recorded and used to interpret the particle growth mechanism. We will present evidence for a diffusion controlled silver deposition process as well as show that the silver nanoparticle size can be controlled by the reactant/complexing agent ratio. In addition, we will present preliminary data on the effect of the curvature of the spherical substrate on the deposition process.

1. P. Barnickel and A. Wokanu, Mol. Phys. 1989, 67, 1355 2. J.-Q. Cui and I. Kretzschmar, Langmuir, 2006, 22, 8281-8284