Gold electrodeposition on n-Si(100) surface was investigated by performing a detailed study on nucleation and growth. The effects of additives such as thallium, applied potential and current density, and bulk gold concentration were studied. With addition of thallium in the solution, enhancement and inhibition of the gold deposition were observed at low potential and high potential, respectively. The nucleation of gold on Si was found to depend on the Au concentration and applied potential as well as the Tl+ addition. At low current densities Tl+ increases the Au nuclei size and decreases the density by catalyzing the nuclei growth. At high current densities, an opposite effect was observed. An adsorbed thallium intermediate species is proposed to explain both the catalytic and suppressive effects. (c) 2006 The Electrochemical Society.