Details of the reaction between Au + and Si atoms involved in the deposition are described elsewhere. The morphology of gold by electroless deposition is rather complex and many fundamental problems remain to be clarified, such as the nature of the interface with silicon in the presence of hydrofluoric acid(HF). In some studies it has been reported that silicides are formed due to the strong interaction of Au atoms with Si. Several contrasting reports have been found in the literature on this topic, but it is generally believed that at critical thicknesses (in the range of 2 to 5 ML), gold appears to be inert and can not be mixed with silicon. For gold deposited on silicon by electrical displacement (GD), it has been proposed to include the growth of the Volmer-Weber and Stranski-Krastanov modes. It has been found that during growth Si atoms diffuse outward through the deposited gold layer, followed by formation of Si oxides on their surfaces. The process stops after forming a certain thickness of the oxide, and gold atoms collect as solid clusters on top of it. The optical properties of these clusters depend on their shape and morphology. It is reported in the literature that the local field enhancement factors of gold nanoparticles depend on their geometries and are higher for spherical particles of good shape than for flat islands.

Gold nanoparticles on silicon substrates have shown interesting applications in Si nanowire (SiNW) catalysis, metal-assisted etching (MAE), or even as an electrical contact in standard miniaturized devices. Their ability to exhibit enhanced surface plasmon resonance (SPR) at optical frequencies makes them excellent for scattering and absorbing visible light. For these reasons, they have found interesting applications in the field of metal-semiconductor hybrid structures for solar energy conversion. Electroless deposition based on galvanic displacement reactions is an effective and versatile technique in the different approaches used to deposit Au nanoclusters on substrates. Which involves manually immersing the sample in a plating bath for several seconds without the need to apply an external current or potential.

Typically, additional post-deposition annealing steps are required to improve the spectral response. In our previous study of GD on Au + ions on a Si substrate, we found that the metal nanoparticles were instantaneously nucleated, and that their subsequent growth was controlled by the diffusion in the solution. In detail, we show that AuNPs are formed by impregnating a Si (100) substrate for several seconds in a solution containing 1 mM KAuCl4 and 4.8 M HF, with an average radius of less than 10 nm and a density higher than 1010 cm-2. In the present work, we show that, with appropriate high frequency processing, the 3D Au cluster takes precedence over the flattened regions obtained by layer-by-layer growth. This beneficial modification only needs to be manually immersed for several seconds in a diluted hydrofluoric acid solution (DHF) with 6% HF, without the need for annealing or high power light irradiation.