Controlled Electroless Deposition of Noble Metals on Silicon Substrates Using Self-Assembled Monolayers as Molecular Resists To Generate Nanopatterned Surfaces for Electronics and Plasmonics

Electroless deposition of noble metals on silicon has applications in a wide range of fields including electronic circuitry, metal plating industry, lithography, and other fabrication techniques. In addition, studies using self-assembled monolayers (SAMs) as resists for electroless deposition for controlled deposition have significant potential for aiding advancement in the fields of nanoelectronics, sensing applications, and fundamental studies. Herein, we discuss the development of appropriate plating solutions for controlled deposition of metallic gold and silver on Si(111) surfaces in the presence of an organic silane monolayer acting as a resist film for directed metal deposition to produce metal-monolayer hybrid surfaces while investigating microscopic plating trends. For this, plating solutions were optimized to deposit metal on bare silicon surfaces while avoiding deposition on the SAM protected areas. Trends in the electroless deposition of gold and silver on a Si(111) surface as a function of concentration of metal ions, NH4F, citric acid, sodium citrate, polyvinylpyrrolidone (PVP), and deposition time have been monitored under ambient conditions. The resulting surfaces were characterized using atomic force microscopy (AFM), and the stability of plating solutions was investigated by UV-vis spectroscopy. For both gold and silver, we observed an increase in metal deposition when the concentration of NH4F, citric acid, and deposition time increased. The addition of PVP and the pH of the solution were also shown to have a significant effect on the metal deposition. The octadecyltrichlorosilane (OTS) SAM films act as effective nanoscale resists when the NH4F concentration is reduced from typical plating conditions. In particular, NH4F concentratidns from 0.02 to 0.50 M and metal ions concentrations from 0.001 to 0.020 M were found to allow deposition of metal nanostructures on a bare Si surface while preserving OTS protected areas.